Auxiliary feedwater

Auxiliary feedwater is a backup water supply system found in pressurized water reactor nuclear power plants (PWRs). This system, sometimes known as Emergency feedwater, can be used for shutdown the reactor, if normal feedwater to the steam generators fails to work. It works by pumping water to the steam generators from reserve tanks or a larger body of water (e.g. lake, river, or ocean) to remove decay heat from the reactor. Often, but not always, the PWRs are equipped with motor driven aux feedwater systems (MDAFWs) and as a diverse mean as well turbine driven aux feedwater systems (TDAFWs), that take their drive not from electricity, but from the steam in the normal secondary side steam circuit of the plant. In difference to the ECCS-system for LOCAs, the auxiliary feedwater system doesn't inject directly into the reactor core, it cools in an indirect manner by cooling the primary circuit with the reactor via the steam generators.