Thermochemical assessment of oxygen gettering by SiC or ZrC in PuO2−x TRISO fuel

Particulate nuclear fuel in a modular helium-cooled reactor is being considered for the consumption of excess plutonium and related transuranics. In this work a thermochemical analysis was performed to predict oxygen potential behavior in plutonia TRISO fuel to burnups of 88% FIMA of the Pu239 content with and without the presence of oxygen gettering SiC and ZrC. The gettering phases are designed to prevent kernel migration, a serious issue in TRISO fuel, and this has been demonstrated with both SiC and ZrC. The phases reduce CO pressure, thus also reducing the peak pressure within the particles by at least 50%, decreasing the likelihood of pressure-induced particle failure. A model for kernel migration based on vapor transport by CO was used to semi-quantitatively assess the effect of controlling oxygen potential with SiC or ZrC and demonstrate the potential dramatic effect of the addition of these phases on carbon transport.