Japan began switching off its last operating nuclear reactor on Sunday for inspection, and no date has been scheduled for a restart amid strong public hostility toward atomic power.
The move leaves the world's third-largest economy without atomic energy for the second time since the Fukushima nuclear crisis erupted in March 2011.
Nuclear power supplied about one-third of the resource-poor nation's electricity before a tsunami knocked out cooling systems and sparked meltdowns at Fukushima, causing tens of thousands to flee their homes.
Prime Minister Shinzo Abe has openly supported a return to the widespread use of atomic energy, but the public remains largely opposed on safety grounds.
Kansai Electric Power on Sunday started to gradually take offline the No 4 reactor at its Oi nuclear plant in western Fukui prefecture.
"The work started at 4:40 pm," a company spokesman said on Sunday. "The reactor will come to a complete stop early tomorrow."
Japan was without any nuclear energy in May 2012, when all of the country's 50 commercial reactors stopped for checkups after the Fukushima disaster.
Utilities were immediately unable to restart them due to public opposition.