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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.

Newly built and modernized older nuclear power plants are equipped with digital I&C systems. However, currently there is no specific guidance internationally agreed for modeling of digital I&C systems in PSA. Thus, the OECD Nuclear Energy Agency (NEA) Committee on the Safety of Nuclear Installations (CSNI) 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 different modeling approaches and identify possible methods and issues for further development. A simplified boiling water reactor design equipped with digital features is used as a common reference plant for the task. Each participating country develops its own PSA model based on the plant description. Through comparison, different approaches to account for e.g. software reliability, fault-tolerant techniques, and network communication in the PSA will be explored. Nine countries are currently participating in the task. The planned duration for the task is 2017-2020. This paper describes the efforts done so far and presents preliminary results and insights.

The overall objective of the OECD Nuclear Energy Agency (NEA) CSNI (Committee on the Safety of Nuclear Installations) Working Group on Risk Assessment (WGRISK) is to permanently enhance the understanding of Probabilistic Risk Assessment (PRA, synonymously used for PSA) and facilitate the use and application of probabilistic approaches as an important tool for nuclear safety assessment. WGRISK therefore carries out activities to exchange risk related information between PRA experts in member countries and to advance the use of this tool for improving safety. The following WGRISK activities are currently ongoing: The task “Human Reliability Analysis in External Events PSA – Survey of Methods and Practice” close to completion, the task “Status of Site Level PSA (including Multi-unit PSA) Developments” ongoing in its second phase, the joint task of WGRISK and the NEA Database Projects on the “Use of OECD/NEA Database Project Operating Experience Data for Probabilistic Safety Assessment”, where a common Workshop took place in spring 2018, and the task “Development and Comparison of Digital I&C Modelling Approaches for PSA (DIGMAP)”started most recently in 2017. Three further tasks are close to completion, the report on “Use and Development of PSA in Member and Non-member Countries” being updated nearly every five years and updates of two WGRISK Technical Opinion Papers (TOPs) on Fire PSA and Seismic PSA highlighting the actual status of PSA for these two types of hazards.