Despite the advantages of using Bayesian networks for probabilistic risk assessment, adoption in practice has been limited due to the lack of realistic, facility-scale studies. Scaling up from systems to facility-level safety assessments poses challenges in (i) integrating external hazards and their cascading effects, and (ii) resolving non-homogeneity of various technical and human reliability models. The novelty of the study is in formalising risk integration using Bayesian networks, at facility scale, and demonstrating its effectiveness in addressing associated challenges. A Bayesian network-based multi-hazard risk framework is introduced and demonstrated for a nuclear power plant subject to flooding and earthquake hazards, capturing dependencies among hazards and consequences. Individual reliability models – conventionally extraneous to facility-wide risk models – are included as subnetworks by using Bayesian network-based surrogate models for technical systems and a Bayesian networks approach for human reliability modelling. Two approaches are used for subnetwork integration – object-oriented and unified Bayesian networks. The unified approach allows for prediction, diagnostics and inter-causal reasoning since Bayesian inference is bi-directional. Conversely, in the object-oriented approach, diagnostics are limited to within individual subnetworks and as a consequence the model can potentially neglect dependencies between objects. However, the object-oriented model requires only 50 % of the computational memory and consumes less than 25% of the runtime as the unified network, while improving visual clarity of the risk model. The model reveals key insights – for example, variations in operator stress or available response time during a hazard event can result in up to a 77 % change in top event probability – demonstrating its effectiveness in capturing critical relationships in complex, facility-scale risk scenarios. These findings can be used to suitably allocate resources towards risk mitigation and plant safety management.

Eighteen academic, research and industrial European institutions from Slovenia (GEN, JSI), Croatia (APOSS), Italy (ENEA, UNIPI), France (CEA, BRGM, IRSN, EDF, Framatome – ex Areva NP), Austria (NUCCON), Poland (NCBJ, WUT), Germany (KIT, Framatome - ex. Areva), Finland (VTT), The Netherlands (TU Delft, NRG), United Kingdom (EDF Energy) formed a consortium and applied to the H2020-Euratom call. The main ambitions of the consortium are to fill some gaps identified in existing external events probabilistic safety analyses (PSA) and to improve parts of the existing methodologies by 3 points: (1) to adapt most up to date frameworks and methodologies already existing or under development outside of nuclear community; (2) to use knowledge and experience on recent national and international projects; (3) to develop demonstration cases at the real NPP scale. Interactions are envisaged with on-going international initiatives and with the International Advisory Board, which will follow and discuss the project results with the aim to propose recommendations for future regulations. The main expected results are the development of an integrated risk framework for safety analyses and the development of a decision-making tool for demonstration of nuclear facility management. The integrated risk framework consists of: • Scenarios comprising single or multiple external hazards. Hazards can be combined or 165-2 cascading and include earthquake, flooding, extreme weather and others, • The physical and functional fragilities and interdependencies between systems/equipment are taken into account, • Human factors are taken into account and may play important role during severe accidents. • A support decision-making tool will be developed to demonstrate nuclear facility management during severe accidents due to external natural events. The project is structured into seven work packages (WP): • WP1: External hazards characterisation, • WP2: Fragility assessment of main NPPs critical elements, • WP3: Integration and safety analysis, • WP4: Applying & comparing various safety assessment approaches on a virtual reactor, • WP5: Supporting tool for severe accident management, • WP6: Dissemination, recommendation, and training, • WP7: Project management and coordination. The NARSIS project started in autumn 2017, with the duration of 4 years.

The INFRARISK project is developing reliable stress tests on European Critical Infrastructure using integrated tools for decision-support. This aims to achieve higher infrastructure network resilience to rare and low probability extreme events. As part of the project, a hazard assessment methodology is developed to account for extreme natural hazards with cascading effects. Often hazard scenarios arising from cascading effects lead to disastrous consequences because such hazards are not prepared for. In particular, this paper focuses on the cascading hazard scenario involving earthquake triggered landslides. Traditional risk analysis considers each risk source as independent from the others. As a consequence, values for risk are usually defined regardless of interactions among the multiple risks present in a region. The current approach accounts for interaction between the two hazards in such a way that the probabilities of occurrence can be aggregated as part of an overall risk assessment methodology. The methodology is then demonstrated on a virtual road network case study as a proof of concept.