Correlations for the specific heat capacity of (UxPu1-x)1-yGdyO2-z derived from molecular dynamics

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 op-eration. 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 mech-anisms -oxygen vacancy formation and the oxidation of U 4+ to U 5+ . 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 analyti-cal fit was applied to the data where Gd3+ was fully charge compensated by either oxygen vacancies or U 5+ . 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 U 5+ , and compared to molecular dynamics data. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Molecular dynamics simulations were used to predict the specific heat capacity of Gd-doped PuO2, UO2, and (U, Pu)O2 MOx, taking into account two charge compensation mechanisms - oxygen vacancy formation and the oxidation of U 4+ to U 5+. The results show a reduction in peak height of specific heat capacity for each composition with the addition of Gd3+.