The operators of the Sellafield Nuclear Reprocessing Plant in Cumbria have pleaded guilty in court to three charges brought by Britain's Health and Safety Executive following the discovery last year of a massive leak of radioactive fluid at the plant.
Representatives of the British Nuclear Group were told by Whitehaven Magistrates Court in Cumbria that they face a fine when a higher court considers sentencing next month.
The THORP plant's thermal oxide reprocessing plant was shut down in April 2005 following a leak.
It had been alleged that staff failed to insure that radioactive material was safely contained.
The prosecution follows a detailed investigation by the UK HSE's Nuclear Installations Inspectorate into the leak.
The executive was notified of the incident on 20 April last year.
It applied to the courts for summonses alleging that BNGSL breached three conditions attached to the Sellafield site licence granted under the Nuclear Installations Act 1965.