Focal-point protection system for power reactors

The development of power-reactor electrical protection circuits and current design practice are briefly discussed, and the performance of these systems is considered in relation to ideal safety concept requirements. A new focal-point protection design is proposed for emergency shut-down. This offers a basically simple, highly reliable, solid-state protection system and provides continuous one-out-of-one tripping for all trip facilities. Continuous cycle testing of all trip circuits, from the primary trip amplifier or transducer to the hold-circuit output, is carried out automatically. The detection of a trip-unit fault, or malfunctioning of the interrogator/responder circuits, produces an audible warning and visual indication of the equipment involved, and at the same time isolates the faulty circuit, without prejudice to the in-line protection, until repairs have been effected. An analysis of focal-point system protection integrity is made. It is demonstrated that any significant in-line and fail-danger component fault will be detected, located, removed and replaced within 3 ms and any fail-safe component fault will be detected and removed from the in-line protection circuits within 20 ms of occurrence without producing a false reactor shut-down trip. The design of the trip-unit equipment is discussed.