3
Facilities and Technologies

This chapter deals with facilities and technologies that underpin the DOE Office of Environmental Management’s characterization and treatment capabilities. The committee obtained information for this chapter primarily from briefings and documents provided by EM and its contractors during the four site visits (see Appendix A) and from the collective knowledge of committee members. In accordance with its task statement, the committee focused on facilities and technologies with applicability to problematic or “orphan” wastes, for which effective disposition paths are needed to achieve accelerated cleanup. As noted in Chapter 1, the committee was aware of many non-technical factors (public concerns, regulations, economics) that will bear on how EM might implement the technical recommendations set forth in this chapter, but did not attempt to prejudge how these factors might limit or foreclose valid technical opportunities. The committee did not seek a comprehensive list of capabilities and facilities.

From its information-gathering and results from other NRC studies, the committee believes that legacy orphan wastes and “odds and ends” that will continue to arise throughout the EM cleanup fall into seven general categories:

  • Low-level and mixed low-level wastes, including combustible and non-combustible materials (NRC, 1999a, 2002b),

  • Spent nuclear fuels (SNF) and fuel fragments that require treatment before prolonged storage or disposal (NRC, 2003a),



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program 3 Facilities and Technologies This chapter deals with facilities and technologies that underpin the DOE Office of Environmental Management’s characterization and treatment capabilities. The committee obtained information for this chapter primarily from briefings and documents provided by EM and its contractors during the four site visits (see Appendix A) and from the collective knowledge of committee members. In accordance with its task statement, the committee focused on facilities and technologies with applicability to problematic or “orphan” wastes, for which effective disposition paths are needed to achieve accelerated cleanup. As noted in Chapter 1, the committee was aware of many non-technical factors (public concerns, regulations, economics) that will bear on how EM might implement the technical recommendations set forth in this chapter, but did not attempt to prejudge how these factors might limit or foreclose valid technical opportunities. The committee did not seek a comprehensive list of capabilities and facilities. From its information-gathering and results from other NRC studies, the committee believes that legacy orphan wastes and “odds and ends” that will continue to arise throughout the EM cleanup fall into seven general categories: Low-level and mixed low-level wastes, including combustible and non-combustible materials (NRC, 1999a, 2002b), Spent nuclear fuels (SNF) and fuel fragments that require treatment before prolonged storage or disposal (NRC, 2003a),

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program Fissile materials (U-235, U-233, Pu-239) that, due to impurities or other factors, cannot be recycled or disposed in the Waste Isolation Pilot Plant (WIPP), Radiation sources (sealed sources, Hanford strontium and cesium capsules) that exceed limits for near-surface disposal, Sludges, slurries, and tank heels encountered in facility decommissioning that require treatment before disposal (NRC, 1999b, 2001b), Large, heavy, highly-contaminated equipment from fuel reprocessing, materials separation, and waste processing, and Radioactively and chemically contaminated in situ soils and ground water that require characterization and monitoring (see Chapter 4). Facilities with unique, currently available capabilities for characterizing and treating many of these wastes are described in the first section of this chapter. The second section describes existing facilities that can be upgraded or their operations extended to treat additional orphans, with the view that upgrades or extended capabilities may be less expensive and more expedient than constructing new facilities. The third section identifies new technologies that would enhance existing capabilities. Recommendation: EM should consider managing the following facilities as corporate assets for the characterization or treatment of both mainstream and special-case or “orphan” wastes: Toxic Substances Control Act (TSCA) incinerator at Oak Ridge H-Canyon at Savannah River T-Plant at Hanford High-level waste (HLW) calciner at Idaho Advanced Mixed Waste Treatment Facility (AMWTF) at Idaho Vitrification Facilities at Savannah River and Hanford Existing groundwater-monitoring wells at all sites. The basis for this recommendation is the match-up between the seven general categories of wastes that will have to be dealt with throughout EM’s cleanup program and EM’s already-existing facilities (see Tables 3.1 and 3.2). In considering the continued operation of these facilities as corporate assets versus closing them, EM will need detailed assessments of the liabilities of maintaining them (cost, ensuring safety, meeting regulatory requirements) versus the same liabilities for providing alternatives. While such detailed assessments are beyond the committee’s ability, maintaining or extending the capabilities of the recommended facilities are worthy options to consider.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program TABLE 3.1 Problem and Orphan Wastes That Can Be Treated in Existing Facilities Waste Type Facility Treatment Capability Product and Disposal Combustible mixed low-level waste solids and liquids Oak Ridge incinerator Incineration Stable solids for near-surface disposal Spent nuclear fuel that requires processing; enriched uranium Savannah River H-Canyon Reprocessing, downblending Recycle or disposal of fissile materials; high-level waste (HLW) is vitrified Large, highly contaminated objects Hanford T-Plant Size reduction, macro-encapsulation Packaged waste for near surface disposal or WIPP TABLE 3.2 Wastes That Can Be Treated By Improving Capabilities in Existing Facilities Waste Type Facility Treatment Capability Product and Disposal Noncombustible liquids and slurries (high-or low-level) INEEL calciner Calcination Stable granular solids that may be low-level waste, HLW, or TRU waste depending on the original waste composition High-volume transuranica or low-level wastes INEEL AMWTF Characterization, sorting, compaction Packaged waste for WIPP Small-volume, highly radioactive sources or fissile materials Savannah River DWPF; Hanford WTP Encapsulation in vitrified HLW Canisters for geologic disposal with SNF and other HLW aIncluding buried TRU that may be retrieved (NRC, 2002b). CURRENTLY AVAILABLE FACILITIES The committee believes that the accelerated cleanup can best be kept on track, or accelerated further, if a limited number of facilities with unique capabilities for characterization or treatment are maintained as corporate resources, instead of being tied to their host site’s decommissioning sched-

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program ules and budgets. Premature closure of these facilities to fit a specific site’s schedule could seriously delay the overall EM program because these facilities’ capabilities cannot be replaced by other DOE or commercial resources. Oak Ridge Toxic Substances Control Act (TSCA) Incinerator The Oak Ridge TSCA incinerator is EM’s only waste incinerator. It has a permit to burn wastes containing chemically hazardous materials,1 TSCA materials (e.g., polychlorinated biphenyls [PCBs]), and low-level radioactive liquids and solids. In addition to wastes from within Tennessee, incineration of approved out-of-state wastes, e.g., from other DOE sites, is allowed by the permit. The incinerator thus has a unique capability to treat a wide variety of EM’s mixed low-level wastes,2 which have been identified previously as a potential obstacle for accelerated cleanup (NRC, 1999a, 2002b) (Figure 3.1). According to Oak Ridge’s accelerated cleanup plan, the incinerator is to be shut down in 2006 and to be fully decommissioned in 2008. This closure date will preclude use of the incinerator for some existing wastes from other DOE sites and even for some Oak Ridge site wastes.3 TSCA mixed wastes along with dioxins and furans now exist at Fernald, Paducah, INEEL, and other national laboratories, according to information presented to the committee. There are no commercial incineration facilities that can serve as replacements. The committee heard rather different viewpoints about the continued need for this incinerator from Oak Ridge and other sites visited. Oak Ridge personnel stated that it is difficult for incinerator operators to get commitments for shipment of wastes to the incinerator, especially from other sites. This makes forecasting, scheduling, and providing sustained funding to operate the incinerator difficult for Oak Ridge management. Other sites mentioned barriers to sending mixed wastes to Oak Ridge, such as restrictive waste acceptance criteria. EM’s Corporate Projects Initiative on Disposing Waste, Reducing Risk4 found similar issues as the committee and recommended that the TSCA incinerator be supported as a corporate asset, i.e., funded by sites 1   As defined by the Resource Conservation and Control Act (RCRA) of 1976, as amended. 2   Mixed wastes contain low-level radioactive wastes mixed with RCRA and/or TSCA chemicals. 3   The committee noted that the large capacity supercompactor, used for crushing metal components from the gaseous diffusion plant decommissioning and which provided another unique treatment capability at Oak Ridge, is being dismantled. 4   Project teams modeled on those used by for-profit corporations were organized within EM in November 2002 to institute top-down reforms in the cleanup program. They provided their results to EM management in November 2003.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program FIGURE 3.1 The TSCA incinerator at Oak Ridge provides EM’s only capability for burning mixed low-level radioactive wastes. Photo courtesy of Oak Ridge Operations Office. sending waste to the incinerator (DOE, 2002c). The EM team found that access to the TSCA incinerator was hindered by regulatory protocol, lack of schedule integration, lack of accurate inventories, and complicated access requirements. The committee believes that closure of the incinerator should be decoupled from the Oak Ridge cleanup schedule, and the incinerator should be managed and funded as an EM-wide asset until near the end of EM’s mission when it is certain to be needed no longer. As a firm closure date approaches, there should be technical opportunities to expand the spectrum of wastes that can be burned. For example, more corrosive materials could be accepted and burned because protecting the interior of the incinerator from corrosion becomes less important as shutdown time approaches. Savannah River H-Canyon The H-Canyon reprocessing plant at SRS is the only active reprocessing plant in the United States. At the present it is being used to blend highly enriched uranium (HEU)5 down to enrichments that are suitable for use in the Tennessee Valley Authority’s (TVA’s) power-producing reactors. DOE has significant quantities of aluminum-clad fuels and uranium-aluminum alloy fuels that could be reprocessed in H-Canyon, including fuels from domestic and foreign research reactors. Unreprocessed spent fuels from 5   In enriched uranium the proportion of U-235 has been increased relative to that in naturally occurring uranium, usually for use in weapons or nuclear reactors.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program research reactors present a challenge for disposal because of their relatively high uranium-235 enrichment (NRC, 1998). It could also be used to stabilize and store plutonium pending final disposition, as well as to package and ship materials for disposal, e.g., to the Yucca Mountain repository if licensed and constructed, the Nevada Test Site, and WIPP. According to the SRS Performance Management Plan, H-Canyon will complete its reprocessing mission and safe shutdown will begin in 2015 (SRS, 2002). Shutdown will be completed and deactivation will begin in 2016. This is only a few years after DOE’s most optimistic estimate of when the Yucca Mountain repository might open (2010) and some 20 years before EM expects to complete its accelerated cleanup. It seems likely that spent fuels that do not meet Yucca Mountain acceptance criteria will be identified during these 20 years. H-Canyon would have a unique capability to reprocess or otherwise treat these materials. Hanford T-Plant The T-Plant was built in 1943 to extract plutonium from uraniuim-238 targets that were bombarded by neutrons in the Hanford production reactors. The plant was shut down as an extraction facility in 1956 and was converted to a decontamination facility for processing and packaging radioactive and hazardous solid waste. The plant was designed for remote operation. It offers large, shielded, operating areas equipped with an overhead crane. The plant provides a unique capability for handling very large, highly contaminated objects, especially transuranic wastes that require remote handling (RH-TRU). Currently, Hanford is using T-Plant to characterize waste by sampling and radiography, to size-reduce and decontaminate equipment, and to treat waste primarily by macroencapsulation. According to Hanford’s final Environmental Impact Statement (EIS) for its solid waste program, T-Plant will be used to store RH-TRU, including K-Basin sludges (ROO, 2004). There are continuing needs and opportunities to use T-Plant for characterizing and treating both on- and off-site wastes that require remote handling. FACILITIES FOR IMPROVEMENT OR EXPANDED USE In initiating this study, EM asked the committee to look for opportunities for upgrading or expanding the use of currently existing facilities. While EM and the committee realize that effort and cost to upgrade or expand the capabilities of existing facilities are appreciable, improving existing facilities is likely to offer advantages for accelerated cleanup versus the cost and time required to build new facilities and eventually decommis-

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program sion them. Table 3.2 summarizes the match-up between wastes that EM will need to treat and these facilities. INEEL Calciner The fluidized bed calciner at INEEL is an existing facility that has potential extended use in treating the approximately one million gallons of sodium-bearing acidic waste (SBW) from reprocessing naval nuclear reactor fuel at that site, as well as a wide variety of other liquid wastes and slurries. Fluidized bed technology has been used in numerous applications for nuclear materials processing, including purifying uranium ore, producing uranium hexafluoride (UF6) and uranium dioxide (UO2) at Oak Ridge, treating power reactor resin wastes at a commercial facility at Erwin, Tennessee, and reprocessing navy fuel by separating zirconium from fission products on a pilot scale. The INEEL calciner was placed in standby condition in June 2000 due to lack of a Resource Conservation and Recovery Act (RCRA) permit and is scheduled for decommissioning (Holmes, 2004). INEEL has considered both direct calcination and steam reforming (see the following section on technology investments) for producing a dry waste from its SBW and has identified no significant gaps for using these technologies (Holmes, 2004). The existing INEEL calciner, upgraded with “maximum available control technology” (MACT) for controlling emissions to the atmosphere as required for a RCRA permit or modified for steam reforming, can provide either of these capabilities. Including other options such as direct evaporation and vitrification, very early engineering estimates of the facility cost for treating the SBW range from $200 million to $700 million (Holmes, 2004). Costs of restarting the calciner would likely be in the middle or lower portion of this range. Time and costs for safety reviews and permitting would be substantial. Because in addition to SBW, the INEEL calciner could treat a variety of other problematic wastes and yield a stable product for disposal, the committee believes that it can provide a treatment capability that will benefit EM throughout the remainder of the accelerated cleanup program. INEEL Advanced Mixed Waste Treatment Facility The AMWTF is designed, and currently being tested, for characterizing and treating approximately 65,000 m3 of stored, mixed CH-TRU waste for shipment to the WIPP. The AMWTF is unique in the DOE complex for handling large amounts of mixed wastes. It is potentially also suitable for mixed RH-TRU and mixed low-level waste (LLW). At the time of the

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program committee’s visit in March 2004, the facility was undergoing a final series of tests before beginning operation. The AMWTF was designed to have a high-throughput capacity and the ability to compact 55-gallon drums of waste. Many of its operations are automated. With appropriately placed shielding and some modification, the AMWTF might be able to characterize and treat RH-TRU. In addition, there is no technical reason that the facility could not be used to characterize and treat mixed LLW—although the AMWTF cannot replace the TSCA incinerator as a means of destroying organics or provide such substantial volume reductions as incineration. Hanford and SRS Vitrification Facilities Technology referred to as “can-in canister” (CIC) was developed by DOE in the late 1990s as an option for disposing of a portion of DOE’s excess plutonium (Gray et al., 1999). The concept included stacking plutonium-ceramic “hockey pucks” in slender stainless steel cylinders (“cans”) and mounting the cans onto a rack, which could be placed in an empty canister designed for disposal of vitrified high-level waste. Molten vitreous HLW poured into the canister would encapsulate the cans, and the filled canister would eventually be disposed in a geologic repository, e.g., Yucca Mountain if licensed and constructed. The concept was developed for the Defense Waste Processing Facility (DWPF) at SRS, and it was demonstrated in nonradioactive tests. The CIC approach was canceled in 2002 because of the estimated cost of a new facility for making the plutonium-ceramic pucks (Siskin, 2002). The DWPF and the Waste Treatment Plant (WTP), which is under construction at Hanford, could provide CIC capability for relatively small-volume problematic or orphan wastes, especially those that are highly radioactive (such as the Sr-90 and Cs-137 capsules stored at Hanford) or that contain fissile materials. One such fissile material is the U-233 stored at Oak Ridge. Currently Oak Ridge has about one metric ton of separated U-233 (Rushton and Forsberg, 2001). Based on the previous plan for disposing of plutonium, this amount of U-233 could be disposed in about 40 DWPF canisters of HLW glass (Gray, 1999). Given the large number and variety of enriched-uranium research reactor fuels, it is likely that some will not meet Yucca Mountain acceptance criteria for direct disposal. The CIC approach could provide a disposal route for these fuels. Current Monitoring Wells Buried wastes and subsurface contamination have been monitored throughout the operation of DOE sites by the use of wells drilled in selected

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program locations to provide samples of the groundwater. Many of these wells are being plugged (usually by grouting) and abandoned in connection with facility closures or the capping of waste disposal areas. Nevertheless, the need to monitor and treat groundwater plumes will continue for an extended period of time. The committee therefore includes currently existing groundwater-monitoring wells among facilities that are essential to EM’s characterization capabilities. The committee observed that the DOE and contractor staff responsible for decommissioning and capping are different from those with long-term site responsibility, so that it is not clear whether plugging and abandoning existing wells is being weighed against future monitoring needs. Because capping is intended to provide a low-permeability barrier against surface water infiltration, drilling new wells through the caps is a poor technical option—yet a decision to remove a monitoring well from such a location forecloses essential characterization capability. The need to continue long-term monitoring of buried wastes and contaminated media is discussed in Chapter 4. NEAR-TERM TECHNOLOGY INVESTMENTS This section addresses the portion of the committee’s statement of task that requests recommendations about technology investments that EM should make to enhance its characterization and treatment capabilities significantly. In reviewing technologies for possible investment, the committee selected four that are directly relevant to EM’s larger characterization and treatment challenges and that are well enough developed that additional EM support should lead to near-term payoffs. Recommendation: EM should continue developing and deploying new or improved technologies that address limitations in current characterization and treatment capabilities. The committee recommends investments in steam reforming, improved high-level waste vitrification, “no-consequence” TRU shipping containers, and state-of-the-art sensors for environmental monitoring. Steam reforming is a commercially developed technology that can potentially treat a wide variety of orphan wastes. High-level waste vitrification is EM’s single most expensive waste treatment process. Incremental technology improvements can produce large schedule and cost advantages. The “no consequence” container is a nearly developed technology that can greatly simplify characterization and reduce re-

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program packaging of flammable-gas-generating-TRU wastes. New sensor technology can be rapidly deployed to reduce costs and increase the knowledge gained in environmental monitoring. Monitoring systems at EM closure sites have been estimated to be some 25 years behind the state-of-art (INEEL, 2003). Steam Reforming Steam reforming is a fluidized bed technology that has great potential for treating a wide variety of wastes, slurries, and sludges—including low-activity tank waste at Hanford, sodium bearing waste at INEEL, and many of the potential orphan wastes listed at the beginning of this chapter. In a typical steam reforming process, superheated steam along with the material to be treated and co-reactants are introduced into a fluidized bed reactor where water evaporates, organic materials are destroyed, and the waste constituents are converted to a granular, leach-resistant solid. Steam reforming is in commercial use at Erwin, Tennessee, for treatment and destruction of radioactively contaminated ion exchange resins, oils, and solvents from commercial nuclear power plants. In the steam reformer, superheated steam is directed through a bed of refractory particles, which are partially suspended by the steam so that collectively they behave like a fluid. The fluidized particles provide a large surface area to promote heat transfer and chemical reactions. In addition, the particles may have a chemical composition or coating that catalyzes the reactions. The process does not require elevated pressure and typically operates at 600-750°C, which is well below the temperature required for incineration or vitrification. The relatively lower temperatures reduce problems associated with equipment corrosion and radionuclide volatility. Chemical conditions in the reactor can be controlled to enable a variety of reactions. RCRA and TSCA organics can be converted to water and carbon dioxide by a combination of the steam and oxidizers. Carbon- and iron-based reductants can convert nitrates and nitrites directly to nitrogen (Cowan et al., 2004). Clay or other inorganic materials can be added to convert radionuclides and bulk waste constituents such as sodium, potassium, sulfate, chloride, phosphates, and nonvolatile heavy metals to a stable ceramic form for disposal. In tests with radioactive materials, steam reforming has produced a waste form that indicated a good ability to stabilize cesium and technetium (Jantzen, 2004). These short- and long-term hazardous radionuclides are volatile in conventional waste vitrification processes and are readily leached from grouts. The most important near-term potential application is for providing supplemental processing capacity for the low-activity waste (LAW) stream from the

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program Hanford WTP. Waste compositions are expected to change significantly as wastes from different tanks or blends of tanks are fed to the WTP. Some additional process development and chemistry studies will likely be required to optimize the operating conditions for these various waste compositions. As noted in the previous discussion of the INEEL calciner, converting that unit to a steam reformer for treating sodium-bearing waste appears straightforward, based on the committee’s limited fact finding. The technology has high potential for application to other waste types where radioactively contaminated liquids are to be treated—for example liquid phases from decontamination operations or from groundwater-pumping operations. Wastes that may contain materials such as mercury and acidic gases pose technical issues that also need to be addressed. High-Level Waste Vitrification Treating HLW is the most expensive, long-term component of the EM cleanup, amounting to over one-third of the total life-cycle cost of the program (DOE, 2000b). The DWPF has been vitrifying high-level tank sludges at SRS since March 1996. The glass melter has been replaced once and more than 1.4 million gallons of waste have been vitrified. In May 2003, a change in the composition of the frit material used to form the glass allowed a 25 percent increase in waste loading, i.e., the amount of waste that can be incorporated into a given quantity of the glass product (Occhipinti, 2004). Hanford’s WTP is scheduled to be in operation by 2011 after its $5.7 billion construction is completed. Technology investments that lead to increasing the waste loading or production rate of vitrified high-level tank waste at SRS and Hanford are likely to provide EM with opportunities for large cost and schedule reductions. In addition to opportunities for incremental technology improvements while the DWPF is operating, such as the improved glass-forming frit, there are opportunities to deploy major new technologies each time a melter is replaced—about every five years. Lessons learned at the DWPF and new commercial technologies can be deployed in the WTP in the early phases of construction. The committee found two broad areas for technology investment for EM to improve HLW vitrification: continued development of frit and glass melting chemistry, and new approaches for putting energy into the melters. Frit Development. Waste vitrification involves trade-offs among waste loading in the glass, viscosity of the melt (so that it is pourable), and quality (durability and homogeneity) of the product glass (NRC, 1999a). Simply

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program increasing the melt temperature, which would improve all three, is generally not possible due to melter corrosion and radionuclide volatility. The only other option is to tailor the glass-forming frit composition closely to the waste composition to improve the match-up among the glass-forming chemicals and the waste components. SRS has increased its waste loading, but at the expense of throughput (pounds of waste vitrified per hour), pressure, and pour stream instabilities. Hanford has a frit composition for the initial waste feed but is challenged by a much wider range of waste compositions than SRS. Therefore the committee believes that continued investments in frit and glass chemistry provide an important opportunity for enhanced vitrification capability. Microwave Heating. Microwave technologies may provide a straightforward means of delivering additional energy to SRS and Hanford melters. Small transmitters could be installed at strategic locations around the melter, with essentially all electronic components outside the melter cell to allow hands-on maintenance. At SRS, the higher waste loading has led to pour stream instabilities, which might be remedied by heating the bellows around the pour spout (Occhipinti, 2004). The higher loading can also lead to precipitation of metals from the waste into the relatively cold area near the bottom of the melter. Accumulations in this area can short-circuit the electrodes that power the melter. Using microwave energy to heat this area might help keep the metals dissolved in the molten glass and improve the overall homogeneity of the product. Additional development will be needed to assess this approach. Unlike the SRS design, the Hanford WTP does not include an evaporator to remove excess water from the waste slurry entering the melter, but rather relies on heat from the melter itself. This raises issues concerning heat transfer through the “cold cap” of unmelted waste and frit that floats between the molten glass in the melter and the incoming aqueous slurry. Microwave heating may be an effective means to evaporate excess water without resorting to air “bubblers,” which are inserted into the molten glass and pass air through the melt to disrupt the cold cap. Bubblers inserted into the melt raise issues that include changes in glass chemistry, corrosion, and radionuclide volatilization. No-Consequence Container For shipping TRU wastes to WIPP, there has long been concern over whether a flammable gas mixture might arise within the shipping cask due to radiolysis or other reactions in the waste and result in deflagration with sufficient energy to breach the containment. The U.S. Nuclear Regulatory

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program Commission (USNRC), which licenses the shipping casks (referred to as TRUPACT-II casks), dealt with the flammable gas issue by requiring that hydrogen and other flammable gases comprise less than 5 percent by volume of the total gas inventory in any confined space within the cask, e.g., a drum or bag within a drum (NRC, 2001a). This requirement caused severe problems at sites, including the need to sort and rupture plastic bags within the waste, and to repackage waste to meet per-drum limits on radioactive materials. There was also considerable work by EM to reassess the shipping requirements derived from the USNRC limit. Revision 19 of the Safety Analysis Report for Packaging for the TRUPACT-II reduced, but did not eliminate, the concern about hydrogen generation (Curl et al., 2002). WIPP representatives believe that even with additional revisions under the “Quick to WIPP” concept (hydrogen removal from the containers before shipment and a shorter shipping period to reduce time available for gas generation), some few thousand drums will continue to face shipping restrictions due to flammable gas concerns. Currently, the only available alternative is repackaging the contents of a problematic drum, with the repacking ratio expected to be 10 to 20 new drums for each problematic one (Italiano, 2004). The concept of a robust “no-consequence container” that could withstand a worst-case hydrogen deflagration is an appealing solution to the problem. A problematic drum would simply be placed in the no-consequence container, which could then be loaded into the TRUPACT-II and shipped. Since 2001 DOE has funded testing of the Arrow-Pak design of a no-consequence container.6 Based on earlier EPA-approved “no-migration” macroencapsulation containers, the new container has an increased wall thickness. Tests showed that the Arrow-Pak container would conservatively withstand a worst-case deflagration. While the Arrow-Pak has demonstrated the no-consequence concept, there are technical issues remaining. These include determining the best container design and construction materials based on cost and compatibility with WIPP waste handling and disposal requirements. Currently, WIPP managers and operators are working on better ways to evaluate the containers and the limits on their contents and to prepare for implementation. However, the committee cautions against setting the performance requirements higher than required to meet WIPP’s permit requirements, and thus increasing cost unnecessarily. Continued EM investment in the no-consequence container can resolve the problem of shipping flammable-gas-generating TRU wastes to WIPP. 6   Arrow-Pak is manufactured by BOH Environmental, LLC.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program Sensors for Environmental Monitoring An improved capability for environmental monotoring would strengthen EM’s plans to leave waste and contaminated media at DOE sites and transition the responsibility for their long-term management to DOE’s new office of Legacy Management (see Chapter 4). Sensors and their associated technologies for environmental monitoring are well developed and continue to be improved. Previous studies of science and technology needs found opportunities for new sensor technology in most aspects of EM’s work (NRC, 2001b, 2002b, 2003a). INEEL recently developed a science and technology roadmap, which listed sensors and sensor systems as key capabilities for long-term site stewardship (INEEL, 2003). Similar needs were raised to the committee in its fact-finding visits (Provencher, 2004). Environmental monitoring at EM sites currently relies heavily on sampling and analyzing groundwater.7 This practice provides individual point measurements that are used to monitor contaminant source areas, evaluate the effectiveness of hydrologic barriers and treatment walls, identify changes in site conditions, and characterize subsurface and waste heterogeneity. Modern, noninvasive geophysical sensor techniques, such as electromagnetic and electrical methods, seismic methods, and ground-penetrating radar can substantially improve current practices and lead to cost-effective means to implement long-term monitoring after site closure. Geophysical sensor technology can provide continuous measurements in time and space that could fill knowledge gaps between monitoring wells; enable rapid mapping of large areas, including soundings to depth; deliver information on waste characteristics as well as subsurface hydrogeology; and be developed into long-term monitoring networks (EPA, 2000). An example of new technology is real time, long-term monitoring using geophysical sensors developed at INEEL. This technology is currently being employed at a waste storage area located at the Ruby Gulch Superfund site in South Dakota (Versteeg et al., 2004). At this site contaminant breakthrough has not been controlled, so there is not yet a quantitative link between the response of the geophysical sensors and contaminant concentration. EM investment in a systematic geophysics program would benefit all of the legacy sites by closing current knowledge gaps that are barriers to implementing modern sensor technology. These gaps include uncertainties in how hydrostratigraphy (i.e., subsurface formations that influence groundwater movement) affects measurement signals, the relationship between measurement scale and process scale, and the long-term robustness of in 7   Costs for groundwater analyses across the DOE complex have been estimated at around $300 million per year (INEEL, 2003).

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program situ geophysical sensors. The types of tests needed to extend current knowledge include evaluation of signal response in sites of varying hydrostratigraphy to better understand measurement sensitivity and noise; comparison of different geophysical techniques to see how signals can be enhanced, which methods work better for different problems, and what synergy can be gained by combining two or more complementary methods; controlled experiments, e.g., Daily et al., 2004, to validate geophysical measurements and make these sensors more widely applicable; and in situ monitoring experiments, e.g., Versteeg et al., 2004, to investigate sensor signal quality and reliability over time. These tests could be conducted as part of ongoing site characterization and remediation projects, supplemented with additional sites to cover a range of settings. For example, nonintrusive geophysical characterization was part of the Pit 9 investigation at INEEL (see Sidebar 3.1). Subsequent excavations conducted to retrieve Pit 9 waste provided actual sampling data to compare with and help verify the geophysical measurements.

OCR for page 28
Improving the Characterization and Treatment of Radioactive Wastes for the Department of Energy’s Accelerated Site Cleanup Program Sidebar 3.1 PIT 9 AT INEEL INEEL’s Radioactive Waste Management Complex (RWMC) was established in 1952 for disposal of solid low-level radioactive waste generated onsite. Wastes from other DOE sites were also buried there, including transuranic waste from Rocky Flats. Wastes were disposed in pits, trenches, soil vaults, an above-ground disposal pad, a transuranic storage area release site, and three septic tanks. One of the trenches contained in the complex is Pit 9, a 1-acre site that was used primarily to dispose of wastes from Rocky Flats between 1967 and 1969. DOE estimates that Pit 9 contains about 7,100 cubic meters (250,000 cubic feet) of sludge and solids contaminated with plutonium and americium. At the time of the committee’s visit, March 2004, INEEL had successfully completed a pilot-scale excavation of portions of Pit 9 (Figure 3.2). To ensure safety, a containment structure was erected over the area to be excavated and the excavation and waste retrievals were done with remotely operated equipment. This procedure, referred to as the Glovebox Excavator Method (GEM) allowed the use of both non-invasive geophysical measurements and actual sampling of the excavated material for characterizing the waste. FIGURE 3.2 The glovebox excavator method (GEM) was a pilot project for retrieving waste at INEEL. While successful, it also demonstrated the cost and difficulty of retrieving some types of wastes at EM sites. Photo courtesy of INEEL.