Mercedes Mullins
The Fukushima Daiichi Nuclear Power Plant in Japan suffered a nuclear accident in March 2011 following the Tōhoku earthquake and resulting tsunami. The accident led to the release of radioactive material, triggering a 30-kilometre evacuation zone around the plant. The extent of fuel loss at Fukushima is not precisely known, but it is estimated that the three damaged reactors at the plant contained 880 tonnes of highly radioactive melted nuclear fuel. The Japanese government and companies utilised radiation-hardened machines to locate and remove the fuel, with the process of removing fuel assemblies from the storage pools of units 3 and 4 completed in recent years. The accident and its aftermath had significant human, environmental, and economic impacts, with ongoing challenges related to decommissioning, decontamination, and the health and well-being of affected individuals and communities.
| Characteristics | Values |
|---|---|
| Amount of fuel lost | 880 tonnes or 1.9 million pounds of highly radioactive molten fuel |
| Amount of fuel removed | 566 fuel assemblies removed from unit 3; 1331 used assemblies removed from unit 4 |
| Cost of decommissioning and decontamination | $195 billion |
| Cost shouldered by TEPCO | $143 billion |
| Cost shouldered by the Ministry of Finance of Japan | $17 billion |
| Number of residents displaced | 119,000 in January 2015, peaking at 164,000 in June 2012 |
| Radiation released into the ocean | 1 to 5.5 PBq 137Cs and 10-20 PBq 131I |
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What You'll Learn
The Fukushima Daiichi Nuclear Power Plant had six reactors
The tsunami waves, reaching up to 14 meters (46 ft), overtopped the seawalls and disabled the emergency generators required to cool the reactors and spent fuel pools in units 1–5. Evidence of partial nuclear meltdowns was observed in units 1, 2, and 3, with visible explosions suspected to be caused by hydrogen gas. Units 5 and 6 initially retained power through diesel generators, but they too eventually lost offsite power. The disaster also affected the sister plant, Fukushima Daini, located 12 kilometers (7.5 mi) to the south, which suffered serious damage but was successfully shut down without experiencing the same level of catastrophe as Fukushima Daiichi.
The total amount of fuel lost at Fukushima Daiichi is estimated to be around 880 tonnes (1.9 million pounds) of highly radioactive molten fuel. This fuel, which should have been submerged in circulating water to prevent overheating, was at least partially exposed, leading to the melting of the uranium fuel. The removal of this fuel has proven challenging, with attempts to utilize robots to extract samples and assist in the decommissioning process. The cost of decommissioning and decontaminating the plant is estimated to be $195 billion, including compensation payouts to victims.
The impact of the Fukushima disaster extended beyond the immediate physical damage and radiation release. There were significant psychological consequences among residents and employees of the nuclear plant, with elevated rates of depression, anxiety, sleep disturbances, and post-traumatic stress disorder. The number of displaced residents peaked at 164,000 in June 2012, and the lack of information and relocation contributed to the stress and mental health challenges experienced by those affected. The Japanese government's handling of the crisis also came under scrutiny, with criticisms of a lack of transparency and inadequate record-keeping during key meetings.
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A tsunami caused a loss of power to the plant
On March 11, 2011, a tsunami caused a loss of power to the Fukushima Daiichi Nuclear Power Plant, resulting in a nuclear accident. The plant, located in Japan, consisted of six General Electric (GE) light water boiling water reactors (BWRs), with Units 1-3 in operation at the time of the accident. The tsunami waves, reaching up to 14 meters (46 feet), overwhelmed the station's seawalls and disabled the emergency generators needed to cool the reactors and spent fuel pools in Units 1-5. This led to evidence of partial nuclear meltdowns in Units 1, 2, and 3 within three weeks, including visible explosions and the uncovering of spent fuel pools.
The loss of power caused by the tsunami had severe consequences for the plant's operations. Without power for cooling, the reactor cores continued to produce heat, generating steam within the reactor pressure vessels (RPVs). This steam, in combination with hydrogen produced by the interaction of the fuel's zirconium cladding with steam, led to a buildup of pressure and subsequent explosions. The explosions caused further damage to the reactor buildings and exposed the spent fuel pools, releasing radioactive material.
The Tokyo Electric Power Company (TEPCO), which operated the plant, had been warned prior to the accident that its seawall was insufficient to withstand a powerful tsunami. Despite this, TEPCO did not increase the seawall height, leading to the subsequent overwhelming of the seawalls during the tsunami. The nearby Onagawa Nuclear Power Plant, operated by Tohoku Electric Power, had stronger and taller seawalls, which allowed it to avoid a severe accident despite being closer to the earthquake's epicenter.
The Fukushima Daiichi accident had far-reaching impacts, including the displacement of thousands of residents and ongoing releases of radioactivity. It also highlighted the lack of transparency and inadequate record-keeping by the Japanese government during the crisis. The cost of decommissioning and decontamination of the plant is estimated to be $195 billion, including compensation for victims.
The removal of fuel assemblies and debris from the damaged reactors has been a challenging and prolonged process. Efforts to cool the reactors and contain the spread of radioactive material were undertaken, including the use of helicopters and fire trucks to inject water into the spent fuel pools. Robots have played a crucial role in navigating the hazardous environment, locating the melted uranium fuel, and collecting samples to inform decommissioning strategies. The total amount of highly radioactive molten fuel at the plant is estimated to be 880 tonnes (1.9 million pounds).
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This resulted in a nuclear meltdown
The Fukushima Daiichi Nuclear Power Plant consisted of six General Electric (GE) light water boiling water reactors (BWRs). On March 11, 2011, a 9.0-magnitude earthquake struck Japan, causing a 14-metre-high tsunami that overwhelmed the plant's seawalls. This resulted in a nuclear meltdown.
The tsunami disabled the reactor cooling systems, leading to a release of radioactivity and triggering a 30-kilometre evacuation zone around the plant. There was evidence of partial nuclear meltdowns in units 1, 2, and 3, with visible explosions suspected to be caused by hydrogen gas. Fuel rods fell in reactor unit 3, causing a nuclear reaction. The core damage started about eight hours after backup cooling was lost, and the fuel melted and probably fell into the water at the bottom of the RPV about 100 hours later.
The Japanese government and companies used radiation-hardened machines to search for the fuel that escaped the ruined reactors. Underwater robots were deployed to locate and assess the damage, including the Mini-Manbo, which successfully navigated the debris and radiation to locate the plant's highly dangerous uranium fuel. The removal of fuel assemblies from the storage pools of units 3 and 4 was completed by the Tokyo Electric Power Company, with work yet to begin on units 1 and 2.
The cost of decommissioning and decontamination of the Fukushima Daiichi nuclear power plant has been estimated at $195 billion, including compensation payouts to victims. The plant contains 880 tonnes of highly radioactive melted nuclear fuel, and attempts to remove this material were halted in 2024 due to technical challenges and concerns about the long-term cleanup timeline. The impact of the disaster on the mental health and well-being of survivors and evacuees has been significant, with high rates of psychological distress, anxiety, and sleep disturbances observed.
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Radioactivity was released into the ocean
The release of radioactivity into the ocean from Fukushima is unprecedented, with more than 80% of the radioactivity from the damaged reactors ending up in the Pacific Ocean. The Kuroshio Current, one of the world's strongest currents, transported the contaminated water far into the Pacific, dispersing the radioactivity. While it was initially believed that the consequences for marine life would be minor, there is now concern over the impact on marine life as radioactive water continues to be released into the ocean.
The radionuclides released into the ocean from Fukushima include caesium-134 and caesium-137, which have been detected in migratory fish species such as Pacific bluefin tuna and albacore tuna caught in the eastern Pacific. These radionuclides were already present in the environment before the Fukushima disaster due to nuclear testing and fuel reprocessing, but the disaster has led to increased levels in the ocean. While the United States Food and Drug Administration (FDA) has stated that there is no evidence that radionuclides from Fukushima are present in the US food supply at unsafe levels, consumers have been slow to regain their trust in Fukushima fishery products.
In August 2023, Japan began releasing treated radioactive water from the Fukushima plant into the Pacific Ocean, despite opposition from its neighbours. The water has been treated using the Advanced Liquid Processing System (ALPS) to remove traces of radiation, with tritium being the primary radionuclide remaining. The International Atomic Energy Agency (IAEA) has stated that the plan meets safety standards, but critics argue that more studies are needed and that the release should be halted. The release of the treated water has sparked protests and led to China expanding its ban on aquatic imports from Japan.
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The cleanup and decommissioning process is ongoing
The Fukushima Daiichi Nuclear Power Plant consisted of six General Electric (GE) light water boiling water reactors (BWRs). The March 2011 disaster disabled the reactor cooling systems, triggering a 30-kilometre (19 mi) evacuation zone surrounding the plant. The accident caused by a powerful tsunami resulted in the loss of about 880 tonnes (1.9 million pounds) of highly radioactive molten fuel.
The removal of fuel assemblies from the storage pool of unit 3 at the damaged Fukushima Daiichi nuclear power plant was completed in 2019. Fuel assemblies have also been removed from the pool at unit 4, but work has yet to start at units 1 and 2. The removal of fuel from unit 3's storage fuel pool began in April 2019 after several years of work to remove debris from the reactor building service floor. The process of removing all 566 fuel assemblies from unit 3 was completed by the Tokyo Electric Power Company.
The Fukushima Daiichi Accident highlighted the need for innovative proposals for removing fuel debris from units 1 to 3. In August 2014, the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) was set up by the government to work with IRID and Tepco Fukushima Daiichi D&D Engineering Co. on developing mid- and long-term decommissioning technologies and implementing policies. Despite the challenges, the cleanup and decommissioning process at Fukushima Daiichi continues, with a focus on safety and the development of advanced technologies.
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Frequently asked questions
It is unclear how much fuel was lost at Fukushima, but the Fukushima Daiichi Nuclear Power Plant consisted of six reactors, and Units 1, 2, and 3 showed evidence of partial nuclear meltdowns.
The fuel loss was caused by a tsunami that disabled the reactor cooling systems, leading to releases of radioactivity.
The tsunami occurred on March 11, 2011, and the fuel loss happened shortly after.
The fuel loss resulted in the release of radioactive material into the ocean, leading to ongoing releases of radioactivity as of February 2025. The accident also had significant human impacts, including the displacement of up to 164,000 residents and various psychological consequences.
Helicopters, fire trucks, and pump trucks were initially used to inject water into the spent fuel pools to cool them. Later, robots were deployed to locate and remove the melted fuel for decommissioning.
