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Title: Experimental Limitations Regarding the Formation and Characterization of Uranium-Mineral Phases in Concrete Waste Forms

Abstract

Predicting the long-term fate of low-level radioactive waste forms requires understanding how the radionuclides interact with the waste form. Concrete encasement is one method being considered for containment of low-level radioactive wastes. The necessary data to conduct an accurate performance assessment of such a waste form requires understanding the behavior and interactions of the radionuclides with the concrete matrix. The formation of uranium mineral phases has been investigated in simulated concrete pore fluids and Ordinary Portland Cement/Pulverized Fuel Ash (fly ash) concrete waste forms. X-Ray diffraction analyses of uranium precipitates from concrete pore fluids suggest diuranate salts, uranium-oxyhydroxides, and –silicates as solubility limiting phases. Scanning electron microscopy – energy dispersive spectroscopic analyses of uranium-spiked concrete suggests that under conditions both under-saturated and over-saturated with respect to the formation of uranium mineral phases, uranyl-oxyhydroxide phases precipitate within the initial two weeks. Subsequently, uranyl-silicate phases form after approximately one month and uranyl-phosphate phases provide a significant contribution to the long-term control over uranium in concrete waste forms after two months. This investigation demonstrates the importance of investigating the solubility of complex contaminants such as uranium in the complete matrix (i.e. concrete matrix versus pore fluids) and suggests the importance of secondary uraniummore » mineral phases in the long-term retention within concrete waste forms.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
899478
Report Number(s):
PNNL-SA-47169
Journal ID: ISSN 0008-8846; CCNRAI; 9799; 830403000; TRN: US200715%%95
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research, 37(2):151-160; Journal Volume: 37; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; CONCRETES; CONTAINMENT; LOW-LEVEL RADIOACTIVE WASTES; PERFORMANCE; RADIOISOTOPES; RETENTION; SCANNING ELECTRON MICROSCOPY; SILICATES; SOLUBILITY; URANIUM; URANIUM MINERALS; WASTE FORMS; X-RAY DIFFRACTION; uranium, concrete, becquerelite, autunite, schoepite, uranophane; Environmental Molecular Sciences Laboratory

Citation Formats

Wellman, Dawn M., Mattigod, Shas V., Arey, Bruce W., Wood, Marcus I., and Forrester, Steven W.. Experimental Limitations Regarding the Formation and Characterization of Uranium-Mineral Phases in Concrete Waste Forms. United States: N. p., 2007. Web. doi:10.1016/j.cemconres.2006.11.004.
Wellman, Dawn M., Mattigod, Shas V., Arey, Bruce W., Wood, Marcus I., & Forrester, Steven W.. Experimental Limitations Regarding the Formation and Characterization of Uranium-Mineral Phases in Concrete Waste Forms. United States. doi:10.1016/j.cemconres.2006.11.004.
Wellman, Dawn M., Mattigod, Shas V., Arey, Bruce W., Wood, Marcus I., and Forrester, Steven W.. Thu . "Experimental Limitations Regarding the Formation and Characterization of Uranium-Mineral Phases in Concrete Waste Forms". United States. doi:10.1016/j.cemconres.2006.11.004.
@article{osti_899478,
title = {Experimental Limitations Regarding the Formation and Characterization of Uranium-Mineral Phases in Concrete Waste Forms},
author = {Wellman, Dawn M. and Mattigod, Shas V. and Arey, Bruce W. and Wood, Marcus I. and Forrester, Steven W.},
abstractNote = {Predicting the long-term fate of low-level radioactive waste forms requires understanding how the radionuclides interact with the waste form. Concrete encasement is one method being considered for containment of low-level radioactive wastes. The necessary data to conduct an accurate performance assessment of such a waste form requires understanding the behavior and interactions of the radionuclides with the concrete matrix. The formation of uranium mineral phases has been investigated in simulated concrete pore fluids and Ordinary Portland Cement/Pulverized Fuel Ash (fly ash) concrete waste forms. X-Ray diffraction analyses of uranium precipitates from concrete pore fluids suggest diuranate salts, uranium-oxyhydroxides, and –silicates as solubility limiting phases. Scanning electron microscopy – energy dispersive spectroscopic analyses of uranium-spiked concrete suggests that under conditions both under-saturated and over-saturated with respect to the formation of uranium mineral phases, uranyl-oxyhydroxide phases precipitate within the initial two weeks. Subsequently, uranyl-silicate phases form after approximately one month and uranyl-phosphate phases provide a significant contribution to the long-term control over uranium in concrete waste forms after two months. This investigation demonstrates the importance of investigating the solubility of complex contaminants such as uranium in the complete matrix (i.e. concrete matrix versus pore fluids) and suggests the importance of secondary uranium mineral phases in the long-term retention within concrete waste forms.},
doi = {10.1016/j.cemconres.2006.11.004},
journal = {Cement and Concrete Research, 37(2):151-160},
number = 2,
volume = 37,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • Interactions between the glass and crystalline phases of ceramic waste forms were investigated via powder X-ray diffraction, scanning electron microscopy, and Si-29, Al-27, Na-23, Li-7, and Cl-35 magic angle spinning nuclear magnetic resonance spectroscopy. LiCl, NaCl, or KCl waste form samples were made with or without glass. The waste forms containing glass consist of sodalite and glass phases with minor amounts of nepheline. Samples without glass form varying amounts of sodalite and nepheline. The glass frit, intended to bind the zeolite particles together, changes in composition, showing marked increases in aluminum and alkali content.
  • Three crystalline ceramic materials, which occur as host phases for the long-lived actinides in many nuclear waste formulations, were doped with Cm-244, and the effects of self-radiation damage from alpha decay on microstructure and physical properties were investigated. The irradiation-induced microstructure consisted of individual amorphous tracks from both the alpha-recoil particles and the spontaneous fission fragments. The eventual overlap of the tracks at higher doses leads to a completely amorphous state. This radiation-induced amorphization process results in measured increases in volume, leachability, and stored energy. Thermal recovery of the radiation-induced swelling and amorphization occurs with full recrystallization to the initialmore » structures. 21 references, 5 figures, 2 tables.« less
  • This investigation outlines the use of natural analogues as a means of assessing the long-term performance of actinide host phases in crystalline nuclear waste forms. We employed several analytical techniques to study the mineral zirconolite, an important actinide host phase in Synroc and tailored ceramics. The following conclusions were reached: (1) Natural zirconolite experiences a crystalline to aperiodic transformation at doses of approximately 10{sup 15} to 10{sup 16} {alpha}/ma (0.08-1.0 dpa), consistent with the results of accelerated damage testing on synthetic zirconolite. (2) Damage microstructures are consistent with the accumulation and overlap of alpha-recoil collision cascades, resulting in aperiodic domainsmore » which increase in volume as a function of dose. (3) There is evidence for long-term annealing of alpha-recoil damage in zirconolite at a rate 2-5 times slower than in the structurally related mineral pyrochlore. (4) Analysis of data from the only documented natural zirconolites to show hydrothermal alteration [resulting from F- and P-rich aqueous fluids at T = 500-600{degrees}C and P = 2 kb, Giere and Williams (14)], suggests that Th and U were released to the fluid phase. (5) The effects of low temperature alteration of radiation damaged zirconolite by a Si-rich ground water or fluid phase were identified in the oldest (2.5 x 10{sup 9} yr) sample in our research collection. Alteration involved incorporation of Si along microfractures at the expense of Ca, Ti, and Fe, but Tb and U remained immobile. In this same sample, there is evidence for migration of at least 50% of the radiogenic Pb from both unaltered and altered areas of zirconolite. Most of the Pb may have been retained within the sample as fine precipitates of galena (PbS).« less