Tokyo Electric Power Co. (TEPCO) announced on Oct. 13 at a meeting of the Nuclear Regulation Authority (NRA) that it will review its plan for reactivation of the No. 6 and 7 reactors at the Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture due to the possibility that ground liquefaction from an earthquake could collapse the plant's tidal levees.
The NRA's safety inspections on TEPCO's reactivation plan for the plant's No. 6 and 7 reactors were nearing completion, but the process is expected to be prolonged.
The Kashiwazaki-Kariwa plant uses boiling water reactors, the same as the crippled Fukushima No. 1 Nuclear Power Plant, which was the site of the 2011 nuclear disaster. If the safety inspections went without a problem, Kashiwazaki-Kariwa was expected to be the first boiling water reactor plant to pass the new safety standards.
The Kashiwazaki-Kariwa plant is divided into a lower area at an elevation of 5 meters above sea level that holds its No. 1 through 4 reactors, and a higher area at an elevation of 12 meters above sea level where its No. 5 through 7 reactors stand. TEPCO has applied to the NRA for safety inspections of the No. 6 and 7 reactors, a precursor to reactivation. The plant was affected by soil liquefaction when the 2007 Chuestu offshore earthquake struck, so the NRA instructed TEPCO to carefully examine the effects that ground liquefaction would have on the plant. It was learned from TEPCO analysis that the levees protecting the No. 1 through 4 reactors could be destroyed if the soil liquefied.
TEPCO estimates that tsunami up to the height of 7.6 meters could hit the plant. If the levees, which stand 15 meters above sea level, were to collapse due to tsunami, the area holding the No. 1 through 4 reactors would become flooded. TEPCO had planned to use the No. 3 reactor building as the "emergency response location" that workers would use as a forward base for operations during times of emergency, but it now intends to use the No. 5 reactor building in order to avoid potential flooding and is seeking understanding from the NRA on this point.
However, the area holding the No. 1 through 4 reactors is also where many facilities are located including an earthquake-resistant structure meant to be used as a disaster response center. These could become unusable if the area was flooded. Furthermore, the No. 5 reactor building is located only around 130 meters from the No. 6 reactor, so if workers used the former to respond to a disaster at the No. 6 reactor, they could be exposed to very high radiation levels of 70 millisieverts per week. The NRA plans to newly examine whether these issues affect the ability to respond to a major disaster at the No. 6 and 7 reactors.
TEPCO also intends to pursue reactivation of the No. 1 through 4 reactors, but large-scale construction expected to take over a year is necessary to deal with the possibility of ground liquefaction. This is expected to prevent TEPCO from applying for safety inspections for these reactors for the time being.