The future of nuclear power in Fukushima-scarred Japan has emerged as a major campaign issue for the first time in weekend polls, but experts warn little thought has gone into how to replace atomic energy.

Environmental issues have rarely topped the agenda in Japanese elections, which tend to focus on the country's moribund economy and a policy drift fuelled by the passage of seven prime ministers in six years.

But Sunday's vote comes as a rising tide of anti-atomic sentiment is forcing an energy policy rethink, putting the fate of a power source that once generated about one-third of Japan's electricity in doubt.

All but two of the nation's 50 reactors now sit idle, switched off after a quake-triggered tsunami slammed into the Fukushima Daiichi plant in March last year, setting off the worst nuclear accident in a generation.

"Restarting (nuclear plants) is absolutely unthinkable," said Hajime Kemuriyama, a Fukushima city resident.

"We are still suffering from the impact of radiation. I want politicians to address our daily problems."

Kemuriyama's view is a typical one in Japan, with recent opinion polls suggesting about 70% of the electorate want atomic power phased out.

Fukushima operator Tokyo Electric Power's recent admission that it knowingly played down the risks to the plant before the tsunami disaster added to a feeling that Japan had been duped by a powerful industry in league with its regulator.

An expert declaration earlier this week that one plant sits on a seismic fault which may still be geologically active, has further underlined apprehensiveness in the quake-prone country.