At the Japanese Mihama 1 reactor, in the prefecture of Fukui, a disturbance in the flow of coolant broke the top 70mm off two fuel rods, scattering pellets of uranium oxide through the cooling system in the reactor core. The uranium fuel may have partially melted. The Owners, Kansai Electrical Power Company, did not consider the incident to be worth reporting officially and kept it a secret for three years.
The Mihama I reactor had previously been plagued by leake in the steam generator tubes and has been repeatedly shut down for repairs. By 1973, one-fifth of the tubes were found to be defective and had to be repaired. Further repairs were carried out in early 1974 but, after its restart, the reactors ran for only 42 days at 40 per cent power before radiation leaks were again detected. Inspection of the Mihama 2 and Mihama 3 plants revealed similar problems.
Damage to the tubing was given as the sole reason for the final shutdown of the Mihama 1 plant in July 1074, but two years later a group of workers from the plant disclosed that damage to the core, caused by the 1073 accident, was the true reason. The owners and the government denied this, but a team from the Ministry of Trade and Industry examined the plant and publicly admitted that there was indeed a problem in the core.
In December 1976, the local anti-nuclear group discovered that the broken rods were to be transported by road to the government research station at Tokai-Mura before radiation had cfallen to the required level./ Trade unionists and political leadwrs joined a sit-down protest to block the gates of the plant, and 250 riot police were called in to break up the demonstration. Source: J Takagi (original contribution); Judith Cook – ‘Red Alert’ (New English Library 1986]
1975, January 10: At the Tsuruga-1 reactor complex in Japan, 13 tons of radioactive waste liquid leaked from a crack in the storage tank and onto the floor of the building. Decontamination teams were exposed to high levels of radiation. Source: J Takagi (original contribution)
1977, July 27: In Japan, a routine inspection revealed one-inch deep cracks on the inside of the Fukushima 1 reactor pressure vessel, raising questions of safety at all Japanese boiling-water reactors. Workers carrying out repairs inside the vessel suffered radiation exposure. Source: J Takagi (original contribution)
1979, December 3: A loosened plug in the primary coolant circuit at the Japanese Takahama 2 reactor caused 80 tons of coolant to leak out over a period of nine hours. Source: J Takagi (original contribution)
1981, March 8: A radioactive waste storage tank at the Japanese Tsuruga 1 reactor overflowed and leaked into Wakasa Bay.The plant’s operators JAPCO kept the incident secret but it came to light a month later when a team from the Kyoto University School of Agriculture, who had been monitoring contamination in the bay for 10 years, took samples of seaweed near the plant’s drain outlet. They found 11 picocuries of cobalt-60 and 40 picocuries of manganese-54, 250 times the level of contamination that JAPCO had claimed was present in the bay.
An inquiry was demanded and the operators finally admitted the scale of an earlier accidental leak in 1975 and disclosed that this latest leakage, the tenth at the plant, had been caused by tons of contaminated water leaking into a drainage system for three hours. Fifty0six workers had been contaminated, as had the sub-contractors invol ved in the clean-up. Several of these had not worn protective clothing while clearing up the radioactive water with mops and buckets. JAPCO paid out 1.2 billion yen in compensation to local fishermen and the tourist industry. Source: J Takagi (original contribution)
1985, August 31: While the Fukushima 1-1 reactor in Japan was shut down for a routine inspection, fire broke out in thee turbine building and destroyed most of the power cables, including those that supply auxiliary equipment in the reactor. Had the plant been operating at the time, the situation could have been extremely dangerous. Source: J Takagi (original contribution)
1986, June 23: Twelve people, including IAEA inspectors, were ‘slightly’ contaminated by plutonium whilst inspecting a store-room of the Power Reactor and Nuclear Fuel Development Corporation, owned by the Japanese government, at Tokaimura, northeast of Tokyo. Source: The Times / 24 Feb 1986
1989, January 6: A violently vibrating recirculation pump at the Fukushima II-3 reactor in Japan was allowed to run for 14 hours, with alarms signalling a fault, before the reactor was shut down. Investigations revealed that a 100kg bearing ri9ng had broken up and, by early March, pieces of metal had been found throughout the core, on 122 of rthe 764 fuel assemblies and at the bottom of the reactor vessel. The largest piece of metal was 10.5cms long and weighed nine grams. The reactor was expected to be out of action for at least nine months. Source: WISE (14 April 1989/28 April 1989); Nuke Info Tokyo (March/April 1989)
ENTRIES FROM WIKIPEDIA:
- 1981: almost 300 workers were exposed to excessive levels of radiation after a fuel rod ruptured during repairs at the Tsuruga Nuclear Power Plant.
- December 1995: the fast breeder Monju Nuclear Power Plant sodium leak.
- March 1997: the Tokai reprocessing waste explosion.
- 1999: a fuel loading system malfunctioned at a nuclear plant in the Fukui Prefecture and set off an uncontrolled nuclear reaction and explosion.
- September 1999: the criticality accident at the Tokai fuel fabrication facility.
- August 2002: a widespread falsification scandal starting in that lead to shut down all of Tokyo Electric Power Company’s 17 nuclear reactors; Tokyo Electric's officials had falsified inspection records and attempted to hide cracks in reactor vessel shrouds in 13 of its 17 units.
- 9 August 2004: five workers were killed after a steam explosion at the Mihama-3 station; the subsequent investigation revealed a serious lack in systematic inspection in Japanese nuclear plants, which led to a massive inspection program.
- 16 July 2007: a severe earthquake (measuring 6.8 on the Richter scale) hit the region where Tokyo Electric's Kashiwazaki-Kariwa Nuclear Power Plant is located and radioactive water spilled into the Sea of Japan; as of March 2009, all of the reactors remain shut down for damage verification and repairs; the plant with seven units was the largest single nuclear power station in the world.
- 2008: an earthquake cracked the reactor cooling towers at the Kurihara Nuclear Power Plant, spilling wastewater and damaging the reactor core.
Source: Benjamin K. Sovacool. A Critical Evaluation of Nuclear Power and Renewable Electricity in Asia, Journal of Contemporary Asia, Vol. 40, No. 3, August 2010, pp. 380.