The Nuclear Regulation Authority (NRA) requested all nuclear operators nationwide, including those that have already passed their safety inspections and those currently undergoing screening, to inspect their facilities for corrosion following the discovery of holes due to corrosion in air conditioning and ventilation ducts in the central control room of Reactor No. 2 at Shimane Nuclear Power Plant (Matsue City) operated by Chugoku Electric Power Co.
The NRA has not set a deadline for the utilities to complete the inspection. However, reactors that have restarted operations, namely Reactors No. 1 and 2 at Sendai Nuclear Power Plant operated by Kyushu Electric Power Co. (Kagoshima Prefecture) and Reactor No. 3 at Ikata Nuclear Power Plant operated by Shikoku Electric Power Co. (Ehime Prefecture), have been asked to report on the results of their inspections swiftly.
The required inspection involves ducts installed in control rooms where operators work in the event of nuclear accidents, including central control rooms and areas leading to emergency response rooms that act as control towers following accidents. If the ducts corrode and become perforated, radioactive materials will flow into the rooms through the holes and workers could be exposed to radiation.
On Dec. 8, 2016, when the Chugoku Electric Power inspectors removed heat insulation material covering ducts during an inspection of Reactor No. 2 at the Shimane plant, a hole measuring approximately 1 m wide and 30 cm long was found in a duct. A following inspection revealed as many as 19 smaller holes due to corrosion.
Duct inspections at other nuclear plants have been conducted without removing heat insulation material in some cases.