This report outlines the progress of Idaho National Laboratory (INL) in improving the fidelity of the multiphysics model of the Microreactor Applications Research Validation and Evaluation (MARVEL) reactor developed in FY24. The multiphysics model firstly developed in FY24 leverages three single-physics models coupled via the MOOSE’s MultiApps and Transfer systems. The first single-physics model, that functions as the driver application, leverages Griffin to model the neutron transport in the core through the discontinuous finite element (DFEM) discrete ordinates solver (SN). The second single-physics model uses BISON to compute the solid temperature in the reactor. Finally, the System Analysis Module (SAM) was used to model the flow of the sodium-potassium eutectic in the primary loop. In this report we detail the following improvement and enhancements: • An updated mesh leveraging the latest feature in the reactor module (see Section 3.1.). • Verification of NEAMS neutronic models against reference MCNP benchmarks (Section 3.2.). • Enhanced representation of material properties in the solid heat transfer model (Section 3.3.). • Development of a thermal-hydraulic sub-channel model to capture NaK temperature distributions (Section 3.4.). Future work will focus on leveraging these improvements to simulate selected transient scenarios, including a reactivity insertion accident.
