= Boiling water reactor
A <boiling water reactor> is a <nuclear reactor> in which water boils inside the reactor vessel and the resulting steam directly drives a turbine. Water serves as both coolant and <neutron moderator>. Moisture separators and dryers remove entrained liquid before steam reaches the turbine; a condenser and feedwater system return it to the vessel.<Boiling Water Reactors by the United States Nuclear Regulatory Commission>[Typical Boiling-Water Reactor, core-to-turbine and return path]{ref}
The heat balance makes its purpose concrete: in a simplified steady model, $\dot Q\simeq\dot m(h_{\mathrm{steam}}-h_{\mathrm{feedwater}})$, where $\dot m$ is the water mass flow and $h$ is specific <enthalpy>. With an illustrative enthalpy increase of $2\,\mathrm{MJ/kg}$, transporting $2\,\mathrm{GW}$ of heat requires approximately $1000\,\mathrm{kg/s}$. This is a thermal balance, not the electrical output, because the turbine cycle rejects heat to the condenser.
A <boiling water reactor> differs from a <pressurized water reactor>, which keeps its primary coolant liquid and transfers heat to a separate steam-producing circuit. Shutting down the chain reaction does not remove <decay heat>, so heat removal remains necessary after shutdown.
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