Designing a solid-fuelled salt-cooled fuel performance experiment in the Jules Horowitz Reactor, Part II: Optimisation

The qualification of nuclear fuels relies on extensive irradiation testing. However, reproducing the nominal operating conditions of advanced reactor concepts in material testing reactors (MTRs) is insufficient to ensure representative fuel behaviour. In this work, irradiation experiment design for an Advanced Gas-cooled Reactor-like Fluoride-Salt-Cooled High-Temperature Reactor (AGR-like FHR) is formulated as a constrained multi-objective optimisation problem under the operational constraints of the Jules Horowitz Reactor (JHR), with the objective of minimising differences in fuel performance metrics between AGR-like FHR reference behaviour and JHR irradiation experiments. Building on a preliminary multiphysics experiment design developed previously, experimentally controllable parameters were tuned using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The optimisation reveals a narrow Pareto-optimal region in coolant temperature-pressure space, demonstrating that no single configuration simultaneously minimises centreline fuel temperature, fission gas release (FGR), and cladding creep strain differences. For helium-filled pins, optimal solutions cluster at coolant inlet temperatures in the range 811 °C to 833 °C and fill gas pressures of 0.170 MPa and 0.237 MPa, substantially improving agreement with AGR-like FHR reference behaviour relative to the baseline experiment. Reformulating the temperature objective as a time-averaged quantity yields consistent convergence on a similar design space. Substitution of helium with hydrogen enables near-atmospheric pin pressures, reducing pressure requirements by approximately 30%, while requiring higher coolant temperatures (834 °C to 863 °C) to maintain comparable performance across objectives. Although full representativeness is not achieved, the optimised designs better reproduce dominant steady-state fuel damage, demonstrating experimental sufficiency. The proposed optimisation framework provides a transferable methodology for targeted irradiation experiment design in support of accelerated fuel qualification within MTR constraints. • Multi-objective optimisation improves fuel performance experiment representativeness. • Experimental sufficiency is achievable in material testing reactors. • Accelerated fuel qualification pathways for advanced reactor designs are supported.