Long-term oxygen depletion from infiltrating groundwaters: model development and application to intra-glaciation and glaciation conditions
2008 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 100, no 1-2, 72-89 p.Article in journal (Refereed) Published
Processes that control the redox conditions in deep groundwaters have been studied. The understanding of such processes in a long-term perspective is important for the safety assessment of a deep geological repository for high-level nuclear waste. An oxidising environment at the depth of the repository would increase the solubility and mobility of many radionuclides, and increase the potential risk for radioactive contamination at the ground surface. Proposed repository concepts also include engineered barriers such as copper canisters, the corrosion of which increases considerably in an oxidising environment compared to prevailing reducing conditions. Swedish granitic rocks are typically relatively sparsely fractured and are best treated as a dual-porosity medium with fast flowing channels through fractures in the rock with a surrounding porous matrix, the pores of which are accessible from the fracture by diffusive transport. Highly simplified problems have been explored with the aim to gain understanding of the underlying transport processes, thermodynamics and chemical reaction kinetics. The degree of complexity is increased successively, and mechanisms and processes identified as of key importance are included in a model framework. For highly complex models, analytical expressions are riot fully capable of describing the processes involved, and in such cases the solutions are obtained by numerical calculations. Deep in the rock the main source for reducing capacity is identified as reducing minerals. Such minerals are found inside the porous rock matrix and as infill particles or coatings in fractures in the rock. The model formulation also allows for different flow modes such as flow along discrete fractures in sparsely fractured rocks and along flowpaths in a fracture network. The scavenging of oxygen is exemplified for these cases as well as for more comprehensive applications, including glaciation considerations. Results show that chemical reaction kinetics control the scavenging of oxygen during a relatively short time with respect to the lifetime of the repository. For longer times the scavenging of oxygen is controlled by transport processes in the porous rock matrix. The penetration depth of oxygen along the flowpath depends largely on the hydraulic properties, which may vary significantly between different locations and situations. The results indicate that oxygen, in the absence of easily degradable organic matter, may reach long distances along a flow path during the life-time of the repository (hundreds to thousands of metres in a million years depending on e.g. hydraulic properties of the flow path and the availability of reducing capacity). However, large uncertainties regarding key input parameters exist leading to the conclusion that the results from the model must be treated with caution pending more accurate and validated data. Ongoing and planned experiments are expected to reduce these uncertainties, which are required in order to make more reliable predictions for a safety assessment of a nuclear waste repository.
Place, publisher, year, edition, pages
2008. Vol. 100, no 1-2, 72-89 p.
Groundwater chemistry; Mineral interaction; Model; Redox front propagation; Association reactions; Chemical reactions; Copper; Elastic moduli; Fluid mechanics; Fracture; Fracture fixation; Free radical polymerization; Garnets; Geological repositories; Glacial geology; Groundwater; Hydraulics; Hydrogeology; Intersections; Matrix algebra; Mineralogy; Minerals; Newtonian flow; Nonmetals; Nuclear physics; Numerical analysis; Organic compounds; Oxygen; Petroleum deposits; Petroleum reservoirs; Radioactive wastes; Radioactivity; Radioisotopes; Reaction kinetics; Risk assessment; Rocks; Silicate minerals; Sulfate minerals; Underground reservoirs; Analytical expressions; Chemical reaction kinetics; Complex modeling; Copper canisters; Deep geological repository; Deep groundwaters; Degree of complexity; Diffusive transport; Discrete fractures; Dual-porosity; Engineered barriers; Flow modes; Flow paths; Flow-paths; Fracture networks; Fractured rocks; Granitic rocks; Ground surfaces; Hydraulic properties; Key input; Life-time; Long distances; Long term perspective; Model development; Model formulation; Model framework; Nuclear waste; Nuclear waste repositories; Numerical calculations; Organic matter (OM); Oxygen depletion; Penetration depths; Porous matrixes; Porous rocks; Potential risks; Radioactive contamination; Redox conditions; Reducing capacity; Reducing conditions; Safety assessments; Short time; Transport processes; Process control; copper; ground water; mineral; organic matter; oxygen; radioisotope; sodium chlorite; chemical reaction; corrosion; glaciation; groundwater; infill; infiltration; kinetics; modeling; numerical method; oxygen; porous medium; radioactive waste; radionuclide; redox conditions; risk assessment; safety; thermodynamics; water chemistry; article; calculation; chemical reaction; conceptual framework; corrosion; depletion; diffusion; dissolution; glaciation; granite; kinetics; mathematical model; oxidation reduction reaction; priority journal; radioactive contamination; rock; thermodynamics; validation process; water contamination; water flow; water supply; Fresh Water; Geologic Sediments; Ice Cover; Models, Theoretical; Oxidation-Reduction; Oxygen; Porosity; Radioactive Waste; Refuse Disposal; Solubility; Sweden; Water Movements
IdentifiersURN: urn:nbn:se:kth:diva-7489DOI: 10.1016/j.jconhyd.2008.05.010ISI: 000259387600007PubMedID: 18644316ScopusID: 2-s2.0-48349117845OAI: oai:DiVA.org:kth-7489DiVA: diva2:12528
QC 20100818. Uppdaterad från Submitted till Published 20100818.2007-09-192007-09-192010-08-18Bibliographically approved