The chain of events caused radiation leaks and permanently damaged several of its reactors, making them impossible to restart.

On April 20, 2011, the Japanese authorities declared the 20-kilometre (12 mi) evacuation zone a no-go area which may only be entered under government supervision.

They described a scene of devastation in which three of the reactor buildings were destroyed; the grounds were covered with mangled trucks, crumpled water tanks and other debris left by the tsunami; and radioactive levels were so high that visitors were only allowed to stay for a few hours.

[6] In April 2021, the Japanese government approved the discharge of radioactive water, which has been treated to remove radionuclides other than tritium,[vague] into the Pacific Ocean over the course of 30 years.

[22] All units were inspected after the 1978 Miyagi earthquake when the ground acceleration was 0.125 g (1.22 m/s2) for 30 seconds, but no damage to the critical parts of the reactor was discovered.

The reactor design plans provided by General Electric specified placing the generators and batteries in that location, but mid-level engineers working on the construction of the plant were concerned that this made the backup power systems vulnerable to flooding.

One reason for lowering the bluff was to allow the base of the reactors to be constructed on solid bedrock in order to mitigate the threat posed by earthquakes.

The project was formally canceled by TEPCO in April 2011 after local authorities questioned the fact that they were still included in the supply plan for 2011, released in March 2011, after the accidents.

[32] In 2008, the IAEA warned Japan that the Fukushima plant was built using outdated safety guidelines, and could be a "serious problem" during a large earthquake.

In December 2013 TEPCO decided to decommission the undamaged units 5 and 6; they may be used to test remote cleanup methods before use on the damaged reactors.

The reactor was reduced to 0% power, which exceeded the 5% threshold that requires event reporting, and pressure dropped back under the regulatory limit at 4:25 am.

The subsequent destructive tsunami with waves of up to 14 metres (46 ft) that over-topped the station, which had seawalls, disabled emergency generators required to cool the reactors and spent fuel pools in units 1–5.

[51] As a precautionary measure, vents in the roofs of these two units were also made to prevent the possibility of hydrogen gas pressurization and then ignition.

[52] The triple meltdown also caused concerns about contamination of food and water supplies, including the 2011 rice harvest, and also the health effects of radiation on workers at the plant.

[58] Toyoshima was focused on organizing a set of important and urgent documents in the main office building of the Fukushima Daiichi Nuclear Power Plant as a member of the accounting team when it happened.

[60] In August, Japanese officials said highly radioactive water was leaking from Fukushima Daiichi into the Pacific Ocean at a rate of 270 tonnes (600 thousand pounds) per day.

[61] By September 2019, 907 thousand tonnes (2 billion pounds) of contaminated cooling water had been collected in tall steel tanks.

[62] TEPCO estimated the immediate site would run out of space by 2022, and planned to solve this problem by disposing of the radioactive water into the Pacific Ocean.

This proposed measure was criticized by environmental groups and several Asian governments, who claimed that storage area was available in the exclusion zone around the reactor.

[64] On August 1, 2013, the Japanese Industry Minister Toshimitsu Motegi approved the creation of a structure to develop the technologies and processes necessary to dismantle the four reactors damaged in the Fukushima accident.

[65] To reduce the flow of contaminated water into the Pacific Ocean, TEPCO spent ¥34.5 billion (approximately US$324 million) to build a 1.5-kilometre-long (0.93 mi) underground wall of frozen soil around the plant, constructed by Kajima Corporation.

1,500 thirty-metre long (ninety-eight-foot), supercooled pipes were inserted into the ground in order to freeze the surrounding groundwater and soil.

A robot, dubbed Telesco attempted to remove 3 grams (0.11 oz)[a] of the estimated 880 tonnes (1.9 million pounds) lethally radioactive molten fuel.

[71] On September 11, 2024, a robotic mission at Fukushima Daiichi restarted to collect a small sample of melted radioactive fuel from a damaged reactor.

[73] Concerns also remain over the impact on marine life as radioactive water is being released into the Pacific Ocean, despite government assurances that it meets safety standards.

[74] In November 2024, TEPCO moved a small piece of melted fuel from Fukushima's reactor for radiation testing, a key step in its complex decommissioning process.