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Effect of γ-radiation on Radionuclide Retention in Compacted Bentonite
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).ORCID iD: 0000-0002-3398-3598
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).ORCID iD: 0000-0003-0663-0751
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
2011 (English)In: Radiation Physics and Chemistry, ISSN 0969-806X, Vol. 80, no 12, 1371-1377 p.Article in journal (Refereed) Published
Abstract [en]

Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly gamma) under anoxic conditions. Because of this, the effects of gamma-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs(+) and Co(2+) were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co(2+) than for Cs(+), which generally showed no significant differences between irradiated and unirradiated clay samples. For Co(2+) however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that gamma-radiation may alter the surface characteristics contributing to surface complexation of Co(2+). With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained D. values.

Place, publisher, year, edition, pages
2011. Vol. 80, no 12, 1371-1377 p.
Keyword [en]
Diffusion, Sorption, Bentonite, Humics, Radionuclides, K(d)
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-34045DOI: 10.1016/j.radphyschem.2011.08.004ISI: 000295665100013ScopusID: 2-s2.0-80052968030OAI: oai:DiVA.org:kth-34045DiVA: diva2:418866
Note

QC 20111107 Updated from submitted to published.

Available from: 2011-06-08 Created: 2011-05-24 Last updated: 2015-02-13Bibliographically approved
In thesis
1. The Bentonite Barrier: Microstructural properties and the influence of γ-radiation
Open this publication in new window or tab >>The Bentonite Barrier: Microstructural properties and the influence of γ-radiation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. iv, 81 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:38
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-34048 (URN)978-91-7501-001-4 (ISBN)
Public defence
2011-06-15, F2, entréplan, Lindstedtsvägen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110608Available from: 2011-06-08 Created: 2011-05-24 Last updated: 2011-08-10Bibliographically approved
2. Stability and sorption capacity of montmorillonite colloids: Investigation of size fractional differences and effects of γ-irradiation
Open this publication in new window or tab >>Stability and sorption capacity of montmorillonite colloids: Investigation of size fractional differences and effects of γ-irradiation
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bentonite clay is intended to form one of the barriers in most repositories of spent nuclear fuel located in granite. One important function of the bentonite barrier is to retard transport of radionuclides in the event of waste canister failure. Bentonite has a high sorption capacity of cations and its main constituent is montmorillonite. In contact with groundwater of low ionic strength, montmorillonite colloids can be released from bentonite and thereby control transport of radionuclides sorbed onto the colloids.

In colloid transport in bedrock fractures, size separation of clay colloids may occur due to physical and chemical interactions with the bedrock fracture surface. This may enhance or retard the overall transport of radionuclides, depending on the sorption capacities and stability of the differently sized clay colloids. The bentonite barrier will be exposed to γ-radiation from the spent nuclear fuel. Irradiation affects surface-related properties of bentonite. If an average sorption capacity value cannot be used for all colloid sizes or if sorption is affected by exposure to γ-irradiation, corrected sorption capacity values would give higher resolution in current reactive transport models.

In order to study the size separation process, a protocol was developed and successfully applied to fractionate montmorillonite into different-sized colloid suspensions by means of sequential or direct centrifugation. The stability and sorption capacity were studied using these fractions. Both stability and sorption capacity were found to be similar for all colloid sizes.

Bentonite exposed to γ-radiation sorbed less divalent cations with increasing radiation dose. The effect was not large enough to have any impact on diffusion. The presence of bentonite enhanced irradiation-induced corrosion of copper under anaerobic atmosphere.

An average sorption capacity value for montmorillonite can be used for all colloid sizes in reactive transport models. The effect of γ-irradiation on sorption capacity is sufficiently large to require consideration in transport modelling.

Abstract [sv]

Bentonite är planerad som en av barriärerna i de flesta slutförvar av använt kärnbränsle. Bentonite har en hög sorptionskapacitet för katjoner. Den huvudsakliga beståndsdelen av bentonit är montmorillonit. Montmorillonitkolloider kommer att frigöras från bentonitbufferten i kontakt med grundvatten av låg jonstyrka och på så vis styra transporten av sorberade radionuklider.

Under den kolloidala transporten i bergsprickorna kan en separation med avseende på storlek uppstå genom interaktioner mellan kolloiderna och bergytan. Detta kan få till följd att den genomsnittliga transporten av radionuklider bromsas eller tilltar beroende på sorptionskapaciteten och stabiliteten av de olika kolloidstorlekarna. Bentonitbarriären kommer även att utsättas för γ-bestrålning från det använda kärnbränslet, vilket påverkar dess ytrelaterade egenskaper. Om inte ett medeltal för sorptionskapaciteten är giltigt för alla kolloidstorlekar eller om sorptionen påverkas av γ-bestrålning, behövs nya sorptionskapaciteter bestämmas och impliceras för noggrannare transportmodeller.

En metod för att separera montmorillonitkolloider med avseende på storlek via direkt och stegvis centrifugering har utvecklats. Stabiliteten och sorptionskapaciteten för dessa fraktioner har studerats. Både stabilitet och sorptionskapacitet visade sig vara lika för alla kolloidstorlekar.

Bestrålad bentonit sorberar mindre andel divalenta katjoner med ökad dos bestrålning. Effekten är dock inte stor nog för att slå igenom i diffusionsexperimenten. Förekomst av bentonit ökar även den strålningsinducerade korrosionen av koppar under anaeroba förhållanden.

Ett medelvärde för sorptionskapaciteten kan användas för alla kolloidstorlekar i transportmodeller. Effekten av γ-bestrålning är dock stor nog för att implementeras i modellerna.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 79 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:8
Keyword
montmorillonite, colloids, size effect, γ-irradiation, sorption, colloid stability, radionuclides, montmorillonit, kolloider, storlekseffekt, γ-bestrålning, sorption, kollodial stabilitet, radionuklider
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-159944 (URN)978-91-7595-444-8 (ISBN)
Public defence
2015-03-06, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150213

Available from: 2015-02-13 Created: 2015-02-12 Last updated: 2015-02-13Bibliographically approved

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