The anisotropic properties of granites – effects of tectonic emplacement mode on potential crystalline host rocks for nuclear waste deposits in Germany

For permanent nuclear waste disposal sites, crystalline rocks, especially granitic/granodioritic batholiths, are considered an appropriate host rock. Principally, three types of granitic plutons occur in the extra-alpine crystalline basement of Germany that were consolidated during the late Paleozoic Variscan orogeny of Central Europe: (i) Pre-Variscan voluminous granodiorites that are hardly affected by the subsequent continent–continent collision; (ii) voluminous granites in various tectonic settings intruded during the late orogenic stage of the Variscides; (iii) post-orogenic granites related to vast Permian intracontinental extension. Thus, in terms of the syn-intrusive tectonic setting and post-intrusive processes there are significant differences. Although it can be expected that different tectonic environments caused significant differences in the material properties, for Germany, however, there is no systematic study regarding the fabric of such plutonites. In order to find the most suitable “granite” we investigate the primary anisotropy of granites evolved during the emplacement and crystallization of the melt. For this we sample rocks of all three principal types and various syn-intrusive tectonic settings, i.e., compression, extension, strike-slip, transtension, and transpression. By means of combined measurements of the “Anisotropy of the Magnetic Susceptibility” and the “Shape Preferred Orientation” we characterize the syn-intrusive flow pattern, i.e., the magmatic foliation and lineation. The Crystallographic Preferred Orientation is analyzed by a combination of neutron time-of-flight experiments and electron backscatter diffraction measurements at the Frank Laboratory of Neutron Physics at JINR, Dubna, Russia, and the TU Bergakademie Freiberg respectively. Furthermore, special attention is given to the systematic mapping of annealed microcracks evolved during late magmatic fluid escape and/or post-crystallization hydrothermal activity. In a second step we compare the primary anisotropy with the post-magmatic fracture pattern of the particular granites. Those fractures constitute probable fluid pathways and, thus, the first-order risk for a potential permanent nuclear waste disposal. All datasets are organized in a Geological Information System allowing for a complete traceability of the different investigation steps. The results of this study will serve as a basis for a future detailed exploration.

Geochemical benchmark tests to validate the conversion of thermodynamic data for TOUGHREACT

According to the ongoing site selection process for a repository for high-level radioactive waste in Germany, rock salt, clay and crystalline rock are possible host rocks. The pore water of these rocks contains saline solutions with high ionic strengths. To model the speciation and/or migration of radionuclides in long-term safety analyses for nuclear waste disposal, a geochemical code that includes thermodynamic data suitable for saline solutions is needed. Thermodynamic equilibrium in saline solutions with high ionic strengths is usually modelled using the Pitzer approach (Pitzer, 1991). Within the context of nuclear waste disposal, the THEREDA project (Moog et al., 2015) provides thermodynamic data for some widely used geochemical codes (PHREEQC, Geochemist's Workbench, ChemApp, and EQ 3/6) using the Pitzer approach; however, for modelling in long-term safety analyses for nuclear waste disposal, another geochemical code, TOUGHREACT, is used. Therefore, scripts were developed to convert thermodynamic data of the THEREDA project to be applicable in TOUGHREACT. The scripts were validated by benchmark tests and by comparing calculations using PHREEQC and TOUGHREACT (Weyand et al., 2021). In total, 50 different benchmark tests were performed considering 3 specific geochemical systems, which are relevant to long-term safety analyses: (1) oceanic salt system, polythermal: K, Mg, Ca, Cl, SO4, H2O(l), (2) actinide system, isothermal: Am(III), Cm(III), Nd(III), Na, Mg, Ca, Cl, OH, H2O(l) and (3) carbonate system, isothermal: Na, K, Mg, Ca, Cl, SO4, HCO3/CO2(g), H2O(l). Each benchmark test considered specific ion concentrations in solution and in gaseous phases in the presence of specific minerals. The benchmark tests derived the geochemical equilibria and the results of both codes were compared to each other and to experimental data. The results of the calculations using both codes showed a good correlation. Remaining deviations can be explained by technical differences of the codes.

Knowledge Management in the Federal Company for Radioactive Waste Disposal (BGE)

With completion of the restructuring of the nuclear waste disposal landscape in Germany, the competences for construction and running of repositories for radioactive waste products are since 2017 with the Federal Company for Radioactive Waste Disposal (BGE). The BGE has over 50 years of experience in the disposal of nuclear waste in Germany. Over a period of several decades substantial effort was put into the research and developmental work on nuclear waste disposal in Germany, which led to a considerable state of knowledge, both thematically and quantitatively; however, so far no consistent overview exists on the various works and therefore on the total state of knowledge, as these works only partially exist or existed in the very different organizations (diffuse and local) within the nuclear waste disposal landscape. The emerging loss of specialist knowledge in Germany caused by the withdrawal from nuclear energy and the recession of national mining activities is doing the rest. This imminent loss of knowledge must be taken into consideration as a critical factor, especially considering the age structure within the BGE and the simultaneously occurring processes on selection of a site for disposal of highly radioactive waste products. For this reason, in the division of research and development/knowledge management (R&D/KM) an independent department for knowledge management was created in order to establish an infrastructure for knowledge management and a connection between knowledge management platforms and knowledge carriers in the company. In addition to the collection and distribution of the available knowledge, current results from research and development are also to be fed into the “learning organization”. For this purpose, knowledge management provides a digital information basis, into which current results from research and development are also entered as a knowledge store. This knowledge store consisting of over 14 000 documents, contains mostly research reports and scientific publications, which are concerned with diverse topics for the final disposal of radioactive waste products in geological formations. The total stock of internal company documents available can be accessed with a browser-based text analysis software. Intelligent search algorithms render the textual contents accessible, combine them with synonyms and dictionaries deposited in the system and make the resulting hits of the search queries available for the user in order of importance in summarized and full text versions. Using specific query terms, as known from search machines or library servers, this software analyzes the available documents of the digital information basis and in a brief summary of results, in addition to a brief description of the contents, the naming of relevant keywords, the identification of sources, compilers, institutions, knowledge carriers and an extended optimized information analysis of hits, also provides the possibility to retrieve the complete document and the download. The research options can, in addition to the queries via the established internet search engines also be combined with queries via the incorporated information or databank catalogue of national and international scientific institutions or libraries, which are concerned with research programs relevant for repositories. In order to further increase and optimize the information possibilities for employees of the BGE, a variety of knowledge landscapes has been implemented in the intranet, which enable specific queries on topics, expert information, institution, country and persons. Using these tools a first essential target of knowledge management, the collection, availability and distribution of written down knowledge in the company has been achieved. For the development of person-related and group-related knowledge the department of knowledge management is compiling concepts, which can only be implemented together and jointly with them, as they border on certain interfaces in the organization/company. This particularly concerns measures that fall into the areas of human resources, such as personnel management and personnel strategies or in the area of the particular project; keyword lessons learnt.