Review of Passive Heat Removal Strategies for Nuclear Microreactor Systems

Microreactors, or very small, transportable or mobile nuclear reactors with a capacity of less than 20 MW(thermal), are being developed to provide heat and power for myriad applications in remote areas, military installations, emergency operations, humanitarian missions, and disaster relief zones. A wide variety of reactor types are under consideration, including sodium-cooled fast reactors, molten-salt reactors, very high-temperature gas reactors, and heat pipe reactors. One issue common to all microreactor designs is the need to remove heat from the core. The objective of this paper is to identify a spectrum of diverse approaches to thermal management that can be used develop advanced, high-performance heat removal systems to further enhance the expected performance of a 1- to 20-MW(thermal) nuclear reactor. The focus here is on concepts that can provide a passive means of heat removal and are new to nuclear reactors. Different types of passive heat removal strategies for microreactors are examined, including latent heat-transfer devices, such as various types of heat pipes, natural convection and conduction-radiation cooling, and other thermal devices, such as thermoelectrics and thermoacoustics, that can be used to provide power for auxiliary cooling. Many of these concepts have already been fielded in renewable energy systems. Concepts at different stages of technical maturity are outlined to present ideas that can push the boundaries of thermal management in present-day nuclear technology. Practical considerations relative to the integration of these concepts into nuclear systems are given.