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--> Cross-Cutting Areas and Technologies of Importance There are several waste-management or site-remediation technologies central to the DOE waste-management technology-development program that will be used across the five focus areas. Some are formally designated as cross-cutting areas, and their development is being managed under that heading. Others, even though they have generic application, are being managed separately within the five focus areas. Often, the development of technologies in the latter categories is further segmented on a site-specific basis. While site-specific development may be justified on the basis that the wastes and remediation targets vary from one location to another, it often leads to duplication of effort or to gaps in technology development. This problem of uncoordinated R&D activity on topics of generic interest across the focus areas and sites is addressed in the main body of this report. In some of the five focus-area working papers in Appendix A, the waste-management activities have been classified in the sequence: characterization, retrieval, treatment, stabilization, and disposal. This sequence, which seems to apply fairly well to the tank waste, mixed waste, and landfill areas, can be used as a framework to treat the CEMT evaluation and discussion of EM-50 activities.
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--> Characterization embraces the areas of site characterization and waste characterization. It also relies heavily on developments in monitoring and sensor technology, a technological area that is critical to all five of the waste-management activities and all five focus areas. Retrieval is often site and waste specific, but it seems likely that robotics will play a critical role in retrieval of certain stored or buried wastes. As noted in the individual working papers, robotics is also widely applicable in the characterization, treatment, stabilization, and disposal of toxic and radioactive waste materials. Treatment is also a waste-specific activity that can employ a variety of generic technologies. Separations is critical to reducing the volume of high-level radioactive waste and to reducing the cost and risk of disposal. For wastes containing high concentrations of organic materials, incineration or supercritical water oxidation can be very effective in reducing the chemical toxicity and volume of wastes, especially when conducted with up-to-date process technology. The treatment technologies may also embrace homogenization of wastes, especially when the stored materials are as varied and heterogeneous as those in the Hanford, Washington, tanks. Robotics have obvious applications in the manipulations involved in homogenizing such dangerous substances. Monitoring process streams and emissions will be a critical activity. Stabilization of treated wastes prepares them for interim or permanent disposal. It appears that vitrification is likely to be the technology for stabilization of high-level radioactive materials at the major tank waste sites. Vitrification, grout production, or encapsulation may be options for low-level wastes. Disposal of solid, stabilized wastes may take place in conventional landfills or in highly secure, radioactive waste repositories. Whatever the disposal mode, monitoring of the disposal site may be needed for long periods of time. As noted in the landfill stabilization focus area discussion, this topic of long-term landfill monitoring seems to have received less attention than it merits. The cross-cutting technologies highlighted in italics above are discussed in more detail below. Site Characterization Site characterization is critical to understanding subsurface conditions and processes and thus to determining the appropriate course of action for remediation at a particular site. Thorough site characterization, along with technical practicability issues and future land-use scenarios, will enable DOE to select appropriate remedial
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--> measures to manage the site. These remedial measures could include one or more of the following: source treatment, containment or removal, where practicable; ground-water pump and treat for dissolved portions of the plumes; in-situ treatment; hydraulic containment; institutional controls; and basinwide ground-water resource management. To justify the selection of any of these alternatives, the scientific basis of the data used as input to the risk-assessment process or the justification for technical impracticability must be sound. Thus, the extent, quality, and type of site characterization are critical. Too often, too much of the wrong data have been collected at sites across the country (not just DOE sites). The need exists for a comprehensive program that incorporates site characterization as a means to an end, rather than an end in itself. DOE seems to have embraced this philosophy in its cross-cutting efforts for site characterization (e.g., the SEAMISTTM13 and related work that has been performed at the Savannah River Site). Before selecting appropriate actions at a site, some of the aspects listed below must be understood: the nature and distribution in space of the subsurface materials, whether the soils are fine or course grained, heterogeneity of subsurface materials, or whether fractured bedrock exists; the hydraulic characteristics of the subsurface and the corresponding behavior of the contaminants in question; the mineralogical composition and organic matter content of the rock; and the type of contaminants present; whether they are metals, radionuclides, dissolved constituents, separate-phase organic liquids (light nonaqueous phase liquids (LNAPLs) or dense phase liquids (DNAPLs)), and their wettability. Most of these aspects of site characterization can be fairly straightforward (albeit time consuming and expensive); however, the technology to detect the presence of DNAPL does not exist. Currently, the industry uses "indicators" to assess whether DNAPL is present (e.g., whether DNAPL compounds are present at a 13 SEAMISTTM (patented trademark of Eastman Cherrington Environmental) is a concept of drill-hole instrumentation and fluid sample collection using a membrane insertion technique.
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--> percentage of its aqueous or vapor solubility, and whether historic practices indicate that separate phase liquids could have been released). DOE is actively engaged in efforts to improve DNAPL characterization Because this problem is not unique to DOE and because several other DNAPL characterization efforts are underway both nationally and internationally, DOE should either de-emphasize this effort internally or work collaboratively with other institutions. DOE should strive to reduce its duplication of efforts in this area. In-field monitoring, imaging, and sensor technology are the best ways to minimize the costs and time associated with detailed site-characterization programs. DOE should concentrate its efforts in this arena, especially if it will attempt to reduce the cost of characterizing plumes and landfills by half in fiscal year 1997, a goal that appears overly optimistic. DOE is particularly well suited to continue its efforts in the development of monitoring, imaging, and sensor technology given the work at several of the national laboratories. For example, Lawrence Livermore National Laboratory's (LLNL) development and use of electrical resistance topography to track subsurface heat differentials should be expanded into other areas (perhaps the tracking of separate phase liquids). The continued development and refinement of cost-effective field detectors that can assess metals and radionuclides in soils should be encouraged. In addition, DOE's efforts in remote sensing and imaging technologies to elucidate subsurface physical and hydraulic conditions should be encouraged. In summary, DOE should continue its efforts in the cross-cutting arena of site characterization. To minimize duplication of effort, it should endeavor to form collaborative coalitions both internally and externally. Finally, DOE should review its program periodically to ensure that its technology-development efforts match the needs of the end users in its ever-evolving environmental-management and restoration program. Waste Characterization A major element in the strategy for dealing with stored wastes is learning the scope and character of the problem at a given site. Major challenges are (1) characterization of the contents of large storage tanks at sites such as Hanford and Savannah River, and (2) identification of the contents of barrels, especially those buried at many sites across the United States. Some knowledge of the nature of the wastes is needed to design the facilities to prepare the waste materials for permanent disposal. The degree of characterization required will vary from site to site, depending on the extent to which the contents of different tanks and drum-storage areas will be combined and homogenized before treatment and the sensitivity of selected treatment technologies to homogeneity and composition of the feed.
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--> Tank wastes are often inhomogeneous with both liquid and solid phases being found in any vertical cross section of a tank. Even worse, the contents may differ in character across a tank at a given depth. The inhomogeneities in the solid phases are determined conventionally by analyzing core samples taken at accessible points across the tank. This approach is slow, hazardous, and incomplete. Two techniques under development offer considerable improvement in speed and cost effectiveness. The cone penetrometer, which is coming into use, provides considerable physical information on the nature of the phases as well as the positions of the interphase boundaries. Attachment of chemical probes to the penetrometer can give added information about aspects such as pH and moisture content. Similarly, new spectroscopic tools are being developed to characterize the organic materials that are of concern. Another tool under development that should help deal with the lateral inhomogeneity problem is the Light Duty Utility Arm (LDUA), which can move a variety of probes to various positions across the surface of the tank contents. Another aspect of tank-waste characterization R&D is development of new probes to measure a variety of waste characteristics. A particularly important property is moisture content, because it is believed that 20-30 percent water is needed to prevent explosions from reaction of organic components with the nitrates present in many of the tanks. A thermal neutron technique is in advanced development at Hanford, but an electromagnetic induction technique may permit measurement of moisture content at greater ranges (one foot or more). Several spectroscopic probes such as infrared and Raman spectroscopy are being adapted for use in tanks, both for analysis of the headspace gases and for characterization of species such as nitrate and ferrocyanide in the liquid phases. The problems of characterizing the wastes stored in drums are as complex at those associated with tank wastes. About 1.5 million barrels of wastes (some radioactive, some hazardous chemicals, and many mixed) are stored at various sites. Apart from the safety aspect, the sheer number of drums makes it impractical to sample intrusively more than a small fraction for conventional chemical or radiological analyses. A major development effort is being applied to nonintrusive techniques, such as acoustic imaging, which can be used to identify the quantity, density, and phases of drum contents. This information, coupled with targeted sampling, can provide the basis for choice and design of treatment techniques to be applied at a site. If nonintrusive characterization can be extended to some assessment of the composition of drum contents, it will be a major contribution to the strategy for drum-storage remediation. For drums containing radioactive material, external multispectral emission radiation spectroscopy can also help identify the whole waste content or anomalous drums. The development of technology for imaging and analytical characterization of wastes stored in tanks and drums seems to receive appropriately high priority in the EM-50 program. The technology development appears to be well focused toward possible applications in the remediation programs. It is not clear how well EM-50's
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--> work in this area is integrated with that of the potential implementers and whether new characterization techniques are being implemented as rapidly as possible. Monitoring and Sensor Technology The technologies for monitoring emissions, controlling processes, and performing in-situ analyses present large opportunities for savings of time and money in waste management and environmental restoration, not just for DOE, but also for other federal agencies and for private industry. Development of advanced sensors and monitoring techniques is important to all five focus areas and plays a critical role in the characterization of tank wastes, as noted in the "Waste Characterization" section above. Monitors that analyze gas composition are needed to characterize the headspace in tanks; the air in work places and drum-storage areas; and emissions from incinerators, plasma hearths, and other waste-treatment facilities. Gas chromatography has been a standard tool for these analyses but is being enhanced continuously in both versatility and specificity by development of new types of detectors such as ion-trap mass spectrometry. Direct sampling mass spectrometry and long-path Fourier Transform Infrared (FTIR) spectroscopy are in advanced development and the early stages of implementation for vapor and gas analyses. DOE National Laboratories are actively developing newer, more sophisticated technologies such as surface-acoustic-wave sensors and thin-film detectors. Monitoring gases in the soil over buried wastes, in atmospheric plumes, and in work areas can utilize both new sensors and new ways of deploying them. Vapor-analysis sensors attached to cone penetrometer probes can provide information on volatile contaminants in soil. Similar devices can provide valuable data on the atmospheres where buried wastes are being excavated and on the need for robotics. Monitoring of soil and ground-water contamination can be expedited by new techniques such as electrical resistance tomography and radar holography in addition to standard techniques such as gas chromatography and metal analyses (see "Site Characterization" section above). The goal for new technology development and implementation in this area is to reduce the cost of characterizing plumes and landfills by half in fiscal year 1997. A variety of new alpha-and beta-particle detectors is being developed to assess and map radioactive soil contamination. Looking to the future, decommissioning and decontamination of storage and waste-treatment facilities will require a variety of techniques to characterize the contamination of surfaces and solids. New tools, such as secondary ion-mass spectroscopy and laser-induced fluorescence techniques may facilitate this work.
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--> The Characterization, Monitoring and Sensors cross-cutting area has outstanding opportunities to contribute to the overall EM program, but two complex, interrelated issues will require continuing management attention: Matching technology development to the needs of the technology implementers. This task is exceptionally difficult because, on the supply side, there are a multitude of technology developers ranging from large defense contractors, universities, and national laboratories, to small entrepreneurial firms offering unique technologies. An "opportunity and challenge" is to make the best use of the outstanding technological expertise in the programs supported by DOE's Office of Energy Research. On the demand side, there are hundreds of needs at a multitude of sites with only loose coordination among the responsible managements. A hitherto unattained level of cooperation and coordination will be needed to fit all the pieces together optimally. Matching technology development to the evolving needs of the waste management and environmental restoration programs. The largest current need is probably for technology for site and waste characterization. When the waste-treatment and waste-disposal operations grow larger, there will be major needs for process and workplace monitoring instrumentation. When site-remediation programs are completed, different monitors will be required during the decommissioning and decontamination operations. Long-term monitors will be required to assess the integrity of landfills and waste-storage facilities. Because the design, development, demonstration, and deployment of new monitoring technologies requires periods of years, it is important that the technology-development strategy be phased to anticipate the evolution of the environmental-remediation activities. Robotics DOE Needs Robots with various levels of complexity and sophistication may be necessary to solve many of the DOE-EM problems. The equipment and systems selected are application dependent and will probably depend on funding available at the time of the work. In many instances, due to the hostile environments, simple commercially available teleoperated devices may be justified due to safety reasons for specialized work that is not labor intensive. For large volumes of repeatable work in structured and unstructured environments, such as for D&D tasks, development of specialized automation (robotic and telerobotic devices) may be justified. These
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--> developments do not require fundamental research nor new technologies but basically require the adaptation of existing proven systems to specific problems. For some cases (tank-waste retrieval, for example), robotic specialty systems will be required. Demonstration, testing, and evaluation of systems are essential. Although robotics is not a new technology, each new and unique application requires specific engineering and some development work. Technology Status Commercial robotic systems are available and currently are being applied to DOE's environmental-restoration and waste-management programs. Typically, robots are computers with mechanical peripheral devices, and robotic-supporting technologies include computer vision, computer graphics, computer architecture, and sensory systems. Much advancement has been made in this area during the past decade. The availability of small, capable, and affordable computers has promoted widespread use of this technology. Computer graphics for robotic control systems provide effective and sophisticated interfaces between humans and robots. A variety of robots is commercially available. Industrial robots (robot arms) are available in a variety of configurations from companies in the United States, Europe, and Japan. Special systems are available for nuclear environments. Mobile robot systems are currently working ''around the clock'' in security applications for the military, industrial warehouses, and art museums (Everett et al., 1995). Unmanned vehicles have been developed for the DOD (Gage, 1995). Various forms of "pipe crawlers" are commercially available. These systems are generally teleoperated sensor packages used for inspection of interior surfaces, such as pipes and ducts, inaccessible by humans. Teleoperated mobile systems with tracks or wheels are available from several companies. These systems have been applied in a variety of applications, including police operations and nuclear process operations (American Nuclear Society, 1984, 1987, 1989, 1991, 1993, 1995). DOE Robotics Development Program The DOE-EM Office of Science and Technology (OST), in cooperation with Morgantown Energy Technology Center (METC), has ongoing projects with industry and academia to develop solutions for DOE-EM problems (USDOE, 1995a,b, in press). The Robotics Technology Development Program (RTDP) is a major technology cross-cutting effort in EM (USDOE, 1993), which is performing applied research and development for all five of DOE's focus areas. The following section focuses on the D&D efforts.
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--> Major emphasis in the RTDP program for D&D is on practical systems and capabilities that can be used in facility de-activation and ongoing surveillance and maintenance activities that will reduce costs, enhance safety, and improve the quality of operations. Four National Laboratories (Oak Ridge National Laboratories, Sandia National Laboratories, Idaho National Engineering Laboratories, and Pacific Northwest Laboratories) and the Savannah River Technology Center are the DOE participants. Six industries and five universities also participate in this program. Major opportunities for robotics have been identified for mapping, characterization, inspection, dismantlement, and decontamination. Current major activities for the program include: a Selective Equipment Removal System (SERS) which is a mobile vehicle system under development for equipment removal in decommissioning operations; the Facility Mapping System (FMS) which is a computer system for the management of characterization data from a facility; and the Mobile Automated Floor Characterization System (MACS) which is an autonomous, mobile floor characterization system for efficient and effective characterization of large floor surfaces, such as the gaseous diffusion plants. The Small Pipe Characterization System (SPCS) and Internal Duct Characterization System (IDCS) will be used to examine remotely interior surfaces for visual inspection and characterization. A Pipe Asbestos Insulation Removal Robot is under development for 4'-8' diameter pipes. A remotely operated vehicle with CO2 blasting for decontamination of surfaces is under development. This unit will remove paint from surfaces, such as floors in K-25 facilities. Other cross-cutting efforts are underway. Robotic technologies are being developed and demonstrated (e.g., the Light Duty Utility Arm) for characterization and removal of underground tank waste at Hanford. Laboratory automation development is underway for the analysis of materials from underground storage tanks at Hanford and samples from other process operations. Autonomous robotic systems are under development for the visual inspection of drums of low-level waste stored in warehouses at Fernald, Oak Ridge, Idaho, Rocky Flats, and Hanford. Related Robotics Development Activities DOD and NASA have in-house R&D programs in robotics. Research programs, existing at major universities, are addressing robotics technology issues such as unique mechanical configurations, path planning and control, mobile navigation, sensory systems and sensor fusion, computer architecture, real-time systems, computer inspection, hardware and software reliability, and computer graphics. Many of these programs are supported by grants and contracts from DOD, DOE, and NASA. Therefore, benefits from this work are available for DOE applications.
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--> Concerns Although robotic technology demonstrations and analyses have been budgeted and scheduled for key components of the DOE RTDP, evaluation criteria for the projects and criteria used for budgeting and prioritization of robotics technology projects are not evident. Fiscal Year 1995 funding within EM-50's RTDP supported a demonstration during September 1995 at the ORNL K-25 plant for MACS. That demonstration was not conducted, and, currently, MACS is not an "active" project. This system has been estimated to have high potential for cost savings in facility D&D projects. In Fiscal Year 1995, EM-50's RTDP program had a task entitled The Surveillance and Maintenance Risk and Cost Reduction Evaluation Methodologies (related to robotic systems). The methodology was scheduled to be applied to an existing DOE facility in September 1995, but apparently, that work has not been completed at a specific site. Although the RTDP appears to have good projects and intentions, it is not clear to CEMT that priorities are ordered correctly to support the overall EM program or if efforts are being made to take advantage of works at other federal agencies. Separations Separations, particularly of short-lived radionuclides from long-lived species, play significant roles in dealing with the waste streams considered in the five focus areas, and are especially important in dealing with wastes containing high-level radioactivity. As outlined in the report Nuclear Wastes: Technologies for Separations and Transmutations (NRC, 1996), separations would be absolutely critical to the transmutation approach to dealing with either military or nuclear fuel waste materials. More immediately, however, both the costs and risks of disposing of tank wastes at Savannah River, Hanford and the Idaho National Engineering Laboratory (INEL) (as well as calcined wastes at INEL) are directly related to the efficiency of separations in the wastes to be vitrified (see section on "Vitrification" below) and the number of separation steps required. The latter point can be illustrated by considering options for disposal of tank wastes. One option would be to vitrify the entire contents of the tanks, without any separations, and to dispose of all the waste material in a high-level repository. This option likely would be excessively expensive because of the cost of disposal in a facility such as Yucca Mountain. The cost could be reduced substantially by separation of the radioactive components from the great mass of nonradioactive salts. On the other hand, the cost of disposal could be minimized by complete separation of low-level waste from the high-level material that requires
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--> expensive disposal. While this option would be attractive from the viewpoint of disposal costs, it is not feasible because the technology for complete separation does not exist currently. The optimal balance of processing cost and risk versus disposal cost and risk generally involves a modest number of separations steps. Determining this balance is a major challenge in the proposal that the separations and vitrification processing of the Hanford tank wastes be privatized. If the contractor were to do an inadequate separation of high-and low-level wastes, the cost of high-level storage to be borne by DOE would be excessive. Beyond the challenge of minimizing costs, the design of separations processes for disposal of tank wastes must also minimize risks to plant personnel and the public. Increases in the number of process steps lead to increased potential for radioactive emissions. Each time a waste stream is moved or processed, the possibility for release of gases, liquids, or solids exists. Each step also generates secondary wastes arising from the reagents used to carry out the desired separations. As with cost, the minimization of risk requires an optimal choice of the number of separations to be performed. Minimization of cost and risk requires a systems approach to the design of the overall disposal process. The conceptual design of the complete waste treatment system should identify both the number and kinds of separations required. It is likely that many of the newly identified separations processes (such as those for 137Cs and 90Sr discussed below) are not developed sufficiently for immediate application. Prompt identification of the separations needs will facilitate the work of organizations such as EM-50 who are responsible for development of the necessary technology. The development path from identification of a promising chemical separations process through bench-scale and pilot-scale demonstration to actual implementation requires years of effort. However, the resources and time spent on technology development can yield substantial benefits in terms of reduced costs and risks in the ultimate application. These benefits accure to all stakeholders in the waste-management process from the residents of nearby communities to the U.S. taxpayer (currently, nuclear utility-rate payers), who must, ultimately, bear the cost for disposing of DOE's wastes. The Efficient Separations and Processing (ESP) cross-cutting area has supported the development of several promising, innovative techniques for separation of cesium and strontium. Approaches for cesium include sequestration into high-capacity, layered silicotitanates; extraction into ion-specific organic ligands that are encapsulated in permeable polymer membranes; and
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--> complexation to cobalt dicarbollide ions that are selective for binding Cs and Sr. These complexants may be used either in liquid-liquid extractions or as components of ion exchange resins. This part of the ESP program has made good use of the expertise of private industry to synthesize developmental quantities of inorganic materials, for proprietary membrane technology, and for ligand design and synthesis. Examples include synthesis of crystalline silicotitanates (CSTs), sodium titanates, and membrane-supported organic extractants that are effective ion-exchange materials for Cs and Sr. These materials, developed under ESP contract, have been brought to pilot scale or commercial production and have been tested on tank wastes or simulants from Savannah River, Oak Ridge, INEL, and Hanford with encouraging results. The CSTs, now commercially available from University of Pennsylvania Molecular Sieves as IONSIV IE-910 and 911, have proven very effective with decontamination factors of one million for Cs and 10,000 for Sr (Brown et al., 1996). Sodium nonatitanate, manufactured as powders or pellets by Allied Signal, Inc. has proven similarly effective for strontium and also appears promising for Am, U, and Pu (Yates et al., 1993). The sodium nonatitanate also has been incorporated in the novel membranes developed by 3M Company, which show mechanical advantages over ion exchange columns in some waste-treatment applications. The 3M EmporeTM membranes also have been used with organic ligands tailored for ion specificity by IBC Advanced Technologies (Kafka, 1996). This technology represents another promising example of an ESP initiative that uses the synthesis and manufacturing capability of private industry very effectively. Some of the techniques developed for cesium also appear promising for strontium, although the systems need more development of the strontium separation processes. To develop an integrated system for separation of the materials contained in complex mixtures such as those in the Hanford tanks, it is desirable that R&D be carried out simultaneously on the various nuclides of interest. For example, one must develop compatible technologies for dealing with technetium and the transuranic elements in addition to cesium and strontium. Technetium is a concern both as a long-lived component of tank wastes and, in other circumstances, as a potential ground-water contaminant. In tank remediation, technetium is a potential source of problems in vitrification. As such, it may possibly require a separate stabilization process to prepare it for long-term storage. The development of selective techniques for the separation of technetium (mainly TcO4-) from waste streams containing high concentrations of other materials appears to be less advanced than for Cs and Sr, but similar extraction and ionexchange techniques may be applicable if extractants and resins can be developed. For the transuranic elements, further refinement of the TRUEX process may lead to
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--> adequate specificity. All these metal-selective processes need to be integrated with each other and with those for priority nonradioactive waste materials. The ESP program seems to be managed quite effectively. There has been considerable emphasis on understanding specific needs for separations in the remediation of tank wastes and other mixed waste streams. The message that "Success is implementation!" seems to be understood by most of the contractors supported by this program, although the response to the message is probably mixed. Most of the contractors presenting their work at the 1995 ESP Technical Information Exchange appear to have defined useful practical objectives for their R&D programs. Although the ESP program is well run and reasonably successful, two concerns remain. First, the effectiveness of the interactions between the ESP participants and those supported by the Office of Basic Energy Sciences (BES) and Office of Health and Environmental Research (HER) programs within the Office of Energy Research (OER) can be improved. Considerable progress has been made in strengthening ties to basic research in areas such as design of metal-selective ligands, but major gaps remain in the coordination of the OER programs with those of potential clients in EM-50. Fundamental research relevant to the needs of DOE-EM is done in BES-and HER-supported programs, but coordination of the research directions in these programs with the needs of EM generally is lacking. EM-50 seems well positioned to serve as an interface between the basic-research programs of OER and the technology implementers in EM. Second, it remains to be demonstrated that innovative developments in separations technology from the ESP program can be moved into the implementation programs of the five major focus areas in a timely and cost-effective manner. As an example, there are obvious problems in replacing the cumbersome tetraphenylborate-based precipitation of cesium in the Savannah River vitrification technology with one of newer cesium separation technologies mentioned above. The time required to replace the tetraphenylborate precipitant with a new inorganic reagent or with an ion-exchange material such as the CSTs described above depends not only on technological requirements, but also on slow, bureaucratic evaluation processes in DOE and in relevant regulatory agencies. Incineration The term "incineration" covers a variety of treatment processes that have the common objectives of volume reduction and destruction of organic (usually nonradioactive) components of wastes, but differ in such essential features as temperature, heating system, residence time, furnace design, post-combustion and off gas purification systems. In the lower temperature ranges (~1000°C), the end
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--> product is in the form of loose ash, which may require a secondary treatment for consolidation. At higher temperatures (>1300°C), the end product may be a slag, which may not require any additional form of consolidation or insolubilization. Common to all forms of incineration, although to very different degrees, is the formation of volatile or semi-volatile components that are vented with the off gases. These volatiles may contain hazardous radioelements (e.g., Cs and Ru) or complex organic components, such as dioxins. However, it should be stressed that emission of the latter can be prevented through optimization of the combustion conditions and the use of an adequate gas-purification system. Volatilities of radionuclides and metals (e.g., Hg) also can be extracted by the gas-purification system. Because of the potential advantages of incineration (flexibility with regard to feed material, broad range of applications, experience), it would be a mistake to apply to all forms of incineration a generalized "poor-quality" label to be avoided and/or substituted by other, still to be proven, processes. Modern incinerators, adequately designed and operated, can comply completely with the most stringent environmental regulations. The Subcommittee on Mixed Wastes will contribute to the evaluation of types and operational conditions of incinerators that meet relevant environmental criteria and identify areas for further development, if needed. Supercritical Water Oxidation (SCWO) A system based on the use of supercritical fluids (e.g., water at pressure and temperature above the critical point) has been proposed for the destruction of the organic fraction of some mixed wastes (oils, detergents, solvents, complexing chemicals, mixtures of organic residues) (see also USDOE, 1994). The SCWO process is still being developed, but it offers some potential advantages over high-temperature processes, such as easy to handle off gases, little or no volatilization of radioactive contaminants, and fewer problems of public acceptance. However, the limitations of SCWO processing include corrosion at high temperature and pressure, handling of solid residues and precipitates in the supercritical fluid reactor,
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--> lack of practical experience and knowledge of basic reaction phenomena, and concerns about handling toxic substances at high temperature and pressures. It also should be noted that, if the waste contains significant quantities of radioactive components, the residue requires an adapted form of treatment or immobilization. Some preliminary impressions of the SCWO process so far are that SCWO has to be followed by another immobilization process, it is not yet clear for which variety of waste streams the process will be applicable, the system appears to be most promising for destruction of organic components in aqueous effluents, practical difficulties (corrosion, handling) have to be solved, and the practical applicability remains to be demonstrated. Therefore, although the SCWO processing offers attractive potential, it is doubtful whether it will assume an important role in the handling of radioactive wastes in the short term. Vitrification Containment of radioactive materials in glass has been selected by DOE as a versatile, widely applicable approach to the safe and efficient management of high-level radioactive wastes. Major vitrification facilities are in place at the Savannah River and the West Valley sites. Planning is well advanced for a facility at Hanford. Installations are in the early construction stages at the Oak Ridge and Fernald sites. The potential applications of vitrification to radioactive wastes are very broad, including HLW and LLW from the Hanford waste tanks, in-situ vitrification of wastes in the soil at several sites, and thorium and radium residues at the Fernald Site from extraction of uranium from very rich Belgian Congo ores during the Manhattan Project. Borosilicate glass has been selected by DOE for production in its vitrification plants. Other potentially useful glasses that might have been chosen include phosphate glass, lead-oxide based glasses, and aluminosilicate-based glasses. Borosilicate glass was chosen because of the broad base of knowledge of its properties as a function of composition, the very large experience base that exists with its use in radioactive waste containment (particularly in France, Germany, and the United
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--> Kingdom), its broad applicability to a variety of wastes, and because of the large investment made in it. This investment is both in dollars and in establishing its acceptance and credibility with policy makers and with the public. Several significant problems exist with the use of borosilicate or any other type of glass for waste containment. The most important problem is that no performance criteria for the waste form have been promulgated by USNRC. Therefore, no target guidelines for waste-form producers exist. Another severe problem is that a very wide range of waste compositions must be accommodated by any waste-vitrification process. Otherwise, there must be very substantial feed pretreatment to produce a uniform feed to the vitrifier. This problem is most severe with the wastes from the Hanford tanks. If vitrified wastes of a spectrum of compositions are produced, it is necessary to qualify them all for disposal, which is very expensive and time consuming. Finally, there are several processes that are not vitrification in the usual sense but have the potential to produce vitrified wastes. Examples of these are the Glass Material Oxidation and Dissolution System (GMODS) process being developed at ORNL and the Quantum-CEPTM process developed by the M4 Company. Disposal Disposal is an integral—albeit the final—part of any waste-management scheme. The selection of a disposal environment as well as the related engineering structures must be based on objective criteria with regard to type, quantities, volumes and characteristics of wastes. Consequently, these criteria will also be important in the selection of treatment/immobilization processes and the many sub-processes they comprise. The treated material eventually becomes the "source term" in any evaluation of the environmental impact of a waste-management program, which includes societal issues such as inadvertent human intrusion into the waste disposal facility. The types of human intrusion scenarios that are assumed are a matter of policy. Disposal environment and source term are two closely interacting factors, because they control the solubility and mobility of radioelements and, hence, their eventual impact on population. This is also the case for nonradioactive but hazardous components of wastes. Therefore, recognizing that final evaluations depend on the selection of a site or geologic formation, waste-treatment or conditioning must be considered as part of any waste-disposal program. Removing hazardous waste materials from an undesirable location (e.g., contaminant plume, disused production or laboratory facilities, unacceptable disposal sites) is often essential. When waste retrieval is required, one must have a clear view
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--> of the final destination of the resulting waste materials. Relocation of materials may be a poor practice if it does not solve the ultimate disposal problem. The foregoing also illustrates the crucial importance of characterizing the treated end products to allow prediction of their behavior in the disposal environment. The inventory of hazardous material is only the first step of characterization. Understanding and quantification of interactions between treated/conditioned wastes and their future disposal environment are at least equally important. Meeting quantifiable regulatory requirements can be a good guide in evaluating compliance with safety criteria. However, more must be done to ensure that the system as a whole meets basic health and safety risk requirements. Evaluation of the latter is the main objective of case-specific quantitative health and safety risk assessments. The volume of material for disposal is an important factor in the total cost of a disposal program. In particular, it can be used as a preliminary guideline to select processes for treatment or preconditioning of wastes with the intention of minimizing the volume of waste requiring expensive disposal site preparation and maintenance. Nevertheless, two caveats are important: Because of the magnitude of general expenses (for R&D, site selection, administrative and legal procedure, which may be independent of volume and quantity, construction of basic infrastructure, and surveillance), there is not necessarily a linear relation between volume and disposal cost. The issue must be analyzed carefully to determine the relative advantages of putting large efforts in volume reduction prior to treatment and disposal. In the case of heat-producing waste, the size of the disposal infrastructure may be determined less by the total volume of waste than by the heat-dissipation capacity of the disposal geologic formation. Choice of Disposal Sites The acceptability of a given waste type and waste form in a given disposal site depends on two different evaluation measures: the confining power of the natural and engineered barriers, including the waste form, which will prevent the radionuclides or toxic chemicals from being released into the environment for several scenarios, and that will meet the regulatory criteria applicable to the specific disposal site. This confining power may limit both the activity of each waste package and the total capacity of a given site.
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--> the duration and type of constraints that will be applied to the future land use when disposal is completed. This factor will generally limit the amount of long-lived radionuclides (mostly alpha emitters) that can be accepted in a given waste form, based on various scenarios of future land use (e.g., residential area, road construction site, etc.). At this stage, it is not clear which of the basic options DOE is considering for the disposal of each type of waste, the constraints that each of these options will put on the maximum loading of the waste (e.g., on alpha emitters), and the confining power of the acceptable waste form. DOE should establish a list of the disposal options considered for waste disposal, both nationally and at each local site, and the constraints that these options impose on the waste composition. The waste form should then be specified, based on generic and site-specific risk assessments. Existing disposal technologies should be used to make these risk assessments. For each disposal option, an estimate of the cost of disposal should be made as a function of the total size of each disposal site, because cost is not linearly dependent on the amount of waste. The adequacy of DOE's options for the safe disposal of wastes generated by each remediation activity needs to be addressed. This adequacy should be evaluated both with the existing (or planned) waste-production technology and characterization and with each new technology that is proposed or developed. Based on the comparison of the chosen disposal options and waste-acceptance criteria, it is recommended that DOE should produce a plan showing the final destination of each waste type. Such a plan may reveal the lack of disposal options for a given waste form; the need to optimize disposal site locations to minimize transportation and costs; the economic incentive to improve a waste form, a waste-separation technique, or a volume-reduction effort, based on the cost of disposal; and the need for improved disposal technology. Landfills Many of DOE's cleanup efforts deal with existing landfills that may cause threats to people or the environment. Waste is characterized, and the risk associated with the presence of the waste in the landfill is assessed. If the risk is considered unacceptable, three options are available as discussed in the Landfills Subcommittee report:
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--> excavation and redisposal elsewhere, possibly after ex-situ treatment of the waste and contaminated soil; in-situ treatment (e.g., vitrification, grouting); and site confinement by additional engineered barriers such as caps, walls, and floors. Choosing between these options should be based on criteria for the long-term land use, risk assessment analysis for each option, including risk to workers, and costs. To put the advantages of each option into perspective, it is essential that the same information be available for the redisposal of the waste (after treatment) in another disposal site, if the excavation option is considered. Therefore, for each landfill reclamation project, DOE should consider potential disposal sites where these risks and costs are known. Until this information is available, the decision for treating a landfill site cannot be complete. New Technologies for Waste Disposal The R&D in the area of landfills addresses issues such as confinement or site characterization (geology, hydrology) that are also relevant for the development of new disposal sites. However, DOE should also devote attention to the following areas: Incentives, benefits, and costs of disposal of certain LLW in underground-mined repositories, as is done in Sweden, and planned in the United Kingdom and Germany. Incentives, benefits, and costs of a disposal option where the objective is not confinement, but enhanced in-situ treatment of the waste in a ''disposal'' unit, to remove as much radioactivity or toxicity as possible. New technologies that are studied for in-situ landfill remediations (bioremediation, oxidation, acid leaching, etc.) in specially designed engineered structures (e.g., trenches where the waste can be leached and the liquids collected from below). The concept is that all elements removed from the waste (such as gas or liquids) must be recovered by an engineered system. Instead of being immobilized, the waste form should be easily leachable. All collected effluents should be treated (immobilized in a good matrix form for, for example, deep disposal). This form of "disposal" could be seen as a volume-reduction operation, because the radioactive materials would be recovered and disposed of elsewhere. The disposal treatment site would eventually be turned into a confining
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--> site (e.g., by capping) when the residual level of activity is considered acceptable for the designated land use of the site14. Finally, it is recommended that DOE devote considerable attention to defining the needs for air, water, and soil monitoring adjacent to landfills and repositories. Once these needs are defined, it will probably be necessary to focus on development of inexpensive but reliable monitoring techniques for long-term surveillance of disposal sites. References American Nuclear Society (ANS). 1984. Proceedings of the Robotics and Remote Handling in Hostile Environments. Topical Meeting, Gatlinburg, Tenn., April 23-27, 1984. American Nuclear Society (ANS). 1987. Proceedings of Remote Systems and Robotics in Hostile Environments, Topical Meeting, Pasco, Wash., March 29-April 2, 1987. American Nuclear Society (ANS). 1989. Proceedings of the Third Topical Meeting on Robotics and Remote Systems, Charleston, S.C., March 13-16, 1989 American Nuclear Society (ANS). 1991. Proceedings of the Fourth Topical Meeting on Robotics and Remote Systems. Albuquerque, N. Mex., February 25-27, 1991. American Nuclear Society (ANS). 1993. Proceedings of the Fifth Topical Meeting on Robotics and Remote Systems, Knoxville, Tenn. April 25-30, 1993. American Nuclear Society (ANS). 1995. Proceedings of the Sixth Topical Meeting on Robotics and Remote Systems, Monterey, Calif. February 5-10, 1995. 14 This concept has been put in operation for a toxic industrial waste site in Montcanin, France, which was closed in 1989 because of unacceptable contamination of the environment (air and water). The site is presently in the construction phase of the drainage system, the capping and leachiong system were installed in 1993. (A description can be found in the work of Marsily, G. de, 1992).
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--> Brown, N.E., J. Miller, and J. Sherman. 1996. Waste Separation and Pretreatment Using Crystallin Silicotitante Ion Exchanges. Proceedings of ESP Technical Information Exchange Meeting, Gaithersburg, Md., January, 24-26, 1995. PNNL-SA-25603, p. 3-5. Everett, H. R., et al. 1995. Mobile Detection Assessment Response System, Unmanned Systems, Volume 13, No. 3, pp. 26-31. Summer 1995. Gage, D. W. 1995. A Brief History of Unmanned Ground Vehicle (UGV) Development Efforts, Unmanned Systems, Volume 13, No. 3, pp. 9-16. Summer 1995. Kafka, T. and R. Bruening. 1996. Novel Cesium, Strontium, and Technetium ion Exchange, Membrane. Proceedings of ESP Technical Exchange Meeting. Gaithersburg, Md. January 24-26, 1995. Pp. 9-11. Marsily, G. de, 1992. Contaminant immobilization and containment: Hydraulics. A case study. Proceedings of The Subsurface Restoration Conference, Dallas, Tex., June 21-24, 1992. Edited by H. Ward. National Research Council. 1996. Nuclear Wastes: Technologies for Separations and Transmutation. Washington, D.C.: National Academy Press. U.S. Department of Energy (USDOE). 1993. Robotics Technology Cross-cutting Program. Office of Environmental Management, Technology Development. DOE/EM-0250. Springfield, Va. June. U.S. Department of Energy (USDOE). 1994. Super Critical Water Oxidation Program (SCWOP), DOE/EM-0121P. February. U.S. Department of Energy (USDOE). 1995a. Technology Development Through Industrial Partnerships, Office of Science and Technology, Morgantown Energy Technology Center, Morgantown, W.Va. October. U.S. Department of Energy (USDOE). 1995b. Environmental Technology Development Through Industrial Partnership: Agenda, Abstracts and Visuals, Office of Science and Technology, Morgantown Energy Technology Center, Morgantown, W.Va. October 3-5.
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--> U.S. Department of Energy (USDOE). In press. Proceedings of the Conference on Environmental Technology Development Through Industrial Partnership, Office of Science and Technology, Morgantown Energy Technology Center, Morgantown, W.Va. Yates, S.F., A. Clearfield, and I.G.G. DeFilippi. 1993. Cesium and Strontium Ion Specific Exchanges for Nuclear Waste Effluent Remediation, Allied signal Company: Des Planes, Il.
Representative terms from entire chapter: