This paper presents the general approach presently developed by ONDRAF/NIRAS/NERAS, the Belgian radioactive waste management agency for dealing with the economic and financial uncertainties of the High-level-Waste (HLW) repository project in clay. This project will be for many more years the object of R&D studies. Many uncertainties thus still exist regarding the final design, the eventual costs, and the realisation schedule. Recommendations from the Electric Power Research Institute (EPRI) are available for computing contingency factors to be applied on top of the basic costs delivered by project engineers. We show in this paper that fuzzy logic is a natural way to use the recommendations of EPRI. Fuzzy logic is a mathematical technique for representing unprecise or relatively vague judgments made by experts, like: ‘this project is preliminary’, ‘this concept is insufficiently mature’, etc. This approach is considered in many fields as being well-suited for coping with uncertainties implied by such judgments. In the present case, distinction is made between uncertainties related to policy, project, technology, and realisation schedule. The paper details the sequence of basic steps used by the agency to produce as a final product the per-unit tariff of the different waste categories. Expert judgments are interpreted by the fuzzy-logic technique to derive EPRI-like contingency factors for each project task, as well as a fuzzy operating schedule within a given political scenario. Conclusions are given on how this approach can be validated and set into practice.

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