The incident was caused by a short circuit in an electric installation in part of the plant that had been closed down for scheduled maintenance. There was no question of any danger to the reactor itself, a spokesperson said.

The incident comes as the government is considering what form “stress-tests” should take. All nuclear installations in Belgium will have to undergo these tests to meet new safety concerns following the meltdown at the Fukushima plant in Japan. According to the Federal Agency for Nuclear Control (FANC), reactors should be able to withstand not only earthquake and tsunami – unlikely events in this part of the world – but also the shock of an air crash.

If that were the case, some experts say, Doel reactors 1 and 2, the oldest in the country, would have to close. Other possible causes of a disaster that would form part of the tests are loss of electricity (such as caused the cooling systems at Fukushima to close down), digital attacks on the plant’s computers and gas leaks from other installations in Antwerp harbour.

Meanwhile, federal interior minister Annemie Turtelboom wrote to the parliament last week to explain that proposals for the stress- tests are an initiative of FANC alone. The government, she said, would reserve the right to adapt the provisions when the decision is made.