Analysis of synergistic transport characteristics and selection of key nuclides for insoluble fission products in molten salt reactors

In liquid-fueled Molten Salt Reactors (MSRs), the non-uniform distribution of insoluble fission products (IFPs) significantly affects source term characterization, decay heat evaluation, and reactor safety. However, the single-atom transport assumption for IFP migration becomes invalid under high-power operations due to significant particle agglomeration. To clarify the relative importance of IFPs across various physical effects and alleviate computational bottlenecks in multiphysics simulations, this study evaluates the evolution characteristics of IFPs in a 150 MWth MSR under a conservative bounding accumulation assumption. By quantitatively screening four macroscopic physical parameters—mass deposition, radioactivity, decay heat, and core neutron absorption—using a hybrid cutoff criterion, this study reduces hundreds of dynamically evolving isotopes to a core inventory of 24 key nuclides. This reduction preserves over 95% of these original system's core physical features characteristics while significantly minimizing computational cost. Analysis of this reduced inventory reveals several critical transport phenomena: First, the macroscopic deposits are driven by a primary framework composed of high-yield, long-lived nuclides (primarily Mo, which accounts for >40%, alongside Ru). Second, a significant disparity between mass and activity/decay heat is observed, wherein trace high-risk nuclides (such as 95 Nb, 103 Ru) undergo coupled transport exclusively through attachment to these Mo Ru particles. Third, from a neutronics perspective, the spatial redistribution of long-lived solid poisons ( 103 Rh, 99 Tc) driven by particle migration induces non-negligible positive reactivity perturbations. Furthermore, decay chains (e.g., 95 Nb 95 Mo, 103 Ru 103 Rh) tightly couple early-stage thermal and safety issues with medium-to-long-term multiphase deposition and neutronics. In conclusion, the IFP transport characteristics and the 24-nuclide benchmark inventory established in this paper provide physically self-consistent inputs for future high-fidelity multiphysics coupled simulations, online purification system design, and surrogate material selection for non-radioactive experimental loops.