[Significance] Aiming at carbon neutrality, energy structure transformation and upgrading has become a trend for global energy system progress. Nuclear energy can effectively fill the power and heat supply gap during coal substitution. It has the advantages of a flexible layout, wide application, and insensitivity to climate change and the global market, which ensures national energy security. A heat pipe (HP) is a passive and efficient heat exchange element with a wide temperature range, stable and reliable performance, and high security. It is ubiquitously applied in the aerospace, energy and chemical industries, as a solar collector, for electronic cooling, and in other fields. HPs are irreplaceable in advanced nuclear energy with multi-domain, multi-scale, and multi-section applications. Therefore, existing studies on HPs must be summarized for advanced nuclear technology. [Progress] According to operation temperature, HP applications in nuclear technology are classified into three parts: nuclear power/propulsion systems, unclear safety facilities, and nuclear urban service. First, heat pipe-cooled reactors (HPRs) use alkali metal high-temperature HPs to passively export the core heat, which has the advantages of inherent safety and storage and transportation. Because of a long phase transition during startup and the unraveling alkali metal dynamic and heat transfer process in the steady state and the transitory state, the startup characteristic and heat transfer performance of alkali metal high-temperature HPs have been the difficult part of HPRs development. To adapt to different energy needs, the designs of HPRs ranging from kilowatts to megawatts and the corresponding thermoelectric conversion schemes have been proposed. HPRs will have broad prospects in aerospace, ship power, deep sea exploration, land-based power supplies and other fields. Second, with passive characteristics, an HP is a better technical choice for safety facilities. In nuclear power plants, separated HPs have been applied to passive heat removal systems, passive emergency core cooling systems, passive containment cooling systems, and passive spent fuel pool cooling systems. In nuclear spacecraft cooling, an HP space radiator composed of an HP and a heat sink is a more promising space radiator, having good thermal properties, temperature conversion characteristics, environmental adaptability, anti-debris impact performance, and anti-single point failure characteristics. In a thermonuclear reactor, HP is also used in first-wall cooling. Third, HPs are mainly used in waste-heat recovery and low-temperature heat transfer to improve energy efficiency and safety in nuclear industry applications and urban services. Researchers have developed several desalination systems based on HP systems and waste heat from steam power plants and generators. Districted heating and nuclear power generation, hydrogen production, and heating triple production systems are promoted and have become popular in China. Finally, challenges in HP performance, adaptive design in HPRs, and HP operation and maintenance were discussed. [Conclusions and Prospects] The HP is perfectly in line with the advanced nuclear safety design concept. Currently, although HPs are widely used in nuclear power/propulsion systems and reactor safety facilities, their practical applications in the nuclear industry and urban service remain relatively scarce, and there is almost no participation in the intermediate temperature segment. At last, we propose the prospects of advanced HP technology. © 2023 Press of Tsinghua University. All rights reserved.
