D David Peeler

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.

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.