Multiphysics assessment including phase change evaluation under severe accident conditions for UO2 doped with burnable absorbers

Multiphysics analyses are crucial for accurately evaluating the performance of nuclear reactors beyond the limitations of traditional single-physics approaches. This study investigates novel fuel materials consisting of traditional UO₂ homogeneously doped with burnable absorbers (BAs). The effect of doping BAs with nuclear fuel on the VVER-1200 was analyzed from both neutronic and thermal-hydraulic perspectives. Initially, the optimal BA concentration for the candidates was determined based on its effectiveness in mitigating excess reactivity while extending the fuel cycle length compared to conventional UO₂ fuel. Then, a detailed neutronic analysis was performed on the optimized compositions to identify the most effective BA material. Utilizing the radial power distribution obtained, thermal-hydraulic analyses were conducted under normal operation, followed by transient simulation of a large LOCA scenario. Phase change modeling was implemented for both proposed fuels and cladding materials to evaluate their thermal resilience and failure thresholds at both beginning of fuel cycle (BOC) and mid of fuel cycle (MOC). Doping BAs with UO₂ achieved various benefits from a neutronic standpoint while quantifying its impact on thermal-hydraulic performance under both normal and severe transient conditions, offering insights into the feasibility of BA-doped fuels for enhanced reactor safety.