The Nuclear Regulation Authority decided Wednesday to urge power companies to inspect for possible problems related to the installation of electric cables for safety equipment at their nuclear power plants.
At Tokyo Electric Power Co.’s Kashiwazaki-Kariwa plant in Niigata Prefecture and other nuclear power stations, safety-related cables were found to have been laid in combination with other cables. That violates the nation’s new safety standards introduced in July 2013, which calls for them to be separated.
The NRA will call on power companies to check if there are similar problems at other nuclear plants and report the results of their probes by the end of March.
But the No. 1 and No. 2 reactors at Kyushu Electric Power Co.’s Sendai plant in Kagoshima Prefecture and the No. 3 and No. 4 reactors at Kansai Electric Power Co.’s Takahama plant in Fukui Prefecture will be exempt from the cable checks.
The two Sendai reactors are the only active reactors in the country at present, while preparations for a restart are under way for the Takahama reactors.
Although these four reactors have passed the NRA’s safety inspections under the new standards, the authority failed to conduct on-site inspections on whether their safety equipment cables are properly separated from other cables.
Even during pre-use inspections, the final procedure required before the restarts, the NRA checked only some of the cables.
Kyushu Electric and Kansai Electric have both said that there is no need to carry out cable investigations at the four reactors because they have already passed the NRA’s safety inspections.
Under the new safety standards, established after the March 2011 nuclear accident at Tepco’s disaster-stricken Fukushima No. 1 plant, cables for safety equipment must be installed separately from other cables for the purpose of fire management. Power firms are required to take necessary measures, such as using boards to separate the cables.
At the No. 6 and No. 7 reactors of the Kashiwazaki-Kariwa plant, where the problem was first discovered, safety equipment cables under the floors of the central control rooms were installed together with other cables.
The NRA decided in August last year to conduct safety inspections of these two units, but it was not aware of the cable problem until Tepco reported it to the authority in September.
Since boiling water reactors (BWRs), including the reactors at the Kashiwazaki-Kariwa plant, feature a design where many cable lines are located under the floors of the central control rooms, the NRA at first regarded the mixing of cables to be a problem unique to BWRs.
Given that the mixing of cables was found to be greater than expected at BWRs, the NRA came to believe the problem might be pervasive at pressurized-water reactors as well.
Cable mixing has so far been discovered at all seven reactors at the Kashiwazaki-Kariwa plant; the No. 3 and No. 4 reactors at Tepco’s Fukushima No. 2 plant; the No. 4 reactor at Chubu Electric Power Co.’s Hamaoka plant in Shizuoka Prefecture; the No. 1 reactor at Hokuriku Electric Power Co.’s Shika plant in Ishikawa Prefecture; the No. 3 reactor at Tohoku Electric Power Co.’s Onagawa plant in Miyagi Prefecture and the No. 1 reactor at Tohoku Electric’s Higashidori plant in Aomori Prefecture.
The NRA has concluded that some of the cable flaws at the Kashiwazaki-Kariwa plant are long-term problems that have existed since the plant’s construction or since before the introduction of the new nuclear safety standards. It has ordered Tepco to report what preventive measures it will take by Jan. 29.