Approach to Inadequate Core Cooling Detection

Abstract

Historically, light water cooled reactors (LWRs) have heen designed with reliance on automatic protection systems to assure that the reactor is shut down and adequate coolant is provided to the core to prevent severe core damage under all design basis accident conditions. A combination of high pressure and low pressure safety injection systems are designed to replenish coolant lost from the reactor coolant system (RCS) for the entire spectrum of potential breaks in the reactor coolant pressure boundary. Design philosophy emphasized that protection systems should be redundant and highly reliable and should require minimal interaction with the plant operators. The latter consideration was based on a dominant concern for the large break loss of coolant accident in which the sequence of events is too fast to permit reliable diagnosis and response by the operator. Consequently, design attention given to accident monitoring instrumentation was generally limited to those instruments required to help the operator assess the effectiveness of long term core cooling in the recirculation mode after termination of an accident transient.