The government may allow nuclear plants to keep operating even if faults are found beneath them, provided that ground displacements are deemed unlikely to affect their buildings.
The Nuclear and Industrial Safety Agency plans new safety rules that OK operations even at plants under which faults are found, despite its current view that reactors must not be built above them, sources said Tuesday.
The agency will soon craft the new criteria for the evaluation of faults beneath nuclear plants based on expert opinions. The watchdog will then hand them over to its successor regulatory authority, which will begin operations in September.
These last-minute efforts by NISA to set new rules have drawn criticism from experts who suspect it is creating loopholes to ensure the safety of nuclear plants. The agency has admitted that measures to properly assess ground displacements have not yet been established.
Specifically, NISA plans to classify faults under nuclear reactors into three types: active faults that could trigger quakes, auxiliary faults that are structurally connected to active faults, and faults deemed weaker than the other two. When faults are determined to be of the last type, the agency will forecast the degree of ground displacements expected in the event of nearby quakes, and then assess their impact on reactor buildings.
When faults are classified as the first or second type, the operation of nuclear plants in that area will be banned.
Mitsuhisa Watanabe, a professor of geomorphology at Toyo University, said it would be hard to distinguish auxiliary faults from rifts with weaker power and both types could cause displacements. “The agency appears to be contemplating how to avoid the decommissioning of reactors just before its disbandment,” he said.