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The Defense Waste Processing Facility (DWPF) is about to process High Level Waste (HLW) Sludge Batch 4 (SB4). This sludge batch is high in alumina and nepheline can crystallize readily depending on the glass composition. Large concentrations of crystallized nepheline can have an adverse effect on HLW glass durability. Several studies have been performed to study the potential for nepheline formation in SB4. The Phase 3 Nepheline Formation study of SB4 glasses examined sixteen different glasses made with four different frits. Melt rate experiments were performed by the Process Science and Engineering Section (PS&E) of the Savannah River National Laboratory (SRNL) using the four frits from the Phase 3 work, plus additional high B 2 O 3 /high Fe 2 O 3 frits. Preliminary results from these tests showed the potential for significant improvements in melt rate for SB4 glasses using a higher B 2 O 3 -containing frit, particularly Frit 503. The main objective of this study was to investigate the durability of SB4 glasses produced with a high B 2 O 3 frit likely to be recommended for SB4 processing. In addition, a range of waste loadings (WLs) was selected to continue to assess the effectiveness of a nepheline discriminator in predicting concentrations of nepheline crystallization that would be sufficient to influence the durability response of the glass. Five glasses were selected for this study, covering a WL range of 30 to 50 wt% in 5 wt% increments.The Frit 503 glasses were batched and melted. Specimens of each glass were heat-treated to simulate cooling along the centerline of a DWPF-type canister (ccc) to gauge the effects of thermal history on product performance. Visual observations on both quenched and ccc glasses were documented. A representative sample from each glass was submitted to the SRNL Process Science Analytical Laboratory (PSAL) for chemical analysis to confirm that the as-fabricated glasses corresponded to the defined target compositions. The Product Consistency Test (PCT, ASTM C1285) was performed in triplicate on each Frit 503 quenched and ccc glass to assess chemical durability. The experimental test matrix also included the Environmental Assessment (EA) glass and the Approved Reference Material (ARM-1) glass. Representative samples of all the ccc glasses were examined for homogeneity visually and by X-ray diffraction (XRD) analysis.Chemical composition measurements indicated that the experimental glasses were close to their target compositions. PCT results showed that all of the Fit 503 quenched glasses had an acceptable durability compared to the EA benchmark glass. The durability of one of the ccc glasses, NEPHB-04, was statistically greater than its quenched counterpart. However, this was shown to be of little practical significance, as the durability of the NEPHB-04 ccc glass was acceptable when compared to the durability of the EA benchmark glass.Visual observations and PCT results indicated that all of the Frit 503 quenched glasses were free of any crystallization that impacts durability. Fo...

The Defense Waste Processing Facility (DWPF) will transition from Sludge Batch 4 (SB4) processing to Sludge Batch 5 (SB5) processing in early fiscal year 2009. Tests were conducted using non-radioactive simulants of the expected SB5 composition to determine the impact of varying the acid stoichiometry during the Sludge Receipt and Adjustment Tank (SRAT) and Slurry Mix Evaporator (SME) processes. The work was conducted to meet the Technical Task Request (TTR) HLW/DWPF/TTR-2007-0007, Rev. 1 1 and followed the guidelines of a Task Technical and Quality Assurance Plan (TT&QAP) 2. SRNS-STI-2008-00024 Revision 0 vi SRAT cycle, but exceeded the process limit during the SME cycle at the highest acid stoichiometry (160%). All of the blend experiments were within the process limits throughout the SRAT and SME cycles. As DWPF will be processing blend sludge, hydrogen likely won't be an issue in DWPF processing but lower acid stoichiometries will minimize hydrogen generation. The nitrous oxide generation peak was relatively insensitive to acid stoichiometry and was relatively low due to the low starting nitrite concentration. Acid quantities and processing times required for mercury removal Mercury was added to the sludge simulant at the start of the SRAT cycle as mercuric oxide at approximately 2.5 wt% (solids basis) based on the expected composition of the SB5 batch and blend. Mercury was not added to the ARP simulant. Because of the high mercury concentration, the time at boiling was increased from 12 hours to 18 hours to allow sufficient time to strip mercury from the SRAT. Boiling flux was maintained at a scaled rate of 5,000 lb/hr so a total of 90,000 lb of steam flow in DWPF will be needed to remove 120 lb of mercury. Acid quantities from 115% to 160% resulted in satisfactory mercury removal with 18 hours of boiling time (including dewater and reflux time), with the exception of the two lowest acid stoichiometry runs with the blend simulant. ARP/MCU processing did not impact mercury reduction and removal. If DWPF experiences problems stripping mercury, increasing the acid stoichiometry is likely to improve mercury removal. Simulant testing does not simulate the DWPF heel so starting mercury concentrations will be lower in DWPF and shorter steam stripping times should be achievable. Acid quantities and processing times required for nitrite destruction Acid quantities from 115% to 160% resulted in satisfactory nitrite destruction with 18 hours of boiling. In all runs, the amount of nitrite present in the SRAT product was less than 100 mg/kg, well below the 1,000 mg/kg target. The longer boiling time and low starting nitrite concentration both helped to reduce the nitrite by the end of the SRAT cycle.

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