The regulator confirmed that “a very low level” of radioactive Tritium was discovered by EDF Energy in the active drain system of the Scotland-based plant in February, triggering a closer investigation by the ONR.
But the subsequent March investigation gave rise to no safety concerns over either the drainage system or the operator’s monitoring regime.
“We are satisfied that there are no safety concerns and we welcome the actions taken by the licensee to investigate the cause of this incident at the active drain system,” a statement from the ONR said.
The incident did not constrain generation at the 1.3GW nuclear power plant which continued to operate at full load after the radiation was detected and remains at full capacity, according to data from the National Grid.
A spokesman for EDF Energy was not immediately able to comment.