| 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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