Studies of geological properties and conditions for deep disposal of radioactive waste, Denmark Phase 1, report no. 10. Characterization and evaluation of geological properties and conditions at 500 meters depth. This is the English version of the report: 2021/60

The present report is a contribution to a major project whose purpose is to investigate whether suitable geological sites for disposal of the Danish radioactive waste can be identified. The Geological Survey of Denmark and Greenland (GEUS) has been given the task of identifying, mapping, and characterizing laterally continuous, low permeability rock formations occurring at 500 meters depth with thicknesses of 100 meters. This report is part of a series of ten reports presenting the results of the first phase of the siting project, which has mainly been carried out as a desk study.

The initial geological characterization and evaluation will provide the geological basis for the selection of two sites where detailed geological site investigations will be carried out in the project’s second phase. These two sites will be selected through a dialogue process between the Ministry of Higher Education and Science (MHES) and the local municipalities. The geological data from the site investigations will be used as input to a safety case once a disposal concept has been identified by the Danish Decommissioning (DD). The safety case must demonstrate that the geological properties in combination with the engineered barriers of the repository can provide the required short- and long-term safety for disposal.

In a preceding feasibility study, it was concluded that at 500 meters depth potential host rocks occur in Jurassic and Lower Cretaceous claystones, in Upper Cretaceous carbonates, and in Precambrian crystalline basement rocks. In the current project phase, the geological properties and subsurface conditions related to these stratigraphic intervals and rock types are reviewed based on existing data. The potential host rocks’ capabilities to retard radionuclides are investigated initially by conceptual 1D numerical modeling. In addition, natural processes potentially influencing short- and long-term subsurface stability are identified and described.

To enable characterization and a qualitative evaluation of the Danish subsurface at depths to 500 meters Denmark has been divided into eleven geological areas based on the information gathered in the geological reports no. 2–8. Each area is characterized by the type of potential host rock occurring at 500 meters depth, the rock types forming barriers in the overlying effective containment zone, and the structural framework. The evaluation is based on requirements and criteria for deep geological disposal, which are defined based on international experience and recommendations from similar projects. Based on the available data, each area is characterized and evaluated with regards to whether the geological properties and conditions are suitable for deep disposal of Danish radioactive waste. The results of the project’s first phase are presented in the following ten geological reports:

1. Requirements and criteria for initial evaluation of geological properties and conditions
2. Geological setting and structural framework of Danish onshore areas
3. Upper Cretaceous – Paleocene chalk, limestone and marl distribution and properties
4. Jurassic and Lower Cretaceous claystone distribution, sedimentology, and properties
5. Precambrian crystalline basement distribution and properties
6. Subsurface distribution of Jurassic and Cretaceous fine-grained formations based on seismic mapping
7. Evaluation of long-term stability related to glaciations, climate and sea level, groundwater, and earthquakes
8. Conceptual 1D modeling of nuclide transport in low permeable formations
9. Karakterisering og evaluering af geologiske egenskaber og forhold i 500 meters dybde (In Danish)
10. Characterization and evaluation of geological properties and conditions at 500 meters
depth (This report is an English translation of report no. 9)

This report is Report no. 10. It presents the basis for a subdivision into 11 geological areas and an initial qualitative evaluation of whether the rock properties and subsurface conditions in each area fulfil the requirements and criteria for deep geological disposal.