Evolution of chemical conditions and estimated solubility controls on radionuclides in the residual waste layer during post-closure aging of high-level waste tanks

Denham, Miles; Millings, Margaret R.

doi:10.2172/1126474

Cited by 8 publications

(46 citation statements)

References 34 publications

(35 reference statements)

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“…The values are also close to the "more realistic" solubility of amorphous plutonium oxide, 3.2E-11 molar as reported by Denham. 1 These results indicate that a larger sample aliquot should be used and perhaps longer alpha counting times to provide a lower quantification limit for the plutonium measurements.…”

Section: Zero Head Space Leaching Tests With Surrogate Tank 18 Solidsmentioning

confidence: 95%

Determining the Release of Radionuclides From Tank Waste Residual Solids

Miller¹,

Roberts²,

Taylor-Pashow³

et al. 2014

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Current practice for closing high-level waste tanks at the Savannah River Site involves removing as much of the HLW as possible, disconnecting all transfer lines and penetrations into the tanks, and filling the internal volume of the tanks with grout. Performance assessment modeling of the release of radionuclides from tank waste solids in these tanks indicated that plutonium, neptunium, technetium, and uranium are among the most likely risk drivers. Waste release testing was identified as needed to provide additional information regarding the residual waste solubility assumptions used in the F-Area and H-Area Tank Farm Performance Assessments' waste release models. The proposed testing was described generally in the Savannah River Site Liquid Waste Facilities Performance Assessment Maintenance Program FY2014 Implementation Plan. Savannah River Remediation LLC requested that the Savannah River National Laboratory perform such testing with available tank waste residuals after method development using surrogate materials. This document reports findings from the testing completed to date and recommendations for continued work. Key findings based on experimental work completed to date with surrogate materials include the following. • Pore water electron transfer potentials (E h) produced in these studies upon contact of synthetic infiltration water with surrogate tank closure solids are lower than those used in PA modeling. This suggests that in short-term experiments, kinetic controls on the E h values of the synthetic pore waters in contact with grout solids dominate over the equilibrium controls assumed in the PA waste release modeling. • The zero head-space method appears viable for testing the release of radionuclides from solids under reducing conditions, but not under oxidizing conditions due to oxygen depletion. • Researchers must account for the alkalinity and redox potential of the tank waste solids to ensure target pH and E h values will be achieved in radionuclide release testing.

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Section: Zero Head Space Leaching Tests With Surrogate Tank 18 Solidsmentioning

confidence: 95%

Determining the Release of Radionuclides From Tank Waste Residual Solids

Miller¹,

Roberts²,

Taylor-Pashow³

et al. 2014

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“…Perhaps one of the key attributes of this model is that it can be parameterized and as such, it has immediate appeal from a practical point of view. While models based on thermodynamic and reactive transport used to describe this process in SRS disposal systems (Denham 2007;Denham and Millings 2012) are theoretically more acceptable, they require more assumptions and many more input values that are often not available for cementitious waste form conditions. As an example of the type of information needed in these more theoretically acceptable calculations, it is not only necessary to know what the reduction capacity is, you must also know what phases are responsible for redox status and the kinetic information about how they change to other phases as a result of oxidation.…”

Section: Porewater Pathway For Oxidizing Reduced-cementitious Materiamentioning

confidence: 99%

Solid Secondary Waste Data Package Supporting Hanford Integrated Disposal Facility Performance Assessment

Flach¹,

Kaplan²,

Nichols³

et al. 2016

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This data package provides recommendations for waste form physical and chemical properties to support the initial analysis of Solid Secondary Waste (SSW) disposals in the 2017 Integrated Disposal Facility (IDF) Performance Assessment (PA). At this time, specific formulations have not been identified for cementitious materials that will be used to encapsulate or solidify SSW, and no IDF-specific experiments were conducted to obtain data for the PA. Thus recommended property values are provided for a range of candidate materials, and based on a review of existing literature. Four key SSW streams were identified for emphasis due to expected inventories for contaminants of potential concern (COPC): HEPA filters, ion exchange resins, carbon adsorber beds and Ag-mordenite. Based on current disposal plans, compacted HEPA filters were considered as an encapsulated waste form and the other three key waste streams were assumed to be blended and solidified in a cementitious matrix. Considerations for alternative disposal methods were also addressed. The IDF PA team identified specific COPCs expected to be the key contributors for the PA calculations: Tc-99, I-129, Cs-137, Sr-90, uranium isotopes (and total uranium), chromium, mercury and nitrate. These species are the focus of this data package.

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“…Much of the chemical evolution analysis was performed with equilibrium chemistry simulation software, namely The Geochemist's Workbench® (GWB) and PHREEQC®. Custom thermodynamic databases formatted for these codes were developed from Denham [3], CEMDATA18.1 [63], and ThermoChimie [64]. Initial simulations defined the equilibrium chemical state of SRS rainwater, soil moisture, groundwater, and hydrated grouts and concrete.…”

Section: Chemical and Physical Effectsmentioning

confidence: 99%

“…In the interim these materials will provide a barrier to the leaching of radionuclides into the soil. The current FTF and HTF PAs [1], [2] are based on multiple studies that consider the chemical and/or physical degradation of cementitious materials, either directly or indirectly [3], [4], [5], [6], [7]. Savannah River Remediation (SRR) is updating relevant portions of these studies to support an imminent revision to the HTF PA and a future update to the FTF PA.…”

Section: Introductionmentioning

confidence: 99%

Corrosion of Steel During Long-Term Exposure to Evolving Cementitious Environments

Wiersma

2021

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Evolution of chemical conditions and estimated solubility controls on radionuclides in the residual waste layer during post-closure aging of high-level waste tanks

Cited by 8 publications

References 34 publications

Determining the Release of Radionuclides From Tank Waste Residual Solids

Determining the Release of Radionuclides From Tank Waste Residual Solids

Solid Secondary Waste Data Package Supporting Hanford Integrated Disposal Facility Performance Assessment

Corrosion of Steel During Long-Term Exposure to Evolving Cementitious Environments

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