DEVELOPMENT OF A FAIL-SAFE CONFIGURATION AND AN ONLINE DIAGNOSIS METHOD FOR THE MICROPROCESSOR-BASED REACTOR PROTECTION SYSTEM

The microprocessor-based reactor protection system (RPS) combining a fail-safe configuration and an on-line diagnosis is presented. This combination further enhances the maintainability and reliability. The signal processing unit which judges the scram action has fail-safe and diagnosis functions. The load driver which drives the scram pilot valves is diagnosed in an on-line state. A failure in any component of the RPS which is insured a majority voting function is by-passed. The failed component is repaired based on the results of an on-line diagnosis and a fail-safe action. A latch circuit is needed to hold a scram action. A configuration of the latch circuit which can fulfill the fail-safe function and its quick response has been proposed. An on-line diagnosis method for the load driver has been developed in which the RPS functions are not interfered with, even if a single failure occurs in the diagnosis circuits. A diagnosis circuit checks a switching element which is a component of the load driver. The test pulse that is outputted from the diagnosis circuit forces the switching element to the open-state rapidly without activating the scram pilot valves. The rapid execution of the fail-safe function and the on-line diagnosis of the load driver was validated by experiments that simulated failures.