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Adsorption av cesium på krossad granit - en faktor inför slutförvaret av kärnbränsle
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Science.
1997 (Swedish)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesisAlternative title
Adsorption of cesium onto crushed granite - a part of the final disposal of nuclear fuel (English)
Abstract [sv]

Sedan några år tillbaks utvecklas vid Institutionen för geovetenskap, sedimentologi, Uppsala Universitet en modell för att simulera transportförloppet av radionuklider vid ett eventuellt läckage av kärnbränsleavfall deponerat långt nere i berggrunden. Som en viktig del av transportförloppet ingår adsorption av cesiumjoner på bergets sprickväggar. Adsorptionsprocessen har i detta examensarbete studerats genom att blanda varierande koncentrationer av granitpartiklar från olika fraktioner med cesiumkontaminerat grundvatten. Koncentrationen av cesiumjoner mättes m h a en gammaräknare tills jämvikt mellan de adsorberade och de lösta jonerna infann sig. Adsorptionen karakteriserades beroende på partikelstorleken av en enstegskinetik eller en tvåstegskinetik. Tvåstegsadsorptionen är en följd av att större partiklar innehåller betydligt fler mikrosprickor än vad de mindre partiklarna gör. Resultaten utvärderades m a p dels distributionskoefficienten kd och dels reaktionskonstanten kr. Anpassningen av kd-värdena gav ett mycket bra resultat med ett R2-värde över 0,99 medan anpassningen av kr inte alls var lika bra (R2 ≈ 0.36), vilket antas bero på att uttrycket för nettoadsorptionen G är felaktigt.

Abstract [en]

Over the last few years, a model that simulates the transport of radionuclides in fractured rock has been developed at the Department of Earth Sciences/Sedimentology, Uppsala University, Sweden. The aim has been to predict the outcome of a possible leak from deposits of nuclear waste fuel in deep bedrock. The adsorption of cesium ions at the fractures is an important part of the transport mechanism. This study has attempted to explore the adsorption kinetics of cesium ions at the surface of granite particles. A certain amount of cesium was mixed with synthetic groundwater along with different fractions and amounts of clean granite particles. The concentration of cesium in the liquid was frequently measured in order to estimate the change in cesium adsorption with time. The measurements were carried out until an equilibrium between adsorbed and solute ions was achieved. Depending on the size of the particles, the adsorption was characterized by either a one- or a two step kinetics. The reason for this was that larger particles contain micro fractures which affect the adsorption curve. The results were evaluated from the estimated values of the distribution coefficient kd and the reactivity coefficient kr. A model that evaluates the available surface of the rock gave very good results for the kd-values with a R2-value above 0.99. The fitting of kr was not by near equally good (R2 ≈ 0.36), and this is assumed to depend on an incorrect expression of the net adsorption G.

Place, publisher, year, edition, pages
1997. , p. 46
National Category
Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-391686OAI: oai:DiVA.org:uu-391686DiVA, id: diva2:1345614
Educational program
Matematisk-naturvetenskaplig linje
Available from: 2019-08-28 Created: 2019-08-26 Last updated: 2019-09-06Bibliographically approved

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