Reactor Protection System

Abstract

In many plant transients, the reactor control system acts to return the reactor to its normal operating condition. However, the more severe transients require that the reactor be shut down by the reactor protection system (RPS). The RPS is designed to provide a highly reliable means of achieving reactor shutdown in the event of one of these severe transients by monitoring certain parameters; a means for the operators to manually scram the reactor from the control room or from the remote shutdown panel is also provided. Plant technical specifications are developed for the reactor scram system instrumentation to assure its operability and accuracy by means of various surveillance requirements. This article provides a high-level description of typical RPS designs found within US commercial nuclear power plants. To meet regulatory requirements, the RPS is comprised of two redundant, identical trains that are physically and electrically independent. Inputs into this system are derived from various sensors located both inside and outside of the primary containment building. The RPS contains a logic section that requires instrumentation input from more than one instrument channels to generate a signal to automatically shutdown the reactor. This prevents a failure in a single instrument channel from shutting down the reactor. Automatic shutdown of the reactor is accomplished by removing electric power from a device that then passively inserts the control rods into the core. Special consideration in RPS design is given to the Anticipated Transient Without Scram event. In response to failures of reactor scram systems at operating plants, additional regulatory requirements were mandated by the US Nuclear Regulatory Commission to further assure that the reactor could be shutdown safely.