Attempt to evaluate functional diversity employed in a reactor protection system

The ability of functional diversity to reduce the probability of common cause failures is evaluated. An emergency core cooling system (ECCS) in a reactor protection system is used. The evaluation is conducted by the comparison of three different system architectures: configuration 0, ECCS without functional diversity; configuration 1, ECCS with functional diversity, although without functional separation; and configuration 2, with functional diversity and separation. The failure logic of each configuration is presented as a fault tree. The results of the analysis indicate that the functional diversity has a potential to reduce the probability of a system failure, provided that the proportion of common cause failures is the same for all configurations.