British Nuclear Group said it would prevent more than 44 years of sea radioactive discharges and save taxpayers �300m in potential costs.

The clean-up has involved liquid waste called medium active concentrate (MAC).

A process was developed at Sellafield, which used a chemical to remove a radioactive isotope from the MAC so it could be enclosed in cement and stored.

The MAC is a by-product of spent Magnox fuel reprocessing and has been stored at a facility called the Medium Active Tank Farm (MATF) at Sellafield since the early 1980s.

Sea discharges

With the increasing age of the MATF facility, there was a need to transfer and process the MAC inventory before new storage facilities were needed.

The processing speed was restricted because of limits on sea discharges of the radioactive isotope Technetium (Tc-99) which was present in MAC.

The process developed at Sellafield involved using a chemical known as TPP to separate Tc-99 from the MAC so it could be sealed in concrete and stored safely on the site.

All current and future production of MAC was diverted to an alternative plant at Sellafield where waste could be melted into glass for safe storage.