Japan ended two months without nuclear power on Thursday when the No. 3 unit at Kansai Electric Power Co's Ohi plant became the first reactor to resume supplying electricity to the grid since a nationwide safety shutdown after the Fukushima disaster.
Japan's last working reactor was idled in early May, leaving the country without nuclear power for the first time since 1970.
The rest of the 50 reactors had already been halted for maintenance and safety checks to see if they could withstand an earthquake and tsunami similar to the disaster that devastated Tokyo Electric Power's Fukushima Daiichi plant in March 2011, causing the worst atomic crisis since Chernobyl in 1986.
The government approved the restart of the No. 3 and No.4 Ohi units in western Japan to avoid a possible summer power crunch. But public safety concerns ovrer nuclear power remain deep, with surveys showing about 70 percent of voters want the country to ditch nuclear eventually.
A panel appointed by parliament to probe the causes of the Fukushima disaster and assess problems with the often-chaotic response, is to issue a final report later on Thursday.
Kansai Electric, Japan's second biggest utility, said it began generating power from the 1,180-megawatt No.3 Ohi reactor at 5 percent of capacity at 7 a.m. on Thursday (2200 GMT on Wednesday) as scheduled, four days after the unit was restarted.
The No. 3 unit is expected to reach full-capacity output around July 9-10. Its sister unit, the 1,180-MW No.4 Ohi reactor, is scheduled to resume operations between July 18-20, start power output from July 21-25 and reach full-capacity generation from July 25-30, a company spokesman said.
Restarting the two reactors will help reduce fossil fuel consumption since utilities have been meeting the power gap created by the shutdown of all 50 reactors, with capacity of 46,148 MW, by firing up plants using costly fuel, especially gas and oil.
Before the Fukushima crisis, Japan relied on nuclear power for about 30 percent of its electricity and was the world's third-biggest user after the United States and France.