DWPF FLOWSHEET STUDIES WITH SIMULANTS TO DETERMINE MCU SOLVENT BUILD-UP IN CONTINOUS RUNS

The Actinide Removal Process (ARP) facility and the Modular Caustic Side Solvent Extraction Unit (MCU) are scheduled to begin processing salt waste in fiscal year 2007. A portion of the streams generated in these salt processing facilities will be transferred to the Defense Waste Processing Facility (DWPF) to be incorporated in the glass matrix. Before the streams are introduced, a combination of impact analyses and research and development studies must be performed to quantify the impacts on DWPF processing. The Process Science & Engineering (PS&E) section of the Savannah River National Laboratory (SRNL) was requested via Technical Task Request (TTR) HLW/DWPF/TTR-2004-0031 to evaluate the impacts on DWPF processing. Simulant Chemical Process Cell (CPC) flowsheet studies have been performed using previous composition and projected volume estimates for the ARP sludge/monosodium titanate (MST) stream. Initial MCU incorporation testing for the DWPF flowsheet indicated unacceptable levels of Isopar{reg_sign}L were collecting in the Sludge Receipt and Adjustment Tank (SRAT) condenser system and unanticipated quantities of modifier were carrying over into the SRAT condenser system. This work was performed as part of Sludge Batch 4 (SB4) flowsheet testing and was reported by Baich et al. Due to changes in the flammability control strategy for DWPF for salt processing, the incorporation strategy for ARP changed and additional ARP flowsheet tests were necessary to validate the new processing strategy. The last round of ARP testing included the incorporation of the MCU stream and identified potential processing issues with the MCU solvent. The identified issues included the potential carry-over and accumulation of the MCU solvent components in the CPC condensers and in the recycle stream to the Tank Farm. Solvent retention in the DWPF condensers contradicts the DWPF solvent control strategy. Therefore, DWPF requested SRNL to perform additional MCU flowsheet studies to better quantify the organic distribution in the CPC vessels. The earlier rounds of testing used a Sludge Batch 4 (SB4) simulant since it was anticipated that both of these facilities would begin salt processing during SB4 processing. The same sludge simulant recipe was used in this round of MCU testing to minimize the number of changes between the three phases of testing so a better comparison could be made. The MCU stream simulant was fabricated to perform the testing. The MCU stream represented the ''Maximum Volume'' case from the material balances provided by Campbell. ARP addition was not performed during this set of runs since the ARP evaluation had been completed in earlier runs. The MCU stream was added at boiling during the normal reflux phase of the SRAT cycle. SRAT cycle completion corresponded to the end of MCU stream addition. A total of ten 4-liter SRAT runs were performed to meet the objectives of the testing. The first series of five tests evaluated the organic portioning and mass balance for the addition of 50 mg/kg solvent. The second series of five tests evaluated the organic portioning and mass balance for the addition of 125 mg/kg solvent. A solvent concentration of 50 mg/kg is close to the nominal concentration anticipated in the effluent from the Salt Waste Processing Facility (SWPF). The organic solvent used in the testing was fabricated by the Chemical Science & Technology section. BOBCalixC6 was not added to this solvent due to the high cost and limited availability. All runs targeted 150% acid stoichiometry and 1% Hg in the sludge slurry dried solids