Module for thermomechanical modeling of LWR fuel in multiphysics simulations

We have developed a new light-weight fuel behavior code FINIX, specifically designed for modeling of LWR fuel rods in multiphysics simulations. A thermomechanical description of the rod is required especially in transient conditions, where the heat transfer and changes in the rod's physical dimensions are strongly coupled. In addition to the mechanical deformations, FINIX solves the temperature distribution in the rod and the heat flux from the cladding to the coolant, allowing two-way coupling of the fuel behavior simulation with both neutronics and thermal hydraulics simulations. In this paper, we describe the FINIX module and compare its performance with experimental data and FRAPTRAN-1.4, a widely used fuel behavior code. The comparison reveals good agreement in both cases. We also demonstrate how FINIX can be integrated into multiphysics simulations. Coupled with the Monte Carlo reactor physics code Serpent, we simulate a fast reactivity transient with the fuel temperature and fission power solved self-consistently. With the reactor dynamics codes TRAB-1D and TRAB3D/SMABRE, we simulate a fast power transient and a PWR main steam line break. The latter serves as an example of coupled fuel behavior, neutronics and system-level thermal hydraulics simulation.