Behavior of heat pipe materials for nuclear passive cooling system: A review on thermal performance, mechanical integrity, and radiation resistance

Heat pipes have emerged as reliable passive cooling devices in nuclear reactors and spent fuel pool systems due to their high heat transfer efficiency and safety properties. Their long-term performance is influenced by the behavior of the sheath and wick materials under thermal, radiation, and corrosive conditions. This review compares several key materials based on their thermal conductivity, mechanical integrity, radiation resistance, corrosion resistance, and fluid compatibility. Copper has excellent thermal conductivity; however, its performance in nuclear environments is affected by radiation damage and corrosion mechanisms, the severity of which depends on factors such as radiation dose, temperature, and water chemistry. Although copper is widely used in a variety of thermal systems, including electronics cooling, space heat pipes, and terrestrial applications, its use in nuclear heat pipes is generally better suited to low-temperature, low-radiation conditions, such as spent fuel pool systems, where degradation can be effectively managed. Stainless steel and nickel alloys exhibit balanced performance in radiation resistance, corrosion resistance, and mechanical strength, making them suitable for reactor applications. Meanwhile, titanium and refractory metals are suitable for high-temperature conditions and space applications, although limited by sensitivity to oxidation and cost. The synthesis results of various studies indicate that no single material is fully optimal, necessitating a multi-material approach. Therefore, strategies such as surface engineering and additive manufacturing are proposed to combine high thermal conductivity with radiation and corrosion resistance in next-generation passive nuclear cooling systems.