Onagawa nuclear reactor in northeastern Japan restarted after issue

Tohoku Electric Power on Wednesday restarted the No. 2 reactor at its Onagawa nuclear power plant in Miyagi Prefecture.
The 825,000-kilowatt reactor had been taken offline soon after resuming operation for the first time in 13 years — since the March 2011 Great East Japan Earthquake and tsunami — after an issue was found with a measurement device.
Tohoku Electric expects to resume power generation using the reactor within this week and says no changes will be made to its plan to restart commercial operation next month.
The Onagawa plant uses boiling water reactors, the same type as those used at Tokyo Electric Power Company Holdings’ Fukushima No. 1 plant in Fukushima Prefecture, which suffered a triple meltdown following the 2011 disaster.
The No. 2 reactor was restarted on Oct. 29 but was halted again on Nov. 4 due to an issue involving the movement of an auxiliary instrument for a neutron detector, which monitors the reactor’s internal conditions.
Tohoku Electric later found that the issue had been caused by part of a guide tube for the device coming off due to a loose nut.
Removal of control rods that suppress fission reaction began Wednesday. Power generation is set to begin after the reactor reaches criticality, or a self-sustaining nuclear chain reaction.
The plant operator plans to then suspend the reactor again to check for any abnormalities before resuming operation.
Another boiling water reactor, the No. 2 reactor at Chugoku Electric Power’s Shimane nuclear power plant, is expected to return online on Dec. 7.