Experts appointed by the Nuclear Regulation Authority started a field survey Saturday to check for active faults running directly beneath the two reactors of the Tsuruga nuclear plant in Fukui Prefecture.
The NRA fears that the major active Urazoko fault, which already has been confirmed to lie only 250 meters away from the reactor buildings, could trigger smaller faults underneath the two units if it were to shift.
Past investigations have suggested that several faults running underneath reactors 1 and 2 extend from the Urazoko fault, raising fears about another disaster on the scale of the Fukushima meltdowns. If the NRA decides the reactors were constructed above faults that could move in the future, Japan Atomic Power Co. would likely be prevented from ever restarting them and could be forced to decommission the two units.
The Tsuruga plant, on the Sea of Japan coast, is the second nuclear complex the NRA has targeted for such an on-site investigation, following surveys at Kansai Electric Power Co.’s Oi power station in the same prefecture. The NRA has yet to reach a conclusion on whether faults detected at the Oi facility are active and what degree of danger they pose.
The Tsuruga plant’s No. 1 unit started operations in 1970, making it the oldest of Japan’s 50 commercial reactors. But it was not until 2008 that Japan Atomic Power confirmed that the Urazoko fault, part of which runs beneath the facility, was active.
The investigative team consists of NRA Commissioner Kunihiko Shimazaki, a seismologist and four other nuclear experts recommended by the academic community. The survey could continue Sunday.
NRA Chairman Shunichi Tanaka said earlier that Japan Atomic Power will find it difficult to bring the reactors back online if an active fault is found to run beneath them.
“The existence of the active (Urazoko) fault raises serious concerns. And I can’t imagine what kind of measures could be taken (by the company) for the safe operation of the two reactors” if it is found to be connected to faults running directly underneath them, Tanaka said.
When asked how long Japan Atomic Power could be prohibited from resuming operations at the plant in such an event, Tanaka said it might have to wait “until the active fault is gone” — suggesting the reactors would probably have to be scrapped.
The government has been reviewing the risks posed by possible active faults near or under atomic plants in light of the Fukushima disaster. Of Japan’s 50 commercial reactors, only two — at Kansai Electric’s Oi plant — have been brought back online since the Fukushima No. 1 plant suffered three core meltdowns in March 2011.