Two electric power companies submitted plans July 25 to the Nuclear and Industrial Safety Agency (NISA) for fresh surveys of possible active faults running under two nuclear plants.
Hokuriku Electric Power Co., which operates the Shika plant in Ishikawa Prefecture, and Kansai Electric Power Co., which runs the Oi plant in Fukui Prefecture, will start the surveys in August.
Hokuriku Electric plans to compile a report in January next year, and Kansai Electric plans to do so by the end of this year.
The government’s nuclear standards prohibit utilities from building key facilities of nuclear power plants directly above active faults.
At the Shika plant, the No. 1 reactor building sits just above the fault in question. If it is confirmed active, authorities could order the decommissioning of the reactor.
At the Oi plant, there is no reactor building above the possible active fault, but a water line used for emergency cooling runs above it. If the fault is active, the operation of the Oi plant could be affected.
In the survey at Shika, a 50-meter-long tunnel will be built beneath the No. 1 reactor building to directly observe the fault and identify when movements occurred there. Investigators will also look into other nearby faults to study whether activity there would trigger corresponding movement at the fault under the reactor.
In the Oi survey, officials will conduct drilling and other types of investigations at eight points to identify the length and activeness of the fault in question.
NISA will assess the validity of the two utilities’ plans at an expert meeting on July 31.
At an expert meeting on July 17, many researchers said the fault at the Shika plant seemed to be a typical active fault, prompting NISA to issue the order for the new survey.
For the Oi plant, the agency instructed Kansai Electric to conduct the survey “just to be safe,” as some experts said the documents submitted by Kansai Electric did not rule out the possibility of the fault being active.
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