Calciner operations and the fuel dissolution process at the Idaho National Engineering and Environmental Laboratory have generated many mixed waste high-efficiency particulate air (HEPA) filters. The HEPA Filter Leach System located at the Idaho Nuclear Technology and Engineering Center lowers radiation contamination levels and reduces cadmium, chromium, and mercury concentrations on spent HEPA filter media to below disposal limits set by the Resource Conservation and Recovery Act (RCRA). The treated HEPA filters are disposed as low-level radioactive waste. The technical basis for the existing system was established and optimized in initial studies using simulants in 1992. The treatment concept was validated for EPA approval in 1994 by leaching six New Waste Calcining Facility spent HEPA filters. Post-leach filter media sampling results for all six filters showed that both hazardous and radiological constituent levels were reduced so the filters could be disposed of as low-level radioactive waste. Since the validation tests the HEPA Filter Leach System has processed 78 filters in 1997 and 1998. The Idaho National Engineering and Environmental Laboratory HEPA Filter Leach System is the only mixed waste HEPA treatment system in the DOE complex. This process is of interest to many of the other DOE facilities and commercial companies that have generated mixed waste HEPA filters but currently do not have a treatment option available

Archibald, Kip Ernest

Argyle, Mark Don

Brewer, Ken Neal

Demmer, Ricky Lynn

Kline, Kelli Suzanne

Pierson, Kenneth Alan

Shackelford, Kimberlee Rene

UNT Digital Library

INEEL/CON-98-00795PREPRINTINEEL HEPA Filter Leach System:  A MixedWaste SolutionM. ArgyleR. DemmerK. ArchibaldK. BrewerK. PiersonK. ShakelfordK. KlineFebruary 28, 1999 – March 4, 1999Waste Management ‘99571.03 - 03/23/98 - Rev. 01This is a preprint of a paper intended for publication in ajournal or proceedings. Since changes may be madebefore publication, this preprint should not be cited orreproduced without permission of the author.This document was prepared as a account of worksponsored by an agency of the United States Government.Neither the United States Government nor any agencythereof, or any of their employees, makes any warranty,expressed or implied, or assumes any legal liability orresponsibility for any third party's use, or the results ofsuch use, of any information, apparatus, product orprocess disclosed in this report, or represents that itsuse by such third party would not infringe privatelyowned rights. The views expressed in this paper arenot necessarily those of the U.S. Government or thesponsoring agency.INEEL HEPA Filter Leach System: A Mixed Waste SolutionBy Mark Argyle, Rick Demmer, Kip Archibald, Ken Pierson,Kimberlee Shackelford, and Ken KlineLockheed Martin Idaho Technology CompanyIdaho National Engineering and Environmental LaboratoryP.O. Box 1625, Idaho Falls, Idaho 83415-5218ABSTRACTCalciner operations and the fuel dissolution process at the Idaho National Engineering andEnvironmental Laboratory have generated many mixed waste high-efficiency particulate air (HEPA)filters.  The HEPA Filter Leach System located at the Idaho Nuclear Technology and Engineering Centerlowers radiation contamination levels and reduces cadmium, chromium, and mercury concentrations onspent HEPA filter media to below disposal limits set by the Resource Conservation and Recovery Act(RCRA).   The treated HEPA filters are disposed as low-level radioactive waste.The technical basis for the existing system was established and optimized in initial studies usingsimulants in 1992.  The treatment concept was validated for EPA approval in 1994 by leaching  six NewWaste Calcining Facility spent HEPA filters.  Post-leach filter media sampling results for all six filtersshowed that both hazardous and radiological constituent levels were reduced so the filters could bedisposed of as low-level radioactive waste.  Since the validation tests the HEPA Filter Leach System hasprocessed 78 filters in 1997 and 1998.The Idaho National Engineering and Environmental Laboratory HEPA Filter Leach System is the onlymixed waste HEPA treatment system in the DOE complex.  This process is of interest to many of theother DOE facilities and commercial companies that have generated mixed waste HEPA filters butcurrently do not have a treatment option available.INTRODUCTIONThe Idaho Nuclear Technology and Engineering Center (INTEC) located at the Idaho NationalEngineering and Environmental Laboratory (INEEL) was originally designed to process spent nuclearfuel.  In the process, spent nuclear fuel was dissolved and the reusable uranium extracted.  The waste iscalcined at New Waste Calciner Facility (NWCF) to form a dry powder, and put into concrete storagebins for indefinite storage.  NWCF operations involve the handling of fission products, transuranic(TRU) materials, and hazardous materials. High-efficiency particulate air (HEPA) filters are used in theoffgas streams to prevent these materials from entering and contaminating the environment.  As a resultmany HEPA filters contaminated with radioactive (5-120 R/hr (β/γ)), transuranic (TRU content >600nCi/g have been observed), and toxic metal constituents (6-12 mg Cd/g media, 2-4 mg Cr/g media, and 3-6 mg Hg/g media) have been generated (1,2,3).  Currently there is no disposal facility that will accept thecontaminated HEPA filters as generated.  Hence, a HEPA Filter Leach system was designed to lowerradiation contamination levels and reduce cadmium, chromium, and mercury concentrations on spentHEPA filter media to allow the treated HEPA filters to be disposed as low-level radioactive waste.LEACHING THEORYLeaching is a separation technique that is often used to remove a soluble solid or solute from a solidmixture with the help of a liquid solvent.  The HEPA Filter Leach System is primarily concerned with theremoval of calcine particles, consisting mostly of metal oxides, that have been trapped by the filter, orsalts that have been deposited on the HEPA filter media from entrained liquid in the gas vapor.  Thetrapped particles and salts are removed from the HEPA filter media by contact with a liquid solvent.This process often requires multiple batch leaching cycles or a countercurrent process to adequatelyremove the contamination from the HEPA filters.  Once the contaminants have been removed from thefilters excess solvent is removed from the filter media using a couple of filter rinse cycles.  The spentsolvent and rinse effluent can then be recycled or treated for disposal.INITIAL PROCESS DESIGNThe HEPA Filter Leach System, located at INTEC in the New Waste Calciner Facility was originallydesigned to remove the TRU constituents so the filters could be disposed as low-level radioactive waste.The filter leach process was demonstrated in 1983 by leaching two NWCF HEPA prefilters which hadbeen on-line for 81 days.  Analysis of these filters showed that the filters were more than 6 times theTRU limit (100 nCi/g).  The leaching operation reduced the TRU activity on the filters by 97.9 percentwith a single leach (1).After the HEPA Filter Leach System was designed and constructed in 1988, the Department of Energydecided to impose the Resource Conservation Recovery Act (RCRA) regulations that required theremoval of hazardous material from any waste prior to disposal.  This changed the operatingrequirements for the HEPA Filter Leach System to decontaminate the filters for disposal as non-hazardous low-level radioactive waste (3).TECHNICAL BASIS STUDIESIn 1992, technical basis studies were initiated to develop a design for the new operating requirements.The purpose of these studies were to 1) improve the ability to remove cadmium, chromium, and mercurycontaminants from spent HEPA filters, 2) improve filter media retention, 3) consider waste minimization,and 4) improve filter processing rates.  Twelve HEPA filters contaminated with cold calcine were used toevaluate and optimize 1) leach solution temperature, 2) nitric acid concentration, 3) multiple leachcycles, 4) acid recirculation, 5) filter orientation, and 6) air sparging. Understanding the effect of thesevariables allowed the system to be modified for optimum removal of cadmium, chromium, and mercury.As a result of the tests the HEPA Filter Leach System was modified to 1) reduce nitric acidconcentrations from 4-8 molar to 1-3 molar, 2) utilize more leach cycles with shorter leach cycle times,3) decrease the rinse cycle times, 4) orient the filters loaded-side down, 5) process HEPA filters one at atime, 6) utilize a new smaller process vessel to minimize leach solution volume, 7) utilize a new basketdesign for loose fiber retention, and 8) incorporate a new drying vessel that is separate from the processvessel (2).VALIDATION TRIALSThe modified HEPA filter leaching concept was validated in 1994 by leaching six spent radioactiveNWCF HEPA filters in the modified Filter Leach System.  Representative filter media samples werecollected and analyzed to show that the filters were no longer characteristically hazardous.  The testresults are shown in Table I (3).  These analyses tested TCLP metals and selected volatile organic levelsfor waste codes that correspond to substances that are not “soluble to at least 5 Wt% in the water or anemulsion as applicable”  (57 FR 37230, August 18, 1992).  The results of these tests indicated that thevolatile organic contamination was undetectable (<10-50 ppb).  In addition to the reduction in hazardousconstituents, the radioactivity dropped from 5-120 R/hr (β/γ) by a factor of 1000 to <100 mR/hr (β/γ)with a transuranic content of 0.4-3.6 nCi/g.  Hence, the HEPA filter was no longer considered hazardousand could be disposed of as low-level radioactive waste.Table I. Six HFLS filter media samples analyzed for RCRA metals in 1994.a,bConstituentRegulatoryLimit(mg/1)Filter #194-022110(mg/1)Filter #294-022512(mg/1)Filter #394-030418(mg/1)Filter #494-031125(mg/1)Filter #594-03169(mg/1)Filter #694-032822(mg/l)Arsenic 5 <0.170 <0.681 <0.671 <0.170 <0.170 <0.170Barium 100 0.240 3.62 <0.865 <0.219 0.48 <0.219Cadmium 1 <0.216 <0.866 <0.853 <0.216 <0.216 <0.216Chromium 5 <0.208 <0.833 <0.820 <0.208 <0.208 <0.208Lead 5 <0.143 <0.575 <0.566 <0.143 <0.143 <0.143Mercury 0.2 <0.0402 <0.0402 0.018 0.016 0.092 0.012Selenium 1 <0.149 <0.599 <0.590 <0.149 <0.149 <0.149Silver 5 <0.194 <0.777 <0.765 <0.194 <0.194 <0.194a This table provides the analytical results for each RCRA TC Metal analyzed for in the filter mediasamples. Detection limits will vary based on the size of the sample dilution.b These analyzes were performed at INTEC laboratories.Testing results were submitted to the Idaho Department of Environmental Quality and forwarded to theUnited States Environmental Protection Agency (USEPA) for a Determination of Equivalent Treatment(DET).  In May of 1996 the USEPA determined that a DET is not necessary or applicable for the HEPAFilter Leach System (5).  It was determined that treatment of HEPA filters in the HEPA Filter LeachSystem should be regulated as a hazardous debris as presented in 40 CFR 268.45 Table 1 “AlternativeTreatment Standards for Hazardous Debris”. Disposal of the spent solvents to the tank farm forsubsequent calcination was determined to be constant with current operating practices. Since then theNWCF HEPA Filter Leach System has been used to process 78 filters in 1997 and 1998.HEPA FILTER LEACH SYSTEM DESCRIPTIONThe existing filter leaching system is shown in Figure 1 and consists of a leaching vessel, dryingvessel, two work tables, associated piping, and instrumentation.  The leach vessel, drying vessel, andwork tables are located in the filter handling cell. Piping lines pass through the cell wall to utility servicelines in the clean operating corridor. Remote handling capabilities are available within the cell via a pairof master-slave manipulators located on either side of the window, an overhead crane, and anelectro-mechanical PaR* with a robotic arm.Figure 1  HEPA Filter Leaching SystemThe filter handling table is located behind the leaching vessel and is directly under the filter handling cellhatch cover. The table is constructed of stainless steel with an open grating working surface. It serves asthe primary work surface for filter handling operations.Contaminated HEPA filters are transferred into the filter handling cell through the PaR parking area andshielding doors using the filter handling tool and decon cell crane. A contaminated filter is placed in abasket which completely encompasses the filter to retain loose media fibers.  This is to prevent vesseldrain plugging during the leaching process. The top and bottom of the basket are constructed of 14 meshstainless steel screens with 1.35 mm (0.053 inch) openings to retain the loose filter media. The openleach basket is placed on the filter handling table. The filter is placed inside the top half of the leachingbasket so that the stainless screen side is facing upward. The lid of the basket is then closed and lockedusing the cell crane, PaR, or manipulator. The leach basket and filter are then placed on the basketsupport inside leaching vessel.A mixing vessel is used to heat 1-2 M nitric acid to 43ºC (110ºF). The volume of the acid per leach cycleis approximately 227 L (60 gallons) which is enough to submerge the HEPA filter. The leachingoperation begins when the acid solution is transferred to the leach vessel and heated by steam to 88ºC(191ºF) keeping the vessel lid closed.  Air sparging at 10 scfm is initiated immediately. The filter isleached for 30 minutes. The leachate waste solution is then drained to a collection vessel. Second andthird leach cycles follow the first leach cycle.  After completion of the three leach cycles, two waterrinses are conducted at ambient temperature for 10 minutes each. The volume of water per rinse cycle isapproximately 227 L (60 gallons).After completion of the leaching and rinsing cycles, the filter is allowed to drain for 10 minutes or untilno more liquid drips out of the filter.  Then the filter is transferred to the drying vessel. The dryingoperation is performed by forcing air through an air heater to raise the air temperature to 149ºC (300ºF).The air is then forced into the bottom of the vessel at 60 SCFM, through the filter, and out to the vent atthe top of the drying vessel. Drying time is usually 4 to 6 hours.After the filter is dried, the leaching basket containing the leached filter is removed from the dryingvessel by the cell crane and placed on the filter handling table. The basket is rotated upside down so thatthe fiberglass screen is upward and the lid of the leach basket is then opened. The filters are sampled on arandom basis to verify that the leaching process is performing adequately.  The filters are then stored inthe cell until enough filters have been accumulated to fill a wooden waste box for disposal.ONGOING DEVELOPMENTAL ACTIVITIESThe Filter Leach System has been successful in reducing radionuclides and hazardous materials on theHEPA filters to allow them to be disposed of as low-level radioactive waste. However there are a fewproblems that are the focus of ongoing developmental activities.  These activities include 1) investigatemethods to prevent the HEPA filters from falling apart during the leaching process, 2) improve rinsingmethods to minimize the amount of contaminated solution retained in the filter media, 3) improve fluidagitation systems to increase solubility rate and minimize damage to the filter media, 4) tools that wouldfacilitate process manipulations or minimize cross contamination during process manipulations,5) investigate methods that would reduce the amount of time required to process a HEPA filter thusimproving process throughput, and 6) investigate solvents that will minimize or eliminate aqueous wastegoing to the Tank Farm.CONCLUSIONThe Idaho National Engineering and Environmental Laboratory HEPA Filter Leach System hassuccessfully treated 78 HEPA filters classified as a TRU mixed waste in accordance with the“Alternative Treatment Standards for Hazardous Debris”.  Radioactivity was reduced from 5-120 R/hr(β/γ) to 30-90 mR/hr (β/γ) while TRU levels were dropped from over 600 nCi/g to 0.4-3.6 nCi/g.Cadmium, chromium, and mercury concentrations on spent HEPA filter media were successfully reducedto below disposal limits set by the Resource Conservation and Recovery Act (RCRA).   The treatedHEPA filters were disposed as low-level radioactive waste.FOOTNOTES* Mention of specific products and/or manufacturers herein implies neither endorsement or preference,nor disapproval by the U.S. Government, any of its agencies, or Lockheed Martin Idaho TechnologiesCompany of the use of a specific product for any purpose.This work supported by the U.S. Department of Energy, Assistant Secretary for EnvironmentalManagement, under DOE Idaho Operations Office Contract DE-AC07-94ID13223.REFERENCES1. Donovan, R. I., O’Brien, B. H., Letter to G. W. Hogg, “NWCF HEPA Filter Leaching DemonstrationResults”, July 31, 1984.2. McCray, C. W., Brewer K. N., “HEPA Filter Leach System Technical Basis Report”, WINCO-1096,May 1992.3. Chakravartty, A. C., “HEPA Filter Leaching Concept Validation Trials at the Idaho ChemicalProcessing Plant”, INEL-95/0182, April 1995.4. Thornton, H. W., “Design and Installation of a Radioactive Filter Leaching System at the IdahoChemical Processing Plant”, Proceedings, 36th Conference on Remote Sytems Technology, 1988,Volume 2.5. Petruska, M., Chief Waste Treatment Branch United States Environmental Protection Agency, Letterto Monson, B., Chief, Bureau of Permits and Enforcement Idaho department of EnvironmentalQuality, “Determination of Equivalent Treatment Not Needed for HEPA Filter Leach System –HEPA Filters Can be Treated as Hazardous Debris”, May 17, 1996.

INEEL HEPA Filter Leach System: A Mixed Waste Solution

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INEEL HEPA Filter Leach System: A Mixed Waste Solution

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