Japan’s Kansai Electric Power Co said on 29 February that unit 4 at its Takahama NPP in Fukui Prefecture had shut down automatically after problems with a generator and a transformer triggered alarms, just three days after the reactor was restarted. The alarm was triggered during preparations to begin power generation after the unit achieved criticality.

The reactor was shut down after the automatic alarm system prompted 48 control rods to be inserted. There is no problem with the reactor’s cooling system and has been no environmental impact from the incident, the company said. "We are investigating the cause now, and we don’t know the future schedule of the (restart) process," Kenji Miyata, a Kansai Electric executive officer told a press conference. The incident was reported to the Nuclear Regulation Authority. It follows a leak of coolant water leak on 20 February in a building attached to the reactor caused by a loose bolt in a pipe valve.

The incidents are expected to increase concerns about the utility’s safety management which is important in face of strong local opposition to the plant’s restart, Japanese media said. The restart was allowed late last year after a district court lifted an injunction filed by local residents that had banned the operation of units 3 and 4 units at the NPP, both of which use mixed oxide (mox) fuel.