Title : Thermal hydraulic and solid mechanics multiphysics safety analysis of a heavy water reactor with thorium based fuel
Abstract:
Growing environmental awareness has renewed interest in thorium as an alternative nuclear fuel, highlighting the need to evaluate reactor performance when conventional fuels are replaced with thorium-based systems. In this work, coupled thermal-hydraulic and solid mechanics simulations were performed using COMSOL Multiphysics to assess the safe operating conditions of a heavy-water reactor employing thorium fuel. The transient thermo-mechanical response of the fuel rod under elevated volumetric heat generation was analyzed to determine strain, displacement, stress, and coolant flow behavior. After 3 s of heating, the fuel exhibits a high-strain core surrounded by a lower-strain periphery, with peak volumetric strain increasing nearly linearly from 0.006 to 0.014 as heat generation rises. Radial deformation is concentrated near the outer surface, while axial elongation remains uniform and scales with power. The corresponding von Mises stress reaches maximum values at the outer surface, increasing from approximately 0.6 to 1.5 GPa with higher heat input, yet remaining within structural safety limits. Cladding simulations show nearly uniform axial expansion, with displacement increasing from ~0.012 mm to 0.03 mm across the studied power range. The average cladding strain remains small (≈10??), and stresses stay well below the yield strength of zirconium alloys, confirming elastic behavior. Coolant velocity decreases smoothly along the axial direction while maintaining flow stability. Overall, the coupled thermo-mechanical and fluid-dynamic analysis confirms structural integrity of both fuel and cladding under the investigated transient conditions.
