Diffusion and Leaching of Selected Radionuclides (Iodine-129, Technetium-99, and Uranium) Through Category 3 Waste Encasement Concrete and Soil Fill Material

Mattigod, Shas V.; Whyatt, Greg A.; Serne, R. Jeffrey; Schwab, Kristen E; Wood, M.I.

doi:10.2172/789913

Cited by 14 publications

(11 citation statements)

References 9 publications

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“…Although, diffusivity values quantified here were on the low end of the diffusion range quantified previously at 4% moisture content, the diffusion of both iodine and rhenium compared well with previous results for the diffusion of iodine and technetium under similar conditions. Results presented here confirm previous findings from (Mattigod et al, 2001) which indicated the diffusion increased with increasing water content. However, results presented here conflict with previous findings that the 1) inclusion of iron did not significantly influence the diffusion of iodine or technetium and/or rhenium and 2) the diffusion of iodine was less than technetium and/or rhenium.…”

Section: Diffusivity Results and Discussionsupporting

confidence: 92%

“…At 4% soil moisture content, the diffusion of iodide was approximately two orders of magnitude greater in concrete containing iron that was carbonated relative to iron containing concrete not subject to carbonation, 3) the diffusion of rhenium was three orders of magnitude greater in carbonated concrete monoliths which contained iron relative to those not subject to carbonation, irrespective of water content, and 4) an approximate 3% increase in moisture content results in a general decrease in diffusivity. Results presented here confirm previous findings from (Mattigod et al, 2001) which indicated the diffusion increased with increasing water content. However, results presented here conflict with previous findings that the 1) inclusion of iron did not significantly influence the diffusion of iodine or technetium and/or rhenium and 2) the diffusion of iodine was less than technetium and/or rhenium.…”

supporting

confidence: 92%

“…At 4% moisture content the diffusion of iodine quantified here, after 357 days, was nearly an order of magnitude less in the soil half-cell; whereas, the diffusion of iodide in concrete was only 4x less. The diffusion of rhenium is approximately an order of magnitude lower than that quantified previously quantified for technetium (Mattigod et al, 2001). This is likely due to molecular size limitation of the perrhenate relative to the pertechnetate ion.…”

Section: Diffusivity Results and Discussionmentioning

confidence: 52%

“…The diffusivities in the soil were reduced using the probit analysis approach previously presented by (Mattigod et al, 2001). The details of the probit analysis are provided in (Finney 1971).…”

Section: Effective Diffusion Coefficient Calculationsmentioning

confidence: 99%

“…The value of θ , 0.1472 cm3 water/cm3 concrete, was estimated based on the assumed free water volume fraction in concrete (Mattigod et al, 2001). The diffusivity coefficients in concrete were calculated using soil diffusivity coefficients derived from probit plots.…”

Section: 2mentioning

confidence: 99%

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Diffusion of Iodine and Rhenium in Category 3 Waste Encasement Concrete and Soil Fill Material

Wellman¹,

Mattigod²,

Whyatt³

et al. 2006

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SUMMARYAssessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e. sorption or precipitation). This understanding will enable accurate prediction of radionuclide fate when the waste forms come in contact with groundwater. A set of diffusion experiments using carbonated and non-carbonated concrete-soil half cells was conducted under unsaturated conditions (4% and 7% by wt moisture content). Spiked concrete half-cell specimens were prepared with and without colloidal metallic iron addition and were carbonated using supercritical carbon dioxide. Spikes of I and Re were added to achieve measurable diffusion profile in the soil part of the half-cell. In addition, properties of concrete materials likely to influence radionuclide migration such as carbonation were evaluated in an effort to correlate these properties with the release of iodine and rhenium.The behavior of rhenium and iodine release was comparable within a given half-cell test. The release of iodine and rhenium at 4% moisture content initiated with an initial concentration spike in the sediment immediately contacting the concrete monolith. The concentration profile rapidly decreased to zero within the first 5 cm of the sediment profile. Normalized concentration profiles for iodine and rhenium in sediments at 7% moisture content were asymmetrical increasing over the first 1 to 4 cm from the interface, reaching maximum concentrations 2 -5 cm from the interface, and decreasing asymptotically thereafter. The apparent release profile for sediments at 7% moisture content may be the result of i) limited diffusion within the concrete monolith which depletes the concentration source, or ii) compaction of the sediment half-cell resulting in separation from the concrete monolith, both of which effectively "cuts off" the source. Because of the method by which the sediment was sampled, it is unknown whether or not the later occurred. However, future efforts to quantify of the concentration profile within the concrete monoliths will aid in further understanding the release profiles. Comparing the release profiles at 4% and 7% moisture content suggests the rate of diffusion increases with increasing moisture content. However, because the source term was "cut-off" from the migrating contaminant at the higher moisture content the rate of diffusion was not sustained throughout the duration of testing.Diffusivity values for iodide in soil ranged from 8.66 x 10 -8 to 1.65 x 10 -7 cm 2 /s, and from 9.70 x 10 -8 to 5.75 x 10 -8 cm 2 /s for rhenium at 4% moisture content. At 7% moisture content diffusivity values for iodide ranged from 9.793 x 10 -7 to 1.52 x 10 -6 cm 2 /s, and from 8.43 x 10 -7 to 1.23 x 10 -6 cm 2 /s for rhenium. This indicates that unsaturated conditions a 3% increase in moisture content affords a one to two order of magnitude increase in diffusivity. The concrete diffusivity of iodide and rhenium ranged from 7.95 x 10 -14 to 1.20 x ...

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Section: Diffusivity Results and Discussionsupporting

confidence: 92%

supporting

confidence: 92%

Section: Diffusivity Results and Discussionmentioning

confidence: 52%

Section: Effective Diffusion Coefficient Calculationsmentioning

confidence: 99%

Section: 2mentioning

confidence: 99%

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