Leachability of technetium from concrete

Brodda, B.-G.

doi:10.1016/0048-9697(88)90350-6

Cited by 12 publications

(10 citation statements)

References 2 publications

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“…No precautions were taken to exclude air from these experiments. Brodda (1988) and Tallent et al (1988) also did D e measurements of slag-cements and reported that nitrate (indicative of a conservative tracer or of how fast water moves) leached about 100 times faster than Tc. Langton (1988) , respectively.…”

Section: Tc Leaching Studies For Cementitious Waste Formsmentioning

confidence: 99%

“…There were a few studies involving Tc and slag-cementitious materials (Serne et al (1992), Langton 1988, Kaplan and Coates 2007, Kaplan et al 2009Brodda 1988;Tallent et al 1988) (Table 12). Studies by Serne et al (1992), Langton (1988), Brodda (1988) and Tallent et al (1988) measured effective diffusion, D e , (or its negative logarithm, leachability index) from monoliths of reducing grout using a standardized method, ANSI/ANS-16.1.…”

Section: Tc Leaching Studies For Cementitious Waste Formsmentioning

confidence: 99%

“…Studies by Serne et al (1992), Langton (1988), Brodda (1988) and Tallent et al (1988) measured effective diffusion, D e , (or its negative logarithm, leachability index) from monoliths of reducing grout using a standardized method, ANSI/ANS-16.1. As such they did not measure K d values.…”

Section: Tc Leaching Studies For Cementitious Waste Formsmentioning

confidence: 99%

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Long-Term Technetium Interactions With Reducing Cementitious Materials

Kaplan¹,

Lilley²,

Almond³

et al. 2011

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Revision 0 can oxidize technetium in a portland cement or saltstone-like monolith. The shrinking core model used in the saltstone performance assessment describes the existence of an oxidized outer layer of concrete surrounding a shrinking core of reducing intact saltstone. A sharp boundary between the two zones moves slowly inward, resulting in oxidation of Tc(IV). This work largely reinforced our conceptual model of the shrinking core model, but more importantly provided clarity regarding process kinetics, mechanisms, and input values for future detailed modeling. The shrinking core model in itself is devoid of geochemical mechanisms. This study provided more geochemical detail to this conceptual numerical model. vii SRNL-STI-2010-00668 Revision 0

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Section: Tc Leaching Studies For Cementitious Waste Formsmentioning

confidence: 99%

Section: Tc Leaching Studies For Cementitious Waste Formsmentioning

confidence: 99%

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Long-Term Technetium Interactions With Reducing Cementitious Materials

Kaplan¹,

Lilley²,

Almond³

et al. 2011

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“…In the 2001 performance assessment, the STORM calculations did not identify any pure U solid phase for which its solubility was exceeded in the leachates. (a) The aqueous phase has a high pH, high radionuclide concentrations, and high ionic strength; the solid phase is dominated by backfill, glass, and glass secondary phases (Table 4. Gilliam et al 1989;Tallent et al 1988;Brodda 1988;Serne 1990;Serne et al 1992 (Allard 1984;Hoglund et al 1985). After 300 days contact with various cements, 77% to 98% iodide and even more iodate sorbed.…”

Section: U 1×10mentioning

confidence: 99%

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

Cantrell¹,

Zachara²,

Dresel³

et al. 2007

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Companion reports that review other subject matter areas relevant to contaminant transport within the vadose zone beneath the SST WMAs, the IDF, and groundwater have been recently published. The specific subject areas include the geology of the SST WMAs iv contaminants released to the vadose zone exhibit a wide range of mobility behaviors. Many tank waste contaminants have been strongly retarded by adsorption and precipitation reactions (e.g., cesium, plutonium, americium, and europium), while others have remained mobile (e.g., technetium, nitrate, and selenium). Still others show variable, waste-specific behaviors (e.g., cesium [where sodium concentrations are very high], strontium, chromium, and uranium) that are closely tied to evolving composition of pore water in the sediments, and for chromium, a change in oxidation state. The temperature of in-ground tank waste has moderated by heat exchange with the subsurface sediment, and high concentrations of base (OH -) have been neutralized through reactions with sediment minerals and secondary mineral precipitation. Major geochemical features that may potentially affect the mobility of key contaminants of interest in the vadose zone include oxidation state, aqueous speciation, solubility, and adsorption reactions.Processes suspected of facilitating the far-field migration of immobile radionuclides, such as formation of stable aqueous complex formation and mobile colloids, were found to be potentially operative, but unlikely to occur in the field. An exception is the enhanced migration of cobalt-60 facilitated by the formation of highly stable aqueous-cyanide complexes. Certain fission-product oxyanions (e. • Adsorption is suppressed by large concentrations of tank waste anions (e.g., NO 3 -, OH -, and CO 3 2-)• Surface charge of clay-size minerals is negative and will therefore tend to repel anions• Unlike chromium, their less-soluble, less-mobile reduced forms are unstable in oxidizing environments.Laboratory studies conducted through PNNL's Vadose Zone Characterization Project and basic-science geochemical studies are expected to continue in partnership to provide information to further refine the conceptual model used for risk assessment modeling. Results of these studies can be used to help ascertain uncertainties associated with the refinement of the conceptual models for contaminant migration in the vadose zone beneath the single-shell tanks. Results can also provide improved parameterization, such as distribution coefficients (K d ), and mathematical constructs used by modelers to predict contaminant mobility under these conditions, and to decrease the degree of conservatism incorporated in these models.For various reasons, risk assessment models typically use various approximations to represent the conceptual model developed for the site. Adsorption is frequently approximated using empirical distribution coefficients (K d s). Although the use of empirical distribution coefficients can potentially lead to erroneous results under certain conditions where the...

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“…A key factor determining the release and transport of redox sensitive radionuclides (e.g., Tc-99, Np-237, U-233, and Se-79) is the redox potential and reduction capacity of the cement-based material. Studies have shown that grouted systems containing blast furnace slag are effective in mitigating the release of Tc-99 [1][2]. Hydration of the blast furnace slag in the grout mixture releases sulfide species into the pore fluid, predominantly as S 2-, which can impose a strongly reducing redox potential (Eh) on the system [3] and can react with technetium to form relatively insoluble Tc 3 S 10 [4] or Tc 2 S 7 [5].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of Contaminant Release from Reducing Grout

Pabalan

Alexander

Waiting

et al. 2013

EPJ Web of Conferences

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Abstract.A column experiment was conducted to study the release behavior of technetium, uranium, and selenium initially sequestered in reducing grout similar in composition to Savannah River Site (SRS) saltstone, a cementitious waste form made by mixing salt solution from SRS liquid waste storage tanks with a dry mix containing blast furnace slag, fly ash, and Portland cement. The data suggest that uranium was retained in the grout possibly as a CaUO 4 phase, whereas most of the selenium was released. Technetium release initially was relatively constant, and then increased significantly after 26 pore volumes. The increase in technetium release was slightly delayed relative to the observed Eh increase. The system Eh-pH started under conditions in which technetium solubility is low, constrained by Tc 3 O 4 solubility, but eventually transitioned into the stability field of the pertechnetate ion. The delay in technetium release relative to the Eh increase was possibly due to slow oxidation of technetium at depth within the grout particles, which in turn was likely controlled by O 2 diffusion into the particles. In contrast to technetium and uranium, selenium release was not solubility limited and selenium likely was present in the pore solution initially as a HSe  species.

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Leachability of technetium from concrete

Cited by 12 publications

References 2 publications

Long-Term Technetium Interactions With Reducing Cementitious Materials

Long-Term Technetium Interactions With Reducing Cementitious Materials

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

Experimental Study of Contaminant Release from Reducing Grout

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