Thorium-based molten salt reactors (TMSRs) are known for enhanced safety, high efficiency, and sustainability. Deterministic safety analysis plays a crucial role in the safety assessment framework, especially when it comes to demonstrating the safety of designs for TMSR nuclear power plants. The RELAP5 code, originally developed for light water reactors, was modified to accommodate the unique characteristics of molten salt reactors, resulting in RELAP5-TMSR. For application in safety analysis reports used for licensing, analysis codes such as RELAP5-TMSR must undergo rigorous validation against experimental data, including separate effects and integral system tests.

Thus, RELAP5-TMSR is validated using experimental data from the direct reactor auxiliary cooling system heat exchanger (DHX) in the Nitrate Salt Natural Circulation Loop facility, considering its specific geometry and operating conditions. The maximum relative deviation between the simulated and experimental data was less than 0.3% for the nine thermocouples in the middle and at the outlet of the DHX, indicating a high level of concordance. The results demonstrate that RELAP5-TMSR is capable of accurately modeling and simulating key equipment with complex geometries and is well suited for the steady-state analysis and safety assessment of TMSR systems.