What is Heat Pipe Reactor?

A nuclear reactor design that uses sealed heat pipes filled with a working fluid (typically sodium or potassium) to passively transport thermal energy from the reactor core to a heat exchanger, eliminating the need for coolant pumps and piping loops.

What category does Heat Pipe Reactor belong to?

Heat Pipe Reactor is a reactor-types concept in nuclear energy and SMR technology.

Heat Pipe Reactor — Nuclear & SMR Glossary

A heat pipe reactor is a nuclear reactor concept that uses sealed heat pipe elements to transfer thermal energy from the reactor core to a power conversion system without any pumped coolant loops, moving parts, or active circulation systems. Each heat pipe is a sealed tube containing a working fluid (typically sodium, potassium, or sodium-potassium alloy) that evaporates at the heated (reactor core) end, transports the vapor to the cooled (heat exchanger) end through the pipe's interior, condenses and releases its latent heat, and returns to the hot end through capillary wicking action in the pipe wall structure. This entirely passive heat transport mechanism eliminates reactor coolant pumps, intermediate heat exchangers, and the complex piping systems that characterize conventional reactor coolant systems, dramatically simplifying the reactor design and enhancing reliability.

Westinghouse's eVinci is the most prominent heat pipe reactor in development. The eVinci is a 5 MWe (13+ MWth) solid-core heat pipe microreactor designed for remote communities, defense installations, and industrial applications. The reactor core consists of a solid metal matrix with embedded heat pipes and fuel elements, creating a monolithic structure with no circulating coolant. Westinghouse is pursuing a 1/5-scale test at the NRIC DOME facility at Idaho National Laboratory as early as 2026, followed by full-scale demonstration in the mid-to-late 2020s. Penn State University partnered with Westinghouse in March 2025 for prototyping and educational deployment, signaling the technology's maturation beyond the conceptual stage. The eVinci targets factory refueling, meaning entire reactor modules would be shipped back to the factory for core replacement rather than performing on-site fuel handling.

The heat pipe reactor concept originated with the KRUSTY (Kilopower Reactor Using Stirling Technology) project, a joint NASA/DOE experiment that successfully demonstrated a heat pipe fission reactor at the Nevada National Security Site in 2018. KRUSTY proved that heat pipe cooling could sustain stable reactor operation, and its success catalyzed commercial interest in the concept. The heat pipe architecture is particularly well-suited to microreactor applications because it scales efficiently at small power levels, provides inherent redundancy (the failure of individual heat pipes does not compromise core cooling, as neighboring pipes compensate), and enables a sealed, transportable reactor unit with no on-site fluid management requirements. BWXT is also developing heat pipe microreactor technology for military and defense applications under the Project Pele program for the Department of Defense.