An interdisciplinary view of the long-term evolution of repository systems across scales: the iCROSS project

Abstract. The interdisciplinary project “Integrity of nuclear waste repository systems – Cross-scale system understanding and analysis (iCROSS)” combines research competencies of Helmholtz scientists related to the topics of nuclear, geosciences, biosciences and environmental simulations in collaborations overarching the research fields energy and earth and environment. The focus is to understand and analyze close-to-real long-term evolutionary pathways of radioactive waste repositories across nanoscales to repository scales. The project is subdivided into work packages dealing with laboratory studies, field experiments in underground research laboratories (URLs), advanced modelling studies and the integration and alignment of data and information using virtual reality methods. In this sense, the project structure aims at a holistic view on relevant processes across scales in order to comprehensively simulate potential repository evolutions. Within the multi-barrier system of a repository for heat-generating radioactive waste, a number of complex reactions proceed, including dissolution, redox processes, biochemical reactions, gas evolution and solid/liquid interface and (co)precipitation reactions. At the same time, thermal and external mechanical stress has an impact on the conditions in a deep geological repository. All those processes are highly coupled, with multiple interdependencies on various scales and have a strong impact on radionuclide mobility and retention. In recent years, substantial progress was achieved in describing coupled thermal-hydro-mechanical-chemical-biological (THM/CB) processes in numerical simulations. A realistic and concise description of these coupled processes on different time and spatial scales is, at present, a largely unresolved scientific and computational challenge. The close interaction of experimental and simulation teams aims at a more accurate quantification and assessment of processes and thus, the reduction of uncertainties and of conservative assumptions and eventually to a close-to-real perception of the repository evolution. One focus of iCROSS is directed to relevant processes in a clay rock repository. In this context, the iCROSS team became a full member of the international Mont Terri consortium and worked in close collaboration with international and German institutions in URL projects. Respective experiments specifically deal with coupled processes at the reactive interfaces in a repository near field (e.g. the steel/bentonite and bentonite/concrete interfaces). Within iCROSS, the impact of secondary phase formation on radionuclide transport is investigated. At Mont Terri, experiments are in preparation to study radionuclide transport phenomena in clay rock formations within temperature gradients and in facies exhibiting significant heterogeneities on different scales (nm to cm). Beside those studies, high resolution exploration methods for rock characterization are developed and tested and the effect of temperature and other boundary conditions on the strength, creep properties and healing of faults within Opalinus clay are quantified. Multiphysics models coupled to reactive transport simulation have been further developed and applied to laboratory and field experiments. Results are digitally analyzed and illustrated in a visualization center, in order to enhance the comprehension of coupled processes in repository systems across scales. The present contribution provides an overview on the project and reports selected results. The impact of considering complex coupled processes in repository subsystems for the assessment of the integrity of a given (generic) repository arrangement is discussed.

Download Full-text

Impact of the heterogeneity of the sandy Opalinus clay facies at the Mont Terri underground research laboratory on radionuclide migration

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-141-2021 ◽

2021 ◽

Vol 1 ◽

pp. 141-142

Author(s):

Naila Ait-Mouheb ◽

Yuankai Yang ◽

Luc R. Van Loon ◽

Martin A. Glaus ◽

Guido Deissmann ◽

...

Keyword(s):

Research Laboratory ◽

Radioactive Wastes ◽

Coupled Processes ◽

Opalinus Clay ◽

Nuclear Waste Repository ◽

Radionuclide Transport ◽

Mont Terri ◽

Underground Research Laboratory ◽

Host Rocks ◽

The Impact

Abstract. The assessment of the safety of a deep geological repository (DGR) for high-level radioactive wastes over assessment time scales of up to 1 million years requires an in-depth understanding of the multi-scale coupled processes that affect the repository system evolution over time, to reduce uncertainties and conservatism in safety analyses. This is in particular required with respect to the challenges of a comparative assessment of different repository concepts in different host rocks within the process of a site selection for a DGR for heat-generating radioactive wastes in Germany. The collaborative project “Integrity of nuclear waste repository systems – Cross-scale system understanding and analysis (iCross)” conducted jointly by five research centres of the Helmholtz Association and co-funded by the Initiative and Networking Fund of the Helmholtz Association and the Federal Ministry of Education and Research (BMBF) has been initiated with the overall objective to improve the understanding of coupled thermal-hydraulic-mechanical-chemical-(micro)biological (THMCB) processes and to develop simulation tools that enable a holistic close to reality description of the long-term evolution of the repository system. Geological formations, such as those foreseen as potential host rocks for DGRs, and their surroundings are heterogeneous on various length scales ranging from nanometers to kilometers. Therefore, the aim of this work in the context of iCross is to evaluate the effects of mineralogical, geochemical and microstructural heterogeneities of repository host rocks on radionuclide transport in the repository far field, using the sandy facies of the Opalinus clay (SF-OPA) from the Mont Terri underground research laboratory (St. Ursanne, Switzerland) as an example. Here, we address in particular the migration behaviour of Ra-226 as an important radionuclide to be considered in safety cases for deep geological disposal of spent nuclear fuel. To assess the impact of the heterogeneities in SF-OPA on radionuclide transport, a complementary approach combining microstructural characterisation methods, experimental techniques for the determination of transport parameters of the rock matrix and the mobility of Ra-226 with innovative developments in reactive transport modelling on the pore and continuum scales was pursued. One of the results was that although the limited clay content in SF-OPA decreases the total amount of Ra bound to the illite phase, the solid solutions of sulphate and carbonate compensate for this and provide a major fixation mechanism.

Download Full-text

From process to system understanding with multi-disciplinary investigation methods: set-up and first results of the CD-A experiment (Mont Terri rock laboratory)

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-79-2021 ◽

2021 ◽

Vol 1 ◽

pp. 79-81

Author(s):

Gesa Ziefle ◽

Tuanny Cajuhi ◽

Sebastian Condamin ◽

Stephan Costabel ◽

Oliver Czaikowski ◽

...

Keyword(s):

Radioactive Waste ◽

Site Selection ◽

Fault Zones ◽

Rock Laboratory ◽

Investigation Methods ◽

Physical Effects ◽

Mont Terri ◽

Mont Terri Rock Laboratory ◽

The Impact

Abstract. A potential repository site for high-level radioactive waste should ensure the highest possible safety level over a period of one million years. In addition to design issues, demonstrating the integrity of the barrier is essential as it ensures the long-term containment of radioactive waste. Therefore, a multi-disciplinary approach is necessary for the characterization of the surrounding rock and for the understanding of the occurring physical processes. For site selection, however, the understanding of the respective system is essential as well: Do fault zones exist in the relevant area? Are these active and relevant for interpreting system behavior? What is the role of the existing heterogeneities of the claystone and how do these site-dependent conditions influence the physical effects? To answer these questions, the site-selection procedure requires underground exploration, which includes geophysical and geological investigations on milli- to decameter scales. Their results serve as the basis for numerical modelling. This combined, multi-disciplinary interpretation requires extensive knowledge of the various methods, their capabilities, limitations, and areas of application. In the cyclic deformation (CD-A) experiment in the Mont Terri rock laboratory, the hydraulic–mechanical effects due to excavation and the climatic conditions within the rock laboratory are investigated in two niches in the Opalinus Clay. The twin niches differ mainly with regard to the relative humidity inside them, but are also characterized by different boundary conditions such as existing fault zones, the technical construction of the neighboring gallery, etc. In order to gain insights into the relevance of the individual influences, comparative studies are being carried out on both niches. The presented results provide a first insight into the initial experimental years of the CD-A long-term experiment and illustrate the benefits of multi-disciplinary investigations in terms of system understanding and the scale dependency of physical effects. Amongst other effects, the assessment of the impact of heterogeneities on the deformation behavior and the evolution of pore water pressure is very complex and benefits from geological interpretation and measurements of for example deformation, water content, and pore pressure. The numerical modeling allows statements about the interaction of different processes and thus enables an interpretation of the overall system, taking into account the knowledge gained by the multi-disciplinary investigation.

Download Full-text

THM analysIs of natural and engineered barriers for large excavations in deep nuclear waste repository

10.5194/egusphere-egu21-7588 ◽

2021 ◽

Author(s):

Matias Alonso ◽

Jean Vaunat ◽

Minh-Ngoc Vu ◽

Antonio Gens

Keyword(s):

Nuclear Waste ◽

Host Rock ◽

Thermal Load ◽

Water Pressure ◽

Large Diameter ◽

Coupled Processes ◽

Nuclear Waste Repository ◽

Damaged Zone ◽

Waste Repository ◽

The Impact

Argillaceous rocks have great potential as possible geological host medium to store radioactive waste. &#160;Andra is leading the design of a deep geological nuclear waste repository to be located in the Callovo-Oxfordian formation. In the framework of this project, excavations of large diameter galleries are contemplated to access and to store intermediate-level long-lived nuclear waste at repository main level. The closure of the repository will be realized by building sealing structures of expansive material.The response of such structures is affected by several thermo-hydro-mechanical coupled processes taking place in the near and far field of the argillaceous formations. They include the formation of an excavation induced damaged zone around the galleries, the impact of the thermal load on host rock pressures and deformations, the long-term interaction with support concrete structural elements and the hydration and swelling of sealing materials. As a result, the study of their performance requires to perform simulation works of increasing complexity in terms of coupling equations, problem geometry and material behaviour. As well, challenging computational aspects, as the ones related to fractures creation and propagation, have to be considered for a representative analysis of the problem.This work presents advanced large scale THM numerical models to provide keys about the response of the host rock around large diameter galleries during excavation and further thermal load as well as to analyse the performance of large diameter sealing structures. Particular features of the models include on one hand advanced constitutive laws to capture the development of the fractured zone around excavations, the behaviour of host rock/gallery support interfaces and the multi-scale response of bentonitic backfill. On the other hand, simulations consider geometries including constructive details of interest at decimetre scale within large discretization domain covering the whole formation stratigraphic column.These challenging simulations provided qualitative and quantitative results on key aspects for natural and engineered barrier integrity, like extension of the damaged zone, impact of the thermal load and water pressure variations in the surrounding geological layers, duration of natural hydration phase, swelling pressure development and seals global stability.

Download Full-text

The Hydrogeologic Environment for a Proposed Deep Geologic Repository in Canada for Low and Intermediate Level Radioactive Waste

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B ◽

10.1115/icem2011-59285 ◽

2011 ◽

Cited By ~ 2

Author(s):

Jonathan F. Sykes ◽

Stefano D. Normani ◽

Yong Yin ◽

Mark R. Jensen

Keyword(s):

Radioactive Waste ◽

Solute Transport ◽

Regional Scale ◽

Intermediate Level ◽

Geologic Repository ◽

Site Specific ◽

Ordovician Limestone ◽

Intermediate Level Radioactive Waste ◽

The Impact

A Deep Geologic Repository (DGR) for low and intermediate level radioactive waste has been proposed by Ontario Power Generation for the Bruce nuclear site in Ontario, Canada. As proposed the DGR would be constructed at a depth of about 680 m below ground surface within the argillaceous Ordovician limestone of the Cobourg Formation. This paper describes the hydrogeology of the DGR site developed through both site characterization studies and regional-scale numerical modelling analysis. The analysis provides a framework for the assembly and integration of the site-specific geoscientific data and examines the factors that influence the predicted long-term performance of the geosphere barrier. Flow system evolution was accomplished using both the density-dependent FRAC3DVS-OPG flow and transport model and the two-phase gas and water flow computational model TOUGH2-MP. In the geologic framework of the Province of Ontario, the DGR is located on the eastern flank of the Michigan Basin. Borehole logs covering Southern Ontario combined with site-specific data from 6 deep boreholes have been used to define the structural contours and hydrogeologic properties at the regional-scale of the modelled 31 sedimentary strata that may be partially present above the Precambrian crystalline basement rock. The regional-scale domain encompasses an approximately 18500km2 region extending from Lake Huron to Georgian Bay. The groundwater zone below the Devonian includes units containing stagnant water having high concentrations of total dissolved solids that can exceed 300g/L. The Ordovician sediments are significantly under-pressured. The horizontal hydraulic conductivity for the Cobourg limestone is estimated to be 2 × 10−14 m/s based on straddle-packer hydraulic tests. The low advective velocities in the Cobourg and other Ordovician units result in solute transport that is diffusion dominant with Peclet numbers less than 0.003 for a characteristic length of unity. Long-term simulations that consider future glaciation scenarios include the impact of ice thickness and permafrost. Solute transport in the Ordovician limestone and shale was diffusion dominant in all simulations. The Salina formations of the Upper Silurian prevented the deeper penetration of basal meltwater.

Download Full-text

Hydrogeological simulation of sedimentary basin evolution during a glacial cycle

10.5194/egusphere-egu21-13299 ◽

2021 ◽

Author(s):

Christian Silbermann

Keyword(s):

Boundary Conditions ◽

Large Scale ◽

Sedimentary Basin ◽

Long Term Evolution ◽

Nuclear Waste Repository ◽

Glacial Cycle ◽

Thermal Problem ◽

Term Evolution ◽

The Impact

Co-authors: Francesco Parisio, Thomas NagelGlaciation cycles affect the long-term evolution of geosystems by crustal deformation, ground freezing and thawing, as well as large-scale hydrogeological changes. In order to properly understand the present and future conditions of potential nuclear waste repository sites, we need to simulate the past history.&#160; For this, a sedimentary basin is considered here as a large-scale hydrogeological benchmark study. The long-term evolution during one glacial cycle is simulated using the open-source multi-field finite element code OpenGeoSys. The impact of the glacial loading (weight and induced shear) is taken into account using appropriate time-dependent stress boundary conditions. As a preliminary study, the hydro-mechanically coupled problem and the thermal problem are considered separately. For comparison with a previously published study by Bense et al. (2008), the entire displacement field is prescribed and the groundwater evolution (hydraulic problem) is regarded. Then, the displacement is only prescribed by means of boundary conditions. The impact of different constitutive assumptions on the deformation and hydraulic behavior is analyzed. The thermal problem is used to simulate the evolution of frost bodies in the subsurface beneath and ahead of the glacier.V. F. Bense and M. A. Person. Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles. Journal of Geophysical Research, 113(F4):F04005, 10 2008.

Download Full-text

Long-term safety of the extended SFR - Methodology and conclusions from the SR-PSU project

MRS Advances ◽

10.1557/adv.2017.192 ◽

2016 ◽

Vol 1 (61) ◽

pp. 4075-4080

Author(s):

Fredrik Vahlund

Keyword(s):

Radioactive Waste ◽

Nuclear Fuel ◽

Nuclear Power ◽

Safety Assessment ◽

Power Plants ◽

Spent Nuclear Fuel ◽

Surface System ◽

Radiological Safety ◽

The Impact

ABSTRACTSince 1988 the Swedish Nuclear Fuel and Waste Management Co. operates a repository for low- and intermediate-level short-lived radioactive waste, SFR, in Forsmark, Sweden. Due to decommissioning of the nuclear power plants additional storage capacity is needed. In December 2014, an application to extend the repository was therefore submitted. One key component of this application was an assessment of post-closure safety of the extended SFR. For this safety assessment, a methodology based on that developed by SKB for the spent nuclear fuel repository was used and the impact of the degradation of repository components, the evolution of the surface system and changes of future climate on the radiological safety of the repository was assessed over a period of 100,000 years. The central conclusion of the SR-PSU safety assessment is that the extended SFR repository meets requirements on protection of human health and of the environment that have been established by the Swedish radiation safety authority for the final disposal of radioactive waste. Furthermore, the design of the repository was shown suitable for the waste selected and the applied methodology suitable for the safety assessment.

Download Full-text

Impact of Long Term Application of Inorganic Fertilizers and Organic Manure on Soil Fertility and Crop Productivity under Soybean-Wheat Cropping System in a Vertisol

International Journal of Environment and Climate Change ◽

10.9734/ijecc/2021/v11i830455 ◽

2021 ◽

pp. 24-30

Author(s):

Nilesh Patidar ◽

A. K. Dwivedi ◽

B. S. Dwivedi ◽

R. K. Thakur ◽

Jalendra Bairwa ◽

...

Keyword(s):

Soil Fertility ◽

Field Experiments ◽

Block Design ◽

Cropping System ◽

Crop Productivity ◽

Organic Manure ◽

Inorganic Fertilizers ◽

Available N ◽

The Impact

The field experiments was conducted is an ongoing All India Co-ordinate Research Project on “Long term Fertilizer Experiment” during 2018-2019 with soybean-wheat cropping sequence at the Research Farm Department of Soil Science, Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (M.P.), India. The objective of the study was the Impact of long term application of inorganic fertilizers and organic manure on soil fertility and crop productivity under soybean-wheat cropping system in a Vertisol. The experiment consists of ten treatments i.e. T1 50% NPK, T2 100% NPK, T3 150% NPK, T4 100% NPK + Hand Weeding, T5 100% NPK + Zn, T6 100% NP, T7 100% N, T8 100% NPK+ Farm Yard Manure, T9 100% NPK–S and T10 unfertilized plot (control) with four replications in a randomized block design. The findings of the present study indicated that the soil pH and EC were remaining unaltered even after continuous application of variable amounts of fertilizers either alone or in combination. A significant positive change in soil organic carbon, available N P K and S content was observed with continuous additions of balanced fertilizers and manures over the imbalanced or unfertilized treatments. The findings showed that the application of recommended dose of N, P and K (20:80:20 kg ha-1 for soybean and 120:80:40 kg ha-1 for wheat) with organic manure (FYM) @ 5 t ha-1 resulted in 185.8% and 325.9% increase over control in soybean and wheat yields, respectively. Thus, the continuous use of balanced fertilization, either alone or in combination with organic manure is necessary for sustaining soil fertility and productivity of crops.

Download Full-text

Microscopic and spectroscopic bioassociation study of uranium(VI) with an archaeal Halobacterium isolate

PLoS ONE ◽

10.1371/journal.pone.0262275 ◽

2022 ◽

Vol 17 (1) ◽

pp. e0262275

Author(s):

Stephan Hilpmann ◽

Miriam Bader ◽

Robin Steudtner ◽

Katharina Müller ◽

Thorsten Stumpf ◽

...

Keyword(s):

Radioactive Waste ◽

Rock Salt ◽

Luminescence Spectroscopy ◽

Spectroscopic Techniques ◽

High Level Radioactive Waste ◽

Long Term Storage ◽

High Level ◽

The Impact ◽

Term Storage

The safe disposal of high-level radioactive waste in a deep geological repository is a huge social and technical challenge. So far, one of the less considered factors needed for a long-term risk assessment, is the impact of microorganisms occurring in the different host rocks. Even under the harsh conditions of salt formations different bacterial and archaeal species were found, e. g. Halobacterium sp. GP5 1–1, which has been isolated from a German rock salt sample. The interactions of this archaeon with uranium(VI), one of the radionuclides of major concern for the long-term storage of high-level radioactive waste, were investigated. Different spectroscopic techniques, as well as microscopy, were used to examine the occurring mechanisms on a molecular level leading to a more profound process understanding. Batch experiments with different uranium(VI) concentrations showed that the interaction is not only a simple, but a more complex combination of different processes. With the help of in situ attenuated total reflection Fourier-transform infrared spectroscopy the association of uranium(VI) onto carboxylate groups was verified. In addition, time-resolved laser-induced luminescence spectroscopy revealed the formation of phosphate and carboxylate species within the cell pellets as a function of the uranium(VI) concentration and incubation time. The association behavior differs from another very closely related halophilic archaeon, especially with regard to uranium(VI) concentrations. This clearly demonstrates the importance of studying the interactions of different, at first sight very similar, microorganisms with uranium(VI). This work provides new insights into the microbe-uranium(VI) interactions at highly saline conditions relevant to the long-term storage of radioactive waste in rock salt.

Download Full-text

Effects of long-term field experiments on early stage litter decomposition in Austria and Sweden

10.5194/egusphere-egu2020-10280 ◽

2020 ◽

Author(s):

Maria Regina Gmach ◽

Martin A. Bolinder ◽

Lorenzo Menichetti ◽

Thomas Kätterer ◽

Taru Sandén

Keyword(s):

Litter Decomposition ◽

Decomposition Rate ◽

Field Experiments ◽

Early Stage ◽

Tillage Systems ◽

K Value ◽

Tea Bag Index ◽

The Impact ◽

Term Field

Soil organic matter decomposition affects the local and global C cycles. Decomposition is mainly affected by soil type and climatic conditions, for a given quality of organic material. This study tested the effect of land use and management, litter type, and climate on the early stage decomposition rate in long-term field experiments (LTEs) in Austria and Sweden. Standardized litter (Rooibos and Green tea) were used according to the Tea Bag Index (TBI) protocol (Keuskamp et al. 2013) for comparison of litter decomposition rate (k) and stabilization factor (S) in 11 sites in Austria (2015 and 2016) and 9 sites in Sweden (2016). The tea bags were buried at 8 cm depth and collected after ~90 days. Austrian LTEs focused on mineral nitrogen fertilization, mineral potassium fertilization, organic fertilization, tillage systems, and crop residues management. The LTEs evaluated in Sweden focused mainly on annual and perennial crops, mineral fertilization, and tillage systems. The impact of environmental parameters (air temperature and precipitation) was modeled to normalize the variance due to climatic effects at each site. The preliminary results show that in Austria TBI decomposition differed more between sites than between treatments at the same LTE. Minimum tillage treatment had significantly higher decomposition rates compared to reduced and conventional tillage. In Sweden, decomposition rate differed more between treatments than between sites. Fertilized plots showed higher stabilization than unfertilized, and maximum N fertilization had the highest k, while unfertilized had the lowest k. The effect of different tillage systems on k and S were variable across sites and treatments, although ploughing tended to result in the lowest k. The northernmost site resulted in the highest k value. Results indicated higher stabilization in perennial forage crops compared to annual crops. We also considered time-series decomposition for some sites with measurements at different time points by the TBI approach (retrieving tea bags after 15, 30, 60, and 90 days), and the use of Random Forest regressions to evaluate the importance of pedo-climatic variables on early stage decomposition.

Download Full-text

Rim Instant Release Radionuclide Inventory From French High Burnup Spent UOX Fuel

MRS Proceedings ◽

10.1557/proc-1193-627 ◽

2009 ◽

Vol 1193 ◽

Cited By ~ 5

Author(s):

D. Roudil ◽

C. Jegou ◽

V. Broudic ◽

M. Tribet

Keyword(s):

Small Volume ◽

Source Term ◽

Nuclear Waste Repository ◽

Spent Fuel ◽

Waste Container ◽

High Burnup ◽

Radionuclide Release ◽

Long Term Behavior ◽

The Impact

AbstractTo assess the long-term behavior of spent fuel in a nuclear waste repository, the chemical reactions between the fuel and possible intruding water must be understood and the resulting radionuclide release must be quantified. The instant release fraction (IRF) source term assumed to be instantaneously accessible to water after the failure of the waste container. Some IRF values for different kinds of spent fuel are available in the literature. However, the possible contribution the rim restructured zone for high-burnup UOX fuels, was not necessary taken into account. A specific study of the leaching behavior of the rim zone has been carried out on a UOX fuel sample with a burnup of 60 GWd·t-1 and 2.8% FGR. The 134/137Cs and 90Sr rim IRF are effectively higher than the gap and grain boundary inventories (respectively 4.4 wt% and 0.3 wt% of the total Cs and Sr inventories). Nevertheless because of the relative small volume of this zone in the pellet, the impact of the rim inventory appears to be limited and the complete Cs and Sr IRF (gap, grain boundaries and rim), were estimated at 1.85 and 0.3 wt%, respectively

Download Full-text