A Computationally Tractable Model for Spatially Resolved Nuclide Concentrations in Flowing Fuel Molten Salt Reactors

Depletion simulations of flowing fuel molten salt reactors commonly do not distinguish between in-core and ex-core regions. Instead, they either irradiate the entire primary loop while scaling the flux, or irradiate the in-core volume alone, which leaves some amount of fuel salt out of the simulation. Either approximation results in some level of inaccuracy in nuclide concentrations. Various methods account for the flow of fuel salt between spatial regions, but a major hurdle is the computational cost. This work investigates a spatially resolved method to account for flow and chemical removal has on concentrations of nuclides rapidly and accurately. Comparisons the impact are made in this work between a spatially resolved method, spatially unresolved scaled flux method, other work from the literature, and experimental data. These comparisons show that the scaled flux method is sufficient for modeling most nuclides unless there is a large spatially dependent loss term, such as a large ex-core removal rate. In such a case, a spatially resolved method is needed.