Excess Pu Disposition in Zirconolite-Rich synroc

Abstract

AbstractThe design philosophy of a zirconolite-rich Synroc variant, hot-pressed at 1200°C/20 MPa, for immobilizing excess weapons Pu is summarized. Phase analysis of Synroc variants containing different (nominated) proportions of zirconolite, Pu and Gd is presented. The presence of hollandite allows the incorporation of radioactive Cs to reduce diversion risks. The influence of chloride impurities on Synroc properties was studied to bear on the usage of encapsulated 137CSCI for this purpose. The maximum incorporation of the neutron poisons Gd and Hf in solid solution in zirconolite from XRD/SEM is 0.5–0.7 and 1.0 formula units respectively, with the value for Gd depending on the charge compensation scheme employed. The use of deep boreholes for disposal would promote the self-annealing of radiation damage from α-decays. The production of zirconolite-rich Synroc ceramics via fired PuO2 or a liquid Pu/microsphere precursor is also discussed. The choice of processing atmosphere for a zirconolite-rich ceramic containing Pu is oxidizing to neutral for Pu-only and Pu + Cs immobilization options, and reducing for a Pu + fission product option