Spelling suggestions: "subject:"buclear waste"" "subject:"anuclear waste""
201 |
Samråden i samband med slutförvaret för använt kärnbränsle i Östhammars kommunLindstrand, Åsa January 2018 (has links)
Detta är en fallstudie där SKBs genomförda samråd i Östhammars kommun under åren 2002-2011 har studerats. Inför den ansökan som SKB lämnade till mark- och miljödomstolen 2011 behövde bolaget upprätta en miljökonsekvensbeskrivning (MKB). För att kunna göra detta behövde samråd genomföras. Det planerade slutförvaret är en komplex verksamhet och kan upplevas besvärlig att samråda kring, både av verksamhetsutövaren och av deltagare. Syftet med samrådet är att få in synpunkter och frågor kring den tänkta verksamheten som sedan kan användas till att utveckla och förbättra miljökonsekvensbeskrivningen. Vanliga sätt att bedriva samråd är att hålla informationsmöten, vilket också var det sätt som SKB valde. Det material som finns från dessa samråd är sammanställningar som SKB själva har gjort. När SKB lämnade in sin ansökan lämnades det också in en samrådsredogörelse där de genomförda samråden beskrivs. SKB har genomfört sina samråd på ett ganska förutsägbart sätt. Då det bara finns skriftligt material från samråden så är det svårt att avgöra om de har återgivits på ett rättvisande sätt. Det är med tveksamhet som syftet med samråd kan ses som uppfyllt. / This is a case study where Swedish nuclear fuel and waste management company's (SKB) consultations in the municipality of Östhammar during the years 2002-2011 have been studied. Together with the application submitted by SKB to the Land and Environmental Court in 2011, the company needed an environmental impact assessment (EIA). In order to do this, consultations was a necessity. The planned repository is a complex activity and may be difficult to consult, both by the operator and by participants. The purpose of the consultation is to bring in comments and questions about the intended activities, which can then be used to develop and improve the environmental impact assessment. Common ways of conducting consultations are holding information meetings, which was also the way SKB chose. The material available from these consultations is summaries that SKB itself has made. When SKB submitted its application, a consultation report was also submitted, describing the consultations conducted. SKB has conducted its consultations in a fairly predictable manner. Since there is only written material from the consultations, it is difficult to determine whether they have been reproduced in a fair way. It is with hesitation that the purpose of the consultations can be seen as fulfilled. / <p>2019-09-13</p>
|
202 |
風險溝通與審議式民主的連結─ 以「核廢何從電視公民討論會」為例 / The link of risk communication and deliberative democracy:The case of“Where Would the Nuclear Waste Go?” TV forum.王憶萍 Unknown Date (has links)
面對高度科技化、工業化及專業化的社會,風險溝通已是政府面對環境爭議時難以規避的課題。回顧台灣近年來各項環境政策所遭遇的激烈抗爭,顯現政府風險溝通的不足。近年來興起的審議式民主,強調在理性與互惠的前提下,讓公民針對議題發表不同意見,成為政府替代傳統風險溝通的另一選項。尤其對於亟需完善風險溝通的高科技議題-「核廢料處置」而言,審議式民主似乎為其帶來契機。本研究透過分析「核廢何從電視公民討論會」審議活動過程政府與民眾的風險溝通關係,以及會議參與者的深度訪談資料,探討審議式會議如何落實風險溝通理念,藉此瞭解並反思審議式民主在台灣的實踐及其能否成為有效的風險溝通機制。
研究發現,在理論層面,審議式民主與風險溝通理論有許多相通之處;而在實踐層面,審議式民主得以落實風險溝通四項核心要素:「雙向互動」、「資訊公開、即時及更新」、「轉譯為常民語言」及「利害關係人參與」;除此之外,與會者及相關人員亦受到審議機制正向的影響;但在此會議中民眾與政府間信任關係的改善程度有限。本研究建議政府未來進行風險溝通時,應健全溝通管道、有效連結「會議結論」與「政策制定」、整合資訊公開管道並縮短數位落差、及處理與核能政策連動問題,方能有助於低放射性廢棄物的風險溝通。 / Risk communication is an unavoidable task when the government faces a highly industrialized and professionalized society. In the past years, environmental policies the government proposed and the protests these policies triggered show the deficiency of the government on risk communication. Recently, the rising deliberative democracy that emphasizes citizen dialogue on the basis of equality, rationality and reciprocity, could become an alternative to traditional risk communication for the government. Especially for the high-tech issue--disposal of nuclear waste-- which is desperate for comprehensive risk communication, deliberative democracy seems to bring the window of opportunity. Through examining the case of “Where Would the Nuclear Waste Go?” TV forum, this study explores risk communication between the government and citizens, and discusses how deliberative forum realizes the idea of risk communication in practice and delivers risk knowledge. Furthermore, this study rethinks the practice of deliberative democracy in Taiwan and accesses whether it could be an effective risk communication mechanism.
This study discovers that there is no contradiction between the practice of deliberative forum and the theory of risk communication. Deliberative democracy facilitates four core elements of risk communication: “two-way communication,” “information disclosure, in time and update,” “transfer into the language of ordinary people” and “the participation of stakeholders.” In addition, the participants and staffs were empowered positively by the deliberative mechanism. However, the improvement of trust between the government and citizens is very limited. This study suggests that when conducting risk communication for the low-level radioactive waste issue, the government should enhance risk communication channels, link the conclusions of citizen forums to policy making, integrate various information disclosure mechanisms, bridge the digital divide, and deal with the problem related to the nuclear energy policy.
|
203 |
Kärnproblem : opinionsbildning i kärnavfallsdiskursen i MalåSjölander, Annika January 2004 (has links)
<p>At the centre of this study lies one of the critical questions faced by (late-)modern society, namely that of taking care of the long-lived radioactive waste from nuclear power production. The problems of nuclear waste management are pictured as embracing a complex web of essential issues for society today, in terms of both its capacities and its shortcomings – so called core issues. The principal aim of the thesis is to examine the nuclear waste discourse in Malå, Västerbotten, from a critical discourse analytical perspective, through applying the approach developed by Michel Foucault in The Order of Discourse.</p><p>During the 1990s, the municipality of Malå played a prominent role as a candidate site for the geological disposal of Sweden’s spent nuclear fuel. A five-year process culminated in a local referendum on whether detailed site investigations should be permitted within the community. Following the result no further investigations have been undertaken. The discourse analysis is carried out through a study of opinion formation in the municipality during the period October 1992 to October 1997. Two main types of empirical material have been collected: interviews with opinion leaders (politicians, activists, journalists, information professionals, etc.) and contemporaneous mass media content (the local newspaper and regional television news).</p><p>In the empirical analysis, a review is made of the workings of the external and internal control mechanisms within the discourse; that is to say, how they serve to set limits on the content and form of the sense-making process concerning nuclear waste management. Important themes in the opinion forming process in Malå include information and expertise, opposition and legitimacy, the centre/periphery relationship and the themes of mistrust, partitioning and rejection. Among other themes identified as being marginalised or absent, one example is the Samish citizens’ views on the nuclear question. Four actors play a prominent role as authors of the discourse, namely the nuclear industry, the experts, Greenpeace and the mass media. The voices of resistance groups are also significant. Representatives from authorities and civil servants were most likely to take the commentary role in the discourse, along with journalists.</p><p>In the concluding analysis of the nuclear waste discourse in Malå, two main types of desire for truth, which form the discourse’s main order, are identified. The stronger concerns the will to know, which places the expert with a scientific background as the principal truth-teller. The other is ‘ordinary’ people’s desire, which influences the content and form of the opinion formation. It is also concluded that the mass media institutions play a significant role in this context, not least as mediators. Reflections on contemporary ‘core issues’ to which the analysis bears witness, such as the crisis of democracy, are also included. In addition, the implications of applying the Foucaultian research programme to a study of the nuclear question have been considered. </p>
|
204 |
Chemistry and Corrosion Mechanisms of Steels Embedded in High-density Slag Concrete for Storage of Used Nuclear FuelNadarajah, Parthiban 15 December 2011 (has links)
The chemistry and corrosion mechanisms associated with reduced sulfur compounds such as calcium sulfide, present in ground granulated blast-furnace slag (GGBFS), have been studied in high-density concrete, mortar and simulated pore-water environments. The high-density concrete and mortar samples were produced to replicate the high-density GGBFS concrete, in the dry storage containers (DSCs), used for radiation shielding from used nuclear fuel. Electrochemical measurements on embedded steel electrodes in high-density GGBFS concrete and mortar samples, showed that sulfide is capable of consuming oxygen to create a stable, reducing environment, though not in all cases, and the high-frequency electrolyte resistance increases with hydration time. Ion chromatography on simulated pore-water environments determined that thiosulfate is quite kinetically stable as a sulfide oxidation product and magnetite is capable of oxidizing sulfide. Microscopy has also been used to provide visual evidence of GGBFS hydration and elemental quantification of the hydrating microstructure in different environments.
|
205 |
Chemistry and Corrosion Mechanisms of Steels Embedded in High-density Slag Concrete for Storage of Used Nuclear FuelNadarajah, Parthiban 15 December 2011 (has links)
The chemistry and corrosion mechanisms associated with reduced sulfur compounds such as calcium sulfide, present in ground granulated blast-furnace slag (GGBFS), have been studied in high-density concrete, mortar and simulated pore-water environments. The high-density concrete and mortar samples were produced to replicate the high-density GGBFS concrete, in the dry storage containers (DSCs), used for radiation shielding from used nuclear fuel. Electrochemical measurements on embedded steel electrodes in high-density GGBFS concrete and mortar samples, showed that sulfide is capable of consuming oxygen to create a stable, reducing environment, though not in all cases, and the high-frequency electrolyte resistance increases with hydration time. Ion chromatography on simulated pore-water environments determined that thiosulfate is quite kinetically stable as a sulfide oxidation product and magnetite is capable of oxidizing sulfide. Microscopy has also been used to provide visual evidence of GGBFS hydration and elemental quantification of the hydrating microstructure in different environments.
|
206 |
Accelerating treatment of radioactive waste by evaporative fractional crystallizationNassif, Laurent 09 January 2009 (has links)
The purpose of the work described in this thesis was to explore the use of fractional crystallization as a technology that can be used to separate medium-curie waste from the Hanford Site tank farms into a high-curie waste stream, which can be sent to a Waste Treatment and Immobilization Plant (WTP), and a low-curie waste stream, which can be sent to Bulk Vitrification. The successful semi-batch crystallization of sodium salts from two single shell tank simulant solutions (SST Early Feed, SST Late Feed) demonstrated that the recovered crystalline product met the purity requirement for exclusion of cesium, sodium recovery in the crystalline product and the requirement on the sulfate-to-sodium molar ratio in the stream to be diverted to the WTP. The experimental apparatus, procedures and results obtained in this thesis on scaled-down experiments of SST Early and Late Feed simulated solutions were adapted and reproduced under hot-cell with actual wastes by our partners at Hanford. To prepare the application of the pretreatment process to pilot scale process, several varation to the feed solutions were investigated including the presence of carboxylates and amines organics compounds and solids particles. Results of the study showed that 4 organics species presented complications to the process (NTA, HEDTA, EDTA and sodium citrate) while the other species (Formate, acetate, glycolate and IDA) and solids particles did not in the conditions of the stored wastes.
In this thesis, the kinetics of the crystalline species formed at the condition of the early feed certification run (66 °C and 25 g/h evaporation) were determined along with the effect of the operating temperature and evaporation rate on these kinetics. On one hand, the study of evaporation rate values ranging from 25g/h to 75g/h showed that an increase in evaporation rate increased the specific nucleation while decreasing the specific growth rate. On the other hand, experiments on operating temperature ranging from 35 °C to 75 °C displayed that the nucleation rate of all species increased with temperature at the exception of sodium carbonate monohydrate and burkeite crystals, and that the growth rate of all species increased with temperature at the exception of sodium nitrate. Furthermore, sulfate based crystals such as trisodium fluoride sulfate were only roduced at 45 °C and 75 °C.
A simple steady state MSMPR population balance model was developed expressing the total population density function as the sum of the specific population density functions. The specific semi-batch crystallization kinetics were implemented in this model.
|
207 |
Kärnproblem : opinionsbildning i kärnavfallsdiskursen i MalåSjölander, Annika January 2004 (has links)
At the centre of this study lies one of the critical questions faced by (late-)modern society, namely that of taking care of the long-lived radioactive waste from nuclear power production. The problems of nuclear waste management are pictured as embracing a complex web of essential issues for society today, in terms of both its capacities and its shortcomings – so called core issues. The principal aim of the thesis is to examine the nuclear waste discourse in Malå, Västerbotten, from a critical discourse analytical perspective, through applying the approach developed by Michel Foucault in The Order of Discourse. During the 1990s, the municipality of Malå played a prominent role as a candidate site for the geological disposal of Sweden’s spent nuclear fuel. A five-year process culminated in a local referendum on whether detailed site investigations should be permitted within the community. Following the result no further investigations have been undertaken. The discourse analysis is carried out through a study of opinion formation in the municipality during the period October 1992 to October 1997. Two main types of empirical material have been collected: interviews with opinion leaders (politicians, activists, journalists, information professionals, etc.) and contemporaneous mass media content (the local newspaper and regional television news). In the empirical analysis, a review is made of the workings of the external and internal control mechanisms within the discourse; that is to say, how they serve to set limits on the content and form of the sense-making process concerning nuclear waste management. Important themes in the opinion forming process in Malå include information and expertise, opposition and legitimacy, the centre/periphery relationship and the themes of mistrust, partitioning and rejection. Among other themes identified as being marginalised or absent, one example is the Samish citizens’ views on the nuclear question. Four actors play a prominent role as authors of the discourse, namely the nuclear industry, the experts, Greenpeace and the mass media. The voices of resistance groups are also significant. Representatives from authorities and civil servants were most likely to take the commentary role in the discourse, along with journalists. In the concluding analysis of the nuclear waste discourse in Malå, two main types of desire for truth, which form the discourse’s main order, are identified. The stronger concerns the will to know, which places the expert with a scientific background as the principal truth-teller. The other is ‘ordinary’ people’s desire, which influences the content and form of the opinion formation. It is also concluded that the mass media institutions play a significant role in this context, not least as mediators. Reflections on contemporary ‘core issues’ to which the analysis bears witness, such as the crisis of democracy, are also included. In addition, the implications of applying the Foucaultian research programme to a study of the nuclear question have been considered.
|
208 |
Use of evaporative fractional crystallization in the pretreatment process of multi-salt single shell tank Hanford nuclear wastesNassif, Laurent 10 April 2007 (has links)
The purpose of the work described in this thesis was to explore the use of fractional crystallization as a technology that can be used to separate medium-curie waste from the Hanford Site tank farms into a high-curie waste stream, which can be sent to a Waste Treatment and Immobilization Plant (WTP), and a low-curie waste stream, which can be sent to Bulk Vitrification.
The successful semi-batch crystallization of sodium salts from two single shell tank simulant solutions (SST Early Feed, SST Late Feed) demonstrated that the recovered crystalline product met the purity requirement for exclusion of cesium, sodium recovery in the crystalline product and the requirement on the sulfate-to-sodium molar ratio in the stream to be diverted to the WTP.
In this thesis, experimental apparatus, procedures and results are given on scaled-down experiments of SST Early Feed for hot-cell adaptation along with operating parameters and crystallization mechanism studies on early feed multi-solute crystallization. Moreover, guidance is given regarding future steps towards adapting the technology to multi-salt crystallization kinetic parameter estimates and modeling.
Crystallization, Evaporative Fractional Crystallization, Nuclear Waste Pretreatment, Cesium Removal, Hanford, SST Early and Late feed, Multi-solute, Multi-salts, Simulant Testing
|
209 |
Influence of Permeation of Synthetic Groundwater Solutions on the Hydro-Mechanical Proerties of Barmer BentoniteShashidhar, S January 2013 (has links) (PDF)
The deep geological repository concept is based on “engineered barriers systems (EBS)” that are constructed in the repository and “natural barriers” provided by the surrounding geological environment. The EBS comprises of variety of sub-systems or components, such as the waste form, canister, buffer, backfill, seals, and plugs. Geological disposal is based on the concept of multiple barriers that work together to provide containment. The buffer is made up of densely compacted bentonite or bentonite-sand mix. Bentonite has both mechanical and physico-chemical functions, to fulfill as a barrier material in DGR. The bentonite buffer should hold the containers in place and prevent collapse of the excavation. A plastic deformability of the bentonite is desired to redistribute the stresses that can result from creep in the rock, and prevent transfer of excessive stresses to the canisters. The bentonite buffer must create an impermeable zone around the containers to ensure that the radionuclide released from the vitrified waste is limited by diffusive transport rather than advective transport in groundwater. Another important property of the highly compacted bentonite is its swelling potential. Its swelling potential should be as high as possible, to guarantee the sealing of any cracks occurring in the buffer material or in the storage gallery and thus ensure good imperviousness. Besides its mechanical function, bentonite buffer must sorb escaping radionuclides and thus retard their migration to the geo-environment. The bentonite buffer must retain its mechanical and physico-chemical functions over a span of several hundred thousand years to fulfill its role as a containment barrier in DGR. The bentonite buffer should maintain its physico-chemical and hydro-mechanical integrity on exposure to groundwater. Nuclear power agencies of several countries have identified suitable bentonites for use as buffer in DGR through laboratory experiments and large scale underground testing facilities. Japan has identified Kunigel VI bentonite, South Korea-Kyungju bentonite, China-GMZ bentonite, Belgium-FoCa clay, Sweden-MX-80 bentonite, Spain-FEBEX bentonite and Canada-Avonseal bentonite as candidate bentonite buffer for deep geological repository program. Bentonite from Barmer (Rajasthan State) was identified as suitable buffer for use in Indian deep geological repositories. The influence of moisture and dissolved salt migration on the physico-chemical and hydro-mechanical properties of Barmer bentonite has not been examined. The study is important to understand the clay’s behaviour under deep geological repository conditions, where, the bentonite buffer would come in contact with groundwater. Infiltration of groundwater with variable chemical composition could alter the physico-chemical and hydro-mechanical properties of the clay. The objectives of the thesis are as follows:
Examine the influence of permeation of distilled water (DW) and synthetic ground water (SGW) solutions under constant volume condition on suction, physico-chemical and moisture content/dry density characteristics of compacted Barmer bentonite specimens as function of permeation period (maximum permeation period– 30 days).
Examine the influence of variation in dry density and gravimetric water content as consequence of DW and SGW solution permeation on swell pressure and unconfined compression strength of Barmer bentonite specimens. Compare experimental swell pressures of re-constituted bentonite specimens with swell pressures predicted by diffuse double layer models.
Examine the influence of total dissolved solids (TDS) concentration of permeating solution on the unsaturated permeability of compacted Barmer bentonite specimens.
Organization of thesis:
After the first introductory chapter, a detailed review of literature is performed in Chapter 2 to review the physicochemical, mineralogical and hydro-mechanical properties of bentonites identified as buffer materials for deep geological repositories of various countries. Based on current understanding and need to perform similar studies with Barmer clay, the chapter develops the scope and objectives of the study. Chapter 3 presents a detailed experimental program of the study. Chapter 4 examines the influence of permeation of distilled water (DW) and synthetic groundwater (SGW) solutions (under constant volume conditions) on the total suction of compacted bentonite specimens at two locations in the clay. The influence of variation in dry density on the moisture migration-suction inter-relations of compacted bentonite specimens is also examined. The associated changes of DW and SGW solution migration under constant volume conditions on the physico-chemical properties, water content and dry density of compacted Barmer bentonite specimens are also examined. The experimental results brought out that matric suction mainly contributed (75 to 92 %) to total suction of the permeated specimens; the permeated specimens experienced reduction in matric suction with increase in gravimetric water content from increase in degree of saturation. Osmotic suction contributed to 10 to 25 % of the total suction of the permeated specimens and was observed to increase with gravimetric water content due to solubilization of salts contained in the voids of the compacted bentonite specimens. The total suction of compacted Barmer bentonite specimen was responsive to the total dissolved solids concentration of the permeating solutions as the specimen permeated with more saline solution (higher TDS value) exhibited lesser total suction. Upon permeation with DW and SGW solutions, the CEC of bentonite was unaltered, while, pH and TDS values were affected. Softening of the bentonite clay occurred from increase in water content and existence of compression zones (material used to seal 1mm gap in relative humidity probe aperture) that in turn facilitated dissipation of swelling stress leading to reduction in dry density values.
Chapter 5 examines influence of reduction in dry density and increase in water content on the swell pressure and compression strength characteristics of compacted Barmer bentonite specimens upon DW and SGW solution migration as the results could provide insight into possible deviations from the design properties upon wetting of bentonite buffer by groundwater under deep geological repository conditions. The experimental swelling pressures are also compared with those predicted by Gouy-Chapman diffuse double layer theory. The dry density of 1.6 Mg/m specimens permeated with DW and SGW solutions reduced to 1.59 to 1.36 Mg/m and water contents increased to 18.9 to 27 % on permeation with distilled water and SGW solutions for 30 days. The reductions in dry density and increase in water content caused 30 to 70 % reductions in swell pressures and 31 to 74 % decrease in unconfined compression strength values. Specimens initially compacted to dry density of 1.8 Mg/m, experienced reduction in dry
density ranging from 1.79 to 1.52 Mg/m and increase in water content from 18.6 to 24.2 % on permeation of DW and SGW solutions for 30 days. These reductions in dry density and increase in water caused the swell pressures to reduce from 4 to 55 % and unconfined compressive strengths to reduce by 31 to 67 %. Comparison of swell pressures gave -8 to 127 % variations between theoretical (from DDL theory) and experimental values due to errors associated with estimation of surface area and dissolved salt concentrations in pore water.
Chapter 6 examines the influence of salinity of permeating solution on the unsaturated permeability of compacted Barmer bentonite specimens. The salinity of permeants was varied by permeating distilled water (DW) and synthetic ground water solutions under constant volume conditions over maximum period of 30 days. Experimental results showed that the saturated permeability coefficients (ksat) of specimens compacted to 1.6 Mg/m, responded to variations in TDS of the permeant. Comparatively, the ksat values of specimens compacted to 1.8 Mg/mwere unaffected by variation in TDS of the permeant. Permeation of DW and SGW solutions decreased the ksat values with time from cation hydration and growth of diffuse ion layers for both, 1.6 and 1.8 Mg/mseries specimens. Increase in gravimetric water content from DW and SGW permeation increased the kunsat values of 1.6 Mg/m specimens from reduction in total suction. Re-orientation of soil structure mobilized larger kunsat values for specimens permeated with SGW solutions than DW at similar total suction. Permeation of DW and SGW solutions had lesser impact on kunsat values of the 1.8 Mg/m specimens in comparison to the 1.6 Mg/m series specimens. Further at both densities, the influence of permeation was more evident at location closer to hydration surface.
Chapter 7 summarizes the main findings of this study.
|
210 |
Etanchéité de l’interface argilite-bentonite re-saturée et soumise à une pression de gaz, dans le contexte du stockage profond de déchets radioactifs / Sealing efficiency of an argillite-bentonite plug subjected to gas pressure, in the context of deep underground nuclear waste storageLiu, JiangFeng 27 June 2013 (has links)
En France, le système de stockage profond de déchets radioactifs envisagé est constitué d’une barrière naturelle (roche hôte argileuse, argilite) et de barrières artificielles, comprenant des bouchons d’argile gonflante (bentonite)-sable pour son scellement. L'objectif de cette thèse est d’étudier l’efficacité du gonflement et du scellement des bouchons placés dans l’argilite, sous l’effet, à la fois, d’une pression d’eau et d’une pression de gaz (tel que formé dans le tunnel). Pour évaluer la capacité de scellement du bouchon bentonite/sable partiellement saturé en eau, on a évalué sa perméabilité au gaz Kgaz sous pression de confinement variable (jusqu’à 12MPa). L'étanchéité au gaz (Kgaz < 10-20m2) est obtenue sous confinement Pc≥9MPa si la saturation est d’au moins 86-91%. Par ailleurs, nous avons évalué le gonflement et l'étanchéité du bouchon de bentonite-sable imbibé d’eau dans un tube d’argilite ou de Plexiglas-aluminium lisse ou rugueux. La présence de gaz diminue la pression effective de gonflement (et la pression de percée de gaz) à partir d’une pression Pgaz= 4 MPa. Après saturation complète en eau, l’écoulement continu de gaz au travers du bouchon seul se fait à Pgaz=7-8MPa s’il dispose d’une interface lisse avec un autre matériau (tube métallique), alors que celui au travers de l’ensemble bouchon/argilite a lieu à Pgaz=7-7,5MPa. Le passage à travers le bouchon gonflé au contact d’une interface rugueuse se fait à une pression de gaz bien supérieure à la pression de gonflement du bouchon. Les essais de percée de gaz montrent que l'interface et l'argilite sont deux voies possibles de migration de gaz lorsque l’ensemble bouchon/roche hôte est complètement saturé / In France, the deep underground nuclear waste repository consists of a natural barrier (in an argillaceous rock named argillite), associated to artificial barriers, including plugs of swelling clay (bentonite)-sand for tunnel sealing purposes. The main objective of this thesis is to assess the sealing efficiency of the bentonite-sand plug in contact with argillite, in presence of both water and gas pressures. To assess the sealing ability of partially water-saturated bentonite/sand plugs, their gas permeability is measured under varying confining pressure (up to 12MPa). It is observed that tightness to gas is achieved under confinement greater than 9MPafor saturation levels of at least 86-91%. We than assess the sealing efficiency of the bentonite-sand plug placed in a tube of argillite or of Plexiglas-aluminium (with a smooth or a rough interface). The presence of pressurized gas affects the effective swelling pressure at values Pgas from 4MPa. Continuous gas breakthrough of fully water-saturated bentonite-sand plugs is obtained for gas pressures on the order of full swelling pressure (7-8MPa), whenever the plug is applied along a smooth interface. Whenever a rough interface is used in contact with the bentonite-sand plug, a gas pressure significantly greater than its swelling pressure is needed for gas to pass continuously. Gas breakthrough tests show that the interface between plug/argillite or the argillite itself are two preferential pathways for gas migration, when the assembly is fully saturated
|
Page generated in 0.3673 seconds