Steady-state and transient thermal-hydraulic analysis for high temperature heat pipe cooled reactors

Heat pipe-cooled reactors (HPR) have become increasingly popular in recent years due to their good thermal conductivity and adaptability. The steady-state and transient characteristics of the high-temperature alkali heat pipe, which is the primary component of the HPR, are crucial for ensuring the safe operation of the reactor. In this study, a CFD model was established to evaluate the steady-state and transient characteristics of heat pipes. Heat pipes using potassium (K), sodium (Na), and lithium (Li) as a medium were examined and the effect of heating power was analyzed under steady-state conditions. The results indicated that Li had the highest operating temperature, followed by Na and K. However, the thermal resistance was the lowest for Li and highest for K. The wall temperature showed a gradual decrease. As the heating power increased from 3 kW to 7 kW, the vapor temperature increased from 1005 K to 1109 K. The axial temperature difference was only 5 K, indicating that the heat pipe had good isothermal properties. Moreover, the startup method and heat pipe failure were analyzed under transient conditions. Compared to the uniform power rise, the phased power start method ensured the heat pipe started up successfully. Case1 has the shortest startup time, with a successful startup time of 1800 s. Single heat pipe failure and fuel assembly failure resulted in local temperature increases, but away from the failure areas were rarely affected. Failure in startup is 63 K higher than steady-state failure, which deserves more attention. Moreover, it is important to note that failures during startup resulted in a temperature increase of 63 K higher than steady-state failures, which warrants further investigation and attention.