Japan is set to go without nuclear energy for the first time since 1970 from Saturday, when the last operating reactor shuts down for maintenance, heightening fears of a looming power crunch this summer.

Only one of Japan's 50 reactors -- at the Tomari nuclear plant in northernmost Hokkaido -- is operating at present, but it is scheduled to stop for maintenance work which will last more than 70 days.

Resource-hungry Japan relied on nuclear energy for about one-third of its electricity demand until a massive earthquake and tsunami in March last year caused reactor meltdowns at the Fukushima Daiichi plant.

Utility firms managed to make up much of the power shortfalls after the nuclear accident by imposing scheduled blackouts on offices, factories and households while cranking up the use of thermal plants and gas turbines.

Since the disaster there has been lingering public distrust over nuclear energy and all but the one reactor at the Tomari plant are suspended for extra safety checks.

Workers at the Tomari plant will move the control rod into reactor No. 3 at about 5:00pm (0800 GMT) on Saturday, which will lower power generation to zero, a spokesman at Hokkaido Electric Power Co. (HEPCO) said.

The long-term future of the reactor -- and Japan's nuclear energy policy -- remains uncertain.

The government of Prime Minister Yoshihiko Noda has said two of the offline units at the Oi nuclear power plant, western Japan, are safe enough to restart and that they could help prevent power shortages in the hot summer months.

But it remains unclear if or when the government will gain approval from regional authorities to resume the reactors.

The Oi plant's operator, Kansai Electric Power, which supplies mid-western Japan, including the commercial hubs of Osaka, Kyoto and Kobe, has said it could face an electricity shortfall of almost 20 percent if temperatures soar in July.

And the utility said it could remain up to 16 percent short in August as increased air conditioner usage zaps the electricity produced by its thermal fuel plants.

Kyushu Electric Power, covering an area further west, as well as HEPCO in the north, also said they will not be able to meet summer demand without nuclear energy.

Increased use of thermal fuel plants hikes costs for utility firms, as well as greenhouse gas emissions for the country.

Critics of atomic energy point to continuing efficiencies that have allowed the world's third largest economy to all but shrug off previous dire warnings of shortages.

A series of anti-nuclear power demonstrations are planned on Saturday, the Children's Day national holiday in Japan, calling for a safer future for younger generations.