Fukushima Nuclear Disaster: Timeline of Failures, Impact and Legacy

25th release of treated water begins Latest

TEPCO began the 25th discharge of ALPS-treated water since August 2023, about 7,800 tonnes diluted with seawater and released through a tunnel roughly 1 km offshore, scheduled to finish by 13 November. The IAEA said its independent check of this batch found tritium far below Japan’s operational limit of 1,500 becquerels per litre, and that about 188,000 cubic metres had been discharged in total since 2023 (IAEA; TEPCO discharge history).

TEPCO plans about 62,400 tonnes in eight rounds in the fiscal year to March 2027. This is a planned, monitored release of treated and diluted water, a different process from the uncontrolled releases of March 2011.

IAEA’s sixth review mission since the discharge began Treated water

Six IAEA officials and eight international experts, from Argentina, Canada, China, France, South Korea, Russia, the United States and Vietnam, reviewed on-site and sea-area monitoring and visited the discharge facilities and tank-dismantling areas (METI, 15 May 2026). The report of the previous, fifth mission (December 2025) found nothing inconsistent with international safety standards (IAEA report, PDF).

The programme remains contested, particularly among fishing communities and in neighbouring countries. The IAEA’s technical findings and those concerns are both part of the continuing debate.

15 years on: 2,519 still missing, 26,281 still displaced People & health

Police put the earthquake and tsunami toll at 15,901 dead and 2,519 missing. Separately, the Reconstruction Agency counted 3,810 “disaster-related” deaths, from causes such as illness and stress during evacuation, as of the end of 2025. About 26,281 people were still listed as evacuees nationwide on 1 February 2026, and evacuation orders remained in parts of seven Fukushima municipalities (Jiji Press via Adnkronos).

Fukushima Prefecture counted 2,351 disaster-related deaths of its own residents as of 1 May 2026, more than any other prefecture (Fukushima Prefecture).

Large cover completed over the Unit 1 reactor building Decommissioning

TEPCO finished installing a large cover over Unit 1 to limit dust and rainwater while rubble is cleared from the damaged upper floor. An overhead crane and dust-monitoring equipment were being commissioned for rubble removal, and removal of the fuel still in Unit 1’s spent-fuel pool is planned for fiscal 2027–2028 (TEPCO unit status).

China halts Japanese seafood imports again Treated water

China banned all Japanese seafood on the day discharges began in August 2023. It allowed imports to resume from most prefectures in June 2025, keeping Fukushima and nine other prefectures excluded, and the first shipment arrived in November (Al Jazeera). On 19 November 2025 China told Japan it was halting imports again, citing the need for further monitoring of the water release, amid a separate row over Prime Minister Sanae Takaichi’s remarks on Taiwan (Adnkronos).

AiTimeline could not find reporting of a change to the November 2025 halt as of 29 October 2026.

Full-scale removal of melted fuel pushed back to 2037 or later Decommissioning

TEPCO said it would need 12 to 15 years of preparation before large-scale removal of fuel debris could begin at Unit 3, moving the start from the early 2030s to 2037 at the earliest. It kept the goal of finishing decommissioning within 30 to 40 years of the accident, meaning by about 2051 (World Nuclear News).

Courts clear former TEPCO executives Courts

Japan’s Supreme Court finalised the acquittal of former TEPCO vice-presidents Sakae Muto and Ichiro Takekuro, ending the only criminal trial from the accident; they had been charged over the deaths of more than 40 hospital patients during evacuation (AFP via Solar Daily). In June the Tokyo High Court overturned a 2022 ruling that four former executives pay TEPCO ¥13.32 trillion in a shareholder suit, finding the tsunami was not foreseeable (JURIST). The shareholders said they would appeal.

First samples of melted fuel retrieved from Unit 2 Decommissioning

Using a remotely operated device inserted into the Unit 2 containment vessel, TEPCO retrieved its first small sample of fuel debris in November 2024, weighing under a gram, and a second sample from a different location in April 2025 (World Nuclear News). The samples are being analysed to plan the much larger removal job.

Japan begins releasing treated water into the Pacific Treated water

Water used to cool the damaged reactors, together with groundwater and rainwater that entered the buildings, had been treated by the Advanced Liquid Processing System (ALPS) and stored in about 1,000 tanks. ALPS removes most radionuclides but not tritium, so the water is diluted with seawater before release. The IAEA’s comprehensive report of July 2023 found the plan consistent with international safety standards, with a negligible radiological impact on people and the environment (IAEA).

China imposed a blanket ban on Japanese seafood the same day; fishing groups in Fukushima said they had not consented. An assessment that the impact is negligible does not mean every public concern has disappeared.

UNSCEAR: no documented radiation health effects among residents People & health

The UN scientific committee concluded that no adverse health effects among Fukushima residents had been documented that could be directly attributed to radiation exposure from the accident, and that none were expected to be discernible in future. It judged the rise in thyroid cancers detected among young people most likely the result of highly sensitive screening rather than radiation (UNSCEAR FAQ).

The committee also stressed the serious effects of the disaster and evacuation on mental and social well-being. Its radiation findings do not mean the accident caused no harm.

Spent fuel removed from the Unit 3 pool Decommissioning

TEPCO removed all 566 fuel assemblies from the spent-fuel pool at the top of the damaged Unit 3 building, working remotely under a dome-shaped cover. Unit 4’s pool had already been emptied in December 2014 (TEPCO).

Worker’s lung cancer death recognised for compensation People & health

The labour ministry ruled that a former worker in his 50s, who had measured radiation at Fukushima Daiichi after the accident, had died of lung cancer linked to occupational radiation exposure, and that his family should be compensated (NPR). It was the first such death recognised.

The ruling applied compensation criteria for workers. It was not a scientific finding about the population, and it is distinct from UNSCEAR’s assessment of residents.

Diet commission calls the accident “man-made” Investigation

The parliamentary commission concluded that the accident was “a profoundly man-made disaster” that could have been foreseen and prevented, blaming collusion between the government, regulators and TEPCO. Its findings fed into the creation of the Nuclear Regulation Authority in September 2012 and new safety standards in 2013. The IAEA later found that the plant’s tsunami assumptions had not been adequately updated (IAEA Director General report).

Government declares ‘cold shutdown condition’ Investigation

The government announced that the reactors had reached a stable cold-shutdown condition, with temperatures held below 100°C and releases under control. It did not mean the reactors had been repaired, the melted fuel removed or the site made safe. A decommissioning roadmap followed that month.

Accident rated Level 7, the highest on the INES scale Accident

Japan raised its provisional rating from Level 5 to Level 7 on the International Nuclear and Radiological Event Scale, the same category as Chernobyl, on the basis of estimated radioactive releases. Officials estimated Fukushima’s releases at roughly a tenth of Chernobyl’s.

Unit 4 explodes; Unit 2 containment damaged Accident

An explosion wrecked the upper Unit 4 building, which had been shut down and defuelled before the earthquake; hydrogen from Unit 3 is thought to have flowed in through shared pipes. At about the same time the Unit 2 containment was damaged, and the largest single release of radioactive material followed (OECD NEA timeline). Residents between 20 and 30 km were told to shelter indoors.

Hydrogen explosion damages Unit 3 Accident

A hydrogen explosion destroyed the upper structure of the Unit 3 reactor building and exposed its spent-fuel pool. Water levels in Units 1, 2 and 3 had fallen below the top of the fuel, and fuel damage was suspected in all three (OECD NEA).

Unit 1 explodes; evacuation zone widened to 20 km Accident

With battery power exhausted and cooling lost, workers vented the Unit 1 containment. A hydrogen explosion then destroyed the building’s upper structure. It was a chemical explosion, not a nuclear detonation. The evacuation zone was extended from 10 km to 20 km, and seawater was injected into Unit 1 that evening, making the reactor unusable but cooling the core (OECD NEA).

Earthquake and tsunami knock out power and cooling Accident

The earthquake shut down the three operating reactors, Units 1, 2 and 3, automatically; Units 4 to 6 were already offline for inspections. Off-site power was lost and emergency diesel generators started. About 50 minutes later a tsunami about 15 metres high, far above the site’s design basis of about 5.7 metres, flooded the generators, switchgear and batteries (IAEA; World Nuclear Association). An evacuation order for a 3 km radius was issued that evening.

Along the coast, the tsunami killed thousands. Those deaths were caused by the earthquake and tsunami, not by radiation. For the earthquake in context, see the deadliest earthquakes since 1906.