Wedged between nuclear-powered France and gas-and-coal-dependent Germany, Belgium relies on about half of its electricity needs from an ageing stable of seven nuclear reactors that are operated by Engie, a French company.

The closure of one of the four reactors at the Doel plant near the port of Antwerp is the first step in Belgium's decision in 2003 to exit nuclear power completely by 2025, an end date that was delayed by a decade for two reactors earlier this year.

In February, another reactor is set for mothballing at Tihange, just 50 kilometres (30 miles) from the border with Germany, where activists and officials have lobbied for decades against Belgium's use of nuclear energy at their doorstep.

Both reactors made headlines in 2012 when cracks were found in their reactor units, leaving them out of service for years.

A political crisis erupted this month when Interior Minister Annelies Verlinden raised the question of postponing the shutdown, enraging the Green party.

The Greens had made an exit from nuclear power a condition of joining a politically fragile seven-party coalition that was painfully cobbled together in 2020, more than a year after inconclusive elections.

Verlinden's request was made in the context of Moscow's invasion of Ukraine and the subsequent squeeze on Europe's energy supplies that has raised fears of blackouts and shortages in the coming months.

Making matters worse, a regular supply of electric power from nuclear-dependent France is also under threat with almost half of the country's ageing reactor fleet offline for maintenance.

"With the risk of a blackout in France this winter, with Germany leaving nuclear power but running out of gas, we know that we are going to have major difficulties," warned former energy minister Marie-Christine Marghem.

Her party, also in the ruling coalition, has long been against the quick exit from nuclear power.

However, Belgian electricity operator Elia said it did not expect any supply risks from the long-planned outage.

"We have enough generating capacity available to meet demand," a spokesman told AFP.