scholarly journals Influence of Hyper-Alkaline pH Leachate on Mineral and Porosity Evolution in the Chemically Disturbed Zone Developed in the Near-Field Host Rock for a Nuclear Waste Repository

2015 ◽  
Vol 107 (2) ◽  
pp. 489-505 ◽  
Author(s):  
Xiaohui Chen ◽  
Steven F. Thornton ◽  
Joe Small
Keyword(s):  
Nuclear Waste ◽  
Host Rock ◽  
Near Field ◽  
Nuclear Waste Repository ◽  
Alkaline Ph ◽  
Porosity Evolution ◽  
Disturbed Zone ◽  
Waste Repository

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 Radiation Effects on Materials in the Near-Field of a Nuclear Waste Repository

2000 ◽  
Vol 663 ◽  
Author(s):  
B.X. Gu ◽  
L.M. Wang ◽  
S.X. Wang ◽  
R.C. Ewing
Keyword(s):  
Ion Exchange ◽  
Nuclear Waste ◽  
Radiation Effects ◽  
Ion Beam ◽  
Near Field ◽  
Energetic Electron ◽  
Layered Silicates ◽  
Nuclear Waste Repository ◽  
Layer Spacing ◽  
Waste Repository

ABSTRACTThe long-term radiation effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments with energetic electron or ion beam irradiation. The materials studied include: zeolites, layered silicates (smectite clay and mica), as well as crystalline silicotitanate (CST) which is an important ion exchange material for the chemical separation of high-level liquid radioactive wastes.In situ transmission electron microscopy (TEM) during irradiation by energetic electrons and ions has shown that all of the studied materials are susceptible to irradiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010 ∼ 1012 Gy or displacement doses on the order of 0.1 dpa (equivalent to doses received in 400-1,000 years for a high-loading nuclear waste form). Amorphization may be preceded or accompanied by dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layered silicates, radiation effects are significantly enhanced at higher temperatures. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction in ion exchange and sorption/desorption capacities for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g. zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release of sorbed or ion-exchanged radionuclides.

In situ experiments on the performance of near-field for nuclear waste repository at KURT

2012 ◽  
Vol 252 ◽  
pp. 278-288 ◽  
Author(s):  
Won-Jin Cho ◽  
Jin-Sub Kim ◽  
Changsoo Lee ◽  
Sangki Kwon ◽  
Jong-Won Choi
Keyword(s):  
Nuclear Waste ◽  
Near Field ◽  
Nuclear Waste Repository ◽  
In Situ Experiments ◽  
Waste Repository

Implications of rock structure on the performance in the near field of a nuclear waste repository

1998 ◽  
Vol 49 (3-4) ◽  
pp. 195-200 ◽  
Author(s):  
Johan Andersson ◽  
Peter Robinson ◽  
Michael Impey
Keyword(s):  
Nuclear Waste ◽  
Near Field ◽  
Nuclear Waste Repository ◽  
Rock Structure ◽  
Waste Repository
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