Sludge Batch 4 Without Tank 4 Simulant Flowsheet Studies: Phase I SRAT Results

A set of simulant flowsheet runs using co-precipitated Sludge Batch 4 (SB4) simulant has been performed by the Savannah River National Laboratory (SRNL) - Immobilization Technology Section (ITS). This simulant reflected updated composition information from the Closure Business Unit since Tank 4 has been excluded from SB4 and settling issues have occurred in Tank 51. The flowsheet testing is part of the planning and qualification effort that is performed by SRNL for every sludge batch to be processed in the Defense Waste Processing Facility (DWPF). The work was performed to meet the requirements outlined in Technical Task Request (TTR) HLW/DWPF/TTR-04-0031 (Washburn 2004). A task technical and quality assurance plan was written by Baich (2004) in response to the TTR and provided guidance for the testing. The main objective of this set of tests was to assist in the determination of the SB4 washing endpoint and to bound SB4 processing based on projected compositions. Previous testing (Baich et. al. 2005) addressed compositions for SB4 that included Tank 4 with different washing endpoints and determined an acceptable operating window. However, the changes in composition and planning necessitated another set of flowsheet tests to be performed. For this set of flowsheet runs, the ITS used sludge simulant fabricated by the ITS Simulant Development program. The target composition was based on a SB4/Tank 51 washing strategy to target a ∼1.6M Na endpoint. Once SB4 is qualified, it will be transferred to a heel of SB3 in Tank 40 to meet accelerated closure commitments. The simulant reflected blending with a 40'' heel of SB3 in Tank 40. This level was selected since it contained the higher concentration of anions to be removed during DWPF processing and a higher concentration of SB4, which less is known about. Two Sludge Receipt and Adjustment Tank (SRAT) cycles were performed at different acid addition levels. The lower acid test was at 130% of stoichiometry and was identified as run SB4-19, while the higher acid test was at 170% of stoichiometry and was identified as run SB4-20. Both runs used the same level of noble metals and mercury, which were the same levels used in earlier SB4 flowsheet testing. Due to the number of samples that were taken and the subsequent small quantity of SRAT product fabricated, a portion of each SRAT product was combined to perform a Slurry Mix Evaporator (SME) cycle with Frit 418 targeting a waste loading of 43% and a total solids loading of 50%. The main objective of the SME cycle was to determine the rheology of the SME product so the feasibility of pumping the material for melt rate testing could be evaluated. In addition, performing the SME cycle allowed insight to be gained into SME processing for the particular wash endpoint. Portions of the SME product were adjusted with frit and water additions to determine rheology at 35% waste loading and 45% total solids to support melt rate testing