Oxygen-to-Metal Ratio Control During Fabrication of Mixed Oxide Fast Breeder Reactor Fuel Pellets

摘要

Oxygen-to-metal ratio (O/M) of mixed oxide fuel pellets can be controlled during fabrication by proper selection of binder (type and content) and sintering conditions. Sintering condition adjustments involved the passing of Ar--8% H sub 2 sintering gas across a cryostat ice bath controlled to temperatures ranging from -5 to -60 exp 0 C to control as-sintered pellet O/M ratio. As-sintered fuel pellet O/M decreased with increasing Sterotex binder and PuO sub 2 concentrations, increasing sintering temperature, and decreasing sintering gas dew point. Approximate relationships between Sterotex binder level and O/M were established for PuO sub 2 --UO sub 2 and PuO sub 2 --ThO sub 2 fuels. O/M was relatively insensitive to Carbowax binder concentration. Several methods of increasing O/M using post-sintering pellet heat treatments were demonstrated, with the most reliable being a two-step process of first raising the O/M to 2.00 (stoichiometric) at 650 exp 0 C in Ar--8% H sub 2 bubbled through H sub 2 O, followed by hydrogen reduction to specification O/M in oxygen-gettered Ar-(% H sub 2 at temperatures ranging from 1200 to 1690 exp 0 C. (ERA citation 04:051153)