An international joint research to explore the method for Digital I&C reliability assessment: OECD/NEA DIGMAP

These days, new NPPs are designed with digital I&C systems for operating as well as safety critical functions. Analogue I&C systems at operating NPPs are also replaced with digital I&C systems, e.g. during back-fitting to increase the operating life of the plants – due to obsolescence, it becomes difficult to continue using analogue systems. This shift entails the adoption of new digital specific features. From a safety point of view, the potential risk caused by the new features needs to be analyzed in an appropriate framework to ensure the dependability and safety of the entire NPP. However, at present there is no agreement on PSA modeling methods of the newly adopted digital features. In this context, the OECD Nuclear Energy Agency (NEA) CSNI (Committee on the Safety of Nuclear Installations) Working Group on Risk Assessment (WGRISK) initiated a task called “Digital I&C PSA – Comparative application of DIGital I&C Modeling Approaches for PSA” (DIGMAP) in July 2017. The objective of the task is to compare the various approaches of PSA modeling for the new features in Digital I&C systems, and identify recommendations on preferred modelling methods and issues for further development. Currently, each participating country has developed their own PSA model based on a common reference plant description. This paper describes the task progress made so far and presents preliminary results and important assumptions of each participant country before reaching a final consensus on general conclusions.