The number of Japan's 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.

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