bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactive transport modeling for assessing coupled hydrogeochemical processes at interfaces in deep geological repositories: from the laboratory to the real world
Authors: Poonoosamy Jenna , Lönartz Mara I. , Yang Yuankai , Deissmann Guido , Kosakowski Georg , Bosbach Dirk 
Published: September 2023

Abstract. Deep geological repositories with a multi-barrier concept are foreseen by various countries for the disposal of high-level radioactive waste. Simulation tools for a close-to-reality description of repository evolution scenarios are required, especially to resolve the challenging task of comparing and assessing the long-term safety of different repository concepts in different host rocks within the German site-selection process.
Chemical, thermal, and pressure gradients at the interfaces of the different barriers in a repository can lead to mineral dissolution and precipitation, generating non-linear responses in transport and mechanical properties of barrier materials and host rocks. Reactive transport modeling (RTM) can be applied to investigate these perturbations and processes across temporal and spatial scales to assess subsurface evolution. Nevertheless, implementing RTM at the continuum scale while accounting for pore-scale heterogeneities and geometry evolution remains a challenge. Pore-scale simulations offer the potential to capture the complex evolution of porous media over a broad range of Peclet and Damköhler numbers, and they can be utilized to improve the RTM by using upscaling methods (Prasianakis et al., 2020). In this context, we developed “lab-on-a-chip” experiments, combining time-lapse high-resolution optical microscopy and confocal Raman spectroscopy to test extended constitutive equations to classically employed Archie's law to improve the description of changes in transport properties (e.g., diffusivity) in evolving porous media in RTM. The 3D Raman tomography of the porous media combined with pore-scale modeling enabled the derivation of upscaled transport parameters. Our results highlight the importance of calibrating pore-scale models with quantitative experiments prior to simulations over a wide range of Peclet and Damköhler numbers, whose results can be further used for the derivation of upscaled modeling parameters. The derived and parameterized constitutive equations based on simple systems have been tested in reactive transport models as a sensitivity case study to evaluate uncertainties in the predictions of the evolution of real subsurface systems such as clay–cement interfaces in deep geological repositories.
Performance assessment of a generic repository in salt host rock based on Task F of DECOVALEX-2023 – BASE's lessons learnt and future work
Authors: Pekala Marek , Dietl Carl Rudolf , Magri Fabiano , Kock Ingo 
Published: September 2023

Abstract. The evaluation of coupled effects of mechanical deformation, fluid and gas
flow, thermal loading, and chemical reactions is an important element of the
performance and safety assessment of disposal systems for high-level
radioactive waste and spent nuclear fuel in deep geological formations.
Early investigations showed that to be able to conduct such an evaluation
there was a need to enhance process understanding and to develop models
capable of simulating coupled thermal–hydro–chemical–mechanical processes
over relevant timescales and spatial scales. Recognising these challenges and
needs, the DECOVALEX (DEvelopment of COupled models and their VALidation
against Experiments) (https://decovalex.org, last access: 24 July 2023) was initiated in
1992 as an international cooperative project of nuclear waste organisations.
BASE is one of the funding organisations for the current phase of
DECOVALEX-2023 (running from 2020 to 2023) and actively contributes to Task F of the project (https://www.base.bund.de/DE/themen/fa/soa/projekte-aktuell/projekte-aktuell_node.html, last access: 24 July 2023, – “Beteiligung an der internationalen Forschungskooperation
DECOVALEX”). Task F (https://www.decovalex.org/D-2023/task-f.html, last access: 24 July 2023) of
DECOVALEX seeks to build confidence in the models, methods, and software
used for performance assessment of deep geologic repositories and to
highlight additional research and development needed to improve performance
assessment methodologies. The task focuses on two illustrative disposal
concepts for spent nuclear fuel: a generic repository in a fractured
crystalline host rock and a generic repository in a salt formation. For each
of the disposal concepts a reference case is defined that includes a set of
conceptual models and parameters describing features, events, and processes
that impact repository performance. Modelling teams work independently and
are responsible for determining how best to implement and couple the models.
Each team develops its own model(s), calculates agreed performance indicator
values, and performs uncertainty and sensitivity analysis. The comparison of
model results is conducted in stages, commencing with a comparison of key
outputs of individual process models, followed by a comparison of a single
deterministic simulation of the full reference case, and proceeding to
uncertainty and sensitivity analysis. The present contribution describes recent BASE activities within Task F
Salt of DECOVALEX-2023. Lessons learnt are discussed and possible future
steps are presented.
Potential and challenges of applying artificial intelligence (AI) in geosciences to the search for a high-level waste repository in Germany
Authors: Magri Fabien , Kock Ingo , Krohn Judith , Krob Florian , Ustohalova Veronika , Wittek Stefan , Bratzel Dimitri 
Published: September 2023

Abstract. In a science-based site selection procedure (StandAV), the Federal Republic of Germany is searching for a site with the best possible safety for a repository for high-level waste (HLW) over a period of 1 million years. This is a challenging task, given the size of Germany, its geological
variability and the verification period required to ensure the best possible long-term safety. In addition, an enormous amount of heterogeneous geodata has to be processed. The application of artificial-intelligence-based methods in geosciences has great potential for dealing with large heterogeneous data sets. In the German Federal Office for the Safety of Nuclear Waste Management (BASE)-funded project “Application of artificial intelligence (AI) in the site selection process for a deep geological repository (FKZ 4721E03210)”, an interdisciplinary assessment tool is being developed to evaluate the applicability of AI methods in the geosciences. This contribution focuses on the potential and challenges of applying AI in geosciences with respect to key geological activities in the StandAV. Limitations that may arise from the use of AI with respect to key activities in the StandAV are highlighted. The necessary conditions for its future applicability are proposed. The results show that AI methods offer clear advantages over conventional
methods for data management and handling large geological datasets and for
modelling complex long-term and coupled geological processes. However, AI
methods are generally only transferable to the geoscientific questions of
the StandAV with methodological and subject-specific adaptations. Furthermore, the use of AI requires sufficient data, both in terms of quality and quantity. The study also shows that AI should only be used in a
supportive way to address geological issues in key activities and should not have any decision-making power when used in StandAV. For example, AI can carry the risk of data and developer bias, which in turn can have serious consequences for the correct interpretation of results. High demands must be placed on the traceability of the AI methods used. AI
methods that do not meet the transparency requirements of the StandAV carry
a significant risk of jeopardising public confidence in the participation
process. This could increase the general mistrust and scepticism towards AI
in the public perception (Krob et al., 2023). It is strongly recommended that all methods should be evaluated and validated iteratively and that the results should be made available to the public when applied to the key activities of the StandAV.
The collection, digitisation, interpretation and publication of geological data in the German site selection procedure – status and challenges
Authors: Reiche Sönke , Schröder Lukas Alexander , Hermann Diana 
Published: September 2023

Abstract. The German site selection procedure for a repository site for high-level nuclear waste is subdivided into three major phases. During the first phase, the subsurface of Germany is evaluated based on existing data,
with the aim of defining siting regions for surface-based underground
exploration. Although Germany is covered by large amounts of geoscientific
data – including ca. 50 000 boreholes deeper than 300 m and more than
340 000 km of reflection seismic lines – the legal obligation to make these data publicly available on a national scale is fairly new and dates back to the Geological Data Act of 2020 (GeolDG: Geologiedatengesetz vom 19. Juni 2020; BGBl. I S. 1387). However, significant amounts of data are available in analogue form only, posing a significant
challenge to the timeline of the site selection procedure. As the German
nuclear waste management organisation, the Federal Company for Radioactive
Waste Disposal (BGE) is in charge of collecting, interpreting and publishing geoscientific data that are relevant to the decisions made within the site selection procedure. In this contribution, we outline the path of data within the first phase of
the site selection procedure. We start with an overview of the BGE's current and past activities related to data collection and digitisation, focussing on a major campaign through which more than 16 000 drilling reports are being digitised in cooperation with the State Office for Mining, Energy and Geology in Lower Saxony (LBEG). We then report on the different approaches of data quality control, processing and supply, highlighting challenges related to the federal organisation of geodata storage in Germany. We present selected examples of how data are used for evaluating the subsurface in terms of suitability as a potential repository site. Finally, we give an outlook of how data could be integrated into a web application that is currently being developed as an interactive tool for the public presentation of results and underlying decisions.
Retention of trivalent actinides (Am, Cm) and lanthanides (Eu) by Ca feldspars
Authors: Lessing Jessica , Neumann Julia , Bok Frank , Lützenkirchen Johannes , Brendler Vinzenz , Schmidt Moritz , Stumpf Thorsten 
Published: September 2023

Abstract. The transport of radionuclides in the environment is a
major problem for the safety assessment of radioactive waste repositories.
Storage in deep geological repositories is considered a safe disposal
strategy because of their ability to isolate hazardous components from the
biosphere for hundreds of thousands of years. Minor actinides (i.e. Am, Cm
and Np) dominate the radiotoxicity of spent nuclear fuel over geological
timescales. In underground repositories, reducing conditions are expected,
and therefore the trivalent oxidation state is dominant for Am and Cm as
well as possibly for Pu. For investigations of the mobility of the trivalent
actinides Am3+ and Cm3+, the less toxic trivalent rare earth
elements, in particular Eu3+, are commonly used. Besides clay and salt, crystalline rock is considered a possible host rock for deep geological repositories. Crystalline rock (e.g. granite) consists mainly of quartz, mica and feldspar. The latter forms common aluminosilicates making up ∼60 vol. % of the earth's crust, but
their sorption behaviour is not well understood, especially for the
Ca-bearing members of the group. Here, we study the sorption of trivalent actinides and their rare earth element homologues on plagioclase which are Ca-bearing feldspars, quantitatively and mechanistically. Zeta potentials of various Ca feldspars show an unexpected increase at pH 4–7, which becomes more pronounced as the amount of Ca in the
crystal lattice increases. This can be interpreted by assuming uptake of
Al3+ and/or the precipitation of an Al phase, where Al originates from
feldspar dissolution at different pH values. Nevertheless, only minor differences were found in the retention and surface speciation of Cm3+ on Ca and K feldspars (Neumann et al., 2021). Ca feldspar has a slightly higher potential to retain trivalent metal ions
compared to K feldspar. An inner-sphere (IS) complex and its two
hydrolysis forms have been identified on both minerals, but the hydrolysis
of the IS complex is stronger in the Ca-rich mineral. A surface complexation model for Ca feldspar was developed by combining the
batch sorption data and the spectroscopically identified surface complexes
to describe the experimental data. These data will be the basis for the
improvement of transport simulations for a reliable safety assessment of
potential radioactive waste repositories in crystalline rock.
Investigations of aged metal seals for interim storage
Authors: Jaunich Matthias , Goral Milan , Wolff Dietmar , Völzke Holger 
Published: September 2023

Abstract. The storage of spent fuel and high-level radioactive waste in
Germany is performed in interim storage containers with double-lid systems.
The lids are bolted and equipped with metal seals (e.g.
Helicoflex®) to ensure the safe containment of the inventory. The used metal seals have a layered structure consisting of three components as can be seen schematically in the cross-sectional view in Fig. 1. In the centre, a helical spring is positioned that is surrounded by two
C-shaped jackets and is mainly responsible for generation of the required
restoring force. The inner jacket is made of stainless steel and homogenises
the restoring force of the helical spring. The outer jacket is made of
silver or aluminium which are both soft metals in comparison to the contact
partners (lid and container body). During bolting of the lid to the
container body, the seal is compressed. The generated restoring force of the
helical spring causes a plastic deformation of the outer jacket and adapts
to the surfaces of the lid and the container body. Hence, leakage paths are
closed, and the sealing function is generated. Typical durations for existing interim storage licenses in Germany are
40 years, but it can be expected that they have to be extended to longer
periods as a final repository will not be available before the end of the
running licence periods. This extension of licence periods requires a solid
understanding of the long-term behaviour of the seals under storage
conditions. To meet this challenge, long-term investigations were
started at the Bundesanstalt für Materialforschung und -prüfung (BAM)
in 2009. These tests focus on seals assembled in test flanges which are
stored at temperatures ranging from room temperature to 150 ∘C
for accelerated ageing. The aged seals are tested repeatedly after certain
ageing steps, and the leakage rate (as indicator for sealing performance), the
remaining seal force, and the useable resilience upon decompression are
determined. An update on the performed investigations with respect to
earlier publications (Grelle et al., 2019; Goral et al., 2023) will be given,
and the implications of the results for resilient, long-term safety will be
presented. Additionally, there will be a focus on the currently planned
further investigations, and the following question will be addressed. What is additionally needed for
evaluation of an interim storage period extension in regard to the used
metal seals?
Future nuclear fission reactors – uncertainties, the effect of parameter choice and an application to small modular reactor concepts
Authors: Steigerwald Björn , Weibezahn Jens , Slowik Martin , von Hirschhausen Christian 
Published: September 2023

Abstract. Today, steep declines in the generation costs of renewable energy systems, particularly solar photovoltaic and wind, combined with a recent spur in storage and flexible technologies mainly driven by batteries and renewable-energy-generated hydrogen are driving a paradigm shift in energy systems across the world, and renewable energy dominates investments in installed electricity generation systems (Ram et al., 2022). In contrast, in 2022 USD 4.8 billion (ca. 21 %) of the total spending in research and development expenditures by countries within the Organisation for Economic Co-operation and Development (OECD) was still spent on nuclear development alongside the current discussion in recent literature about the role of new nuclear developments in combating the recent energy crisis and climate change (Asuega et al., 2023; Ingersoll et.al., 2020; IEA, 2023). Since predicting future costs of technologies not yet developed is a complex exercise, we start this paper with a comparison of two different approaches from production theory and show that they have a theoretically equal structure (Steigerwald et al., 2023). This we then apply to estimate a range of potential production costs for 15 so-called small modular reactor (SMR) concepts for which sufficient data are available. These include light-water, high-temperature and fast reactors. In a third step, we apply the Monte Carlo method to benchmark the cost projections assumed by the manufacturers by varying production parameters in simulations of the net present value (NPV) and the levelized cost of electricity (LCOE). Besides this, we test whether the differences between the manufacturer estimates and ours differ between technology families of SMR concepts and apply a sensitivity analysis. This contributes to an intensifying debate in the literature on the economics and finance of SMR concepts (Steigerwald et al., 2023). In a final step we compared our results with current costs of renewable energy technologies and could conclude that none of the tested concepts is able to compete economically with existing renewable technologies, not even when taking their variability and necessary system integration costs into account. We conclude that any technology foresight has to take the case specifics into account as much as possible, including technological and institutional specifics; this also holds for SMR concepts.
Corrosion evaluation for engineered barriers in crystalline host rock – challenges for container development in the German site selection process
Authors: Stephan-Scherb Christiane , Philipp Thimo , Weyand Torben , Fass Thorsten , Maerten Lena 
Published: September 2023

Abstract. Crystalline rock is being considered as a potential host rock
for a deep geological disposal facility for high-level radioactive waste in
the ongoing site selection process in Germany. As crystalline rock is
commonly highly fractured, the designation of a containment-providing rock
zone is potentially not possible. In this case, according to German law
(§ 23 (1) and (4) StandAG), the safe containment of the nuclear
waste for 1 million years must be guaranteed by engineered and
geo-engineered barriers. Therefore, it is of great importance to evaluate
and understand processes that might lead to corrosion of the canister from
the outside or from the inside. The long-term integrity of the waste
canister depends on various parameters such as the material, microstructure, and coating of the canister; the properties of the geo-engineered
barriers; the local pore water composition; the radiolysis on the inside of the
container; and the tectonic strain. In a recent project (Long-Term Integrity of Canisters in Crystalline Host Rock – LaKris), the challenges of determining the durability of waste canisters in crystalline host rock have been addressed by comparing and evaluating different international concepts for canister design and discussing their applicability to the requirements in Germany. Further focus lies on the
evaluation of predominant corrosion mechanisms while also considering the
geochemical environment of the crystalline host rock in Germany that the
canisters might be subjected to. This contribution will highlight the activities within the project with
regard to evaluating the corrosion properties of different potential
canister materials such as copper, cast iron, and stainless steel. The aim is
to deepen the understanding of individual processes and their combined effects as well as their classification into favourable or unfavourable processes and
conditions for the derivation or justification of requirements. It also
includes a review of the existing requirements on canister integrity
according to the regulatory framework as well as a discussion about
important hydrogeochemical parameters, which could influence the corrosion
of the canister, including the limited availability and uncertainty of such
data.
A note on the duration of claystone exploration programs
Authors: Mann Thomas , Schuck Bernhard , Kneuker Tilo , Pollok Lukas , Bornemann André , Erbacher Jochen 
Published: September 2023

Abstract. In a recent report, the German Federal Company for Radioactive Waste Disposal (BGE) estimated the probable duration of exploration activities within potential siting regions (BGE, 2022). Based on many years of expertise regarding the exploration of the subsurface, we outline in this contribution that the BGE (2022) likely underestimates the time necessary to characterize claystones within potential siting regions. Our latest experience originates from two research projects that developed sequence stratigraphic frameworks for the largely homogenous claystone successions of the Lower Cretaceous in northern Germany (Thöle et al., 2020) and the Middle Jurassic in southern Germany, respectively. Although the specific study areas are not considered in the site selection procedure, both stratigraphic units are reviewed to potentially host a nuclear waste repository. Accordingly, our hands-on experience might constitute a highly relevant contribution to the ongoing debate. Within each study area, drill cores were extracted from four boreholes with a total length of ∼660 m (northern Germany) and ∼930 m (southern Germany). After the drilling campaigns, each having taken approx. 5–6 weeks, the cores were split, photographed in high resolution, lithologically described, scanned with an X-Ray fluorescence (XRF) core scanner (10 mm scan interval) to determine the elemental distribution, and sampled for lithological, mineralogical and geochemical analyses at a resolution of 1 m, which took approx. 12 months. However, the most time-consuming steps were the analysis and interpretation of the stratigraphy and particularly the mineralogical investigations. With a sampling resolution of 1 m, an analysis time of approx. 6 months per 250 core meters is a robust reference. We reckoned a total duration of 5 years for the workload in each of the abovementioned research projects. Obviously, the duration of claystone exploration will vary, depending on the number and length of the core drillings per siting region, in addition to the sampling resolution. However, if BGE aims to characterize claystones with a degree of detail comparable to our
projects, the estimated 42 months (see Table 3 in BGE, 2022) will likely be
insufficient.