Change search
ReferencesLink to record
Permanent link

Direct link
Natural uranium in Forsmark, Sweden: The solid phase
The Swedish Nuclear Fuel and Waste Management Company (SKB), Sweden.
2015 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 59, 178-188 p.Article in journal (Refereed) Published
Abstract [en]

U-bearing solid phases from Forsmark, Sweden, a proposed host for radioactive waste repositories, havebeen identified and characterized. Elevated dissolved U was found in some groundwater samples duringthe site investigations, prompting a need to study the local U geochemistry. Previous hydrochemical andwhole-rock geochemical studies indicated that U was derived from local pegmatites, and mobilized andre-deposited during several geological events. In this study, down-hole gamma logs guided sampling oflocal pegmatites, cataclasites, and fracture fillings. Back-scattered electron-imaging, petrographic microscopy,and electron microprobe analyses were used to find and analyze U phases in thin sections. Theresults show that the principal U sources at Forsmark include pegmatitic uraninite (PbO up to22 wt%) and metamict uranothorite. These primary minerals show variable degrees of alteration suchas enrichment in Ca and Al and/or replacement by secondary Ca–U(VI)-silicates, haiweeite and uranophane.The haiweeite contains up to 5 wt% Al2O3, a chemical signature reflecting early (Proterozoic)events of hydrothermal fluid migration. Coffinitized, secondary uraninite is found in association withFeAl-silicates or Palaeozoic sulfide/sulfate minerals, indicating remobilization-precipitation and/or a secondary,sedimentary source of U. It is inferred that U was oxidized during geologically early periods.Later, U(IV) phases formed in fractures open to fluid circulation during the Palaeozoic. This study establishesthe phases available as local U sources and/or sinks, and which will be considered in future isotopicand hydrochemical studies aimed to constrain the mechanisms and timing of water–U phase interaction.

Place, publisher, year, edition, pages
2015. Vol. 59, 178-188 p.
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-135736DOI: 10.1016/j.apgeochem.2015.04.020OAI: oai:DiVA.org:su-135736DiVA: diva2:1048602
Available from: 2016-11-21 Created: 2016-11-21 Last updated: 2016-11-24Bibliographically approved
In thesis
1. The mobility of natural uranium at Forsmark, Sweden, through geologic time
Open this publication in new window or tab >>The mobility of natural uranium at Forsmark, Sweden, through geologic time
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the response of uranium minerals and poorly crystalline phases to changes in geochemical conditions through geological time has been assessed in order to understand the mobility of natural uranium in the fracture network of a proposed site for a spent nuclear fuel repository in Forsmark, Sweden. Identification and characterization of solid phase uranium have been performed through electron microprobe analysis and optical petrography (Article I). The identified uraninite, haiweeite, and uranophane crystals have been dated using U-Pb and Pb-Pb isotope ratios obtained from secondary ion mass spectrometry and laser ablation-inductively coupled plasma-mass spectrometry (Article II). The mobility of uranium in current Forsmark groundwaters and fracture system has been modelled using the PHREEQC geochemical program and Ra and Rn isotope systematics (Article IV). The rate of submarine groundwater discharge (SGD) from the Forsmark coast to Öregrundsgrepen has also been modelled using Ra isotopes (Article V). Results from these studies support a geologically early (~1200 Ma) oxidation of U(IV) to U(VI). It is further suggested that the old U(VI) minerals present in the bedrock are soluble at the pe values and alkalinities observed in the Forsmark groundwaters. At pe < −4.6 and alkalinity < 60 mg/L, U(VI) can be reduced to U(IV) and deposited in the fracture network. Although a non-negligible rate of SGD has been observed, this cannot be attributed to the discharge of deep (>200 m.b.s.l.) Forsmark groundwaters on the basis of current data.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2016. 28 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 365
Keyword
uranium, radium, mineralogy, geochronology, submarine groundwater discharge, spent nuclear fuel, geochemical modelling
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-135735 (URN)978-91-7649-595-7 (ISBN)978-91-7649-596-4 (ISBN)
Public defence
2017-01-10, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: In press. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2016-12-16 Created: 2016-11-21 Last updated: 2016-12-05Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Krall, Lindsay
In the same journal
Applied Geochemistry
Geology

Search outside of DiVA

GoogleGoogle Scholar

Altmetric score

Total: 11 hits
ReferencesLink to record
Permanent link

Direct link