Government research indicates the fault running beneath Hokuriku Electric Power Co.’s Shika Nuclear Power Station may be active, raising questions about the utility’s claim in the late 1990s to the contrary, according to sources.
Government regulations do not allow construction of a nuclear reactor above an active fault. If it is confirmed active, the Shika nuclear plant in Ishikawa Prefecture may not qualify to operate.
The plant is currently shut down for scheduled safety checks plus the state-ordered stress tests introduced because of the crisis at Tokyo Electric Power Co.’s Fukushima No. 1 plant.
The research by the Nuclear and Industrial Safety Agency shows the fault — named S-1, which runs southeast to northwest within the plant’s premises — moved sometime after 130,000 to 120,000 years ago, the sources said Monday.
Hokuriku Electric Power conducted excavation surveys when it applied in 1997 to build a second reactor at the plant and claimed it found the fault “does not indicate activity.”
In a review of fault lines after the Great East Japan Earthquake of March 11, 2011, NISA went through excavation data presented by Hokuriku Electric and concluded the research indicated the strong possibility that S-1 may have been active in a relatively recent period.
Geological layers comprised not just of bedrock from ancient periods but also sand and pebbles dating back to 130,000 to 120,000 years suggest the fault was deformed, the sources said.
It remains unknown at this point if S-1 could generate a quake on its own or move in tandem if a temblor hits nearby active faults. Given that another fault lies beneath reactor 2, if the two faults shake at the same time, it could endanger the plant.
“I would say Hokuriku Electric’s assessment that the geological layers of 130,000 to 120,000 years ago have not morphed is far-fetched,” said Mitsuhisa Watanabe, a geomorphology professor at Toyo University.
Watanabe even suspects the fault was active more recently.
Research and surveys by NISA have suggested that a soft fault layer, called a crushed zone, could move at Japan Atomic Power Co.’s Tsuruga nuclear power station in Fukui Prefecture, raising the possibility that the plant, also now idle, may have to be permanently shut down.
Citizens are calling for research into Kansai Electric Power Co.’s Oi nuclear power plant in Fukui, which also has a soft fault layer. Reactor 3 has been restarted at the Kepco plant and reactor 4′s operations are in the process of being resumed.