Japan has restarted its first nuclear reactor since the Fukushima disaster in 2011.
The Sendai plant in the south of the country began operating four years after the 2011 meltdowns caused by an earthquake and tsunami.
The disaster displaced more than 100,000 people due to radioactive contamination in the area and spurred a national debate over this resource-scarce country's reliance on nuclear power.
The Nuclear Regulation Authority affirmed the safety of the Sendai reactor and another one at the plant last September under stricter safety rules imposed after the 2011 accident.
Tomomitsu Sakata, a spokesman for nuclear firm Kyushu Electric Power, said the reactor was put back online as planned without any problems.