Japan has begun the process to become nuclear power-free for just third time in more than 40 years, after the country's only reactor was disconnected from the power grid ahead of planned maintenance.

Nuclear power has provided about a third of Japan's electricity, but the industry came to a virtual halt following the 2011 Fukushima nuclear disaster.

Kansai Electric Power will gradually take offline the No. 4 reactor at its Oi nuclear plant in Fukui prefecture in western Japan.

The work was scheduled to start Sunday evening, with the reactor expected to stop power generation after several hours before coming to a complete stop early Monday.

The Kansai reactor was the only one of Japan's 50 reactors in operation, although several operators have applied to restart their reactors under new rules which were developed following leaking at Fukushima.

The last time Japan went without nuclear power was in the period between May and June 2012 and that was the first shutdown since 1970.

However, the nuclear-free energy is expected to only be temporary, with industry projections pointing to reactor restarts as soon as December.

But opinion polls show a majority of Japanese are opposed to restarts and want to end the country's reliance on atomic power.

"The argument that no nuclear power dents the economy would be myopic, considering that if by mistake we had another tragedy like Fukushima, Japan would suffer from further collateral damage and lose global trust," the head of the Institute for Sustainable Energy Policies, Tetsunari Iida, said.

"In the new economy, the less you use energy, the more value-added you become. The big chorus for nuclear power is hampering the efforts to move to a new, more open economy."

As a result of the nuclear shutdowns, utility companies have had to spend billions of dollars to import oil, gas and coal to make up for the energy shortfall.

The ruling Liberal Democratic Party is keen to get reactors running again, with Prime Minister Shinzo Abe pushing for the need to reduce soaring fuel costs.

But some in the industry accuse the government of prioritising the economy over safety.

"There's talk the Abe administration is putting heavy pressure on the regulator to re-start reactors," oil economist Osamu Fujisawa said.

"It's obviously the economy the administration is after. Otherwise, the business community will look away, dealing an end to the Abe administration."

Neighbourly advice

Meanwhile, Japan's former Prime Minister Naoto Kan has advised Taiwan to close all of its nuclear power plants and abandon nuclear energy.

Taiwan's legislature is expected to deal with the matter when it reconvenes next week.

Japanese prime minister Naoto Kan points at the devastated area of the tsunami-ravaged town of Rikuzentakata. ( AFP: Japan Prime Minister Residence, file photo )

Mr Kan was Japan's prime minister in 2011 when the nuclear disaster unfolded and he says his experiences have changed his views on nuclear power.

"Nuclear power is not cheap and as a matter of fact quite risky," he said.

"It takes a long time for radiation to decay. We should ask ourselves whether it is responsible to leave it for our children and grandchildren to take care of."

Taiwan has three nuclear power plants which provide nearly 20 per cent of the country's electricity.

A report from the country's nuclear watchdog, published in August, revealed one of those may have been leaking radioactive water for three years.

A fourth is expected to open in 2015, although many are opposed to the plant and have called for its construction to be suspended.

The use of nuclear power on resource-poor and small Taiwan has long been controversial because it's widely believed that any major nuclear accident would affect its entire land area.

AFP/Kyodo/Reuters