Alteration of UO2+x under oxidizing conditions, Marshall Pass, Colorado, USA

A. P. Deditius, Satoshi Utsunomiya, R. C. Ewing

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

As a natural analogue of the processes and products of spent nuclear fuel (SNF) alteration, we have examined the sequence of phases that form during the alteration of natural UO2+x in a U-deposit at Marshall Pass, Colorado. We have determined the paragenesis of U(VI)-phases including the fate of trace elements: W, Mo, As, Sb, Cu, Ba, Ce, Y, Pb and Th. Enrichment of trace elements, especially W and Mo, in this system resulted in a unique alteration sequence: uraninite → amorphous U-oxyhydrate gel → schoepite(I)/vandendriesscheite/compreignacite → uranophane → schoepite(II)/"dehydrated" schoepite(I) → Ba-Mo-W-U phase/U-arsenates/U-Sb phase → "dehydrated schoepite" (II) → soddyite/swamboite. In this sequence, the Ba-Mo-W uranyl phase and U-Sb phase are newly characterized phases. These results suggest that the UO2+x alteration, involving higher concentrations of certain radionuclides and metallic compounds, may lead to a different paragenesis of U(VI)-phases, as compared with the expected alteration sequence of UO2 interacting with a typical groundwaters. This was also noted in a previous study of the alteration of Pb-rich uraninite [R.J. Finch, R.C. Ewing, J. Nucl. Mater. 190 (1992) 133-156]. Some trace elements, such as CaO 2.08 wt.%, PbO 1.69 wt.%, WO3 1.39 wt.%, As2O3 0.50 wt.% and MoO3 0.41 wt.%, can locally concentrate, but still form uranyl phases. As a consequence, the mobility of U and radionuclides is governed by the stability of these metal-uranyl phases, such as Pb-oxide hydrates, Ba-uranyl molybdates/ tungstates and U-antimonate.

Original languageEnglish
Pages (from-to)584-589
Number of pages6
JournalJournal of Alloys and Compounds
Volume444-445
Issue numberSPEC. ISS.
DOIs
Publication statusPublished - Nov 1 2007
Externally publishedYes

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Trace Elements
Trace elements
Radioisotopes
Arsenates
Metallic compounds
Spent fuels
Nuclear fuels
Hydrates
Oxides
Groundwater
Deposits
Gels
Metals
carbosulfan

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Alteration of UO2+x under oxidizing conditions, Marshall Pass, Colorado, USA. / Deditius, A. P.; Utsunomiya, Satoshi; Ewing, R. C.

In: Journal of Alloys and Compounds, Vol. 444-445, No. SPEC. ISS., 01.11.2007, p. 584-589.

Research output: Contribution to journalArticle

Deditius, A. P. ; Utsunomiya, Satoshi ; Ewing, R. C. / Alteration of UO2+x under oxidizing conditions, Marshall Pass, Colorado, USA. In: Journal of Alloys and Compounds. 2007 ; Vol. 444-445, No. SPEC. ISS. pp. 584-589.
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AB - As a natural analogue of the processes and products of spent nuclear fuel (SNF) alteration, we have examined the sequence of phases that form during the alteration of natural UO2+x in a U-deposit at Marshall Pass, Colorado. We have determined the paragenesis of U(VI)-phases including the fate of trace elements: W, Mo, As, Sb, Cu, Ba, Ce, Y, Pb and Th. Enrichment of trace elements, especially W and Mo, in this system resulted in a unique alteration sequence: uraninite → amorphous U-oxyhydrate gel → schoepite(I)/vandendriesscheite/compreignacite → uranophane → schoepite(II)/"dehydrated" schoepite(I) → Ba-Mo-W-U phase/U-arsenates/U-Sb phase → "dehydrated schoepite" (II) → soddyite/swamboite. In this sequence, the Ba-Mo-W uranyl phase and U-Sb phase are newly characterized phases. These results suggest that the UO2+x alteration, involving higher concentrations of certain radionuclides and metallic compounds, may lead to a different paragenesis of U(VI)-phases, as compared with the expected alteration sequence of UO2 interacting with a typical groundwaters. This was also noted in a previous study of the alteration of Pb-rich uraninite [R.J. Finch, R.C. Ewing, J. Nucl. Mater. 190 (1992) 133-156]. Some trace elements, such as CaO 2.08 wt.%, PbO 1.69 wt.%, WO3 1.39 wt.%, As2O3 0.50 wt.% and MoO3 0.41 wt.%, can locally concentrate, but still form uranyl phases. As a consequence, the mobility of U and radionuclides is governed by the stability of these metal-uranyl phases, such as Pb-oxide hydrates, Ba-uranyl molybdates/ tungstates and U-antimonate.

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