National Repository of Grey Literature 7 records found  Search took 0.00 seconds. 
Geochemical study of processes, relevant to safety assessment of deep geological repository: Uranium forms and enrichment scenario in a sedimentary system at the Ruprechtov natural analogue site
Havlová, Václava ; Jelínek, Emil (advisor) ; Pačes, Tomáš (referee) ; Zeman, Josef (referee)
U migration was studied in order to better understand to processes of safety relevant elements, particularly U. The rock sequence on the site can be analogous to a potential rock overburden of deep geology repositories. A multidisciplinary approach was undertaken in order to identify and characterise U mobilisation/immobilisation processes within sedimentary clayey rocks with organic matter enriched interlayers. Both conventional methods and modern sophisticated spectroscopic methods were combined. Sequential extraction, wet chemical method and even spectroscopic methods proved that U prevailed in the U(IV) form in low-oxidised samples. It moved towards more easily releasable fractions with sample ageing (oxidation). The combination of SE, µ-XRF and µ-XAFS results proved U to be unexpectedly associated with As and P, leading to the presumption that U(VI) from groundwater was reduced to U(IV) on As pyrite. The evaluation of the hydrogeochemical conditions and isotope analyses then brought the results into broader context: Sedimentary organic matter within the sedimentary layers was microbially oxidised, releasing dissolved organic matter and providing H+ in order to dissolve sedimentary inorganic carbonates. SO4 2- could be reduced under reducing groundwater conditions, thus causing FeS2 formation....
The influence of temperature and hydration on the long term stability of the buffer material
Švandová, Jana ; Přikryl, Richard (advisor) ; Galamboš, Michal (referee) ; Havlová, Václava (referee)
The influence of temperature and hydration on the long term stability of the buffer material was studied during two experimental studies - "Mock-Up-CZ" experiment and "Long-term stability of engineering barriers" project. The objectives of these studies is to identify mineralogical, chemical and geochemical changes and describe transformation processes in the bentonite materials due to heating and interaction with various saturation media (with different chemical composition) under controlled laboratory and in situ conditions. The Rokle bentonite suitability for its use in the Czech deep repository of high-level radioactive waste was investigated. Mineralogical changes in the bentonites were evaluated by X-ray diffraction. The material of the barrier of the Mock-Up-CZ experiment is a mixture of non­activated Rokle bentonite (85 vol.%), quartz sand (10 vol.%) and graphite (5 vol.%). The barrier has been subjected to thermal stress (up to 90 řC) and synthetic granitic water for 45 months. No sample from 70 analysed samples taken at different depth levels and distances from the source of the heat and/or water showed measurable transformation of original smectites. Newly formed gypsum bordered by illite aureole was detected in the upper part of the experimental set-up (backfill samples), i.e. in the...
Investigation of the thermo-hydro-mechanical behavior of Czech bentonite used as a model material for planning of high level nuclear waste disposal
Sun, Haiquan ; Mašín, David (advisor) ; Hausmannová, Lucie (referee) ; Havlová, Václava (referee)
The work involved in the thesis is mainly focused on the Czech bentonite which is originally from Cerny vrch deposit (north western region of the Czech Republic). The compacted bentonites are prepared from the industry provided bentonite powder with an initial water content around 10%. Dry densities from 1.27 to 2 g/cm3 were used for laboratory testing, specifically 1.27, 1.60 and 1.90 g/cm3 were used for water retention measurements, microstructures and fractal pore analysis. Dry densities of 1.25 to 1.95 g/cm3 were used for mechanical tests such as one dimensional swelling strain and oedometer load-unload tests. The vapor equilibrium method was used to impose the suction on samples ranging from 3.29 MPa to 286.7 MPa. Mercury intrusion porosimetry (MIP) and environmental scanning electron microscope (ESEM) were utilized for the microstructure analysis. The water retention measurements were performed at 20, 40, 60 and 80 řC respectively, results show that the increasing of temperature can decrease the water retention capacity. The influence of compaction and suction on microstructure was compared and studied. MIP tests were performed on the samples which were equilibrated at suction of 3.29, 38 and 286.7 MPa on wetting path of both low and high dry densities. The samples equilibrated at suction of...
The influence of temperature and hydration on the long term stability of the buffer material
Švandová, Jana ; Přikryl, Richard (advisor) ; Galamboš, Michal (referee) ; Havlová, Václava (referee)
The influence of temperature and hydration on the long term stability of the buffer material was studied during two experimental studies - "Mock-Up-CZ" experiment and "Long-term stability of engineering barriers" project. The objectives of these studies is to identify mineralogical, chemical and geochemical changes and describe transformation processes in the bentonite materials due to heating and interaction with various saturation media (with different chemical composition) under controlled laboratory and in situ conditions. The Rokle bentonite suitability for its use in the Czech deep repository of high-level radioactive waste was investigated. Mineralogical changes in the bentonites were evaluated by X-ray diffraction. The material of the barrier of the Mock-Up-CZ experiment is a mixture of non­activated Rokle bentonite (85 vol.%), quartz sand (10 vol.%) and graphite (5 vol.%). The barrier has been subjected to thermal stress (up to 90 řC) and synthetic granitic water for 45 months. No sample from 70 analysed samples taken at different depth levels and distances from the source of the heat and/or water showed measurable transformation of original smectites. Newly formed gypsum bordered by illite aureole was detected in the upper part of the experimental set-up (backfill samples), i.e. in the...
Geochemical study of processes, relevant to safety assessment of deep geological repository: Uranium forms and enrichment scenario in a sedimentary system at the Ruprechtov natural analogue site
Havlová, Václava ; Jelínek, Emil (advisor) ; Pačes, Tomáš (referee) ; Zeman, Josef (referee)
U migration was studied in order to better understand to processes of safety relevant elements, particularly U. The rock sequence on the site can be analogous to a potential rock overburden of deep geology repositories. A multidisciplinary approach was undertaken in order to identify and characterise U mobilisation/immobilisation processes within sedimentary clayey rocks with organic matter enriched interlayers. Both conventional methods and modern sophisticated spectroscopic methods were combined. Sequential extraction, wet chemical method and even spectroscopic methods proved that U prevailed in the U(IV) form in low-oxidised samples. It moved towards more easily releasable fractions with sample ageing (oxidation). The combination of SE, µ-XRF and µ-XAFS results proved U to be unexpectedly associated with As and P, leading to the presumption that U(VI) from groundwater was reduced to U(IV) on As pyrite. The evaluation of the hydrogeochemical conditions and isotope analyses then brought the results into broader context: Sedimentary organic matter within the sedimentary layers was microbially oxidised, releasing dissolved organic matter and providing H+ in order to dissolve sedimentary inorganic carbonates. SO4 2- could be reduced under reducing groundwater conditions, thus causing FeS2 formation....

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