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Title: Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff

Abstract

No abstract prepared.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Savannah River Ecology Laboratory (SREL), Aiken, SC
Sponsoring Org.:
USDOE
OSTI Identifier:
898805
Report Number(s):
SRE:-3009
Journal ID: ISSN 0013-936X; ESTHAG; TRN: US0701696
DOE Contract Number:
DE-FC09-07SR22506
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science and Technology; Journal Volume: 40
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; OXIDATION; PLUTONIUM; TUFF; YUCCA MOUNTAIN

Citation Formats

Powell, B. A., Duff, M. C., Kaplan, D. I., Field, R. A., Newville, M., Hunter, D. B., Bertsch, P. M., Coates, J. T., Eng, P., Rivers, M. L., Serkiz, S. M., Sutton, S. R., Triay, I. R., and Vaniman, D. T. Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff. United States: N. p., 2006. Web. doi:10.1021/es052353+.
Powell, B. A., Duff, M. C., Kaplan, D. I., Field, R. A., Newville, M., Hunter, D. B., Bertsch, P. M., Coates, J. T., Eng, P., Rivers, M. L., Serkiz, S. M., Sutton, S. R., Triay, I. R., & Vaniman, D. T. Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff. United States. doi:10.1021/es052353+.
Powell, B. A., Duff, M. C., Kaplan, D. I., Field, R. A., Newville, M., Hunter, D. B., Bertsch, P. M., Coates, J. T., Eng, P., Rivers, M. L., Serkiz, S. M., Sutton, S. R., Triay, I. R., and Vaniman, D. T. Sun . "Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff". United States. doi:10.1021/es052353+.
@article{osti_898805,
title = {Plutonium Oxidation and Subsequent Reduction by Mn(IV) Minerals in Yucca Mountain Tuff},
author = {Powell, B. A. and Duff, M. C. and Kaplan, D. I. and Field, R. A. and Newville, M. and Hunter, D. B. and Bertsch, P. M. and Coates, J. T. and Eng, P. and Rivers, M. L. and Serkiz, S. M. and Sutton, S. R. and Triay, I. R. and Vaniman, D. T.},
abstractNote = {No abstract prepared.},
doi = {10.1021/es052353+},
journal = {Environmental Science and Technology},
number = ,
volume = 40,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Plutonium sorbed to rock tuff was preferentially associated with manganese oxides. On tuff and synthetic pyrolusite (Mn{sup IV}O{sub 2}), Pu(IV) or Pu(V) was initially oxidized, but over time Pu(IV) became the predominant oxidation state of sorbed Pu. Reduction of Pu(V/VI), even on non-oxidizing surfaces, is proposed to result from a lower Gibbs free energy of the hydrolyzed Pu(IV) surface species versus that of the Pu(V) or Pu(VI) surface species. This work suggests that despite initial oxidation of sorbed Pu by oxidizing surfaces to more soluble forms, the less mobile form of Pu, Pu(IV), will dominate Pu solid phase speciation duringmore » long term geologic storage. The safe design of a radioactive waste or spent nuclear fuel geologic repository requires a risk assessment of radionuclides that may potentially be released into the surrounding environment. Geochemical knowledge of the radionuclide and the surrounding environment is required for predicting subsurface fate and transport. Although difficult even in simple systems, this task grows increasingly complicated for constituents, like Pu, that exhibit complex environmental chemistries. The environmental behavior of Pu can be influenced by complexation, precipitation, adsorption, colloid formation, and oxidation/reduction (redox) reactions (1-3). To predict the environmental mobility of Pu, the most important of these factors is Pu oxidation state. This is because Pu(IV) is generally 2 to 3 orders of magnitude less mobile than Pu(V) in most environments (4). Further complicating matters, Pu commonly exists simultaneously in several oxidation states (5, 6). Choppin (7) reported Pu may exist as Pu(IV), Pu(V), or Pu(VI) oxic natural groundwaters. It is generally accepted that plutonium associated with suspended particulate matter is predominantly Pu(IV) (8-10), whereas Pu in the aqueous phase is predominantly Pu(V) (2, 11-13). The influence of the character of Mn-containing minerals expected to be found in subsurface repository environments on Pu oxidation state distributions has been the subject of much recent research. Kenney-Kennicutt and Morse (14), Duff et al. (15), and Morgenstern and Choppin (16) observed oxidation of Pu facilitated by Mn(IV)-bearing minerals. Conversely, Shaughnessy et al. (17) used X-ray Absorption near-edge spectroscopy (XANES) to show reduction of Pu(VI) by hausmannite (Mn{sup II}Mn{sub 2}{sup III}O{sub 4}) and manganite ({gamma}-Mn{sup III}OOH) and Kersting et al., (18) observed reduction of Pu(VI) by pyrolusite (Mn{sup IV}O{sub 2}). In this paper, we attempt to reconcile the apparently conflicting datasets by showing that Mn-bearing minerals can indeed oxidize Pu, however, if the oxidized species remains on the solid phase, the oxidation step competes with the formation of Pu(IV) that becomes the predominant solid phase Pu species with time. The experimental approach we took was to conduct longer term (approximately two years later) oxidation state analyses on the Pu sorbed to Yucca Mountain tuff (initial analysis reported by Duff et al., (15)) and measure the time-dependant changes in the oxidation state distribution of Pu in the presence of the Mn mineral pyrolusite.« less
  • The sorption of simple cations in tuff is dominated by adsorption on aluminosilicates that have charged surfaces, such as zeolites and clays. The most significant sorbing minerals present in Nevada tuff are clinoptilolite, heulandite, mordenite, and montmorillonite. The kinetics of sorption on tuffs containing the minerals clinoptilolite and montmorillonite has been determined by studying the uptake of strontium, cesium, and barium on thin tuff wafers. The rate constants for uptake of these elements on tuff are consistent with a model of sorption that is diffusion limited but where diffusion occurs in two stages. First the cations diffuse into the rockmore » through the water-filled pore space. Next, the cations must diffuse into the much narrower channels within the aluminosilicate crystals. After they are within the zeolite framework or between the clay planes, the cations may rapidly sorb on the negatively charged surfaces. The actinide elements have a time constant for the apparent sorption that is inconsistent with this model and may have a radically different mechanism of removal from solution. 12 references, 4 tables.« less