The Heat Pipe Reactor Fire Mitigation and Suppression System from Los Alamos National Laboratory, transforms the heat pipes inside an alkali metal-cooled nuclear reactor from passive thermal conduits into active, sensor-driven fire defense components, giving designers of advanced small and microreactors a layered, automated safeguard against one of the most challenging hazards in their systems. By combining an inert gas buffer, a phase change material jacket, automated suppressant injection at multiple points and optional neutron-absorber dispersion into the reactor core, the system delivers redundant protection that responds within milliseconds of detecting fire-like conditions. This system enables advanced reactor developers to meet stringent safety expectations for remote, unattended and space-constrained deployments without redesigning the core architecture around bulky external suppression equipment. How it Works During normal operation, each heat pipe carries thermal energy away from the reactor core through the evaporation and condensation of an alkali metal working fluid, while valves connecting the heat pipe to external suppressant chambers remain closed. Temperature and pressure sensors continuously monitor the heat pipe reactor core and the valves near each heat pipe end, feeding data to a controller that compares readings against predefined thresholds. When a reading crosses the first threshold, the controller opens a valve and forces a fire suppressant material, typically a boron compound, into the interior of the heat pipe. If conditions worsen and a second threshold is crossed, additional valves activate to inject suppressant from the opposite end of the heat pipe, evacuate the working fluid through a dedicated valve and release suppressant into an inert gas chamber that annularly surrounds the heat pipe at the heat exchanger interface. Technical Description The system architecture centers on a heat pipe reactor core engaging a plurality of dual-ended or single-ended heat pipes, where both ends of each heat pipe extend externally of the core block so that suppressant can be introduced from either side of the core. A heat exchanger device sits at the heat rejection end of each heat pipe and defines an enclosed inert gas chamber that annularly surrounds the heat pipe, creating a physical gap between the alkali metal working fluid and any water-based cooling fluid. The chamber adds a second point of failure that must occur before incompatible fluids can interact, and the inert gas itself can serve as a blanketing agent for active flames. A layer of phase change material, typically a salt that doubles as a Class D fire extinguishing agent and alkali metal fire retardant, is disposed on the outer surface of the gas chamber, partitioned by fin-bearing components that both store thermal energy and improve heat transfer to the surrounding cooling fluid. The active suppression and shutdown logic is governed by a controller comprising memory…