David K. Peeler

Measurement of kinetic rate law parameters on a NaCaAl borosilicate glass for low-activity waste

Abstract The dissolution kinetics of a NaCaAl borosilicate glass, being studied for immobilization of low-activity waste, were measured between 20 and 90°C and solution pH between 6 and 12 using the single-pass flow-through method. Dissolution kinetics measurements are needed to parameterize a mechanistic model that is being used to compute the corrosion rate of the glass waste form as a function of temperature, pH, and the concentrations of the other glass components in water percolating through a proposed shallow-land disposal facility. The key factors that were found to influence the test results include test duration and background subtraction of the raw data. Background subtraction is shown to be important to prevent a non-physical increase in the computed rate with increasing flow rate, particularly in tests run at higher flow rates. Experimental factors that were found to have no detectable influence on the test results included the glass particle size and buffer type. We also illustrate how flow rate variations can be used to obtain information about the reaction order and equilibrium constant parameters in a conventional transition-state theory rate law.

High-Level Waste Melter Study Report

At the Hanford Site in Richland, Washington, the path to site cleanup involves vitrification of the majority of the wastes that currently reside in large underground tanks. A Joule-heated glass melter is the equipment of choice for vitrifying the high-level fraction of these wastes. Even though this technology has general national and international acceptance, opportunities may exist to improve or change the technology to reduce the enormous cost of accomplishing the mission of site cleanup. Consequently, the U.S. Department of Energy requested the staff of the Tanks Focus Area to review immobilization technologies, waste forms, and modifications to requirements for solidification of the high-level waste fraction at Hanford to determine what aspects could affect cost reductions with reasonable long-term risk. The results of this study are summarized in this report.

Formulation and Characterization of Waste Glasses with Varying Processing Temperature

This report documents the preliminary results of glass formulation and characterization accomplished within the finished scope of the EM-31 technology development tasks for WP-4 and WP-5, including WP-4.1.2: Glass Formulation for Next Generation Melter, WP-5.1.2.3: Systematic Glass Studies, and WP-5.1.2.4: Glass Formulation for Specific Wastes. This report also presents the suggested studies for eventual restart of these tasks. The initial glass formulation efforts for the cold crucible induction melter (CCIM), operating at {approx}1200 C, with selected HLW (AZ-101) and LAW (AN-105) successfully developed glasses with significant increase of waste loading compared to that is likely to be achieved based on expected reference WTP formulations. Three glasses formulated for AZ-101HLW and one glass for AN-105 LAW were selected for the initial CCIM demonstration melter tests. Melter tests were not performed within the finished scope of the WP-4.1.2 task. Glass formulations for CCIM were expanded to cover additional HLWs that have high potential to successfully demonstrate the unique advantages of the CCIM technologies based on projected composition of Hanford wastes. However, only the preliminary scoping tests were completed with selected wastes within the finished scope. Advanced glass formulations for the reference WTP melter, operating at {approx}1200 C, were initiated with selected specific wastes to determine the estimated maximum waste loading. The incomplete results from these initial formulation efforts are summarized. For systematic glass studies, a test matrix of 32 high-aluminum glasses was completed based on a new method developed in this study.

Glass Formulation Development for INEEL Sodium-Bearing Waste

For about four decades, radioactive wastes have been collected and calcined from nuclear fuels reprocessing at the Idaho Nuclear Technology and Engineering Center (INTEC), formerly Idaho Chemical Processing Plant (ICPP). Over this time span, secondary radioactive wastes have also been collected and stored as liquid from decontamination, laboratory activities, and fuel-storage activities. These liquid wastes are collectively called sodium-bearing wastes (SBW). About 5.7 million liters of these wastes are temporarily stored in stainless steel tanks at the Idaho National Engineering and Environmental Laboratory (INEEL). Vitrification is being considered as an immobilization step for SBW with a number of treatment and disposal options. A systematic study was undertaken to develop a glass composition to demonstrate direct vitrification of INEELs SBW. The objectives of this study were to show the feasibility of SBW vitrification, not a development of an optimum formulation. The waste composition is relatively high in sodium, aluminum, and sulfur. A specific composition and glass property restrictions, discussed in Section 2, were used as a basis for the development. Calculations based on first-order expansions of selected glass properties in composition and some general tenets of glass chemistry led to an additive (fit) composition (68.69 mass % SiO{sub 2}, 14.26 mass% B{sub 2}O{sub 3}, 11.31 mass% Fe{sub 2}O{sub 3}, 3.08 mass% TiO{sub 2}, and 2.67 mass % Li{sub 2}O) that meets all property restrictions when melted with 35 mass % of SBW on an oxide basis, The glass was prepared using oxides, carbonates, and boric acid and tested to confirm the acceptability of its properties. Glass was then made using waste simulant at three facilities, and limited testing was performed to test and optimize processing-related properties and confirm results of glass property testing. The measured glass properties are given in Section 4. The viscosity at 1150 C, 5 Pa{center_dot}s, is nearly ideal for waste-glass processing in a standard liquid-fed joule-heated melter. The normalized elemental releases by 7-day PCT are all well below 1 g/m{sup 2}, which is a very conservative set point used in this study. The T{sub L}, ignoring sulfate formation, is less than the 1050 C limit. Based on these observations and the reasonable waste loading of 35 mass 0/0, the SBW glass was a prime candidate for further testing. Sulfate salt segregation was observed in all test melts formed from oxidized carbonate precursors. Melts fabricated using SBW simulants suggest that the sulfate-salt segregation seen in oxide and carbonate melts was much less of a problem. The cause for the difference is likely H{sub 2}SO{sub 4} fuming during the boil-down stage of wet-slurry processing. Additionally, some crucible tests with SBW simulant were conducted at higher temperatures (1250 C), which could increase the volatility of sulfate salts. The fate of sulfate during the melting process is still uncertain and should be the topic of future studies. The properties of the simulant glass confirmed those of the oxide and carbonate glass. Corrosion tests on Inconel 690 electrodes and K-3 refractory blocks conducted at INEEL suggest that the glass is not excessively corrosive. Based on the results of this study, the authors recommend that a glass made of 35% SBW simulant (on a mass oxide and halide basis) and 65% of the additive mix (either filled or raw chemical) be used in demonstrating the direct vitrification of INEEL SBW. It is further recommended that a study be conducted to determine the fate of sulfate during glass processing and the tolerance of the chosen melter technology to sulfate salt segregation and corrosivity of the melt.

Iron Phosphate Glass as an Alternative Waste-Form for Hanford LAW

Although the current baseline Hanford flowsheet for immobilizing low-activity waste (LAW) assumes borosilicate-based glass, opportunities exist to improve or change this baseline to reduce the current schedule and cost requirements of accomplishing the mission of site cleanup. Development of an alternative glass-forming system can lead to this goal of cost and schedule reduction through enhanced waste loading and higher plant throughput. The purpose of this project is to investigate the iron-phosphate glass system as an alternative for immobilizing Hanford LAW. Previous studies on the iron phosphate glass systems and their potential advantages for immobilizing Hanford LAW have been reviewed and technical uncertainties and data required before implementing this technology have been presented. A team of researchers and engineers from the MO-SCI Corporation, the Pacific Northwest National Laboratory, the Savannah River Technology Center, and the University of Missouri at Rolla has performed a series of tests to address some of the open questions about the potential use of iron phosphate glass for immobilizing Hanford LAW. The results of this team effort are summarized along with recommendations regarding the further laboratory study needs. Additional longer-term testing requirements for implementing the iron phosphate glass-based immobilization process at Hanford are also presented.

Chemistry of Rare Earth Oxalate Vitrification

Mixtures of rare earth and actinide oxalates will be vitrified into boro-aluminosilicate-based glasses for intermediate term stabilization according to current plans. The reaction chemistry involved with converting these oxalate feed stocks into glass products determines the potential for foaming, redox, and other melt and off gas related phenomena associated with this process. The authors have undertaken a detailed study of this conversion process using a variety of complementary techniques. A closed quartz crucible contained in a vertical furnace equipped with a quartz window and video camera was used to study volume expansion of the feed/melt during heating while monitoring the off-gas using a gas chromatograph-mass spectrometer. Simultaneous thermogravimetric and differential thermal analyses were conducted on small samples of feed and frit mixtures. Samples containing Ce were analyzed using established wet chemical techniques to determine Ce{sup 3+}:Ce{sup 4+} ratio (redox) as a function of temperature. The authors evaluate the results and provide a description of the reaction chemistry of these oxalate feeds during vitrification.

Americium-Curium Vitrification Process Development (U)

The successful demonstration of sequentially drying, calcining and vitrifying an oxalate slurry in the Drain Tube Test Stand (DTTS) vessel provided the process basis for testing on a larger scale in a cylindrical induction heated melter. A single processing issue, that of batch volume expansion, was encountered during the initial stages of testing. The increase in batch volume centered on a sintered frit cap and high temperature bubble formation. The formation of a sintered frit cap expansion was eliminated with the use of cullet. Volume expansions due to high temperature bubble formation (oxygen liberation from cerium reduction) were mitigated in the DTTS melter vessel through a vessel temperature profile that effectively separated the softening point of the glass cullet and the evolving oxygen from cerium reduction. An increased processing temperature of 1470 degrees C and a two hour hold time to fine any remaining bubbles successfully reduced bubbles in the poured glass to an acceptable level. The success of the preliminary process demonstrations provided a workable process basis that was directly applicable to the newly installed Cylindrical Induction Melter (CIM) system, making the batch flowsheet the preferred option for vitrification of the americium-curium surrogate feed stream.

Expanded High-Level Waste Glass Property Data Development: Phase I

Two separate test matrices were developed as part if the EM-21 Glass Matrix Crucible Testing. The first matrix, developed using a single component-at-a-time design method and covering glasses of interest primarily to Hanford, is addressed in this data package. This data package includes methods and results from glass fabrication, chemical analysis of glass compositions, viscosity, electrical conductivity, liquidus temperature, canister centerline cooling, product consistency testing, and the toxicity characteristic leach procedure.

Augmenting a Waste Glass Mixture Experiment Study with Additional Glass Components and Experimental Runs

A glass composition variation study (CVS) for high-level waste (HLW) stored in Idaho is being statistically designed and performed in phases over several years. The purpose of the CVS is to investigate and model how HLW-glass properties depend on glass composition. The resulting glass property–composition models will be used to develop desirable glass formulations and for other purposes. Phases 1 and 2 of the CVS have been completed and are briefly described. This paper focuses on the CVS Phase 3 experimental design, which was chosen to augment the Phase 1 and 2 data with additional data points, as well as to account for additional glass components not studied in Phases 1 and/or 2. In total, 16 glass components were varied in the Phase 3 experimental design. The paper describes how these Phase 3 experimental design augmentation challenges were addressed using the previous data, preliminary property–composition models, and statistical mixture experiment and optimal experimental design methods and software. The resulting Phase 3 experimental design of 30 simulated HLW glasses is presented and discussed.

Hanford Immobilized LAW Product Acceptance: Tanks Focus Area Testing Data Package II

This report is a continuation of the Hanford Immobilized Low Activity Waste (LAW) Product Acceptance (HLP): Initial Tanks Focus Area Testing Data Package (Vienna et al. 2000). In addition to new 5000-h product consistency test (PCT), vapor hydration test (VHT), and alteration products data, some previously reported data together with relevant background information are included for an easily accessible source of reference when comparing the response of the various glasses to different test conditions. A matrix of 55 glasses was developed and tested to identify the impact of glass composition on long-term corrosion behavior and to develop an acceptable composition region for Hanford LAW glasses. Of the 55 glasses, 45 were designed to systematically vary the glass composition, and 10 were selected because large and growing databases on their corrosion characteristics had accumulated. The targeted and measured compositions of these glasses are found in the Appendix A. All glasses were fabricated according to standard procedures and heat treated to simulate the slow cooling that will occur in a portion of the waste glass after vitrification in the planned treatment facility at Hanford.