Coupling methodology for the multidimensional fuel performance code offbeat and the Monte Carlo neutron transport code SERPENT

During irradiation, a radial power profile establishes in the fuel pellets and affects the behavior of the rod. Many traditional fuel performance codes include a simplified neutronics model for tracking the fuel composition over the burnup and calculating the radial power profile. These models often use few-groups diffusion theory approximation for determining the neutron flux. This approach compares well with experiments and neutronics code for traditional PWR fuel rods. However, larger deviations are expected in the presence of strong absorbers such as Gadolinium or for unusual fuel configurations such as those found in many experimental reactors. Coupling a fuel performance code with an accurate neutronics solver is an alternative option, which would improve the accuracy of the power profiles at the cost of higher computational requirements. This work presents the development of a coupling methodology between the fuel performance code OFFBEAT (OpenFOAM^® Fuel BEhavior Analysis Tool) and the Monte Carlo neutron transport code Serpent. Two tests are presented, namely a UO2 rod and a Gd-doped UO2 rod. The isotopic concentration and power profile are calculated and compared with those obtained with TUBRNP, a well-known neutronics model included in the TRANSURANUS and FRAPCON codes.