CONTROLLING OF NUCLEAR REACTOR FEED WATER

PURPOSE:To change a setting point of nuclear reactor water level at tripping occasions of a recirculation pump or a driving motor of an MG set to avoid a rising of a nuclear reactor water level, and to prevent a scram by providing a suppressing circuit for water level rising at a specific feed water system and a comparator. CONSTITUTION:In case of a trip of a recirculation pump (A) or (B), and an opening signal (A) or (B) of a PLR breaker is output instead of no turbine tripping signal nor quick closing signal of a CV being output, a changing signal of water level setting point to lower the nuclear reactor water level is output to a comparator 11 from a suppression circuit 18 of water level rising, in order to prevent the water level rising caused by an excess feed water. A flow rate demanding signal (e) to be fed to a feed water system 14 is a flow rate demanding signal to decrease a feed water flow rate along with a water level rising of a conventional system and a mismatch flow rate between a main steam flow rate and a feed water flow rate, added with a changing signal of water level setting point from the suppression circuit 18 of water level rising to lower a water level setting point, therefore, the feed water flow rate can be more quickly decreased than a conventional system thus the mismatch flow rate decreases.