Restarting reactors at the Tsuruga nuclear plant in Fukui Prefecture will be difficult because a zone of small rocks and sediment under the plant is likely an active fault, a team of experts under the Nuclear Regulation Authority said Monday.
Kunihiko Shimazaki, an NRA commissioner who investigated the geological layer under the plant along with other experts earlier this month, reported to fellow members Monday that it is “highly possible” the so-called crush zone running underneath reactor No. 2 is an active fault.
With the development, “we cannot conduct safety checks for the Tsuruga reactors to restart at this point,” NRA Chairman Shunichi Tanaka said.
Plant operators are not allowed to build reactors and facilities important for safe operations directly above active faults.
If the crush zone beneath the Tsuruga plant is determined to be active, its two reactors would theoretically have to be scrapped.
Japan Atomic Power Co., which runs the plant, said in a statement that the outcome was “totally unacceptable” and vowed to have a separate investigation conducted on the premises. If a different finding isn’t reached, it will have no option but to scrap the reactors.
The team conducted a field survey earlier this month to check whether some faults could move in conjunction with an active fault called the Urazoko, which is about 250 meters from the reactor buildings.
The focus of the discussion is a zone of crushed rock called D-1, which is believed to extend from the Urazoko fault toward the plant’s No. 2 reactor.
The experts agreed that an extended portion of D-1 had likely moved as an active fault in the past, together with the movement of the Urazoko fault, Shimazaki said in wrapping up Monday’s meeting.
In a press conference after the meeting, Shimazaki said the fact that a large fault like Urazoko exists on the plant’s premises was also taken into account.
“If plant operators know there is an active fault at the site in the first place, they will usually not build (a nuclear complex) there,” he added.
The Tsuruga plant has two reactors. The No. 1 reactor started commercial operation in 1970 and the No. 2 reactor in 1987.
It was not until 2008 that the Urazoko fault was confirmed as active by Japan Atomic Power.
NRA Chairman Tanaka said earlier that the utility would likely have a hard time bringing the units back online if an active fault is found running directly beneath them. He then suggested the reactors may have to be scrapped.
Japan has been reviewing the risks that could be posed by active faults ever since the nuclear crisis erupted at Tokyo Electric Power Co.’s Fukushima No. 1 complex in Fukushima Prefecture. The culprit in that event was the huge earthquake and tsunami on March 11, 2011.
Of the 50 commercial reactors in Japan, only two at Kansai Electric Power Co.’s Oi plant, also in Fukui, are online.
Another NRA-appointed team has visited the Oi plant to check for faults but hasn’t yet reached a conclusion.