T Tommy Edwards

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.

INITIAL SLUDGE BATCH 4 TANK 40 DECANT VARIABILITY STUDY WITH FRIT 510

Sludge Batch 4 (SB4) is currently being processed in the Defense Waste Processing Facility (DWPF) using Frit 510. The slurry pumps in Tank 40 are experiencing in-leakage of bearing water, which is causing the sludge slurry feed in Tank 40 to become dilute at a rapid rate. Currently, the DWPF is removing this dilution water by performing caustic boiling during the Sludge Receipt and Adjustment Tank (SRAT) cycle. In order to alleviate prolonged SRAT cycle times that may eventually impact canister production rates, decant scenarios of 100, 150, and 200 kilogallons of supernate were proposed for Tank 40 during the DWPF March outage. Based on the results of the preliminary assessment issued by the Savannah River National Laboratory (SRNL), the Liquid Waste Organization (LWO) issued a Technical Task Request (TTR) for SRNL to (1) perform a more detailed evaluation using updated SB4 compositional information and (2) assess the viability of Frit 510 and determine any potential impacts on the SB4 system. As defined in the TTR, LWO requested that SRNL validate the sludge--only SB4 flowsheet and the coupled operations flowsheet using the 100K gallon decant volume as well as the addition of 3 wt% sodium on a calcined oxide basis. Approximately 12 historical glasses were identified during a search of the ComProTM database that are located within at least one of the five glass regions defined by the proposed SB4 flowsheet options. While these glasses meet the requirements of a variability study there was some concern that the compositional coverage did not adequately bound all cases. Therefore, SRNL recommended that a supplemental experimental variability study be performed to support the various SB4 flowsheet options that may be implemented for future SB4 operations in DWPF. Eighteen glasses were selected based on nominal sludge projections representing the current as well as the proposed flowsheets over a WL interval of interest to DWPF (32-42%). The intent of the experimental portion of the variability study is to demonstrate that the glasses of the Frit 510-modified SB4 compositional region (Cases No.1-5) are both acceptable relative to the Environmental Assessment (EA) reference glass and predictable by the current DWPF process control models for durability. Frit 510 is a viable option for the processing of SB4 after a Tank 40 decant and the addition of products from the Actinide Removal Process (ARP). The addition of ARP did not have any negative impacts on the acceptability and predictability of the variability study glasses. The results of the variability study indicate that all of the study glasses (both quenched and centerline canister cooled (ccc)) have normalized releases for boron that are well below the reference EA glass (16.695 g/L). The durabilities of all of the study glasses are predictable using the current Product Composition Control System (PCCS) durability models with the exception of SB4VAR24ccc (Case No.2 at 41%). PCCS is not applicable to non-homogeneous glasses (i.e. glasses containing crystals such as acmite and nepheline), thus SB4VAR24ccc should not be predictable as it contains nepheline. The presence of nepheline has been confirmed in both SB4VAR13ccc and SB4VAR24ccc by X-ray diffraction (XRD). These two glasses are the first results which indicate that the current nepheline discriminator value of 0.62 is not conservative. The nepheline discriminator was implemented into PCCS for SB4 based on the fact that all of the historical glasses evaluated with nepheline values of 0.62 or greater did not contain nepheline via XRD analysis. Although these two glasses do cause some concern over the use of the 0.62 nepheline value for future DWPF glass systems, the impact to the current SB4 system is of little concern. More specifically, the formation of nepheline was observed in glasses targeting 41 or 42% WL. Current processing of the Frit 510-SB4 system in DWPF has nominally targeted 34% WL. For the SB4 variability study glasses targeting these lower WLs, nepheline formation was not observed and the minimal difference in PCT response between quenched and ccc versions supported its absence.

AN EXPERIMENTAL ASSESSMENT OF THE IMPACT OF SLUDGE VARIATION ON THE FRIT 202-A11 - SB3 GLASS SYSTEM

Twenty-seven glasses were designed to assess the impacts of both sludge variation ({+-}5 or {+-}10% for the major sludge components) and waste loading (WL) (50 or 52%) on the Product Consistency Test (PCT) response after two thermal histories (quenching and a modified ccc schedule) within the Frit 202-A11-Sludge Batch 3 (SB3) system. The PCT results of the quenched glasses (regardless of compositional view) indicate that all Frit 202-A11-Sludge SB3 (referred to as HTLG) variability study glasses are very acceptable relative to the Environmental Assessment (EA) glass benchmark. More specifically, the normalized boron releases (NL [B] in g/L) range from 0.8 g/L (for HTLG-60VS based on the measured composition) to 1.384 g/L (HTLG-79VS based on the measured bias-corrected (bc) composition). These results can be compared to the NL [B] for the EA benchmark of 16.695 g/L. The PCT results of the quenched glasses are consistent with previous data in the Frit 202-A11-SB3 system. The PCT results for the ccc glasses are not as straight forward. The NL [B]s for the slow cooled glasses range from 0.607 g/L (for HTLG-57ccc based on the measured composition) to 9.42 g/L (for HTLG-67ccc based on the measured bc compositional view). Although these glasses would be classified as acceptable relative to the EA glass benchmark, the relatively high release of the slow cooled glasses would be of concern if this system were to be implemented into the Defense Waste Processing Facility (DWPF). The PCT responses for those glasses in which either nepheline or both nepheline and aegirine formed upon slow cooling lead to a significant reduction in PCT response. Although the formation of aegirine has (in general) a slightly negative impact on the PCT response, the formation of nepheline and aegirine is a combination that has a high probability of leading to a significant reduction in durability upon slow cooling. With respect to the Cold Crucible Induction Melter (CCIM) demonstration, a clear cut delineation of sludge compositions and/or targeted WLs is desirable to avoid the formation of either of these phases. However, based on a statistical assessment of the PCT and X-ray diffraction (XRD) data, this direct relationship does not appear to exist for this sludge/frit system and identifying the nepheline and/or aegirine primary phase field is not readily apparent based on the limited data. In addition, the possibility to target higher WLs (> 50%) to avoid any negative impacts on durability as a result of crystallization, as previously done with the nominal SB3 composition, was dependent upon the sludge component combinations. Moreover, when composition variation is applied to the sludge, multiple sludge and frit combinations fall within the nepheline and/or aegirine phase fields even at 52% WL, which ultimately lead to a negative impact on durability. Nonetheless, the PCT results do suggest that the probability of observing the negative impact is lower at the higher WLs. Only 2 of the inner layer, 52% WL based glasses have NL [B] > 2 g/L after slow cooling as compared to 4 of the 9 inner layer EVs targeted 50% WL.

ENHANCED DOE HIGH LEVEL WASTE MELTER THROUGHPUT STUDIES: SRNL GLASS SELECTION STRATEGY

The Department of Energy has authorized a team of glass formulation and processing experts at the Savannah River National Laboratory (SRNL), the Pacific Northwest National Laboratory (PNNL), and the Vitreous State Laboratory (VSL) at Catholic University of America to develop a systematic approach to increase high level waste melter throughput (by increasing waste loading with minimal or positive impacts on melt rate). This task is aimed at proof-of-principle testing and the development of tools to improve waste loading and melt rate, which will lead to higher waste throughput. Four specific tasks have been proposed to meet these objectives (for details, see WSRC-STI-2007-00483): (1) Integration and Oversight, (2) Crystal Accumulation Modeling (led by PNNL)/Higher Waste Loading Glasses (led by SRNL), (3) Melt Rate Evaluation and Modeling, and (4) Melter Scale Demonstrations. Task 2, Crystal Accumulation Modeling/Higher Waste Loading Glasses is the focus of this report. The objective of this study is to provide supplemental data to support the possible use of alternative melter technologies and/or implementation of alternative process control models or strategies to target higher waste loadings (WLs) for the Defense Waste Processing Facility (DWPF)--ultimately leading to higher waste throughputs and a reduced mission life. The glass selection strategy discussed in this report was developed to gain insight into specific technical issues that could limit or compromise the ability of glass formulation efforts to target higher WLs for future sludge batches at the Savannah River Site (SRS). These technical issues include Al-dissolution, higher TiO{sub 2} limits and homogeneity issues for coupled-operations, Al{sub 2}O{sub 3} solubility, and nepheline formation. To address these technical issues, a test matrix of 28 glass compositions has been developed based on 5 different sludge projections for future processing. The glasses will be fabricated and characterized based on the protocols outlined in the SRNL Task and Quality Assurance (QA) plan.

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.