The Defense Waste Processing Facility (DWPF) at the Savannah River Site vitrifies High Level Waste (HLW) for repository internment. The process consists of three major steps: waste pretreatment, vitrification, and canister decontamination/sealing. The HLW consists of insoluble metal hydroxides (primarily iron, aluminum, magnesium, manganese, and uranium) and soluble sodium salts (carbonate, hydroxide, nitrite, nitrate, and sulfate). The HLW is processed in large batches through DWPF; DWPF has recently completed processing Sludge Batch 3 (SB3) and is currently processing Sludge Batch 4 (SB4). The composition of metal species in SB4 is shown in Table 1 as a function of the ratio of a metal to iron. Simulants remove radioactive species and renormalize the remaining species. Supernate composition is shown in Table 2

Dan Lambert, D

David Koopman, D

Paul Burket, P

Russell Eibling, R

Stone, M

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 This document was prepared in conjunction with work accomplished under Contract No. DE-AC09-96SR18500 with the U.S. Department of Energy.    This work was prepared under an agreement with and funded by the U.S. Government. Neither the U. S. Government or its employees, nor any of its contractors, subcontractors or their employees, makes any express or implied:  1. warranty or assumes any legal liability for the accuracy, completeness, or for the use or results of such use of any information, product, or process disclosed; or  2. representation that such use or results of such use would not infringe privately owned rights; or  3. endorsement or recommendation of any specifically identified commercial product, process, or service. Any views and opinions of authors expressed in this work do not necessarily state or reflect those of the United States Government, or its contractors, or subcontractors. WSRC-STI-2007-00251  Simulant Development for Savannah River Site High Level Waste   R. E. Eibling D.C. Koopman D.P. Lambert P.R. Burket M.E. Stone Savannah River National Laboratory, Aiken, SC 29808  The Defense Waste Processing Facility (DWPF) at the Savannah River Site vitrifies High Level Waste (HLW) for repository internment.  The process consists of three major steps: waste pretreatment, vitrification, and canister decontamination/sealing.  The HLW consists of insoluble metal hydroxides (primarily iron, aluminum, magnesium, manganese, and uranium) and soluble sodium salts (carbonate, hydroxide, nitrite, nitrate, and sulfate).  The HLW is processed in large batches through DWPF; DWPF has recently completed processing Sludge Batch 3 (SB3) and is currently processing Sludge Batch 4 (SB4).  The composition of metal species in SB4 is shown in Table 1 as a function of the ratio of a metal to iron.  Simulants remove radioactive species and renormalize the remaining species.  Supernate composition is shown in Table 2.  Table 1.  Metal species in SB4 as Ratios to Fe  40-inch Heel Case 15C, Blend 1 15C, Batch 1 Al 1.057 0.707 1.874 Ba 0.0088 0.0059 0.0067 Ca 0.0920 0.0919 0.0946 Ce 0.0108 0.0070 0.000 Cr 0.0115 0.0081 0.0109 Cu 0.0041 0.0027 0.00033 Fe 1.000 1.000 1.000 K 0.0953 0.0156 0.0410 La 0.0047 0.0048 0.0075 Mg 0.0433 0.0811 0.0385 Mn 0.249 0.228 0.238 Na 1.170 0.881 1.394 Ni 0.183 0.0666 0.0870 Pb 0.0122 0.00430 0.00033 Si 0.0859 0.104 0.237 Th 0.0027 0.0032 0.0092 Ti 0.0007 0.0011 0.0008 U 0.402 0.349 0.244 Zn 0.0061 0.0043 0.0003 Zr 0.0135 0.0097 0.0117  Table 2.  Supernate Species and Solids Content of SB4  40-inch heel case 15C, Blend 1 15C, Batch 1 SpGr, kg/L 1.0585 1.0410 1.0403 Na+, M 1.3363 0.9180 0.9606 NO2-, M 0.5073 0.3970 0.4124 NO3-, M 0.2445 0.1910 0.2426 OH-, M 0.3369 0.1770 0.1389 Cl-, M 0.0013 0.0010 0.0007 SO42-, M 0.0208 0.0220 0.0235 F-, M 0.0019 0.0040 0.0004 CO32-, M 0.0763 0.0510 0.0490 AlO2-, M 0.0598 0.0190 0.0178 C2O42-, M 0.0033 0.0080 0.0015 PO43-, M 0.0012 0.0010 0.0005 K+, M 0.0034 0.0040 0.0017        wt% Insoluble Solids 14.90 12.20 10.29 wt% Total Solids 21.82 17.41 15.90  Simulants are utilized to perform tests of the DWPF process.  The sludge is non-Newtonian and is typically described as a Bingham Plastic.  The yield stress of actual waste is typically higher than the simulants prepared by the current preparation technique.  Improvement of the simulant was desired to allow more accurate representations of plant processes to allow optimization studies and to incorporate techniques developed during preparation of simulants for the Hanford vitrification process.  The original simulant preparation process is performed in four steps:  1) Manganese nitrate precipitation by addition of potassium permanganate 2) Ferric and nickel nitrate addition to the MnO2 slurry followed by precipitation by addition of sodium hydroxide 3) Solids washing to remove soluble sodium and potassium nitrate 4) Trim chemical addition to add remaining metals (Al, Ba, Ca, Cr, Mg, Na, etc.) and anions (nitrite, sulfate, oxalate).  Solids washing can be performed by gravity settling, decanting the supernate, and addition of dilution water; repeating as required to hit the targeted nitrate level.  Continuous washing using a cross-flow or rotary microfilter can also be utilized.  Small batches can be washed using a centrifuge to aid gravity settling.  The simulant testing proceeded in phases, based on available funding and need dates for process simulants.  During Phase 1, the original preparation method was compared to revised processes to determine if the process was sensitive to changes and could be tuned to match the actual waste properties.  Phase 2 consisted of testing the simulants through the DWPF Chemical Process Cell (CPC) process to ensure that the changes noted persisted through the process and additional refinement of the revised methods.  Phase III was performed after scaling issues were identified during Phase II testing.  Phase IV involved testing and implementation of a CSTR process for simulant production.  During Phase I, testing was conducted using a SB3 composition (similar to SB4, but with less Al and more Fe).  A revised process was developed that added all species as metal nitrates prior to the manganese strike1.  Trim chemical additions were limited to base-reactive species (silica and titanium oxide).  Different washing techniques were evaluated during the development of the revised process, as well as inclusion of post treatment processes such as heat treatment at boiling and high shear mixing2.  As shown in Figures 1 and 2, the revised recipe resulted in yield stresses above the actual waste samples (SB2/3 sample results).  The baseline case for this testing was the precipitation of all metals except aluminum during the hydroxide addition.  As shown in Figure 1, addition of aluminum to the precipitation process (Tests 7 and 8) lowered the yield stress while the application of shear during washing (Test 2 and Test 3) increased yield stress.  Heat treatment provided a small benefit.    Figure 1. Phase I Test Results for Al Precipitation  Figure 2.  Phase I Test Results:  Application of Shear  During Phase II testing, the physical property differences were shown to persist through the DWPF pretreatment process3.  In addition, irradiation and thermal treatment processes were performed on the simulants to evaluate the impact of these treatments on physical properties.  Irradiation did not impact the yield stress, particle size, or crystalline composition of the simulants.  The thermal treatment that was performed in an attempt to accelerate any aging processes did impact the yield stress and crystalline makeup of the simulant.  The impacts on yield stress were much smaller than the impacts of varying makeup and washing methods, but small benefits were noted as shown in Figure 3.   Figure 3.  Impact of Thermal Treatment at 90°C on Yield Stress of SB3 Sludge Simulant  During the Phase II testing, a large batch of Sludge Batch 4 simulant was needed.  Simulants produced by the original recipe were performing in a marginal manner; therefore, the revised recipe where all species were precipitated together was chosen to produce the needed simulant.  The large batch exhibited extremely viscous behavior, likely due to scaling issues with mixing during the precipitation process.  The precipitated slurry thickens considerably when the pH reaches ~4, and then thins as the pH exceeds 8.  Mixing during the time period with high yield stress was difficult to maintain in the large scale batch.  Phase III testing was performed to evaluate the scaling issues, but efforts were hampered by the requirements to produce batches of SB4 simulant for testing.  Modifications were made to the mixing protocols, addition rates of reagents, and the manganese strike prior to metal nitrate additions was reinstated.  These changes led to improvements in yield stress as the batch size increased, but all batches greater than 2 liters were significantly higher in yield stress than the 2 liter batches4,5,6,7, as shown in Figure 4.   Figure 4.  Yield Stress from Batches of SB4 Simulant  A small-scale continuous process was proposed and developed to allow large batches to be produced without the scale-up issues noted during the batch process.  The continuous process consisted of a small (2L) CSTR as shown in Figure 5.  The automated control system is not shown.   1101007 8 9 10 11 12 13 14 15 16wt. % Insoluble SolidsYield Stress, PaSB3-T1 SB3-T2 SB3-T4 SB4-40T2 SB4-40T4SB4 120-L SB4-40T5 SB4 2-LCaustic FeedTankNitrate FeedTankpH MeterTempCSTRPrecipitatorMasterflexPumpsMixerpH probeTemp probeMasterflexPumpHold TankMixerCWCWLevel Bubbler Figure 5.  Diagram of CSTR Precipitation Apparatus  The manganese strike is performed in a batch manner in the nitrate feed tank, similar to the original preparation process.  Metal nitrates are added to the manganese slurry and a small batch precipitation is then performed and used as the precharge to the CSTR vessel.  The remaining metal nitrate slurry is fed to the CSTR concurrently with 50% NaOH to perform the hydroxide precipitation.  An automated control system was implemented to maintain a constant level and pH in the CSTR.  The CSTR is water-jacketed to maintain a constant temperature.  The precipitated slurry is collected in an unmixed container without temperature control.  The CSTR process was utilized to produce large scale batches (20 to 100 liters) with yield stresses typical of those seen with the lab-scale batches (2 liters)8, as shown in Figure 6 (line SB4-15C-MS2).  The process has been successful utilized to prepare simulants of SB4 and SB5 composition and has been adopted as the baseline process.  0.11101008 9 10 11 12 13 14 15 16wt. % insoluble solidsYield Stress, PaSB4-40T4 SB4 120-L 40" SB4-15CT1SB4-15CT2 15CT3 precipitate SB4-15CT3 finalSB4-15CT4 SB4-15CT6 SB4-15C-MS2 Figure 6.  Yield Stress Results from CSTR Testing  Particle size measurements were made throughout the testing.  General trends were seen in the data that shearing produced more fines while heat treatment removed some of the fines.  The particle size distribution of the simulants was generally similar, with the exception of the CSTR runs.  As shown in Figure 7, the particle size distribution was narrower for the CSTR than the batch process.  Particle size measurements of actual waste indicate a peak at 3 microns, few fines below 0.8 microns, and a maximum particle size of 50 microns.  048121620240.1 1 10 100 1000Equiv. Diameter, micronsVolume %SB4-15CT1 SB4-15CT2 SB4-15CT3 SB4-15C-MS2 Figure 7.  Impact of CSTR Process on Simulant Particle Size  Future testing will prepare a matrix of sludge compositions to determine the impact of varying the sludge composition on the simulant preparation process as well as the DWPF pretreatment and vitrification processes.  Additional testing to refine the parameters for the CSTR operation and to scale-up the process to a 20L vessel is under consideration.    References                                                1 Eibling, R. E., 2004,”Impact of Simulant Production Methods on the Physical Properties of DWPF Sludge Batch 3 Simulant”, WSRC-TR-2004-00578, Washington Savannah River Company, Aiken, SC. 2 Eibling, R. E. and M. E. Stone, 2006,”Impact of Irradiation and Thermal Aging on DWPF Simulated Sludge Properties”, WSRC-TR-2005-00543, Washington Savannah River Company, Aiken, SC. 3 Lambert, D. P., M. E. Stone, and Eibling, R. E., 2005,”Impact of Sludge Production Methods on SRAT Product”, WSRC-TR-2005-00294, Washington Savannah River Company, Aiken, SC. 4 Koopman, D. C. and Eibling, R. E., 2005,”Preparation and Heat Treatment of DWPF Simulants with and without Co-Precipitated Noble Metals”, WSRC-TR-2005-00285, Washington Savannah River Company, Aiken, SC. 5 Koopman, D. C., Lambert, D. P. , Best, D. R., Barnes, M. J., 2006,”Rheology Improvements during Preparation of 40-inch Heel Case Simulants for Sludge Batch 4”, WSRC-STI-2006-00067, Washington Savannah River Company, Aiken, SC. 6 Koopman, D. C., Lambert, D. P., Best, D. R., Barnes, M. J., 2006,”Impact of Preparation Method and Scale Factors on Sludge Batch 4 Simulant Properties”, WSRC-STI-2006-00088, Washington Savannah River Company, Aiken, SC.                                                                                                                                             7 Koopman, D. C., Lambert, D. P., Barnes, M. J., 2006,”Preparation of Sludge Batch 4 Qualification Simulants for DWPF Process Simulations”, WSRC-STI-2006-00242, Washington Savannah River Company, Aiken, SC. 8 Lambert, D. P., 2007,”SB5A Sludge Simulant: Basis, Preparation, and Chemical Processing”, SRNL-PSE-2007-00130, Washington Savannah River Company, Aiken, SC. 

SIMULANT DEVELOPMENT FOR SAVANNAH RIVER SITE HIGH LEVEL WASTE

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SIMULANT DEVELOPMENT FOR SAVANNAH RIVER SITE HIGH LEVEL WASTE

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