Last year, the Japanese government ordered the nuclear authorities to conduct tests on all Japan's reactors after the 11 March meltdown at Fukushima Daiichi raised questions about the safety of nuclear power, particularly in a country prone to earthquakes and tsunami.

...Currently only three of Japan's 54 reactors - just over 6% of its total nuclear capacity - are in operation after the Fukushima accident forced the closure of active reactors for safety checks. The latest closure came on Friday when a reactor at a plant near the Japan Sea was shut down for inspection.

Without approval for restarts, all Japan's reactors could all be shut by the end of April, boosting the use of fossil fuels and adding more than $30bn (£19bn) a year to energy costs, according to a government estimate.

...But Masashi Goto, a former nuclear power plant designer, said the stress tests at Ohi and elsewhere were next to useless.

...Hiromitsu Ino, an emeritus professor at Tokyo University and a fellow member of the nuclear safety agency advisory panel, said the tests were flawed because they had been introduced before the full facts of the Fukushima disaster were known.