The Number 3 reactor at the Genkai nuclear power plant in Saga Prefecture, southwestern Japan, has been restarted for the first time in 7 years and 3 months.
Kyushu Electric Power Company initiated restart procedures on Friday by removing the control rods that suppress atomic fission.
The company says the reactor will reach criticality -- a self-sustained nuclear reaction -- early on Saturday, and begin power generation and transmission on Sunday. The reactor is expected to go into commercial operation in late April.
The reactor runs on MOX fuel, which is a mixture of plutonium extracted from spent nuclear fuel and uranium.
It is the 7th reactor to be restarted under new regulations introduced for commercial nuclear power plants after the 2011 Fukushima accident.
The six reactors currently in operation are 2 at the Sendai plant in Kagoshima Prefecture, one at the Ikata plant in Ehime Prefecture, 2 at the Takahama plant in Fukui Prefecture, and one at the Ohi plant, also in Fukui.
Kyushu Electric plans to restart the No. 4 reactor at the Genkai plant in May.
The Genkai plant is located in a coastal area, with 20 small islands within a 30-kilometer radius. Experts point out the importance of evacuation plans for the islanders in the event of a nuclear accident in bad weather.