The new requirements approved today by the Nuclear Regulation Authority will take effect on July 8, when operators will be able to apply for inspections. If plants pass inspection, they can reopen.
All but two of Japan's 50 reactors have been offline since the March 2011 earthquake and tsunami led to multiple meltdowns and massive radiation leaks at the Fukushima plant.
The new requirements for the first time make it compulsory that plants take steps to guard against radiation leaks in the case of severe accidents, install emergency command centers and enact anti-terrorist measures.