Through the Tanks Focus Area, the Savannah River Technology Center (SRTC) and the Oak Ridge National Laboratory participated in a joint project in which supernate waste from the Melton Valley Storage Tanks at Oak Ridge was treated by passage through a crystalline silicotitanate (CST) ion exchange column. CST was designed to sorb Cs- 137, Sr-90 and several other radionuclides from highly alkaline solutions containing large quantities of sodium.2 After demonstrating the effectiveness of CST as an ion exchange medium, ORNL shipped some of the loaded sorbent to SRTC where it was mixed with glass formers and processed in a joule-heated melter within the SRTC Shielded Cells. This report details the results of the melter run, along with the preparations that were required to complete the campaign

Andrews, M. K.

Fellinger, T. L.

Ferrara, D. M.

Harbour, J. R.

Herman, D. T.

M Andrews

T Fellinger

D Ferrara

J Harbour

D Herman

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Vitrification of cesium-loaded crystalline silicotitanate (CST) in the shielded cells melter

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WSRC-TR-97-O0314Vitrification of Cesium-Loaded Crystalline Silicotitanate (CST) inthe Shielded Cells MelterbyM. K. AndrewsWestinghouse Savannah River CompanySavannah River SiteAiken, South Carolina 29808T. L. FellinaerD. M. FerraraJ. R. HarbourD. T. HermanDOE Contract No. DE-AC09-96SR18500This paper was prepared in connection with work done under the above contract number with the U. S.Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S.Government’s right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper,along with the right to reproduce and to authorize others to reproduce all or parl of the copyrighted paper.DISCLAIMERW report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability orresponsibility for the accuracy, completeness, or usefuhess of any information, apparatus,product, or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specific commercial product, process, or service by trade name,trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement,recommendation, or favoring by the United States Government or any agency thereof. Theviews and opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.~s report has been reproduced directly from the best available copy.Available to DOE and DOE contractors from the Office of Scientific and Technical Information,P. O. Box 62, Oak Ridge, TN 37831; prices available from (423)576-8401.Available to the public from the National Technical Information Service, U. S. Department ofCommerce, 5285 Port Royal Road, Springfield, VA 22161.Westinghouse Savannah River CompanySavannah River Technology CenterWSRC-TR-97-O0314September 30, 1997VITRIFICATION OF CESIUM-LOADED CRYSTALLINESILICOTITANATE (CST) IN THE SHIELDED CELLS MELTER (U)M. K. Andrews, T. L. Fellinger, D. M. Ferrara, J. R. Harbour and D. T. HermanWestinghouse Savannah River CompanyIntroduction and SummaryThrough the Tanks Focus Area, the Savannah River Technology Center (SRTC) and theOak Ridge National Laboratory (ORNL) participated in a joint project in which supernatewaste from the Melton Valley Storage Tanks at Oak Ridge was treated by passagethrough a crystalline silicotitanate (CST) ion exchange column. 1 CST was designed tosorb Cs- 137, Sr-90 and several other radionuclides from highly alkaline solutionscontaining large quantities of sodium.2 After demonstrating the effectiveness of CST asan ion exchange medium, ORNL shipped some of the loaded sorbent to SRTC where itwas mixed with glass formers and processed in a joule-heated melter within the SRTCShielded Cells.The remotely operated process included the preparation of the melter feed, vitrification inan 1150”C melter and analysis of the glass product both for its composition and itsdurability. The campaign processed approximately 20 kg of Cs-loaded CST in 80 hoursof operation of the Shielded Cells melter. The glass produced contained between 50 and55 wt% loaded CST. This report details the results of the melter run, along with thepreparations that were required to complete the campaign.CST CharacterizationA small sample of loaded CST from ORNL was removed from the top of the drum anddissolved for analysis using a peroxide/hydrofluoric acid/nitric acid dissolution. Theresulting samples were analyzed using Inductively Coupled Plasma-EmissionSpectroscopy (ICP-ES), Atomic Absorption (AA), and Gamma Spectroscopy. Themanufacturer of the CST has requested that the elemental composition not be released,and therefore, only the radionuclide composition is reported in Table 1. It should benoted that ORNL also performed some analyses on the CST and determined that it wasneither characteristically hazardous nor TRU (less than 100 nCi/g alpha). Theradionuclide composition that ORNL determined to have loaded on the CST is alsoincluded in Table 1.E. W. Holtzscheiter WSRC-TR-97-O0314Table 1- Major Radionuclide Composition of Loaded CST(SRTC Analyzed and ORNL Calculated)I Element I SRTC (Ci) I ORNL (Ci)I CS-137 19 24 ICS-134 0.2 0.3Sr-90 0.1 0.2The elemental composition of the loaded CST was compared to the unloaded CSTcomposition. The main difference was in the concentrations of sodium and potassium.The loaded CST was pretreated at ORNL with a sodium hydroxide solution to conditionthe CST and to remove fine particulate and therefore, contained more sodium andpotassium. The loaded CST also contained cesium and strontium. The development ofthe final glass formulation for the melter run addressed these compositional differences.Glass Formulation DevelopmentPrior to the vitrification in the SRTC Shielded Cells, a glass formulation had to bedeveloped to incorporate sufficient CST sorbent without significant crystallization. Areport detailing the development of a glass formulation using unloaded CST has beenwritten.s Since the composition of the loaded CST was slightly different from theunloaded composition, the original formulation, along with four additional formulationswere tested using pretreated (but unloaded) CST, at waste loadings of 50 wt~o.The electrical conductivities for the five formulations were calculated to ensure that theywould be compatible with the joule-heated melter. Typically, electrical conductivitiesbetween 0.36 and 1.1 Siemans/cm at 1150°C are considered reasonable. Twocompositions were at the higher end, but were within the acceptable range, one was abovethe high end and two were only slightly above the 1.1 Siemans/cm. The calculationswere only estimates since the exact contributions of all of the elements present in theglass were not known. Therefore, it was decided to continue testing of all fiveformulations.Two samples of each of the five formulations were melted at 1150°C. The first samplewas poured, and the second was subjected to a slower cooling rate, similar to thatexpected in the Shielded Cells melter. Two of the five samples, including the originalformulation, were too fluid when poured. Two of the remaining samples formed crystalswhen slowly cooled. The fifth composition was within the required viscosity range anddid not form crystals upon slow cooling. However, this composition had a calculatedelectrical conductivity slightly above the acceptable range. Since changing thecomposition to improve the conductivity could adversely affect the viscosity or thecrystallization, it was decided to proceed with this formulation without reducing thewaste loading.E. W. Holtzscheiter 3 WSRC-TR-97-O0314During the development of the glass formulation, a waste loading of 50 wt% dried CSTwas used. To ensure that the formulation was robust enough to handle variations in wasteloadings, the selected composition was tested at lower and higher waste loadings. Basedon the results of these experiments, it was determined that the formulation could easilyincorporate CST loadings between 40 and 55 wt% dry CST. Since the CST receivedfrom ORNL contained 8 to 15 wt% water, the waste loading targeted was equivalent to afinal CST loading in the glass between 50 and 55 wt%, depending on the water content ofthe CST. The appropriate reagent-grade chemicals were then combined to produce theglass-forming chemicals for the melter campaign.Feed Delivery SystemOnce the glass-forming chemicals were combined with the CST, a feed system with the ability toremotely provide feed for the entire melter campaign was required. The feed system needed toaccommodate the possibility that several transfers of CST from the drum would be necessary. Itwas also necessary for the feed system to be able to mix the CST and chemicals to such a degreeas to obtain a reasonably homogeneous feed for the melter. The feed was to be delivered to themelter at approximately 25 cc/minute, and the system had to be able to withstand the highradiation fields in the Shielded Cells environment.Most efforts focused on the delivery of the CST resin as a slurry because SRTC has experiencepumping slurries to melters. Early tests with unloaded CST and water indicated that there wasessentially no suspension of the solids in the liquid. The extremely low flow at which the feedwas to be delivered to the melter did not allow for a velocity high enough to suspend the solids.Agitation in the feed drum was also not sufficient to suspend the solids. A recirculation loopusing a diaphragm pump was added. The first system had a smaller line for feeding the melteroff of the recirculation loop and used a needle valve for controlling the feed rate. Seriousplugging was encountered in the lines and especially in the needle valve.It was then decided that in order to increase the suspension of the CST solids, the materialneeded to be ground. The diaphragm pump and the agitator in the feed drum were allowed togrind the material through recirculation. A 90-degree elbow was added to the system to increasethe turbulence in the recirculation line. The erosion of this elbow would not be of concern due tothe relatively short duration of the demonstration. A private company would have the option ofadding an emulsifier to the recirculation line to allow more efficient and consistent grinding ofthe particles. The implementation of a recirculation loop in conjunction with agitation resulted inthe grinding of the CST particles to a small enough size to maintain sufficient suspension andallow the delivery of the material in a reasonably homogeneous slurry. The needle valve in themelter feed line was replaced with a ball valve. A Masterflex pump after the ball valve was usedto control the feed rate of the CST material to the melter. A schematic of the slurry feed systemis shown in Figure 1. Several connections were added to allow for water flushing of the lines toprevent pluggage.E. W. Holtzscheiter 4 WSRC-TR-97-O0314To theMeltern~ 3J8°~“~/LineMasterflexPump< Ball Valve*/DiaphragmPumptMetalTubing—SupportClamps —Recirculationloop4(DoubleBraided7*Nylon Tubing)Air DrivenMotor for,. the Agitator(attachedto;’:4, the baffleassemble)BaffleAssemblyAgitatorCST Resin SolutionFigure 1- Schematic of the Melter Feed Tank System in the Shielded CellsThe addition of the glass formers to the CST changed the rheology of the slurry from a thinwater-like fluid to a fluid with the consistency of house paint. The particles tended to staysuspended for a longer period of time. Full-scale mock-up testing of the feed indicated that theuse of a diaphragm pump and agitator caused sufficient grinding of the material to allow thematerial to remain suspended. The pumping/mixing setup successfully fed a CST and glassformers solution to the melter at a feed rate of approximately 27 cc/rein. Several full pump-downtests were successfully conducted with the CST as well as the CST plus glass former slurries.Since the slurry feeding system required the addition of water to the CST, additionalwaste would be created from the condensate generated during vitrification. Therefore, adry feed system was also tested. A sample of the radioactive CST was combined with theappropriate amount of glass-forming chemicals and was successfully vitrified in aplatinum crucible in the Shielded Cells, indicating that dry CST and chemicals could besufficiently mixed remotely. In addition, nonradioactive frit was added to the ShieldedCells melter as a dry mixture. No problems were encountered during the dry additions.E. W. Holtzscheiter 5 WSRC-TR-97-O0314Based on the results of this testing, the dry feed system was selected for use during theradioactive melter campaign. However, since both feed systems have been developed andtested, a private vendor would have the option of slurry feeding or dry feeding.Vitrification ProcessThe research melter is a joule-heated melter with two pairs of Inconel@ electrodesproviding the power to maintain a melt pool temperature of 1150°C. The cylindrical meltchamber is eight inches in diameter and six inches deep and holds approximately tenkilograms of glass. Two additional heaters are located in the melter above the melt poolto provide supplemental heat which increases the melt rates by vaporizing any water fromthe feed.Glass pouring is initiated by tilting the entire melter. The glass flows from the melt poolthrough a riser cut in the refractory, and out a heated pour spout into 0.5 liter stainlesssteel beakers. During the CST campaign, the melter ran continuously for 85 hoursproducing nearly 30 kg of glass, or the equivalent of three melter turnovers.Prior to the initiation of CST feeding, the melter contained approximately 10 kg ofnonradioactive glass. As feeding of the CST material progressed, the conductivity of themelt pool increased as expected since the CST glass was calculated to be moreconductive than the nonradioactive glass. After more than 20 kg of glass had beenproduced, the melt temperature was reduced from 1150”C to 1125°C to lower the currentdensity across the electrodes. With a different melter, this may not have been necessary,but since the Shielded Cells melter has been operating for seven years, it was decided tobe conservative. No other melter differences were encountered.Glass CharacterizationSince the melter contained nonradioactive glass prior to the start of the CST run, samplesof glass were taken from the last can poured during the campaign. The last can waschosen because it would have a composition most representative of the feed. Glass fromthe CST campaign was taken for the purpose of determining its composition and itsdurability by leaching it according to the Product Consistency Test (PCT) protocol.4The composition of the glass is being measured by dissolving samples of the glass induplicate and analyzing the resulting solutions by ICP-ES, AA and Gamma Spectroscopy.Appropriate standards are being analyzed along with the CST glass samples to check theaccuracy of the analyses.The PCT is currently being used to determine the durability of the glass. The PCT is acrushed glass leach test that measures the releases of boron, lithium, sodium, and siliconfrom the glass in 90°C ASTM Type 1 water over a period of seven days. The averageconcentrations are normalized to the chemical composition of the glass. The normalizedresults for CST glass will be provided in a revision to this report. The HLW acceptancecriteria, which states that the glass produced must be more durable than theEnvironmental Assessment (EA) glass, will be used as the basis for determiningacceptability of the CST glass.E. W. Holtzscheiter WSRC-TR-97-O0314AcknowledgmentsWe would like to acknowledge the contributions of Phyllis Workman, Kathy Marshall,Debbie Marsh, Sherry Vissage, B ao Ha, the Shielded Cells Operations, and the AnalyticalDevelopment Section. This project would not have been successful without theirassistance.References1. Joe Walker, LMER Pretreatment, OR1-6-WT-41, (1996).2. R. Braun et al, “Crystalline Silicotitanate - Novel Commercial Cesium IonExchangers”, Spectrum ’96, Proceedings - International Topical Meeting on Nuclearand Hazardous Waste Management, (1996).3. M. K. Andrews, “Glass Formulation Development and Testing for the Vitrification ofCesium-Loaded Crystalline Silicotitanate (CST)”, 97-MP23.05, Proceedings of theAir & Waste Management Association’s 90’h Annual Meeting and Exhibition, (1997).4. ASTM Procedure, C-1286-94, “Determining Chemical Durability of Nuclear WasteGlasses: The Product Consistency Test (PCT)”.5. U. S. Department of Energy, “Environmental Assessment Waste Form Selection forSRP High-Level Waste”, USDOE Report DOE-EA-0179, (1982).E. W. HoltzscheiterDistribution:M. K. Andrews, 773-AN. E. Bibler, 773-AD. A. Crowley, 773-43AJ. R. Harbour, 773-43AD. T. Herman, 773-41AE. W. Holtzscheiter, 773-AT. L. Fellinger, 773-AD. M. Ferrara, 773-43AL. F. Landon, 704-lTK. M. Marshall, 773-43AL. M. Papouchado, 773-AC. T. Randall, 704-TSTI, 703-43AWSRC-TR-97-O0314

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Vitrification of cesium-loaded crystalline silicotitanate (CST) in the shielded cells melter

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