Including subsurface uncertainties in the early screening phase for a geological disposal facility for high-level nuclear waste

The current early phase of the German Site Selection Procedure includes screening of large areas of Germany’s subsurface, via preliminary safety assessments, in order to identify the most-suited regions for a geological disposal facility. The procedure leads to a gradual reduction of these vast areas, resulting in series of relatively small, high-potential site regions.

The subsurface uncertainties, relevant for the site regions’ robustness evaluation, need to be assessed already during this early screening phase. Consequently, the uncertainty estimation concept includes methods for different geographical scales: screening methods applicable to large areas and detailed methods applicable to the relatively small, high-potential regions.

A semi-quantitative method for the assessment of the subsurface uncertainties is applied to large areas. This method consistently and efficiently estimates the “degree of confidence”, which represents the reliability of given statements concerning the interpretation of the subsurface. The “degree of confidence” can be estimated for each given area or structure from the combination of data quality and quantity, on one the hand, and the geological complexity, on the other.

Quantitative methods are used for the estimation of the uncertainty of key geological safety elements in the smaller, high-potential areas. These methods include statistical and geostatistical approaches.