Evaporation of ruthenium from simulated fission-produced alloy precipitates in a nuclear fuel

Abstract To evaluate the effect of each constituent element on the evaporation loss rate of ruthenium (Ru) from Ru-Molybdenum (Mo)-palladium (Pd)-rhodium (Rh) alloy powders, the oxidation and evaporation behaviors of metallic Ru, Mo, Pd, Rh and Mo0.231Ru0.558Pd0.123Rh0.088 alloy powders were investigated by thermogravimetric analysis under air and Ar-1% O2 atmospheres in the temperature range from 1473 to 1723 K. The evaporation loss rates for metallic Ru powders linearly increased with an increase in the overall vapor pressures of various Ru oxides gases over powders. The Mo powders were found to be quickly oxidized to solid MoO2 and then vaporized, which make the oxygen partial pressure in powders lower. The Pd and Rh powders were confirmed to be chemically stable in the experimental conditions. For alloy powders, it was concluded that the oxidation and evaporation of Ru were delayed due to the lower oxygen partial pressure controlled by the formed Mo(s)/MoO2(s) redox couple. After total release of Mo, the evaporation loss rate of Ru from Ru-Pd-Rh alloy powders would be directly influenced by the Ru activity in alloys.