The head of the Nuclear Regulation Authority (NRA) apologized at a meeting on April 18 for the lack of news on the state of nuclear plants in the wake of deadly earthquakes in Kumamoto Prefecture.
"We must humbly reflect on this," NRA Chairman Shunichi Tanaka said.
At the meeting, the NRA confirmed that none of the recent earthquakes had created shocks large enough to trigger automatic shutdowns at nearby nuclear power plants. "Currently there is no problem with safety" at the plants, Tanaka said.
The largest shocks recorded at nearby nuclear plants in gal, a unit of acceleration, were 8.6 at the Sendai Nuclear Power Plant in Kagoshima Prefecture, 20.3 at the Genkai Nuclear Power Plant in Saga Prefecture, 10 at the Ikata Nuclear Power Plant in Ehime Prefecture and 2 at the Shimane Nuclear Power Plant in Shimane Prefecture.
Power utilities have safety standards in place so that a nuclear reactor will automatically turn off when quake-related ground acceleration reaches 140 to 190 gal for sideways movement and 70 to 90 gal for vertical movement.