A commissioner at the government nuclear watchdog has called for substantially expanding the definition of "active fault lines" in relation to nuclear reactor safety.
All geological fault lines that have shifted at least once during the past 400,000 years should be labeled as active and considered in discussions about the quake resistance of nuclear reactors, Kunihiko Shimazaki, the deputy chairman of the Nuclear Regulation Authority, told reporters Oct. 23.
The government's current anti-seismic guidelines define active faults as those that have shifted during the last 120,000 to 130,000 years.
But Shimazaki said current subsurface stresses have remained unchanged for 400,000 years, a view widely shared by experts based on observations of topographical uplifts and other features.
He said a geological fault line that has shifted during the past 400,000 years could, therefore, move again in the future.
If the definition of active faults is broadened, some faults currently labeled as inactive may be earmarked for consideration in future discussions over anti-seismic design, possibly necessitating further reinforcement work at some nuclear reactors.
The Nuclear Regulation Authority is examining the anti-seismic guidelines as part of its review of safety standards for nuclear reactors. Shimazaki is the only seismologist among the five commissioners of the body, which means forthcoming discussions on the review are likely to be centered around his ideas.
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