"There has been a continuous failure to produce and keep operating records to permit accounting for all nuclear material in the B30 site at Sellafield," said an official at the EU executive Commission, which enforces laws in this field.He said European Commission inspectors had been unable to gain full access to B30, a series of reinforced concrete ponds that store radioactive waste under water at the plant run by British Nuclear Fuels (BNFL).
The 20-member Commission is to decide next Wednesday on whether to ask Britain to submit a plan to Brussels by the beginning of May, detailing how it accounts for the waste.
London said it was working with the European Commission to solve the problem.
"Safeguard arrangements for B30 have been the subject of discussion with the Commission dating back some 15 years," a British government statement said, adding that Sellafield received regular Commission inspections.
If Britain fails to comply with the Commission decision, it could ultimately face EU fines.
The Commission official also said the issue set a bad example for the 10 states joining the EU on May 1.
"We can't ask new EU countries to respect nuclear safety rules... impose monitoring... if it is not applied to all states," he added.