Selection and evaluation of potential burnable absorbers incorporated into modified TRISO particles

Graphical abstract: - Highlights: • We evaluate possible burnable absorbers for modified TRISO fuels. • We model modified TRISO particle performance in MCNPX. • Modified particles decrease reactivity swing and increase reactor lifetime. • Modified particles generally result in negative thermal feedback. - Abstract: The quadruple isotropic (QUADRISO) particle concept modifies tri-structural-isotropic (TRISO) particles to add a layer of burnable absorber next to the fuel kernel. Previous studies have evaluated QUADRISO fuel particle designs for the transmutation of neptunium and plutonium, as a modification to the plutonium–thorium fuel cycle, and for excess reactivity management. This study screens the available nuclear isotope database to identify potential burnable absorbers for incorporation into modified TRISO fuel particles in a representative Very High-Temperature Reactor (VHTR). Based on this screening, eleven potential burnable absorbers are tested as QUADRISO burnable absorber layers, in either oxide or carbide forms. The addition of a burnable absorber layer to the TRISO fuel resulted in an increase in reactor operational lifetime in all cases considered in the present work when compared to a reactor with the same excess reactivity without burnable absorbers. The B₄C, CdO and Gd₂O₃ cases resulted in the greatest operational lifetime, for the same initial excess reactivity, and the addition of these burnable absorbers to TRISO fuel particles decreased the magnitude of the excess reactivity change over the reactor lifetime when compared to the unmodified TRISO case. Thermal cross-section effects in QUADRISO particles generally result in excess reactivity decreasing with increasing temperature