B205 is the name of the Magnox nuclear reprocessing plant at Sellafield in northern England. This plant uses PUREX chemistry (based on tributyl phosphate (TBP)) to extract plutonium and uranium from used nuclear fuel. The plant was originally constructed and operated by the United Kingdom Atomic Energy Authority (UKAEA), but in 1971 control was transferred to British Nuclear Fuels Limited (BNFL).
B205 was commissioned in 1964 as a replacement for the UK's first nuclear reprocessing plant, B204, which was converted into a pre-handling plant for B205 and recommissioned in 1969. In 1973, after both plants had been shut down for one year for repairs, a violent reaction in the B204 plant occurred which contaminated the entire plant and 34 workers with ruthenium-106. Following this event the B204 plant was permanently decommissioned.
Over its lifetime, the B205 plant has handled over 35,000 tons of expended Magnox fuel, and returned over 15,000 tons of uranium to the fuel cycle. Currently the British nuclear industry is in the process of discontinuing the use of all Magnox fuelled reactors, with a target date of 2010, and the B205 plant is slated for decommissioning around 2020 after all fuel has been reprocessed.
Process
The process uses mixer settlers as the basis of the plant operation. The Magnox fuel is dissolved in Nitric acid within the Dissolver Cell. The aqueous stream is conditioned to the correct temperature and acidity and then passes to the first mixer settler system where fission products are separated from the Uranium (U) and Plutonium (Pu) by extraction of the U/Pu into the solvent phase comprising tri-butyl-phosphate in odourless kerosene. This has the effect of reducing the radiation levels in subsequent stages of the process and the resulting degradation of the solvents.
The solvent stream of U, Pu and remaining fission products then passes to the critical mixer settler stages where the U and Pu are transferred into the aqueous phase and fission products remains in the aqueous phase. Separation of the U and Pu is achieved by adding a reductant, which causes the Pu, but not the U, to transfer into the solvent phase. Once separated, further removal of fission products is undertaken by more mixer settler units.
The U and Pu streams are then passed to evaporators to concentrate the U and PU before further processing in other plants