TY - JOUR
T1 - In-situ radionuclide transport and preferential groundwater flows at INEEL (Idaho)
T2 - Decay-series disequilibrium studies
AU - Luo, Shangde
AU - Ku, Teh Lung
AU - Roback, Robert
AU - Murrell, Michael
AU - McLing, Travis L.
N1 - Funding Information:
We are indebted to Roy Bartholomay, Brennen Orr, DeWayne Cecil, Linda Davis, and LeRoy Knobel of the U.S. Geological Survey and Robert Smith of INEEL for their assistance in sample collection and discussions with us on the geochemical and hydrologic aspects of the Snake River Plain aquifer, and to Benmin Sun and Steve Colbert for their assistance in radiochemical analysis. We also thank Thomas Johnson for sharing his ideas on modeling the water-rock interaction. Thoughtful comments made by William M. Murphy and an anonymous reviewer on an earlier version of the paper are gratefully acknowledged. This research was sponsored by the U.S. Department of Energy Environmental Management Science Program (EMSP) grants to Ku and Murrell.
PY - 2000/3
Y1 - 2000/3
N2 - Uranium and thorium-decay series disequilibria in groundwater occur as a result of water-rock interactions, and they provide site-specific, natural analog information for assessment of in-situ, long-term migration of radionuclides in the far field of a nuclear waste disposal site. In this study, a mass balance model was used to relate the decay-series radionuclide distributions among solution, sorbed and solid phases in an aquifer system to processes of water transport, sorption-desorption, dissolution-precipitation, radioactive ingrowth-decay, and α recoil. Isotopes of U (238U, 234U), Th (232Th, 230Th, 228Th, 234Th), Ra (226Ra, 228Ra, 224Ra), and Rn (222Rn) were measured in 23 groundwater samples collected from a basaltic aquifer at the Idaho National Engineering and Environmental Laboratory (INEEL), Idaho. The results show that ground-water activities of Th and Ra isotopes are 2-4 orders lower than those of their U progenitors which average 1.35 ± 0.40 dpm 238U/L, with 234U/238U ratios of ~1.6-3.0. 222Rn activities range from 20 to 500 dpm/L. Modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water-rock interaction at INEEL: (1) Time for sorption is minutes for Ra and Th; time for desorption is days for Ra and years for Th; and time for precipitation is days for Th, years for Ra, and centuries for U. (2) Retardation factors due to sorption average >106 for 232Th, ~104 for 226Ra, and ~103 for 238U. (3) Dissolution rates of rocks are ~70 to 800 mg/L/y. (4) Ages of groundwater range from <10 to 100 years. Contours of groundwater age, as well as spatial patterns of radionuclide disequilibria, delineate two north-south preferential flow pathways and two stagnated locales. Relatively high rates of dissolution and precipitation and α-recoil of 222Rn occur near the groundwater recharging sites as well as in the major flow pathways. Decay of the sorbed parent radionuclides (e.g., 226Ra and 228Ra) on micro-fracture surfaces constitutes an important source of their daughter (222Rn and 228Th) activities in groundwater. Copyright (C) 2000 Elsevier Science Ltd.
AB - Uranium and thorium-decay series disequilibria in groundwater occur as a result of water-rock interactions, and they provide site-specific, natural analog information for assessment of in-situ, long-term migration of radionuclides in the far field of a nuclear waste disposal site. In this study, a mass balance model was used to relate the decay-series radionuclide distributions among solution, sorbed and solid phases in an aquifer system to processes of water transport, sorption-desorption, dissolution-precipitation, radioactive ingrowth-decay, and α recoil. Isotopes of U (238U, 234U), Th (232Th, 230Th, 228Th, 234Th), Ra (226Ra, 228Ra, 224Ra), and Rn (222Rn) were measured in 23 groundwater samples collected from a basaltic aquifer at the Idaho National Engineering and Environmental Laboratory (INEEL), Idaho. The results show that ground-water activities of Th and Ra isotopes are 2-4 orders lower than those of their U progenitors which average 1.35 ± 0.40 dpm 238U/L, with 234U/238U ratios of ~1.6-3.0. 222Rn activities range from 20 to 500 dpm/L. Modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water-rock interaction at INEEL: (1) Time for sorption is minutes for Ra and Th; time for desorption is days for Ra and years for Th; and time for precipitation is days for Th, years for Ra, and centuries for U. (2) Retardation factors due to sorption average >106 for 232Th, ~104 for 226Ra, and ~103 for 238U. (3) Dissolution rates of rocks are ~70 to 800 mg/L/y. (4) Ages of groundwater range from <10 to 100 years. Contours of groundwater age, as well as spatial patterns of radionuclide disequilibria, delineate two north-south preferential flow pathways and two stagnated locales. Relatively high rates of dissolution and precipitation and α-recoil of 222Rn occur near the groundwater recharging sites as well as in the major flow pathways. Decay of the sorbed parent radionuclides (e.g., 226Ra and 228Ra) on micro-fracture surfaces constitutes an important source of their daughter (222Rn and 228Th) activities in groundwater. Copyright (C) 2000 Elsevier Science Ltd.
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U2 - 10.1016/S0016-7037(99)00373-7
DO - 10.1016/S0016-7037(99)00373-7
M3 - Article
AN - SCOPUS:0033995326
SN - 0016-7037
VL - 64
SP - 867
EP - 881
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 5
ER -