Reprocessing and recycling facilities

In the closed NFC, SF is reprocessed to extract useful uranium and pluto­nium. Several reprocessing facilities are currently in operation worldwide,

).

including those at Sellafield (UK), La Hague (France) and Chelyabinsk (Russia). These were initially set up to extract material for weapons pro­grammes, but the Pu and U can be recycled for use in PWRs as mixed oxide (MOX) fuel.

Reprocessing of SNF involves removal of the fuel rod metal cladding followed by dissolution of the remainder in the nitric acid, followed by chemical solvent extraction of the uranium and plutonium formed during the fuel burn-up process via the Purex (Plutonium and Uranium Extrac­tion) process. The remnant solution is HLW and contains the dissolved fission products together with impurities from the cladding materials, inac­tive process chemicals, transuranic elements formed by neutron capture, and traces of unseparated plutonium. HLW is concentrated by evaporation to reduce the volume and stored in aqueous nitric acid solution in stainless steel tanks. HLWs contain a host of products ranging from uranium fission products to fuel alloying elements, including F, Al, Si and Mo; cladding ele­ments including Zr, Mo, Nb, and Mg; transuranic elements including Np, Am, Cm and residual Pu. HLWs also contain some of the process chemicals including kerosene, tributyl phosphate and related organic materials.

Decommissioning wastes are generated at the end of operation of NFC facilities including nuclear reactors. As well as waste from the radioactive ceramic fuel, some structural materials become activated by elements undergoing neutron capture. The high alloy steel end caps from each fuel bundle in an advanced gas-cooled reactor (AGR), for example, become so activated they are treated as HLW; since there are approximately 100 of these in each AGR assembly and a complete refuel occurs every two years, the amount of waste is significant. The alloying elements of particular concern in steels are Co, Nb, Ni and Mo. After the SNF is removed, the NFC facilities must be decommissioned, demolished and eventually returned to greenfield or brownfield use. During this process, large volumes of waste are generated, although most is not radioactive. The amount of waste arising from decommissioning a typical NPP is 10,000-15,000 tonnes. Much of this waste is concrete and other building material containing only small amounts of radioactivity. About a tenth of the decommissioning waste contains some radioactivity up to the intermediate level.

Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *