EDF Energy tritium alert over Dungeness B groundwater
Groundwater at a nuclear power station has been found to contain a radioactive substance above agreed levels.
EDF Energy, which owns and operates Dungeness B in Kent, said the tritium was found during routine sampling.
The energy firm said there was no risk to the public or its workers from the leak, which had been contained.
The Environment Agency said it and the Office for Nuclear Regulation had been informed. EDF is investigating the source of the tritium.
EDF said the tritium had been identified and isolated to one small area and the environmental impact was negligible.
"Boreholes on the station boundary have been checked and tritium levels have been confirmed to be at background levels - this means no more than is naturally occurring," a statement from the energy firm said.
It said the local water company had confirmed the local water system was unaffected.
EDF said it was still rectifying the problem, but the tritium levels had already been reduced by more than half.
The company said it operated within a highly-regulated industry that had an open and transparent reporting structure, and it notified regulators as soon as the tritium was found.
The Environment Agency said EDF found the elevated levels of tritium in September and December.
The agency said tritium was a substance produced by nuclear reactors and also found naturally in the environment, and Dungeness B discharged tritium into the environment under an Environment Agency permit.
The agency confirmed the tritium found at Dungeness B was in three on-site boreholes that were all close to each other, but levels elsewhere at Dungeness were normal.
It said Dungeness B was a significant distance from any boreholes used for drinking water abstraction, and the local water authority had been informed as a precaution.
Dungeness B is due to stop generating power by 2018.