Irradiation of uranium carbides in JMTR.

Abstract

Post-irradiation examinations were performed on three types of uranium carbide UC, UC2 and U2C3, that were irradiated with a relatively high thermal neutron flux (7×1013 n/cm2·s or 9×l012 fission/cm3·s for UC) and in a dose range between 2.7×l015 and 3.3×1018 fission/cm3 (i.e. 2.1×l016 and 2.4× 1019 nvt) in the JMTR (Japan Material Testing Reactor). On UC and UC2, trends similar to previous works were obtained in the irradiation effects. New preliminary results, however, were obtained on U2C3 for changes in the electrical resistivity and the lattice parameter which showed reduced values after attaining a maximum at 1017 fission/cm3. Successive annealing effects on the resistivity and the lattice parameter following the reactor irradiations were examined by pulse heating. Two major steps were observed, at around 400 and 600°C, in the recovery processes. A low temperature step, which was revealed previously at about 200°C in UC and UC2, was missing in this study, because of higher irradiation temperatures (about 300°C) in the JMTR. Considering the results of quenching works on UC and partly on UC2, it was suggested that rather simple defects played roles for the recovery processes below 1,000°C in all three carbides.