Overview of Plutonium Pyro-processing By-Products Management

CEA/DAM has been operating Plutonium pyro-processes for several decades. These processes generate mainly three types of by-products that may contain significant amounts of plutonium associated with americium: spent salts where the plutonium is trapped in a chloride gangue, metal scraps such as dross and highly impure buttons, metallic and ceramic pieces with both metal and salt adherences. The composition of these by-products varies from one batch to another, according to process and interim storage conditions, and they cannot be discarded as waste. Processes have been developed to recover the plutonium from these products and to decontaminate the substrates in order to meet the requirements for low or middle activity waste discard. The process baseline is aqueous nitrate polishing including nitric dissolution, purification using ion exchange or solvent extraction, and oxalate conversion to recover plutonium as pure dioxide. For each type of by-product, a front-end process has been developed to produce a plutonium oxide feed material suitable for aqueous nitrate polishing in terms of both efficiency, and waste and effluents management. Metal oxidation was developed to convert metal scraps to oxide as well as to remove plutonium from refractory metal and ceramic pieces. The front-end process for chloride spent salts was challenging to develop. The process consists in a pyrochemical oxidation, using carbonate and chlorine to convert plutonium species into oxide, followed by vacuum distillation at high temperature. The high efficiency of the process has been demonstrated in terms of both decontamination factor and plutonium conversion to oxide. The obtained plutonium oxide products were then suitable for subsequent aqueous nitrate processing using oxidizing or nitro-fluor-hydric dissolution processes