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Case Study – The 2011 Japan Earthquake

Cambridge iGCSE Geography > The Natural Environment > Earthquakes and Volcanoes > Case Study – The 2011 Japan Earthquake

Background Information

Location : The earthquake struck 250 miles off the northeastern coast of Japan’s Honshu Island at 2:46 pm (local time) on March 11, 2011.

Japan 2011 Earthquake map

Magnitude : It measured 9.1 on the Moment Magnitude scale, making it one of the most powerful earthquakes ever recorded.

Japan is a highly developed country with advanced infrastructure, technology, and a robust economy. The nation has a high GDP, an efficient healthcare system, and extensive education. However, it’s also located in the Pacific Ring of Fire, making it prone to earthquakes.

What caused the 2011 Japan earthquake?

Japan is located on the eastern edge of the Eurasian Plate. The Eurasian plate, which is continental, is subducted by the Pacific Plate, an oceanic plate forming a subduction zone to the east of Japan. This type of plate margin is known as a destructive plate margin . The process of subduction is not smooth. Friction causes the Pacific Plate to stick. Pressure builds and is released as an earthquake.

Friction has built up over time, and when released, this caused a massive ‘megathrust’ earthquake. The enormous tension released as the plates shifted caused the seafloor to uplift, triggering the earthquake and subsequent tsunami .

The amount of energy released in this single earthquake was 600 million times the energy of the Hiroshima nuclear bomb.

Scientists drilled into the subduction zone soon after the earthquake and discovered a thin, slippery clay layer lining the fault. The researchers think this clay layer allowed the two plates to slide an incredible distance, some 164 feet (50 metres), facilitating the enormous earthquake and tsunami.

The earthquake occurred at a relatively shallow depth of 20 miles below the surface of the Pacific Ocean. This, combined with the high magnitude, caused a tsunami (find out more about  how a tsunami is formed  on the BBC website).

What were the primary effects of the 2011 Japan earthquake?

• Ground Shaking : Extensive damage to buildings and infrastructure.
• Landfall: Some coastal areas experienced land subsidence as the earthquake dropped the beachfront in some places by more than 50 cm.

What were the secondary effects of the 2011 Japan earthquake?

• Tsunami : A giant tsunami wave resulted in widespread destruction along the coast.
• Fatalities : Around 16,000 deaths were reported, mainly resulting from the tsunami.
• Injuries : 26,152 were injured, mainly as a result of the tsunami.
• Nuclear Crisis : The Fukushima Daiichi nuclear power plant was damaged, leading to radiation leaks.
• Economic Loss : Estimated at over $235 billion.
• Displacement : Around 340,000 people were displaced from their homes.
• Damage: The tsunami destroyed or damaged 332,395 buildings, 2,126 roads, 56 bridges, and 26 railways. Three hundred hospitals were damaged, and 11 were destroyed.
• Environmental Damage : Coastal ecosystems were heavily impacted.
• Blackouts: Over 4.4 million households were left without electricity in North-East Japan.
• Transport: Rural areas remained isolated for a long time because the tsunami destroyed major roads and local trains and buses. Sections of the Tohoku Expressway were damaged. Railway lines were damaged, and some trains were derailed.

What were the immediate responses to the 2011 Japan earthquake?

Tsunami Warnings and Prediction :

• The Japan Meteorological Agency issued tsunami warnings three minutes after the earthquake.
• Scientists predicted where the tsunami would hit using modelling and forecasting technology.

Search and Rescue Operations:

• Rescue workers and 100,000 members of the Japan Self-Defence Force were dispatched within hours.
• Some individuals were rescued from beneath rubble with the aid of sniffer dogs.

Radiation Protection Measures:

• The government declared a 20 km evacuation zone around the Fukushima nuclear power plant.
• Evacuees from the area around the nuclear power plant were given iodine tablets to reduce radiation poisoning risk.

International Assistance:

• Japan received help from the US military.
• Search and rescue teams from New Zealand, India, South Korea, China, and Australia were sent.

Access and Evacuation :

• Access was restricted to affected areas due to debris and mud, complicating immediate support.
• Hundreds of thousands were evacuated to temporary shelters or relocated.

Health Monitoring :

• Those near the Fukushima Daiichi nuclear meltdown had radiation levels checked and their health monitored.
• Measures were taken to ensure individuals did not receive dangerous exposure to radiation.

What were the long-term responses to the 2011 Japan earthquake?

Reconstruction Policy and Budget:

• Establishment of the Reconstruction Policy Council in April 2011.
• Approval of a budget of 23 trillion yen (£190 billion) for recovery over ten years.
• Creation of ‘Special Zones for Reconstruction’ to attract investment in the Tohoku region.

Coastal Protection Measures:

• Implementing coastal protection policies like seawalls and breakwaters designed for a 150-year recurrence interval of tsunamis.

Legislation for Tsunami-Resilient Communities:

• Enactment of the ‘Act on the Development of Tsunami-resilient Communities’ in December 2011.
• Emphasis on human life, combining infrastructure development with measures for the largest class tsunami.

Economic Challenges and Recovery:

• Japan’s economy wiped 5–10% off the value of stock markets post-earthquake.
• Long-term response priority: rebuild infrastructure, restore and improve the economy’s health.

Transportation and Infrastructure Repair:

• Repair and reopening of 375 km of the Tohoku Expressway by the 24th of March 2011.
• Restoration of the runway at Sendai Airport by the 29th of March, a joint effort by the Japanese Defence Force and the US Army.

Utility Reconstruction:

• Energy, water supply, and telecommunications infrastructure reconstruction.
• As of November 2011: 96% of electricity, 98% of water, and 99% of the landline network had been restored.

How does Japan prepare for earthquakes, and what was its impact?

Japan has a comprehensive earthquake preparedness program, including:

• Strict Building Codes : Buildings are constructed to withstand seismic activity.
• Early Warning Systems : Advanced technology provides early warnings to citizens.
• Education and Drills : Regular earthquake drills in schools, offices, and public places.

Impact of the 2011 Earthquake

The extensive preparation in Japan likely saved lives and reduced damage during the 2011 earthquake. However, the unprecedented magnitude of the event still led to significant destruction, particularly with the tsunami and nuclear crisis.

The 2011 Japan earthquake illustrates the complexity of managing natural disasters in even the most developed and prepared nations. The event prompted further refinements in disaster preparedness and response in Japan and globally, highlighting the need for continuous assessment and adaptation to seismic risks.

The 2011 earthquake occurred off Japan’s Honshu Island, measuring 9.1 on the Moment Magnitude scale, one of the strongest ever recorded.

Triggered by a ‘megathrust’ in a destructive plate margin, the Pacific Plate subducted the Eurasian Plate, releasing energy equivalent to 600 million Hiroshima bombs.

Primary effects included extensive ground shaking and significant land subsidence in coastal areas.

Secondary effects included a massive tsunami, around 16,000 deaths, 26,152 injuries, a nuclear crisis at Fukushima, over $235 billion in economic loss, displacement of 340,000 people, and widespread damage to infrastructure and the environment.

Immediate responses included rapid tsunami warnings, extensive search and rescue operations, radiation protection measures, international assistance, and evacuation strategies.

Long-term responses focused on reconstruction policies, coastal protection, tsunami-resilient community development, economic recovery, and transportation and utility restoration.

Japan’s extensive earthquake preparedness, including strict building codes and early warning systems, likely reduced damage, but the magnitude still caused significant destruction.

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Case Study: How does Japan live with earthquakes?

Japan lies within one of the most tectonically active zones in the world. It experiences over 400 earthquakes every day. The majority of these are not felt by humans and are only detected by instruments. Japan has been hit by a number of high-intensity earthquakes in the past. Since 2000 there are have been 16000 fatalities as the result of tectonic activity.

Japan is located on the Pacific Ring of Fire, where the North American, Pacific, Eurasian and Philippine plates come together. Northern Japan is on top of the western tip of the North American plate. Southern Japan sits mostly above the Eurasian plate. This leads to the formation of volcanoes such as Mount Unzen and Mount Fuji. Movements along these plate boundaries also present the risk of tsunamis to the island nation. The Pacific Coastal zone, on the east coast of Japan, is particularly vulnerable as it is very densely populated.

The 2011 Japan Earthquake: Tōhoku

Japan experienced one of its largest seismic events on March 11 2011. A magnitude 9.0 earthquake occurred 70km off the coast of the northern island of Honshu where the Pacific and North American plate meet. It is the largest recorded earthquake to hit Japan and is in the top five in the world since records began in 1900. The earthquake lasted for six minutes.

A map to show the location of the 2011 Japan Earthquake

The earthquake had a significant impact on the area. The force of the megathrust earthquake caused the island of Honshu to move east 2.4m. Parts of the Japanese coastline dr[[ed by 60cm. The seabed close to the focus of the earthquake rose by 7m and moved westwards between 40-50m. In addition to this, the earthquake shifted the Earth 10-15cm on its axis.

The earthquake triggered a tsunami which reached heights of 40m when it reached the coast. The tsunami wave reached 10km inland in some places.

What were the social impacts of the Japanese earthquake in 2011?

The tsunami in 2011 claimed the lives of 15,853 people and injured 6023. The majority of the victims were over the age of 60 (66%). 90% of the deaths was caused by drowning. The remaining 10% died as the result of being crushed in buildings or being burnt. 3282 people were reported missing, presumed dead.

Disposing of dead bodies proved to be very challenging because of the destruction to crematoriums, morgues and the power infrastructure. As the result of this many bodies were buried in mass graves to reduce the risk of disease spreading.

Many people were displaced as the result of the tsunami. According to Save the Children 100,000 children were separated from their families. The main reason for this was that children were at school when the earthquake struck. In one elementary school, 74 of 108 students and 10 out of 13 staff lost their lives.

More than 333000 people had to live in temporary accommodation. National Police Agency of Japan figures shows almost 300,000 buildings were destroyed and a further one million damaged, either by the quake, tsunami or resulting fires. Almost 4,000 roads, 78 bridges and 29 railways were also affected. Reconstruction is still taking place today. Some communities have had to be relocated from their original settlements.

What were the economic impacts of the Japanese earthquake in 2011?

The estimated cost of the earthquake, including reconstruction, is £181 billion. Japanese authorities estimate 25 million tonnes of debris were generated in the three worst-affected prefectures (counties). This is significantly more than the amount of debris created during the 2010 Haiti earthquake. 47,700 buildings were destroyed and 143,300 were damaged. 230,000 vehicles were destroyed or damaged. Four ports were destroyed and a further 11 were affected in the northeast of Japan.

There was a significant impact on power supplies in Japan. 4.4 million households and businesses lost electricity. 11 nuclear reactors were shut down when the earthquake occurred. The Fukushima Daiichi nuclear power plant was decommissioned because all six of its reactors were severely damaged. Seawater disabled the plant’s cooling systems which caused the reactor cores to meltdown, leading to the release of radioactivity. Radioactive material continues to be released by the plant and vegetation and soil within the 30km evacuation zone is contaminated. Power cuts continued for several weeks after the earthquake and tsunami. Often, these lasted between 3-4 hours at a time. The earthquake also had a negative impact on the oil industry as two refineries were set on fire during the earthquake.

Transport was also negatively affected by the earthquake. Twenty-three train stations were swept away and others experienced damage. Many road bridges were damaged or destroyed.

Agriculture was affected as salt water contaminated soil and made it impossible to grow crops.

The stock market crashed and had a negative impact on companies such as Sony and Toyota as the cost of the earthquake was realised.  Production was reduced due to power cuts and assembly of goods, such as cars overseas, were affected by the disruption in the supply of parts from Japan.

What were the political impacts of the Japanese earthquake in 2011?

Government debt was increased when it injects billions of yen into the economy. This was at a time when the government were attempting to reduce the national debt.

Several years before the disaster warnings had been made about the poor defences that existed at nuclear power plants in the event of a tsunami. A number of executives at the Fukushima power plant resigned in the aftermath of the disaster. A movement against nuclear power, which Japan heavily relies on, developed following the tsunami.

The disaster at Fukushima added political weight in European countries were anti-nuclear bodies used the event to reinforce their arguments against nuclear power.

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Stanford experts discuss the lessons and legacy of the Fukushima nuclear disaster

A decade after a powerful earthquake and tsunami set off the Fukushima Daiichi nuclear meltdown in Japan, Stanford experts discuss revelations about radiation from the disaster, advances in earthquake science related to the event and how its devastating impact has influenced strategies for tsunami defense and local warning systems.

On a Friday afternoon in the spring of 2011, the largest earthquake in Japan’s recorded history triggered a tsunami that crashed through seawalls, flattened coastal communities and pummeled the Fukushima Daiichi nuclear power plant.

Damage from the earthquake and tsunami. (Image credit: Shutterstock)

More than 19,000 people died and tens of thousands more fled as radiation belched from the world’s worst nuclear accident since Chernobyl.

A decade later, large swaths of land remain contaminated and emptied of most of their former residents. The deadly natural disasters of March 11, 2011, and the catastrophic nuclear meltdown that followed have left a lasting impact on earthquake science, tsunami defense and the politics of nuclear power.

Here, Stanford nuclear security expert Rod Ewing and geophysicists Eric Dunham and Jenny Suckale discuss that legacy, as well as how scientists are continuing to discover new details about the disaster.

What lessons did the damage from Tohoku provide about preparing for tsunamis?

SUCKALE : The Tohoku tsunami highlighted that even a highly sophisticated and expensive tsunami mitigation system can fail. There has also been increasing interest in alternative approaches to mitigating tsunami risks such as nature-based or hybrid approaches. We need to learn a lot more about these types of approaches, but it’s exciting to see progress in that area. It might not be coincidental that a lot of that thinking comes from Miyagi Prefecture, which was hard hit by the tsunami.

How have local tsunami warning systems changed since the 2011 disaster in Japan?

DUNHAM : Most tsunamis are caused by offshore earthquakes, like the 2011 Tohoku-Oki earthquake, uplifting the seafloor and the ocean surface so that water begins to flow back toward land in the form of a tsunami. Local tsunami warning systems are still currently based on a two-step workflow: analysis of seismic waves constrain the earthquake location and size, and relations from tsunami simulations are then used to predict tsunami arrival times and wave heights.

But this is about to radically change.

Japan has deployed offshore networks of pressure gauges and seismometers connected to each other and back to computers on land by thousands of miles of fiber optic cable. Scientists have new methods for reconstructing the tsunami waves, in real-time, using the seafloor pressure data. (Pressure increases when the wave passes over a sensor.) These methods completely bypass the need to first estimate earthquake properties, and they also work for tsunamis that are caused by non-earthquake sources like underwater landslides.

Recent offshore earthquakes and tsunamis in Japan have demonstrated that these methods are ready for real-world use, and I anticipate they will start to become part of local tsunami warning systems in Japan within the next few years. Hopefully, other countries that face similar tsunami hazards will invest in offshore sensor networks.

What important insights have scientists gained about earthquakes by studying data from the Tohoku-Oki earthquake and tsunami?

DUNHAM : The Tohoku-Oki earthquake and tsunami were much larger than had been expected for that part of the Japan Trench subduction zone. Scientists now have a much better appreciation for the variability in earthquake (and tsunami) size that can occur in a given region, although the reasons for that variability are still being explored.

Computer simulations of earthquakes have advanced considerably in the past decade, to the point where they can be used to test hypotheses about the role of frictional properties, fluids and other properties and processes on the fault slip behavior. The international scientific community studying earthquake and tsunami hazards from subduction zones is currently planning ambitious experiments involving onshore and offshore instrumentation, which paired with computer modeling, will revolutionize our understanding of these dangerous regions.

Ten years after the event, what have scientists learned about the particles released from the Fukushima Daiichi Nuclear Power Plant? 

EWING : ​I think that during the past ten years, one of the most important findings is that volatile radionuclides, such as the isotopes of cesium, were actually transported by micro- to nano-scale particles. Initially, the volatile radionuclides were thought to be simple, chemical complexes that were generally soluble and thus would be washed out of the soil column, i.e., during rain events. However, if a significant fraction of the highly radioactive Cs is incorporated into more durable particles, then they may persist for longer periods of time. This is important information for designing the remediation strategy.

The other important discovery is that, depending on their size, these particles can be found kilometers to over one hundred kilometers from the nuclear reactors at Fukushima Daiichi. Finally, these particles are heterogeneous, forming under the different conditions within the reactor at the time of the meltdown; thus, they provide samples of what was happening during the meltdown events.

What do we know about the radiation, how far it traveled and its impact?

EWING : Generally, the level of radiation for any individual particle is relatively low, but the size and chemical form of the particle affects its potential for causing radiation exposure. Also, the chemical speciation of the particle is a critical aspect of designing strategies for remediation. There is an increasing scientific effort to follow specific radionuclides through the environment. The fate of these radionuclides in the environment contributes to assessments of safety.

If an earthquake and tsunami like the Tohoku-Oki event occurred in the same region today, what would play out differently and why?

DUNHAM : Local tsunami warning systems have improved greatly since 2011, particularly in their ability to handle extremely large events like Tohoku. And they will only continue to improve in the next few years as the offshore sensor data starts to be used for real-time warnings. Data from those offshore sensors could also be used to explore the pattern of foreshocks and slow fault slip that might precede large earthquakes. There are intriguing hints of precursory behavior prior to large subduction zone earthquakes, but conclusive evidence for this requires high-resolution data of the type that can only be collected with offshore sensor networks.

What are the lessons for future power plants?

EWING : The tragedy at Fukushima Daiichi was not an “accident” in the sense that it could not have been anticipated. From a geologic perspective, there were many “red flags” related to the probability of a tsunami event and its scale. I think that one of the important lessons is that we have spent too much time using risk assessments to demonstrate that a reactor site is safe and not enough time imagining how it might fail.

Ewing is the Frank Stanton Professor in Nuclear Security in Stanford’s Center for International Security and Cooperation (CISAC), a senior fellow at the Freeman Spogli Institute for International Studies and at the Precourt Institute for Energy, and a Professor of Geological Sciences in the School of Earth, Energy & Environmental Sciences (Stanford Earth). Dunham is an Associate Professor of Geophysics. Suckale is an Assistant Professor of Geophysics and, by courtesy, of Civil and Environmental Engineering and a center fellow, by courtesy, at the Stanford Woods Institute for the Environment .

• GREAT ENERGY CHALLENGE

The Fukushima Accident’s Legacy One Year Later

A look at things a year after one of the world’s worst nuclear accidents.

On March 11, 2011, a magnitude 9.0 earthquake erupted some 50 miles off Japan’s Tohoku coast. The ensuing tsunamis set off by the quake devastated communities up and down the Japanese coast, killing some 20,000 people . The one-two natural-disaster punch also triggered the shutdown and subsequent meltdown of three reactors at the Fukushima Daiichi Nuclear Power Station run by the Tokyo Electric Power Company.

While Fukushima is not the world’s worst nuclear accident (Chernobyl holds that dubious distinction having leaked about 10 times more radioactive material into the environment than Fukushima), there is plenty of fallout from the Japanese disaster still playing out.

Japan Still Reeling

Perhaps the greatest enduring tragedy is what’s been transpiring in the 12 miles surrounding the Fukushima plants. Some 80,000 people have had to abandon their homes because of radiation contamination, and it’s estimated that it will be more than 20 years before the land will be habitable for humans. That’s a lot of real estate for a small nation of islands to give up.

Another set of problems stems from the nuclear plants themselves. Completely dismantling them is projected to take 30–40 years . And while authorities seemed to have passed a major milestone last December, their announced cold shutdown (a technical term normally describing the safe and stable conditions in an intact nuclear reactor fuel core deemed necessary to prevent a chain reaction) was anything but normal . Although temperatures in the reactors had fallen below the 100-degree Celsius cutoff necessary for a cold shutdown, more than a hundred thousand gallons of water have had to be injected into the reactors daily to keep things copacetic. Even so, as recently as last month, radiation was discovered leaking from the plant.

FREE BONUS ISSUE

Since the disaster, the Japanese nuclear industry has been in free fall. In the aftermath of the natural disasters and subsequent meltdown, all but two of the country’s 51 nuclear plants* were shut down; the two still operating are scheduled to cease operation in late April . Following the accident, then-Prime Minister Naoto Kan pledged a nuclear-energy-free Japan. However, Yoshihiko Noda, Japan’s current prime minister, acknowledging in one breath “that the government shared the blame for the disaster at the Fukushima Daiichi nuclear power plant,” in another indicated a desire to get the country back on the nuclear-energy track.

Debris Field: Heading for North American Shores

Meanwhile, ocean currents are carrying eastward the debris knocked from Japanese coastal towns by the tsunamis. In September, a Russian training ship spotted debris from Japan , including a television set and a refrigerator, adrift some 1,800 miles from Japan . The find occurred just north of the Midway Islands, the northernmost atoll of the Papahānaumokuākea Marine National Monument , the largest marine reserve in the United States.

The National Oceanic and Atmospheric Administration estimates that bits of debris will begin washing up on small islands northwest of Hawaii soon and on the coasts of Oregon, Washington, Alaska and Canada between March 2013 and 2014 . Fortunately, whatever floats ashore will not arrive as a flotilla; the stuff will have spread out over such a wide swath of ocean that just bits and pieces will make the full voyage and even then only a tiny proportion of the estimated 20-25 million tons of debris will make it .

The good news is that this debris field is a legacy of the tsunami and unrelated to the nuclear accident. No need to worry about the stuff being radioactive, but it will be hazardous to marine life .

(For an interesting simulation of the debris field check out this site .)

Global About-Face

In Fukushima’s wake came a wholesale reassessment of nuclear energy. Germany and Switzerland elected to end their nuclear power programs . Belgium also announced plans to exit the nuclear power game, but it has become torn by, among other things, the short deadline of 2015 and Europe’s mandated carbon targets. Recent U.S. moves show the United States is similarly of two minds.

The State of U.S. Nuclear Power

The U.S. nuclear energy program has been at a standstill since our own little nuclear mishap at Three Mile Island in Pennsylvania in 1979. (Note 3/12/2012: A colleague of mine pointed out after this was published that this sentence might give the wrong impression that Three Mile Island was the cause of America’s nuclear plant stoppage. In fact, as noted in a recent piece in the   Economist ,   “America’s nuclear bubble burst not after the accident at Three Mile Island but five years before it.” The reason: “building nuclear power plants is no longer a commercially feasible option: they are simply too expensive.”) A steady number of about 100 nuclear power plants has been active for decades; today’s 104 reactors supply about 20 percent of the nation’s electricity . In contrast, U.S. renewable energy generation (including hydroelectric) has been growing, so much so that it surpassed that of nuclear for the first three months of 2011 .

But, Fukushima or no Fukushima, nuclear energy is not down for the count. In February the U.S. Nuclear Regulatory Commission (NRC) approved the construction of two new reactors at the Vogtle nuclear power plant in Georgia near the South Carolina border. And while the latest assessment by the U.S. Energy Information Administration sees the race between nuclear and renewable as essentially neck and neck, nuclear power seems to get a slight edge: projections for 2035 have nuclear supplying about 18 percent of the nation’s electricity and renewables only 16 percent.

But building a nuclear power plant requires lots and lots of bucks for capital costs — costs that translate into lots and lots of risk for investors. And that capital outlay can scare investors away, and then bye-bye, new nuclear plant. But the nuclear industry has found other ways to raise the necessary funds. (See here and here .) The latest is called Construction Work in Progress — a financing scheme that allows utilities to charge financing costs to their ratepayers in advance .

Whether incurred upfront or after the fact, the costs and overruns that nuclear plant construction inevitably leads to can hurt — just look at the inflated electricity costs folks living in eastern North Carolina are paying (hundreds of millions of dollars in 2009 more than average state rates) thanks in part to the bulging debt from a nuclear deal sealed in 1982 .

Safe or Safety Myth

Though it’s just a year since Fukushima, and it will be another twenty or so before the damage recedes and can be fully assessed, folks are getting bullish about nuclear power, including the world’s top three electricity users .

The U.S. NRC characterized its decision about the Vogtle plant as a “clarion call to the world that the United States recognizes the importance of expanding nuclear energy.”

Mere weeks after the green light for the new Vogtle reactors was announced, and after not approving any new nuclear power projects in 2011 , the Chinese government announced plans for a new plant in Fujian province .

Chen Bingde, chief engineer of the Nuclear Power Institute of China and a member of a prominent government advisory body, is so confident about the safety of nuclear power plants he proclaimed that “in the near future, nuclear plants can be built right next to cities.” (Maybe, but those future urbanites might well want to know that Japan had considered evacuating Tokyo even as it played a PR game of playing down risks to the public . And, if Italians are any indication, the general public is not keen on nearby nukes . And as for current city-dwellers in close proximity to nuclear plants, even as I write, the fate of the Indian Point nuclear power plant some 35 miles from the island of Manhattan is being hotly debated .)

Japan’s Prime Minister Noda, reflecting on the causes of the Fukushima accident, provided a somewhat more somber assessment than Bingde: “The government, operator and the academic world were all too steeped in a safety myth.”

Here’s my take: There’s a world of difference between safety, acceptable risk, and too much risk . Nuclear power plants lie somewhere between the second and the third. Anyone who tells you they’re unqualifyingly safe is blowing smoke. Hopefully it won’t be radioactive.

More Information

Frontline ‘s “Inside Japan’s Nuclear Meltdown” Frontline ‘s “Inside Japan’s Nuclear Meltdown”

Nuclear Crisis in Japan

The Nuclear Option: Waste Plan or a Wasteland?

______________

* Depending on the source, the number of nuclear reactors reported to be in Japan varies from 50 to 55. I suspect this variation arises from how reactor units are distinguished from a reactor. The number 51 reported here comes from the World Nuclear Association .

(Author’s note added 3/12/2012)

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The Fukushima Nuclear Disaster: Causes, Consequences, and Implications

By: Jochen Reb, Yoshisuke Iinuma, Havovi Joshi

This case study discusses the causes, consequences and implications of the nuclear disaster at Tokyo Electric Power Company's (TEPCO's) Fukushima Dai-ichi nuclear power plant that was triggered by a…

• Length: 11 page(s)
• Publication Date: Oct 25, 2012
• Discipline: General Management
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This case study discusses the causes, consequences and implications of the nuclear disaster at Tokyo Electric Power Company's (TEPCO's) Fukushima Dai-ichi nuclear power plant that was triggered by a massive 9.0 magnitude earthquake and subsequent tsunami waves on March 11, 2011. There are two essential questions: First, "How could it have come so far?" Japan is rightfully considered a technologically advanced nation and is known for its diligence and high-quality products. While the combined earthquake/tsunami triggered the catastrophe, there are a number of deeper underlying causes that are described in the first section of the case. Second, "What next?" While the plant technically achieved cold shutdown with all damaged reactors reaching temperatures below 100°C, this did not mean that the Fukushima disaster was over. Instead, numerous consequences and implications extend into the future.

Learning Objectives

Students will become more aware of the psychological, interpersonal, organisational, and institutional contributors to crises. They will learn to recognise the development, characteristics, and negative consequences of groupthink; and understand the crucial role of communications during crisis management. Students will also discuss broader implications such as the future of nuclear energy and the responsibility of organisations in catastrophes.

Oct 25, 2012

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General Management

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Energy and natural resources sector

Singapore Management University

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Fukushima Daiichi Accident

(Updated August 2023)

• Following a major earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident beginning on 11 March 2011. All three cores largely melted in the first three days.
• The accident was rated level 7 on the International Nuclear and Radiological Event Scale, due to high radioactive releases over days 4 to 6, eventually a total of some 940 PBq (I-131 eq).
• All four Fukushima Daiichi reactors were written off due to damage in the accident – 2719 MWe net.
• After two weeks, the three reactors (units 1-3) were stable with water addition and by July they were being cooled with recycled water from the new treatment plant. Official 'cold shutdown condition' was announced in mid-December.
• Apart from cooling, the basic ongoing task was to prevent release of radioactive materials, particularly in contaminated water leaked from the three units. This task became newsworthy in August 2013.
• There have been no deaths or cases of radiation sickness from the nuclear accident, but over 100,000 people were evacuated from their homes as a preventative measure. Government nervousness has delayed the return of many.
• Official figures show that there have been 2313 disaster-related deaths among evacuees from Fukushima prefecture. Disaster-related deaths are in addition to the about 19,500 that were killed by the earthquake or tsunami.

The Great East Japan Earthquake of magnitude 9.0 at 2.46 pm on Friday 11 March 2011 did considerable damage in the region, and the large tsunami it created caused very much more. The earthquake was centred 130 km offshore the city of Sendai in Miyagi prefecture on the eastern coast of Honshu Island (the main part of Japan), and was a rare and complex double quake giving a severe duration of about 3 minutes. An area of the seafloor extending 650 km north-south moved typically 10-20 metres horizontally. Japan moved a few metres east and the local coastline subsided half a metre. The tsunami inundated about 560 km 2 and resulted in a human death toll of about 19,500 and much damage to coastal ports and towns, with over a million buildings destroyed or partly collapsed.

Eleven reactors at four nuclear power plants in the region were operating at the time and all shut down automatically when the earthquake hit. Subsequent inspection showed no significant damage to any from the earthquake. The operating units which shut down were Tokyo Electric Power Company's (Tepco's) Fukushima Daiichi 1, 2, 3, and Fukushima Daini 1, 2, 3, 4, Tohoku's Onagawa 1, 2, 3, and Japco's Tokai, total 9377 MWe net. Fukushima Daiichi units 4, 5&6 were not operating at the time, but were affected. The main problem initially centred on Fukushima Daiichi 1-3. Unit 4 became a problem on day five.

The reactors proved robust seismically, but vulnerable to the tsunami. Power, from grid or backup generators, was available to run the residual heat removal (RHR) system cooling pumps at eight of the eleven units, and despite some problems they achieved 'cold shutdown' within about four days. The other three, at Fukushima Daiichi, lost power at 3.42 pm, almost an hour after the earthquake, when the entire site was flooded by the 15-metre tsunami. This disabled 12 of 13 backup generators onsite and also the heat exchangers for dumping reactor waste heat and decay heat to the sea. The three units lost the ability to maintain proper reactor cooling and water circulation functions. Electrical switchgear was also disabled. Thereafter, many weeks of focused work centred on restoring heat removal from the reactors and coping with overheated spent fuel ponds. This was undertaken by hundreds of Tepco employees as well as some contractors, supported by firefighting and military personnel. Some of the Tepco staff had lost homes, and even families, in the tsunami, and were initially living in temporary accommodation under great difficulty and privation, with some personal risk. A hardened onsite emergency response centre was unable to be used in grappling with the situation, due to radioactive contamination.

Three Tepco employees at the Daiichi and Daini plants were killed directly by the earthquake and tsunami, but there have been no fatalities from the nuclear accident.

Among hundreds of aftershocks, an earthquake with magnitude 7.1, closer to Fukushima than the 11 March one, was experienced on 7 April, but without further damage to the plant. On 11 April a magnitude 7.1 earthquake and on 12 April a magnitude 6.3 earthquake, both with the epicentre at Fukushima-Hamadori, caused no further problems.

The two Fukushima plants and their siting

The Daiichi (first) and Daini (second) Fukushima plants are sited about 11 km apart on the coast, Daini to the south.

The recorded seismic data for both plants – some 180 km from the epicentre – shows that 550 Gal (0.56 g) was the maximum ground acceleration for Daiichi, and 254 Gal was maximum for Daini. Daiichi units 2, 3 and 5 exceeded their maximum response acceleration design basis in an east-west direction by about 20%. The recording was over 130-150 seconds. (All nuclear plants in Japan are built on rock – ground acceleration was around 2000 Gal a few kilometres north, on sediments).

The original design basis tsunami height was 3.1 m for Daiichi based on assessment of the 1960 Chile tsunami and so the plant had been built about 10 metres above sea level with the seawater pumps 4 m above sea level. The Daini plant was built 13 metres above sea level. In 2002 the design basis was revised to 5.7 metres above, and the seawater pumps were sealed. In the event, tsunami heights coming ashore were about 15 metres, and the Daiichi turbine halls were under some 5 metres of seawater until levels subsided. Daini was less affected. The maximum amplitude of this tsunami was 23 metres at point of origin, about 180 km from Fukushima.

In the last century there have been eight tsunamis in the region with maximum amplitudes at origin above 10 metres (some much more), these having arisen from earthquakes of magnitude 7.7 to 8.4, on average one every 12 years. Those in 1983 and in 1993 were the most recent affecting Japan, with maximum heights at origin of 14.5 metres and 31 metres respectively, both induced by magnitude 7.7 earthquakes. The June 1896 earthquake of estimated magnitude 8.3 produced a tsunami with run-up height of 38 metres in Tohoku region, killing more than 27,000 people.

The tsunami countermeasures taken when Fukushima Daiichi was designed and sited in the 1960s were considered acceptable in relation to the scientific knowledge then, with low recorded run-up heights for that particular coastline. But some 18 years before the 2011 disaster, new scientific knowledge had emerged about the likelihood of a large earthquake and resulting major tsunami of some 15.7 metres at the Daiichi site. However, this had not yet led to any major action by either the plant operator, Tepco, or government regulators, notably the Nuclear & Industrial Safety Agency (NISA). Discussion was ongoing, but action minimal. The tsunami countermeasures could also have been reviewed in accordance with International Atomic Energy Agency (IAEA) guidelines which required taking into account high tsunami levels, but NISA continued to allow the Fukushima plant to operate without sufficient countermeasures such as moving the backup generators up the hill, sealing the lower part of the buildings, and having some back-up for seawater pumps, despite clear warnings.

A report from the Japanese government's Earthquake Research Committee on earthquakes and tsunamis off the Pacific coastline of northeastern Japan in February 2011 was due for release in April, and might finally have brought about changes. The document includes analysis of a magnitude 8.3 earthquake that is known to have struck the region more than 1140 years ago, triggering enormous tsunamis that flooded vast areas of Miyagi and Fukushima prefectures. The report concludes that the region should be alerted of the risk of a similar disaster striking again. The 11 March earthquake measured magnitude 9.0 and involved substantial shifting of multiple sections of seabed over a source area of 200 x 400 km. Tsunami waves devastated wide areas of Miyagi, Iwate and Fukushima prefectures.

(See also background on Earthquakes and Seismic Protection for Nuclear Power Plants in Japan )

Events at Fukushima Daiichi 1-3 & 4

It appears that no serious damage was done to the reactors by the earthquake, and the operating units 1-3 were automatically shut down in response to it, as designed. At the same time all six external power supply sources were lost due to earthquake damage, so the emergency diesel generators located in the basements of the turbine buildings started up. Initially cooling would have been maintained through the main steam circuit bypassing the turbine and going through the condensers.

Then 41 minutes later, at 3:42 pm, the first tsunami wave hit, followed by a second 8 minutes later. These submerged and damaged the seawater pumps for both the main condenser circuits and the auxiliary cooling circuits, notably the residual heat removal (RHR) cooling system. They also drowned the diesel generators and inundated the electrical switchgear and batteries, all located in the basements of the turbine buildings (the one surviving air-cooled generator was serving units 5&6). So there was a station blackout, and the reactors were isolated from their ultimate heat sink. The tsunamis also damaged and obstructed roads, making outside access difficult.

All this put reactors 1-3 in a dire situation and led the authorities to order, and subsequently extend, an evacuation while engineers worked to restore power and cooling. The 125-volt DC back-up batteries for units 1&2 were flooded and failed, leaving them without instrumentation, control or lighting. Unit 3 had battery power for about 30 hours.

At 7:03 pm Friday 11 March a nuclear emergency was declared, and at 8:50pm the Fukushima prefecture issued an evacuation order for people within 2 km of the plant. At 9:23 pm the prime minister extended this to 3 km, and at 5:44 am on 12 March he extended it to 10 km. He visited the plant soon after. Later on Saturday 12 March he extended the evacuation zone to 20 km.

Inside the Fukushima Daiichi reactors

The Fukushima Daiichi reactors were GE boiling water reactors (BWRs) of an early (1960s) design supplied by GE, Toshiba and Hitachi, with what is known as a Mark I containment. Reactors 1-3 came into commercial operation 1971-75. Reactor capacity was 460 MWe for unit 1, 784 MWe for units 2-5, and 1100 MWe for unit 6.

When the power failed at 3:42 pm, about one hour after shutdown of the fission reactions, the reactor cores would still have been producing about 1.5% of their nominal thermal power, from fission product decay – about 22 MW in unit 1 and 33 MW in units 2&3. Without heat removal by circulation to an outside heat exchanger, this produced a lot of steam in the reactor pressure vessels (RPVs) housing the cores, and this was released into the dry primary containment (PCV) through safety valves. Later this was accompanied by hydrogen, produced by the interaction of the fuel's very hot zirconium cladding with steam after the water level dropped.

As pressure started to rise here, the steam was directed into the suppression chamber/wetwell under the reactor, within the containment, but the internal temperature and pressure nevertheless rose quite rapidly. Water injection commenced, using the various systems provide for this and finally the emergency core cooling system (ECCS). These systems progressively failed over three days, so from early Saturday water injection to the RPV was with fire pumps, but this required the internal pressures to be relieved initially by venting into the suppression chamber/wetwell. Seawater injection into unit 1 began at 7:00 pm on Saturday 12, into unit 3 on Sunday 13 and unit 2 on Monday 14. Tepco management ignored an instruction from the prime minister to cease the seawater injection into unit 1, and this instruction was withdrawn shortly afterwards.

Inside unit 1 , it is understood that the water level dropped to the top of the fuel about three hours after the scram (about 6:00 pm) and the bottom of the fuel 1.5 hours later (7:30 pm). The temperature of the exposed fuel rose to some 2800°C so that the central part started to melt after a few hours and by 16 hours after the scram (7:00 am Saturday) most of it had fallen into the water at the bottom of the RPV. After that, RPV temperatures decreased steadily.

As pressure rose, attempts were made to vent the containment, and when external power and compressed air sources were harnessed this was successful, by about 2:30 pm Saturday, though some manual venting was apparently achieved at about 10:17 am. The venting was designed to be through an external stack, but in the absence of power much of it apparently backflowed to the service floor at the top of the reactor building, representing a serious failure of this system (though another possibility is leakage from the drywell). The vented steam, noble gases and aerosols were accompanied by hydrogen. At 3:36 pm on Saturday 12, there was a hydrogen explosion on the service floor of the building above unit 1 reactor containment, blowing off the roof and cladding on the top part of the building, after the hydrogen mixed with air and ignited. (Oxidation of the zirconium cladding at high temperatures in the presence of steam produces hydrogen exothermically, with this exacerbating the fuel decay heat problem.)

In unit 1 most of the core – as corium, composed of melted fuel and control rods – was assumed to be in the bottom of the RPV, but later it appeared that it had mostly gone through the bottom of the RPV and eroded about 65 cm into the drywell concrete below (which is 2.6 m thick). This reduced the intensity of the heat and enabled the mass to solidify.

Much of the fuel in units 2&3 also apparently melted to some degree, but to a lesser extent than in unit 1, and a day or two later. In mid-May 2011 the unit 1 core would still have been producing 1.8 MW of heat, and units 2&3 about 3.0 MW each.

In mid-2013 the Nuclear Regulation Authority (NRA) confirmed that the earthquake itself had caused no damage to unit 1.

In unit 2 , water injection using the steam-driven back-up water injection system failed on Monday 14, and it was about six hours before a fire pump started injecting seawater into the RPV. Before the fire pump could be used RPV pressure had to be relieved via the wetwell, which required power and nitrogen, hence the delay. Meanwhile the reactor water level dropped rapidly after backup cooling was lost, so that core damage started about 8 pm, and it is now understood that much of the fuel then melted and probably fell into the water at the bottom of the RPV about 100 hours after the scram. Pressure was vented on Sunday 13 and again on Tuesday 15, and meanwhile the blowout panel near the top of the building was opened to avoid a repetition of the hydrogen explosion at unit 1. Early on Tuesday 15, the pressure suppression chamber under the actual reactor seemed to rupture, possibly due to a hydrogen explosion there, and the drywell containment pressure inside dropped. However, subsequent inspection of the suppression chamber did not support the rupture interpretation. Later analysis suggested that a leak of the primary containment developed on Tuesday 15. Most of the radioactive releases from the site appeared to come from unit 2.

In unit 3 , the main backup water injection system failed at about 11:00 am on Saturday 12, and early on Sunday 13 water injection using the high pressure system failed also and water levels dropped dramatically. RPV pressure was reduced by venting steam into the wetwell, allowing injection of seawater using a fire pump from just before noon. Early on Sunday venting the suppression chamber and containment was successfully undertaken. It is now understood that core damage started about 5:30 am and much or all of the fuel melted on the morning of Sunday 13 and fell into the bottom of the RPV, with some probably going through the bottom of the reactor pressure vessel and onto the concrete below.

Early on Monday 14 PCV venting was repeated, and this evidently backflowed to the service floor of the building, so that at 11:00 am a very large hydrogen explosion here above unit 3 reactor containment blew off much of the roof and walls and demolished the top part of the building. This explosion created a lot of debris, and some of that on the ground near unit 3 was very radioactive.

In defuelled unit 4 , at about 6:00 am on Tuesday 15 March, there was an explosion which destroyed the top of the building and damaged unit 3's superstructure further. This was apparently from hydrogen arising in unit 3 and reaching unit 4 by backflow in shared ducts when vented from unit 3.

Units 1-3: Water had been injected into each of the three reactor units more or less continuously, and in the absence of normal heat removal via external heat exchanger this water was boiling off for some months. In the government report to the IAEA in June it was estimated that to the end of May about 40% of the injected water boiled off, and 60% leaked out the bottom. In June 2011 this was adding to the contaminated water onsite by about 500 m 3 per day. In January 2013 4.5 to 5.5 m 3 /h was being added to each RPV via core spray and feedwater systems, hence 370 m 3 per day, and temperatures at the bottom of RPVs were 19 °C in unit 1 and 32 °C in units 2&3, at little above atmospheric pressure.

There was a peak of radioactive release on Tuesday 15, apparently mostly from unit 2, but the precise source remains uncertain. Due to volatile and easily-airborne fission products being carried with the hydrogen and steam, the venting and hydrogen explosions discharged a lot of radioactive material into the atmosphere, notably iodine and caesium. NISA said in June that it estimated that 800-1000 kg of hydrogen had been produced in each of the units.

Nitrogen was being injected into the PCVs of all three reactors to remove concerns about further hydrogen explosions, and in December this was started also for the pressure vessels. Gas control systems which extract and clean the gas from the PCV to avoid leakage of caesium were commissioned for all three units.

Throughout 2011 injection into the RPVs of water circulated through the new water treatment plant achieved relatively effective cooling, and temperatures at the bottom of the RPVs were stable in the range 60-76 °C at the end of October, and 27-54 °C in mid-January 2012. RPV pressures ranged from atmospheric to slightly above (102-109 kPa) in January, due to water and nitrogen injection. However, since they were leaking, the normal definition of 'cold shutdown' did not apply, and Tepco waited to bring radioactive releases under control before declaring 'cold shutdown condition' in mid-December, with NISA's approval. This, with the prime minister's announcement of it, formally brought to a close the 'accident' phase of events.

The AC electricity supply from external source was connected to all units by 22 March. Power was restored to instrumentation in all units except unit 3 by 25 March. However, radiation levels inside the plant were so high that normal access was impossible until June.

Event sequence following earthquake (timing from it: 14:46, 11 March)

* according to 2012 MAAP (Modular Accident Analysis Program) analysis

By March 2016 total decay heat in units 1-3 had dropped to 1 MW for all three, about 1% of the original level, meaning that cooling water injection – then 100 m 3 /d – could be interrupted for up to two days.

Results of muon measurements in unit 2 in 2016 indicate that most of the fuel debris in unit 2 is in the bottom of the reactor vessel.

Tepco has written off the four reactors damaged by the accident, and is decommissioning them.

Summary : Major fuel melting occurred early on in all three units, though the fuel remained essentially contained except for some volatile fission products vented early on, or released from unit 2 in mid-March, and some soluble ones which were leaking with the water, especially from unit 2, where the containment is evidently breached. Cooling is provided from external sources, using treated recycled water, with a stable heat removal path from the actual reactors to external heat sinks. Access has been gained to all three reactor buildings, but dose rates remain high inside. Tepco declared 'cold shutdown condition' in mid-December 2011 when radioactive releases had reduced to minimal levels.

(See also background on nuclear reactors at Fukushima Daiichi .)

Fuel ponds: developing problems

Used fuel needs to be cooled and shielded. This is initially by water, in ponds. After about three years underwater, used fuel can be transferred to dry storage, with air ventilation simply by convection. Used fuel generates heat, so the water in ponds is circulated by electric pumps through external heat exchangers, so that the heat is dumped and a low temperature maintained. There are fuel ponds near the top of all six reactor buildings at the Daiichi plant, adjacent to the top of each reactor so that the fuel can be unloaded underwater when the top is off the reactor pressure vessel and it is flooded. The ponds hold some fresh fuel and some used fuel, the latter pending its transfer to the onsite central used/spent fuel storage. (There is some dry storage onsite to extend the plant's capacity.)

At the time of the accident, in addition to a large number of used fuel assemblies, unit 4's pond also held a full core load of 548 fuel assemblies while the reactor was undergoing maintenance, these having been removed at the end of November, and were to be replaced in the core.

A separate set of problems arose as the fuel ponds, holding fresh and used fuel in the upper part of the reactor structures, were found to be depleted in water. The primary cause of the low water levels was loss of cooling circulation to external heat exchangers, leading to elevated temperatures and probably boiling, especially in the heavily-loaded unit 4 fuel pond. Here the fuel would have been uncovered in about 7 days due to water boiling off. However, the fact that unit 4 was unloaded meant that there was a large inventory of water at the top of the structure, and enough of this replenished the fuel pond to prevent the fuel becoming uncovered – the minimum level reached was about 1.2 m above the fuel on about 22 April.

After the hydrogen explosion in unit 4 early on Tuesday 15 March, Tepco was told to implement injection of water to unit 4 pond which had a particularly high heat load (3 MW) from 1331 used fuel assemblies in it, so it was the main focus of concern. It needed the addition of about 100 m 3 /day to replenish it after circulation ceased.

From Tuesday 15 March attention was given to replenishing the water in the ponds of units 1, 2&3 as well. Initially this was attempted with fire pumps but from 22 March a concrete pump with 58-metre boom enabled more precise targeting of water through the damaged walls of the service floors. There was some use of built-in plumbing for unit 2. Analysis of radionuclides in water from the used fuel ponds suggested that some of the fuel assemblies might have been damaged, but the majority were intact.

There was concern about the structural strength of unit 4 building, so support for the pond was reinforced by the end of July.

New cooling circuits with heat exchangers adjacent to the reactor buildings for all four ponds were commissioned after a few months, and each reduced the pool temperature from 70 °C to normal in a few days. Each has a primary circuit within the reactor and waste treatment buildings and a secondary circuit dumping heat through a small dry cooling tower outside the building.

The next task was to remove the salt from those ponds which had seawater added, to reduce the potential for corrosion.

In July 2012 two of the 204 fresh fuel assemblies were removed from the unit 4 pool and transferred to the central spent fuel pool for detailed inspection to check damage, particularly corrosion. They were found to have no deformation or corrosion. Unloading the 1331 spent fuel assemblies in pond 4 and transferring them to the central spent fuel pool commenced in mid-November 2013 and was completed 13 months later. These comprised 783 spent fuel plus the full fuel load of 548.

The next focus of attention was the unit 3 pool. In 2015 the damaged fuel handling equipment and other wreckage was removed from the destroyed upper level of the reactor building. Toshiba built a 74-tonne fuel handling machine for transferring the 566 fuel assemblies into casks and to remove debris in the pool, and a crane for lifting the fuel transfer casks. Installation of a cover over the fuel handling machine was completed in February 2018. Removal and transferral of the fuel to the central spent fuel pool began in mid-April 2019 and was completed at the end of February 2021.

The onsite central spent fuel pool in 2011 held about 60% of the Daiichi used fuel, and is immediately west (inland) of unit 4. It lost circulation with the power outage, and temperature increased to 73 °C by the time mains power and cooling were restored after two weeks. In late 2013 this pond, with capacity for 6840*, held 6375 fuel assemblies, the same as at the time of the accident. In June 2018, Tepco announced it would transfer some of the fuel assemblies stored in the central spent fuel pool to an onsite temporary dry storage facility to clear sufficient space for the fuel assemblies from unit 3's pool. The dry storage facility has a capacity of at least 2930 assemblies in 65 casks – each dry cask holds 50 fuel assemblies. Eventually these will be shipped to JNFL’s Rokkasho reprocessing plant or to Recyclable Fuel Storage Company’s Mutsu facility.

* effectively 6750, due to one rack of 90 having some damaged fuel.

Summary: The spent fuel storage pools survived the earthquake, tsunami and hydrogen explosions without significant damage to the fuel, significant radiological release, or threat to public safety. The new cooling circuits with external heat exchangers for the four ponds are working well and temperatures are normal. Analysis of water has confirmed that most fuel rods are intact. All fuel assemblies have been removed from the unit 3&4 pools.

(See also background on Fukushima Fuel Ponds  and Decommissioning section below.)

Radioactive releases to air

Regarding releases to air and also water leakage from Fukushima Daiichi, the main radionuclide from among the many kinds of fission products in the fuel was volatile iodine-131, which has a half-life of 8 days. The other main radionuclide is caesium-137, which has a 30-year half-life, is easily carried in a plume, and when it lands it may contaminate land for some time. It is a strong gamma-emitter in its decay. Cs-134 is also produced and dispersed; it has a two-year half-life. Caesium is soluble and can be taken into the body, but does not concentrate in any particular organs, and has a biological half-life of about 70 days. In assessing the significance of atmospheric releases, the Cs-137 figure is multiplied by 40 and added to the I-131 number to give an 'iodine-131 equivalent' figure.

As cooling failed on the first day, evacuations were progressively ordered, due to uncertainty about what was happening inside the reactors and the possible effects. By the evening of Saturday 12 March the evacuation zone had been extended to 20 km from the plant. From 20 to 30 km from the plant, the criterion of 20 mSv/yr dose rate was applied to determine evacuation, and is now the criterion for return being allowed. 20 mSv/yr was also the general limit set for children's dose rate related to outdoor activities, but there were calls to reduce this. In areas with 20-50 mSv/yr from April 2012 residency is restricted, with remediation action taken. See later section on Public health and return of evacuees .

A significant problem in tracking radioactive release was that 23 out of the 24 radiation monitoring stations on the plant site were disabled by the tsunami.

There is some uncertainty about the amount and exact sources of radioactive releases to air (see also background on Radiation Exposure ).

Japan’s regulator, the Nuclear & Industrial Safety Agency (NISA), estimated in June 2011 that 770 PBq (iodine-131 equivalent) of radioactivity had been released, but the Nuclear Safety Commission (NSC, a policy body) in August lowered this estimate to 570 PBq . The 770 PBq figure is about 15% of the Chernobyl release of 5200 PBq iodine-131 equivalent. Most of the release was by the end of March 2011.

Tepco sprayed a dust-suppressing polymer resin around the plant to ensure that fallout from mid-March was not mobilized by wind or rain. In addition it removed a lot of rubble with remote control front-end loaders, and this further reduced ambient radiation levels, halving them near unit 1. The highest radiation levels onsite came from debris left on the ground after the explosions at units 3&4.

Reactor covers

In mid-May 2011 work started towards constructing a cover over unit 1 to reduce airborne radioactive releases from the site, to keep out the rain, and to enable measurement of radioactive releases within the structure through its ventilation system. The frame was assembled over the reactor, enclosing an area 42 x 47 m, and 54 m high. The sections of the steel frame fitted together remotely without the use of screws and bolts. All the wall panels had a flameproof coating, and the structure had a filtered ventilation system capable of handling 40,000 cubic metres of air per hour through six lines, including two backup lines. The cover structure was fitted with internal monitoring cameras, radiation and hydrogen detectors, thermometers and a pipe for water injection. The cover was completed with ventilation systems working by the end of October 2011. It was expected to be needed for two years. In May 2013 Tepco announced its more permanent replacement, to be built over four years. It started demolishing the 2011 cover in 2014 and finished in 2016. In December 2019 it decided to install the replacement cover before removing debris from the top floor of the building. A crane and other equipment for fuel removal will be installed under the cover, similar to that over unit 4.

More substantial covers were designed to fit around units 3&4 reactor buildings after the top floors were cleared up in 2012.

A cantilevered structure was built over unit 4 from April 2012 to July 2013 to enable recovery of the contents of the spent fuel pond. This is a 69 x 31 m cover (53 m high) and it was fully equipped by the end of 2013 to enable unloading of used fuel from the storage pond into casks, each holding 22 fuel assemblies, and removal of the casks. This operation was accomplished under water, using the new fuel handling machine (replacing the one destroyed by the hydrogen explosion) so that the used fuel could be transferred to the central storage onsite. Transfer was completed in December 2014. A video of the process is available on Tepco's website.

A different design of cover was built over unit 3, and foundation work began in 2012. Large rubble removal took place from 2013 to 2015, including the damaged fuel handling machine. An arched cover was prefabricated, 57 m long and 19 m wide, and supported by the turbine building on one side and the ground on the other. A crane removed the 566 fuel assemblies from the pool and some remaining rubble. Spent fuel removal from unit 3 pool began in April 2019 and was completed in February 2021. Spent fuel removal from units 1&2 pools was scheduled in 2018, but is now scheduled to begin in 2023.

Maps from the Ministry of Education, Culture, Sports, Science and Tehcnology (MEXT) aerial surveys carried out approximately one year apart show the reduction in contamination from late 2011 to late 2012. Areas with colour changes in 2012 showed approximately half the contamination as surveyed in 2011, the difference coming from decay of caesium-134 (two-year half-life) and natural processes like wind and rain. In blue areas, ambient radiation is very similar to global background levels at <0.5 microsieverts per hour, which is equal to <4.4 mSv/yr.

Tests on radioactivity in rice have been made and caesium was found in a few of them. The highest levels were about one-quarter of the allowable limit of 500 Bq/kg, so shipments to market are permitted.

Summary : Major releases of radionuclides, including long-lived caesium, occurred to air, mainly in mid-March. The population within a 20km radius had been evacuated three days earlier. Considerable work was done to reduce the amount of radioactive debris onsite and to stabilize dust. The main source of radioactive releases was the apparent hydrogen explosion in the suppression chamber of unit 2 on 15 March. A cover building for unit 1 reactor was built and the unit is now being dismantled, a more substantial one for unit 4 was built to enable fuel removal during 2014. Radioactive releases in mid-August 2011 had reduced to 5 GBq/hr, and dose rate from these at the plant boundary was 1.7 mSv/yr, less than natural background.

Sequence of evacuation orders based on the report by The National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission : 11 March 14:46 JST The earthquake occurred. 15:42 TEPCO made the first emergency report to the government. 19:03 The government announced nuclear emergency. 20:50 The Fukushima Prefecture Office ordered 2km radius evacuation. 21:23 The government ordered 3km evacuation and to keep staying inside buildings in the area of 3-10km radius. 12 March 05:44 The government ordered 10km radius evacuation. 18:25 The government ordered 20km evacuation. 15 March 11:01 The government ordered to keep staying inside buildings in the area of 20-30km from the plant. 25 March The government requested voluntary evacuation in the area of 20-30km. 21 April The government set the 20km radius no-go area.

Radiation exposure on the plant site

By the end of 2011, Tepco had checked the radiation exposure of 19,594 people who had worked on the site since 11 March. For many of these both external dose and internal doses (measured with whole-body counters) were considered. It reported that 167 workers had received doses over 100 mSv. Of these 135 had received 100 to 150 mSv, twenty-three 150-200 mSv, three more 200-250 mSv, and six had received over 250 mSv (309 to 678 mSv) apparently due to inhaling iodine-131 fumes early on. The latter included the units 3&4 control room operators in the first two days who had not been wearing breathing apparatus. There were up to 200 workers onsite each day. Recovery workers wear personal monitors, with breathing apparatus and protective clothing which protect against alpha and beta radiation. The level of 250 mSv was the allowable maximum short-term dose for Fukushima Daiichi accident clean-up workers through to December 2011, 500 mSv is the international allowable short-term dose "for emergency workers taking life-saving actions". In January 2012 the allowable maximum reverted to 50 mSv/yr.

No radiation casualties (acute radiation syndrome) occurred, and few other injuries, though higher than normal doses, were being accumulated by several hundred workers onsite. High radiation levels in the three reactor buildings hindered access there.

Monitoring of seawater, soil and atmosphere is at 25 locations on the plant site, 12 locations on the boundary, and others further afield. Government and IAEA monitoring of air and seawater is ongoing. Some high but not health-threatening levels of iodine-131 were found in March, but with an eight-day half-life, most I-131 had gone by the end of April 2011.

A radiation survey map of the site made in March 2013 revealed substantial progress: the highest dose rate anywhere on the site was 0.15 mSv/h near units 3 and 4. (Soon after the accident a similar survey put the highest dose rate at 300 mSv/h near rubble lying alongside unit 3.) The majority of the power plant area was at less than 0.01 mSv/h. These reduced levels are reflected in worker doses: during January 2013, the 5702 workers at the site received an average of 0.86 mSv, with 75% of workers recorded as receiving less than 1 mSv. In total, only about 2% of workers received over 5 mSv and the highest dose in January was 12.65 mSv for one worker.

Media reports have referred to 'nuclear gypsies' – casual workers employed by subcontractors on a short-term basis, and allegedly prone to receiving higher and unsupervised radiation doses. This transient workforce has been part of the nuclear scene for at least four decades, and at Fukushima their doses are very rigorously monitored. If they reach certain levels, e.g. 30 mSv but varying according to circumstance, they are reassigned to lower-exposure areas.

Tepco figures submitted to the NRA for the period to end January 2014 showed 173 workers had received more than 100 mSv (six more than two years earlier) and 1578 had received 50 to 100 mSv. This was among a total of 32,024, 64% more than had worked there two years earlier. Since April 2013 none of the 13,154 who had worked onsite had received more than 50 mSv, and 96% of these had less than a 20 mSv dose. Early in 2014 there were about 4000 onsite each weekday.

Summary : Six workers received radiation doses apparently over the 250 mSv level set by NISA, but at levels below those which would cause radiation sickness.

Radiation exposure and fallout beyond the plant site

On 4 April 2011, radiation levels of 0.06 mSv/day were recorded in Fukushima city, 65 km northwest of the plant, about 60 times higher than normal but posing no health risk according to authorities. Monitoring beyond the 20 km evacuation radius to 13 April showed one location – around Iitate – with up to 0.266 mSv/day dose rate, but elsewhere no more than one-tenth of this. At the end of July the highest level measured within 30km radius was 0.84 mSv/day in Namie town, 24 km away. The safety limit set by the central government in mid-April for public recreation areas was 3.8 microsieverts per hour (0.09 mSv/day).

In June 2013, analysis from Japan's Nuclear Regulation Authority (NRA) showed that the most contaminated areas in the Fukushima evacuation zone had reduced in size by three-quarters over the previous two years. The area subject to high dose rates (over 166 mSv/yr) diminished from 27% of the 1117 km 2 zone to 6% over 15 months to March 2013, and in the ‘no residence’ portion (originally 83-166 mSv/yr) no areas remained at this level and 70% was below 33 mSv/yr. The least-contaminated area is now entirely below 33 mSv/yr.

In August 2011 The Act on Special Measures Concerning the Handling of Radioactive Pollution was enacted and it took full effect from January 2012 as the main legal instrument to deal with all remediation activities in the affected areas, as well as the management of materials removed as a result of those activities. It specified two categories of land: Special Decontamination Areas consisting of the 'restricted areas' located within a 20 km radius from the Fukushima Daiichi plant, and 'deliberate evacuation areas' where the annual cumulative dose for individuals was anticipated to exceed 20 mSv. The national government promotes decontamination in these areas. These areas are subdivided into three: dose 1-20 mSv/yr (green); dose 20-50 mSv/yr (yellow); and dose over 50 mSv/yr and over 20 mSv/yr averaged over 5 years (red). Intensive Contamination Survey Areas including the so-called Decontamination Implementation Areas, where an additional annual cumulative dose between 1 mSv and 20 mSv was estimated for individuals. Municipalities implement decontamination activities in these areas.

Following a detailed study by 80 international experts, the UN Scientific Committee on the Effects of Atomic Radiation's (UNSCEAR's) May 2013 Report to the General Assembly concluded: "No radiation-related deaths or acute diseases have been observed among the workers and general public exposed to radiation from the accident. The doses to the general public, both those incurred during the first year and estimated for their lifetimes, are generally low or very low. No discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants."

However, the report noted: "More than 160 additional workers received effective doses currently estimated to be over 100 mSv, predominantly from external exposures. Among this group, an increased risk of cancer would be expected in the future. However, any increased incidence of cancer in this group is expected to be indiscernible because of the difficulty of confirming such a small incidence against the normal statistical fluctuations in cancer incidence."

These workers are individually monitored annually for potential late radiation-related health effects. UNSCEAR’s follow-up white paper in October 2015 said that none of the new information appraised after the 2013 report “materially affected the main findings or challenged the major assumptions of the 2013 Fukushima report."

By contrast, the public was exposed to 10-50 times less radiation. Most Japanese people were exposed to additional radiation amounting to less than the typical natural background level of 2.1 mSv per year.

In 2018 UNSCEAR decided to update the 2013 report to reflect the latest findings. In March 2021, UNSCEAR published its 2020 Report , which broadly confirms the major findings and conclusions of the 2013 report. The 2020 Report states: "No adverse health effects among Fukushima residents have been documented that are directly attributable to radiation exposure from the Fukushima Daiichi nuclear plant accident. The Committee’s revised estimates of dose are such that future radiation-associated health effects are unlikely to be discernible."

People living in Fukushima prefecture are expected to be exposed to around 10 mSv over their entire lifetimes, while for those living further away the dose would be 0.2 mSv per year. The UNSCEAR conclusion reinforces the findings of several international reports to date, including one from the World Health Organization (WHO) that considered the health risk to the most exposed people possible: a postulated girl under one year of age living in Iitate or Namie that did not evacuate and continued life as normal for four months after the accident. Such a child's theoretical risk of developing any cancer would be increased only marginally, according to the WHO's analysis.

Despite the conclusions of reports from UNSCEAR and the WHO, the Japanese government in 2018 acknowledged a connection between the death of a former plant worker and radiation exposure. The man had been diagnosed with lung cancer in February 2016.

Eleven municipalities in the former restricted zone or planned evacuation area, within 20 km of the plant or where annual cumulative radiation dose is greater than 20 mSv, are designated 'special decontamination areas', where decontamination work is being implemented by the government. A further 100 municipalities in eight prefectures, where dose rates are equivalent to over 1 mSv per year are classed as 'intensive decontamination survey areas', where decontamination is being implemented by each municipality with funding and technical support from the national government. Decontamination of all 11 special decontamination areas has been completed.

In October 2013 a 16-member IAEA mission reported on remediation and decontamination in the special decontamination areas. Its preliminary report said that decontamination efforts were commendable but driven by unrealistic targets. If annual radiation dose was below 20 mSv, such as generally in intensive decontamination survey areas, this level was “acceptable and in line with the international standards and with the recommendations from the relevant international organizations, e.g. ICRP, IAEA, UNSCEAR and WHO.” The clear implication was that people in such areas should be allowed to return home. Furthermore the government should increase efforts to communicate this to the public, and should explain that its long-term goal of achieving an additional individual dose of 1 mSv/yr is unrealistic and unnecessary in the short term. Also, there is potential to produce more food safely in contaminated areas.

Radioactivity, primarily from caesium-137, in the evacuation zone and other areas beyond it has been reported in terms of kBq/kg (compared with kBq/m 2  around Chernobyl. A total of 3000 km 2  was contaminated above 180 kBq/m 2 , compared with 29,400 km 2  from Chernobyl). However the main measure has been presumed doses in mSv/yr. The government has adopted 20 mSv/yr as its goal for the evacuation zone and more contaminated areas outside it, and supports municipal government work to reduce levels below that. The total area under consideration for attention is 13,000 km 2 . In 2016 the Ministry of Environment announced that material with less than 8 kBq/kg caesium would no longer be specified as waste, and subject to restrictions on disposal. It allowed use of contaminated soil for embankments, where the activity was less then 8 kBq/kg, and unrestricted use if less than 100 Bq/kg. Most of the stored wastes have decayed to below the 8 kBq/kg level.

Summary : There have been no harmful effects from radiation on local people, nor any doses approaching harmful levels. However, some 160,000 people were evacuated from their homes and only from 2012 were allowed limited return. As of July 2020 over 41,000 remained displaced due to government concern about radiological effects from the accident.

Public health and return of evacuees

Permanent return remains a high priority, and the evacuation zone is being decontaminated where required and possible, so that evacuees can return. There are many cases of evacuation stress including transfer trauma among evacuees, and once the situation had stabilized at the plant these outweighed the radiological hazards of returning, with 2313 deaths reported (see below ).

In December 2011 the government said that where annual radiation dose would be below 20 mSv/yr, the government would help residents return home as soon as possible and assist local municipalities with decontamination and repair of infrastructure. In areas where radiation levels are over 20 mSv/yr evacuees will be asked to continue living elsewhere for “a few years” until the government completes decontamination and recovery work. The government said it would consider purchasing land and houses from residents of these areas if the evacuees wish to sell them.

In November 2013 the NRA decided to change the way radiation exposure was estimated. Instead of airborne surveys being the basis, personal dosimeters would be used, giving very much more accurate figures, often much less than airborne estimates. The same criteria would be used, as above, with 20 mSv/yr being the threshold of concern to authorities.

In February 2014 the results of a study were published showing that 458 residents of two study areas 20 to 30 km from the plant and a third one 50 km northwest received radiation doses from the contaminated ground similar to the country’s natural background levels. Measurement was by personal dosimeters over August-September 2012.

By September 2020, 2313 disaster-related deaths among evacuees from Fukushima prefecture*, that were not due to radiation-induced damage or to the earthquake or to the tsunami, had been identified by the Japanese authorities. About 90% of deaths were for persons above 66 years of age. Of these, about 30% occurred within the first three months of the evacuations, and about 80% within two years.

* An additional 1454 disaster-related deaths have been reported among evacuees from other tsunami- and earthquake-related prefectures. Disaster-related deaths are in addition to the over 19,500 that died in the actual earthquake and tsunami.

The premature disaster-related deaths were mainly related to (i) physical and mental illness brought about by having to reside in shelters and the trauma of being forced to move from care settings and homes; and (ii) delays in obtaining needed medical support because of the enormous destruction caused by the earthquake and tsunami. 

However, the radiation levels in most of the evacuated areas were not greater than the natural radiation levels in high background areas elsewhere in the world where no adverse health effect is evident.

In its December 2018 report , the Fukushima prefectural government said that the number of ‘indirect’ deaths in the prefecture was greater than the number (1829) killed in the earthquake and tsunami. It put the figure then at 2259 (since revised up to 2313) as determined by municipal panels that examine links between the disaster’s aftermath and deaths. The figure is greater than for Iwate and Miyagi prefectures, with 469 and 929 respectively, though they had much higher loss of life in the earthquake and tsunami – over 14,000. The disparity is attributed to the older age group involved among Fukushima’s evacuated earthquake/tsunami survivors, about 90% of indirect deaths being of people over 66. Causes of indirect deaths include physical and mental stress stemming from long stays at shelters, a lack of initial care as a result of hospitals being disabled by the disaster, and suicides. Evaluation of ‘indirect deaths’ is according to a model developed by Niigata prefecture after the 2004 earthquake there ( Japan Times 20/2/14 ). As of July 2020, over 41,000 people from Fukushima were still living as evacuees.

Evacuees over a period of six years received ¥100,000 (about $1000) per month in psychological suffering compensation. The money was tax-exempt and paid unconditionally. In October 2013, about 84,000 evacuees received the payments. Statistics indicate that an average family of four has received about ¥90 million ($900,000) in compensation from Tepco. As of January 2021 the Fukushima accident evacuees had received ¥9.7 trillion in personal and property compensation.

The Fukushima prefecture had 17,000 government-financed temporary housing units for some 29,500 evacuees from the accident. The prefectural government said residents could continue to use these until March 2015 ( Japan Times 17/11/13 ). The number compared with very few built in Miyagi, Iwate and Aomori prefectures for the 222,700 tsunami survivor refugees there.

In April 2019, the first residents of Okuma, the closest town to the plant, were allowed to return home. In August 2022 the last remaining evacuation order – for Futaba, the town that hosts the Fukushima plant – was lifted.

According to a survey released by the prefectural government in April 2017, the majority of people who voluntarily evacuated their homes after the accident and who are now living outside of Fukushima prefecture do not intend to return. A  Mainichi  report said that 78.2% of respondents to the survey preferred to continue living in the area to which they had moved, while only 18.3% intended to move back to the prefecture. Of the voluntary evacuees still living in Fukushima prefecture, 23.6% planned to stay where they were, while 66.6% hoped to return to their original homes.

An August 2012 Reconstruction Agency report also considered workers at Fukushima power plant. Of almost 1500 surveyed, many were stressed, due to evacuating their homes (70%), believing they had come close to death (53%), the loss of homes in the tsunami (32%), deaths of colleagues (20%) and of family members (6%) mostly in the tsunami. The death toll directly due to the nuclear accident or radiation exposure remained zero, but stress and disruption due to the continuing evacuation remains high.

Tokyo’s Board of Audit reported in October 2013 that 23% of recovery funding – about ¥1.45 trillion ($14.5 billion) – had been misappropriated. Some 326 out of about 1400 projects funded had no direct relevance to the natural disaster or Fukushima Daiichi accident (Mainichi 1/11/13).

Summary : Many evacuated people remain unable to fully return home due to government-mandated restrictions based on conservative radiation exposure criteria. 2313 premature disaster-related deaths were caused by the evacuations, with 90% of the deaths occuring in people aged 66 and older. Decontamination work is proceeding while radiation levels decline naturally. The October 2013 IAEA report made clear that many evacuees should be allowed to return home. As of July 2020, over 41,000 people from Fukushima were still living as evacuees.

Managing contaminated water

Removing contaminated water from the reactor and turbine buildings had become the main challenge by week 3, along with contaminated water in trenches carrying cabling and pipework. This was both from the tsunami inundation and leakage from reactors. Run-off from the site into the sea was also carrying radionuclides well in excess of allowable levels. By the end of March all storages around the four units – basically the main condenser units and condensate tanks – were largely full of contaminated water pumped from the buildings. 

Accordingly, with government approval, Tepco over 4-10 April released to the sea about 10,400 cubic metres of slightly contaminated water (0.15 TBq total) in order to free up storage for more highly-contaminated water from unit 2 reactor and turbine buildings which needed to be removed to make safe working conditions. Unit 2 was the main source of contaminated water, though some of it comes from drainage pits. NISA confirmed that there was no significant change in radioactivity levels in the sea as a result of the 0.15 TBq discharge in April 2011.

By the end of June 2011, Tepco had installed 109 concrete panels to seal the water intakes of units 1-4, preventing contaminated water leaking to the harbour. From mid-June some treatment with zeolite of seawater at 30 m 3 /hr was being undertaken near the water intakes for units 2&3, inside submerged barriers installed in April. From October, a steel water shield wall was built on the sea frontage of units 1-4. It extends about one kilometre, and down to an impermeable layer beneath two permeable strata which potentially leak contaminated groundwater to the sea. The inner harbour area which has some contamination is about 30 ha in area. The government in September 2013 said: “At present, statistically-significant increase of radioactive concentration in the sea outside the port of the Tepco’s Fukushima Daiichi NPS has not been detected.” And also: “The results of monitoring of seawater in Japan are constantly below the standard of 10 Bq/L” (the WHO standard for Cs-137 in drinking water). In 2012 the Japanese standard for caesium in food supply was dropped from 500 to 100 Bq/kg. In July-August 2014 only 0.6% of fish caught offshore from the plant exceeded this lower level, compared with 53% in the months immediately following the accident.

Long-term management and disposal

Tepco in 2011 built a new wastewater treatment facility to treat contaminated water. The company used both US proprietary adsorption and French conventional technologies in the new 1200 m 3 /day treatment plant. A supplementary and simpler SARRY (simplified active water retrieve and recovery system) plant to remove caesium using Japanese technology and made by Toshiba and The Shaw Group was installed and commissioned in August 2011. These plants reduce caesium from about 55 MBq/L to 5.5 kBq/L – about ten times better than designed. Desalination is necessary on account of the seawater earlier used for cooling, and the 1200 m 3 /day desalination plant produces 480 m 3 of clean water while 720 m 3 goes to storage. A steady increase in volume of the stored water (about 400 m 3 /d net) is due to groundwater finding its way into parts of the plant and needing removal and treatment. 

Some 1000 storage tanks were set up progressively after the accident, including initially 350 steel tanks with rubber seams, each holding 1200 m 3 . A few of these developed leaks in 2013.

Early in 2013 Tepco started to test and commission the Advanced Liquid Processing System ( ALPS ), developed by EnergySolutions and Toshiba. Each of six trains is capable of processing 250 m 3 /day to remove 62 remaining radioisotopes. By the end of 2014, an ALPS of 500 m 3 /d had been added, making total capacity 2000 m 3 /d. The NRA approved the extra capacity in August 2014.

Earlier in September 2013 report from the Atomic Energy Society of Japan recommended diluting the ALPS-treated water with seawater and releasing it to the sea at the legal discharge concentration of 0.06 MBq/L, with monitoring to ensure that normal background tritium levels of 10 Bq/L are not exceeded. (The WHO drinking water guideline is 0.01 MBq/L tritium.) The IAEA supports release of tritiated water to the ocean, as does Dale Klein, chairman of Tepco’s Nuclear Reform Monitoring Committee (NRMC) and former chairman of the US Nuclear Regulatory Commission. 

ALPS is a chemical system which removes radionuclides to below legal limits for release. However, because tritium is contained in water molecules, ALPS cannot remove it, which gives rise to questions about the discharge of treated water to the sea. Tritium is a weak beta-emitter which does not bio-accumulate (half-life 12 years), and its concentration has levelled off at about 1 MBq/L in the stored water, with dilution from groundwater balancing further release from the fuel debris.

In 2014 a new Kurion strontium removal system was commissioned. This is mobile and can be moved around the tank groups to further clean up water which has been treated by ALPS.

In June 2015 108 m 3 /day of clean water was being circulated through each reactor (units 1-3). Collected water from them, with high radioactivity levels, was being treated for caesium removal and re-used. Apart from this recirculating loop, the cumulative treated volume was then 1.232 million cubic metres. In storage onsite was 459,000 m 3  of fully treated water (by ALPS), and 190,000 m 3  of partially-treated water (strontium removed), which was being added to at 400 m 3 /day due to groundwater inflow. Almost 600 m 3  of sludge from the water treatment was stored in shielded containers.

In 2016 Kurion (now owned by Veolia) completed a demonstration project for tritium removal at low concentrations, with its new Modular Detritiation System (MDS),* in response to a ¥1 billion commission from METI.

* In this, an electrolyser produces hydrogen and oxygen, with the tritium reporting in the hydrogen. This is fed through a catalytic exchange column with a little water which preferentially takes up the tritium. The concentrated tritiated water is fed through a ‘getter bed’ of dry metal hydrate, where the tritium replaces hydrogen, and the material is stored, being stable up to 500 °C. It can be incorporated into concrete and disposed as low-level waste. The tritium is concentrated 1000 to 20,000 times. The MDS is the first system to be able economically to treat large volumes of water with low tritium concentrations, and builds on existing heavy water tritium removal systems. Each module treats up to 7200 litres per day.

In November 2019 the trade and industry ministry stated that annual radiation levels from the release of the tritium-tainted water are estimated at between 0.052 and 0.62 microsieverts if it were disposed of at sea and 1.3 microsieverts if it were released into the atmosphere, compared with the 2100 microsieverts (2.1 mSv) that humans are naturally exposed to annually.

In March 2020, TEPCO released a study in relation to two disposal methods of the ALPS-treated water – discharge into the sea and vapour discharge.

In April 2021 the Japanese government confirmed that the water would be released into the sea in 2023. In August 2021 Tepco announced plans for the construction of an undersea tunnel about 1 kilometre in length, which will allow the release of the water into an area where no fishing rights are in place. In May 2022 the NRA endorsed Tepco’s plans.

ALPS-treated water is currently stored in more than 1000 tanks onsite with a storage capacity of 1.37 million cubic metres which are expected to reach full capacity by late 2023 or early 2024. Some of the ALPS treated water will require secondary processing to further reduce concentrations of radionuclides in line with government requirements.

In August 2023 the Japanese government asked Tepco to begin preparations for the release of the treated water, with the first water set to be discharged from 24 August 2023. Tepco plans to discharge the water using a two-step process. First, a small amount of treated water will be diluted with seawater and stored in a vertical discharge shaft in order to sample, measure and verify the tritium levels of the water. The water will then be discharged into the sea via the 1km undersea tunnel. The IAEA opened an office at the Fukushima Daiichi plant in July 2023 in order to continuously monitor and assess the activities related to the release of the treated water and ensure alignment with safety standards. The IAEA will also provide real-time monitoring data.

Apart from the above-ground water treatment activity, there is now a groundwater bypass to reduce the groundwater level above the reactors by about 1.5 metres, pumping from 12 wells and from May 2014, discharging the uncontaminated water into the sea. This prevents some of it flowing into the reactor basements and becoming contaminated. In addition, an impermeable wall was constructed on the sea-side of the reactors, and inside this a frozen soil wall was created to further block water flow into the reactor buildings.

In October 2013 guidelines for rainwater release from the site allowed Tepco to release water to the sea without specific NRA approval as long as it conformed to activity limits. Tepco has been working to 25 Bq/L caesium and 10 Bq/L strontium-90.

Summary: A large amount of contaminated water has accumulated onsite and has been treated to remove radioactive elements, apart from tritium. In April 2021, the Japanese government confirmed that the water would be released into the sea. Some radioactivity has already been released to the sea, but this has mostly been low-level and it has not had any significant impact beyond the immediate plant structures. Concentrations outside these structures have been below regulatory levels since April 2011. The release of the treated water will commence in August 2023 and will be continuously monitored by IAEA staff present at the site.

IRID and NDF involvement

The International Research Institute for Nuclear Decommissioning ( IRID ) was set up in August 2013 Japan by the Japan Atomic Energy Agency (JAEA), Japanese utilities and reactor vendors, with a focus on Fukushima Daiichi 1-4.

In September 2013 IRID called for submissions on the management of contaminated water at Fukushima. In particular, proposals were sought for dealing with: the accumulation of contaminated water (in storage tanks, etc ); the treatment of contaminated water including tritium removal; the removal of radioactive materials from the seawater in the plant's 30 ha harbour; the management of contaminated water inside the buildings; measures to block groundwater from flowing into the site; and, understanding the flow of groundwater. Responses were submitted to the government in November.

In December 2013 IRID called for innovative proposals for removing fuel debris from units 1-3 about 2020.

In August 2014 the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) was set up by the government as a planning body with management support for R&D projects, taking over IRID’s planning role. It works with IRID, whose focus now is on developing mid- and long-term decommissioning technologies. The NDF also works with Tepco Fukushima Daiichi D&D Engineering Co., which has responsibility for operating the actual decommissioning work there. The NDF will be the main body interacting with the government (METI) to implement policy.

Fukushima Daiichi 5&6

Units 5&6, in a separate building, also lost power on 11 March due to the tsunami. They were in 'cold shutdown' at the time, but still requiring pumped cooling. One air-cooled diesel generator at unit 6 was located higher and so survived the tsunami and enabled repairs on Saturday 19, allowing full restoration of cooling for units 5&6. While the power was off their core temperature had risen to over 100 °C (128 °C in unit 5) under pressure, and they had been cooled with normal water injection. They were restored to cold shutdown by the normal recirculating system on 20 March, and mains power was restored on 21-22 March.

In September 2013 Tepco commenced work to remove the fuel from unit 6. Prime minister Abe then called for Tepco to decommission both units. Tepco announced in December 2013 that it would decommission both units from the end of January 2014. Unit 5 was a 760 MWe BWR the same as units 2-4, and unit 6 was larger – 1067 MWe. They entered commercial operation in 1978 and 1979 respectively. It is proposed that they will be used for training.

Remediation on site and decommissioning units 1-4

Tepco published a six- to nine-month plan in April 2011 for dealing with the disabled Fukushima reactors, and updated this several times subsequently. Remediation over the first couple of years proceeded approximately as planned. In August 2011 Tepco announced its general plan for proceeding with removing fuel from the four units, initially from the spent fuel ponds and then from the actual reactors. At the end of 2013 Tepco announced the establishment of an internal entity to focus on measures for decommissioning units 1-6 and dealing with contaminated water. The new company, Fukushima Daiichi Decontamination & Decommissioning Engineering Company, commenced operations in April 2014.

In June 2015 the government revised the decommissioning plan for the second time, though without major change. It clarified milestones to accomplish preventive and multi-layered measures, involving the three principles of removing the source of the contamination, isolating groundwater from the contamination source, and preventing leakage of the contaminated water. It included a new goal of cutting the amount of groundwater flowing into the buildings to less than 100 m 3 per day by April 2016. The schedule for fuel removal from the pond at unit 1 was postponed from late FY17 to FY20, while that for unit 2 was delayed from early FY20 to later the same fiscal year, and that at unit 3 from early FY15 to FY17. Fuel debris removal was to begin in 2021, as before. In September 2017 the government updated the June 2015 decommissioning roadmap, with no changes to the framework, and confirming first removal of fuel debris from unit 1 in 2021. Treatment of all contaminated water accumulated in the reactor buildings was to be completed by 2020.

However, Tepco’s latest roadmap shows fuel removal from the pond at unit 1 is now expected FY27-28, and from unit 2 FY24-FY26. For unit 3, fuel removal was completed in February 2021.

Tepco has a website giving updates on decommissioning work and environmental monitoring.

Storage ponds : Debris has been removed from the upper parts of the reactor buildings using large cranes and heavy machinery. Casks to transfer the removed fuel to the central spent fuel facility have been designed and manufactured using existing cask technology.

In July 2012 two unused fuel assemblies were removed from unit 4 pond, and were found to be in good shape, with no deformation or corrosion. Tepco started removal of both fresh and used fuel from the pond in November 2013, 22 assemblies at a time in each cask, with 1331 used and 202 new ones to be moved. This was uneventful, and the task continued through 2014. By 22 December 2014, all 1331 used as well as all 202 new fuel assemblies had been moved in 71 cask shuttles without incident. All of the radioactive used fuel was removed by early November, eliminating a significant radiological hazard on the site. The used fuel went to the central storage pond, from which older assemblies were transferred to dry cask storage. The fresh fuel assemblies are stored in the pool of the undamaged unit 6.

Tepco completed moving fuel from unit 3 in February 2021. It will now focus on 292 used fuel assemblies and 100 new ones from unit 1, and then 587 used assemblies and 28 new ones from unit 2 will be transferred. The NRA has expressed concern about the unit 1 used fuel.

Reactors 1-3 order of work : The locations of leaks from the primary containment vessels (PCVs) and reactor buildings should first be identified using manual and remotely controlled dosimeters, cameras, etc. , then the conditions inside the PCVs should be indirectly analysed from the outside via measurements of gamma rays, echo soundings, etc . Any leakage points will be repaired and both reactor vessels (RPVs) and PCVs filled with water sufficient to achieve shielding. Then the vessel heads will be removed. The location of melted fuel and corium will then be established. In particular, the distribution of damaged fuel believed to have flowed out from the RPVs into PCVs will be ascertained, and it will be sampled and analysed. After examination of the inside of the reactors, states of the damaged fuel rods and reactor core internals, sampling will be done and the damaged core material will be removed from the RPVs as well as from the PCVs. Updated plans are on the IRID website.

The four reactors will be completely demolished in 30-40 years – much the same timeframe as for any nuclear plant. As noted above, units 5&6 commenced decommissioning in 2014 and will be used for training.

Earlier, consortia led by both Hitachi-GE and Toshiba submitted proposals to Tepco for decommissioning units 1-4. This would generally involve removing the fuel and then sealing the units for a further decade or two while the activation products in the steel of the reactor pressure vessels decay. They can then be demolished. Removal of the very degraded fuel will be a long process in units 1-3, but will draw on experience at Three Mile Island in the USA.

Tepco has allocated ¥207 billion ($2.5 billion) in its accounts for decommissioning units 1-4. In March 2020, Tepco announced that ¥1.37 trillion ($12.6 billion) would be required for the removal of damaged fuel from units 2&3, with no estimates being made for the fuel in unit 1 which suffered the most damage of the three reactors.

The government has allocated ¥1150 billion ($15 billion) for decontamination in the region, with the promise of more if needed.

The Agency for Natural Resources and Energy (ANRE) calculated that as of January 2017 Tepco needed an estimated ¥22,000 billion ($190 billion), double the original estimate, to implement fuel debris removal, cleanup and for compensation to firms and individuals in Fukushima prefecture. Of this amount, Tepco would pay ¥16 trillion. Other Japanese nuclear operators would pay ¥4 trillion through the Nuclear Damage Compensation and Decommissioning Facilitation Corp (NDF), and the Japanese government would pay ¥2 trillion for cleanup in Fukushima prefecture.

A 12-member international expert team assembled by the IAEA at the request of the Japanese government carried out a fact-finding mission in October 2011 on remediation strategies for contaminated land. Its  report focused on the remediation of the affected areas outside of the 20 km restricted area. The team said that it agreed with the prioritization and the general strategy being implemented, but advised the government to focus on actual dose reduction. They should "avoid over-conservatism" which "could not effectively contribute to the reduction of exposure doses" to people. It warned the government against being preoccupied with "contamination concentrations ... rather than dose levels," since this "does not automatically lead to reduction of doses for the public." The report also called on the Japanese authorities to "maintain their focus on remediation activities that bring the best results in reducing the doses to the public." A follow-up mission was carried out in October 2013.

Fukushima Daini plant

The four units at Fukushima Daini were shut down automatically due to the earthquake. The tsunami – here only 9 m high – affected the generators and there was major interruption to cooling due to damaged heat exchangers, so the reactors were almost completely isolated from their ultimate heat sink. Damage to the diesel generators was limited and also the earthquake left one of the external power lines intact, avoiding a station blackout as at Daiichi units 1-4. Staff laid and energized 8.8 km of heavy-duty electric cables in 30 hours to supplement power.

In units 1, 2&4 there were cooling problems still evident on Tuesday 15. Unit 3 was undamaged and continued to 'cold shutdown' status on the 12th, but the other units suffered flooding to pump rooms where the equipment transfers heat from the reactor heat removal circuit to the sea. Pump motors were replaced in less than 30 hours. All units achieved 'cold shutdown' by 16 March, meaning core temperature less than 100 °C at atmospheric pressure (101 kPa), but still requiring some water circulation. The almost complete loss of ultimate heat sink for a day proved a significant challenge, but the cores were kept fully covered.

Radiation monitoring figures remained at low levels, little above background.

There was no technical reason for the Fukushima Daini plant not to restart. However, Tepco in October 2012 said it planned to transfer the fuel from the four reactors to used fuel ponds, and this was done. In February 2015 the prime minister said that restarting the four units was essentially a matter for Tepco to decide. In July 2019 Tepco announced its decision to decommission the four reactors.

International Nuclear Event Scale assessment

Japan's Nuclear & Industrial Safety Agency originally declared the Fukushima Daiichi 1-3 accident as level 5 on the International Nuclear Events Scale (INES) – an accident with wider consequences, the same level as Three Mile Island in 1979. The sequence of events relating to the fuel pond at unit 4 was rated INES level 3 – a serious incident.

However, a month after the tsunami the NSC raised the rating to level 7 for units 1-3 together, 'a major accident', saying that a re-evaluation of early radioactive releases suggested that some 630 PBq of I-131 equivalent had been discharged, mostly in the first week. This then matched the criterion for level 7. In early June NISA increased its estimate of releases to 770 PBq, from about half that, though in August the NSC lowered this estimate to 570 PBq.

For Fukushima Daini, NISA declared INES level 3 for units 1, 2, 4 – each a serious incident.

Accident liability and compensation

Beyond whatever insurance Tepco might carry for its reactors is the question of third party liability for the accident. Japan was not party to any international liability convention but its law generally conforms to them, notably strict and exclusive liability for the operator. Early in 2015 Japan ratified the Convention on Supplementary Compensation for Nuclear Damage (CSC). Two laws governing liability are revised about every ten years: the Law on Compensation for Nuclear Damage and Law on Contract for Liability Insurance for Nuclear Damage. Plant operator liability is exclusive and absolute (regardless of fault), and power plant operators must provide a financial security amount of JPY 120 billion ($1.5 billion) – it was half that to 2010. The government may relieve the operator of liability if it determines that damage results from “a grave natural disaster of an exceptional character” (which it did not do here), and in any case total liability is unlimited.

In mid-April 2011, the first meeting was held of a panel to address compensation for nuclear-related damage. The panel established guidelines for determining the scope of compensation for damage caused by the accident, and to act as an intermediary. It was established within the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and was led by law professor Yoshihisa Nomi of Gakushuin University in Tokyo.

On 11 May 2011, Tepco accepted terms established by the Japanese government for state support to compensate those affected by the accident at the Fukushima Daiichi plant. The scheme included a new state-backed institution to expedite payments to those affected by the Fukushima Daiichi accident. The body receives financial contributions from electric power companies with nuclear power plants in Japan, and from the government through special bonds that can be cashed whenever necessary. The government bonds total JPY 5 trillion ($60 billion). Tepco accepted the conditions imposed on the company as part of the package. That included not setting an upper limit on compensation payments to those affected, making maximum efforts to reduce costs, and an agreement to cooperate with an independent panel set up to investigate its management.

This Nuclear Damage Compensation Facilitation Corporation, established by government and nuclear plant operators, includes representatives from other nuclear generators and also operates as an insurer for the industry, being responsible to have plans in place for any future nuclear accidents. The provision for contributions from other nuclear operators is similar to that in the USA. The government estimates that Tepco will be able to complete its repayments in 10 to 13 years, after which it will revert to a fully private company with no government involvement. Meanwhile it will pay an annual fee for the government support, maintain adequate power supplies and ensure plant safety. Tepco estimated its extra costs for fossil fuels in 2011-12 (April-March) would be about JPY 830 billion ($11 billion).

On 14 June 2011, Japan's cabinet passed the Nuclear Disaster Compensation Bill, and a related budget to fund post-tsunami reconstruction was also passed subsequently.

In September 2011 the Nuclear Damage Compensation Facilitation Corporation started by working with Tepco to compile a business plan for the next decade. This was approved by the Ministry of Economy, Trade and Industry (METI) so that some ¥900 billion ($12 billion) could be released to the company through bonds issued to the Nuclear Damage Facilitation Fund to cover compensation payments to March 2012. The plan also involved Tepco reducing its own costs by ¥2545 billion ($33 billion) over the next ten years, including shedding 7400 jobs. This special business plan was superseded by a more comprehensive business plan in March 2012, involving compensation payments of ¥910 billion ($12 billion) annually. Tepco wanted to include an electricity rate increase of 17% in the plan, to cover the additional annual fuel costs for thermal power generation to make up for lost capacity at idled nuclear power plants.

In February 2012 METI approved a further ¥690 billion ($9 billion) in compensation support from the Nuclear Damage Liability Facilitation Fund, subject to Tepco's business plan giving the government voting rights. In June 2012 shareholders voted to sell the Japanese government 50.11% of Tepco's voting shares and an additional 25.73% with no voting rights, for ¥1 trillion (about $13 billion), paid through the Nuclear Damage Liability Facilitation Fund. This was effected at the end of July, so that Tepco then became government-controlled, at least temporarily. Tepco said it appreciated the chance to "transform to New Tepco".

The government and 12 utilities are contributing funds into the new institution to pay compensation to individuals and businesses claiming damages caused by the accident. It received ¥7 billion ($90 million) in public funds as well as a total of ¥7 billion from 12 nuclear plant operators, the Tepco share of ¥2379 million ($30 million) being the largest. The percentage of utility contributions was fixed in proportion to the power output of their plants, so Kansai Electric Power provided ¥1229 million, followed by ¥660 million by Kyushu Electric Power and ¥622 million by Chubu Electric Power. Japan Nuclear Fuel Ltd., which owns a used nuclear fuel reprocessing plant in Aomori prefecture, provided ¥117 million to the entity. The utility companies also pay annual contributions to the body. Tepco is required to make extra contributions, with the specific amount to be decided later.

In June 2013 Tepco requested a further ¥666 billion ($6.7 billion) in government support through the Nuclear Damage Liability Facilitation Fund, bringing the total amount requested by Tepco to ¥3.79 trillion ($40 billion). The company said that more than half of the request – some ¥370 billion ($4 billion) – resulted from the re-evaluation of the evacuation zone around the damaged plant and a re-examination of the estimated amount "regarding compensation for mental damages, loss or depreciation of valuables such as housing lands and buildings." About ¥43 billion ($430 million) was due to a higher estimate of compensation coming from damages to the agriculture, forestry and fisheries industries, as well as the food processing and distribution industries. This, it said, also resulted from "harmful rumours" about the possible health effects of consuming food products from the region near the damaged power plant. As restrictions on the transport of foodstuffs from the Fukushima area seemed set to continue, an additional ¥240 billion ($2 billion) was included to cover for the further compensation claims resulting from this.

By mid-May 2014, Tepco had paid ¥3808 billion ($40 billion) in compensation, fairly evenly split between businesses and individuals, based on decisions of the Nuclear Damage Compensation Facilitation Corporation, and covered by loans from the NDLF Fund. Some $16 billion of this was distributed evenly among 85,000 evacuees – $188,200 each person including children, as directed early in 2011.

In July 2015 the government approved Tepco’s recovery plan, including compensation payments of ¥7075 billion ($57 billion), enabling it to receive ¥950 billion more than the ¥6125 billion estimated in April, according to METI.

As of January 2021 the Fukushima accident evacuees had received ¥9.7 trillion in personal and property compensation.

Earlier, in December 2013 the government raised the upper limit of its financial assistance to Tepco from ¥5 trillion to ¥9 trillion ($86 billion). Early in 2014 the government estimated it would take ¥11 trillion and 40 years to clean up the Fukushima site. The 2013 Japan trade deficit was ¥11.5 trillion.

In September 2019 Tokyo District Court acquitted three former executives – Tsunehisa Katsumata, Ichiro Takekuro and Sakae Muto – with failing to prevent the accident at the company's Fukushima Daiichi plant. The court found all three men not guilty of professional negligence resulting in death and injury and ruled that they could not have foreseen the earthquake and tsunami that led to the meltdown of three of the plant's reactors. In January 2023 the Tokyo High Court upheld the acquittal of the three former executives.

Inquiries and reports: the accident itself and decommissioning

In October 2014 the NRA published its Analysis of the TEPCO Fukushima Daiichi NPS Accident interim report. A provisional translation in English was published in February 2015. This focuses on a number of questions which remained unexplained in the 2012 National Diet Investigation Commission report .

Earlier in May 2011 a team of 18 experts from 12 countries spent a week at the plant on behalf of the International Atomic Energy Agency (IAEA), and that mission's final report was presented to the IAEA Ministerial Conference in Vienna in June. At the IAEA General Conference in 2012 the Director General promised a comprehensive report which would be "an authoritative, factual and balanced assessment, addressing the causes and consequences of the accident as well as the lessons learned." This report on The Fukushima Daiichi Accident was published in August 2015, accompanied by five technical volumes.

In February 2015 the IAEA completed its third review mission (as follow-up to that of late 2013, and involving some 180 experts from 42 IAEA member states and other organizations over two years) and reported on decommissioning to METI. In May 2015 its final report was delivered to member states, and was published in September. It was broadly positive regarding progress since 2013, but said that some challenging issues remain. It contains advisory points on topics such as long-term radioactive waste management, measures concerning contaminated water, and issues related to the removal of used fuel and fuel debris.

The Foreword to the Director General’s report in 2015 states: "A major factor that contributed to the accident was the widespread assumption in Japan that its nuclear power plants were so safe that an accident of this magnitude was simply unthinkable. This assumption was accepted by nuclear power plant operators and was not challenged by regulators or by the government. As a result, Japan was not sufficiently prepared for a severe nuclear accident in March 2011." The accident exposed "certain weaknesses" in Japan's regulatory framework, with responsibilities divided among a number of bodies. It also said there were certain weaknesses "in plant design, in emergency preparedness and response arrangement and in planning for the management of a severe accident".

The Director General said: "I am confident that the legacy of the Fukushima Daiichi accident will be a sharper focus on nuclear safety everywhere. I have seen improvements in safety measures and procedures in every nuclear power plant that I have visited. There is widespread recognition that everything humanly possible must be done to ensure that no such accident ever happens again." He added: "This is all the more essential as global use of nuclear power is likely to continue to grow in coming decades.” Furthermore, "there can be no grounds for complacency about nuclear safety in any country. Some of the factors that contributed to the Fukushima Daiichi accident were not unique to Japan. Continuous questioning and openness to learning from experience are key to safety culture and are essential for everyone involved in nuclear power."

The Executive Summary includes recommendations, but the following paragraphs indicate some salient points from the actual investigation.

Before the accident, there was a basic assumption in Japan that the design of nuclear power plants and the safety measures that had been put in place were sufficiently robust to withstand external events of low probability and high consequences. Because of the basic assumption that nuclear power plants in Japan were safe, there was a tendency for organizations and their staff not to challenge the level of safety. The reinforced basic assumption among the stakeholders about the robustness of the technical design of nuclear power plants resulted in a situation where safety improvements were not introduced promptly.

Before the accident, the operator had conducted some reassessments of extreme tsunami flood levels, using a consensus based methodology developed in Japan in 2002, which had resulted in values higher than the original design basis estimates. Based on the results, some compensatory measures were taken, but they proved to be insufficient at the time of the accident.

There were no indications that the main safety features of the plant were affected by the vibratory ground motions generated by the earthquake on 11 March 2011. This was due to the conservative approach to earthquake design and construction of nuclear power plants in Japan, resulting in a plant that was provided with sufficient safety margins. However, the original design considerations did not provide comparable safety margins for extreme external flooding events, such as tsunamis.

Despite the efforts of the operators at the Fukushima Daiichi nuclear power plant to maintain control, the reactor cores in units 1-3 overheated, the nuclear fuel melted and the three containment vessels were breached. Hydrogen was released from the reactor pressure vessels, leading to explosions inside the reactor buildings in units 1, 3&4 that damaged structures and equipment and injured personnel. Radionuclides were released from the plant to the atmosphere and were deposited on land and on the ocean. There were also direct releases into the sea.

Venting of the containment was necessary to relieve pressure and prevent its failure. The operators were able to vent units 1 and 3 to reduce the pressure in the primary containment vessels. However, this resulted in radioactive releases to the environment. Even though the containment vents for units 1 and 3 were opened, the primary containment vessels for units 1 and 3 eventually failed. Containment venting for unit 2 was not successful, and the containment failed, resulting in radioactive releases.

People within a radius of 20 km of the site and in other designated areas were evacuated, and those within a radius of 20-30 km were instructed to shelter before later being advised to voluntarily evacuate. Restrictions were placed on the distribution and consumption of food and the consumption of drinking water. Many people are still living outside the areas from which they were evacuated.

No early radiation induced health effects were observed among workers or members of the public that could be attributed to the accident.

Earlier reports 2011-2012

Early in June 2011 the independent Investigation Committee on the Accident at the Fukushima Nuclear Power Stations ( ICANPS ), a panel of ten experts, mostly academics and appointed by the Japanese cabinet, began meeting. It had two technological advisers. An initial report was published in December 2011 and a final report in July 2012. The panel set up four teams to undertake investigations on the causes of the accident and ensuing damage and on measures to prevent the further spread of damage caused by the accident, but not to pursue the question of responsibility for the accident.

The national Diet later set up the legally-constituted Nuclear Accident Independent Investigation Commission ( NAIIC , or National Diet Investigation Commission) of ten members which started its work in December 2011. One of the purposes of NAIIC was to provide suggestions including the “re-examination of an optimal administrative organization” for nuclear safety regulation based on its investigation of the accident. The NAIIC reported in July 2012, harshly criticizing the government, the plant operator and the country’s national culture. After conducting 900 hours of public hearings and interviews with more than 1100 people and visiting several nuclear power plants, the commission’s report concluded that the accident was a “manmade disaster,” the result of “collusion between the government, the regulators and Tokyo Electric Power Co.” It said the “root causes were the organizational and regulatory systems that supported faulty rationales for decisions and actions.” The NAIIC criticized the regulator for insufficiently maintaining independence from the industry in developing and enforcing safety regulations, the government for inadequate emergency preparedness and management, and Tepco for its poor governance and lack of safety culture. The report called for fundamental changes across the industry, including the government and regulators, to increase openness, trustworthiness and focus on protecting public health and safety.

The NAIIC Chairman wrote: "What must be admitted – very painfully – is that this was a disaster 'Made in Japan.' Its fundamental causes are to be found in the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to 'sticking with the programme'; our groupism; and our insularity.” The mindset of the government and industry led the country to avoid learning the lessons of the previous major nuclear accidents at Three Mile Island and Chernobyl. "The consequences of negligence at Fukushima stand out as catastrophic, but the mindset that supported it can be found across Japan. In recognizing that fact, each of us (every Japanese citizen) should reflect on our responsibility as individuals in a democratic society."

The NAIIC reported that Tepco had been aware since 2006 that Fukushima Daiichi could face a station blackout if flooded, as well as the potential loss of ultimate heat sink in the event of a major tsunami. However, the regulator, NISA, gave no instruction to the company to prepare for severe flooding, and even told all nuclear operators that it was not necessary to plan for station blackout. During the initial response to the tsunami, this lack of readiness for station blackout was compounded by a lack of planning and training for severe accident mitigation. Plans and procedures for venting and manual operation of emergency cooling were incomplete and their implementation in emergency circumstances proved very difficult as a result. NISA was also criticized for its "negligence and failure over the years" to prepare for a nuclear accident in terms of public information and evacuation, with previous governments equally culpable. Then Tepco’s difficulty in mitigation was compounded by government interference which undermined NISA.

Earlier, on 7 June 2011 the government submitted a 750-page report to the IAEA compiled by the nuclear emergency task force, acknowledging reactor design inadequacies and systemic shortcomings. It said: "In light of the lessons learned from the accident, Japan has recognized that a fundamental revision of its nuclear safety preparedness and response is inevitable."

On 11 September 2011 a second report was issued by the government and submitted to the IAEA, summarising both onsite work and progress and offsite responses. It contained further analysis of the earthquake and tsunami, the initial responses to manage and cool the reactors, the state of spent fuel ponds and the state of reactor pressure vessels. It also summarised radioactive releases and their effects.

Meanwhile a July 2011 report from MIT's Centre for Advanced Nuclear Energy Systems provided a useful series of observations, questions raised, and suggestions. Its Appendix has some constructive comment on radiation exposure and balancing the costs of dose avoidance in circumstances of environmental contamination.

In November 2011 the US Institute of Nuclear Power Operations (INPO) released its Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station , with timeline. This 97-page report gives a detailed account of events.

Also in November 2011 the Japan Nuclear Technology Institute published a 280-page report on the accident, with proposals to be addressed in the future.

On 2 December 2011 Tepco released its interim investigation report on the accident (in Japanese).

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) undertook a 12-month study on the magnitude of radioactive releases to the atmosphere and ocean, and the range of radiation doses received by the public and workers. A follow-up white paper was published in 2016.

An analysis by the Carnegie Endowment in March 2012 said that if best practice from other countries had been adopted by Tepco and NISA at Fukushima, the serious accident would not have happened, underlining the need for greater international regulatory collaboration.

In April 2012 the US Electric Power Research Institute (EPRI) published Fukushima Daiichi Accident – Technical Causal Factor Analysis , which identified the root cause beyond the flooding and its effects as a failure to consider the possibility of the rupture of combinations of geological fault segments in the vicinity of the plant.

Inquiries and reports: radiation effects

A preliminary report from the World Health Organization (WHO) in May 2012 estimated the radiation doses that residents of Japan outside the evacuated areas received in the year following the accident. The report's headline conclusion is that most people in Fukushima prefecture would have received a radiation dose of between 1 and 10 mSv during the first year after the accident. This compares with levels of about 2.4 mSv they would have received from unavoidable natural sources. In two places the doses were higher – between 10 and 50 mSv, still below any harmful level. Almost all were “below the internationally-agreed reference level for the public exposure due to radon in dwellings” (about 10 mSv/yr).

The UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in May 2012 reported that despite skin contamination of several workers, no clinically-observable effects have been reported and there is no evidence of acute radiation injury in any of the 20,115 workers who participated in Tepco’s efforts to mitigate the accident at the plant. Eighteen UNSCEAR member states provided 72 experts for the assessment. UNSCEAR also surveyed Fukushima prefecture to compare its data with Japanese measurements of exposures of some 2 million people living there at the time of the accident.

The results of UNSCEAR’s 12-month study on the magnitude of radioactive releases to the atmosphere and ocean, and the range of radiation doses received by the public and workers were announced in May 2013 are reported above in the subsection above on Radiation exposure .

UNSCEAR’s April 2014 report on radiation effects concluded that the rates of cancer or hereditary diseases were unlikely to show any discernible rise in affected areas because the radiation doses people received were too low. People were promptly evacuated from the vicinity of the nuclear power plant, and later from a neighbouring area where radionuclides had accumulated. This action reduced their radiation exposure by a factor of ten, to levels that were "low or very low." Overall, people in Fukushima are expected on average to receive less than 10 mSv due to the accident over their whole lifetime, compared with the 170 mSv lifetime dose from natural background radiation that people in Japan typically receive. "The most important health effect is on mental and social well-being, related to the enormous impact of the earthquake, tsunami and nuclear accident, and the fear and stigma related to the perceived risk of exposure to radiation." UNSCEAR’s follow-up white paper in October 2015 said that none of the new information appraised after the 2013 report “materially affected the main findings in, or challenged the major assumptions of, the 2013 Fukushima report."

UNSCEAR's update of its 2013 report , published in March 2021, broadly confirms the major findings and conclusions of the 2013 report. It concludes: "The Committee’s revised estimates of dose are such that future radiation-associated health effects are unlikely to be discernible."

In October 2013 a 16-member IAEA mission visited at government request and reported on remediation and decontamination in particular. Its preliminary report said that decontamination efforts were commendable but driven by unrealistic targets.

'Stress tests' on Japanese reactors and new regulatory authority

The government ordered nuclear risk and safety reassessments – so-called 'stress tests' – based on those in the EU for all Japan's nuclear reactors except Fukushima's before they restart following any shutdown, including for routine checks. These were in two stages, and are described in the Japan Nuclear Power information page.

The government then created the separate Nuclear Regulatory Agency (NRA) under the authority of the Environment Ministry and combining the roles of NISA and the NSC, commissioned in September 2012. The new Nuclear Regulatory Commission (NRC) replaced the NSC and will review the effectiveness of the NRA and be responsible for the investigation of nuclear accidents.

Notes & references

General sources.

Tepco NISA IAEA METI JAIF NSC Acton J.M. & Hibbs M, Why Fukushima was preventable , March 2012 Carnegie Paper INPO 11-005 Addendum, Aug 2012, Lessons learned from the Nuclear Accident at Fukushima Daiichi Nuclear Power Station Government’s Decision on Addressing the Contaminated Water Issue at TEPCO’s Fukushima Daiichi NPS , 3 Sept 2013, on Ministry of Foreign Affairs website K. Tateiwa, Decommissioning Fukushima Daiichi NPS, January 2014 UNSCEAR webpage on The Fukushima-Daiichi nuclear power plant accident IAEA Report by the Director General on The Fukushima Daiichi Accident , STI/PUB/1710 (ISBN:978-92-0-107015-9), August 2015 A. Komori, Current status and the future of Fukushima Daiichi NP station , World Nuclear Association 2015 Symposium presentation OECD Nuclear Energy Agency, Fukushima Daiichi Nuclear Power Plant Accident, Ten Years On: Progress, Lessons and Challenges , 2021

Earthquakes and Seismic Protection for Japanese Nuclear Power Plants

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Committee on Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants; Nuclear and Radiation Studies Board; Division on Earth and Life Studies; National Research Council. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants. Washington (DC): National Academies Press (US); 2014 Oct 29.

Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants.

• Hardcopy Version at National Academies Press

The March 11, 2011, Great East Japan Earthquake and tsunami sparked a humanitarian disaster in northeastern Japan and initiated a severe nuclear accident at the Fukushima Daiichi nuclear plant. Three of the six reactors at the plant sustained severe core damage and released hydrogen and radioactive materials. Explosion of the released hydrogen damaged three reactor buildings and impeded onsite emergency response efforts.

At the time of the Fukushima Daiichi accident, the Blue Ribbon Commission on America's Nuclear Future was completing an assessment of options for managing spent nuclear fuel and high-level radioactive waste in the United States ( BRC, 2012 ). The Commission recommended that the National Academy of Sciences (NAS) conduct an assessment of lessons learned from the Fukushima Daiichi accident. This recommendation was taken up by the U.S. Congress, which subsequently directed the U.S. Nuclear Regulatory Commission to contract with NAS for this study.

The statement of task for this study is shown in Sidebar S.1 . Study charges 1, 3, and 4 are addressed in this report; study charge 2 (on spent fuel safety and security) will be addressed in a future report.

SIDEBAR S.1

Statement of Task for This National Research Council Study. The National Research Council will provide an assessment of lessons learned from the Fukushima nuclear accident for improving the safety and security of nuclear plants in the United States. This (more...)

A committee of 21 experts was appointed by NAS to carry out this study (see Appendix A ). The committee held 39 meetings during the course of this study to gather information and develop this report (see Appendix B for a list of the committee's information-gathering meetings). One of these meetings was held in Tokyo, Japan, to enable in-depth discussions about the accident with Japanese technical experts from industry, academia, and government. The committee also visited the Fukushima Daini, Fukushima Daiichi, and Onagawa nuclear plants (see Chapter 3 ) to learn about their designs, operations, and responses to the earthquake and tsunami. Subgroups of the committee visited two nuclear plants in the United States that are similar in design to the Fukushima Daiichi plant to learn about their designs and operations.

S.1. CAUSES OF THE FUKUSHIMA DAIICHI ACCIDENT (Study Charge 1)

NAS's examination of the Fukushima Daiichi accident is provided in Chapters 3 and 4 of this report. Chapter 3 describes the March 11, 2011, Great East Japan Earthquake and tsunami and their impacts on Japanese nuclear plants. Chapter 4 describes the accident at the Fukushima Daiichi plant, including the accident time line, key actions taken by plant personnel, and challenges faced in taking those actions. One finding emerged from this examination:

FINDING 4.1 1 : The accident at the Fukushima Daiichi nuclear plant was initiated by the March 11, 2011, Great East Japan Earthquake and tsunami. The earthquake knocked out offsite AC power to the plant and the tsunami inundated portions of the plant site. Flooding of critical plant equipment resulted in the extended loss of onsite AC and DC power with the consequent loss of reactor monitoring, control, and cooling functions in multiple units. Three reactors sustained severe core damage (Units 1, 2, and 3); three reactor buildings were damaged by hydrogen explosions (Units 1, 3, and 4); and offsite releases of radioactive materials contaminated land in Fukushima and several neighboring prefectures. The accident prompted widespread evacuations of local populations and distress of the Japanese citizenry, large economic losses, and the eventual shutdown of all nuclear power plants in Japan. Personnel at the Fukushima Daiichi plant responded with courage and resilience during the accident in the face of harsh circumstances; their actions likely reduced the severity of the accident and the magnitude of offsite radioactive material releases. Several factors prevented plant personnel from achieving greater success—in particular, averting reactor core damage—and contributed to the overall severity of the accident: 1. Failure of the plant owner (Tokyo Electric Power Company) and the principal regulator (Nuclear and Industrial Safety Agency) to protect critical safety equipment at the plant from flooding in spite of mounting evidence that the plant's current design basis for tsunamis was inadequate. 2. The loss of nearly all onsite AC and DC power at the plant—with the consequent loss of real-time information for monitoring critical thermodynamic parameters in reactors, containments, and spent fuel pools and for sensing and actuating critical valves and equipment—greatly narrowed options for responding to the accident. 3. As a result of (1) and (2), the Unit 1, 2 and 3 reactors were effectively isolated from their ultimate heat sink (the Pacific Ocean) for a period of time far in excess of the heat capacity of the suppression pools or the coping time of the plant to station blackout. 4. Multiunit interactions complicated the accident response. Unit operators competed for physical resources and the attention and services of staff in the onsite emergency response center. 5. Operators and onsite emergency response center staff lacked adequate procedures and training for accidents involving extended loss of all onsite AC and DC power, particularly procedures and training for managing water levels and pressures in reactors and their containments and hydrogen generated during reactor core degradation. 6. Failures to transmit information and instructions in an accurate and timely manner hindered responses to the accident. These failures resulted partly from the loss of communications systems and the challenging operating environments throughout the plant. 7. The lack of clarity of roles and responsibilities within the onsite emergency response center and between the onsite and headquarters emergency response centers may have contributed to response delays. 8. Staffing levels at the plant were inadequate for managing the accident because of its scope (affecting several reactor units) and long duration.

S.2. LESSONS LEARNED FOR THE UNITED STATES (Study Charges 3 and 4)

Findings and recommendations on lessons learned from the Fukushima Daiichi accident are provided in Chapters 3 - 7 . They are organized into five sections in this summary.

Seek out and act on new information about hazards.

Improve nuclear plant systems, resources, and training to enable effective ad hoc responses to severe accidents.

Strengthen capabilities for assessing risks from beyond-design-basis events.

Further incorporate modern risk concepts into nuclear safety regulations.

Examine offsite emergency response capabilities and make necessary improvements.

Improve the nuclear safety culture.

S.2.1. Seek Out and Act on New Information About Hazards

FINDING 3.1: The overarching lesson learned from the Fukushima Daiichi accident is that nuclear plant licensees and their regulators must actively seek out and act on new information about hazards that have the potential to affect the safety of nuclear plants. Specifically, 1. Licensees and their regulators must continually seek out new scientific information about nuclear plant hazards and methodologies for estimating their magnitudes, frequencies, and potential impacts. 2. Nuclear plant risk assessments must incorporate new information and methodologies as they become available. 3. Plant operators and regulators must take timely actions to implement countermeasures when such new information results in substantial changes to risk profiles at nuclear plants.

S.2.2. Improve Nuclear Plant Systems, Resources, and Training

Many national governments and international bodies initiated reviews of nuclear plant safety following the Fukushima Daiichi accident (see Table 1.1 in Chapter 1 ). Two major initiatives are now under way in the United States—one by the U.S. Nuclear Regulatory Commission and the other by the U.S. nuclear industry—and are resulting in changes to U.S. nuclear plant systems, operations, and regulations.

FINDING 5.1: Nuclear plant operators and regulators in the United States and other countries have identified and are taking useful actions to upgrade nuclear plant systems, operating procedures, and operator training in response to the Fukushima Daiichi accident. In the United States, these actions include the nuclear industry's FLEX (diverse and flexible coping strategies) initiative as well as regulatory changes proposed by the U.S. Nuclear Regulatory Commission's Near-Term Task Force. Implementation of these actions is still under way; consequently, it is too soon to evaluate their comprehensiveness, effectiveness, or status in the regulatory framework. RECOMMENDATION 5.1A: As the nuclear industry and its regulator implement the actions referenced in Finding 5.1 , they should give specific attention to improving plant systems in order to enable effective responses to beyond-design-basis events, including, when necessary, developing and implementing ad hoc responses 2 to deal with unanticipated complexities. Attention to availability, reliability, redundancy, and diversity of plant systems and equipment is specifically needed for DC power for instrumentation and safety system control; Tools for estimating real-time plant status during loss of power; Decay-heat removal and reactor depressurization and containment venting systems and protocols; Instrumentation for monitoring critical thermodynamic parameters in reactors, containments, and spent fuel pools; Hydrogen monitoring (including monitoring in reactor buildings) and mitigation; Instrumentation for both onsite and offsite radiation and security monitoring; and Communications and real-time information systems to support communication and coordination between control rooms and technical support centers, between control rooms and the field, and between onsite and offsite support facilities The quality and completeness of the changes that result from this recommendation should be adequately peer reviewed. RECOMMENDATION 5.1B: As the nuclear industry and its regulator implement the actions referenced in Finding 5.1 , they should give specific attention to improving resource availability and operator training to enable effective responses to beyond-design-basis events, including, when necessary, developing and implementing ad hoc responses to deal with unanticipated complexities. Attention to the following is specifically needed: 1. Staffing levels for emergencies involving multiple reactors at a site, that last for extended durations, and/or that involve stranded-plant conditions. 3 2. Strengthening and better integrating emergency procedures, extensive damage mitigation guidelines, and severe accident management guidelines, in particular for Coping with the complete loss of AC and DC power for extended periods, Depressurizing reactor pressure vessels and venting containments when DC power and installed plant air supplies (i.e., compressed air and gas) are unavailable, Injecting low-pressure water when plant power is unavailable, Transitioning between reactor pressure vessel depressurization and low-pressure water injection while maintaining sufficient water levels to protect the core from damage, Preventing and mitigating the effects of large hydrogen explosions on cooling systems and containments, and Maintaining cold shutdown in reactors that are undergoing maintenance outages when critical safety systems have been disabled. 3. Training of operators and plant emergency response organizations, in particular, Specific training on the use of ad hoc responses for bringing reactors to safe shutdown during extreme beyond-design-basis events, and More general training to reinforce understanding of nuclear plant system design and operation and enhance operators' capabilities for managing emergency situations. The quality and completeness of the changes that result from this recommendation should be adequately peer reviewed.

S.2.3. Strengthen Capabilities for Assessing Risks from Beyond-Design-Basis Events

A “design-basis event” is a postulated event that a nuclear plant system, including its structures and components, must be designed and constructed to withstand without a loss of functions necessary to protect public health and safety. An event that is “beyond design basis” has characteristics that could challenge the design of plant structures and components and lead to a loss of critical safety functions. The Great East Japan Earthquake and tsunami were beyond-design-basis events.

FINDING 5.2: Beyond-design-basis events—particularly low-frequency, high-magnitude 4 (i.e., extreme) events—can produce severe accidents at nuclear plants that damage reactor cores and stored spent fuel. Such accidents can result in the generation and combustion of hydrogen within the plant and release of radioactive material to the offsite environment. There is a need to better understand the safety risks 5 that arise from such events and take appropriate countermeasures to reduce them. RECOMMENDATION 5.2A: The U.S. nuclear industry and the U.S. Nuclear Regulatory Commission should strengthen their capabilities for identifying, evaluating, and managing the risks from beyond-design-basis events. Particular attention is needed to improve the identification of such events; better account for plant system interactions and the performance of plant operators and other critical personnel in responding to such events; and better estimate the broad range of offsite health, environmental, economic, and social consequences that can result from such events. RECOMMENDATION 5.2B: The U.S. Nuclear Regulatory Commission should support industry's efforts to strengthen its capabilities by providing guidance on approaches and by overseeing independent review by technical peers (i.e., peer review). RECOMMENDATION 5.2C: As the U.S. nuclear industry and the U.S. Nuclear Regulatory Commission carry out the actions in Recommendation 5.2A , they should pay particular attention to the risks from beyond-design-basis events that have the potential to affect large geographic regions and multiple nuclear plants. These include earthquakes, tsunamis and other geographically extensive floods, and geomagnetic disturbances.

S.2.4. Further Incorporate Modern Risk Concepts into Nuclear Safety Regulations

A design-basis accident is a stylized accident—for example, a loss-of-coolant accident or transient overpower accident—that is required (by regulation) to be considered in a reactor system's design. The Fukushima Daiichi accident was a beyond-design-basis accident. Other major nuclear accidents (Three Mile Island in 1979 and Chernobyl in 1986) are also considered to be beyond-design-basis accidents.

FINDING 5.3: Four decades of analysis and operating experience have demonstrated that nuclear plant core-damage risks are dominated by beyond-design-basis accidents. Such accidents can arise, for example, from multiple human and equipment failures, violations of operational protocols, and extreme external events. Current approaches for regulating nuclear plant safety, which traditionally have been based on deterministic concepts such as the design-basis accident, are clearly inadequate for preventing core-melt accidents and mitigating their consequences. Modern risk assessment principles are beginning to be applied in nuclear reactor licensing and regulation. The more complete application of these principles in licensing and regulation could help to further reduce core-melt risks and their consequences and enhance the overall safety of all nuclear plants, especially currently operating plants. RECOMMENDATION 5.3: The U.S. Nuclear Regulatory Commission should further incorporate modern risk concepts into its nuclear reactor safety regulations. This effort should utilize the strengthened capabilities for identifying and evaluating risks that are described in Recommendation 5.2A .

The committee uses the term “modern risk concepts” to mean risk that is defined in terms of the risk triplet (What can go wrong? How likely is that to happen? What are the consequences if it does happen?) and subject to the limitations for quantitative analyses discussed in Section 5.2 in Chapter 5 . Implementing this recommendation fully would likely require changes to some current U.S. Nuclear Regulatory Commission regulatory procedures, for example, those used for backfit analyses.

S.2.5. Examine Offsite Emergency Response Capabilities and Make Necessary Improvements

Emergency response to the Fukushima Daiichi accident was greatly inhibited by the widespread and severe destruction caused by the March 11, 2011, earthquake and tsunami. Japan is known to be well prepared for natural hazards; however, the earthquake and tsunami caused devastation on a scale beyond what was expected and prepared for. Twenty prefectures on three of Japan's major islands (Hokkaido, Honshu, and Shikoku) were affected by the earthquake and tsunami.

FINDING 6.1: The Fukushima Daiichi accident revealed vulnerabilities in Japan's offsite emergency management. The competing demands of the earthquake and tsunami diminished the available response capacity for the accident. Implementation of existing nuclear emergency plans was overwhelmed by the extreme natural events that affected large regions, producing widespread disruption of communications, electrical power, and other critical infrastructure over an extended period of time. Additionally: Emergency management plans in Japan at the time of the Fukushima Daiichi accident were inadequate to deal with the magnitude of the accident, requiring emergency responders to improvise. Decision-making processes by government and industry officials were challenged by the lack of reliable, real-time information on the status of the plant, offsite releases, accident progression, and projected doses to nearby populations. Coordination among the central and local governments was hampered by limited and poor communications. Protective actions were improvised and uncoordinated, particularly when evacuating vulnerable populations (e.g., the elderly and sick) and providing potassium iodide. Different and revised radiation standards and changes in decontamination criteria and policies added to the public's confusion and distrust of the Japanese government. Cleanup of contaminated areas and possible resettlement of populations are ongoing efforts 3 years after the accident with uncertain completion time lines and outcomes. Failure to prepare and implement an effective strategy for communication during the emergency contributed to the erosion of trust among the public for Japan's government, regulatory agencies, and the nuclear industry. FINDING 6.2: The committee did not have the time or resources to perform an in-depth examination of U.S. preparedness for severe nuclear accidents. Nevertheless, the accident raises the question of whether a severe nuclear accident such as occurred at the Fukushima Daiichi plant would challenge U.S. emergency response capabilities because of its severity, duration, and association with a regional-scale natural disaster. The natural disaster damaged critical infrastructure and diverted emergency response resources. RECOMMENDATION 6.2A: The nuclear industry and organizations with emergency management responsibilities in the United States should assess their preparedness for severe nuclear accidents associated with offsite regional-scale disasters. Emergency response plans, including plans for communicating with affected populations, should be revised or supplemented as necessary to ensure that there are scalable and effective strategies, well-trained personnel, and adequate resources for responding to long-duration accident and/or disaster scenarios involving Widespread loss of offsite electrical power and severe damage to other critical offsite infrastructure, for example, communications, transportation, and emergency response infrastructure; Lack of real-time information about conditions at nuclear plants, particularly with respect to releases of radioactive material from reactors and/or spent fuel pools; and Dispersion of radioactive materials beyond the 10-mile emergency planning zones for nuclear plants that could result in doses exceeding one or more of the protective action guidelines. RECOMMENDATION 6.2B: The nuclear industry and organizations with emergency management responsibilities in the United States should assess the balance of protective actions (e.g., sheltering in place, evacuation, relocation, and distribution of potassium iodide) for offsite populations affected by severe nuclear accidents and revise the guidelines as appropriate. Particular attention should be given to the following issues: Protective actions for special populations (children, ill, elderly) and their caregivers; Long-term impacts of sheltering in place, evacuation and/or relocation, including social, psychological and economic impacts; and Decision making for resettlement of evacuated populations in areas contaminated by radioactive material releases from nuclear plant accidents.

S.2.6. Improve the Nuclear Safety Culture

The term “safety culture” is generally understood to encompass a set of attitudes and practices that emphasize safety over competing goals such as production or costs. There is universal acceptance by the nuclear community that safety culture practices need to be adopted by regulatory bodies and other organizations that set nuclear power policies; by senior management of organizations operating nuclear power plants; and by individuals who work in those plants.

FINDING 7.1: While the Government of Japan acknowledged the need for a strong nuclear safety culture prior to the Fukushima Daiichi accident, TEPCO and its nuclear regulators were deficient in establishing, implementing, and maintaining such a culture. Examinations of the Japanese nuclear regulatory system following the Fukushima Daiichi accident concluded that regulatory agencies were not independent and were subject to regulatory capture. 6 FINDING 7.2: The establishment, implementation, maintenance, and communication of a nuclear safety culture in the United States are priorities for the U.S. nuclear power industry and the U.S. Nuclear Regulatory Commission. The U.S. nuclear industry, acting through the Institute of Nuclear Power Operations, has voluntarily established nuclear safety culture programs and mechanisms for evaluating their implementation at nuclear plants. The U.S. Nuclear Regulatory Commission has published a policy statement on nuclear safety culture, but that statement does not contain implementation steps or specific requirements for industry adoption. RECOMMENDATION 7.2A: The U.S. Nuclear Regulatory Commission and the U.S. nuclear power industry must maintain and continuously monitor a strong nuclear safety culture in all of their safety-related activities. Additionally, the leadership of the U.S. Nuclear Regulatory Commission must maintain the independence of the regulator. The agency must ensure that outside influences do not compromise its nuclear safety culture and/or hinder its discussions with and disclosures to the public about safety-related matters. RECOMMENDATION 7.2B: The U.S. nuclear industry and the U.S. Nuclear Regulatory Commission should examine opportunities to increase the transparency of and communication about their efforts to assess and improve their nuclear safety cultures.

All committee members agree with the safety culture findings and recommendations (i.e., Findings 7.1 - 7.2 and Recommendations 7.2A , B ), but members have a range of views about the current status of the nuclear safety culture in the United States. A selection of views is provided in Section 7.4 in Chapter 7 .

The first digit denotes the chapter in which the finding (or recommendation) appears; the second digit denotes the serial order of the finding (or recommendation) in the chapter.

The term “ad hoc” refers to responses that are not planned and trained on in advance but rather are developed on the spot.

That is, when the plant is cut off from outside supply of materials and personnel.

The term “extreme event” refers to high-magnitude environmental events, such as large earthquakes or floods, that occur very infrequently, for example, on the order of once every few centuries to millennia. The Great East Japan Earthquake and tsunami are examples of extreme events.

Risk is defined and discussed in Appendix I.

The term “regulatory capture” refers to the processes by which regulated entities manipulate regulators to put their interests ahead of public interests.

• Cite this Page Committee on Lessons Learned from the Fukushima Nuclear Accident for Improving Safety and Security of U.S. Nuclear Plants; Nuclear and Radiation Studies Board; Division on Earth and Life Studies; National Research Council. Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants. Washington (DC): National Academies Press (US); 2014 Oct 29. Summary.
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• CAUSES OF THE FUKUSHIMA DAIICHI ACCIDENT (Study Charge 1)
• LESSONS LEARNED FOR THE UNITED STATES (Study Charges 3 and 4)

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