The number of Japanese nuclear reactors likely to restart in the next few years has halved, hit by legal challenges and worries about meeting tougher safety standards imposed in the wake of the Fukushima disaster, a Reuters analysis shows.

The country has been inching back to nuclear energy, turning on its first reactor in mid-August after a two-year blackout, with Prime Minister Shinzo Abe and many in industry looking to cut fuel bills despite widespread public opposition to atomic power.

But Reuter's analysis shows that of the other 42 operable reactors remaining in the country, just seven are likely to be turned on in the next few years, down from the 14 predicted in a similar survey last year.

The findings are based on reactor inspection data from industry watchdog the Nuclear Regulation Authority, court rulings and interviews with local authorities, utilities and energy experts. They also show that nine reactors are unlikely to ever restart and that the fate of the remaining 26 looks uncertain.

"Four-and-a-half years after the events started unfolding at Fukushima Daiichi, the Japanese government, the nuclear utilities and the NRA have not succeeded in overcoming complete planning insecurity for investors. The outlook for restarts is as cloudy as ever," said Mycle Schneider, an independent energy consultant in Paris.

Legal challenges from local residents have hit all atomic plants, with the country's most nuclear-reliant utility Kansai Electric Power issued with court rulings preventing the restart of four reactors despite two of them already receiving NRA approval to switch on.

Tougher safety standards and stricter implementation of rules since Fukushima have also been hitting restarts. Japan Atomic Power has been battling a regulatory ruling that one of its reactors sits above an active fault, meaning it must be decommissioned.