Curium vaporization from (Cm,Pu)2O3 and from irradiated oxide fuel: Mass spectrometric measurement

The equilibrium vapour pressure over a mixed curium oxide of type (244Cm0.76,240Pu1.24)O3 was measured by Knudsen-effusion experiments. Plutonium was formed in the samples during 25 years decay of curium in an initial Cm2O3 sintered pellet. The same measurements were repeated on seven reactor-irradiated UO2 and MOX samples to obtain the vaporization enthalpy of curium present in typical spent nuclear fuel. The samples were annealed in a tungsten Knudsen cell up to 2800 K and the effusion rates of the different vapour components were analyzed on line by a quadrupole mass spectrometer. The vapour pressures of the curium-bearing species were accurately measured and the results compared with published data obtained under different conditions. The obtained results show that CmO(g) is the only effective vapour species and the measured equilibrium pressure confirms the trend observed in the actinide oxides that the high temperature volatility is more pronounced in compounds where the cation can easily attain a higher oxidation state than that of the condensed phase.