Surplus plutonium disposition via immobilisation in synroc

The immobilization of excess weapons plutonium into Synroc yields wasteforms that satisfy the key criteria of the U.S. National Academy of Sciences for geological disposal. Synroc-C with a {sup 137}Cs spike to provide an internal radiation barrier can immobilize up to about 12wt.% PuO{sub 2} as well as adequate amounts of Gd{sub 2}O{sub 3} and HfO{sub 2} as neutron absorbers to limit risks of nuclear criticality. New results are presented on zirconolite-rich Synroc that has the potential to accept up to about 20 wt.% PuO{sub 2} if the internal radiation barrier is not included. An external radiation barrier to improve diversion resistance can be utilized with the can-in-canister concept. The implications of the various radiation barriers on processing and eventual geological disposal of Pu-rich Synroc wasteforms are discussed briefly.