Numerical simulation of a small high-temperature heat pipe cooled reactor with CFD methodology

Heat pipe cooled reactor is a new type nuclear reactor system designed for unconventional application fields, especially in deep space exploration, planetary surface power plants, and in decentralized electricity market. Heat pipe with alkali metal working fluid and porous wick is considered to be an ideal cooling method of small and special purpose nuclear reactors. In this work, a CFD model is established to simulate the heat transfer characters of a high temperature heat pipe, consisting of three parts: heat pipe wall, wick and vapor space. Commercial software including user defined functions (UDFs) is adopted to obtain the temperature and flow field inside the heat pipe. Validation of methodology is carried out with experimental data, proving that the calculation model is capable simulating the thermal-hydraulics characteristics of potassium heat pipes. On this basis, the heat pipe CFD model and methodology are applied to an originally designed 20kWt small heat pipe cooled reactor, consisting of a reactor core, heat pipes, a static conversion system, and heat removal system. The 1/6 reactor is 3-dimensionally simulated to analyze the thermal behaviors under steady-operation state and heat pipe failure accident conditions, which bring safety threat to reactor core. Under steady operating condition, the heat pipes show well isothermality and the temperature distribution satisfies the limit of materials, verifying the rationality of the design scheme. When part of the heat pipes fail, it causes a local high temperature area in the active zone, requiring the heat removal system to feature enough safety margin to take the fission heat away from reactor. This work provides reference in heat pipe cooled reactor design, as well as a CFD method in simulation of heat pipe with alkali metal working fluid.