Analysis of the Unavailability of I&C Functions Important to Safety in a Nuclear Power Plant

To optimize the proof intervall of a reactor limitation system the unavailability analysis has been carried out. First of all the relevant operation and failure behaviour of the 2-out-of-4 I&C system with high redundancy has been described by an analytical model. The maximal, minimal and average values of the unavailability are calculated. After that a Petri net model for describing the system behaviour has been developed. The results gathered by Petri net simulation are quite comparable with the analytical calculation.