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• Transient analysis code is developed and validated for heat-pipe-cooled reactor system. • Multi-node thermal resistance network coupling closed-form solution is setup for heat pipe heat transfer analysis. • Safety analysis is performed on KRUSTY under three postulated accidents. The heat pipe cooled reactor is a type of nuclear reactor system that utilizes heat pipe technology for core cooling. It characterizes in high reliability, compactness and modularity, making it suitable for deep-space exploration, and other applications. To gain a deeper understanding of the system's dynamic behavior and evaluate its performance, a transient analysis code is developed with the reactor point kinetics model, core heat transfer model, improved heat pipe startup and operation models, and Stirling engine model established. The reliability and accuracy of the models and code are validated by comparing the simulation results of the various models with experimental data based on heat pipe startup, operation experiments and KRUSTY test results. The safety limits are developed for the KRUSTY and this paper conducts the transient analysis on KRUSTY and evaluates the safety performance of KRUSTY in accidents including the unexpected shutdown of the Stirling engine, reactivity insertion accident (RIA), and combined partial Stirling engine failure and RIA accidents. KRUSTY shows good thermal stability and controllability under hypothetical accident conditions where no safety limit is exceeded. [ABSTRACT FROM AUTHOR]

• An additional force model is implemented in 3-D numerical simulation code. • Thermal-hydraulic analysis is performed on the HP-cooled MSR core under ocean conditions. • Improved flow and heat transfer performance can be obtained for the core in rolling conditions. The Heat-Pipe-cooled Molten Salt Reactor (HP-MSR) has been seen as a promising potential candidate for powering ocean vehicles with long endurance while reducing the carbon emissions in the shipping industry. By combining the operation merits of HPs and MSRs, this type of reactor can characterize no need for fuel fabrication, inherent safety, short waste lifespan, and elimination of in-core thermal stress issues, which is typical in other HP-cooled Reactors. In the ocean application, the reactor vessel, embedded in the ocean vehicle, is often led to continuous motion due to the wave action. This motion significantly influences the flow and heat transfer characteristics of liquid fuel within the reactor core. This paper performs numerical simulation on the thermal-hydraulics of the reactor core of HP-cooled MSR under the influence of ocean conditions through computational fluid dynamics (CFD) code. The ANSYS FLUENT is implemented to develop an additional force model to simulate motion conditions. Through exploring changes in the fuel flow field, heat transfer, and heat pipes, the evaluation of the HP-cooled MSR performance in ocean conditions is conducted. With the temperature gradient decreasing from 57 K to 14 K in the rolling motion condition, the temperature distribution becomes more uniform. The average temperature of fuel from the static to motion condition only drops 8.1 K, leading to less thermal stress on the core vessel and more balanced heat pipe power output without bringing abrupt temperature-related reactivity change. The tangential movement with vortex pairs in gaps of heat pipes predominates the flow field in the rolling motion condition. It mixes the fuel salt and strengthens the heat transfer of heat pipes. This implies that the basic design and operation of the MSR are robust when situated in an oceanic environment. On the other hand, this study also reveals that the surface heat flux of heat pipes at certain positions within the core is considerably influenced by the fuel salt flow. This means that while the overall reactor performance remains stable, specific components within the system may experience more significant impacts due to the ocean motion. [ABSTRACT FROM AUTHOR]