The Nuclear Regulation Authority (NRA) is set to require power companies and other operators to complete waterproofing measures of their nuclear facilities within the next year, following an incident in which tons of rainwater flowed into the No. 2 reactor building at the Shika nuclear plant last fall, it has been learned.
The NRA conducted a survey on nuclear plant operators across the country to detect possible similar problems and released the results on Feb. 8. The survey found that measures to shut off the influx of water into reactor buildings had not been carried out on at least 655 parts of such structures at 10 nuclear facilities.
The facilities mentioned in the survey are: the No. 1 and 2 reactors at the Shika nuclear plant in Ishikawa Prefecture, the No. 2 reactor at Tohoku Electric Power Co.’s Onagawa nuclear plant in Miyagi Prefecture, the No. 1 through 4 reactors at Tokyo Electric Power Co. (TEPCO)’s Fukushima No. 2 nuclear plant in Fukushima Prefecture, the No. 1 through 7 reactors at TEPCO’s Kashiwazaki-Kariwa nuclear plant in Niigata Prefecture, the No. 3 through 5 reactors at Chubu Electric Power Co.’s Hamaoka nuclear plant in Shizuoka Prefecture, the No. 1 and 2 reactors at Chugoku Electric Power Co.’s Shimane nuclear plant in Shimane Prefecture, the No. 1 reactor at the Japan Atomic Power Co.’s Tsuruga Power Station in Fukui Prefecture, the Monju prototype fast-breeder reactor also in Fukui Prefecture, the Tokai Reprocessing Plant in Ibaraki Prefecture and the Rokkasho Reprocessing Plant in Aomori Prefecture. The Shimane nuclear plant’s No. 1 reactor and the Tsuruga Power Station’s No. 1 reactor are under decommissioning work, while the Monju reactor and the Tokai Reprocessing Plant are set to be dismantled.
All the reactors in question are boiling-water reactors. Meanwhile, waterproofing measures have been completed on all of the country’s pressurized-water reactors — including the No. 1 and 2 reactors at Kyushu Electric Power Co.’s Sendai nuclear plant in Kagoshima Prefecture, which were reactivated amid much controversy.
Following heavy rainfall in late September last year, approximately 6.6 metric tons of rainwater flowed into the building housing the No. 2 reactor at the Shika nuclear plant by way of cracks and gaps around plumbing, causing short circuits in lighting switchboards. The crisis occurred as the amount of precipitation surpassed the capacity of makeshift drainage pumps, raising the risk that a storage battery for cooling the reactor in emergencies and other key safety equipment would become submerged and unusable.
The NRA’s new safety regulations introduced in the wake of the 2011 meltdowns at the Fukushima No. 1 nuclear plant call on power companies and other plant operators to take measures to prevent an influx of rainwater and tsunami in reactor buildings from affecting key facilities. However, the regulations do not oblige plant operators to take such measures as fill in the gaps in pipes that penetrate reactor buildings. In response to the recent incident at the Shika plant, which the NRA views seriously, the agency has decided to effectively mandate plant operators to implement waterproofing measures at all nuclear facilities.