By Risa Maeda
TOKYO (Reuters) - Japanese governor Tokihiro Nakamura believes nuclear power is vital for the resource-poor land, but even he says the central government must put safety pledges in writing before he'll agree to restart off-line reactors -- a sign of the tough battle ahead to repair tattered public trust after the Fukushima crisis.
The myth that nuclear power was cheap, clean and safe was shattered when a March quake and tsunami triggered the world's worst nuclear crisis in 25 years at Tokyo Electric Power Co's Fukushima plant, spewing radiation and forcing mass evacuations.
Japan is drafting a new energy mix plan to reduce reliance on nuclear power longer-term, but with 51 of the country's 54 reactors halted mostly for checks, the government wants to avoid a potentially serious power crunch in the summer.
Japan's nuclear reactors had met a third of electricity demand in the world's third-biggest economy before the crisis.
"It is the central government that must take ultimate responsibility, so at the very least, the trade and industry minister should come to the prefecture and discuss this with me openly," Nakamura, whose Ehime prefecture in western Japan hosts Shikoku Electric Power Co's Ikata nuclear power plant.
"As a final gesture, in order to show they will take responsibility ... I want the four relevant cabinet ministers to sign a document," he told Reuters in an interview in Tokyo.
"We cannot trust verbal assurances."
All three of the 2,022 megawatt Ikata plant's reactors have been halted for checks, but Shikoku Electric has submitted the results of a computer-simulated stress test on one. The government's nuclear watchdog is now reviewing those results.
Tokyo is hoping the stress tests, which the UN's nuclear watchdog, the International Atomic Energy Agency, endorsed earlier this week, will help persuade a wary public to accept reactor restarts.
Nakamura, a 52-year-old former member of parliament, said electricity supply in the summer, when annual demand usually peaks, was likely to be tight in his region if no reactors came back on line.
"In this situation, I think they will have to be restarted at some point," he said.
The Ikata plant had supplied 40 percent of electricity demand in Shikoku Electric's service area, including Ehime prefecture, before the reactors went off line.
The utility has filled the gap by restarting a mothballed oil-fired plant, buying in-house power from companies and by keeping others running beyond the time they would ordinarily have been shut for regular maintenance.
Nakamura stressed, however, that he was in no position now to say whether the stress test meant the reactor was safe and ready to run. Local authorities' signoff is not legally required but it would be politically risky for Tokyo to ignore them.
"I don't understand the central government's policy. There has been no request (for restart) and no explanation," he said.
"Everything is still up in the air."
Still, Nakamura said Japan would need atomic energy for some time to come, given its dependence on imports for fossil fuel and the hurdles to generating a bigger share of electricity from renewable sources such as solar and wind power.
"I think it is necessary for Japan to develop alternatives to nuclear power and promote electricity storage technology, even using public funds. Then, for the first time we will see a path to giving up nuclear power," he said.
"But at a stage when we cannot see that, the practical option that Japan should take is to engage with nuclear power while thoroughly pursuing safety."
(Writing by Linda Sieg; Editing by Neil Fullick)