A PROTOTYPE DESIGN FOR CONTAMINATED FILTER REMEDIATION AND STABILIZATION

Vincent R. Fusconi, Daniel G. Marshall, Clinton P. Richardson, Gregory Mathios and Angel Vega
Department of Mineral and Environmental Engineering
New Mexico Institute of Mining and Technology
Socorro, New Mexico 87801

ABSTRACT

Currently, the Department of Energy (DOE) stores 100's of metric tons of mixed transuranic (TRU) waste forms at its many facilities throughout the country. One such waste form, a spiral wound polypropylene filter contaminated with hydraulic oil, carbon tetrachloride, plutonium, and chromium, was the basis of Task II at the 6th annual Waste-management, Education and Research Consortium (WERC) environmental design contest held April 21-25 1996 in Las Cruces, New Mexico.

Storage space for radioactively contaminated materials is limited and costly, making environmentally sound reduction of volume the focus of this design. Several opportunities for reuse of materials were projected in initial design stages and represent the scope of the actual project. Polypropylene, separated and distilled CCl4, decontaminated oil, and recycled packaging are all recovered by this process. An in-depth research of legal parameters shaped all aspects of the process with focuses on waste characterization, worker training and safety, emergency planning, and also packaging, storage and transportation of waste. A business plan was outlined to project an actual cost estimate; public relations guidelines were also created to inform potentially affected communities. The following paper outlines the work performed by New Mexico Tech's (NMT) Task II team.

INTRODUCTION

This document describes a process developed by New Mexico Tech (NMT) for the remediation of a Department of Energy (DOE) mixed organic transuranic (TRU) waste containing plutonium (Pu), chromium (CrVI) and carbon tetrachloride (CCl4). Approximately 10,000 lb. of contaminated polypropylene (PP) filters have been stored at an industrial warehouse and will be prepared for permanent disposal at the Waste Isolation Pilot Plant (WIPP) in accordance with Waste Acceptance Criteria (WAC) and Department of Transportation (DOT) regulations. Lack of information has necessitated the following assumptions: 1) the waste is in a properly vented container; 2) the Pu present is Pu239 (the predominant isotope used in weapons manufacturing) and exists as greater than 0.3 µm particles; 3) the waste is homogeneous; 4) the process is set up on-site; 5) the Pu239 stays in the filter matrix with none becoming airborne. The process addresses five major sections: mass reduction; volume reduction; free liquid removal; liquid stream separation; waste packaging and transport.

PROCESS DESIGN

NMT's process is a mechanical reduction of mass and volume with decontamination of all waste streams. The Pu is enmeshed in the filter matrix, any that may escape this matrix, with the liquid, will be captured on a 0.1µm filter. The CCl4 and Cr contaminated oil is removed, separated, and "cleaned" with a sequence of filtration, distillation, and ion exchange. Clean oil, and CCl4 are recycled. The process removes several portions of the filter as solid PP; these components are decontaminated (by solvent scrubbing) and recycled. The remaining filter mass is cryogenically reduced to below its glass transition temperature (Tg), allowing for fracture compression.(1) Bulk packaging of contaminated elements further reduces overall volume.

Process Justification

Volume Reduction: Overall volumetric reduction is a focus of this design. The filter material consists of fibrous PP having an experimentally determined porosity of 0.885, presenting a significant volume reduction potential; shredding, melting, and compaction were considered as options. Shredding would increase total volume and produce a spongy waste capable of storing energy. Heating above melting temperature (Tm) with subsequent compression would reduce volume, but produce gases and potential fire hazards. Super cooling with liquid nitrogen was chosen as it reduces the polymer below Tg allowing maximum volumetric reduction through compaction, producing a stable, robust waste form.(1) Original waste containers (poly-bottles and drums) are decontaminated and sent to recycling centers. Portions of the filters are removed and decontaminated contributing to mass and volume reduction. Bulk packaging further reduces the number of WIPP storage containers.

Chromium Removal: Chromium removal from oil is mandated for any reuse of oil in energy recovery (40CFR261 and 279).(2) Chemical precipitation, proprietary ion exchange resin, and surface-modified zeolite were considered for Cr removal; however, no research literature was available on Cr removal capabilities from oil. Literature review and consultation with experts led to subsequent laboratory experiments using surface-modified zeolites.(3,4) These tests demonstrated that modified zeolite can be a proficient ion exchange media for the removal of Cr from oil (see Test Methods and Results section). Modified zeolites are stable, economical, and as an ion exchange process are easy to implement into this remediation design; therefore, the surface modified zeolite ion exchange media was selected for removal of Cr from oil.

Free Liquid Removal: Free liquid in the current waste form poses potential problems; CCl4 can volatilize, react with, and decompose polyethylene or PVC bags causing integrity failure.(5) Removal of free liquid through hydraulic compression of the matrix will reduce CCl4 residuals, thereby reducing potential damage. Free liquid removal is also necessary to meet WIPP WAC criteria of <1% by volume of free liquid. A distillation process will remove and purify CCl4 from the liquid waste stream. Removed CCl4 is used as the solvent in all decontaminating systems making it the most practical and economical solvent choice.

Transportation and Packaging: Storage and transportation of filters is in accordance with TRUPACT-II Content Codes (TRUCON) and Safety Analysis Report (SAR). The waste is also packaged in accordance with Land Disposal Requirements (LDR) under the Resource Conservation and Recovery Act (RCRA), WIPP WAC, DOE, and DOT requirements. The waste has determined to be non-corrosive, and non-reactive, but toxic according to 40CFR261. The solid organic filters are of a type III.1A4 waste form requiring a minimum of 1 liner and 3 inner bags.(6,7) Chemical resistant bags and heavy 14 mil liners were chosen to comply with TRUCON standards. Clinoptilolite added to the packaging prevents trace CCl4 from forming corrosive compounds, absorbs any residual liquid and fills void volumes in each layer to eliminate shifting during transportation. TRUCON standards specify a maximum energy output of 0.0207 watts per container; the packaged waste will produce approximately 26.6E-6 watts, which is below both container and overpack wattage limits.(6,7) Minimum WIPP WAC activity requirements are met, with an average activity of 1.87E9 Bq/drum.

PROTOTYPE

The NMT process is a modular system capable of being disassembled, packaged in a single enclosed trailer, and relocated to other sites. The entire process is shown in Fig. 1. Filter processes are contained in a glovebox within an airtight containment work area. Drums are moved inside the work area through an airlock and placed in a high density polyethylene (HDPE) containment rack. Sealed drums are opened, using a standard drumhead removal unit, and poly-bottles are immediately placed in the glove box. Double-bagged filters are removed from poly-bottles; a central vacuum system removes free liquid and particulate matter from each bag. Filters are removed and placed in a HDPE tray; bags are packaged in a WIPP "prepared" storage drum. WIPP "prepared" drums are chemically resistant, lined with a 90 mil HDPE liner, two 14 mil HDPE bags and two 8 mil chemical resistant bags; reducing potential chemical attack and integrity failure.


Fig. 1. Process and Instrumentation Diagram

Knowledge of the Pu239 machining industry indicates that large chips greater than 0.5mm will not be present and finer particles will not puncture inner bags.(8) The innermost bag is prepared with a two inch layer of clinoptilolite. A two step process is used to puncture the lower filter "cap" and sever the "nipple". Filter centerposts and nipple flanges are sent to a decontamination unit. Remaining filter matrix is squeezed using a hydraulic press, and flushed with CCl4 recycled from the distillation apparatus, removing any free liquid. Immersion in liquid nitrogen reduces the PP matrix 150°C below Tg allowing for fracture compression using a hydraulic press. Fractured filters are brought to ambient temperature and packaged in a "prepared" WIPP disposal drum. The filters are strategically placed maximizing usage of every layer. Upon packing to a specified height, the remaining head space is filled with clinoptilolite, and each bag individually horse-tailed and taped. Drums are vented, sealed and transported to WIPP via Transuranic Package Transporter-II (TRUPACT-II) containers.

Liquid entering the distillation apparatus is passed through a 0.1µm effective pore size filter to ensure the stream is free of any Pu239. The liquid will be tested for Pu239 content monthly by alpha spectrometry.(9) Recycled portions of CCl4 are used in the decontamination and filter washing processes, eliminating solvent costs. Oil is passed through a surface-modified zeolite exchange column using a vacuum to increase flow rate.

Chromium concentration is monitored, with the zeolite being replaced at contaminant breakthrough. Removed centerpost, nipple flange, filter plugs, drum lids, and poly-bottle caps are decontaminated via high pressure solvent (CCl4) spray scrubbing. Original drums and poly-bottles are decontaminated using a solvent spray unit and then hydraulically crushed to reduce shipping volume. Particulate filters (0.1µm) are used to remove any Pu239 from the decontaminated solvent stream, and after use are packed in the "bag" drum for disposal, ensuring it will meet minimum WIPP activity requirements.

Labeling, transportation, and disposal of the contaminated zeolite, clean oil, and reclaimed CCl4 are contracted to a waste clearinghouse. The oil will fire a cement kiln; CCl4 may be further refined and used as a laboratory solvent; exhausted zeolite is solidified implementing portland cement techniques and disposed of in a RCRA permitted landfill. Decommissioned materials are crushed, packaged, and sent to plastic and metal recycling operations.

TEST METHODS AND RESULTS

Volume Reduction

Volumetric reduction of the filter material was tested in the lab using liquid nitrogen super-cooling, slide hammer compaction, and mechanical advantage compression. Tests were performed on 100-300 cm3 samples. Crushed filter matrix was pressed into a confining mold and measured periodically for 60 days showed little material expansion, indicating a static waste form. Resultant porosity calculations supported a minimum of 50% volume reduction. Removal of the filter nipple and centerpost further facilitated volume reduction.

Chromium Removal

Three different surface modified zeolites were analyzed in batch tests to determine their ability to remove Cr from oil. Zeolite was modified with iron (II) sulfate-hepta hydrate, hexadecyltrimethylammonium (HDTMA), and iron (II) sulfate-hepta hydrate with sodium sulfate. Two different Cr (Na2CrO4 and K2Cr2O7) contaminated oil samples contained Cr concentrations of 24.9 ppm and 42.8 ppm (as chromium). Three test sets were analyzed with a ratio of 2.5 grams modified zeolite to 10 milliliters of contaminated oils. Samples were shaker-mixed to equilibrium (12hrs), after which the oil and zeolite were separated by centrifugation. The clarified oil, digested in accordance with Method 3050, was analyzed with flame atomic absorption spectroscopy.(10) Results are shown in Table I.

TABLE I Chromium Removal Test Results.

Table I shows that all modified zeolites will remove Cr from oil, with HDTMA modified zeolite having the greatest efficiency. HDTMA modified zeolite was chosen as the ion exchange media based on the above test results. At the zeolite loading of 250g/L no shrink-swell in oil was noted. Based on the isotherm data developed above estimated zeolite requirements for 10,000 lb. of filters will be approximately 500 Kg. Additionally, zeolite exhibits several favorable characteristics: high absorbency capabilities, stability throughout a wide pH range, and low cost at $400/ton.(3,4,11)

Carbon Tetrachloride Removal

With large differences in boiling points between carbon tetrachloride and Texaco Regal R&O 32 oil, distillation and vacuum separation were considered as appropriate separation technologies. Vacuum separation proved difficult, due to process design and system control. Separation of liquids by distillation is a well proven technique with published literature available.(12) Laboratory results indicate that a serially distilled solution retained only 2% (by weight) of the CCL4; further distillation can yield high purity CCL4.

ECONOMIC CONSIDERATIONS AND BUSINESS REVIEW

Equipment specifications were determined by design needs and recommendations from field professionals. Research of standard operation requirements concerning nuclear waste remediation led to contact and requests for information throughout the nuclear community. Estimation of equipment costs were obtained from numerous contacts with both nuclear remediation professionals and industrial supply representatives. Costs were then used to compute the Fixed Capital Investment (FCI). Indirect costs were derived using standard engineering cost factors and the FCI. Table II. summarizes this information.

TABLE II. Fixed Capital Investments and Costs

The business plan is based on three years of continuous work. Straight line depreciation over three years is assumed as is zero salvage value at the end of this period. A net present value of $15,447 was determined using the following assumptions: corporate tax rate is 35%, inflation rate is 5%, and the discount rate is 10%.

Simple payback period for this project is 2.20 years. This analysis indicates that not only is this project feasible, but should have a good return for investors. Table III summarizes basic business costs obtained from a time value cost flow analysis.

TABLE III. Business Summary (all costs given in thousands)

Assuming 10,000 lb. of contaminated filters per worksite, and the performance of eight complete remediations per year (including transport time), the three year cost of operation is estimated at $3,115,380. This yields an average cost of $12.98/lb. of waste or $25,962/ton, and translates to an average remediation charge of $13.43/lb. of waste.

REGULATORY OVERVIEW

Legal

Process design has been shaped by mandated laws and regulations in the following areas: waste handling, facility operations, worker safety and transportation, storage, and disposal of waste. WIPP acceptance criteria has placed further legal constraints on the waste destined for that facility. Codified citations in Table IV & V cover regulatory aspects of the process from opening of waste drums to final clean-up. It should be noted that the National Environmental Policy Act (NEPA), Resource Conservation and Recovery Act (RCRA), Emergency Planning and Community Right to Know Act (EPCRA), Toxic Substance Control Act (TSCA), Clean Air Act (CAA), Hazardous Materials Transportation Act (HMTA), and the Occupational Safety and Health Act (OSHA) have all guided the development of the process detailed in this report. Residual Pu239 in the waste has made it necessary to also consider the Atomic Energy Act (AEA), and Nuclear Regulatory Commission (NRC) statutes in dealing with the waste form.

Tables IV and V cover specific regulations that have impacted development of the process outlined in this report. Codified tables cover: transport, storage and disposal facilities, containers for storage and transport of hazardous wastes, reclaimed oil guidelines, health and safety for workers, emergency planning and response for hazardous waste accidents, and TRU waste specifics concerning transportation, waste characterization and package requirements for WIPP disposal.

TABLE IV Hazardous waste, TDSF, Containers, Reclaimed Oil, Health and Safety, and Emergency Planning.

TABLE V Transportation, Waste Characterization, and Package Requirements.

Safety and Health

The safety and health hazards for this process are associated with Pu239 handling and with the hazardous materials, Cr and CCl4. All workers are trained in technical aspects of the process and also are qualified in: CPR, HAZWOPER, and as radiation workers (see law tables). The process is designed to ensure that exposure to personnel is As Low As Reasonably Achievable (ALARA).(17)

Since "Pu239 is primarily an alpha-emitter...protection...is simple and usually no shielding is required".(8) There will be minimal handling of the filters, with some worker contact required and "lead lined gloves are recommended".(8) With inhalation of Pu239 and CCl4 the prevailing concern, workers directly handling filters shall wear self contained breathing apparatus, full body chemical resistant suits, and lead lined chemical resistant gloves. All machine procedures involving the filters will be conducted in a standard negative air glove box fitted with a sodium carbonate powder fire system. Workers shall be monitored using a strategically placed continuous air monitor (CAM); exit control will be conducted using hand and foot alpha monitors.(9) Accident scenarios were considered, but not calculated, since the Pu239 will not become airborne unless burned.(18)

PUBLIC RELATIONS

A public relations and community right to know package has been developed using 40CFR300 and 370 as guidelines. This package includes advertisements in local papers and radio stations. A public site has also been selected as an information repository. Scheduled community meetings will notify townspeople of the impending process, operation dates, and shipment of contaminated waste via TRUPAC-II. Emergency plans and contingencies have been developed, and are available for public examination. The company's safety record is open for public examination and included in posted advertisements. Remediation work will not be considered complete until the worksite has been inspected and tested by NRC Inspectors under 10CFR75.(17) No shipment of material or equipment shall be released until meeting standards outlined in 10CFR835, Appendix D.(17)

CONCLUSION

The NMT WERC team has developed a process, based primarily on mechanical operations, that is: mobile (fits into a trailer), expeditious (less than thirty days processing time per 10,000 lb. of raw waste), economical ($13.43/lb. of waste), and recycles or reuses almost all of the initial waste (6000 lb.) in a safe, legal, and technically feasible manner. Techniques presented are proven by current industrial applications, or have basis in available literature. The simplicity of these methods make them reliable, easy to implement and operate.

The process has a low capital and operating cost, a positive net present value, and a payback period within the project life. Furthermore, disposal expenses are reduced by: volume reduction (yielding fewer drums for WIPP), CCl4 purification and reuse, container recycling, and oil energy recovery. Legal and regulatory mandates guided development of the NMT process. Waste processing is within all DOE, NRC, and EPA provisions. Transportation and packaging meet DOE and DOT requirements.

OSHA requirements are maintained by providing adequate training and protective equipment for all personnel. Worker and public safety programs have been implemented to eliminate any radiation or hazardous waste exposure. Containment of all hazardous and radioactive waste has been addressed through the use of proven engineering controls. Public relations have been formed through open and honest dialogue with the surrounding community, while following the legal and moral guidelines of safe engineering. Storage of nuclear waste is a responsibility that carries with it a financial burden imposed on many future generations. As the guardians of our future, responsible projects like the one outlined here should be implemented as soon as possible.

REFERENCES

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  2. Code of Federal Regulations. 1995. Protection of the Environment, Chapter 40. Office of the Federal Register, National Archives and Records Administration. U.S. Govt. Printing Office, Washington, D.C.
  3. BOWMAN, R.S. and NI, G. Interview on Chromium Removal From Oil. February 22, 1996
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  7. National Technical Information Service. 1994. TRUPACT-II Content Codes (TRUCON), DOE/WIPP 89-004, Rev. 3. U.S. Department of Commerce, Springfield, V.A.
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  9. WASIOLEK, MARYLA. Interveiw on Health Physicists. March 3, 1996.
  10. U.S. EPA. 1986. Test Methods for Evaluating Solid Wastes, EPA SW 846, Office of SWER. U.S. Government Printing Office, Washington, D.C.
  11. AUSTIN, G.S. and MOJTABAI, C. "Cat Litter: A growing market for industrial minerals", Program With Abstracts, 31st Forum on the Geology of Industrial Minerals. El Paso,TX. April 23-28, 1995.
  12. NELSON, W.L. 1969. Petroleum Refinery Engineering, Chemical Engineering Series. 4th edition. McGraw-Hill Book Co. New York, NY.
  13. Code of Federal Regulations. 1995. Labor, Chapter 29. Office of the Federal Register, National Archives and Records Administration. U.S. Government Printing Office, Washington, D.C.
  14. Code of Federal Regulations. 1995. Transportation, Chapter 49. Office of the Federal Register, National Archives and Records Administration. U.S. Government Printing Office, Washington, D.C.
  15. U.S. DOE. 1991. Waste Acceptance Criteria for the Waste Isolation Pilot Plant, WIPP/DOE-069, Rev. 4. U.S. Government Printing Office, Washington, D.C.
  16. New Mexico Statutes 1978 Annotated. 1994. Environmental Improvement, Chapter 74, with Replacement Pamphlet 120. Michie Company, Charlottesville, VA.
  17. Code of Federal Regulations. 1995. NRC, Chapter 10. Office of the Federal Register, National Archives and Records Administration. U.S. Government Printing Office, Washington, D.C.
  18. GUILMETTE, RAY. Interveiw on Pu239 Solubility in Air. March 26,1996.