An improvement notice has been issued to Sellafield nuclear reprocessing plant after an electric cable was damaged.
The Office for Nuclear Regulation (ONR) said although no-one was hurt, Sellafield Ltd has until April to improvement management at the plant.
Sellafield Ltd confirmed a high voltage underground cable was damaged during excavations in May last year.
A spokesman for the firm said improvements were being made.
Dr Mina Golshan, deputy chief inspector and director of ONR's Sellafield Decommissioning Fuel and Waste Division, said: "This incident involved damage to a high voltage underground electric cable during excavation works.
"Although the incident did not result in an injury, it had the potential to impact the health and safety of workers working in the vicinity.
"The notice requires Sellafield Ltd to make improvements ensuring that risks arising from excavation work on the site are controlled and managed appropriately."
'No environmental impact'
The ONR said the notice was issued in response to a significant electric cable strike incident in September 2018, during construction activities on the Fellside Steam Generating Plant.
During work at the site a cable was damaged and a power dip in a few buildings led to workers being evacuated as a precaution, Sellafield LTD said.
"Those plants impacted by the dip applied their loss of power procedures to maintain the safety and security of the site," he said.
"No-one was injured and there were no environmental consequences."
She added the firm was liaising with the ONR and was in the "process of implementing the findings".