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Sintering of CaF2 pellets as nuclear fuel analog for surface stability experiments
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
2011 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 419, no 1-3, 46-51 p.Article in journal (Refereed) Published
Abstract [en]

To enable a detailed study of the influence of microstructure and surface properties on the stability of spent nuclear fuel, it is necessary to produce analogs that closely resemble nuclear fuel in terms of crystallography and microstructure. One such analog can be obtained by sintering CaF2 powder.

This paper reports the microstructures obtained after sintering CaF2 powders at temperatures up to 1240 °C. Pellets with microstructure, density and pore structure similar to that of UO2 spent nuclear fuel pellets were obtained in the temperature range between 900 °C and 1000 °C. When CaF2 was sintered above 1100 °C the formation of CaO at the grain boundaries caused the disintegration of the pellet due to hydration occurring after sintering.

First results from a novel set-up of dissolution experiments show that changes in roughness, dissolution rate and etch pit shape of fluorite surfaces are strongly dependent on the crystallographic orientation of the expose surface. Consequently, the differences observed for each orientation will affect the overall dissolution rate and will lead to uncertainties in the estimation of dissolution rates of spent nuclear fuel.

Place, publisher, year, edition, pages
Elsevier, 2011. Vol. 419, no 1-3, 46-51 p.
National Category
Materials Chemistry
Research subject
Mineralogy, Petrology and Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-65942DOI: 10.1016/j.jnucmat.2011.08.031ISI: 000298936600007OAI: oai:DiVA.org:su-65942DiVA: diva2:466522
Note
We describe the microstructures of CaF2 that can be obtained by sintering. ► Microstructures that resemble nuclear waste pellets were obtained in the range 900 °C–1000 °C. ► We demonstrate the importance of surface orientation on dissolution behavior and surface properties of a mineral. ► New procedure for studying the role of crystallography and surface chemistry in dissolution using 3-D confocal profilometry.Available from: 2011-12-16 Created: 2011-12-16 Last updated: 2017-12-08Bibliographically approved
In thesis
1. A surface approach to understanding the dissolution of fluorite type materials: Implications for mineral dissolution kinetic models
Open this publication in new window or tab >>A surface approach to understanding the dissolution of fluorite type materials: Implications for mineral dissolution kinetic models
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Traditional dissolution models are based in the analyses of bulk solution compositions and ignore the fact that different sites of a surface dissolve at different rates. Consequently, the variation of surface area and surface reactivity during dissolution are not considered for the calculation of the overall dissolution rate, which is expected to remain constant with time. The results presented here show the limitations of this approach suggesting that dissolution rates should be calculated as a function of an overall surface reactivity term that accounts for the reactivity of each of the sites that constitute the surface. In contrast to previous studies, here the focus is put on studying the surface at different dissolution times. Significant changes in surface topography of CaF2 were observed during the initial seconds and up to 3200 hours of dissolution. The observed changes include the increase of surface area and progressive exposure of the most stable planes, with consequent decrease in overall reactivity of the surface. The novelty of a proposed dissolution model for fluorite surfaces, when compared with traditional dissolution models, is that it differentiates the reactivity of each characteristic site on a surface, e.g. plane or step edge, and considers the time dynamics. The time dependency of dissolution rates is a major factor of uncertainty when calculating long term dissolution rates using equations derived from dissolution experiments running for short periods of time and using materials with different surface properties. An additional factor of uncertainty is that the initial dissolution times are the most dynamic periods of dissolution, when significant variations of surface area and reactivity occur. The results are expected to have impact in the field of nuclear waste management and to the larger geological and material science community.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2013. 26 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 352
Keyword
dissolution, topography, fluorite, surface
National Category
Geochemistry
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-89257 (URN)978-91-7447-701-6 (ISBN)
Public defence
2013-05-29, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.

Available from: 2013-05-07 Created: 2013-04-17 Last updated: 2013-08-09Bibliographically approved

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