Heat pipe-cooled reactors: A comprehensive review of evolution, challenges, research status, and outlook

Amid the growing demand for sustainable and efficient energy solutions, Heat Pipe-Cooled Reactors (HPRs) have emerged as a promising innovation in nuclear energy, offering inherent safety, modularity, and high energy density. However, despite significant progress in HPR research, critical challenges still remain in system design, fuel enrichment, material performance, and heat transfer limitations. This review aims to provide a comprehensive overview of HPR development, systematically summarizing its evolution, key characteristics, and current research advances. First, a detailed timeline of HPR technology evolution is outlined to contextualize its current status. The concept and design principles of HPRs are subsequently introduced, with an in-depth analysis of challenges in core configurations, high-temperature heat pipes design, and energy conversion systems. Moreover, the latest advancements of HPR-related studies are reviewed, including fundamental studies, technological improvement, innovation designs and experimental validations. Finally, future research directions are identified, focusing on enhancing reliability, optimizing designs, and broadening application areas to address existing challenges and unlock the full potential of HPRs.