The single-unit Gösgen nuclear power station in Switzerland will return to service later than planned because further improvements are needed too the feedwater system, owner and operator Kernkraftwerk Gösgen said.

The 1,010-MW pressurised water reactor unit, which began commercial operation in 1979, has been offline for an annual outage that began at the end of May and was originally expected to last one month.

On 25 June Kernkraftwerk Gösgen said the restart would be delayed because of an issue with plans to replace valves in the feedwater system.