Analysis of heat pipe cooled reactor startup characteristics by multi-physics coupling simulation based on MOOSE framework

A Heat pipe reactor utilizes heat pipes to transfer fission heat from the reactor core, providing a high level of passive safety and thus representing a promising application for micro-reactors. The startup process of a heat pipe reactor is characterized by a wide range of temperature variations and a dominant expansion reactivity feedback, while also necessitating consideration of the startup issues of the frozen alkali metal heat pipes, which adds significant complexity. To analyze the characteristics of the startup process of the heat pipe reactor, this study couples the MOOSE framework with the two-dimensional high-temperature heat pipe numerical simulation code KMC-HPs, to conduct a high-precision multi-physics coupling simulation study of the nuclear-thermal–mechanical dynamics, and the accuracy and feasibility of this coupling method were validated through simulations of the ground prototype reactor KRUSTY. The analysis indicates that the heat transfer characteristics during the startup process of the heat pipes determine the temperature distribution within the reactor core. Initially, the heat transfer capability of the heat pipes is limited, resulting in a significant temperature difference. However, as the temperature rises and continuous vapor flow occurs in the evaporation section of the heat pipes, the heat transfer capability improves, leading to a more uniform temperature increase across the core with a smaller temperature difference. Mechanical analysis reveals that large thermal stresses occur at the edges of the contact surfaces between the heat pipes and the core, although these stresses remain well below the material’s yield limits. This paper elucidates the multi-physical characteristics of the heat pipe reactor startup process from a numerical simulation perspective, and the developed coupling framework provides high-precision validation for the conceptual design of heat pipe reactors.