Comparative neutronic analysis of UO2 and Thorium-based fuels for TRU transmutation in dual-cooled annular PWR assemblies

This study evaluates transuranic (TRU) management in dual-cooled annular PWR fuel using UO 2 and ( 232 Th- 233 U- 235 U)O 2 matrices, with solid-pin assemblies as references. Pin-cell screening and assembly depletion calculations were performed to assess criticality, cycle performance, fissile-inventory retention, actinide evolution, and temperature feedback. Under a 3% leakage allowance, the best-performing configuration, Case-9 with a 0.3 mm TRUO 2 ring in the thorium-based matrix, achieved a discharge burnup of 71.36 GWd/tHM and a cycle length of 594.70 effective full-power days (EFPDs), representing a 29.5% increase over the solid UO 2 reference. Its end of the irradiation cycle fissile inventory ratio reached 0.469. In UO 2 -based assemblies, 238 U conversion sustained plutonium production, preventing systematic net depletion of the principal Pu isotopes. Conversely, the absence of 238 U from the thorium-based matrix eliminated matrix-driven 239 Pu production, while 233 U regeneration supported late-cycle reactivity. In Case-9, 239 Pu, 240 Pu, 241 Pu, and 241 Am decreased by approximately 97.5%, 73.6%, 59.0%, and 91.9%, respectively; however, 242 Pu, 243 Am, and curium accumulated through successive capture chains. All configurations exhibited negative fuel and moderator temperature coefficients, ranging from -1.72 to -2.60 pcm/K and -20.90 to -55.15 pcm/K, respectively. These results identify thorium-based annular fuel with localized TRU loading as the most promising configuration from a neutronic point of view examined for combining TRU consumption, extended irradiation potential, and favorable reactivity feedback.