TREATMENT OF GASEOUS EFFLUENTS ISSUED FROM RECYCLING – A REVIEW OF THE CURRENT PRACTICES AND PROSPECTIVE IMPROVEMENTS

The objectives of gaseous waste management for the recycling of nuclear used fuel is to reduce by best practical means (ALARA) and below regulatory limits, the quantity of activity discharged to the environment. The industrial PUREX process recovers the fissile material U(VI) and Pu(IV) to re-use them for the fabrication of new fuel elements e.g. recycling plutonium as a Mixed Oxide (MOX) fuel or recycling uranium for new enrichment for Pressurized Water Reactor (PWR). Meanwhile the separation of the waste (activation and fission product) is performed as a function of their pollution in order to store and avoid any potential danger and release towards the biosphere. Raffinate, that remains after the extraction step and which contains mostly all fission products and minor actinides is vitrified, the glass package being stored temporarily at the recycling plant site. Hulls and end pieces coming from PWR recycled fuel are compacted by means of a press leading to a volume reduced to 1/5th of initial volume. An organic waste treatment step will recycle the solvent, mainly tri-butyl phosphate (TBP) and some of its hydrolysis and radiolytic degradation products such as dibutyl phosphate (HDPB) and monobutyl phosphate (H2MBP). Although most scientific and technological development work focused on high level waste streams, a considerable effort is still under way in the area of intermediate and low level waste management. Current industrial practices for the treatment of gaseous effluents focusing essentially on Iodine-129 and Krypton-85 will be reviewed along with the development of novel technologies to extract, condition, and store these fission products. As an example, the current industrial practice is to discharge Kr-85, a radioactive gas, entirely to the atmosphere after dilution, but for the large recycling facilities envisioned in the near future, several techniques such as 1) cryogenic distillation and selective absorption in solvents, 2) adsorption on activated charcoal, 3) selective sorption on chemical modified zeolites, or 4) diffusion through membranes with selective permeability are potential technologies to retain the gas