Reactor Physics Benchmark of the First Criticality in the Molten Salt Reactor Experiment

The deployment of molten salt reactors requires validation of the computational tools used to support the licensing process. The Molten Salt Reactor Experiment (MSRE), built and operated in the 1960s, offers a unique inventory of experimental data for reactor physics benchmarks. The first benchmark based on the MSRE appeared in “The 2019 Edition of the IRPhEP [International Reactor Physics Experiment Evaluation Project] Handbook.” The benchmark refers to the first criticality experiment at zero power, stationary salt, and uniform temperature with ²³⁵U fuel. Simulations carried out for the developed benchmark model with the Monte Carlo code Serpent and ENDF/B-VII.1 cross-section library found that the calculated neutron multiplication is 1.02132 (±3 pcm) and that the combined bias of the model and experimental uncertainty is below 500 pcm. Such discrepancy between the experimental and calculated k_eff is not uncommon in benchmarks for graphite-moderated systems. The model created through this effort paves the way to additional benchmarks targeting reactor physics quantities of interest beyond multiplication factor.