Japan has restarted a nuclear reactor for the first time since the Fukushima disaster in 2011, as the government seeks to reassure a nervous public that the industry is now safe with the new safety standards.
Prime Minister Shinzo Abe and much of Japanese industry want the reactors to be switched on again to cut fuel bills, but opinion polls show a majority of the public oppose the move after the nuclear crisis triggered by the earthquake and tsunami four years ago.
Kyushu Electric Power began the restart on Tuesday of the No 1 reactor at its Sendai plant, about 1,000km southwest of Tokyo, a spokesman said.
The 31-year-old reactor, operating under tougher post-Fukushima safety rules, was expected to reach full capacity around 11pm Tuesday and would start generating power by Friday.
Commercial operations are to begin early next month, a company spokesman said.
Abe has said only reactors that were deemed to have cleared the "world's most stringent regulation standards" would be allowed to restart.
The head of Japan's atomic watchdog said that new safety rules meant a repeat of the Fukushima disaster would not happen.
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"A disaster like that at Tokyo Electric Power's Fukushima Daiichi nuclear plant will not occur," under the new rules, Nuclear Regulation Authority Chairman Shunichi Tanaka said in an interview with the Nikkei newspaper published at the weekend.
However, Tanaka conceded there was "no such thing as absolute safety", and Japan's people are sceptical as the country remains deeply scarred by the legacy of Fukushima.
Anti-nuclear sentiment runs high in Japan and television showed protesters scuffling with police in front of the Sendai plant, which is on the southernmost main island of Kyushu.
Local media said about 200 protesters gathered at the site, including former Prime Minister Naoto Kan who has become a high-profile anti-nuclear activist.
The Sendai plant is the furthest away of Japan's reactors from the capital Tokyo, where protesters also regularly gather to oppose atomic energy, mostly outside Abe's official residence.
In the worst nuclear disaster since Chernobyl 25 years earlier, the meltdowns at the Fukushima Daiichi plant caused a release of radioactive material and forced 160,000 from their homes, with many never to return.