Most of Japan’s 42 operable commercial nuclear reactors have not had detailed check-ups performed on the air conditioning and ventilation systems of their central control rooms, Japanese media reported on 17 January. According to Japan Atomic Power Co and nine utilities that operate NPPs, checkups have been conducted at only two of the plants so far and were carried out without removing the insulation on the pipes, Jiji Press reported.
In December, Chugoku Electric Power Co found extensive corrosion and holes, including one measuring 30cm by 100cm, in the ventilation pipes of the unit 2 reactor at the Shimane NPP. It was the first time the utility had removed the covering on the pipes since the reactor began operation up in 1989. Chugoku Electric reported the degradation to the Nuclear Regulation Authority (NRA).
In the event of an accident, control rooms, which are staffed around the clock, must be self-contained to prevent outside air from entering.
Five reactors at the three NPPs have been restarted since 2015 and none has undergone pipe inspections in which their insulation was removed. Of the five, unit 1 at Kyushu Electric Power Co’s Sendai plant in Kagoshima Prefecture and unit 3 at Shikoku Electric Power Co’s Ikata plant in Ehime Prefecture are currently in operation. Following the discovery of the pipe degradation at Shimane 2, NRA plans to check conditions at all nuclear plants, Jiji said, citing “sources”.
NRA suspects that the pipe corrosion at the Shimane 2 may violate nuclear regulatory standards. “As the plant is located near the sea, salt-containing air may have flowed into the pipes and hastened corrosion,” a Chugoku Electric official said. Most NPPs are in coastal areas because they use seawater to cool their turbines.
Hokuriku Electric Power Co detected rust in the ventilation pipes of the unit 1 reactor at its Shika NPP in Ishikawa Prefecture in 2003. After removing the covers and conducting further inspections, the company replaced the equipment in 2008.
