What is the hydrogeological data you need for a site assessment, and how can you obtain this? Kf values for shale are not easy to determine with just one or two orders of magnitude accuracy.

Site characterization needs for a deep horizontal borehole repository are similar to those of any other disposal concept. We can rely on well-established characterization methods used in other nuclear waste isolation programs, as well as the methods used in the oil, gas and geothermal industries, geological carbon sequestration projects, resource exploration and other areas in geosciences. Note that many of these characterization methods are borehole-based. The impact of residual uncertainties in some key factors (such a shale permeability) must be accounted for when defining performance requirements for the related barrier component. However, our sensitivity and uncertainty analyses indicate that the performance metric (maximum radiological exposure dose) can be calculated with sufficient accuracy to obtain useful insights despite assuming a wide uncertainty range of the model’s input parameters, including the determination of permeability, K. While we will rely on our ability to determine site- specific property values with sufficient confidence, we also rely on inherent safety features of the concept (such as depth, limited intrusion and perturbation of the host rock environment, geometrical features and other design factors).