A Japanese power firm on Saturday began switching off the country’s last working reactor, a spokesman said, leaving it withoutnuclear power just over a year after the world’s worst atomic accident in a quarter of a century.

As technicians took the initial step to close down the No. 3 unit at Tomari in Hokkaido, the debate over whether Japan needs nuclear power has been reignited, amid increasingly shrill warnings of summer power blackouts.

Hokkaido Electric Power, which runs the plant, said they started inserting control rods at 5:00 pm (0800 GMT) that would halt the chain reaction and bring the reactor to “cold shutdown” some time on Monday.

“Power output started declining at the No. 3 unit,” said Tomohiko Shibuya, a Hokkaido Electric Power spokesman. “We have not heard of any trouble so far. Power generation there is scheduled to stop completely in about six hours.”

The shuttering will mark the first time since the 1970s that resource-poor and energy-hungry Japan has been without nuclear power, a technology that had provided a third of its electricity until meltdowns at Fukushima.

The tsunami-sparked disaster forced tens of thousands of people from their homes in an area around the plant — some of whom may never be allowed to return.

It did not directly claim any lives, but has devastated the local economy, leaving swathes of land unfarmable as radiation spewed from the ruins.

With the four reactors at Fukushima crippled by the natural disaster public suspicion of nuclear power grew, so much so that no reactor shut for routine safety checks has since been allowed to restart.