The Nuclear Regulation Authority conducted a one-day investigation Friday at the Oi nuclear power plant in Fukui Prefecture to check whether a disputed fault running underneath it should be viewed as active.
Depending on the outcome of the investigation, Japan’s only operating nuclear plant could be told to shut down, just months after two of its reactors were allowed to restart.
It is the first time the NRA, established in September, has conducted an on-site inspection at a nuclear plant.
At the government’s request, Kansai Electric Power Co. is further studying the F-6 fault, which runs north to south, separating the plant’s reactors 1 and 2 from units 3 and 4.
Kepco has said it has yet to find data suggesting movements in the last 120,000 to 130,000 years, the current definition of an active fault in Japan.
The NRA plans to make its own judgment based on Friday’s check, which was carried out by a team consisting of NRA Commissioner Kunihiko Shimazaki and four other experts selected from outside the authority.
They include Toyo University professor Mitsuhisa Watanabe, who has highlighted the risk posed by the F-6 fault, where a zone of crushed rocks has been found in the bedrock.
The shattered zone will not trigger an earthquake, but it is feared it could move together with active faults near the plant and damage a water channel that would be used to take in seawater to cool the reactors in the event of an emergency.
Utilities are not allowed to build reactors and other related facilities important for safe operation of reactors directly above active faults.
Prior to the investigation, NRA Chairman Shunichi Tanaka said that if F-6 is determined to be active, or if it is strongly suspected, the authority would call for the currently operating reactors be shut down.
The investigation team is expected to meet Sunday to discuss the outcome of the on-site inspection.
The regulators plan to conduct similar investigations at five other nuclear facilities, including Hokuriku Electric Power Co.’s Shika plant in Ishikawa Prefecture and Kepco’s Mihama plant in Fukui.
Cities draft disaster plan
Representatives of all 30 municipalities in Niigata Prefecture met Friday to discuss a variety of evacuation options in the event of a disaster at the Kashiwazaki-Kariwa nuclear plant, the world’s biggest nuclear energy complex.
On the agenda was how to coordinate shelters and accommodations for residents in each city, town and village based on wind direction if one or more of the facility’s seven reactors suffer a catastrophic meltdown.
The officials also discussed specific actions to ensure they fall in line with the prefectural government’s disaster mitigation plan and relevant laws and ordinances.
It is the first time an evacuation plan has been drafted across municipalities, according to an official from the city of Nagaoka, which acts as the group’s coordinator.
The draft was based on a prior study that assessed the population spread within 50 km of the power station and possible options for evacuations shelters, such as inns and hotels. The study assumed private vehicles would be the principal means of transportation at the time of a disaster occurring at the 8.21 million kw plant.
Issues that need to be addressed in the weeks ahead include finding additional shelters and accommodations outside the prefecture, depending on various wind direction scenarios.