Corrosion and holes have been found in ventilation ducts at 12 reactors at seven nuclear plants across Japan, the Nuclear Regulation Authority said Wednesday, raising concerns that workers could be exposed to radiation in the event of an accident.
The governmental nuclear watchdog released the results of a nationwide survey it had ordered following a revelation in December 2016 that corrosion had left multiple holes in the air ducts of the No. 2 reactor at Chugoku Electric Power Co's Shimane plant in western Japan. The reactor was not included in the survey.
Serious corrosion was found at the No. 3 unit of the Kashiwazaki-Kariwa plant in Niigata Prefecture operated by Tokyo Electric Power Company Holdings Inc and this may have abnormally affected ventilation of the central control room, the watchdog said.
Although the No. 7 unit at the same plant has passed a test to resume operation, the NRA said it will inspect any impact of corrosion found at the reactor. No abnormality associated with corrosion has been found at the remaining 10 units, it said.
Corrosion or holes were found in steel or galvanized steel ducts at Tohoku Electric Power Co's Onagawa nuclear plant, Japan Atomic Power Co's Tokai No. 2 nuclear plant, TEPCO's Fukushima Daiichi nuclear plant and Kashiwazaki-Kariwa nuclear plant, Chubu Electric Power Co's Hamaoka plant, Hokuriku Electric Power Co's Shiga nuclear plant and Chugoku Electric's Shimane plant.
If an accident occurs, radioactive materials could flow into a plant's central control room through such holes, putting plant workers in danger of radiation exposure.
At the No. 3 reactor at the Kashiwazaki-Kariwa plant, a crack as large as 13 centimeters in length and 5 cm in width was found. A total of nine holes and cracks have been discovered at the Nos. 3 and 7 units at the plant.
