EDF Energy switched off one of the reactors at Heysham 1 nuclear power plant last night after a water leak linked to a turbine.
The generator said there was no risk of a radiation leak at unit 2 of the power station.
It could not say when it would restart the unit – which refers to the reactor and the generating turbine – for commercially sensitive reasons.
The unit is not the one which prompted EDF to shut all reactors at Heysham and Hartlepool nuclear plants for safety inspections when a “defect” was found. All plants were back in action by the start of 2015.