Japan's idled nuclear reactors could restart if they pass the first stage of two-step post-Fukushima safety checks.
The stress tests will target reactors that have already completed routine checks and are ready for restart, the government said. They will assess resistance to severe earthquakes and other events more extreme than those for which they were designed.
A second stage of tests will make a comprehensive safety assessment of all 54 of Japan's reactors.
Four months after the Fukushima Daiichi plant was smashed by a tsunami and began leaking radiation, only 19 reactors are running. If some do not resume operation, Japan could be without nuclear power by next April. The country relied on atomic power for almost 30 per cent of its electricity before the crisis.
Last week's surprise announcement of the stress tests alarmed corporate Japan and outraged some local authorities, who had been prepared to approve reactor restarts after receiving safety assurances from the government.