A Formal Process for Elicitation and Validation of Expert Judgements for Safety Case in the Context of Spent Nuclear Fuel Management

The report introduces a proposal for a formal expert judgment elicitation and validation prosess for Posiva in the construction of the safety case of the spent fuel disposal facility at Olkiluoto. The procedure has been developed by adopting a systemic, interaction-based approach to elicitation and validation. The concept for the formal procedure has been developed by taking the support for collaboration as the primary requirement for the development. The procedure provides systematic practices and a forum for joint assessment and makes it possible for the domain experts to participate in the discussions and decisions on the validity of the input data. In addition to the experts, also the safety analysts are elicited, in a way. The two-way elicitation enhances mutual understanding between the participants and assures collaboration of equal parties. The procedure provides also conceptual tools that support decision making in validation by enhancing transparency of reasoning. The predefined forms and descriptions serve as shared frames of reference and enhance the comprehension of, e.g., the nature and impact of the uncertainties of the input data, the ways of thinking underlying the different disciplines and the significance of one's role as part of the construction of the safety case.