SENDAI (Kyodo) -- A nuclear reactor in northeastern Japan, hit by the devastating 2011 earthquake and tsunami, was restarted Wednesday after a temporary suspension due to an instrument problem, the plant operator said.

In late October, the Onagawa plant's No. 2 unit became the first reactor to operate in eastern Japan since the natural disaster, but it was halted earlier this month after a checking device became stuck inside the containment vessel.

Tohoku Electric Power Co., the operator of the Onagawa nuclear plant in Miyagi Prefecture, said it detected that a nut on a joint of a guide tube -- designed to send devices into the reactor -- was not tightened adequately when it was replaced in May.

The operator said it plans to begin power generation possibly this week after the reactor reaches stable criticality and hopes to start commercial operations around December.

The Onagawa unit cleared safety screening in February 2020 under stricter safety standards set after the 2011 nuclear accident at the Fukushima Daiichi power plant. The reactor is the same type as those at the Fukushima plant.