Effects of porosity and Cr₂O₃ doping on transient behavior of high‐burnup UO₂ under simulated RIA/LOCA

Abstract This paper reports the fabrication of UO₂ fuels mimicking high‐burnup structures (HBS) using spark plasma sintering (SPS), with precise control over porosity, pore structure, and grain size. Thermal shock tests at ramping rates of 10–500°C/s were performed to study the transient behavior of these fuels under simulated loss‐of‐coolant accident (LOCA) and reactivity‐initiated accident (RIA) scenarios. Both undoped and Cr 2 O 3 ‐doped fuels resist cracking under LOCA conditions. Under RIA transients, however, fuel cracking occur and crack density increases significantly with higher porosity. Cr 2 O 3 ‐doped fuels exhibit superior thermal shock resistance due to enhanced thermomechanical properties. Finite element analysis (FEA) was employed to model temperature and stress distributions, offering insights into cracking mechanisms under extreme conditions. Temperature gradients across fuel pellets during thermal shock testing drive cracking and fragmentation. These results highlight the critical roles of chemical doping and microstructure in the performance and safety assessment of high‐burnup fuels. The methodologies developed, including advanced synthesis, microstructure control, transient testing and FEA, extend beyond nuclear fuels and are applicable to designing and evaluating materials for extreme thermal shocks and rapid temperature changes in high‐performance applications.