Enhanced Fuel Performance Analysis in the AGR-like FHR: A Two-Dimensional Approach Using OFFBEAT

This study investigates the behaviour of fuel in an Advanced Gas-cooled Reactor (AGR)-like Fluoride-salt-cooled High-Temperature Reactor (FHR) using a two-dimensional (2D) thermal-mechanical analysis. The AGR-like FHR concept integrates the fuel geometry and refuelling strategy of AGRs with a molten salt coolant, aiming to leverage existing AGR technology while addressing the unique challenges posed by conventional molten salt-fuelled reactors. A 2D modelling approach is implemented using the OFFBEAT fuel performance tool to evaluate the impact of azimuthal power distribution asymmetries within a fuel pellet on fuel temperature distribution, cladding deformation, and fission gas release. The results highlight significant differences between one-dimensional (1D) and 2D analyses. The 2D model more accurately captures temperature gradients, particularly in regions where the fuel experiences asymmetric heating due to its proximity to the moderator. The study reveals that 1D models tend to underestimate fuel temperatures and fission gas release, especially in outer fuel rings, potentially leading to underestimation of safety margins. Additionally, the impact of eccentric pellet positioning within the cladding is examined, showing that uneven fuel-clad gap distributions further influence thermal conductivity and fuel performance. By incorporating a 2D perspective, this research shows the necessity of considering azimuthally nonuniform power distributions when assessing the fuel behaviour in AGR-like FHR designs. The findings emphasise the impor-tance of advanced modelling techniques to enhance the accuracy of fuel performance predictions in next-generation molten salt-cooled reactors.