Faults under Japan’s Shika NPP said to be active

4 March 2016

An investigative panel of experts with the Nuclear Regulation Authority (NRA) compiled a new draft report on March 3 in which it says that a fault running just below the the unit 1 reactor at the Shika NPP in Ishikawa Prefecture is likely to be active. Hokuriku Electric Power Co, the operator of the Shika plant, may have to decommission the reactor to comply with the new safety standards, put in place after the March 2011 Fukushima accident. It is "reasonable" to interpret the fault as active, said a final draft of the planned evaluation report. In its first draft report prepared in July 2015, the group of experts had pointed to the possibility of the fault being active. Unless Hokuriku Electric, can overturn the NRA expert group's conclusion, decommissioning is the likely outcome.

The NRA Secretariat will draw up a formal version of the report. The NRA is expected to make its final judgment on the faults as part of safety screenings that would be necessary to restart the 540MWe reactor. In July last year, the team found that the part of the S-1 fault directly under the reactor building may have moved during the late Pleistocene period, some 120,000-130,000 years ago. Under Japan's current definitions, faults that moved during that period are regarded as active.

Two other faults run below a key facility of the unit 2 reactor that has been undergoing NRA safety screening, the draft report said, "There is a possibility that they had moved." The expert panel pointed to the possibility of those faults also being active. Restarting unit 2 will likely be delayed substantially as large-scale work such as relocation of its facilities will be necessary if it is unable to clear the NRA screening process.

The investigative panel is to draw up a formal report and submit it to the NRA. If Hokuriku Electric were to seek to reactivate the reactors, the NRA would then conduct further safety screenings to determine whether the faults are active. Attention will be focused on whether the utility will be able to produce any new data to overturn the NRA's final conclusion during the fresh round of screening.

Hokuriku Electric has said its own studies show the faults are not active."We can't accept the decision that was made based on assumptions," Hokuriku Electric Executive Vice President Akizumi Nishino said after the meeting. There are three faults in question: the 780-metre-long "S-1" fault situated just below the unit 1 reactor; and the "S-2" and "S-6" faults just beneath cooling pipes for releasing sea water, extending a combined total of 550 metres.

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