Belgium’s Doel 3 reactor will be kept offline until the end of August after a possible crack was found.
The European Union said Belgium had notified other countries using nuclear power of the possible hairline crack found in a steel tank that contains the reactor.
The possible flaw was discovered while the plant was shut for annual maintenance.
Plant officials have said there is no threat to health but the possible problem will keep the facility offline until the end of August.
Marlene Holzner, a spokesman for the European Commission, the EU's executive branch, said that Belgian authorities had notified other countries so they could check whether their reactors used the same kind of steel tank.