Designing a solid-fuelled salt-cooled fuel performance experiment in the Jules Horowitz Reactor, Part I: Multiphysics preliminary design

The qualification of advanced reactor fuels requires irradiation experiments that reproduce the expected performance of the target system. This work presents a sequential, physics-based framework for the preliminary design and screening of fuel performance experiments in light-water material testing reactors. This is demonstrated through a solid-fuelled, salt-cooled irradiation experiment in the Jules Horowitz Reactor (JHR) for an Advanced Gas-cooled Reactor-like Fluoride-Salt-Cooled High-Temperature Reactor (AGR-like FHR). Neutronic, thermal hydraulic, and fuel performance simulations are coupled one-directionally using Serpent-2, CTF, and TRANSURANUS with Sciantix, prioritising computational ease and affordability and rapid iteration at the exploratory design stage. The framework is applied to evaluate candidate JHR irradiation positions based on neutron spectrum, axial power shape, linear power, and achievable coolant temperature gradients. Fuel performance modelling of the candidate experiments provides the decisive discriminator. Short burnup simulations eliminate configurations exhibiting early fuel-cladding gap closure and unrepresentative thermal behaviour. Burnup simulations up to 20 MWd/kgU show that, while the selected reflector position (P322) best reproduces early-life behaviour, it does not adequately reproduce long-term degradation mechanisms such as fission gas release, gap closure, and cladding creep relative to the target AGR-like FHR system. These results demonstrate that fuel-performance-driven screening is an effective first step in experimental design, while motivating subsequent modification of controllable parameters to achieve more representative degradation behaviour. This is addressed in a companion paper focusing on multi-objective optimisation of the selected baseline experimental configuration. • Sequential multiphysics framework developed for fuel performance experiment design. • Framework supports down-selection of candidate irradiation experiments. • Applied to test AGR-like FHR fuel performance in a material testing reactor.