The Nuclear Regulation Authority said Thursday it will investigate geologic faults existing at Tokyo Electric Power Co.’s Kashiwazaki-Kariwa plant as part of the safety assessment process for two reactors there.
The investigation will be conducted because the data submitted by Tepco is “insufficient,” an official of the NRA secretariat told reporters after regulators held a second safety screening session on the plant’s reactors 6 and 7.
Clearing doubts over possible movements of faults at the plant site is essential for Tepco to bring the two idled units back online.
All seven reactors at the plant in Niigata Prefecture are known to be sitting above small faults.
Tepco claims those faults are not active, but the official of the NRA secretariat stressed the need for a field survey, given that “a number of active faults exist in areas outside the plant site and that fracture zones run beneath the reactors (1 to 7).”
In quake-prone Japan, nuclear power plant operators are not permitted to build reactors and other facilities with important safety functions directly above faults that could move.
The NRA plans to send its staff to the Kashiwazaki-Kariwa plant early next year and order Tepco to make preparations for the on-site probe, including digging survey trenches, before the NRA starts its investigation.
During the safety screening process that started earlier this month, the NRA is also seeking further information about a key safety system that Tepco plans to install to satisfy new regulations introduced in light of the triple-meltdown catastrophe at its Fukushima No. 1 nuclear complex.
The safety equipment is a filtered venting system that can reduce radioactive substances if gas and steam need to be released to prevent damage to reactor containment vessels. But there is concern over the system’s radiation exposure risk to residents living in surrounding areas.
Tepco, facing strong public distrust, has said the equipment’s operational procedures will be decided based on talks with local governments. But regulators have shown wariness over assessing such procedures that could change in the future depending on talks with local governments.