Some Aspects of Reactor Safety Systems

Ostensibly, reactor safety systems compare nuclear and process measurements with predetermined operating limits and initiate automatic warning and protective functions. The importance of system engineering and establishing the levels of safety and availability required for reactor installations are discussed. Safety system logic schemes, operator confidence in the equipment, and protection against the effects of chance failures in safety circuits are considered. The authors suggest that existing reactor safety systems should be examined in light of the philosophical, logical and circuit considerations. Possible component failures should be evaluated on a system effects basis to determine the need for the automatic annunciation of these failures and to provide a measure of the system´s capability of providing the required automatic corrective actions and protection against unnecessary plant shutdowns. Since reactor safety systems are a combination of different circuits in which the analog to digital interface is not always displayed, failures are not necessarily annunciated and a cascading of failures is possible. The development of the basic philosophy for these systems is a complex process employing broad and complex technical considerations.