George G. Wicks

Durability of simulated waste glass - effects of pressure and formation of surface layers☆

The leaching behavior of simulated Savannah River Plant (SRP) waste glass was studied at elevated pressures and anticipated storage temperatures. An integrated approach, which combined leachate solution analysis with both bulk and surface studies, was used to study the corrosion process. Compositions of leachates were evaluated by colorimetry and atomic absorption. Used in the bulk and surface analyses were optical microscopy, scanning electron microscopy, X-ray energy spectroscopy, wide-angle X-ray diffraction, electron microprobe analysis, infrared reflectance spectroscopy, electron spectroscopy for chemical analysis, and Auger electron spectroscopy. Results from this study show that there is no significant adverse effect of pressure, up to 1500 psi and 90°C, on the chemical durability of simulated SRP waste glass leached for one month in deionized water. In addition, the leached glass surface layer was characterized by an adsorbed film rich in minor constituents from the glass. This film remained on the glass surface even after leaching in relatively alkaline solutions at elevated pressures at 90°C for one month. The sample surface area to volume of leachant ratios (SA/V) was 10:1 cm−1 and 1:10 cm−1. The corrosion mechanisms and the subsurface layers produced will be discussed along with the potential importance of these results to repository storage.

Porous-wall hollow glass microspheres as novel potential nanocarriers for biomedical applications

UNLABELLED Porous-wall hollow glass microspheres (PW-HGMs) are a novel form of glass material consisting of a 10- to 100-microm-diameter hollow central cavity surrounded by a 1-microm-thick silica shell. A tortuous network of nanometer-scale channels completely penetrates the shell. We show here that these channels promote size-dependent uptake and controlled release of biological molecules in the 3- to 8-nm range, including antibodies and a modified single-chain antibody variable fragment. In addition, a 6-nm (70-kDa) dextran can be used to gate the porous walls, facilitating controlled release of an internalized short interfering RNA. PW-HGMs remained in place after mouse intratumoral injection, suggesting a possible application for the delivery of anticancer drugs. The combination of a hollow central cavity that can carry soluble therapeutic agents with mesoporous walls for controlled release is a unique characteristic that distinguishes PW-HGMs from other glass materials for biomedical applications. FROM THE CLINICAL EDITOR Porous-wall hollow glass microspheres (PW-HGMs) are a novel form of glass microparticles with a tortuous network of nanometer-scale channels. These channels allow size-dependent uptake and controlled release of biological molecules including antibodies and single-chain antibody fragments. PW-HGMs remained in place after mouse intratumoral injection, suggesting a possible application for the delivery of anti-cancer drugs.

Stability of radioactive waste glasses assessed from hydration thermodynamics

Assessment of the geologic performance of radioactive waste glasses requires extrapolation of finite tests to very long times. Hydration thermodynamics provides a means to compare the stability of waste glasses to natural analogues and to ancient synthetic glasses. The glass composition is separated into structural components of known free energy of hydration. These are then summed to provide a discrete measure of the stability of a given glass to aqueous attack. Hydration thermodynamics can be used to extend the results of laboratory tests of Savannah River waste glass to the repository environment. 15 references, 3 figures, 1 table.

Leaching Chemistry of Defense Borosilicate Glass

Interdiffusion and matrix dissolution corrosion modes are inadequate to describe fully the leaching behavior of the more complicated waste glasses that contain large amounts of iron, manganese, and aluminum as will many other elements. A further process, surface layer formation, that must be considered when developing a model describe waste glass leaching has been identified. This process consists of the formation of a layer of insoluble material such as the hydroxides of iron, manganese and other insoluble compounds on the surface of waste glass as it corrodes. This paper describes work leading to the development of a leaching model in which the effect of surface layer formation is considered.

US field testing programs and results

The US has been active in four major international in situ or field testing programs over the past two decades, involving the burial of simulated high-level waste forms and package components. These joint international efforts include: (1) burial of over 100 simulated Savannah River Site (SRS) high-level waste glass samples in the granite site at Stripa in Sweden, (2) burial of SRS glasses in clay at Mol, Belgium, (3) in situ testing of SRS waste forms and natural glass analogs in limestone at Ballidon in the UK, and (4) field testing of almost 2000 SRS and international waste form samples and package components in the salt site at the Waste Isolation Pilot Plant (WIPP) in the US. These programs are designed to supplement laboratory testing studies in order to obtain the most complete and realistic picture possible of waste glass behavior under realistic repository-relevant conditions. Waste glass performance thus far has been seen to be very good, and even better in the field than would be predicted by many so-called standardized laboratory leaching tests.

Leaching behavior of nuclear waste glass heterogeneities

Abstract The results of a six-month burial experiment in granite are discussed. An alkali borosilicate simulated nuclear waste glass was buried in 3 m boreholes at the 345 m level in the Stripa mine. Some glass specimens containing crystallites exhibit preferential attack of the interface between crystalline and glassy phases. The crystalline phase, identified as spinel solid solution, exhibits better chemical resistance than the glassy phase. Results obtained from homogeneous and heterogeneous glasses (i.e., those containing a crystalline phase) are compared.

Nuclear waste vitrification - the geology connection

Abstract Located at the Savannah River Plant (SRP) site are approximately 30 million gallons of high-level radioactive waste. Starting in 1989, this waste will be removed from temporary storage tanks and immobilized in borosilicate glass. The resulting waste glass product will ultimately be transported to federal repositories. At the geologic repository site, the waste glass will then be placed approximately one-half mile underground and become an important component of a multibarrier isolation system, aimed at permanent disposal of radioactive material. Nowhere in this waste disposal scenario is it more important to have good waste form performance than in the final resting place of the product, that of the geologic repository. In order to assess and understand waste glass performance in the geologic environment, a multiphase experimental program is in progress at Savannah River. An overview of experimental efforts along with selected data is presented.

Interactions of SRP waste glass with potential canister and overpack metals

Abstract The leachability of Savannah River Plant (SRP) simulated waste glass was evaluated in the presence of potential canister and overpack metals. Modified MCC-1 static leach tests were used to leach waste glass in the presence of the following metals: A516 low-carbon steel, 304L stainless steel, 409 and 430 ferritic steels, E-brite, Ticode 12, Inconel 600 and lead. Results indicated that only two of the metals studied, A516 low-carbon steel and lead, exhibited a significant effect on glass leaching. In an oxic environment, A516 low-carbon steel had a detrimental effect on glass durability, while leaching in the presence of lead significantly improved the performance of the waste glass. For the rest of the metals studied, including the SRP reference canister material, 304L stainless steel, no significant effect on glass leachability was observed.

Preliminary report on a glass burial experiment in granite

Preliminary results of a two-year burial experiment in granite are discussed. Three compositions of simulated alkali borosilicate waste glasses were placed in boreholes approximately 350 meters deep. The glass sample configurations include mini-cans (stainless steel rings into which glass has been cast) and pineapple slices (thin sections from cylindrical blocks). Assemblies of these glass samples were prepared by stacking them together with granite, compacted bentonite and metal rings to provide several types of interfaces that are expected to occur in the repository. The assemblies were maintained at either ambient mine temperature (8 to 10/sup 0/C) or 90/sup 0/C. The glasses were analyzed before burial and after one month storage at 90/sup 0/C. The most extensive surface degradation occurred on the glasses interfaced with bentonite. In general, very little attack was observed on glass surfaces in contact with the other materials. The limited field and laboratory data are compared.

Microwave technology for waste management applications: Treatment of discarded electronic circuitry

Significant quantities of hazardous wastes are generated from a multitude of processes and products in today`s society. This waste inventory is not only very large and diverse, but is also growing at an alarming rate. In order to minimize the dangers presented by constituents in these wastes, microwave technologies are being investigated to render harmless the hazardous components and ultimately, to minimize their impact to individuals and the surrounding environment.