Japan's nuclear regulator is inspecting the Shika nuclear power plant on the Sea of Japan coast to determine whether a fault beneath a reactor building is active.
The two-day inspection by the Nuclear Regulation Authority began at the plant in Ishikawa Prefecture on Thursday with 14 NRA experts taking part.
They went into a ditch dug for the survey, observed cross sections of geological strata and touched soil walls to confirm the layers' conditions near faults.
Hokuriku Electric Power Company, which operates the plant, applied for screenings of the Number 2 reactor, which has been offline since 2011.
The NRA launched the screenings in 2014 with a focus on whether 10 faults at the plant, including one beneath the building that houses the Number 2 reactor, are active. In 2016, a panel of the authority said it could not deny that some of the faults could move.
In response, the firm insisted that the faults are not active, citing new data on constituents of mineral samples collected from the faults.
New guidelines for nuclear safety do not allow operators to build important facilities such as reactor buildings above active faults that could move.
If the fault beneath the Number 2 reactor is found to be active, operation of the facility cannot resume and it may eventually be dismantled.
The experts are expected to confirm on Friday the length of an active fault that runs near the complex.