Oxygen potentials of mixed oxide fuels for fast reactors

Oxygen potentials of homogenous (Pu0.2U0.8)O2−x and (Am0.02Pu0.30Np0.02U0.66)O2−x which have been developed as fuels for fast breeder reactors were measured at temperatures of 1473-1623 K by a gas equilibrium method using an (Ar, H2, H2O) gas mixture. The measured oxygen potentials of (Pu0.2U0.8)O2−x were about 25 kJ mol−1 lower than those of (Pu0.3U0.7)O2−x measured previously and were consistent with the values calculated by Besmann and Lindemer's model. The measured oxygen potentials of (Am0.02Pu0.30Np0.02U0.66)O2−x were slightly higher than those of MOX without minor actinides. No fuel-cladding chemical interaction is affected significantly by adding their minor actinides.