Fault Detection and Isolation in a Nuclear Reactor

Abstract

A fault detection and identification methodology has been developed for sensor and plant component validation, with special emphasis on applications to nuclear powerplants. The methodology is particularly suitable for on-line fault diagnostics and does not rely on detailed knowledge of sensor and plant noise statistics. The algorithm has been computer coded for real-time applications and validated by on-line demonstration in an operating nuclear reactor. ARIOUS methods for fault detection and identification (FDI) of sensors have been reported in the literature.14 However, current practice in the nuclear industry is restricted to a few rather rudimentary techniques such as like-sensor comparisons, limit checking, auctioneering, etc. Although these techniques generally serve to improve system safety, availability, and operability, some limitations, such as the inability to identify gradual drifts and to detect common mode failures, significantly curtail their effectiveness. (If two or more elements fail identically, due to a common cause, the failure is called common mode.) The above limitations can often be circumvented with the aid of advanced computer-aided diagnostic techniques that have been developed for aerospace systems. In addition to improvement of plant availability and operability, these techniques promise to aid plant operators in making valid and timely decisions, thereby enhancing plant safety. The FDI methodology reported in this paper is developed on the basis of the parity space concept,3 which takes into account inconsistencies among all data sources. Any malfunctioning sensors are isolated by sequential checking until a relative consistency among the remaining (normal) sensors is achieved. This methodology does not require a detailed knowledge of sensor and plant noise statistics. Error bounds that are allowed for normal operation of the sensors are sufficient for making decisions. Real-time computer codes have been developed for detection and identification of failed sensors and plant components. As a proof of concept, these codes were verified by demonstration of on-line detection and identification of sensor failures in the 5 MW(t) nuclear reactor presently in operation at MIT, Cambridge, Mass.