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Title: Effect of Reducing Groundwater on the Retardation of Redox-Sensitive Radionuclides

Abstract

Laboratory batch sorption experiments were used to investigate variations in the retardation behavior of redox-sensitive radionuclides. Water-rock compositions used during these experiments were designed to simulate subsurface conditions at the Nevada Test Site (NTS), where a suite of radionuclides were deposited as a result of underground nuclear testing. Experimental redox conditions were controlled by varying the oxygen content inside an enclosed glove box and by adding reductants into the testing solutions. Under atmospheric (oxidizing) conditions, the radionuclide distribution coefficients varied with the mineralogical composition of the sorbent and the water chemistry. Under reducing conditions, distribution coefficients showed marked increases for {sup 99}Tc and {sup 237}Np in devitrified tuff, but much smaller variations in alluvium, carbonate rock, and zeolitic tuff. This effect was particularly important for {sup 99}Tc, which tends to be mobile under oxidizing conditions. Unlike other redox-sensitive radionuclides, iodine sorption may decrease under reducing conditions when I{sup -} is the predominant species. Overall, sorption of U to alluvium, devitrified tuff, and zeolitic tuff under atmospheric conditions was less than in the glove-box tests. However, the mildly reducing conditions achieved here were not likely to result in substantial U(VI) reduction to U(IV). Sorption of Pu was not affected by themore » decreasing redox conditions achieved in this study, as the predominant sorbed Pu species in all conditions was expected to be the low-solubility and strongly sorbing Pu(OH){sub 4}. Depending on the aquifer lithology, the occurrence of reducing conditions along a groundwater flowpath could potentially contribute to the retardation of redox-sensitive radionuclides {sup 99}Tc and {sup 237}Np, which are commonly identified as long-term dose contributors in the risk assessment in various nuclear facilities.« less

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1019057
Report Number(s):
LLNL-JRNL-409009
Journal ID: ISSN 1467-4866; TRN: US1103564
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Geochemical Transactions
Additional Journal Information:
Journal Volume: 9; Journal ID: ISSN 1467-4866
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AQUIFERS; CARBONATE ROCKS; DISTRIBUTION; GLOVES; IODINE; LITHOLOGY; NEVADA TEST SITE; NUCLEAR FACILITIES; OXYGEN; RADIOISOTOPES; RADIONUCLIDE KINETICS; RISK ASSESSMENT; SORPTION; TESTING; TUFF; WATER CHEMISTRY

Citation Formats

Hu, Q, Zavarin, M, and Rose, T P. Effect of Reducing Groundwater on the Retardation of Redox-Sensitive Radionuclides. United States: N. p., 2008. Web. doi:10.1186/1467-4866-9-12.
Hu, Q, Zavarin, M, & Rose, T P. Effect of Reducing Groundwater on the Retardation of Redox-Sensitive Radionuclides. United States. https://doi.org/10.1186/1467-4866-9-12
Hu, Q, Zavarin, M, and Rose, T P. 2008. "Effect of Reducing Groundwater on the Retardation of Redox-Sensitive Radionuclides". United States. https://doi.org/10.1186/1467-4866-9-12. https://www.osti.gov/servlets/purl/1019057.
@article{osti_1019057,
title = {Effect of Reducing Groundwater on the Retardation of Redox-Sensitive Radionuclides},
author = {Hu, Q and Zavarin, M and Rose, T P},
abstractNote = {Laboratory batch sorption experiments were used to investigate variations in the retardation behavior of redox-sensitive radionuclides. Water-rock compositions used during these experiments were designed to simulate subsurface conditions at the Nevada Test Site (NTS), where a suite of radionuclides were deposited as a result of underground nuclear testing. Experimental redox conditions were controlled by varying the oxygen content inside an enclosed glove box and by adding reductants into the testing solutions. Under atmospheric (oxidizing) conditions, the radionuclide distribution coefficients varied with the mineralogical composition of the sorbent and the water chemistry. Under reducing conditions, distribution coefficients showed marked increases for {sup 99}Tc and {sup 237}Np in devitrified tuff, but much smaller variations in alluvium, carbonate rock, and zeolitic tuff. This effect was particularly important for {sup 99}Tc, which tends to be mobile under oxidizing conditions. Unlike other redox-sensitive radionuclides, iodine sorption may decrease under reducing conditions when I{sup -} is the predominant species. Overall, sorption of U to alluvium, devitrified tuff, and zeolitic tuff under atmospheric conditions was less than in the glove-box tests. However, the mildly reducing conditions achieved here were not likely to result in substantial U(VI) reduction to U(IV). Sorption of Pu was not affected by the decreasing redox conditions achieved in this study, as the predominant sorbed Pu species in all conditions was expected to be the low-solubility and strongly sorbing Pu(OH){sub 4}. Depending on the aquifer lithology, the occurrence of reducing conditions along a groundwater flowpath could potentially contribute to the retardation of redox-sensitive radionuclides {sup 99}Tc and {sup 237}Np, which are commonly identified as long-term dose contributors in the risk assessment in various nuclear facilities.},
doi = {10.1186/1467-4866-9-12},
url = {https://www.osti.gov/biblio/1019057}, journal = {Geochemical Transactions},
issn = {1467-4866},
number = ,
volume = 9,
place = {United States},
year = {Mon Apr 21 00:00:00 EDT 2008},
month = {Mon Apr 21 00:00:00 EDT 2008}
}

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