The quake fault running under reactor 2 at the Tsuruga nuclear power plant in Fukui Prefecture is probably active, a panel from the Nuclear Regulation Authority stated in a draft report Monday, effectively condemning the two-reactor complex.
The report, compiled from the panel’s search for potentially active faults at the Tsuruga plant, is a heavy blow to Japan Atomic Power Co., which may have to scrap the reactor at great cost.
“If new knowledge is obtained, the judgment could be reviewed. However, at least at this point, the fault at the plant site is highly likely an active fault that needs to be considered in terms of seismic design,” the report said.
The draft report said the fault or zone of small rocks and sediment called D-1 could move simultaneously with a major active fault called the Urazoko, which is about 200 to 300 meters from the reactor buildings.
If that happens, “it could impact the critical facility right above,” the report said.
The report pointed out that the D-1 zone is possibly an extension of the K fault, which showed traces it has moved within the past 130,000 years or so.
It also said the K fault would probably move together with the Urazoko fault.
The safety guidelines for nuclear power plants do not allow utilities to build reactors or critical cooling equipment directly above an active fault. The guidelines define a fault as active if it has moved within the past 120,000 to 130,000 years. The NRA is planning new rules that will expand that time frame by thousands of years.
During the meeting Monday at which the draft report was submitted, Kunihiko Shimazaki, an NRA commissioner who heads the panel, said the report will be checked by other outside experts before it is finalized.
The panel investigated the Tsuruga site in December, when its experts quickly leaned toward the conclusion that the fault appeared active.
Japan Atomic Power has criticized the panel, saying its view lacks scientific support.
NRA chief Shunichi Tanaka has said the Tsuruga plant’s No. 2 reactor will not undergo the safety exam required to be restarted if D-1 is active, because the unit will no longer be allowed to operate.
The Tsuruga plant has two reactors, with two faults also running under reactor 1, and Japan Atomic Power is still examining them. But reactor 1 is over 40 years old, and the new rules will not allow reactors over 40 to run in principle. The NRA has been examining possible active faults at other plants, including Kansai Electric Power Co.’s Oi atomic plant, also in Fukui Prefecture.