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Diffusion of Iodine and Technetium-99 Through Waste Encasement Concrete and Unsaturated Soil Fill Material

Published online by Cambridge University Press:  17 March 2011

Shas V. Mattigod ,
Greg A. Whyatt ,
J. R. Serne  and
Marcus I. Wood
Shas V. Mattigod
Affiliation:
Pacific Northwest National Laboratory, Richland, Washington, 99352, U.S.A, shas.mattigod@pnl.gov
Greg A. Whyatt
Affiliation:
Pacific Northwest National Laboratory, Richland, Washington, 99352, U.S.A
J. R. Serne
Affiliation:
Pacific Northwest National Laboratory, Richland, Washington, 99352, U.S.A
Marcus I. Wood
Affiliation:
Fluor Hanford Inc., Richland, Washington, 99352, U.S.A
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Abstract

An assessment of long-term performance of low level waste-enclosing cement grouts requires diffusivity data for radionuclide species such as, 129I and 99Tc. The diffusivity of radionuclides in soil and concrete media was collected by conducting soil-soil and concrete-soil half-cell experiments. The soil diffusivity coefficients for iodide were 7.03 × 10−8 cm2/s and 2.42 × 10−7cm2/s for soils at 4% and 7% moisture contents, respectively. Iodide diffusivity in soil is a function of moisture content and is about an order of magnitude slower at lower moisture content. The soil diffusivity coefficients for 99Tc were 5.89±0.80 × 10−8 cm2/s (4% moisture content) and 2.04±0.57 × 10−7 cm2/s (7% moisture content), respectively. The soil diffusivity of iodide and 99Tc were similar in magnitude at both water contents, indicating that these ions have similar diffusion mechanisms in unsaturated coarse-textured Hanford soil. The diffusivity of iodide in concrete ranged from 2.07 × 10−14 cm2/s (4% soil moisture content) to 1.31 × 10−12 cm2/s (7% soil moisture content), indicating that under unsaturated soil moisture conditions, iodide diffusivity is highly sensitive to changing soil moisture conditions. Depending on the soil moisture content, the diffusivity of 99Tc in concrete ranged from 4.54 × 10−13 cm2/s to 8.02 × 10−12 cm2/s. At 4% soil moisture content, iodide diffused about 20 times more slowly than 99Tc, and at 7% soil moisture content, iodide in concrete diffused about 6 times slower than 99Tc.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 824: Symposium CC – Scientific Basis for Nuclear Waste Management XXVIII , 2004 , CC7.6
Copyright
Copyright © Materials Research Society 2004

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