In the 2 1/2 years since Japan’s Nuclear Regulation Authority (NRA) set up an experts panel to evaluate faults at six of Japan’s nuclear power plants, the panel has definitively ruled on just two of them — with one, Tsuruga-2, deemed too dangerous on seismic grounds to restart, and Ohi-3 and-4 judged by the same criteria to be safe enough. But the panel remains active, and on Jul. 17 it tentatively reached a decision on another reactor — Shika-1 and-2 — saying that active faults under the plant cannot be ruled out (NIW Jul.24’15). A final decision that would clear the Mihama plant is expected in a few months. The reviews which started after Fukushima are now subject to regulatory requirements that stipulate that any facility with important safety functions cannot operate on an active fault. Faults are deemed active if there has been evidence of activity since the Late Pleistocene era 120,000 to 130,000 years ago. In some cases, such as when strata from the Late Pleistocene does not exist, activities after the Middle Pleistocene 400,000 years ago are to be investigated.
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