A Prospective Review of Scenario Analysis of Nuclear Waste Repositories

Ongoing projects of nuclear waste repositories –which involve interacting natural and technological hazards– have brought renewed attention to Risk Assessment methodologies. With the aim of guiding methodological research... [ view full abstract ]

Ongoing projects of nuclear waste repositories –which involve interacting natural and technological hazards– have brought renewed attention to Risk Assessment methodologies. With the aim of guiding methodological research in this areas, this structured review identifies open challenges in Scenario Analysis, which is the most popular approach for supporting the Risk Assessment of these repositories. In particular, we discuss the salient properties and concerns in Scenario Analysis, such as (i) the comprehensiveness of the set of generated scenarios; (ii) the structure of Scenario Analysis as a step-wise process which starts with the identification of Features, Events and Processes (FEPs) in Scenario Development and ends with the generation of scenarios; (iii) the relevance of and dependence on a large array of uncertainties, of which the evolution of the system is the overarching one. More specifically, we discuss pluralistic and the probabilistic approaches which are portrayed as distinct approaches in the literature as to the specific step of scenario generation. The choice between these two approaches entails deep methodological divergences: (i) in the pluralistic approach, a scenario is interpreted as a combination of assumptions rather than a realization in a sample space as is the case in the probabilistic approach; (ii) the probabilistic approach sees comprehensiveness as the broadest possible coverage of the future, whereas the pluralistic one re-interprets it as representativeness; (iii) the pluralistic approach identifies carefully the interactions between the FEPs, and the probabilistic one typically overlooks them to simplify the exploration of the future; (iv) the pluralistic approach tends to generate relatively few scenario whilst the probabilistic approach produces very detailed ones. Open challenges include the following: (i) there is not as of yet an exhaustive definition of comprehensiveness to properly characterize system evolution uncertainty and thus support the generation of a comprehensive set of scenarios; (ii) the links between the identification of the FEPs and the generation of scenarios are not usually very strong; (iii) there are tensions in establishing a compromise between the interactions and the broad coverage of the future; (iv) more rigorous approaches to the characterization of the uncertainties, together with solutions to the other challenges, would plausibly improve the quality of Scenario Analysis by making it more systematic.