Heat pipe reactors rely on long, thin tubes to transfer heat away from the reactor core without any pumps or moving parts. The heat from the core evaporates a working fluid (typically liquid sodium) inside the pipes. The sodium vapor travels from the core to a heat exchanger where it condenses back to a liquid. The liquid then flows back to the core. The collected heat from the condensing vapor is used for electricity production or other applications. This effective cooling system can significan