Modelling common cause failures of large digital I&C systems with coloured Petri nets

Abstract: The purpose of this study is the representation of Common Cause Failures (CCF) in large digital systems. The system under study is representative of a control system of a nuclear plant. The model for CCF is the generalized Atwood model. It can represent independent failures, CCF non-lethal for some system elements and CCF lethal to all. The Atwood model was modified to "direct" non-lethal DCC on certain parts of the system and take into account the different possible origins of DCC. Maintenance and repairs are taken into account in the model that is thus dynamic. The main evaluation results are probabilistic, the considered indicator is the probability of failure on demand (PFD). A comparison is made between the estimator of the PFD taking into account all the failures and the estimator taking into account only the detected failures.