LAUSR

Abstract The measurement of oxygen potential was conducted at 1673, 1773, and 1873 K for (U0.623Pu0.350Am0.027)O2 and at 1873 and 1923 K for (U0.553Pu0.285Am0.015Np0.147)O2 by using a thermo-gravimeter and an oxygen sensor. Am inclusion in terms of substituting the U significantly increased the oxygen potential. Similarly, the inclusion of Np as a substitute for U increased the oxygen potential; however, the effect was not as large as that with the Pu addition at the same rate. The results were analyzed via defect chemistry and certain defect formations were suggested in the reducing region and the near-stoichiometric region by plotting the relationship between PO2 and the deviation from the stoichiometry. The equilibrium constants of the defect reactions were arranged to reproduce the experiment such that Am/Np contents were included in the entropy with coefficients fitting the experimental data.