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Title: ALTERATION OF U(VI)-PHASES UNDER OXIDIZING CONDITIONS

Abstract

Uranium-(VI) phases are the primary alteration products of the UO{sub 2} in spent nuclear fuel and the UO{sub 2+x}, in natural uranium deposits. The U(VI)-phases generally form sheet structures of edge-sharing UO{sub 2}{sup 2+} polyhedra. The complexity of these structures offers numerous possibilities for coupled-substitutions of trace metals and radionuclides. The incorporation of radionuclides into U(VI)-structures provides a potential barrier to their release and transport in a geologic repository that experiences oxidizing conditions. In this study, we have used natural samples of UO{sub 2+x}, to study the U(VI)-phases that form during alteration and to determine the fate of the associated trace elements.

Authors:
; ;
Publication Date:
Research Org.:
Yucca Mountain Project, Las Vegas, Nevada
Sponsoring Org.:
USDOE
OSTI Identifier:
884959
Report Number(s):
NA
MOL.20060330.0282, DC#47102; TRN: US0603732
DOE Contract Number:
NA
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; ELEMENTS; NATURAL URANIUM; NUCLEAR FUELS; POTENTIALS; RADIOISOTOPES; TRACE AMOUNTS; TRANSPORT

Citation Formats

A.P. Deditius, S. Utsunomiya, and R.C. Ewing. ALTERATION OF U(VI)-PHASES UNDER OXIDIZING CONDITIONS. United States: N. p., 2006. Web. doi:10.2172/884959.
A.P. Deditius, S. Utsunomiya, & R.C. Ewing. ALTERATION OF U(VI)-PHASES UNDER OXIDIZING CONDITIONS. United States. doi:10.2172/884959.
A.P. Deditius, S. Utsunomiya, and R.C. Ewing. Tue . "ALTERATION OF U(VI)-PHASES UNDER OXIDIZING CONDITIONS". United States. doi:10.2172/884959. https://www.osti.gov/servlets/purl/884959.
@article{osti_884959,
title = {ALTERATION OF U(VI)-PHASES UNDER OXIDIZING CONDITIONS},
author = {A.P. Deditius and S. Utsunomiya and R.C. Ewing},
abstractNote = {Uranium-(VI) phases are the primary alteration products of the UO{sub 2} in spent nuclear fuel and the UO{sub 2+x}, in natural uranium deposits. The U(VI)-phases generally form sheet structures of edge-sharing UO{sub 2}{sup 2+} polyhedra. The complexity of these structures offers numerous possibilities for coupled-substitutions of trace metals and radionuclides. The incorporation of radionuclides into U(VI)-structures provides a potential barrier to their release and transport in a geologic repository that experiences oxidizing conditions. In this study, we have used natural samples of UO{sub 2+x}, to study the U(VI)-phases that form during alteration and to determine the fate of the associated trace elements.},
doi = {10.2172/884959},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Feb 21 00:00:00 EST 2006},
month = {Tue Feb 21 00:00:00 EST 2006}
}

Technical Report:

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  • U{sup 6+} phases are common alteration products of spent nuclear fuel under oxidizing conditions, and they may potentially incorporate actinides, such as long-lived {sup 239}Pu and {sup 237}Np, delaying their transport to the biosphere. In order to evaluate the ballistic effects of {alpha}-decay events on the stability of the U{sup 6+}-phases, they report, for the first time, the results of ion beam irradiations (1.0 MeV Kr{sup 2+}) for six different structures of U{sup 6+}-phases: uranophane, kasolite, boltwoodite, saleeite, carnotite, and liebigite. The target uranyl-minerals were characterized by powder X-ray diffraction and identification confirmed by SAED in TEM. The TEM observationmore » revealed no initial contamination of uraninite in these U{sup 6+} phases. All of the samples were irradiated with in situ TEM observation using 1.0 MeV Kr{sup 2+} in the IVEM (intermediate-voltage electron microscope) at the IVEM-Tandem Facility of Argonne National Laboratory. The ion flux was 6.3 x 10{sup 11} ions/cm{sup 2}/sec. The specimen temperatures during irradiation were 298 and 673 K, respectively. The Kr{sup 2+}-irradiation decomposed the U{sup 6+}-phases to nanocrystals of UO{sub 2} at doses as low as 0.006 dpa. The cumulative doses for the pure U{sup 6+}-phases, e.g., uranophane, at 0.1 and 1 m.y. are calculated to be 0.009 and 0.09 dpa using SRIM2003. However, with the incorporation of 1 wt.% {sup 239}Pu, the calculated doses reach 0.27 and {approx} 1.00 dpa in ten thousand and one hundred thousand years, respectively. Under oxidizing conditions, multiple cycles of radiation-induced decomposition to UO{sub 2} followed by alteration to U{sup 6}-phases should be further investigated to determine the fate of trace elements that may have been incorporated in the U{sup 6+}-phases.« less
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  • Reactions from adding orthophosphates to nine soils with widely different physical and chemical properties were studied to develop a better method of predicting phosphorus movement in soils used for sewage disposal. Conclusions: amorphous aluminum hydroxide or crystalline gibbsite control Al/sup +3/ solubility in acid soils. Soils with higher clay content fixed more phosphorus, while acid soils generally had more phosphorus fixation capacity than alkaline soils. Monocalcium phosphate monohydrate in acid soils were transformed to compounds having higher solubility than variscite, which with time changed to crystalline variscite. Several calcium compounds controlled phosphorus solubility when calcium orthophosphate, mono-(prim.) was added tomore » neutral and alkaline soils. Phosphorus applied at rates similar to those found near a fertilizer granule site saturated the soil zone with calcium orthophosphate, DI-(sec.) and CaHPO/sub 4/ in acid as well as alkaline soils. Intermediary compounds converted to crystalline variscite relatively rapidly at low phosphorus rates. Sandy soils should be avoided as waste disposal sites, due to the likelihood of high phosphorus movement. 24 references, 8 figures, 5 tables.« less