Redundant reactivity control system

Abstract

A redundant reactivity control system, operating in conjunction with other systems in a nuclear power plant, to mitigate the potential consequences of an anticipated transient without scram event, is described. The invention interfaces to a boiling water nuclear reactor with the reactor's neutron monitoring system, standby liquid control system, control rod drive system, reactor recirculation system, reactor water clean-up feed water control system, and control room and local panels. Two divisionally separated control panels include associated detection and actuation logic and the necessary interface logic to other systems to perform the specific functions in response to an anticipated transient without scram event. Each separate division includes two identical channels. Actuation of any associated reactor system by the invention requires the agreement of the two channels within a division. A one channel indication actuates appropriate annunciators and alarm equipment to notify plant personnel of a possible system fault. Each divisional panel receives independent analog signals from high dome pressure transmitters, reactor low water level transmitters, and average power range monitor down-scale trip units. These inputs are combined and processed by solid state logic circuits to produce output actuation signals for interfacing systems. The present invention actuates a stand-by liquid control system to inject sodium pentaborate into a reactor core if an anticipated transient without scram event is sensed. Such insertion is made only after all other means of mitigation have not been able to reduce radioactivity, i.e. control rod insertion, recirculation pump trip, etc. The present invention provides a high degree of reliability and adds further levels of nuclear plant safety, while avoiding the possiblity of inadvertent stand-by liquid control actuation.