A multi-criteria decision-analysis framework for ranking geoscientific weighting criteria in the site selection process for a deep geological repository for high-level radwaste in Germany

RWTH Publications (RWTH Aachen)

Abstract

The German Site Selection Act (StandAG) defines geoscientific weighting criteria (GeoWCs) for evaluating potential repository sites, and the Repository Safety Investigation Ordinance (EndlSiUntV) mandates their assessment across multiple dimensions. Yet the regulatory framework provides no methodological guidance for conducting these assessments. This dissertation addresses this gap by developing a multi-criteria decision analysis framework for ranking GeoWCs according to their contribution to repository safety functions- One of several assessment dimensions mandated by EndlSiUntV. The methodology is applied illustratively to the containment-providing rock zone (CPRZ) in claystone. The Analytic Network Process (ANP) was selected for its capacity to model interdependencies and feedback loops between criteria- A property that most MCDA methods do not accommodate. GeoWCs were organized according to two control criteria, representing two safety function groups: radionuclide retention and integrity. Subdivided into thermal, hydraulic, mechanical, chemical, and spatial sub-criteria. Pairwise comparisons were conducted at multiple levels: between safety function sub-criteria, between the geological indicators within each GeoWC, and between GeoWCs with respect to each safety function. Interdependencies between GeoWCs were identified and weighted, and the resulting decision network captured both direct influences and process couplings between criteria. Sensitivity analysis tested how variations in control criteria weighting and network structure affect the final rankings. Rankings remained stable under various assumptions with no criterion shifting to more than two ranking positions. The resulting rankings are illustrative, demonstrating how the framework operates. The actual implementation would require the involvement of a multidisciplinary panel of experts from all relevant fields to conduct the pairwise comparisons. The framework enables such groups to document their assessments in an explicit and auditable way. While developed for claystone, it can be extended to other host rocks, repository components, and additional EndlSiUntV assessment dimensions.

Authors 1

1. El Fatihi Hajar corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen