Effect of oxygen-to-metal ratio on melting temperature of uranium and plutonium mixed oxide fuel for fast reactor

The melting temperatures of uranium plutonium mixed oxide fuel for fast reactor were investigated as functions of Pu content, Am content, and oxygen-to-metal (O/M) ratio using the thermal arrest technique. Rhenium inner was used for the measurement to prevent the reaction between the sample and capsule materials. The solidus temperatures decreased with increasing Pu and Am contents and increased with decreasing O/M ratio. It is considered that the maximum temperature in the U-Pu-O system varies in the hypostoichiometric composition region. The melting temperatures were evaluated by the ideal solid solution model derived to calculate the solidus and liquidus temperatures in the UO₂-PuO₂-AmO₂-PuO_1.7 system. The derived model reproduced the experimental data within an accuracy of ±25 K.