Development and validation of thermal network-based transient heat pipe analysis code incorporating melting/solidification effects

Heat Pipe-cooled Microreactors (HPMRs) are emerging as a sustainable solution for off-grid power. The multiphysics simulations are required for the safety analysis of HPMRs, where the modeling of transient phenomena within alkali metal heat pipes is important for cooling capacity. This study introduces SNUHTP, a transient heat pipe analysis code developed based on a thermal resistance network model. The melting/solidification effect of the working fluid, which influences the startup and shutdown behavior, was modeled through an effective heat capacity method. The code underwent transient verification against analytic solutions of the 1D Stefan problem and a lumped heat pipe model. Steady-state validation used sodium heat pipe experimental data, showing good agreement. Transient validations on a water heat pipe and the SAFE-30 sodium heat pipe module test were also conducted. Both cases matched the experiments well. Especially in the sodium heat pipe, the latent heat effect resulted in a delay in temperature rise. Additionally, an OpenFOAM-SNUHTP coupled calculation was performed on the sodium heat pipe for the realistic modeling of adjacent structures. The validations of SNUHTP demonstrated its capability to predict transient behavior in heat pipes, including frozen startup.