Reactor coolant refers to a fluid that is used in nuclear reactors to remove heat generated during fission. This fluid, usually water or a gas like helium, circulates through pipes surrounding the reactor core and absorbs the heat produced by the radioactive decay of materials within the core. The heated coolant then travels through heat exchangers where it transfers its thermal energy to another working fluid, such as steam, which can be used to generate electricity in a turbine generator set. By removing this heat, reactor coolants play an essential role in maintaining safe and stable operation of nuclear power plants.