scholarly journals Diffusive transport of uranium and americium through clay rock down to ultra-trace levels

2021 ◽  
Vol 1 ◽  
pp. 153-154
Author(s):  
Daniel Glückman ◽  
Karin Hain ◽  
Claudia Joseph ◽  
Volker Metz ◽  
Francesca Quinto ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Host Rock ◽  
Diffusion Profile ◽  
Thin Layers ◽  
Opalinus Clay ◽  
Nuclear Waste Repository ◽  
Clay Rock ◽  
Wide Range ◽  
Ultra Trace ◽  
Geological Formations

Abstract. Clay rock is a potential host rock for the final disposal of nuclear waste in deep geological formations. In the scenario of ground water intrusion into the nuclear waste repository and subsequent corrosion of canisters and waste, possibly released actinides, such as uranium (U) and americium (Am), would be transported through the engineered barrier and clay host rock mainly by diffusion. Actinides are known to exhibit low solubility and are strongly sorbing under the reducing conditions of deep geological formations. Diffusion experiments are therefore difficult to perform due to analytical constraints. To our knowledge, the diffusion of U in clay rock has not been investigated below concentrations of 10-7molkg-1 clay (e.g., Joseph et al., 2013) and for Am, no diffusion experiments have been performed in a clay rock, considered suitable as host rock, such as Opalinus clay (OPA). This work aimed at the investigation of the diffusive behavior of U and Am down to ultra-trace concentrations (≪10-7molkg-1) in OPA. Laboratory-scale diffusion experiments were conducted with samples of OPA, obtained from the Mont Terri underground laboratory, Switzerland for up to 240 d. The OPA samples were placed in contact with synthetic pore water (I=0.22molL-1, pH=7.24), spiked with 5×10-9molL-1 of 233U and 243Am, respectively. After termination of the experiment, the OPA samples were segmented into thin layers of 20–400 µm. The obtained clay segments were analyzed for the 233U and 243Am content with accelerator mass spectrometry. Concentration profiles were determined down to 10-12molkg-1 clay for 233U and 5×10-10molkg-1 clay for 243Am. U showed a typical diffusion profile which can be interpreted by applying Fick's laws, while the Am profile was more complex, requiring further investigation of transport modes. These results will provide relevant insights into the transport behavior of U and Am in OPA over a wide range of concentrations down to ultra-trace levels.

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

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

<p>Argillaceous rocks have great potential as possible geological host medium to store radioactive waste.  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.</p><p>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.</p><p>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.</p><p>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.</p>

Hydro-geochemical processes in the emplacement cavern of a low and intermediate-level waste repository in an indurated clay-rock

2021 ◽  
Author(s):  
Vanessa Montoya ◽  
Jaime Garibay-Rodriguez ◽  
Olaf Kolditz
Keyword(s):  
Chemical Evolution ◽  
Nuclear Waste ◽  
Host Rock ◽  
Numerical Models ◽  
Intermediate Level ◽  
High Level Waste ◽  
Nuclear Waste Repository ◽  
Case Scenario ◽  
Damaged Zone ◽  
Waste Repository

<p>By 2080, Germany will have to store around 600 000 m<sup>3</sup> of low and intermediate-level nuclear waste (L-ILW) with negligible heat generation. This kind of waste is largely made up of used parts of nuclear power stations such as pumps, pipelines, filters, etc. placed in various types of waste containers made from either steel, cast iron, or reinforced concrete in different designs and sizes (i.e. cylindrical or box shaped). It is already decided that a total of 303 000 of the 600 000 m<sup>3</sup> L-ILW will be disposed in a final storage facility in the former iron ore mine Schacht Konrad which is under construction. However, it is still not clear where the L-ILW emplaced in in the old salt mine Asse (200 000 m<sup>3</sup>) will be stored in the future. The situation is particularly critical, as the waste have to be retrieved from the instable mine shafts partially flooded with groundwater, causing strong socio-political concerns as radioactive waste could contaminate the water nearby. For this reason, the new search for a nuclear waste repository for high-level waste (HLW), started in 2017, should also consider the possibility to accommodate the waste from Asse. Obviously, this is still subject to critics as this will make finding a final repository more difficult as storing HLW and L-ILW together requires different concepts and designs for each other and, above all, much more space.</p><p>In this context, in this contribution we have defined conceptual and numerical models to assess the hydro-chemical evolution of a L-ILW disposal cell in indurated clay rocks, involving the interaction of different components/materials and the expected hydraulic and/or chemical gradients over 100 000 years. The L-ILW disposal cell leverages a multi-barrier concept buried 400 m below the surface. The multi-barrier system is comprised of the waste matrix (i.e. backfilling the waste drums), the disposal container, the mortar backfill in the emplacement tunnel (where the disposal containers are located) and the clay host rock. The dimensions and design of the emplacement tunnel (e.g. 11 × 13 m) and disposal cells represent and consider some aspects taken into account in the designs of some European countries. In addition, tunnel walls reinforced with a shotcrete liner and the Excavation Damaged Zone is considered in the concept. The model is implemented in OpenGeoSys-6, an open-source version-controlled scientific software based on Finite Element Method which is capable of handling fully coupled hydro-chemical models by coupling OpenGeoSys to iPHREEQC. First calculation results, demonstrate that the most important processes affecting the near-field chemical evolution are i) the degradation of the concrete and cementitious grouts with porewater migrating inwards from the host rock and ii) the significant quantities of reactive and non-reactive gases (i.e. hydrogen, carbon dioxide and methane) that are generated as a result of: i) the anaerobic corrosion of metals present in the waste and containers and ii) the degradation of organic compounds by microbial and chemical processes. As a first approximation, some assumptions and simplifications have been considered, probably resulting in a wort case scenario.</p>

scholarly journals Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

2019 ◽  
Vol 107 (7) ◽  
pp. 623-634
Author(s):  
Aleksandr N. Vasiliev ◽  
Nidhu L. Banik ◽  
Rémi Marsac ◽  
Stepan N. Kalmykov ◽  
Christian M. Marquardt
Keyword(s):  
Solvent Extraction ◽  
Complex Formation ◽  
Nuclear Waste ◽  
Equilibrium Constants ◽  
Extraction Technique ◽  
Nuclear Waste Repository ◽  
Clay Rock ◽  
Complex Formation Constants ◽  
Solvent Extraction Technique

Abstract Natural clay rocks like Opalinus (OPA) and Callovo-Oxfordian (COx) clay rock are considered as potential host rocks for deep geological disposal of nuclear waste. However, small organic molecules such as propionate and lactate exist in clay rock pore water and might enhance Np mobility through a complexation process. Therefore, reliable complex formation data are required in the frame of the Safety Case for a nuclear waste repository. A solvent extraction technique was applied for the determination of ${\rm{NpO}}_2^ + $ complexation with propionate and lactate. Extraction was conducted from isoamyl alcohol solution containing 10−3 M TTA and 5 · 10−4 M 1,10-phenanthroline. Experiments were performed in 0.5–2.6 m NaCl solutions at temperatures ranging from 22 to 60 °C. Formation of 1:1 Np(V) complexes for propionate and lactate was found under the studied conditions. The SIT approach was applied to calculate equilibrium constants β°(T) at zero ionic strength from the experimental data. Log β°(T) is found linearly correlated to 1/T for propionate and lactate, evidencing that heat capacity change is near 0. Molal reaction enthalpy and entropy ( ${\Delta _{\rm{r}}}H_{\rm{m}}^ \circ $ and ${\Delta _{\rm{r}}}S_{\rm{m}}^ \circ $ ) could therefore be derived from the integrated van’t Hoff equation. Data for log β° (298.15 K) are in agreement with literature values for propionate and lactate. Np(V) speciation was calculated for concentrations of acetate, propionate and lactate measured in clay pore waters of COx. In addition, the two site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model was applied to quantitatively describe the influence of Np(V) complexation on its uptake on Na-illite, a relevant clay mineral of OPA and COx.

A tool to draw chemical equilibrium diagrams using SIT: Applications to geochemical systems and radionuclide solubility

2014 ◽  
Vol 1665 ◽  
pp. 111-116 ◽  
Author(s):  
I. Puigdomènech ◽  
E. Colàs ◽  
M. Grivé ◽  
I. Campos ◽  
D. García
Keyword(s):  
Experimental Data ◽  
Ionic Strength ◽  
Undergraduate Students ◽  
Nuclear Waste ◽  
Chemical Equilibrium ◽  
Equilibrium Constants ◽  
Nuclear Waste Repository ◽  
Wide Range ◽  
Java Programs ◽  
Institute Of Technology

ABSTRACTA set of computer programs has been developed to draw chemical-equilibrium diagrams. This new software is the Java-language equivalent to the Medusa/Hydra software (developed some time ago in Visual basic at the Royal Institute of Technology, Stockholm, Sweden). The main program, now named “Spana” calls Java programs based on the HaltaFall algorithm. The equilibrium constants that are needed for the calculations may be retrieved from a database included in the software package (“Database” program). This new software is intended for undergraduate students as well as researchers and professionals.The “Spana” code can be easily applied to perform radionuclide speciation and solubility calculations of minerals, including solubility calculations relevant for the performance assessment of a nuclear waste repository. In order to handle ionic strength corrections in such calculations several approaches can be applied. The “Spana” code is able to perform calculations based on three models: the Davies equation; an approximation to the model by Helgeson et al. (HKF); and the Specific Ion-Interaction Theory (SIT). Default SIT-coefficients may be used, which widens the applicability of SIT significantly.A comparison is made here among the different ionic strength approaches used by “Spana” (Davies, HKF, SIT) when modelling the chemistry of radionuclides and minerals of interest under the conditions of a geological repository for nuclear waste. For this purpose, amorphous hydrous Thorium(IV) oxide (ThO2(am)), Gypsum (CaSO4·2H2O) and Portlandite (Ca(OH)2) solubility at high ionic strengths have been modelled and compared to experimental data from the literature. Results show a good fitting between the calculated values and the experimental data especially for the SIT approach in a wide range of ionic strengths (0-4 M).

The Salton Sea Geothermal Field as a Natural Analog for the Near-Field in a Salt High-Level Nuclear Waste Repository

1984 ◽  
Vol 44 ◽  
Author(s):  
Wilfred A. Elders ◽  
Judith B. Moody
Keyword(s):  
Nuclear Waste ◽  
Near Field ◽  
Geothermal Field ◽  
Salton Sea ◽  
High Level Waste ◽  
Nuclear Waste Repository ◽  
Natural Analog ◽  
Naturally Occurring ◽  
Wide Range ◽  
High Level

AbstractThe Salton Sea Geothermal Field (SSGF), on the delta of the Colorado River in southern California, is being studied as a natural analog for the near-field environment of proposed nuclear waste repositories in salt. A combination of mineralogical and geochemical methods is being employed to develop a three dimensional picture of temperature, salinity, lithology, mineralogy, and chemistry of reactions between the reservoir rocks and the hot brines. Our aim is to obtain quantitative data on mineral stabilities and on mobilities of the naturally occurring radionuclides of concern in Commercial High-Level Waste (CHLW). These data will be used to validate the EQ3/6 geochemical code under development to model the salt near-field repository behavior.Maximum temperatures encountered in wells in the SSGF equal or exceed peak temperatures expected in a salt repository. Brines produced from these wells have major element chemistry similar to brines from candidate salt sites. Relative to the rocks, these brines are enriched in Na, Mn, Zn, Sr, Ra and Po, depleted in Ba, Si, Mg, Ti, and Al, and strongly depleted in U and Th. However the unaltered rocks contain only about 2–3 ppm of U and 4–12 ppm of Th, largely in detrital epidotes and zircons. Samples of hydrothermally altered rocks from a wide range of temperature and salinity show rather similar uniform low concentrations of these elements, even when authigenic illite, chlorite, epidote and feldspar are present. These observations suggest that U and Th are relatively immobile in these hot brines. However Ra, Po, Cs and Sr are relatively mobile. Work is continuing to document naturally occurring radionuclide partitioning between SSGF minerals and brine over a range of temperature, salinity, and lithology.

scholarly journals Claystone formations in Germany: what we (don't) know about them and how we can change this

2021 ◽  
Vol 1 ◽  
pp. 47-48
Author(s):  
Bernhard Schuck ◽  
Tilo Kneuker
Keyword(s):  
Phase I ◽  
Nuclear Waste ◽  
Site Selection ◽  
Numerical Models ◽  
Selection Procedure ◽  
Opalinus Clay ◽  
Nuclear Waste Repository ◽  
Fracture Density ◽  
Clay Formation

Abstract. Deep geological formations are considered for safe long-term disposal of high-level radioactive waste. Such a repository would be requested to prevent radionuclides from entering the biosphere for a period of 1 million years (StandAG, 2017). Consequently, a holistic characterization including lithological, mineralogical, geochemical, hydrological, structural and geomechanical properties of any potential repository-hosting rock formation is required. Nine claystone formations have been identified as “sub-areas” within the German site-selection procedure (BGE, 2020). The area covered by these formations comprises about half of the total area considered as being qualified for further exploration. However, despite its relevance to act as a geological barrier for, e.g. hydrocarbons or radionuclides, the characterization of clay-rich formations at depths exceeding 300 m in Germany has attained substantially less attention than economically more relevant units hosted by, e.g. sandstones or rock salt, which have been intensively explored. The BGR project BASTION aims at contributing to characterizing these claystone formations and emphasizes properties relevant to host a repository for nuclear waste. Investigations comprise (micro)structural/petrographic, mineralogical, geochemical, geophysical, hydraulic and thermomechanical analyses. In project phase I (2013–2019), claystones deposited in Northern Germany during the Lower Cretaceous were studied. These rocks belong to the fourth largest sub-area hosting claystones. Two of the main foci were to explore variations in lithology, mineralogy and geochemistry, and to identify deformation mechanisms (natural and artificial) by microstructural analyses. Although rocks appeared to be quite homogeneous on the 10–100 m scale, the results revealed distinct structural and sedimentary heterogeneities on the meter scale affecting fracture density. Another sub-area located in Southern Germany hosts the Opalinus Clay Formation (OPA). This up to 150 m thick claystone formation was deposited during the Middle Jurassic (Franz and Nitsch, 2009). Owing to its self-sealing capacity and ability to retain fluids, it is supposed to host the nuclear waste repository of Switzerland (Bossart et al., 2017). The OPA is quite well understood in terms of its lithology and (bio)stratigraphy, and there have been mineralogical, hydrological and petrophysical analyses, mostly documented in university theses a few decades old and sometimes difficult to access. However, it is questionable to what extent these investigations reflect the situation at depths relevant for the site-selection procedure. Well-documented data on the OPA and its properties relevant for nuclear waste disposal are available via the Swiss site-selection procedure (Bossart et al., 2017). However, as there remain substantial questions regarding the nature of the German portions of the OPA (e.g. spatial distribution of lithology, mineralogy, microstructures) at depths greater than a few decameters, it is unclear to what degree insights obtained in the Swiss site-selection procedure also account for Germany. Therefore, phase II of BASTION, which began in 2020, aims to use the multidisciplinary approach developed during phase I to characterize properties of the OPA relevant for the save long-term disposal of nuclear waste by identifying and quantifying structural and rheological heterogeneities. This will constitute important input for numerical models in any long-term safety assessment.

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