Japan's resurgent nuclear industry will miss a government target of providing at least a fifth of the country's electricity by 2030, a Reuters analysis shows.

With eight reactors running and one more set to come online in November, nuclear has this year overtaken non-hydro renewables in power output for the first time since the 2011 catastrophe, when all of the country's nuclear plants were idled.

Yet operators can expect as few as six units to restart in the next five years, and fewer than 20 by 2030, the analysis shows. That is far short of the 30 needed to meet the government target reiterated this year.

Based on the analysis, the world's third-largest economy may get about 15 percent of its power from nuclear in 2030, compared with a government target of 20-22 percent.

"It's impossible to meet the target, that's pretty much confirmed," said Takeo Kikkawa, an energy studies professor at Tokyo University of Science, who sat on an official panel that reviewed Japan's energy policy this year.

He said he did not expect another round of restarts before 2020.

One major trading house predicts nuclear will account for 14 percent of power production in 2030, according to a presentation given at a private seminar this year and shown to Reuters.

Nuclear remains an unpopular energy option in Japan and the country will reboot only a fraction of the 54 reactors it had before the disaster.

Six reactors at the Fukushima No. 1 nuclear power plant are being dismantled in a decades-long exercise that is fraught with technological challenges and radioactive waste. Operators have decided to decommission another 10 units across the country since Fukushima.

The Nuclear Regulation Authority created new safety standards from scratch after the disaster highlighted failings in the industry and its overseers. All reactors must be relicensed before restarting.

Yet Japan's nuclear industry, which before Fukushima operated the world's third-largest number of reactors and provided about 30 percent of the country's electricity, has staged a significant recovery.

The turnaround has exceeded expectations of analysts and the utilities themselves. Kansai Electric Power and Kyushu Electric Power, for instance, have won approval to restart or are on course to win approval for all the reactors they applied to relicense.

Those units are far from Tokyo and are pressurized water reactors (PWR), unlike the boiling water reactor (BWR) designs favored in eastern Japan, including those that melted down at Fukushima.

Many court cases are pending for reactors in the east of the country. Local political support varies, and the regulator is locked in disputes with operators over earthquake risk assessment.

The older BWR technology used in many of the reactors under review is also an issue because the stigma of Fukushima hangs over them.

"When you come to the BWRs, the issue becomes very politicized," said Nobuo Tanaka, the chairman of the Sasakawa Peace Foundation who was the head of the International Energy Agency between 2007 and 2011 after a stint in Japan's industry ministry.

The reputation of TEPCO, which operates two nuclear plants that have been damaged in natural disasters, also looms large, Tanaka said.

"TEPCO does not have any support as a nuclear operator," he said. The utility has to be removed from the equation before progress on BWR reactors can be made, he said.

TEPCO has reached the first stage of approval, but faces strong opposition from local residents. But Japan's utility lobby group said progress was being made.

"The safety reviews of PWR plants took time but they have been progressing steadily and there have been some developments in the BWR category as well," Satoru Katsuno, the chairman of Japan's federation of electric utilities and president of Chubu Electric, said of the outlook for restart approvals.

Chubu Electric has been locked in a dispute for years with the regulator over disaster resilience measures at its Hamaoka plant, which uses BWR reactors.

The analysis suggests that Japan will rely on fossil fuels, particularly liquefied natural gas and coal, as the pace of renewables expansion slows. That will make it harder to meet its emissions targets under international agreement.

The government estimates costs for replacement fuel--mostly liquefied natural gas--to compensate for idled reactors totaled 14.6 trillion yen ($130 billion) across the industry in the six years through March.

The lack of realistic energy targets makes it harder for the industry to plan for investment, utility officials say.