The Tihange 2 reactor is the second to be taken offline by Belgium in the last four months as part of a two-decade-old plan to rid itself off nuclear power.
Belgium is set to shut down an ageing nuclear reactor that has long caused controversy in neighbouring Germany, despite delaying its overall exit from atomic energy.
German officials have for years called for the 40-year-old facility to be shuttered over security concerns after thousands of hairline cracks were found in its pressure vessels.
Brussels rebuffed those calls - but was finally set to turn off Tihange 2 just before midnight on Tuesday as part of its longer-term plans.
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"The shutdown of the plant guarantees significantly increased security in our two countries," Germany's environment minister Steffi Lemke told local media.
The reactor is located just 50 kilometres (30 miles) from Belgium's border with Germany.
The promise of a gradual phase-out of nuclear power has been enshrined in Belgian law since 2003.
(VIDEO) Tihange 2 nuclear reactor, operating in Belgium's Huy city for 40 years, will be permanently shut down pic.twitter.com/AkNZqjAW2s— ANADOLU AGENCY (@anadoluagency) January 31, 2023
But the country last year decided to delay its planned exit in 2025 by a decade in the face of high energy prices caused by Russia's attack on Ukraine.
The authorities nonetheless decided to push ahead at the same time with closing down two of its oldest reactors - mothballing another at the Doel plant near Antwerp in September.
Electricity dependency on reactors
The decision to delay the overall nuclear power moratorium has been fiercely resisted by Belgium's Green Party, which is in the ruling coalition.
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Belgium in January announced a deal with French energy firm Engie to extend the life of two other of its reactors by a decade.
Wedged between nuclear-powered France and gas-and-coal-dependent Germany, Belgium has relied on about half of its electricity needs from its stable of reactors.