| 1. |
- Hatem, Mohammed, et al.
(författare)
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Interaction of clay and concrete relevant to the deep disposal of high-level radioactive waste
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 118, s. 178-187
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Tidskriftsartikel (refereegranskat)abstract
- A concept for the disposal of highly radioactive waste at depth in the Earth’s crust using very deep bore-holes requires that the upper 2 km’s of the 800 mm diameter, steeply drilled holes, be effectively sealed. This can be achieved by using dense smectitic clay where the rock is weakly fractured and strengthening with concrete when fracture zones are encountered. Earlier investigations have shown that chemical reactions between the clay and concrete can be expected both in the upper part where the temperature is lower than 90oC and in the deeper section where the temperature reaches up to 150oC. To study further this interaction, hydrothermal experiments were conducted using mixed-layer (illite/smectite) Holmehus clay and a low pH slag-based concrete placed in contact under isothermal conditions at 21°C, 100oC and 150oC for a period of 8 weeks. The sample sets, which consisted of two clay discs separated by concrete cast on the lower clay disc, were extracted in undisturbed form and exposed to uniaxial pressure for measuring the compressive strength at successively increasing pressures. Compression tests underenhanced thermal conditions led to strengthening of both the clay and concrete. X-ray diffraction and electron microscopy analysis of the material revealed an increasing degree of cation exchange at higher temperatures with the cement, whereby Ca replaced Na in the interlayer sites of smectite layers. Dissolution of illite/smectite was also evident occurring at enhanced temperatures, with a decrease in K, Mg and Fe content with advanced alteration. The enhanced strength of clay can be partly attributed to the precipitation of cement phases from circulating fluids, including precipitation of gypsum.
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| 2. |
- Hoang-Minh, Thao, et al.
(författare)
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Mineralogical Characterization of Di Linh Bentonite, Vietnam: A Methodological Approach of X-ray Diffraction and Transmission Electron Microscopy
- 2014
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Ingår i: Proceedings of 13th International Symposium on Mineral Exploration (ISME-XIII). - Hanoi : Vietnam National University Press, Hanoi. - 9786046215400 ; , s. 143-148
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Konferensbidrag (refereegranskat)abstract
- Vietnam has decided to establish nuclear power as further energy option. In order to develop a Vietnamese reference bentonite as potential barrier in a final repository for high radioactive waste, a detailed mineralogical investigation of Di Linh bentonite (Lam Dong province), lacustrine clay, was carried out by different methods especially transmission electron microscopy (TEM) linked with energy-dispersive X-ray (EDX). From a sample homogenized from 5 tones of the bentonite, mineral formulae of clay particles was calculated The calculation also focuses on randomly interstratifications of two and three members. The fraction <2 μm of Di Linh bentonite is composed mainly by montmorillonite (Ca0.06Mg0.03Na0.09K0.03Al1.39Fe0.25Mg0.26(OH)2 Si3.96Al0.04O10) and regular ordering (R1) illite-smectite interstratifications with K- and charge-deficiency (Ca0.04Mg0.07Na0.18K0.16Al1.76Fe0.08Mg0.16(OH)2Si3.62Al0.38O10). Additionally, Fe-poor kaolinite-smectite-vermiculite interstratifications and trace of Fe-rich chloritesmectite- vermiculite interstatifications were identified. TEM-investigations showed analytical proofs of the sedimentary character of smectite formation in the Di Linh deposit. Parent muscovite was weathered in several steps in two different environments: (i) K-leaching and layer-wise alteration into kaolinite; (ii) further edge- controlled alteration of mica into lathlike montmorillonite particles under dissolution of kaolinite layers from former kaolinite-mica intergrowths. Mineralogical composition of the Di Linh bentonite with mainly montmorillonite and illite-rich illite-smectite interstratifications shows that the Di Linh bentonite can be a suitable barrier candidate in final repositories.
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| 3. |
- Hoang-Minh, Thao, et al.
(författare)
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Use of TEM-EDX for structural formula identification of clay minerals : a case study of Di Linh bentonite, Vietnam
- 2019
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Ingår i: Journal of applied crystallography. - : International Union of Crystallography (IUCr). - 0021-8898 .- 1600-5767. ; 52:1, s. 133-147
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Tidskriftsartikel (refereegranskat)abstract
- Transmission electron microscopy linked with energy-dispersive X-ray spectroscopy (TEM-EDX) was applied to characterize mineralogical signals ofweathering processes in the Di Linh bentonite deposit (Vietnam) and to visualize the effects of Na activation on the smectitic phases. Modelling of X ray diffraction patterns (oriented mount) was applied in order to refine the computed structural formula. X-ray diffraction, X-ray fluorescence and Fouriertransform infrared spectroscopy (FT-IR) methods were also applied to verify the TEM-EDX results. An Excel-based routine has been developed in this research to allow fast computation of structural formulae and classification of the investigated clay particles. This routine supports the acquirement of 100 300 TEM-EDX analyses as a representative set of individual particles for each sample. The Excel-based routine involves end members of different clay mineral groups and interstratifications with two or three members (e.g. illite smectite interstratifications – IS-ml; dioctahedral vermiculite–smectite interstratifications – diVS-ml; and kaolinite–montmorillonite–dioctahedral vermiculite interstratifications – KSV-ml). The routine is now freely available. According to the identification procedure, the <2 mm fraction of the Di Linh bentonite (Vietnam) is composed mainly of K- and charge-deficient illite smectite interstratifications (or diVS-ml): montmorillonite-rich randomly ordered (R0) type and illite-rich regularly ordered (R1) type. Additionally, Fe-poor KSV-ml was identified.Industrial Na activation of the Di Linh bentonite resulted in an increase of theR1 diVS-ml portion and dissolution of a large part of the smectite-rich phases.The TEM-EDX approach also gave analytical proof of a sedimentary processfor Di Linh smectite. The parent muscovite was altered in two different environments: (i) K-leaching and layer-wise alteration into kaolinite (weathering), and (ii) further edge-controlled alteration of mica into lath-like montmorillonite particles associated with a dissolution of kaolinite layers from the former kaolinite–mica intergrowths by heat impact (basalt flow).
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| 4. |
- Kasbohm, Jörn, et al.
(författare)
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Lab-scale performance of selected expandable clays under HLW repository conditions
- 2013
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 69:8, s. 2569-2579
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Tidskriftsartikel (refereegranskat)abstract
- Smectite clay has been proposed for embedding canisters with highly radioactive waste in deep repositories because of its isolating capacity. Montmorillonite-rich bentonite is a premier buffer candidate for many national organizations that are responsible for disposal of such waste. Experience from the use of drilling mud at large depths indicates that other smectite clay minerals are more stable chemically and saponite is one of them. The physical properties of smectitic mixed-layer minerals like Friedland clay are known to be less sensitive to high salt contents and such clay may also be a buffer candidate. Montmorillonite-rich MX-80 clay, Greek saponite with a minor amount of palygorskite, and Friedland clay were investigated in hydrothermal tests with dense samples confined in oedometers with 95 °C temperature at one end, which was made of copper, and 35 °C at the other, for 8 weeks. A 1 % CaCl 2 solution was circulated through a filter at the cold end. At the end of the tests, the samples were sliced into three parts, which were tested with respect to expandability, hydraulic conductivity, and chemical composition. The tests showed that while the saponite was hardly changed at all and did not take up any copper, MX-80 underwent substantial changes in physical performance and adsorbed significant amounts of copper. The Friedland clay sample was intermediate in both respects
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| 5. |
- Popov, Viktor, et al.
(författare)
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Disposal of Radioactive Waste in Abandoned Mines
- 2019
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 9:3, s. 1-38
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Tidskriftsartikel (refereegranskat)abstract
- Countries using nuclear energy tend to favour disposal of Low-Level and Intermediate-Level radioactive waste in mined repositories consisting of series of tunnels or drifts connected to disposal tunnels at a few hundred meters depth. Abandoned mines can serve as repositories for such waste and the present study indicates that this would be possible also for High-Level Waste in the form of spent reactor fuel. The technique implies encapsulation of such waste in metal canisters surrounded by densely compacted smectite clay in relatively shallow mined repositories as well as in very deep bored holes. Intermediate-Level radioactive waste can be disposed of in caverns in the form of packages of metal containers cast in low-pH concrete and embedded in dense smectitic clay.
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| 6. |
- Pusch, Roland, et al.
(författare)
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Deep Boreholes for Storage of Spent Reactor Fuel and Use of the Heated Rock for Production of Electric Energy or hot fluid for heating purposes
- 2020
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Ingår i: Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040. ; 10:1, s. 127-153
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Tidskriftsartikel (refereegranskat)abstract
- Lack of energy is a serious threat to the prosperity of many developed states that have access to or plan to use nuclear power. The paper describes a concept for solving two major problems related to these conditions, namely safe disposal of spent reactor fuel and generation of electric energy or hot fluid by use of heat produced by the disposed waste. The challenge in storing spent nuclear fuel can be met with by installing such highly radioactive waste in deep boreholes with fuel rods encapsulated in canisters of copper-lined iron or titanium. Electric energy can be generated by utilizing the accumulated heat in the same rock mass by pumping up hot water or clayey mud from series of deep holes bored parallel and between corresponding holes with nuclear waste. The amounts of heat in each of the hot-water holes overlap and raise the initial rock temperature at 1,500-3,000 m depth to about 80-90oC after some 50 years and to 70-80oC in 500 years, after which the temperature in the hot-fluid holes goes down successively to the initial value 60-70oC in about 500 years. If these holes are subsequently deepened from 3,000 to 5,000 meters, utilization of the hot fluid can continue for another 500 years.
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| 7. |
- Pusch, Roland, et al.
(författare)
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Deep disposal of spent nuclear fuel
- 2019
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Ingår i: Waste Management and the Environment IX. - : WIT Press. ; , s. 399-414
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Konferensbidrag (refereegranskat)abstract
- An alternative but still untested approach is to dispose of highly radioactive waste in very deep boreholes, a concept being considered in the UK and the US. One version of this concept known as Very-Deep-Hole (VDH) storage proposes drilling of up to 4 km deep holes and placing in a series of stacked super-containers sealed by a combination of dense clay and concrete. In this case the risk of losing clay material by dispersion and erosion where the holes intersect fracture zones would be eliminated by casting concrete of a new type. VDH containment relies on the use of copper or Navy Bronze tubes filled with dense clay in the upper parts of the holes and with clay-embedded canisters with waste in the lower parts. The maturation and isolating function of the clay seals in the holes and their chemical interaction with concrete and waste canisters are considered and assessed. The work has focused on the mechanical testing and microscope investigations of the clay/concrete. Hydrothermally treated clay and concrete, exposed to 20-150°C, which represents the conditions over the entire length of a real VDH, have been tested. The recorded impact of strong heating showed stiffening and some reduction in hydraulic conductivity of the clay and concrete.
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| 8. |
- Pusch, Roland, et al.
(författare)
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Degradation Mechanisms in Smectitic Clay for Isolating Radioactive Waste
- 2019
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 9:3, s. 115-130
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Tidskriftsartikel (refereegranskat)abstract
- Most of the proposed techniques for chemical shielding of radioactive waste implies use of smectite clay, which degrades according to a well-known scheme. Since such “buffer” clay has to serve for many thousands of years, the mechanisms in the unavoidable long-term degradation process must be understood and accounted for as described in the paper. In addition to conversion of smectite to non-expandable minerals cementation by precipitation of siliceous matter created in the degradation process is of concern since it can reduce the self-sealing capacity of desiccated or mechanically damaged clay.
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| 9. |
- Pusch, Roland, et al.
(författare)
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Disposal of Low- and Intermediate-Level Radioactive Waste
- 2019
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 9:3, s. 237-272
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Tidskriftsartikel (refereegranskat)abstract
- As for isolation of high-level radioactive waste by use of smectite clay it serves very well also for hindering radionuclides from low- and intermediate-level waste to contaminate groundwater. It can be used for minimizing groundwater flow through and along waste packages and for providing them with ductile embedment for eliminating the risk of damage caused by displacements in host rock or concrete vaults. The clay can have the form of liners placed and compacted on site over vaults constructed on the ground surface, or consist of compacted blocks of clay granules that are tightly placed around waste packages in underground drifts and rooms. In either case the initially incompletely water saturated clay will swell in conjunction with water uptake until tight contact with the confining medium has been established. The clay seals must be sufficiently dense to fulfill criteria set with respect to hydraulic conductivity and swelling capacity, paying due attention to the salt content in the porewater. Their physical and chemical stabilities must be acceptable in short- and long-term perspectives, which is a few hundred years for most low-level wastes up to tens of thousands of years for long-lived waste.
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| 10. |
- Pusch, Roland, et al.
(författare)
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Holmehus clay — A Tertiary smectitic clay of potential use for isolation of hazardous waste
- 2015
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Ingår i: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 188, s. 38-47
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Tidskriftsartikel (refereegranskat)abstract
- The Danish Tertiary Holmehus clay belongs to the series of illite-smectite mixed-layer clays in northern Europe and has a potential to serve as an effective engineered barrier for isolating hazardous waste. Mineralogical specification was made of the components illite/smectite mixed-layer and dioctahedral vermiculite/smectite mixed-layer structures. The lower content of expandable phase than of smectite- rich clays like MX-80 gives somewhat higher hydraulic conductivity and somewhat lower swelling pressure but both are deemed suitable for isolating canisters with high-level radioactive waste in deeprepositories for densities at water saturation of at least 1900 kg/m3. The lower swelling pressure, the potential of being chemically more stable, and the high buffer capacity by providing dissolved Si makes Holmehus clay a candidate for use in both deep and near-surface repositories.
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| 11. |
- Pusch, Roland, et al.
(författare)
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Mechanisms Involved in Maturation of Clay Seals in Boreholes for Storing Spent Reactor Fuel
- 2019
-
Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 9:3, s. 197-226
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Tidskriftsartikel (refereegranskat)abstract
- Smectite clay, especially montmorillonite, is proposed for isolating canisters containing highly radioactive waste (HLW) like spent reactor fuel placed in deep boreholes. It is used for minimizing groundwater flow around and along waste packages (“Buffer Clay”) and for providing them with ductile embedment for eliminating risk of canister damage caused by displacements in the host rock. The clay has the form of heavily compacted blocks of granules that swell in conjunction with water uptake until their full hydration potential has been utilized. The dense clay blocks are fitted in perforated supercontainers that are submerged in smectite mud. The long-term chemical stability of the clay is sufficient for providing the required waste-isolating capacity, which is primarily supplied by the heavyness of stagnant, very salt groundwater at depth.
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| 12. |
- Pusch, Roland, et al.
(författare)
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Possibilities and Limitations in Using Smectite Clay for Isolating High-Level Radioactive Waste (HLW)
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:5, s. 87-130
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Tidskriftsartikel (refereegranskat)abstract
- Global interim storage of HLW has reached a level that requires large extension of the storage capacity, which puts pressure on regulatory authorities and national parliaments for finding and applying ways of safe disposal of such waste. An important option is to use very dense natural expandable clay for isolating spent nuclear fuel in boreholes where it will be exposed to high temperature for hundreds to a few thousand years. The clay must be placeable and homogeneous and be able to sustain significant shear strain and temperatures up to 150oC without leaking or losing its ductile behaviour and self-healing potential. In this document the long-term function of such seals, which have the form of dense smectite blocks and soft smectite mud surrounding the containers/canisters will be described with respect to the impact of degrading physical/chemical mechanisms. Focus is on clay barriers for isolating spent nuclear fuel in up to 3-4 km deep boreholes but aspects are also provided on disposal in mined repositories at a few hundred m depth below the ground surface.In either case the dense clay surrounding the waste containers will expand and enclose them, and consolidate the surrounding mud, which successively becomes denser, while the dense clay seal softens until its swelling pressure and the pressure of the mud is the same. The clay seals in deep boreholes used for disposal of spent nuclear fuel consist of a central core of dense expandable clay in perforated tubes (“supercontainers”) submerged in clay mud according to a concept termed VDH. In the lower parts of 3-4 km deep boreholes these tubes, made of copper, Navy Bronze, titanium or steel, host canisters lined with highly compacted expandable clay. In the upper parts of the holes the same type of supercontainers with no waste but with dense smectite clay blocks make up a primary barrier to possibly released radionuclides. A second barrier is the heaviness of the strongly saline groundwater at depth, which prevents such water to reach high up to the biosphere. The role of the mud is to save the supercontainers from touching the borehole walls when being placed, and to seal voids in the borehole walls with clay. The dense clay and soft clay mud will interact physically and ultimately become a homogeneous silicified clay body. Creep strain in the rock causes the deposition holes to con, which increases the radial pressure on the clay seals and thereby eliminates flow and diffusive migration of possibly contaminated porewater from the deployment part to move to the ground surface.
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| 13. |
- Pusch, Roland, et al.
(författare)
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Rational and Economic Disposal of Hazardous Waste –Use of Abandoned Mines
- 2014
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scienpress Ltd. - 1792-9040 .- 1792-9660. ; 4:2, s. 33-54
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Tidskriftsartikel (refereegranskat)abstract
- Deep geological disposal of dangerous waste like mercury, solidified organic pesticides and radioactive rest products, requires suitable engineered barriers. Use of deep abandoned mines is a rational and economic alternative to construction of a repository in virgin rock but requires knowledge of the structural constitution of the rock for assessment of groundwater flow and rock mechanical conditions. Such information is much more detailed through the activities of mining companies than from exploration of virgin rock. Organizations responsible for disposal of radioactive waste in crystalline rock count on the host rock as a barrier to migration of released radionuclides to the biosphere but present investigations reduce its role to provide mechanical support of the waste packages while effective hindrance of migration of contaminants can be offered by engineered barriers, i.e. waste containers and clay embedding them. For certain waste in granular form, like Hg batteries, mixing with expandable clay and layerwise placement and compaction is deemed possible as described in the paper. The primary role of the clay is to make the clay-mixed waste very tight and ductile. By constructing liners of highly compacted clay blocks along the periphery of the disposal rooms the rock is given sufficient support and effective isolation of the waste. If the liners have a thickness of 0.5-1 m and placed in dry form the time for complete water saturation of the clay/waste mixture can be several thousands of years. Not until then migration of hazardous waste elements to the rock can start.A major role in the hydrological performance of the host rock is that of the excavation-disturbed zone (EDZ). It short-circuits the natural system of flow paths and causes quick transport of released contaminants to downstream wells.
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| 14. |
- Pusch, Roland, et al.
(författare)
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Roles of clay and concrete in isolating high-level radioactive waste in very long holes
- 2013
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Ingår i: International Journal of Research and Reviews in Applied Sciences. - 2076-734X .- 2076-7366. ; 16:2, s. 263-273
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater flow transports possibly released radionuclides from underground repositories to the biosphere. It can also make construction difficult as is obvious from examining technical solutions for disposal of high-level radioactive waste (HLW) in long subhorizontally bored holes (KBS-3H) and in very deep boreholes (VDH). The presence of intersected, water-bearing fracture zones requires concrete for sealing these parts of the holes while the rest contains canisters surrounded and separated by dense, expandable clay. Casting of the concrete should be preceded by grouting of the fractured rock using cementitious materials composed so that mutual physical and chemical interaction do not degrade either of them. For the sake of rock stability the horizontal holes have to be located at very moderate depth, 400-500 m, where the rock has a high average hydraulic conductivity, while the slimmer, steep holes reaching down to 4 km are kept stable by using clay mud in the construction phase and dense clay for long term performance. The rock at this depth is much less permeable than higher up and the groundwater sufficiently salt to be maintained there, causing only local thermally induced circulation of possibly contaminated water. The KBS-3H concept involves practical difficulties and risks in the installation of the clay seals and waste canisters, for which the risk of shearing by slip of frequently intersected steep fractures is a major threat after closure of the repository. The VDH concept relies on effective sealing of the upper part of the deep holes and puts less demand on the seals in the lower, waste-bearing part, for which the buoyancy conditions of the groundwater make it a major barrier to upward migration of possibly released radionuclides.
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| 15. |
- Pusch, Roland, et al.
(författare)
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The concept of highly radioactive waste (HLW) disposal in very deep boreholes in a new perspective
- 2012
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scienpress Ltd. - 1792-9040 .- 1792-9660. ; 2:3, s. 1-24
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Tidskriftsartikel (refereegranskat)abstract
- Two basically different concepts for disposal of highly radioactive waste are the often cited KBS-3 method and a concept termed VDH (Very Deep Boreholes). So far, the deep hole concept has been ranked as number two because the canisters are not assumed to be retrievable and because some of the techniques for installation of the waste are not yet at hand. Reconsideration of the design and function of VDH shows that, in addition to the advantage of no transport of released radionuclides by groundwater flow up to the ground level because of the almost stagnant salt groundwater at depth, the rock at depth is considerably less permeable than for mined repositories at shallow depth. A further advantage is that VDH will be less affected by future glaciations. Less good is that precise adaption of canister and seal positions to the rock structure cannot be made until boring of the deep holes is complete. Furthermore, the deep holes need to be supported by casings and all work deeper than 500 m must be made with mud in them. Retrieval of damaged casings and stuck canisters may be more difficult than in mined repositories.
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| 16. |
- Pusch, Roland, et al.
(författare)
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The role of smectite clay barriers for isolating high-level radioactive waste (HLW) in shallow and deep repositories
- 2015
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Ingår i: Procedia Earth and Planetary Science. - : Elsevier. - 1878-5220. ; 15, s. 680-687
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Tidskriftsartikel (refereegranskat)abstract
- The major engineered barriers to migration of radionuclides from HLW in repositories are the canister and surrounding smectite clay. They interact physically and chemically by which the properties of both are changed, especially of the smectite “buffer” clay that is examined in the paper. The canisters are made of copper-lined iron according to the Swedish and Finnish concepts, steel being an alternative. The function of the host rock is of importance and the paper examines the role of two repository concepts with long subhorizontal or deep vertical holes for placing the waste. The hydraulic conductivity of the canister-embedding smectite clay can be significantly raised by high temperature and temperature gradients, which generate precipitation of salt and silica in different parts of the buffer clay. The impact of the degrading processes on the waste-isolating capacity is different for shallow repositories in permeable rock and for very deep disposal with higher temperature. The latter has stagnant groundwater as major barrier to the migration of radionuclides.
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| 17. |
- Pusch, Roland, et al.
(författare)
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Two genuinely geological alternatives for disposal of highly radioactive waste (HLW)
- 2016
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Ingår i: Comunicações Geológicas. - : Laboratório Nacional de Energia e Geologia (LNEG). - 0873-948X .- 1647-581X. ; 103, s. 25-39
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Tidskriftsartikel (refereegranskat)abstract
- Disposal of highly radioactive waste (HLW) can be environmentally acceptable if radionuclides are kept isolated from the groundwater, which has inspired planners of repositories to work out multibarrier concepts that postulate defined functions of the host rock and engineered waste confinements. Assessment of the role of the host rock involves groundwater flow modelling and rock mechanical analysis, which are both highly speculative and ignore future changes in rock structure, stress conditions, and groundwater flow. Widening the perspective by considering the integrated physical performance of contacting geological strata respecting groundwater flow conditions can provide excellent isolation of HLW with a minimum of engineered barriers as illustrated by the principle of very deep boreholes (VDH) for which the very high salt content of deep water is the primary barrier by maintaining possibly contaminated groundwater at depth. Such isolation of groundwater regimes can also be obtained by constructing relatively shallow repositories in crystalline rock covered by clay-containing sedimentary rock in regions with no or very low hydraulic gradients. The paper describes a possible case of this type, showing that effective isolation of HLW in repositories of commonly discussed types, KBS-3H and VDH, can be achieved under present climatic conditions.The paper compares the short- and long-term functions of repositories located at the southern end of the Swedish island Gotland, being an example of desired geological conditions that are found also in other parts of Sweden and in Lithuania, Germany, Holland and the UK. Here, 500 m of sediment rock series cover gneiss bedrock in which a KBS-3H repository of SKB-type can be built under virtually “dry” conditions because of the tightness of the overlying sedimentary rock and lack of hydraulic gradients in the crystalline rock. Shafts leading down from the ground surface to the repository level are constructed by use of freezing technique and lined with low-pH concrete before installation of waste after which they have to be sealed with expanding clay. Use of initially largely water-saturated clay provides suitable physical properties of the embedment of waste containers. Alternatively, a VDH repository consisting of a number of steep 4 km deep boreholes with about 8oo mm diameter can be driven for installing waste below 2 km depth, leaving the upper 2 km for sealing with clay. The geological conditions, which are also believed to provide acceptable rock pressure conditions for construction of a KBS-3H repository at about 600 m depth, are believed to be suitable for the construction and short- and long-term performance of either repository type.
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| 18. |
- Yang, Ting
(författare)
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Borehole sealing with expandable buffer clays in HLW disposal : Lab-scale performance
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two basically different multibarrier concepts for high-level radioactive waste (HLW) are the often cited KBS-3 V/H concepts, for isolating nuclear waste at 400-600 m depth and Very Deep Boreholes concepts (VDH) for placement at 2000-4000 m depth. Both make use of expandable clay as isolating medium of canisters with HLW and as backfill material in shafts and tunnels in repositories for safe disposal of such waste. This licentiate thesis is based on three papers related to the properties of clays for use as engineered barriers, and to their performance at geological disposal. The first paper deals with the buffer criteria for the two disposal concepts. In this paper the possibilities and limitations of using clays of montmorillonite-, saponite- and mixed layer clay type are considered. The second paper discusses the swelling property and permeability of Na-montmorillonite clays (MX-80, GMZ) and illite-smectite mixed layer clay (Holmehus) saturated and percolated by distilled water and a salt solution. The third paper describes a lab-scale performance of VDH holes sealing using Holmehus clay. In this paper, methods for solving the problem of too quick hydration of the dense clay are investigated and evaluated.
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