Japan will allow nuclear reactors to operate for up to 60 years in revised regulations on power plant operators, the government said on Wednesday, even as it looks to shift gradually away from atomic power in the wake of the Fukushima disaster.

The move, which marks the first time Japan will set a limit on a reactor's maximum lifespan, comes while the country debates a new energy strategy that is expected to give a greater role to renewable, clean energy sources.

The government said it aims to introduce the 60-year limit in a year from now as part of a comprehensive revision of laws regulating nuclear plant operators in the wake of Fukushima, where reactor cooling systems were stopped by the March 11 earthquake and tsunami, triggering meltdowns and radiation leaks that led to mass evacuations and caused widespread contamination.

Public anxiety sparked by Fukushima has prevented the restart of reactors shut for routine checks, and only five of the nation's 54 reactors remain online, prompting utilities to import more fossil fuels to bridge the gap and prevent power cuts.

Stress tests are now being carried out on reactors to reassure the public and persuade local governments to allow them to be restarted.

Chief Cabinet Secretary Osamu Fujimura told reporters details are still under consideration but the lifespan of a reactor would in principle be 40 years, as suggested by Environment and Nuclear Accident Prevention Minister Goshi Hosono earlier this month.

The government will allow plant operators to apply for one extension of up to 20 years for each reactor, in line with U.S. standards, and approval would only be granted if certain conditions were met.

There will be no change in the fact that the number of reactors will decline, as will Japan's reliance on them. But we're not talking about the immediate future, Fujimura said at a news conference.

Under the current system, plant operators can apply for an extension after 30 years and are usually granted 10-year extensions with no limit on how often they reapply as long as the nuclear watchdog approves.

1970s REACTORS

The six reactors at the wrecked Fukushima Daiichi plant are among the oldest, having started operations between 1971 and 1979.

Twelve other reactors date back to the 1970s, the two oldest having been operating since 1970.

Public sentiment is for Japan to end the use of nuclear power. The public wants the country to move away from nuclear power as soon as possible, let alone an extension in the life of nuclear reactors, said Hiroshi Takakashi, a research fellow at the Fujitsu Research Institute.

But if backed up by safety regulations legally deemed adequate, one has to admit there would be little reason the regulation should not be implemented. What has to be considered is that unlike Germany, which is aiming to shut down all its nuclear plants by 2022, Japan is still discussing the future role of nuclear power, allowing for such logic, Takahashi said.

The government plans to submit bills on limiting the length of reactor operations as well as on reorganising the country's nuclear regulators in a parliament session starting later this month.

But it is also keen to bring existing reactors back into operation to avert a power crunch and ease the impact on the economy.

The bills would create a more independent nuclear safety regulator separated from the trade ministry, which oversees the existing watchdog, the Nuclear and Industry Safety Agency.

The new regulator would require plant operators to prepare for severe accidents and make public their assessments of safety and ensure their facilities comply with new safety measures.

The new agency would also be responsible for nuclear accident investigations, government officials said.

The agency's sole principle is protect people's safety, health and environment, Toru Ogino, a senior government official drafting the bills, said in a briefing on Tuesday.

(Additional reporting by Rie Ishiguro; Editing by Michael Watson)