Characterization and Actual Waste Tests With Tank 5f Samples

This report addresses the characterization and actual waste tests with tank 5F samples

Impact of Irradiation on Solvent used in SRS Waste Treatment Processes -9122

ABSTRACT Savannah River Site (SRS) will use a Caustic Side Solvent Extraction (CSSX) process to selectively remove radioactive Cs-137 from the caustic High Level Waste (HLW) salt solutions stored in the large carbon steel waste tanks in the SRS Tank Farm. This HLW resulted from several decades of operations at SRS to produce nuclear materials for the United States Government. The removed Cs-137 will be sent to the Defense Waste Processing Facility (DWPF) where it will be immobilized along with the HLW sludges from the SRS Tank Farm into a borosilicate glass that will be put into permanent disposal. Currently the CSSX process is operating on an interim basis in the Modular Caustic Side Solvent Extraction Unit (MCU) facility. Eventually the process will occur in the full scale Salt Waste Processing Facility (SWPF) currently being built. The organic solvent developed for the process is primarily a mixture of the Isopar ® L (a blend of C 10 -C 12 branched alkanes such as dodecane) and an alkyl aryl polyether added as a Modifier (commonly called Cs-7SB) to enhance the solubility of the extractant which is a calixarene-crown ether. The solvent also includes trioctylamine to mitigate the adverse impact of lipophilic agents on the stripping of the cesium into nitric acid. Since the mixture is primarily organic hydrocarbons, it is expected that radiolysis of the mixture with gamma rays and beta particles from the Cs-137 will produce the flammable gas H 2 and also eventually degrade the solvent. For example, much research has been performed on the radiolysis of the organic solvent used in the tributylphosphate (TPB) extraction process (PUREX process) that has been used at SRS and in many other countries for several decades to separate U and Pu from radioactive U-235 fission products such as Cs-137. [1] The purpose of this study was to investigate the radiolysis of the organic solvent for the CSSX process. Researchers at Savannah River National Laboratory (SRNL) irradiated samples of solvent with Co-60 gamma rays. Prior to the irradiation, the solvent was contacted with the aqueous solutions that will be used in the MCU and SWPF facilities. These were the aqueous caustic salt feed, the scrub solution, and wash water. The rates of radiolytic H 2 production were measured both by determining the composition of the gases produced and by measuring pressures produced during radiolysis. The irradiated solvents were then analyzed by various analytical techniques to assess how much of the Isopar ® L, the Modifier, and the extractant had decomposed

CHARACTERIZATION AND ALUMINUM DISSOLUTION DEMONSTRATION WITH A 3 LITER TANK 51H SAMPLE

A 3-liter sludge slurry sample was sent to SRNL for demonstration of a low temperature aluminum dissolution process. The sludge was characterized before and after the aluminum dissolution. Post aluminum dissolution sludge settling and the stability of the decanted supernate were also observed. The characterization of the as-received 3-liter sample of Tank 51H sludge slurry shows a typical high aluminum HM sludge. The XRD analysis of the dried solids indicates Boehmite is the predominant crystalline form of aluminum in the sludge solids. However, amorphous phases of aluminum present in the sludge would not be identified using this analytical technique. The low temperature (55 C) aluminum dissolution process was effective at dissolving aluminum from the sludge. Over the three week test, {approx}42% of the aluminum was dissolved out of the sludge solids. The process appears to be selective for aluminum with no other metals dissolving to any appreciable extent. At the termination of the three week test, the aluminum concentration in the supernate had not leveled off indicating more aluminum could be dissolved from the sludge with longer contact times or higher temperatures. The slow aluminum dissolution rate in the test may indicate the dissolution of the Boehmite form of aluminum however; insufficient kinetic data exists to confirm this hypothesis. The aluminum dissolution process appears to have minimal impact on the settling rate of the post aluminum dissolution sludge. However, limited settling data were generated during the test to quantify the effects. The sludge settling was complete after approximately twelve days. The supernate decanted from the settled sludge after aluminum dissolution appears stable and did not precipitate aluminum over the course of several months. A mixture of the decanted supernate with Tank 11 simulated supernate was also stable with respect to precipitation

IN-SITU MONITORING OF CORROSION DURING A LABORATORY SIMULATION OF OXALIC ACID CHEMICAL CLEANING

The Savannah River Site (SRS) will disperse or dissolve precipitated metal oxides as part of radioactive waste tank closure operations. Previously SRS used oxalic acid to accomplish this task. To better understand the conditions of oxalic acid cleaning of the carbon steel waste tanks, laboratory simulations of the process were conducted to determine the corrosion rate of carbon steel and the generation of gases such as hydrogen and carbon dioxide. Open circuit potential measurements, linear polarization measurements, and coupon immersion tests were performed in-situ to determine the corrosion behavior of carbon steel during the demonstration. Vapor samples were analyzed continuously to determine the constituents of the phase. The combined results from these measurements indicated that in aerated environments, such as the tank, that the corrosion rates are manageable for short contact times and will facilitate prediction and control of the hydrogen generation rate during operations

REMOVING SLUDGE HEELS FROM SAVANNAH RIVER SITE WASTE TANKS BY OXALIC ACID DISSOLUTION

The Savannah River Site (SRS) will remove sludge as part of waste tank closure operations. Typically the bulk sludge is removed by mixing it with supernate to produce a slurry, and transporting the slurry to a downstream tank for processing. Experience shows that a residual heel may remain in the tank that cannot be removed by this conventional technique. In the past, SRS used oxalic acid solutions to disperse or dissolve the sludge heel to complete the waste removal. To better understand the actual conditions of oxalic acid cleaning of waste from carbon steel tanks, the authors developed and conducted an experimental program to determine its effectiveness in dissolving sludge, the hydrogen generation rate, the generation rate of other gases, the carbon steel corrosion rate, the impact of mixing on chemical cleaning, the impact of temperature, and the types of precipitates formed during the neutralization process. The test samples included actual SRS sludge and simulated SRS sludge. The authors performed the simulated waste tests at 25, 50, and 75 C by adding 8 wt % oxalic acid to the sludge over seven days. They conducted the actual waste tests at 50 and 75 C by adding 8 wt % oxalic acid to the sludge as a single batch. Following the testing, SRS conducted chemical cleaning with oxalic acid in two waste tanks. In Tank 5F, the oxalic acid (8 wt %) addition occurred over seven days, followed by inhibited water to ensure the tank contained enough liquid to operate the mixer pumps. The tank temperature during oxalic acid addition and dissolution was approximately 45 C. The authors analyzed samples from the chemical cleaning process and compared it with test data. The conclusions from the work are: (1) Oxalic acid addition proved effective in dissolving sludge heels in the simulant demonstration, the actual waste demonstration, and in SRS Tank 5F. (2) The oxalic acid dissolved {approx} 100% of the uranium, {approx} 100% of the iron, and {approx} 40% of the manganese during a single contact in the simulant demonstration. (The iron dissolution may be high due to corrosion of carbon steel coupons.) (3) The oxalic acid dissolved {approx} 80% of the uranium, {approx} 70% of the iron, {approx} 50% of the manganese, and {approx} 90% of the aluminum in the actual waste demonstration for a single contact. (4) The oxalic acid dissolved {approx} 100% of the uranium, {approx} 15% of the iron, {approx} 40% of the manganese, and {approx} 80% of the aluminum in Tank 5F during the first contact cycle. Except for the iron, these results agree well with the demonstrations. The data suggest that a much larger fraction of the iron in the sludge dissolved, but it re-precipitated with the oxalate added to Tank 5F. (5) The demonstrations produced large volumes (i.e., 2-14 gallons of gas/gallon of oxalic acid) of gas (primarily carbon dioxide) by the reaction of oxalic acid with sludge and carbon steel. (6) The reaction of oxalic acid with carbon steel produced hydrogen in the simulant and actual waste demonstrations. The volume produced varied from 0.00002-0.00100 ft{sup 3} hydrogen/ft{sup 2} carbon steel. The hydrogen production proved higher in unmixed tanks than in mixed tanks

DEMONSTRATION OF THE DWPF FLOWSHEET IN THE SRNL SHIELDED CELLS USING ARP PRODUCT SIMULANT AND SB4 TANK 40 SLUDGE SLURRY

The radioactive startup of two new SRS processing facilities, the Actinide Removal Process (ARP) and the Modular Caustic-Side-Solvent-Extraction Unit (MCU) will add two new waste streams to the Defense Waste Processing Facility (DWPF). The ARP will remove actinides from the 5.6 M salt solution resulting in a sludge-like product that is roughly half monosodium titanate (MST) insoluble solids and half sludge insoluble solids. The ARP product will be added to the Sludge Receipt and Adjustment Tank (SRAT) at boiling and dewatered prior to pulling a SRAT receipt sample. The cesium rich MCU stream will be added to the SRAT at boiling after both formic and nitric acid have been added and the SRAT contents concentrated to the appropriate endpoint. A concern was raised by an external hydrogen review panel that the actinide loaded MST could act as a catalyst for hydrogen generation (Mar 15, 2007 report, Recommendation 9). Hydrogen generation, and it's potential to form a flammable mixture in the off-gas, under SRAT and Slurry Mix Evaporator (SME) processing conditions has been a concern since the discovery that noble metals catalyze the decomposition of formic acid. Radiolysis of water also generates hydrogen, but the radiolysis rate is orders of magnitude lower than the noble metal catalyzed generation. As a result of the concern raised by the external hydrogen review panel, hydrogen generation was a prime consideration in this experiment. Testing was designed to determine whether the presence of the irradiated ARP simulant containing MST caused uncontrolled or unexpected hydrogen production during experiments simulating the DWPF Chemical Process Cell (CPC) due to activation of titanium. A Shielded Cells experiment, SC-5, was completed using SB4 sludge from Tank 405 combined with an ARP product produced from simulants by SRNL researchers. The blend of sludge and MST was designed to be prototypic of planned DWPF SRAT and SME cycles. As glass quality was not an objective in this experiment, no vitrification of the SME product was completed. The results from this experiment were compared to the results from experiment SC-1, a similar experiment with SB4 sludge without added ARP product. This report documents: (1) The preparation and subsequent composition of the ARP product. (2) The preparation and subsequent compositional characterization of the SRAT Receipt sample. Additional details will be presented concerning the noble metal concentration of the ARP product and the SRAT receipt sample. Also, calculations related to the amount of formic and nitric acid added during SRAT processing will be presented as excess formic acid will lead to additional hydrogen generation. (3) Highlights from processing during the SRAT cycle and SME cycle (CPC processing). Hydrogen generation will be discussed since this was the prime objective for this experiment. (4) A comparison of CPC processing between SC-1 (without ARP simulant) and SC-5. This work was controlled by a Task Technical and Quality Assurance Plan (TTQAP)6, and analyses were guided by an Analytical Sample Support Matrix (ASSM)7. This Research and Development (R&D) was completed to support operation of DWPF

Characterization of the March 2004 Tank 40 (Sludge Batch 3) Dip Samples

The Defense Waste Processing Facility (DWPF) has begun processing Sludge Batch 3 (SB3). Sludge Batch 3 consists of the heel in Tank 40 (Sludge Batch 2), the contents of Tank 51, and a Np stream from H Canyon. Two dip samples were pulled from Tank 40 in March 2004 after the initial Tank 51 to 40 transfer and the first transfer of Np material from H Canyon. These samples were combined into one sample and characterized by the Savannah River Technology Center (SRTC). The purpose of this characterization is to provide DWPF with a current Tank 40 (SB3) composition for comparison to Sludge Receipt and Adjustment Tank (SRAT) receipt analyses as they transition to the new sludge batch. The conclusions from this analysis are: coal content of the Tank 40 sample was similar to that predicted using analysis of the Tank 51 qualification sample; most, if not all, the sulfur was soluble and in the form of sulfate. Ion Chromatography (IC) analysis of the water dilution of the slurry is adequate for sulfate determination in the SB3 sample. Most, if not all, the oxalate was soluble. IC analysis of the water dilution of the slurry is adequate and the acid strike method is not necessary for oxalate determination in SB3. The yield stress and the consistency for the March 2004 SB3 sample is within the DWPF Operating Region

Durability Testing of Fluidized Bed Steam Reforming Products

Fluidized Bed Steam Reforming (FBSR) is being considered as a potential technology for the immobilization of a wide variety of radioactive wastes but especially aqueous high sodium wastes at the Hanford site, at the Idaho National Laboratory (INL), and at the Savannah River Site (SRS). The FBSR technology converts organic compounds to CO{sub 2} and H{sub 2}O, converts nitrate/nitrite species to N{sub 2}, and produces a solid residue through reactions with superheated steam, the fluidizing media. If clay is added during processing a ''mineralized'' granular waste form can be produced. The mineral components of the waste form are primarily Na-Al-Si (NAS) feldspathoid minerals with cage-like and ring structures and iron bearing spinel minerals. The cage and ring structured minerals atomically bond radionuclides like Tc{sup 99} and Cs{sup 137} and anions such as SO{sub 4}, I, F, and Cl. The spinel minerals appear to stabilize Resource Conservation and Recovery Act (RCRA) hazardous species such as Cr and Ni. Durability testing of the FBSR products was performed using ASTM C1285 (Product Consistency Test) and the Environmental Protection Agency (EPA) Toxic Characteristic Leaching Procedure (TCLP). The FBSR mineral products (bed and fines) evaluated in this study were found to be two orders of magnitude more durable than the Hanford Low Activity Waste (LAW) glass requirement of 2 g/m{sup 2} release of Na{sup +}. The PCT responses for the FBSR samples tested were consistent with results from previous FBSR Hanford LAW product testing. Differences in the response can be explained by the minerals formed and their effects on PCT leachate chemistry

Fluidized Bed Steam Reformed Mineral Waste Forms: Characterization and Durability Testing

Fluidized Bed Steam Reforming (FBSR) is being considered as a potential technology for the immobilization of a wide variety of high sodium low activity wastes (LAW) such as those existing at the Hanford site, at the Idaho National Laboratory (INL), and the Savannah River Site (SRS). The addition of clay, charcoal, and a catalyst as co-reactants with the waste denitrates the aqueous wastes and forms a granular mineral waste form that can subsequently be made into a monolith for disposal if necessary. The waste form produced is a multiphase mineral assemblage of Na-Al-Si (NAS) feldspathoid minerals with cage and ring structures and iron bearing spinel minerals. The mineralization occurs at moderate temperatures between 650-750 C in the presence of superheated steam. The cage and ring structured feldspathoid minerals atomically bond radionuclides like Tc-99 and Cs-137 and anions such as SO4, I, F, and Cl. The spinel minerals stabilize Resource Conservation and Recovery Act (RCRA) hazardous species such as Cr and Ni. Granular mineral waste forms were made from (1) a basic Hanford Envelope A low-activity waste (LAW) simulant and (2) an acidic INL simulant commonly referred to as sodium bearing waste (SBW) in pilot scale facilities at the Science Applications International Corporation (SAIC) Science and Technology Applications Research (STAR) facility in Idaho Falls, ID. The FBSR waste forms were characterized and the durability tested via ASTM C1285 (Product Consistency Test), the Environmental Protection Agency (EPA) Toxic Characteristic Leaching Procedure (TCLP), and the Single Pass Flow Through (SPFT) test. The results of the SPFT testing and the activation energies for dissolution are discussed in this study