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dc.contributor.authorIwalewa, Tajudeen
dc.date.accessioned2017-07-17T16:09:12Z
dc.date.available2017-07-17T16:09:12Z
dc.date.issued2017-05-01
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/265633
dc.descriptionPart of this study has been published in Applied Geochemistry. Another publication is in line in Environmental Science & Technology.
dc.description.abstractThe focus of this work is to investigate the dissolution of MW25, a non-radioactive simulant of UK high-level nuclear waste borosilicate glass, and to predict its performance in the near field of a geological repository. A single-pass flow-through (SPFT) experimental system was used to measure the forward dissolution rates of MW25. Experiments were conducted in two parts. Experiment Part 1 considers the dissolution of the waste glass in deionised water at 40 and 90 oC and circum-neutral pH. Experiment Part 2 considers the dissolution of the waste glass in simulant groundwaters, with similar compositions to groundwaters of Callovo-Oxfordian clay (lower-strength sedimentary rock (LSSR)) and Borrowdale Volcanic Group rocks (higher-strength rock (HSR)), at 40 oC and pH 7. The forward dissolution rate measured in deionised water was found to be approximately one order of magnitude higher at 90 oC than at 40 oC. A similar release was observed for Si, Mg and Al at 40 oC and 90 oC, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 oC for low q/S values. The activation energy (Ea) of the reactions shows that the dissolution process is a surface phenomenon. At 90 oC the net effect of the processes governing MW25 dissolution led to the preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at a higher temperature has a weak influence on the release of the mobile elements. The forward dissolution rate measured in LSSR simulant groundwater was found to be slightly higher than that measured in HSR simulant groundwater. The dissolution behaviour of MW25 in both groundwaters is consistent with its behaviour in deionised water at 40 oC, with the dissolution rates of elements increasing as flow rates were increased. However, forward dissolution rates measured in the simulant groundwaters were lower than the forward dissolution rates measured in deionised water under these experimental conditions. This is attributable to the interaction of the components of the simulant groundwaters with the glass, as revealed by post-reaction surface analyses, and a consequential lower alkalinity of the leachates collected in the experiments with simulant groundwater than in deionised water. Reactive chemical transport simulations of waste glass dissolution and radionuclide release in a hypothetical near field were conducted over a time span of a million years with GoldSim. The results showed that enclosing the waste glass in a steel canister covered by a copper canister and emplacing the waste package in a granite host rock is optimal for the long-term isolation of the radionuclides. The waste glass was found to play a significant role in the overall performance of the near field. This study features a new method for estimating the surface area of reacted glass powder more accurately than the geometric surface area estimate, which is the preferred standard method among researchers.
dc.description.sponsorshipCambridge Trust and Islamic Development Bank (IDB)
dc.formatGoldSim Academic License
dc.formatGoldSim Academic License
dc.formatGoldSim Academic License
dc.formatGoldSim Academic License
dc.language.isoen
dc.rightsAll Rights Reserveden
dc.rights.urihttps://www.rioxx.net/licenses/all-rights-reserved/en
dc.subjectMW25
dc.subjectborosilicate glass
dc.subjectnuclear waste
dc.subjectgeological repository
dc.subjectradionuclide
dc.subjectdissolution
dc.subjecttemperature
dc.subjectflow rate
dc.subjectUK
dc.subjectGoldSim
dc.subjectreactive transport
dc.subjectmodelling
dc.subjectsurface area
dc.subjectdisposal option
dc.subjectaqueous geochemistry
dc.subjectSEM
dc.subjectEDX
dc.subjectXRD
dc.subjectsingle-pass flow-through
dc.subjectSPFT
dc.subjectenvironmental impact
dc.subjectperformance assessment
dc.subjectLSSR
dc.subjectHSR
dc.subjectCallovo-Oxfordian clay
dc.subjectBorrowdale Volcanic Group rock
dc.subjecthigh-level waste
dc.subjectHLW
dc.subjection exchange
dc.subjecthydrolysis
dc.subjectforward dissolution rate
dc.titleCoupling source term, mineral reactivity and flow in radionuclide transport
dc.typeThesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.publisher.departmentEarth Sciences
dc.date.updated2017-07-17T14:06:22Z
dc.identifier.doi10.17863/CAM.11803
dc.publisher.collegeDarwin College
dc.type.qualificationtitlePhD in Earth Sciences
cam.supervisorFarnan, Ian
rioxxterms.freetoread.startdate2019-07-17


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