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 percent 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.

Last month, anti-nuclear parties banded into the Tomorrow Party of Japan, headed by high-profile regional politician Yukiko Kada, on a platform of phasing out atomic power.

"We will create a new party, in response to people saying they don't have any party to choose from," Kada told a press conference near Lake Biwa in a region with a number of ageing nuclear reactors.

The ruling Democratic Party of Japan vowed earlier this year to ditch nuclear power by 2040, bowing to public pressure as thousands gathered to protest outside Prime Minister Yoshihiko Noda's official residence.

But it quickly backpedalled on that pledge with a more vague promise to work towards a nuclear-free country.

To plug its power gap as reactors have gone offline, Japan has turned to pricey fossil-fuel alternatives, sending energy imports soaring and generating widening trade deficits for the world's third-largest economy.

None of the anti-nuclear parties have specified exactly how the energy gap would be overcome, offering only general discussion about "efficiency" and renewables.

Zero-nuclear advocates say investing in renewable energy would pay off by spawning new industries, stoking job creation and economic growth -- vital in an indebted country that has seen nearly two decades of deflation.

But Shinzo Abe, leader of the business-friendly Liberal Democratic Party (LDP) and frontrunner to become Japan's next leader, has derided the zero-nuclear goal as unrealistic and "irresponsible".

The LDP has hinted at keeping nuclear power, saying it would decide on reactor restarts in three years and the nation's "best energy mix" within a decade.

His opponents say the LDP's cosy attitude to regulation was a big factor in the lax supervision that worsened the disaster at Fukushima.

The polarising debate on atomic energy is one of the key differences among a dozen parties contesting the election including the Communists who also have a zero-nuclear platform.

But opinion polls indicate that despite their apparently popular stance on ridding Japan of nuclear power, Tomorrow and the Communists are struggling to gain popular support.

Sadafumi Kawato, professor of politics at Tokyo University, warns the debate is not being played out in a serious way that would allow citizens to balance the risks of nuclear safety against those of energy security.

"Not many people have a deep understanding of the nuclear industry," he said. "It's hard for voters to judge the safety of nuclear plants."

That leaves the average citizen wrestling with little more than gut feelings, which they find difficult to weigh against what they know are real needs for an energy-hungry country.