How to handle uncertainties in modelling due to human reliability issues for nuclear disposals

Abstract. Modelling plays a crucial role in assessing the design for future technical or geological development of a repository for radioactive waste. Models and the application of these models to scenarios are used to weigh different safety-related designs or to assess the suitability of sites. Even if the models simulate and evaluate a system in a geological context that is designed as a passively safe system, the human factor plays a significant role in the overall assessment process and thus in finding a site with the best possible safety, in accordance with the Site Selection Act in Germany. This influence is not seen at the level of repository operation, as is traditionally viewed with regard to human factors, but rather in the design of the repository – particularly in the decision-making process and the definition of the system's fundamental design parameters. Thus, considerations of human reliability are also of utmost importance for the passively safe system of a repository, especially in the current phase of the search and evaluation process. Given that severe accidents in human-made technological systems depend heavily on the reliability of human behaviour, not only in operation but also in design and conceptualisation, considering human reliability aspects is essential for a successful site selection (Straeter, 2019). This article first provides an overview of the technical, organisational, cross-organisational, and individual aspects of human reliability that are crucial in the modelling phase of radioactive waste management. Human aspects include variations in the selection of models, the definition of input parameters, and the interpretation of results as individual or group efforts. Based on a review of relevant guidelines on the topic (VDI 4006), suggestions are presented for dealing with these human factors at different levels. The approach is supported by a study on the importance of these factors, which was carried out in the context of the TRANSENS project conducted jointly by the University of Kassel and TU Clausthal. Overall, based on these considerations, the Assessment of Human Reliability in Concept phases (AHRIC) method is proposed to assess the negative effects of trust issues in the site selection work processes and to derive mitigating measures (Fritsch, 2025). The method applies to all work processes of the key actors.