Correlations for the specific heat capacity of [formula omitted] derived from molecular dynamics

Abstract

UO2 is the primary conventional fuel used in most nuclear reactors with Gd2O3 commonly added as a burnable absorber to produce a more level power distribution in the reactor core at the beginning of operation. It can also be mixed with other actinide oxides to produce mixed oxide (MOx) fuel. In this study, molecular dynamics simulations were used to predict the specific heat capacity of Gd-doped PuO2, UO2 and (U,Pu)O2 MOx accommodating Gd3+ substituted at cation sites via two charge compensation mechanisms - oxygen vacancy formation and the oxidation of U4+ to U5+. The specific heat capacity values for PuO2 and UO2 are in good agreement with other studies showing a distinct peak at high temperatures - above 1800 K. As Gd3+ is added, the peak height reduces for each composition considered. An analytical fit was applied to the data where Gd3+ was fully charge compensated by either oxygen vacancies or U5+. The expression was then validated by predicting the specific heat capacity for three compositions of (UxPu1−x)1−yGdyO2−z containing both oxygen vacancies and U5+, and compared to molecular dynamics data.