The Nuclear and Industrial Safety Agency (NISA) will reopen its investigation into whether Tohoku Electric Power Co.’s Higashidori plant in Aomori Prefecture is sitting on active seismological faults.
Tohoku Electric has insisted that the faults “would not trigger seismic activity in the future” and pose no safety risks to the single reactor plant, which is currently suspended for routine maintenance, but some experts at NISA are unconvinced.
If the faults are found to be active, Tohoku Electric would be required to revise costly analysis of the plant’s tolerance of ground movement due to an earthquake. The analysis would be required to clear the government’s “stress test,” which must be passed before reopening.
Similar displacement of geological layers has also been discovered at Tokyo Electric Power Co.’s Higashidori plant, which neighbors Tohoku Electric’s plant, and at the Electric Power Development Co.’s (J-Power) Oma plant in the same prefecture. TEPCO and J-Power’s facilities are under construction.
Tohoku Electric’s survey was conducted in response to revisions to the government’s quake resistance guidelines in 2006. Those guidelines urged plant operators to prepare for the movement of active faults around their plants and for more powerful earthquakes.
Tohoku Electric, TEPCO and J-Power released an interim report each in March 2008, saying that at least one reactor at each plant was not threatened by safety problems.
NISA has yet to examine the operators’ estimates of the threat from tsunami to their plants, a subject that has seen significant changes in standards over the past 30 years.
Operators of nuclear plants built prior to the late 1980s tended to claim that no tsunami were expected at their plants or that tsunami could not reach their premises. In the late 1980s, a methodology for predicting the height of possible tsunami striking some plants was introduced and, in 2002, utilities reviewed their tsunami preparedness assessments at their initiative.