Ameer Randolph
The Fukushima Daiichi Nuclear Power Plant in Ōkuma, Japan, suffered a major nuclear accident in 2011. The accident was caused by the Tōhoku earthquake and tsunami, which damaged nearly all of the power plant's backup energy sources and cooling systems. This led to the release of radioactive contaminants into the environment, including the ocean, and triggered a large-scale evacuation of the surrounding areas. The accident is considered the worst nuclear incident since the Chernobyl disaster, and the clean-up process has been challenging and prolonged. As of 2024, attempts to remove highly radioactive material from the damaged reactor were halted, with around 880 tonnes of lethal molten fuel remaining. The Japanese government and companies have utilised robots and radiation-hardened machines to locate and manage the fuel, with the total cost of decommissioning and decontamination estimated at $195 billion.
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What You'll Learn
- The Fukushima Daiichi Nuclear Power Plant has 880 tonnes of highly radioactive fuel
- The 2011 Tōhoku earthquake and tsunami caused the nuclear accident
- TEPCO removed 566 fuel assemblies from the Unit 3 spent fuel pool by February 2021
- The Japanese government used underwater robots to find the melted uranium fuel
- The cooling systems were disabled, causing the release of radioactive contaminants
The Fukushima Daiichi Nuclear Power Plant has 880 tonnes of highly radioactive fuel
The Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, experienced a major nuclear accident on March 11, 2011, triggered by the Tōhoku earthquake and tsunami. The disaster led to the release of radioactive contaminants into the surrounding environment, including the ocean, and resulted in a long-term cleanup process.
The Fukushima Daiichi Nuclear Power Plant has an estimated 880 tonnes (1.9 million pounds) of highly radioactive melted nuclear fuel across its three reactors. The removal of this fuel has proven challenging and has been a key focus of the cleanup efforts. In 2024, a robotic mission was restarted to collect samples of the melted radioactive fuel from a damaged reactor. The mission encountered difficulties, including a glitch that halted the robot, underscoring the complexities of the fuel retrieval process.
The presence of 880 tonnes of highly radioactive fuel at Fukushima Daiichi Nuclear Power Plant poses significant risks and challenges. The fuel melting occurred early on in all three units, and while the fuel remained largely contained, there were releases of volatile fission products and soluble radioactive contaminants. The cooling systems for the reactors failed, leading to the release of steam and hydrogen, further complicating the situation.
The removal of the highly radioactive fuel from the damaged reactors is crucial for the decommissioning and decontamination of the Fukushima Daiichi Nuclear Power Plant. The process has been challenging due to the high radiation levels and the need to develop specialized technology and robots capable of operating in the hazardous environment. The cost of decommissioning and decontamination, including compensation payouts to victims, is estimated to be $195 billion, with TEPCO shouldering $143 billion of this amount.
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The 2011 Tōhoku earthquake and tsunami caused the nuclear accident
On March 11, 2011, a magnitude 9.0 earthquake struck Japan, causing a massive tsunami that led to one of the worst nuclear incidents since Chernobyl. The Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, was particularly affected, with the earthquake and tsunami resulting in electrical grid failure and damaging almost all of the power plant's backup energy sources. This led to a loss of cooling capabilities for the reactors, causing them to overheat and release radioactive contaminants into the surrounding environment.
The Fukushima Daiichi plant had six reactors containing 880 tonnes of highly radioactive nuclear fuel. The loss of cooling capabilities resulted in major fuel melting in all three units, with some volatile fission products released into the atmosphere and groundwater. The containment of the fuel was largely successful, except for some releases from Unit 2, where the containment was breached.
The spent-fuel pools, which are meant to keep the fuel submerged in circulating water to prevent overheating, were also affected. Helicopters and fire trucks were used to pump water into the pools, particularly in reactor No. 3, which houses MOX (mixed oxide) fuel that melts at lower temperatures. The high radiation levels posed challenges for operators trying to get close enough to refill the pools.
The accident had significant consequences, including the release of radioactive contaminants into the Pacific Ocean through the strong Kuroshio Current. This led to concerns about the impact on marine life, despite government assurances that the released water met safety standards. The accident also had profound psychological effects on the residents of Fukushima, with increased rates of depression, anxiety, sleep disturbances, and post-traumatic stress disorder.
The cost of decommissioning and decontaminating the Fukushima Daiichi plant is estimated to be $195 billion, including compensation payouts to victims. TEPCO, the company operating the plant, is responsible for a significant portion of this cost. Efforts to remove the remaining nuclear fuel material and decommission the reactors are ongoing, with challenges and delays due to the hazardous nature of the site.
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TEPCO removed 566 fuel assemblies from the Unit 3 spent fuel pool by February 2021
The Fukushima Daiichi Nuclear Power Plant, operated by the Tokyo Electric Power Company (TEPCO), experienced a major disaster in March 2011 due to an earthquake and tsunami. The tsunami caused a loss of power supply, water injection, and heat removal functions, leading to a hydrogen explosion in Unit 3 and damage to the building.
As a result of the explosion, large pieces of debris fell into the spent fuel pool of Unit 3, which contained 566 fuel rod assemblies. These fuel assemblies are stored in the spent fuel pool and are put into transport containers (casks) for removal and storage in the common pool located on-site. The spent fuel pools contain radioactive material that must be submerged in circulating water to prevent overheating and potential release.
TEPCO began the challenging task of removing the debris and fuel assemblies from Unit 3 in April 2019, with the aim of completing the fuel removal during the fiscal year 2020. This process involved navigating through a heavily damaged reactor building and required the development of new tools and techniques to safely remove the fuel while minimising worker radiation exposure.
By February 2021, TEPCO successfully completed the removal of all 566 fuel assemblies from the Unit 3 spent fuel pool. This was a significant milestone in the decommissioning process and reduced a major risk associated with the damaged building. The removal of the fuel assemblies allowed for safer storage and management of the fuel in a structurally sound building.
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The Japanese government used underwater robots to find the melted uranium fuel
The Fukushima Daiichi nuclear disaster, caused by an earthquake and tsunami in 2011, was the worst atomic disaster since Chernobyl. In the aftermath, the Japanese government and companies used underwater robots to search for the fuel that escaped the ruined reactors. The robots were also used to assess the damage inside the reactors.
The underwater robots were equipped with radiation-hardened materials and sensors. They were used to locate the highly radioactive melted nuclear fuel that had evaded detection for six years. The robots successfully navigated around debris and avoided excess radiation to locate the fuel.
One such robot, nicknamed "Little Sunfish", was about the size of a loaf of bread and was equipped with five propellers, a transparent dome, front and rear video cameras, and an array of lights and sensors. It was designed to operate underwater, in total darkness, and amid intense radiation. It was developed by Matsuzaki and a team of engineers over more than a year.
Another robot, the Mini-Manbo, successfully located the melted uranium fuel in the Unit 3 reactor in July 2017. It beamed back video footage of a gaping hole at the bottom of the reactor and clumps of solidified lava, which were the first images ever taken of the plant's melted uranium fuel. The discovery was a turning point in the disaster's cleanup, which is expected to take decades.
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The cooling systems were disabled, causing the release of radioactive contaminants
The Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, was the site of the worst nuclear incident since the Chernobyl disaster in 1986. The accident began on March 11, 2011, when a magnitude 9.0 earthquake struck off the coast of Tohoku, triggering a tsunami. The earthquake and tsunami caused electrical grid failure and damaged nearly all of the power plant's backup energy sources, including the seawater pumps for the main condenser circuits and the auxiliary cooling circuits. This resulted in the loss of cooling for the reactors, which were automatically shut down in response to the earthquake.
The inability to sufficiently cool the reactors led to a rise in core temperature and pressure. In Unit 1, the temperature and pressure dropped unexpectedly quickly, and operators turned the emergency cooling system on and off repeatedly to slow the rate of cooling. However, the cooling system was disabled when the tsunami struck, causing the core temperature to rise above 100 °C.
In Units 5 and 6, an air-cooled diesel generator survived the tsunami and enabled repairs, allowing the restoration of cooling and a return to cold shutdown by March 20. In Unit 3, fuel rods fell into the reactor, causing a nuclear reaction and requiring seven and a half hours to reposition. The RCIC (removal of decay heat using the reactor pressure vessel) was not functional due to insufficient steam pressure, and the RHR (residual heat removal) cooling system was damaged by the tsunami. The HPCI (high-pressure coolant injection) system was activated, but it ultimately failed.
The loss of cooling in Units 1, 2, and 3 led to a nuclear meltdown, with all three cores largely melting within the first three days. This resulted in the release of radioactive contaminants into the surrounding environment, including contaminated water leaked from the units. The accident was rated as a level 7 on the International Nuclear and Radiological Event Scale due to high radioactive releases, particularly during days 4 to 6. The total release was estimated at 940 PBq (I-131 eq).
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Frequently asked questions
There are 880 tonnes (1.9 million pounds) of highly radioactive melted nuclear fuel at the Fukushima Daiichi Nuclear Power Plant.
Unit 3 at Fukushima Daiichi Nuclear Power Plant had 566 fuel assemblies.
Unit 4 at Fukushima Daiichi Nuclear Power Plant had 1535 fuel assemblies.
