Waste Salt Disposal at the Savannah River Plant†

Langton, C.A.; Oblath, S.B.; Pepper, Darrell W.; Wilhite, E.L.

doi:10.1080/00986448808940267

Cited by 8 publications

(4 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Cementitious waste forms (CWFs) present a viable method to immobilize liquid nuclear waste present at many global nuclear waste storage sites. The most widely used category of reducing CWF, slag saltstone (45 wt% blast furnace slag (BFS), 45 wt% fly ash, and 10 wt% ordinary Portland cement (OPC)), was developed by Langton et al 101 at the Savannah River site, South Carolina, by substituting a high content of hydraulic BFS for OPC, in combination with fly ash as a functional extender to control heat of hydration and reduce permeability. Substitution of the BFS significantly reduces release of TcO 4 − and Cr(VI) 2 O 7 2− from the monolithic CWF through maintenance of reducing conditions.…”

Section: Technetium Sulfide In Radioactive Wastementioning

confidence: 99%

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Pearce

Icenhower²,

Asmussen

et al. 2018

ACS Earth Space Chem.

View full text Add to dashboard Cite

Technetium (Tc) contamination remains a major environmental problem at nuclear reprocessing sites, e.g., the Hanford Site, Washington State, USA. At these site, Tc is present in liquid waste destined for immobilization in a waste form or has been released into the subsurface environment. The high environmental risk associated with Tc is due to its long half-life (213,000 years) and the mobility of the oxidized anionic species Tc(VII)O 4-. Under reducing conditions, TcO 4 is readily reduced to Tc(IV), which commonly exists as a relatively insoluble and therefore immobile, hydrous Tc oxide (TcO 2 •nH 2 O). The stability of Tc(IV) sequestered as solid phases depends on the solubility of the solid and susceptibility to re-oxidation to TcO 4-, which in turn depend on the (bio-geo)chemical conditions of the environment and/or nuclear waste streams. Unfortunately, the solubility of crystalline TcO 2 or amorphous TcO 2 •H 2 O is still above the maximum contaminant level (MCL) established by the US EPA (900 pCi/L), and the kinetics of TcO 2 oxidative dissolution can be on the order of days to years. In addition to oxygen, sulfur can form complexes that significantly affect the adsorption, solubility and re-oxidation potential of Tc, especially Tc(IV). The principal technetium sulfides areTcS 2 and Tc 2 S 7 but much less is known about the mechanisms of formation, stabilization and re-oxidation of Tc sulfides. A common assumption is that sulfides are less soluble that their oxyhydrous counterparts. Determination of the molecular structure of Tc 2 S 7 in particular has been hampered by the propensity of this phase to precipitate as an amorphous substance. Recent work indicates that the oxidation state of Tc in Tc 2 S 7 is Tc(IV), in apparent contradiction to its nominal stoichiometry. Technetium is relatively immobile in reduced sediments and soils, but in many cases the exact sink for Tc has not been identified. Experiments and modeling have demonstrated that both abiotic and biologic mechanisms can exert strong controls on Tc mobility and that Tc binding or uptake into sulfide phases can occur. These and similar investigations also show that extended exposure to oxidizing conditions results in transformation of sulfide-stabilized Tc(IV) to a Tc(IV)O 2-like phase without formation of measurable dissolved TcO 4-, suggesting a solid-state transformation in which Tc(IV)-associated sulfide is preferentially oxidized before the Tc(IV) cation. This transformation of Tc(IV) sulfides to Tc(IV) oxides may be the main process that limits remobilization of Tc as Tc(VII)O 4-. The efficacy of the final waste form to retain Tc also strongly depends on the ability of oxidizing species to enter the waste and convert Tc(IV) to Tc(VII). Many waste form designs are reducing (e.g., cementitious waste forms such as salt stone), therefore, attempt to restrict access of oxidizing species such that diffusion is the ratelimiting step in remobilization of Tc.

show abstract

Section: Technetium Sulfide In Radioactive Wastementioning

confidence: 99%

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Pearce

Icenhower²,

Asmussen

et al. 2018

ACS Earth Space Chem.

View full text Add to dashboard Cite

show abstract

“…Currently, DOE is using low-temperature waste forms and engineered barriers as an effective means for disposal of low-level wastes where assessments can be developed to validate waste form and disposal system performance (Flach and Smith 2013;Langton and Dukes 1984).The decontaminated aqueous waste stream resulting from pretreating HLW tank waste is classified as waste incidental to reprocessing, which can be disposed of in a near-surface facility provided that the workers, public, and environment are protected. Establishing the performance and predictability of low-temperature, low-level waste forms are essential to demonstrating their suitability for disposal.…”

Section: Low-temperature Waste Formsmentioning

confidence: 99%

Basic Research Needs for Environmental Management

Clark

Buchanan

Wilmarth

2016

View full text Add to dashboard Cite

Schematic diagram of glass dissolution mechanisms in aqueous solution, coupled with both hydrated amorphous surface layer formation and crystallization/precipitation from solution ........... 23 Contaminant fate and transport in geological environments is governed by coupled hydrological, physical, geochemical, and microbiological properties and processes that occur over a wide range of spatial and temporal scales ..

show abstract

“…The dry reagents consist of 1) Portland cement, 2) fly ash, 3) blast furnace slag (BFS), and 4) ferrous sulfate monohydrate. This formulation is essentially equivalent to salt stone grout formulations used at the Savannah River site (LANGTON et al, 1988;LANGTON, 1989).…”

Section: Cast Stonementioning

confidence: 99%

A Strategy to Assess Performance of Selected Low-Activity Waste Forms in an Integrated Disposal Facility

McGrail¹,

Bacon²,

Serne³

et al. 2003

View full text Add to dashboard Cite

Low-activity tank wastes will be generated during cleanup of high-level radioactive tank wastes on the Hanford site. The low-activity tank waste will be among the largest volumes of radioactive waste within the U.S. Department of Energy (DOE) complex and is one of the largest inventories of long-lived radionuclides planned for disposal in a low-level waste facility. The Department of Energy's Office of River Protection is evaluating several options for immobilization of low-activity tank wastes for eventual disposal in a shallow subsurface facility at the Hanford Site. A significant portion of the waste will be converted into low-activity waste (LAW) glass with a conventional Joule-heated ceramic melter. In addition, three supplemental treatment processes are presently under consideration by the DOE to treat wastes in selected tanks with the goal of accelerating the overall cleanup mission at the Hanford site. These are: 1) bulk vitrification (BV), 2) cementation or the cast stone (CS) process, and 3) steam reformation (SR). The DOE is expected to select by October 2003 one or more of these supplemental treatment technologies for more detailed evaluation. As part of the selection process, a preliminary risk assessment is being performed to evaluate the impacts of the disposal facility on public health and environmental resources.The same computational framework used to conduct the 2001 ILAW performance assessment will be used for all three waste forms. Cast stone will be modeled with a diffusion-advection transport model and bulk vitrified glass and steam reformed LAW will be modeled with a reactive chemical transport simulator. Modeling waste form performance requires the determination of a number of wasteform specific input parameters. The required input parameters for BV and SR waste forms are derived from a mechanistic model that describes the effect of solution chemistry on contaminant release rates. The single-pass flow-through test is the principal method used to obtain these input parameters, supplemented by product consistency test measurements and physical property measurements. The diffusiveadvective transport model for cast stone requires measurements of effective diffusion coefficients and hydraulic properties.

show abstract

Waste Salt Disposal at the Savannah River Plant†

Cited by 8 publications

References 1 publication

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Basic Research Needs for Environmental Management

A Strategy to Assess Performance of Selected Low-Activity Waste Forms in an Integrated Disposal Facility

Contact Info

Product

Resources

About