The realization method is presented for a logic configuration of the reactor protection system (RPS) for BWRs which enhances their reliability. Higher reliability requires a majority voting logic even when a single logic component has been bypassed. Furthermore the load driver of the RPS on the output side must actuate two separate operation objects. To fulfill the above conditions, a general realization of the 2-out-of-4 logic with a minimum hardware component is proposed. Then, the structure of the microprocessor-configured RPS employing this logic is presented. The reliability of the above RPS is evaluated by computations. The results show that the average frequency of improper operation is less than that with the conventional 1-out-of-2-twice logic under the conditions that the repair rate is 0.1 and the failure detection rate is above 92%. The average probability of failure to operate is reduced by two orders of magnitude under the above conditions.
