Methods

3D geological model of underground workings and the resulting numerical 3D calculation model for the northern central zone in ERA Morsleben Source: BGR

BGR systematically and continuously develops special methods, instruments, working methods, verification methods, and evaluation criteria required for answering geoscientific questions concerning the final disposal of radioactive waste in all relevant host rock types in Germany. The objective of this development work is to generate the necessary principles for the evaluation of geoscientific properties and processes relevant to long-term safety aspects, as well as various quantitative safety verifications (e.g. verifying the fitness for purpose, the stability of cavities, and barrier integrity). These principles are not only applicable to geologic repositories, but also to other geotechnical structures such as mines, caverns and underground depots.
Developing these methods includes following a value chain encompassing several phases, with different geoscientific topics, which build on each other and are closely linked:

• Geological exploration and interpretation of geological structures
• Geological-mineralogical-geochemical characterisation of host rocks and their barrier properties
• Associated geophysical surveys in the field
• Generation of geological cross sections and three-dimensional geological models
• Laboratory tests to determine the thermal, hydraulic and mechanical parameters of various host rocks and geotechnical barriers, as well as the development of material models
• Mineralogical-geochemical investigations to clarify the special characteristics of host rocks that are relevant for long-term safety, such as occurrence and origin of hydrocarbons in evaporites, deformation and healing of rocks, genesis and properties of fractures and fault zones
• In-situ-measurements and field experiments to determine thermal, hydraulic and mechanical geological properties
• Formulation of FEPs (features, events, processes) and scenario analyses
• Further development of criteria for the selection of sites and for the evaluation of geologic repository safety
• Generating two-dimensional and three-dimensional numerical calculation models
• Carrying out thermal (T), hydraulic (H) and mechanical (M) model calculations, which also take coupled THMC processes into consideration
• Evaluation and verification of the safety of a geologic repository according to various criteria (e.g. stability, barrier integrity, long-term safety).

Each of the various phases involved in this chain of evaluations is concluded with comprehensive measures of quality assurance, documentation and archiving for the acquired data and findings.

The geomechanical laboratory at the Federal Institute for Geosciences and Natural Resources (BGR) was inspected in 2018 by a German accreditation company (Deutsche Akkreditierungsstelle GmbH, DAkks), and has been accredited since 07.11.2018 as a testing laboratory pursuant to DIN EN ISO/IEC 17025:2005 (standard applying to laboratory competence). This supplements the previous stipulations in the "DIN/ISO EN 9001:2015" and "KTA 1401" standards. The accreditation of the geomechanical laboratory encompasses geophysical investigations, including sampling solid and saline rocks, and sample preparation.