Effect of the Surveillance Test Frequency of SDS1 on the Core Damage Probability

A new technique for analyzing the effect of testing on shutdown system (SDS) number 1 (SDS1) in Canadian deuterium uranium (CANDU) nuclear power plants is proposed. The effect of the test on the core damage probability is quantified using a Markov process model. The model is used to derive the effect of the test frequency on the unavailability and the spurious reactor trip probability. Two core damage scenarios are considered: one from a process failure with the unavailable SDS and the other from a spurious reactor trip. The Markov process model is then used with the core damage scenarios to analyze the effect of the test frequency on the core damage probability. The quantified core damage probabilities indicate that performing more frequent surveillance tests does not necessarily decrease the risk. In fact, there exists an optimal test frequency beyond which the probability of core damage starts to increase. This optimal test frequency is of significance in practice.