The Self-Testing of a Solid State Safety System

An automatic, on-line self-test system is employed in the General Electric BWR/6 solid state Nuclear System Protection System (NSPS) control room cabinets to rapidly detect hardware failures and facilitate repair. Each of the four NSPS cabinets in the control room contains a microprocessor based selftest controller in whose memory are stored sets of input stimulii test patterns and expected output results. For each set of input patterns the expected and actual outputs are compared and discrepancies annunciated to the plant´s operators. These sets of test patterns comprehensively test all essential circuits and wiring within and between the NSPS cabinets such that the self-test system is able to determine the exact location of all failures in safety related hardware. The cabinets were designed to ensure that operation of and failures in the selftest system do not influence the correctness of the safety system´s outputs.