ENEL position on digital control and protection systems for new generation nuclear power plants and related safety implications

The present paper briefly describes the architecture of the C and PS and its safety implications and solutions ENEL intends to adopt in designing the new NPPs. This architecture is based on extended use of Digital Technology and Human Factor techniques, with computerized control rooms provided of software driven work stations, connected to the field through a hierarchical multi-level network system. The same approach is being adopted also for the dual-cycle thermal plants presently under construction and therefore the design of I and C and M-MIS will profit of the experience that will be gained in this field in the coming years. However, despite proper design and operation, software based systems maintain a high vulnerability to latent faults affecting mainly the software. ENEL approach to cope with digital system faults is based on both the principles of high reliability: fault avoidance and fault tolerance. Fault avoidance is pursued mainly by adopting a very systematic and thorough design process, stringent requirements on hardware component reliability and severe and complete software Q and A and V and V. Fault tolerance is pursued by redundancy, segmentation of control and protection functions, physical separation among redundant channels, environmental compatibility. Last but not least, a diverse protection system for the most important prevention and mitigation functions is considered, based on a simple and proven conventional technology. (author). 4 refs, 5 fig, 2 tabs