Mothballing the reactor at Japan's oldest nuclear station would be the most stringent measure adopted in Japan since the meltdowns at the Fukushima Daiichi nuclear station north of Tokyo in March 2011 exposed failings in nuclear oversight.
"It is no longer business as usual. This is the beginning of a long-term restructuring of the nuclear power business in Japan," said a senior adviser on atomic policy, speaking anonymously.
A panel of seismologists advising the Nuclear Regulation Authority (NRA) issued their assessment that a fault known as D-1 under the Tsuruga nuclear plant is active. This paves the way for the NRA to rule the station is too risky to operate.
Meanwhile, reactors at five other nuclear stations are under review over the possibility they also sit on active faults.