Oxygen Potential Analysis to Evaluate Irradiation Behavior in MOX and MA-Bearing MOX Fuels

摘要

Oxygen potentials of oxide nuclear fuels are important thermodynamic data in development of nuclear fuel technologies. Minor actinide bearing MOX (mixed oxide) fuels have been developed as sodium cooled fast reactor fuels. Content of Am which is one of the minor actinide elements causes oxygen potentialto increase. The effects of the oxygen potential increase on the irradiation behavior were evaluated. Profiles of temperature and O/M (oxygen-to-metal) ratio in the pellets were evaluated to better understand the irradiation behavior. From these data, local oxygen potential in the radial direction of the pellets was calculated, and was compared with free energy of compounds composed of fission products. Based on this comparison, it was concluded that Cs_2MoO_4 was likely formed at pellet periphery of (U_(0.7)Pu_(0.3))O_(1.98) and (U_(0.66)Pu_(0.3)Am_(0.016)Np_(0.016))O_(1.976) The extent of cladding tube inner surface oxidation was predicted by using the calculated oxygen potential. No significant difference between irradiation behaviors of (U_(0.7)Pu_(0.3))O_(2-x) and (U_(0.66)Pu_(0.3)Am_(0.016)Np_(0.016))O_(2-x) pellets was confirmed.