Affordable Cleanup? Opportunities for Cost Reduction in the Decontamination and Decommissioning of the Nation's Uranium Enrichment Facilities (1996) / Chapter Skim
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3 DECONTAMINATION PROCESSES
3 DECONTAMINATION PROCESSES
Pages 49-78
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From page 49... ...
D&D operations are conducted under strict regulations in hazardous environments and require extensive safety and health protection equipment, as well as criticality controls. Characterizations of both radioactive and hazardous materials must be carried out before, during, and after decontamination.
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From page 50... ...
Two major technologies for deposit removal have been demonstrated: hot gaseous decontamination, normally performed while the process train is in operating condition; and mechanical removal, normally performed on nonoperating units after disassembly. Following bulk uranium deposit removal, internal surfaces of the process equipment are additionally cleaned.
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From page 51... ...
Hazardous materials, such as PCBs, CFCs, asbestos, and lead paint, are known to be present in the GDPs and can also be handled with proven decontamination technologies. The waste streams generated from the decontamination processes must be purified to release levels, recycled, or disposed of in burial sites.
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From page 52... ...
Ongoing or planned deposit removal activities at the Oak Ridge and Portsmouth GDPs are addressed. The primary objective of the K-25 Site Deposit Removal Program is to bring the Oak Ridge GDP site into compliance with DOE Order 5480.24 by removing, safely packaging, and relocating quantities of enriched uranium contamination deposited in piping and equipment (DOE, 1994a)
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From page 53... ...
; in situ deposit removal in physically isolated sections using a portable gaseous decontamination unit at relatively low temperatures (suitable for Oak Ridge) ; and removal of the process equipment and piping followed by treatment in a specially designed hot gaseous decontamination cell in a high-assay decontamination facility or a low-assay decontamination facility.
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From page 54... ...
C1F3 treatment is an expensive operation.5 However, removal of uranium deposits using an elevated temperature gaseous treatment has the potential to reduce costs substantially during subsequent decontamination of the cascade equipment as a result of reduced security controls, worker protection requirements, and contamination containment needs (Bundy and Munday, 19911. This advantage would apply primarily to the high-enrichment sections of the cascades.
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From page 55... ...
Research and development is currently in progress to determine whether an ion exchange process can be developed in which specific ions are introduced to stimulate the extensive removal of uranium and 99Tc (technetium) retained by the barrier material during gas phase treatment.8 Mechanical Removal Uranium deposits can be removed by mechanical means, which requires the disassembly and dismantling of the process equipment, such as converters and compressors.
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From page 56... ...
DECONTAMINATION OF CASCADE EQUIPMENT The use of aqueous decontamination techniques for the GDP cascade equipment is addressed immediately below; farther details of the aqueous process used at the Capenhurst GDP are given later in the chapter. Despite some suggestions that~gaseous treatment with CIF3 might be used for decontamination of cascade equipment to free-release levels, available data from maintenance programs and CIP/CUP activities indicate that some uranium deposits are slow to react and will be difficult to remove with CIF3.9 In the committee's opinion, cleanup of the cascade equipment to- free-release levels will require aqueous decontamination methods and cannot be reliably achieved solely by gaseous CIF3 treatment.
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From page 57... ...
It is likely that many pieces- perhaps the majority would be sufficiently clean initially to bypass the spray booths and go directly to the dip tanks. The spray booth treatment could still make unnecessary much of the labor-intensive mechanical removal, while giving good uranium recovery in a criticality-free arrangement.
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From page 58... ...
This principle requires that two unlikely, independent, and concurrent changes in process conditions occur before criticality is possible. The aqueous decontamination process produces radioactive wastes that must be managed safely.
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From page 59... ...
Robotic equipment may be effective for much of the work, as discussed below. The large volume of material resulting from such mechanical decontamination processes will require disposal as low-level radioactive waste.
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From page 60... ...
All decontamination processes yield some form of waste that must be managed safely and economically. These waste streams vary considerably, ranging from fragments of solids removed mechanically from converters to water from washing down walls.
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From page 61... ...
The following discussion addresses the characterization approach and technologies for radionuclides and for hazardous nonradioactive substances. Radionuclide Measurement Techniques Survey techniques and detection instruments for radionuclides have been widely used at the three GDPs for monitoring routine operations, repairs, and plant upgrading.
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From page 62... ...
The repetitive nature of the process equipment and building structure can also be used to advantage to minimize the physical and chemical characterization program for hazardous materials. AUTOMATION AND ROBOTICS The enormous physical size of the GDPs and the many modules of repetitive, standardized equipment may provide opportunities for automation of processes and data management.
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From page 63... ...
The Mobile Autonomous Characterization System, a mobile robot, is under development at Oak Ridge National Laboratory, and evaluation tests are planned for the Oak Ridge GDP (see Appendix F; Richardson, 1994~. Characterization of less accessible areas, such as walls and ceilings, the cluttered areas around piping and process equipment, underground piping, and the internal surfaces of tanks, is not as easy for robots and will require some development work and demonstrations.
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From page 64... ...
that could not be treated cost effectively by the aqueous decontamination process. The costs of D&D for Capenhurst are presented and analyzed in Chapter 4, and other details are presented in Appendix H
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From page 65... ...
Removal of Uranium from the Capenhurst Enrichment Cascades At the Capenhurst plant, gaseous C1F3 (chlorine trifluoride) was circulated through the cascade equipment prior to shutdown and dismantling to convert residual uranium deposits to volatile fluorides prior to opening up the cascade system.
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From page 66... ...
The total volume of spent ion exchange resins arising from the aqueous decontamination process was about 100 y63 for the whole plant. The liquors were neutralized, filtered, and run through ion exchange columns to remove heavy metals and radioactive species prior to release to the environment via heavy dilution with other plant wastewater streams to stay within allowable discharge concentrations.
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From page 67... ...
Following disassembly of the converters, the barriers were removed and stored in a secured area. BNFL staff report that, following a number of tests and trials, they now have a satisfactory method of recovery and recycle of the nickel from the barriers.~9 Decontamination of Supporting Systems and Building Surfaces Following process equipment removal, the remaining cell enclosures were demolished.
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From page 68... ...
Research and development on cost-effective techniques for D&D formed a significant part of the Capenhurst D&D effort, constituting about 20 percent of the total project cost.2i Given the repetitive nature of GDP process equipment and building structures, the percentage of total D&D project cost spent on research and development should be much smaller for larger plants. The development of metal melting and wet chemistry decontamination processes for transuranic and fission products on metals permitted minimization of waste from the Capenhurst D&D and allowed extensive materials recycling to commercial markets.
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From page 69... ...
. Well-known wet decontamination methods using citric acid, nitric acid, and ammonium carbonate were used to clean the process equipment for reuse.
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From page 70... ...
At Oak Ridge, mechanical removal or spray booth treatment appear to be the most attractive methods for most of the deposits. At Portsmouth and Paducah, CIF3 treatment at shutdown followed by spray booth treatment for removal of visible uranium deposits could be used, although spray booth treatment alone may suffice.
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From page 71... ...
Decontamination of Support Systems and Buildings Conclusion There is no need to pursue extensive research and development programs on new building decontamination technologies because many existing technologies have been demonstrated to work. Waste Management and Recycling Conclusions I
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From page 72... ...
Further, D&D operations are conducted in environments that, under current and anticipated future regulations, often require extensive safety and health protection programs for implementation. The use of robotics could eliminate some safety risks and costs of corresponding worker protection measures.
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From page 73... ...
Decontamination Processes Recommendations 73 I The use of robotics should be considered as a possible way to reduce costs, Improve safety, and enhance data quality in D&D.
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From page 74... ...
1989. British Nuclear Fuels pIc Process for Decontamination and Decommissioning of Capenhurst Gaseous Diffusion Plant and Information from the International Conference on Decommissioning of Major Radioactive Facilities.
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From page 75... ...
Presented to the Committee on Decontamination and Decommissioning of the Uranium Enrichment Facilities, Portsmouth Uranium Enrichment Facility, Piketon, Ohio, August 22, 1994. Cross, I
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From page 76... ...
Gaseous Diffusion Plants. Presented to Committee on Decontamination and Decommissioning of the Uranium Enrichment Facilities, National Academy of Sciences, Washington, D.C., May 8, 1995.
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From page 77... ...
1988. Decommissioning and Decontamination of Enrichment Facilities.
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