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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The SRAT product samples indicated mercury limits were met except for the run with extended processing time, but the mercury balances were not fully closed. Up to 86% of the mercury was unaccounted for during runs with high acid stoichiometry. High mercury losses during tests at high acid stoichiometry have been noted during previous testing, including SB6 flowsheet testing. Unlike the Phase III SB6 high acid runs, there was no visible deposition of mercury or mercury amalgams on the agitator shaft or blades.

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