Japanese utility Kyushu Electric Power Co (KEPCO) on Thursday night restarted the No. 1 reactor at its Sendai nuclear power plant in Kagoshima Prefecture.
KEPCO said the reactor is expected to achieve criticality by Friday morning and commence power generation on Sunday.
The reactor, which went online in August 2015, had been shut down since October for maintenance. The plant's No. 2 reactor, also in operation, is scheduled to be shut down for maintenance on Dec 16.
Kagoshima Gov Satoshi Mitazono, who opposes nuclear power, approved the reactor's restart last week after KEPCO said it planned new measures to re-inspect the safety of the plant to ease any local concerns following the Kumamoto quakes in April.
Only three reactors are currently online in Japan: two at the Sendai plant and one at Shikoku Electric Power's Ikata station.
Reactors in Japan are required to be shut for maintenance after 13 months of commercial operation.© Japan Today/ Thomson Reuters