Multiscale multiphysics coupling analysis of UO2–SiCw accident-tolerant fuel with optimized whisker orientation

Doping with high thermal conductivity second-phase materials such as SiC is a promising strategy for enhancing fuel performance. This study focuses on SiC whiskers (SiC w ) and evaluates the feasibility of further enhancing in-reactor fuel performance via orientation optimization through a multiscale and multi-physics coupling approach. A whisker generation finite element (FEM) algorithm is developed to construct random or aligned SiC w . Based on the FEM model, the anisotropic effects of whisker orientation on thermal conductivity, thermal expansion coefficient, Young’s modulus, and Poisson’s ratio are investigated. Interfacial thermal resistance is also incorporated into the FEM model, and the results show that the predicted thermal conductivity agrees well with experimental data, with an error of only 8.16%. A COMSOL-based multi-physics model is built, incorporating heat transfer, stress-strain, burnup, thermal and irradiation creep, porosity evolution, fission gas behavior, swelling, densification, and gas plenum pressure. The model is validated against the BISON and CAMPUS codes. The results show that, compared with UO 2 and randomly dispersed UO 2 -15 vol% SiC w , the UO 2 -15 vol% SiC w op exhibits notable improvements, including reductions in peak temperature (1307→1166→1074 K), radial temperature gradient (1430→1130→938 K/cm), and fission gas plenum pressure (21.00→19.70→19.06 MPa), as well as delaying fuel-cladding gap closure time (841→910→944 MWh/kgU). Furthermore, the axial temperature distribution and displacement remain stable, and cladding stress is well below the yield strength of Zr cladding. These findings theoretically demonstrate the feasibility of further enhancing fuel performance through the optimization of second-phase structure.