Leaching patterns and secondary phase formation during unsaturated leaching of UO{sub 2} at 90{degrees}C

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Experiments are being conducted that examine the reaction of UO{sub 2} with dripping oxygenated ground water at 90{degrees}C. The experiments are designed to identify secondary phases formed during UO{sub 2} alteration, evaluate parameters controlling U release, and act as scoping tests for studies with spent fuel. This study is the first of its kind that examines the alteration of UO{sub 2} under unsaturated conditions expected to exist at the proposed Yucca Mountain repository site. Results suggest the UO{sub 2} matrix will readily react within a few months after being exposed to simulated Yucca Mountain conditions. A pulse of rapid U ... continued below

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56 p.

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Wronkiewicz, D.J.; Bates, J.K.; Gerding, T.J.; Veleckis, E. & Tani, B.S. November 1, 1991.

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Description

Experiments are being conducted that examine the reaction of UO{sub 2} with dripping oxygenated ground water at 90{degrees}C. The experiments are designed to identify secondary phases formed during UO{sub 2} alteration, evaluate parameters controlling U release, and act as scoping tests for studies with spent fuel. This study is the first of its kind that examines the alteration of UO{sub 2} under unsaturated conditions expected to exist at the proposed Yucca Mountain repository site. Results suggest the UO{sub 2} matrix will readily react within a few months after being exposed to simulated Yucca Mountain conditions. A pulse of rapid U release, combined with the formation of dehydrated schoepite on the UO{sub 2} surface, characterizes the reaction between one to two years. Rapid dissolution of intergrain boundaries and spallation of UO{sub 2} granules appears to be responsible for much of the U released. Differential release of the UO{sub 2} granules may be responsible for much of the variation observed between duplicate experiments. Less than 5 wt % of the released U remains in solution or in a suspended form, while the remaining settles out of solution as fine particles or is reprecipitated as secondary phases. Subsequent to the pulse period, U release rates decline and a more stable assemblage of uranyl silicate phases are formed by incorporating cations from the ground water leachant. Uranophane, boltwoodite, and sklodowskite appear as the final solubility limiting phases that form in these tests. This observed paragenetic sequence (from uraninite to schoepite-type phases to uranyl silicates) is identical to those observed in weathered zones of natural uraninite occurrences. The combined results indicate that the release of radionuclides from spent fuel may not be limited by U solubility constraints, but that spallation of particulate matter may be an important, if not the dominant release mechanism affecting release.

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56 p.

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INIS; OSTI as DE94008483

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  • Other Information: PBD: Nov 1991

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  • Other: DE94008483
  • Report No.: ANL/CMT/PP--71738
  • Grant Number: W-31109-ENG-38
  • DOI: 10.2172/140730 | External Link
  • Office of Scientific & Technical Information Report Number: 140730
  • Archival Resource Key: ark:/67531/metadc628285

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • November 1, 1991

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • Dec. 14, 2015, 2:18 p.m.

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Wronkiewicz, D.J.; Bates, J.K.; Gerding, T.J.; Veleckis, E. & Tani, B.S. Leaching patterns and secondary phase formation during unsaturated leaching of UO{sub 2} at 90{degrees}C, report, November 1, 1991; Illinois. (digital.library.unt.edu/ark:/67531/metadc628285/: accessed April 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.