Reference Material: Main Accidents and Breakdowns Occurring at Nuclear Power Plants and Nuclear Fuel-Related Facilities (FY2021)

By Kamisawa Chihiro (CNIC)

We summarize here the main accidents and breakdowns at nuclear power plants and nuclear fuel-related facilities in FY2021. The materials are based on reports from the Nuclear Regulation Authority, reports issued under the Nuclear Reactor Regulation Act or the Radioisotope Regulation Act (, excerpts from the Nuclear Facilities Information Disclosure Library NUCIA (, and information taken from the press releases and reports of each company. Of these, accidents and breakdowns considered to be important from the viewpoint of safety are noted in the table. Three cases involving a legal requirement to submit a report to the NRA are indicated by a “○” in the legal requirement (LR*) column.

There are many reports of problems related to emergency diesel generators.

Of the damage to the heat transfer tubes of steam generators in Takahama Unit 3, the thinning on the outer surface is thought to have the same cause as in the similar problem at Takahama Unit 4 in November last year, but it seems it was not possible to take preventative measures.

Two incidents involving iodine leaks occurred due to pinholes in the fuel rod cladding.

Worrying problems have also occurred involving breakdowns of spent fuel pool cooling pumps at Onagawa, and Fukushima Daiichi and Daini Nuclear Power Stations due to earthquakes off the coast of Fukushima Prefecture.

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