evelopment and Preliminary Validation of an Efficient Alkali Metal Heat Pipe Analysis Model for Long Time Transient Simulations

Heat pipe cooled reactors are ideal for space power, military, and marine energy applications. A key aspect in the safety analysis of the heat pipe cooled reactor is the efficient modeling of heat pipes and their coupling with the solid reactor core. When a heat pipe begins in a cold state, the working substance within the vapor core transitions through several stages, moving from rarefied vapor flow to continuous vapor flow. This progression complicates the analysis of transient heat pipe behaviors. This work aims to develop a core analysis model for the heat pipe cooled reactor based on the coupling of ANSYS/Fluent and a newly developed transient heat pipe analysis code HePIRE-HA. A compressible two-equation model for the heat pipe vapor core is developed and solved alongside the heat pipe wall and wick through a fully-implicit solution scheme. A comprehensive interface tracking scheme has been developed to effectively manage the transition from a rarefied vapor state to a continuous vapor state. This transition scheme is demonstrated to work reasonably well and shows great efficiency. The coupling of ANSYS/Fluent and HePIRE-HA is achieved through the User Defined Function (UDF) capability of ANSYS/Fluent. A series of verification and validation studies is conducted to assess the performance and capabilities of the newly developed model. The results highlight that the new coupling model effectively predicts the transient response of the reactor core, making it a trustworthy tool for designing and ensuring the safety of the heat pipe cooled reactor.