* Of Japan's 48 nuclear reactors, 17 unlikely to restart
* Japan's nuclear reliance could be as low as 10 pct
* Utilities must clear seismological, economic, political hurdles
TOKYO, April 2 (Reuters) - Three years after the Fukushima disaster prompted the closure of all Japan's nuclear reactors, Prime Minister Shinzo Abe is moving to revive nuclear power as a core part of the energy mix, but many of those idled reactors will never come back online.
Fewer than a third, and at most about two-thirds, of the reactors will pass today's more stringent safety checks and clear the other seismological, economic, logistical and political hurdles needed to restart, a Reuters analysis shows.
This means Japan is likely to remain heavily reliant on imported fuel to power the world's third-largest economy, straining a trade balance that has been in the red for nearly two years. Electric utilities will face huge liabilities to decommission reactors and pay for fossil fuels.
Hokkaido Electric Power Co, facing a third year of financial losses, is seeking a capital infusion from a state-owned lender, which would make it the second utility, after Fukushima operator Tokyo Electric Power Co, to get a government bailout since the March 2011 disaster.
Continuing indefinitely to burn more coal and gas also means Tokyo will find it much harder to meet targets for reducing greenhouse-gas emissions.
"A VERY GOOD GUESS"
Japan had 54 nuclear reactors supplying about 30 percent of the nation's electricity before an earthquake and tsunami destroyed the Fukushima Daiichi nuclear power station in 2011. The six reactors at that plant are shut forever, slated for decades-long decommissioning.
Of Japan's remaining four dozen reactors, 14 will probably restart at some point, a further 17 are uncertain and 17 will probably never be switched back on, the analysis suggests. As a result, nuclear energy will eventually make up less than 10 percent of Japan's power supply.
The Reuters analysis is based on questionnaires and interviews with more than a dozen experts and input from the 10 nuclear operators. It takes into account such factors as the age of the plants, nearby seismic faults, additional work needed to address safety concerns, evacuation plans and local political opposition.
It's impossible to say how many reactors will eventually pass safety inspections and win local approval to restart, but the Reuters analysis constitutes "a very good guess," said Tatsujiro Suzuki, who stepped down this week as vice chairman of the government's Japan Atomic Energy Commission.
Japan previously had the third-highest number of nuclear reactors, behind France and the United States. In Asia, China currently has 21 reactors and South Korea 23.
A number at the low end of the Reuters calculations could make it impossible for Japan to reinstate nuclear as a "base-load" power source - enough to feed a constant minimum supply to the grid - as specified in a draft national energy plan that the government may adopt as soon as this week.
In a measure of the keen interest in, and lack of hard information about Japan's nuclear restarts, shares of uranium producers such as Canada's Cameco Corp and Australia's Paladin Energy Ltd jumped as much as 15 percent last month just on news that Tokyo had compiled a final draft of the energy plan.
HARD SLOG AHEAD
The public has turned against nuclear power after watching Tokyo Electric (Tepco) struggle to deal with the Fukushima disaster. Recent polls put opposition to nuclear restarts at about two-to-one over support.
Abe's government, which reversed the previous government's policy of phasing out nuclear power by 2030, has set no timetable for restarting nuclear plants, saying the process is in the hands of a tough, more independent safety regulator set up after Fukushima.
Some power companies have business plans that assume restarts by this summer, but that looks highly unrealistic as the NRA says the utilities aren't taking the process seriously enough.
Eight power companies have requested safety inspections to allow the restart of 17 reactors at 10 power stations. The NRA has fast-tracked two reactors at the Sendai plant in southern Japan after operator Kyushu Electric Power Co broke ranks with its peers and said it would provision for far greater seismic shocks to the plant.
Three reactors in southern Japan are considered next in line, among 11 pressurised-water reactors at five plants run by Shikoku Electric, Kansai Electric and Hokkaido Electric being actively vetted by the regulator.
"I think the government is incredibly clever by doing the restarts in the most modern, advanced places that have the most local support and are yet far from centres of political activity," said Jeff Kingston, director of Asian Studies at Temple University's Japan campus. "Then you use that to create momentum for the agenda of restarting as many reactors as possible."
Even after the NRA says a reactor is safe to restart, the government will defer to local areas for the final decision. Some of the front-runners have local governments strongly behind nuclear power and the wealth it brings to communities through jobs and government subsidies.
Other communities may balk at disaster preparedness. A survey of 134 mayors of towns and villages near reactors by the Asahi newspaper found that 10 of the country's 16 nuclear plants do not have evacuation plans to cover a full 30 km (18.6 miles) radius - the size of the Fukushima exclusion zone.
Some reactors can essentially be ruled out, like Tepco's Fukushima Daini station, which is well within the Daiichi plant evacuation zone and faces near-universal opposition from a traumatised local population. Also highly unlikely to switch back on is Japan Atomic Power Co's Tsuruga plant west of Tokyo. It sits on an active fault, according to experts commissioned by the NRA.
Twelve reactors will reach or exceed the standard life expectancy of 40 years within the next five years, probably sealing their fate in the new, harsher regulatory climate. These include reactor No. 1 at Shikoku Electric's Ikata power station.
The outlook is less clear for about a third of the other 48 reactors.
Tepco's Kashiwazaki Kariwa plant on the Japan Sea coast north of Tokyo, the world's biggest nuclear station by output capacity, faces a politically fraught process. Although two of the 7 reactors look likely to restart on technical grounds, the head of the local prefecture has accused the operator of "institutionalised lying" and says Tepco cannot be trusted to operate another facility.
Chubu Electric Power Co's Hamaoka plant on the Pacific coast 190 km southwest of Tokyo has been branded by one Japanese seismologist as the country's most dangerous nuclear facility as it is located in an area where four major tectonic plates meet. Any restart would face significant opposition from local legislators even in Abe's own party, and the prefectural governor supports a referendum on the issue.
The government will probably revise Japan's energy framework in the next three years, and if Abe's party is still in power, it may push to build new reactors to replace aging units, said Suzuki at the Japan Atomic Energy Commission.
"They may say it's better to replace older reactors with safer new reactors, and the public may accept it."
(Editing by Billy Mallard and Ian Geoghegan)