Safety and reliability aspects

Important operational aspects of instruments in the protective circuits of nuclear reactors are safety and availability, which may be considered under the term reliability. Basic reliability concepts are briefly surveyed. Failure rate is considered a more significant measure of performance than mean time between failures. The problem of lack of failure rate data of new equipment is noted and also the delay in obtaining practical fault rate data from highly reliable equipment with low rates of failure. The importance of considering environmental effects in the reliability of sensors is stressed. Prediction using Poisson distribution to deal with statistically rare events is considered appropriate. (U.K.)