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CHEMLAB - in situ diffusion experiments using radioactive tracers
KTH, Tidigare Institutioner                               , Kemi.
KTH, Tidigare Institutioner                               , Kemi.
1998 (engelsk)Inngår i: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 82, s. 153-156Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionuclides are in good agreement with predicted profiles obtained from modelling based on apparent diffusivities and sorption coefficients obtained in laboratory experiments with corresponding clay density and ground water composition.

sted, utgiver, år, opplag, sider
1998. Vol. 82, s. 153-156
Emneord [en]
in situ experiment, radionuclide, diffusion, cation
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-13483ISI: 000077683000025OAI: oai:DiVA.org:kth-13483DiVA, id: diva2:325551
Merknad
QC 20100618Tilgjengelig fra: 2010-06-18 Laget: 2010-06-18 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Diffusion of cations in bentonite clay: laboratory and in-situ studies
Åpne denne publikasjonen i ny fane eller vindu >>Diffusion of cations in bentonite clay: laboratory and in-situ studies
1999 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
sted, utgiver, år, opplag, sider
Stockholm: KTH, 1999. s. vii, 33
Serie
Trita-KKE, ISSN 0349-6465 ; 9901
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-932 (URN)KTH/KKE--99/1--SE (ISRN)
Merknad
QC 20100618Tilgjengelig fra: 2000-09-26 Laget: 2000-09-26 Sist oppdatert: 2010-06-18bibliografisk kontrollert
2. Diffusion of Radionuclides in Bentonite Clay: Laboratory and in sity Studies
Åpne denne publikasjonen i ny fane eller vindu >>Diffusion of Radionuclides in Bentonite Clay: Laboratory and in sity Studies
2002 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis deals with the diffusion of ions in compactedbentonite clay. Laboratory experiments were performed toexamine in detail different processes that affect thediffusion. To demonstrate that the results obtained from thelaboratory investigations are valid under in situ conditions,two different kinds of in situ experiments were performed.

Laboratory experiments were performed to better understandthe impact of ionic strength on the diffusion of Sr2+ and Cs+ions, which sorb to mineral surfaces primarily by ion exchange.Furthermore, surface related diffusion was examined anddemonstrated to take place for Sr2+ and Cs+ but not for Co2+,which sorbs on mineral surfaces by complexation.

The diffusion of anions in bentonite clay compacted todifferent dry densities was also investigated. The resultsindicate that anion diffusion in bentonite clay consists of twoprocesses, one fast and another slower. We ascribe the fastdiffusive process to intralayer diffusion and the slow processto diffusion in interparticle water, where anions are to someextent sorbed to edge sites of the montmorillonite.

Two different types of in situ experiments were performed,CHEMLAB and LOT. CHEMLAB is a borehole laboratory, where cation(Cs+, Sr2+ and Co2+) and anion (I- and TcO4-) diffusionexperiments were performed using groundwater from a fracture inthe borehole. In the LOT experiments cylindrical bentoniteblocks surrounding a central copper rod were placed in a 4 mdeep vertical borehole. The borehole was then sealed and theblocks are left for 1, 5 or>>5 years. When the bentonitewas water saturated the central copper rod is heated tosimulate the temperature increase due to radioactive decay ofthe spent fuel. Bentonite doped with radioactive Cs and Co wasplaced in one of the lower blocks.

Interestingly, the redox-sensitive pertechnetate ion (TcO4-)which thermodynamically should be reduced and precipitate asTcO2·nH2O, travelled unreduced through the bentonite.However, at some spots in the clay, the Tc activity wasconsiderably higher. We ascribe these activity peaks toiron-containing minerals in the bentonite, by which Tc(VII) hasbeen reduced to Tc(IV) and precipitated. The cations Sr2+, Cs+and Co2+, as well as the anion I-, behaved in the CHEMLABexperiments as expected from laboratory studies.

Three experiments in the LOT series are completed. The firsttwo diffusion experiments in LOT were less successful, thefirst due to the fact that saturation of the bentonite was notobtained during the experimental period and the radionuclidesdid not move at all. In the second, the uptake of the bentoniteparcel was less successful. Water from the drilling flushedaway large pieces of the top part of the bentonite and thelower part of the test parcel was super-saturated with waterand expanded when released from the rock.

The activity distribution in the second experiment wasanalysed. The Co2+ profile looked as we had expected, while Cs+had spread more than our calculations indicated. However, thethird experiment was successful from emplacement, watersaturation and heating to uptake. The activity distribution forboth cations was as expected from laboratory studies.

Altogether the three different types of experiments give auniform picture of radionuclide diffusion in bentonite clay forthe ions investigated.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2002. s. x, 53
Serie
Trita-KKE, ISSN 0349-6465 ; 0202
Emneord
Bentonite, montmorillonite, cation, anion, diffusion, sorption, cobalt, caesium, strontium, iodide, pertechnetate, surface diffusion, in situ
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-3443 (URN)
Disputas
2002-12-06, 00:00
Merknad
QC 20100621Tilgjengelig fra: 2002-12-03 Laget: 2002-12-03 Sist oppdatert: 2010-06-21bibliografisk kontrollert

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