Kevin M. Fox

INTERNATIONAL STUDY OF ALUMINUM IMPACTS ON CRYSTALLIZATION IN U.S. HIGH LEVEL WASTE GLASS

The objective of this task was to develop glass formulations for (Department of Energy) DOE waste streams with high aluminum concentrations to avoid nepheline formation while maintaining or meeting waste loading and/or waste throughput expectations as well as satisfying critical process and product performance related constraints. Liquidus temperatures and crystallization behavior were carefully characterized to support model development for higher waste loading glasses. The experimental work, characterization, and data interpretation necessary to meet these objectives were performed among three partnering laboratories: the V.G. Khlopin Radium Institute (KRI), Pacific Northwest National Laboratory (PNNL) and Savannah River National Laboratory (SRNL). Projected glass compositional regions that bound anticipated Defense Waste Processing Facility (DWPF) and Hanford high level waste (HLW) glass regions of interest were developed and used to generate glass compositions of interest for meeting the objectives of this study. A thorough statistical analysis was employed to allow for a wide range of waste glass compositions to be examined while minimizing the number of glasses that had to be fabricated and characterized in the laboratory. The glass compositions were divided into two sets, with 45 in the test matrix investigated by the U.S. laboratories and 30 in the test matrix investigated by KRI. Fabrication and characterization of the US and KRI-series glasses were generally handled separately. This report focuses mainly on the US-series glasses. Glasses were fabricated and characterized by SRNL and PNNL. Crystalline phases were identified by X-ray diffraction (XRD) in the quenched and canister centerline cooled (CCC) glasses and were generally iron oxides and spinels, which are not expected to impact durability of the glass. Nepheline was detected in five of the glasses after the CCC heat treatment. Chemical composition measurements for each of the glasses were conducted following an analytical plan. A review of the individual oxides for each glass revealed that there were no errors in batching significant enough to impact the outcome of the study. A comparison of the measured compositions of the replicates indicated an acceptable degree of repeatability as the percent differences for most of the oxides were less than 5% and percent differences for all of the oxides were less than 10 wt%. Chemical durability was measured using the Product Consistency Test (PCT). All but two of the study glasses had normalized leachate for boron (NL [B]) values that were well below that of the Environmental Assessment (EA) reference glass. The two highest NL [B] values were for the CCC versions of glasses US-18 and US-27 (10.498 g/L and 15.962 g/L, respectively). Nepheline crystallization was identified by qualitative XRD in five of the US-series glasses. Each of these five glasses (US-18, US-26, US-27, US-37 and US-43) showed a significant increase in NL [B] values after the CCC heat treatment. This reduction in durability can be attributed to the formation of nepheline during the slow cooling cycle and the removal of glass formers from the residual glass network. The liquidus temperature (T{sub L}) of each glass in the study was determined by both optical microscopy and XRD methods. The correlation coefficient of the measured XRD TL data versus the measured optical TL data was very good (R{sup 2} = 0.9469). Aside from a few outliers, the two datasets aligned very well across the entire temperature range (829 C to 1312 C for optical data and 813 C to 1310 C for XRD crystal fraction data). The data also correlated well with the predictions of a PNNL T{sub L} model. The correlation between the measured and calculated data had a higher degree of merit for the XRD crystal fraction data than for the optical data (higher R{sup 2} value of 0.9089 versus 0.8970 for the optical data). The SEM-EDS analysis of select samples revealed the presence of undissolved RuO{sub 2} in all glasses due to the low solubility of RuO{sub 2} in borosilicate glass. These particles tended to form agglomerates with varying sizes and shapes that were located close to the bottom of crucibles. The results of this study provide further insight into the ability of borosilicate waste glass to incorporate increased (>16 wt %) concentrations of aluminum. The glass composition and properties data will be incorporated into a database of glass composition-property relationships (ComPro) to support further optimization of waste glass compositions at DOE sites.

HIGH LEVEL WASTE (HLW) SLUDGE BATCH 4 (SB4) WITH FRIT 418: RESULTS OF A PHASE II VARIABILITY STUDY

In early October 2006, the Liquid Waste Organization (LWO) began to consider decanting Tank 40 at the end of Sludge Batch 3 (SB3) processing and transferring the aqueous phase from the decant to Tank 51. This transfer would be done to remove water added to Tank 40 by a slurry pump bearing water leak. Tank 40 decant water would be used to decrease Tank 51 yield stress and facilitate a transfer of Tank 51 to Tank 40. The projected composition of Sludge Batch 4 (SB4) was adjusted by LWO to reflect the impact of the Tank 40 decant leading to new projected compositions for SB4, designated as the 10-04-06 and the 10-10-06 compositions. A comparison between these SB4 compositions and those provided in June 2006 indicated that the new compositions are slightly higher in Al2O3, Fe2O3, and U3O8 and slightly lower in SiO2. The most dramatic change, however, is the new projections Na2O concentration, which is more than 4.5 wt% lower than the June 2006 projection. This is a significant change due to the frit development teams approach of aligning the Na2O concentration in a candidate frit to the Na2O content of the sludge. Questions surfaced regarding the applicability of Frit 503 to these revised compositions since the Savannah River National Laboratory (SRNL) recommended Frit 503 for use with SB4 based on the June 2006 compositional projection without the Tank 40 decant. Based on paper study assessments, the change in SB4s expected Na2O content had a significant, negative impact on the projected operating window for the Frit 503/SB4 glass system. Frit 418 had a slightly larger operating window for the 10-04-06 projection (as compared to a lower Na2O frit, Frit 503) and the Frit 418/10-04-06 glass system was no longer nepheline limited. Thus, strictly from the perspective of this paper study, Frit 418 was more attractive than Frit 503 for the new SB4 projected compositions. This comparison, however, did not reflect other aspects of interest for the glass systems such as their respective melt rates or the development of alternative frits to balance the projected operating windows, melt rate, waste throughput, and robustness to compositional variation. In discussions with Waste Solidification Engineering (WS-E) regarding the paper study results, their decision was to utilize Frit 418 for initial processing of SB4. This decision was not only based on the paper study assessments, but also on the fact that Frit 418 is currently being used to process SB3 and, perhaps more importantly, frit optimization efforts for SB4 may be premature given the uncertainties in tank transfers, volumes, and any operational issues associated with the decant transfer from Tank 40 to Tank 51 and the sludge transfer from Tank 51 to Tank 40. Given this decision and recognizing that a SB4/Frit 503 variability study had been initiated as part of the qualification process, questions regarding the need for a supplemental variability study to demonstrate applicability of the process control models for a Frit 418 based system surfaced. In response to the change in the projected composition for SB4 and the selection of Frit 418 by WS-E, SRNL complemented the SB4/Frit 503 variability study with 13 additional glasses using Frit 418. The composition region for the new glasses (or the SB4/Frit 418 variability study) was determined using the October 2006 projections of the SB4 composition.

SB5 WITH THE ESTIMATED IMPACT OF LOW TEMPERATURE ALUMINUM DISSOLUTION: PRELIMINARY FRITS FOR MELT RATE TESTING

Composition projections for Sludge Batch 5 (SB5) were developed to evaluate possible impacts of the Al-dissolution process on the availability of viable frit compositions for vitrification at the DWPF. The study included two projected SB5 compositions that bound potential outcomes (or degrees of effectiveness) of the Al-dissolution process, as well as a nominal SB5 composition projection based on the results of the recent Al-dissolution demonstration at SRNL. A Nominal Stage assessment was used to evaluate the two SB5 projections combined with an array of 19,305 frit compositions over a range of waste loading (WL) values against the DWPF process control models. The Nominal Stage results allowed for the down-selection of a small number of frits that provided reasonable projected operating windows (typically 25 to 40 wt %) and permitted some compositional flexibility (i.e., the ability to further tailor the frit to improve melt rate). Variation Stage assessments were then performed using the down-selected frits and the two SB5 composition projections with variation applied to each sludge component. The Variation Stage results showed that the operating windows were somewhat reduced in width, as expected when sludge variation is applied. Three of the down-selected frits continued to perform well for both SB5 projections through the Variation Stage, providing WL windows of approximately 26 to 35 wt %. The maximum WLs were limited by a processing constraint, TL, rather than a waste form affecting constraint (e.g., nepheline crystallization) in the Variation Stage assessments. Subsequent Nominal Stage assessments were performed with an updated SB5 projection based on the results of the Al-dissolution demonstration performed in the SRNL Shielded Cells facility (representing 40% removal of Al). The three frits identified in the earlier paper studies continued to perform well with this updated projection. The available operating windows were slightly wider, although maximum WL was limited by both the TL and nepheline constraints for all three frits. Changes in the projected SB5 composition are anticipated before processing begins at the DWPF, which will likely require additional paper study assessments as well as experimental frit development studies. This study identifies several frits which provide insight into potential operating windows for SB5 vitrification in DWPF. However, until experimental studies can be performed to gain information on melt rate and other parameters needed to optimize frit selection, no final frit recommendation can be made. Information regarding melt rate cannot be inferred from the paper study results. Experimental studies to evaluate this critical factor in DWPF processing must be performed to support frit optimization for any projected sludge composition. Five frit compositions were identified for melt rate testing at SRNL with simulated SB5 Case F SRAT product. The results of these tests will be used to evaluate the impact of the frit components--particularly B{sub 2}O{sub 3} and Na{sub 2}O--that are expected to influence melt rate for SB5-like sludges. The results of the melt rate testing will be documented in a separate report and will be used to help guide the frit recommendation process as the final SB5 composition becomes clearer.

SULFATE RETENTION IN HIGH LEVEL WASTE SLUDGE BATCH 4 GLASSES: A PRELIMINARY ASSESSMENT

Early projections of the Sludge Batch 4 (SB4) composition predicted relatively high concentrations of alumina (Al{sub 2}O{sub 3}, 23.5 wt%) and sulfate (SO{sub 4}{sup 2-}, 1.2 wt%) in the sludge. A high concentration of Al{sub 2}O{sub 3} in the sludge, combined with Na{sub 2}O additions in the frit, raises the potential for nepheline crystallization in the glass. However, strategic frit development efforts at the Savannah River National Laboratory (SRNL) have shown that frits containing a relatively high concentration of B{sub 2}O{sub 3} can both suppress nepheline crystallization and improve melt rates. A high sulfate concentration is a concern to the DWPF as it can lead to the formation of sulfate inclusions in the glass and/or the formation of a molten, sulfate-rich phase atop the melt pool. To avoid these issues, a sulfate concentration limit of 0.4 wt% SO{sub 4}{sup 2-} in glass was originally set in the Product Composition Control System (PCCS) used at DWPF. It was later shown that this limit could be increased to 0.6 wt% SO{sub 4}{sup 2-} in glass for the Frit 418, Sludge Batch 3 (SB3) system.

Vitrification of High-Level Waste at the Savannah River Site

The objective of this study was to experimentally measure the properties and performance of a series of glasses with compositions that could represent high level waste Sludge Batch 5 (SB5) as vitrified at the Savannah River Site Defense Waste Processing Facility. These data were used to guide frit optimization efforts as the SB5 composition was finalized. Glass compositions for this study were developed by combining a series of SB5 composition projections with a group of candidate frits. The study glasses were fabricated using depleted uranium and their chemical compositions, crystalline contents and chemical durabilities were characterized. Trevorite was the only crystalline phase that was identified in a few of the study glasses after slow cooling, and is not of concern as spinels have been shown to have little impact on the durability of high level waste glasses. Chemical durability was quantified using the Product Consistency Test (PCT). All of the glasses had very acceptable durability performance. The results of this study indicate that a frit composition can be identified that will provide a processable and durable glass when combined with SB5.

Plutonium Feed Impurity Testing in Lanthanide Borosilicate (LaBS) Glass

A vitrification technology utilizing a lanthanide borosilicate (LaBS) glass is a viable option for dispositioning excess weapons-useable plutonium that is not suitable for processing into mixed oxide (MOX) fuel. A significant effort to develop a glass formulation and vitrification process to immobilize plutonium was completed in the mid-1990s. The LaBS glass formulation was found to be capable of immobilizing in excess of 10 wt % Pu and to be tolerant of a range of impurities. A more detailed study is now needed to quantify the ability of the glass to accommodate the anticipated impurities associated with the Pu feeds now slated for disposition. The database of Pu feeds was reviewed to identify impurity species and concentration ranges for these impurities. Based on this review, a statistically designed test matrix of glass compositions was developed to evaluate the ability of the LaBS glass to accommodate the impurities. Sixty surrogate LaBS glass compositions were prepared in accordance with the statistically designed test matrix. The heterogeneity (e.g. degree of crystallinity) and durability (as measured by the Product Consistency Test - Method A (PCT-A)) of the glasses were used to assess the effects of impurities on glass quality.

Development of a Validation Approach for an Integrated Waste Glass Melter Model

Abstract Integrated models are being developed to represent the physics occurring within the high-level and low-activity waste melters that will be used to vitrify legacy tank waste at the Hanford site. These models couple the melt pool, cold cap, and plenum region within a single computational domain. Validation of the models is essential to ensure the reliability of the numerical predictions of the operational melters. Experimental data from laboratory- and pilot-scale tests are thus being used to inform and validate various aspects of the melter model. This paper presents a tiered approach to model validation consisting of a series of progressively more complex test cases designed to model the physics occurring in the full-scale system. A hierarchical methodology has been developed to segregate and simplify the physical phenomena affecting the multiphase flow and heat transfer within a waste glass melter. Four hierarchical levels are defined in a validation pyramid and built up in levels of increasing complexity from unit problems to subsystem cases, to pilot-scale systems, and then to the full-scale system.

TECHNOLOGY DEMONSTRATION OF SLUDGE MASS REDUCTION VIA ALUMINUM DISSOLUTION: GLASS FORMULATION PROCESSING WINDOW PREDICTIONS FOR SB5

Composition projections for Sludge Batch 5 (SB5) were developed, based on a modeling approach at the Savannah River National Laboratory (SRNL), to evaluate possible impacts of the Al-dissolution process on the availability of viable frit compositions for vitrification at the Defense Waste Processing Facility (DWPF). The study included two projected SB5 compositions that bound potential outcomes (or degrees of effectiveness) of the Al-dissolution process, as well as a nominal SB5 composition projection based on the results of the recent Al-dissolution demonstration at SRNL. The three SB5 projections were the focus of a two-stage paper study assessment. A Nominal Stage assessment combined each of the SB5 composition projections with an array of 19,305 frit compositions over a wide range of waste loading (WL) values and evaluated them against the DWPF process control models. The Nominal Stage results allowed for the down-selection of a small number of frits that provided reasonable projected operating windows (typically 27 to 42 wt% WL). The frit/sludge systems were mostly limited by process related constraints, with only one system being limited by predictions of nepheline crystallization, a waste form affecting constraint. The criteria applied in selecting the frit compositions somewhat restricted the compositional flexibility of the candidate frits for each individual SB5 composition projection, which may limit the ability to further tailor the frit for improved melt rate. Variation Stage assessments were then performed using the down-selected frits and the three SB5 composition projections with variation applied to each sludge component. The Variation Stage results showed that the operating windows were reduced in width, as expected when variation in the sludge composition is applied. However, several of the down-selected frits exhibited a relatively high degree of robustness to the applied sludge variation, providing WL windows of approximately 30 to 39 wt%. The maximum WLs were limited by processing constraints, liquidus temperature and low viscosity, rather than a waste form affecting constraint (e.g., nepheline crystallization) in the Variation Stage assessments. These paper study assessments have identified candidate frits which, when combined with the SRNL projected SB5 compositions after Al-dissolution, have projected operating windows that should be reasonable for DWPF processing. As more information is obtained on the SB5 composition to be processed in DWPF, including the actual Al removed and Tank 7 mass transferred, additional paper study assessments will be performed as well as experimental frit development studies. The frits identified in this study provide insight into potential processing windows but are not the recommended frits for SB5. No information regarding melt rate can be inferred from the paper study results. Experimental studies to evaluate this critical factor in DWPF processing must be performed on the best SB5 projection before a frit recommendation could be made for any projected sludge composition.