Simulation and optimization of performance during normal operating conditions of a minor actinide-bearing fuel pin

Minor actinides are the main contributors to medium- and long-term radiotoxicity and heat production in spent nuclear fuels. Research efforts are currently ongoing to explore different options to dispose of such radionuclides, e.g., their burning and transmutation in fast reactors within mixed-oxide fuels. The MYRRHA sub-critical reactor is one of the future facilities with envisaged burning and transmutation capabilities. This work assesses the thermal-mechanical performance of homogeneous Am-bearing fuel pins both in the In-Pile test Section (IPS) position of the MYRRHA “Revision 1.8” core and under driver irradiation. The normal operating conditions of MYRRHA are considered, with a focus on the safety design limits and involving sensitivity analyses to evaluate the impact of increasing americium contents (in the range 0-5 wt.%) on safety-relevant simulation outcomes. The simulations are performed with the TRANSURANUS fuel performance code coupled with the SCIANTIX physics-based module for inert gas behaviour. They rely on a dedicated surrogate model for the helium source term during MYRRHA irradiation, accounting for the relevant contribution of the fuel americium enrichment, besides advanced models for the properties and behaviour of the specific pin materials. Specifically, models for Am-fuel thermal properties (thermal conductivity, melting temperature, specific heat) developed in Task 5.1 of the PATRICIA Project are used for the simulations. Moreover, high-fidelity boundary conditions (cladding outer temperature, axial coolant pressure) on the MYRRHA pins under IPS irradiation, provided by sub-channel analyses achieved within PATRICIA Task 5.4, are accounted for and their impact showcased on the fuel central temperature as a figure of merit. The analyses reveal the suitability and safety under irradiation of MOX fuels with low Am enrichments according to the current MYRRHA design.