TOKYO, Dec. 10 (Kyodo) — A team of experts under Japan's nuclear regulatory authority agreed Monday that a fault running underneath a reactor at Japan Atomic Power Co.'s Tsuruga plant is likely to be active, an assessment that could leave the company with no option but to scrap the unit.
The Nuclear Regulation Authority will release its own judgment based on the outcome of the experts' discussions, but NRA Chairman Shunichi Tanaka, who also attended the meeting, said he feels the authority "cannot implement safety assessments for the resumption (of the plant) in the current situation."
It has been known for years that a major active fault called Urazoko lies only about 250 meters from the reactor buildings. But the focus of the latest discussions has been on whether a fault zone of crushed rock called D-1, located beneath the plant's No. 2 reactor, could move in conjunction with the Urazoko fault.
The experts agreed that what appears like an extended section of D-1 had moved as an active fault in the past, together with the movement of the Urazoko fault, Kunihiko Shimazaki, an NRA commissioner who leads the team, said in wrapping up the meeting.
It is the first time that a panel under the newly launched NRA has reached the conclusion that an existing reactor may be sitting directly above an active fault, a situation not allowed under safety screening guidance for nuclear power plants in the quake-prone country.
Japan Atomic Power said in a statement that the outcome was "totally unacceptable," noting that the experts focused largely on geological formation data and not other aspects, and vowed to continue an additional investigation on the plant's premises to counter the assessment.
But Shimazaki suggested during a press conference later in the day that he feels no need to wait for the company to carry out further studies, saying his team had "reached a decision based on the data we have now."
The extended section of D-1 falls within the definition of an active fault that Shimazaki thinks appropriate, which is a fault that has moved in the last 400,000 years.
Shimazaki also said the fact that a large fault like Urazoko exists on the premises of the plant was also taken into consideration by the experts.
He added, "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."
The Tsuruga plant on the Sea of Japan coast has two units, with the No. 1 reactor starting commercial operation in 1970 and the No. 2 reactor in 1987. But it was not until 2008 that the Urazoko fault was confirmed to be active by Japan Atomic Power.
Japan Atomic Power, which owns the Tsuruga plant and the Tokai No. 2 plant, has run its business by selling electricity to its major shareholders such as Tokyo Electric Power Co. and Kansai Electric Power Co.
Some local residents were stunned by the NRA-led team's judgment. Tsuruga Mayor Kazuharu Kawase said the outcome was "very tough" but added there is a possibility that safety could be confirmed through additional investigations.
Japan has been reviewing the risks posed by active faults in the wake of the nuclear crisis at Tokyo Electric Power Co.'s Fukushima Daiichi complex, which was triggered by a huge earthquake and tsunami on March 11, 2011.
Of the 50 surviving commercial reactors in Japan, only two reactors at Kansai Electric Power Co's Oi plant, also in Fukui Prefecture, are currently online.
Another NRA-appointed team has already visited the Oi plant to check faults there, but it has not yet reached a conclusion.
The NRA plans to send similar teams of experts to at least four other facilities in the country.