Irradiation behavior and thermodynamic properties of metallic fuel

Applicability of metallic U-Pu-Zr fuel to commercial fast reactors is being studied in Japan. This requires evaluation of the integrity of the metallic fuel to be used under severe irradiation conditions of commercial reactors, such as higher coolant temperature and higher burnup. When the high temperature application of the metallic fuel is considered, one of the fuel design limits is elimination of fuel centerline melting. The author presents review on some thermal properties of the fuel alloys for fuel temperature estimation. Another design limit is elimination of liquefaction at the fuel-cladding interface during normal reactor operation. The experiments and analyses to determine the liquefaction condition are summarized, where thermodynamic assessments of the relevant alloy systems play an important role as well as in estimation of the fuel alloy properties. The computer code prediction of the irradiation behavior up to a peak burnup ∼20at % is also presented. This suggests that appropriate estimations of cladding wastage by rare-earth elements and accumulation of non-gaseous fission products are important for the analysis of the metallic fuel performance up to such a high burnup. (author)