There was a plant-scale trial of the process at the end of last year.

British Nuclear Fuels (BNFL) has begun a chemical treatment process which it says will reduce discharges of Technetium-99 (TC99) by 90%.

It follows years of research and development by the firm and comes after concerns about the discharges.

There was a plant-scale trial of the process at the end of last year.

'Landmark achievement'

The process enables TC99 to be taken out of liquid discharges and stored as solid waste instead of being discharged into the sea.

After the trial, results were sent to the Environment Agency and Health and Safety Executive's Nuclear Installations Inspectorate and Nirex for assessment.

Their assessments have now been completed and permission granted for the new waste treatment method.

Sellafield head of environment, health & safety, John Clarke, hailed it as a "landmark achievement".

He said: "In addition to addressing issues of international concern and fulfilling government and regulatory requirements, this will also mean that the clean up of certain facilities at Sellafield can be accelerated."

The success of the trial was welcomed by Defra.

Environment Minister Elliott Morley said: "Although there is no evidence that the discharge of TC99 into the sea at its current discharge limit is harmful to man or the environment, it has prompted some concern, particularly in Scandinavia, because TC99 can be detected at very low levels in coastal waters and in certain shellfish and seaweed."

"I am therefore very pleased that the collective efforts of BNFL, the Environment Agency, the Nuclear Installations Inspectorate and Nirex have led to the successful reduction of discharges some two years ahead of schedule."