3
Research Needs and Opportunities

In this chapter the committee offers its views and recommendations on research opportunities for the Environmental Management Science Program (EMSP) to address challenges in managing transuranic and mixed low-level wastes. Based on its discussion of the issues that frame these challenges in Chapter 2 and its visits to Department of Energy (DOE) sites (Appendix E), the committee concluded that the most significant needs and opportunities lie in

  • waste characterization and how waste characteristics may change with time,

  • location and retrieval of buried wastes,

  • waste treatment, and

  • long-term monitoring.

The committee has been selective in its recommendations to encourage the EMSP to concentrate its limited funding in a few specific areas where the committee believes research can lead to the most significant improvements. Some technology areas, although clearly important, were excluded because in the committee’s view the science and technology base already exists to address them on a relatively short time scale—less than five years.

Each recommendation is illustrated with a brief discussion of the current baseline technologies and technology gaps,1 challenges for next-generation technologies, and research opportunities. Some examples are included, but these should not be construed as the only opportunities that the research community might perceive. Although the selection of examples was influenced to some degree by the back-

1  

Baseline technologies are those that are being used at DOE sites or that are commercially available and included in DOE’s site cleanup plans.



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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes 3 Research Needs and Opportunities In this chapter the committee offers its views and recommendations on research opportunities for the Environmental Management Science Program (EMSP) to address challenges in managing transuranic and mixed low-level wastes. Based on its discussion of the issues that frame these challenges in Chapter 2 and its visits to Department of Energy (DOE) sites (Appendix E), the committee concluded that the most significant needs and opportunities lie in waste characterization and how waste characteristics may change with time, location and retrieval of buried wastes, waste treatment, and long-term monitoring. The committee has been selective in its recommendations to encourage the EMSP to concentrate its limited funding in a few specific areas where the committee believes research can lead to the most significant improvements. Some technology areas, although clearly important, were excluded because in the committee’s view the science and technology base already exists to address them on a relatively short time scale—less than five years. Each recommendation is illustrated with a brief discussion of the current baseline technologies and technology gaps,1 challenges for next-generation technologies, and research opportunities. Some examples are included, but these should not be construed as the only opportunities that the research community might perceive. Although the selection of examples was influenced to some degree by the back- 1   Baseline technologies are those that are being used at DOE sites or that are commercially available and included in DOE’s site cleanup plans.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes grounds and expertise of committee members, the research recommendations were arrived at by a consensus process that considered input to the committee, the needs of the end user,2 the existence of critical knowledge gaps, the potential for future cost and schedule savings, and the possibility of achieving technology breakthroughs. Characterization The EMSP should support research to improve the efficiency of characterizing DOE’s TRU and mixed waste inventory. This should include research toward developing faster and more sensitive characterization and analysis tools to reduce costs and accelerate throughput. It should also include research to develop a fuller understanding of how waste characteristics may change with time (chemical, biological, radiological, and physical processes) to aid in decision making about disposition paths and to simplify the demonstration of regulatory compliance. Waste characterization is defined as “the determination of the physical, chemical and radiological properties of the waste to establish the need for further adjustment, treatment, conditioning, or its suitability for further handling, processing, storage or disposal” (IAEA, 1993, p. 52). Current regulations require detailed characterization of waste for shipping and disposal, especially for transuranic (TRU) wastes destined for the Waste Isolation Pilot Plant (WIPP) as described in Sidebar 3.1. Characterization is also necessary to determine treatment options (see “Treatment” section later in this chapter). Information needed for waste characterization generally includes the identity and amount of radionuclides, liquids, volatile organic compounds (VOCs), polychlorinated biphenyls (PCBs), mercury, other metals regulated by the Environmental Protection Agency (EPA), and the rate of hydrogen generation. Such characterization increases the time and cost of preparing waste for offsite shipment as well as the potential for worker exposure to radiation. Most transuranic and mixed wastes (TM wastes) are packaged in 55-gallon drums—hundreds of thousands of them as noted in Chapter 2. In addition, the Transuranic and Mixed Waste Focus Area (TMFA)3 esti- 2   End users are those who will use a given method or technology to accomplish a task. They are usually contractor personnel at DOE sites. 3   During most of the time this study was in progress, the TMFA, a part of the DOE Environmental Management Office of Science and Technology (EM-OST), was responsible for ensuring that technologies were available to manage this waste. Organizational changes in EM that occurred as this report was being finalized are described in Appendix A.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes mates that there are at least 12,500 large containers at five DOE sites that present special challenges for characterization because of their size. The sites cannot be closed without dispositioning these containers.4 One type of characterization is physical—an assembly-line style of nondestructive examination (NDE) and assay (NDA) to identify the contents of an unopened drum (see Figure 3.1). Is it sludge or debris, plastic or metal, solid or liquid? Has it been sealed, stabilized or treated properly? NDE methods also permit assessment of the heterogeneity of the drum contents and provide the means to screen for prohibited items (e.g., gas cylinders). A second type of characterization determines the chemical and radiological composition of the waste. Does the composition of the waste meet transportation and regulatory requirements for disposal? If not, how should the waste be treated? While these types of characterization provide snapshots of the waste, another consideration is that waste characteristics will change with time through radiological, chemical, and biological processes. The potential for gas generation, particularly hydrogen, is of concern. Understanding how the characteristics of containerized waste may change with time is especially important for its continued storage, shipping, and eventual disposal. Baseline Technologies and Technology Gaps For heterogeneous debris (see Chapter 2), the baseline characterization methodology for contact-handled TRU (CH-TRU) wastes comprises a number of steps, including radiography and opening the container for visual inspection to validate process knowledge (see Sidebar 3.1). Swipes or sampling and analysis are required to obtain contaminant information. If NDA is required, waste must be repackaged into containers sized for the available instrumentation. For homogeneous solids, a statistical number of drums require coring and analysis (St. Michel and Lott, 2002). For TRU wastes that must be handled remotely because they also contain substantial amounts of gamma-emitting isotopes (RH-TRU), the current baseline requires the same characterization steps as CH-TRU. DOE is seeking to change this requirement because of the difficulty of making such detailed characterization in remotely operated facilities and the increased risks of worker exposure (NRC, 2002b). From a cost-saving standpoint, DOE would like to characterize RH-TRU based on process knowledge only. More realistically, however, DOE believes that 4   Several sites also have buried wastes or contaminated media. These materials may not be containerized or their containers may be breached. They are discussed in the section “Waste Retrieval.”

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes SIDEBAR 3.1 BASELINE CHARACTERIZATION STEPS FOR TRU WASTE The characterization steps described here were developed for contact-handled TRU waste and have been applied to TRU mixed waste. The methods, equipment, procedures, determination of uncertainty, and other protocols used at DOE sites to perform these characterizations were approved by the DOE Carlsbad Field Office, New Mexico Environment Department, and EPA. The major steps depicted are as follows: Determination of the Origin and Composition of the Waste by Acceptable Knowledge (AK). Acceptable knowledge of the origin and composition of the waste must be documented to provide evidence that the waste has a defense origin (by the terms of the Land Withdrawal Act, only defense-related TRU waste may legally be sent to WIPP) and to provide characterization information on the waste constituents. The DOE Carlsbad Area Office and the EPA use acceptable knowledge documentation to certify each waste stream (i.e., waste-generating process). TRU waste sent to WIPP must come from a certified waste stream. Real-Time Radiography (RTR). Radiography using X-rays is performed on all waste containers to look for items such as pressurized cans or free-standing liquids that are prohibited from being transported

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes under U.S. Department of Transportation (DOT) regulations. If any of these items are present in a waste container, the prohibited materials are removed and the contents repackaged. This radiographic examination is also used to confirm the acceptable knowledge characterization information. Radioassay and Determination of Fissile Isotope Content. The number of curies of each transuranic isotope is determined by radioassay (e.g., gamma scans) to a specified precision and accuracy. The fissile isotope content is assessed using nondestructive assay (NDA) methods, such as passive-active neutron systems. This information is used to meet the U.S. Nuclear Regulatory Commission (USNRC) requirement restricting the amount (several hundred grams) per container of each fissile species to ensure criticality safety. Headspace Gas (HSG). Headspace gas sampling is used to check all waste containers for flammable gases (specifically, volatile organic compounds, hydrogen, and methane). This procedure, including resealing drums that have been vented and waiting specified times until gases regain equilibrium (drum aging to equilibrium criteria [DAC]), has been proposed as a means of ensuring conformity with the DOT (e.g., 40 CFR 173 and 40 CFR 177) and USNRC (e.g., 10 CFR 71) regulations that address the transport of flammable and/or gas-generating substances with radioactive materials. DOE proposed the HSG sampling procedure in its application to the USNRC for a licensing certificate on the transportation package (named the Transuranic Package Transporter, or TRUPACT-II) that is loaded with waste containers for transport by truck to WIPP. Visual Examination (VE). A visual examination is performed on a fraction of the waste containers by placing the waste contents into a glovebox to verify the AK and RTR information. DOE proposed that 2 percent of the initial population of containers of each waste stream be examined visually, and if these evaluations resulted in few miscertifications, then the percentage of subsequent waste containers to undergo visual examination would be reduced. In October 1999, New Mexico in its Resource Conservation and Recovery Act (RCRA) Permit stipulated the initial fraction of containers to undergo visual examination to be 11 percent. Coring and Assay of Homogeneous Waste for RCRA Constituents. Most of the TRU waste is heterogeneous in nature and requires no further characterization beyond acceptable knowledge to satisfy the regulatory requirements of RCRA. For homogeneous waste, a fraction of the waste containers (e.g., 55-gallon drums or standard waste boxes) are cored to extract representative samples that are analyzed for constituents (e.g., volatile and semivolatile organic compounds, toxic metals, other hazardous chemicals) regulated by RCRA. SOURCES: NRC, 2002b, and DOE.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes FIGURE 3.1 X-ray examination of a waste drum allows operators to determine if it contains prohibited items that must be removed before shipping the waste to a disposal site. Such visual inspection of a drum, at various positions and angles, may take several hours. Source: DOE Carlsbad Field Office. some additional characterization will be required to validate the process knowledge (St. Michel and Lott, 2002). DOE would like to simplify the characterization baseline for TRU wastes in order to increase the rate of shipping these wastes to WIPP. The main approach is to seek changes in current transportation and disposal requirements, for example, to reduce the many detailed characterization steps illustrated in Sidebar 3.1. In addition, the TMFA was developing improved characterization technologies. An example of state-of-the-art TMFA technology is the assay system being developed at the Idaho National Engineering and Environmental Laboratory (INEEL [see Sidebar 3.2]). The committee believes that a gap exists in the lack of technologies available to automate sampling and characterization in a more reliable fashion. The problem becomes particularly complex for certain classes of wastes for which a single sample may not be representative (e.g., debris waste). Other technology needs include methods to nondestructively assay for radiological and nonradiological constituents (e.g., Resource Conservation and Recovery Act [RCRA] metals, low levels of TRU isotopes) and improved statistical methods to support approaches such as compositing.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes SIDEBAR 3.2 STATE-OF-THE-ART TECHNOLOGIES BEING DEVELOPED BY THE TMFA The Prompt Gamma Coincidence technique is a relatively new, nondestructive approach to measure isotopic ratios of plutonium and uranium. The technique overcomes the limitation of other approaches by measuring radiation associated with the fission process. When elements fission, a pair of fragments is produced. These fragments contain the same number of protons as the original isotope, emit neutrons and gamma rays, are in an excited state, and are short-lived. The system uses coincidence measurement of gamma rays from the fission fragments. These gamma rays are distinct and are used to identify the fragment elements. Once the fragment elements are identified, the original, fissioning isotope can be confirmed. The system is a breakthrough technology because of its ability to distinguish among isotopes. This is important to determine the presence of weapon components and also to nondestructively qualify transuranic wastes and materials. SOURCE: St. Michel and Lott, 2002. Chemical and physical assays provide only a snapshot of the waste. An improved understanding of reactions that can change the waste characteristics with time is fundamental to making informed decisions on storing, shipping, and disposal. The Strategic Laboratory Council’s analysis of DOE’s environmental quality research and development portfolio found that the primary gaps in research in TRU and mixed waste disposal (DOE, 2000c, p. 28) involve research to reduce uncertainties in waste and system performance driving conservatism in characterization and transportation requirements for TRU wastes. Improved performance knowledge may support reduction of characterization requirements, modified backfill requirements, and expansion of acceptable waste categories for WIPP. The current state of the art is that simple drum-by-drum methods are employed to empirically derive the thermodynamic and kinetic parameters for changes that occur in the waste as a function of broad waste categories. These methods often form the basis for assessment of the compliance of wastes with the waste acceptance criteria (e.g., gas generation rates, stability) for the pertinent disposal site. There is a gap in basic knowledge of waste behavior, both in mechanistic understanding and in understanding other types of chemical behavior that may impact waste composition or physical integrity. These include the chemical form (speciation) of contaminants, metal-catalyzed redox reactions of waste constituents, sorption to the waste matrix, and effects of pH and ionic strength on the waste matrix. One example of

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes unanticipated chemical reactivity is the recent demonstration that hydrogen can be generated by reduction of water by plutonium dioxide in oxygen-lean environments (Haschke et al., 2000). This serves as a pathway for hydrogen generation in addition to radiolysis, and has potential implications for how the plutonium might migrate from the waste. There are gaps in understanding microbial effects in waste. Little has been done regarding the microbiology of TM wastes. Conversely, much has been done toward characterizing and exploiting the microbiota of more traditional hazardous wastes, resulting in significant cost savings over traditional disposal and remediation technologies (Harkness, 2000; Steffan et al., 2000). Microbial effects may be important in organic materials stored for long periods or in mixed waste landfills. Knowledge gaps include (1) what microbes are present in mixed and TRU waste and at what abundance; (2) what the activities of the microbes are and how their activity affects the waste material; and (3) how these microbes can be exploited to improve the treatment or disposal of TM wastes (Brockman, 1995; Newman and Banfield, 2002; Reysenbach and Shock, 2002). In recent years, significant strides have been made toward developing methods and tools for analyzing microorganisms in environmental samples. Application of these techniques to TM wastes should lead to a better understanding of biogeochemical reactions occurring in the waste materials. This information will be important for assessing treatment options or monitoring the progress of biological treatment technologies applied to the material (Brockman, 1995; Newman and Banfield, 2002). Many of these methods and tools should be directly applicable for studying and characterizing the microbiology of TM wastes. For example, some of the more popular modern molecular biology-based techniques currently being used for environmental analysis include density gradient gel electrophoresis (DGGE [Muyzer, 1999]), terminal restriction fragment length polymorphism analysis (T-RFLP [Takai et al., 2001]), and whole or partial genome sequencing, but other equally useful methods clearly exist. Other studies have demonstrated that microbial DNA can be extracted from complex environmental samples, such as soil, and cloned to assess the genetic and functional diversity of uncultured organisms (Rondon et al., 2000). Still other technologies rely on identifying chemical signatures to confirm the presence of microorganisms or evaluate their activities in environmental samples (Nichols and McMeekin, 2002; Rütter et al., 2002; Zhang, 2002). Likewise, measuring the presence and abundance of specific biomarkers (e.g., peptides) can provide an understanding of microbial activities occurring in complex matrices (Elias et al., 1999). The combination of traditional culturing methods and modern molecular or chemical ana-

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes lytical techniques provides powerful tools for evaluating microbial populations in complex environments. Challenges for Next-Generation Characterization Technologies From its fact-finding visits to DOE sites and committee members’ expertise, the committee believes that the greatest challenges for the next generation of waste characterization technologies will be to provide the following: more rapid, automated, NDA and NDE methods; more sensitive NDA and NDE technologies for larger containers and hard-to-detect chemical and radioactive contaminants; and improved methods, based on fundamental modeling, to derive present and future waste characteristics from a limited number of sampling parameters. As uranium and transuranic elements such as plutonium decay, alpha particles are emitted. Associated with these alpha particles are mostly low-energy, nonpenetrating gamma rays and neutrons. Instruments for safeguarding nuclear materials rely on detecting these types of radiation. However, these measurements have drawbacks for waste assays because the radiation is subject to self-attenuation and shielding by extraneous materials, especially in larger containers. The resulting energy spectra are degraded to the extent that the resolution of currently available detectors is often insufficient to identify the specific fissioning isotope. Multiple high-purity germanium detectors can be used to improve the sensitivity of gamma-ray spectroscopy (as can coincidence counting, see Sidebar 3.2), but this dramatically increases instrument expense and limits the number of stations that can be placed in service. Information about the spatial distribution of radioactivity within the containers is absent, which does not allow the detection of radiological “hot spots.” Calibrating the results of such measurements may become complex and require statistical methods with assumptions about waste homogeneity and source location, which can introduce substantial error. Neutron activation analysis identifies the chemical elements and thus can be used to search for transuranics noninvasively. It is, in fact, capable of identifying several radionuclides present that do not emit high-enough-energy photons to be readily detected using gamma-ray spectroscopy. Neutron activation analysis, however, suffers from the same turnaround, expense, calibration, and inhomogeneity problems associated with gamma-ray spectroscopy. Neutron activation analysis

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes requires a high flux of neutrons, which is expensive, difficult, and potentially hazardous to provide. Inexpensive, bulk detection of TRU radionuclides by NDA presents a challenge for next-generation technologies. DOE is presently developing new technologies for facility deactivation and decommissioning and subsurface contamination applications that are equally relevant for the characterization of containerized waste. Examples include portable “laboratory-on-a-chip” sensor technology for the quantitative identification of radionuclides and metals such as uranium, plutonium, cesium, strontium, mercury, and lead (Collins and Lin, 2001; Collins et al., 2002); the microcantilever sensor array technology for real-time characterization of the chemical, physical, and radiological content of ground water and mixed waste (Ji et al., 2000, 2001); and the micro-chemical sensor for in situ monitoring and characterization of volatile contaminants (Ho et al., 2001). Similarly, the Department of Defense (DOD) has invested heavily in the development and deployment of both contact and standoff (non-contact) detectors for chemical and biological warfare agents.5 The ultimate program goals are to develop robust, portable, real-time sensors capable of detecting agents well below incapacitating levels. The sensors are usually connected to air sample collecting or concentrating devices, although methods to analyze water and soil samples have also been developed. Chemical sensor technologies under development are based on ion mobility, surface acoustic wave (SAW), and miniature mass spectrometry. For biomolecules and organisms, sensor development includes fiber-optic waveguide, polymerase chain reaction (PCR), and DNA chip technologies. The present sensors are either chemical or biological only, but plans are to develop combined nuclear-biological-chemical sensors. Microorganisms can potentially affect the chemical composition and physical properties of both the contaminants and the waste matrix. Radiation-resistant bacteria were first discovered in the mid-1950s (Anderson et al., 1956). The best-studied of these organisms is Deinococcus radiodurans, which can withstand up to 5,000 grays of gamma radiation without significant loss of viability (Battista, 1997). The bacterium has been used as a host organism to create radiation-resistant recombinant organisms for degrading pollutants (Lange et al., 1998) and for treating wastes contaminated with heavy metals (Brim et al., 2000). Its entire genome sequence has been elucidated (White et al., 1999). Recent studies suggest that many TM waste materials may 5   For examples, see the articles in the special issue of Biosensors & Bioelectronics, Vol. 14 (2000).

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes contain viable and active microbial populations (Heitkamp, 2001). A previous National Research Council (NRC, 2001d) report summarized studies indicating that gas generation due to microbial degradation of cellulosic waste within WIPP will be insignificant, but it recommended monitoring. The types of microbes present in TM wastes and the effect of microbes and microbial activity on the waste materials have largely been unstudied. These microbes could have profound effects on the ultimate fate of waste materials. The microorganisms may play a positive role by reducing the concentration of toxic organic constituents in the waste. They may play deleterious roles by increasing hydrogen or methane production, enhancing corrosion, or converting waste components into more toxic or mobile forms. Controlling or developing microorganisms to play a positive role is a challenge for future biotechnologies. Research Opportunities Research opportunities include noninvasive standoff imaging and image recognition methods and in-drum sensors to provide faster and more sensitive technologies for waste characterization. Research to develop predictive models of how waste characteristics may change with time, including microbial effects, can reduce the need for detailed waste analysis and provide better decision-making tools for storing, shipping, and disposing of TM wastes. New Characterization Methods Research toward new, nondestructive and noninvasive, characterization methods may lead to significant savings in time and cost, and decreased risk of worker exposure. While these methods are currently employed in the form of real-time radiography for physical characterization and various gamma and neutron imaging techniques for radionuclide inventory determination, basic research could also yield significant improvements in these methods, as well as means of identifying other constituents of waste drums. For example, it may be feasible to identify and image RCRA metal contaminants by devising new techniques in which neutron irradiation of the waste would activate stable metals, yielding products that could subsequently be mapped for concentration and location. Other approaches might include using the radioisotopes present in the waste drums to image the contents of the drum. New methods might also include the use of alternative forms of energy to image constituents, ranging from the use of ultrasound to identify physical forms of waste to the use of customized imaging or

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes for homogeneous waste forms, in which the waste is incorporated into the matrix (e.g., sludges in grout or glass). These current tests may not be good predictors of susceptibility to leaching under conditions different from those specified in the protocol (see the discussion of predictive modeling). As DOE and its subcontractors seek to reduce the costs of treating MLLW by greater use of encapsulation, developing methods to ensure the long-term durability of these heterogeneous waste forms will become increasingly important. As noted earlier, there are essentially no durability data for micro- or macroencapsulated wastes. Research Opportunities There are research opportunities in areas of chemical treatments (including advanced alternatives to incineration), biological treatments, stabilization, and waste form durability. Chemical Treatment Essential to developing publicly acceptable alternatives to incineration is research to develop sensitive, reliable, and practical detection methods to track both radionuclide and hazardous chemical materials during the treatment processes. Answering the question, How much hazardous material is being released to the environment? is particularly important for public acceptance of treatment methodologies. It is also essential for controlling potential risks to workers during treatment operations. Research opportunities for treating TM wastes are in accord with opportunities reported in a recent study of the technical needs for the Deactivation and Decommissioning Focus Area (NRC, 2001b). In particular, research in the speciation of inorganic constituents in wastes may have an impact on the selection of future treatment options. The state of the art in examining metal ion speciation is much more developed for actinide constituents in wastes than for other inorganic constituents.18 Further research is needed to assess the chemical forms of other metals (e.g., oxidation state, speciation) in the presence of complex matrices and a variety of co-contaminants. More research is needed to understand the nature of the oxide-substrate interaction. With the advent of new molecular design tools associated with nanotechnology applications, a wealth of new opportunities exists to generate novel 18   See MRS Bulletin, Vol. 26, No. 9, September 2001.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes separation schemes based on the design of porous materials with chemical functionality specific to the separation tasks at hand. Research can improve methods to dissolve plutonium oxide selectively in the presence of other metals and organics or lead to methods of controlling high-activity, finely divided particulate materials. For example, the Pu-238 isotope in waste from plutonium processing at the Savannah River Site exists as very finely divided oxide powder contaminating heterogeneous wastes. Due to the wattage restrictions on waste to be packaged for WIPP, it is unclear whether this waste will meet DOT requirements. The general practice for treating mixed waste would be to destroy the organic constituents through incineration or an alternative technology. The danger of dispersal of the powder precludes most thermal treatments, however, suggesting the need for a new method for removing and stabilizing the oxide powder. This raises several interesting technical challenges, such as ensuring efficient removal of finely divided powders, controlling particle dispersion and perhaps inducing agglomeration, and avoiding the generation of additional waste streams. Hydrogen generation remains a factor in the shipment of containerized waste to WIPP. The TMFA actively sponsored work on hydrogen getters (absorbers). During a visit to the Savannah River Site, the committee heard a presentation describing significant advancements made toward the development of polymeric hydrogen getters to capture the hydrogen produced in waste drums (Duffey, 2001). These getters have proven useful for most wastes tested to date, but poisoning of the polymers—evidently by organic vapors—can occur, thereby reducing their efficiency. There are research opportunities for understanding the fundamental processes of both hydrogen production and hydrogen adsorption. Biological Treatment There are also opportunities to develop efficient and cost-effective biological treatment technologies for TM wastes, including recovered soils and sediments (see Table 2.1). Research should focus on the treatment of readily degradable organic material and the combined application of biological and physical or chemical treatment technologies. Although physical methods such as steam stripping, heating, or vacuum extraction may be the most common for separating the various waste components, biological treatment may be appropriate for some waste types. For example, sludges containing water and biologically degradable organic compounds may be amenable to biological treatment for removal of the hazardous components.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes Research opportunities include the identification of enzyme or whole-cell treatment approaches that target specific contaminants (e.g., PCBs, mercury) or broad categories of contaminants (e.g., combustible solvents, cutting oils, chlorinated hydrocarbons). Treatment technologies must be amenable to application in the environment of the containerized waste. For example, enzyme systems that function at extreme pH levels, high salinity, or under high solvent or nonaqueous conditions would be desirable. Application of advanced molecular techniques such as directed evolution (Stemmer, 1994) might help develop appropriate biocatalysts. Research directed toward identifying ways to apply the biocatalysts, such as novel immobilization matrices, is also necessary to facilitate successful use of these catalysts. Fundamental research may identify biological treatment processes that can facilitate the removal of RCRA wastes (e.g., Hg, Pb) and radioactive metals from contaminated media. Like hazardous organic chemicals, some toxic metals are susceptible to biological transformations. For example, mercuric ion (Hg2+) can undergo a range of biological transformation processes including reduction to elemental mercury, which is volatile at room temperature, or methylation, which forms the highly toxic monomethylmercury or the volatile dimethylmercury. These biotransformations have shown promise for removing mercury from wastewater (Wagner-Dobler et al., 2000). Recent research has shown that some common iron-reducing soil bacteria can solubilize plutonium hydrous oxides that bind tightly to soils (Rusin et al., 1994). Adding a chelator enhances the solubilization process. These findings suggest that biological treatment, via either bioaugmentation or biostimulation, coupled with soil washing technologies could provide a mechanism to remediate actinide-contaminated soils. Similarly the common soil microbe Microbacterium flavescens can absorb and accumulate Pu(IV) if the siderophore desferrioxamine-B is provided (John et al., 2001). Siderophores are chelators that are produced and released by many iron-utilizing bacteria in soil environments. The siderophores bind iron, and the iron-siderophore complex is captured by iron-utilizing microbes. The fact that these iron chelator compounds can also bind actinides suggests that they can be exploited to treat TM waste. Bioremediation approaches could involve either stimulating siderophore production by indigenous organisms or adding exogenous siderophore-producing organisms or siderophore-containing extracts to the waste or contaminated media. Once chelated, the soluble actinides could potentially be removed by soil washing or related methods. Research is needed to develop reliable processes to transform or remove heavy and radioactive metals from mixed waste. The research should be based on the large existing volume of research on heavy-

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes metal biotransformation and should evaluate the effects of multiple contaminants, radioactivity, and extreme environmental conditions (e.g., low or high pH, high salts, cementing agents) on metal mobilization, immobilization, accumulation, speciation, and related transformations. The research should include multidisciplinary studies combining microbiology and genetic engineering, materials handling, reactor design, and process engineering to develop cost-effective technologies for treating TM wastes. Biotechnology research opportunities include the identification and development of improved hydrogen and methane scavengers that can be added to waste drums. Potential scavengers could include efficient hydrogen- or methane-scavenging microorganisms or enzymes capable of binding or oxidizing hydrogen or methane. The enzymes could be improved by using genetic engineering and directed evolution of enzymes (Stemmer, 1994) to enhance their hydrogen- and methanescavenging efficiency. Additional research could include identification or development of improved methods for applying such organisms or enzymes to the drums. This could include development of immobilization techniques (e.g., sol gels, polyurethane) that improve activity and allow long-term survival of the biocatalyst while not exceeding the free liquid limits imposed by waste disposal facilities. This also could lead to studies to identify artificial electron donors that could be added to hydrogen and methane oxidation enzyme preparations to maintain their oxidative activity over long periods. Enzymes such as methane monooxygenase also may destroy other compounds such as carbon tetrachloride that poison some chemical hydrogen scavengers. Stabilization Retrieval of buried waste or contaminated media has generally required the use of very expensive engineering controls to ensure the safety of workers and the surrounding environment. A tremendous reduction in costs could be realized if waste were stabilized prior to or in the early stages of retrieval. Current containment methods involve either application of simple barriers or, in some cases, methods that partially stabilize the waste (e.g., grouting). Research should address new systems for stabilization. One could envision the development of smart materials that react with waste constituents to generate optimized coatings or combined chemical and biological processes that would stabilize the waste selectively by alteration of the matrix or generation of additional barrier layers. A recent paper describes a smart Portland cement that senses environmental conditions (Wen and Chung, 2001). A previous report recommended research for stabilizing or contain-

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes ing contamination in soils or ground water (NRC, 2000a). There are important distinctions, however, between technology needs associated with the containment of subsurface contaminants in a particular geological environment and the stabilization of buried waste or contaminated media to facilitate retrieval. The need to control subsurface contaminants suggests research to devise barriers that function over the time scale envisioned for long-term site stewardship, whereas stabilization of buried waste may require only interim containment until such time as the waste is emplaced in a disposal facility. A need exists for fundamental proof-of-concept investigations to determine the potential for microbial processes to stabilize buried TM waste by altering its composition. Promising biocatalysts may be obtained by applying traditional microbial selection and enrichment approaches to target waste materials or by “biomining” other radioactive waste materials to identify promising radiation-resistant degradative microbes. Genetic engineering could be applied to improve the metabolic capabilities of radiation-resistant organisms to develop improved biocatalysts for treating mixed waste (Brim et al., 2000; Lange et al., 1998). Organisms also can be developed to function in the extreme environmental conditions (e.g., high salt, extreme pH) found in some waste types. Research on microbiology should be coupled with research in chemistry, materials science, and process and reactor engineering to develop integrated systems to handle and treat difficult waste materials. Waste Form Durability The NRC study of waste forms found that the matrices (e.g., grout, glass, polymers) available to stabilize MLLW for disposal are adequate (NRC, 1999a). However, the report noted that most repository performance assessments do not take credit for waste forms because quantitative tests for their long-term durability have not been developed. The report recommended that DOE’s Office of Science and Technology (OST) support work aimed at fundamental understanding of waste form durability and suggested that EMSP evaluate and fund proposed research in this area. The committee agrees that this is a valuable area for research. Research to understand the chemical and physical processes that may leach or degrade waste forms in RCRA-compliant landfills should be combined to develop predictive models and more appropriate test procedures. As noted earlier, very little is know about the long-term durability of heterogeneous waste forms or microbiological effects on waste forms. A specific opportunity would be evaluation of the long-term stability of, and effects of biological activity on, metals immobi-

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes lized in sulfur cements and related materials. Bacteria are able to metabolize sulfur compounds in a variety of ways, including oxidation of reduced species (which can form sulfuric acid) and reduction of oxidized species, depending on the organisms present and the redox potential. Understanding how these reactions affect the leachability of RCRA metals from these new immobilization materials is needed. Long-Term Monitoring The EMSP should support research to improve long-term monitoring of stored and disposed TRU and mixed wastes. Research should emphasize remote methods that will help verify that the storage or disposal facility works as intended over the long term, provide data for improved waste isolation systems, and inform stewardship decisions. Long-term monitoring will play an important role in many of DOE’s site cleanup activities, especially in continuing stewardship of the sites (NRC, 2000c). In the context of TM waste, long-term monitoring will be important both during storage and after the waste has been emplaced in a disposal facility. The storage phase is likely to be long for some wastes, and it will be necessary to ascertain that the containers maintain their integrity and that internal processes in the containers are as predicted (see the section on “Characterization”). Prudence requires that wastes disposed in a RCRA-type landfill or in a repository such as WIPP be monitored until the facility is closed. Post-closure monitoring of waste in RCRA landfills will be important to ensure continuing safety and to provide data for maintaining the landfill. In providing advice on ensuring the long-term safety of WIPP, a previous NRC committee found that “. . . the activity that would best enhance confidence in the safe and long-term performance of the repository is to monitor critical performance parameters during the long pre-closure phase of repository operations (35 to possibly 100 years)” (NRC, 2001d, p.1). For example, chambers to hold waste in the WIPP will be excavated as needed, drums will be emplaced, and lithostatic forces gradually will close the chambers—crushing the containers and sealing the waste in place. Early emplacements will be sealed during the operational life of the WIPP. Monitoring the waste during this sealing process can yield important scientific understanding of the actual closure process and also enhance safety by determining if the closure occurred properly.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes Baseline Technologies and Technology Gaps In its review of DOE’s environmental quality portfolio, the Strategic Laboratory Council found a significant gap in the “fate and transport of contaminants and performance monitoring to support waste repositories and inform stewardship decisions” (DOE, 2000c, p. iii). DOE has no established plan for monitoring its MLLW disposal facilities (e.g., Hanford, the Nevada Test Site) beyond the 30-year RCRA compliance period. There are no plans for mechanical or chemical monitoring of closed rooms in WIPP during its operating period or thereafter. Understanding and verifying the long-term behavior of these wastes and their disposition systems require more attention to monitoring than is apparent in DOE’s current planning. Research begun now to develop scientifically sound, simpler, and more reliable technologies for long-term monitoring can help ensure the safety of stored or disposed TM waste, reassure concerned citizens, provide data for new disposal facilities in the United States or abroad, and contribute generally to scientific knowledge. Challenges for Next-Generation Technologies Based on its fact-finding visits to DOE sites and committee members’ own expertise and judgment, the committee believes that future challenges for long-term monitoring technologies will be to extend the next-generation technologies described in the section on characterization to enhance reliability, stability, and remote operation, including long-lived, reliable sensors (and power supplies) that can be remotely interrogated, and airborne or satellite imaging. The sensor technology discussed previously is generally applicable for long-term monitoring. State-of-the-art improvements in technology are making it possible to interrogate sensors from remote locations and to provide remote, standoff detection of both chemical and radiological hazards. Distributed sensors can be monitored by Internet and wireless technologies (Pottie and Kaiser, 2000). In one example of a next-generation sensor technology, an electric utility prevents the overheating and shutdown of its power grid by monitoring a network of transformers and nodal sites with distributed sensors and the Internet.19 This replaces the expensive patchwork of 19   See http://www.graviton.com/.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes wired networks and human intervention required by present technologies to keep the grid in operation. The wireless sensors used in the new technology work above or below ground, and their spread-spectrum signal is impervious to electromagnetic interference. If the temperature of a transformer exceeds a safe level, the sensors trigger an alarm that alerts the utility. The utility reroutes electricity around the problem area or shuts down affected areas. By avoiding transformer failures, the utility is able to prevent costly shutdowns and blackouts. Sensors to measure other parameters can be implemented readily within the system’s architecture. Another example includes the monitoring of mobile platforms. Transportation of materials on trucks, trains, ships, planes, and buses produces an array of potential data management system needs. These needs include environmental and safety monitoring, preventive maintenance, global positioning, antitheft measures, and real-time engine sensor data. Platform mobility and the lack of cost-effective wireless connections have been the limiting factors in developing sensor systems for mobile platform services. Again, the data can be managed through wireless sensor networks for mobile platforms. The internal temperature of a compartment can be measured to ensure that the temperature stays within range, video monitors can be utilized for theft prevention and for ensuring compliance with safety regulations, and noxious fumes can be detected to allow for timely correction. Sensor data are transmitted by a wireless wide-area network connection. Clients on mobile platforms gain cost-effective access to data about location, safety, security, engine stability, inventory, and many other parameters that can be accessed in the field or from corporate command centers. All materials and objects (e.g., soil, water, trees, vegetation, structures, metals, paints, fabrics) create a unique spectral fingerprint. An optical sensor can determine these fingerprints by measuring reflected light, most of which registers in wavelengths, or bands, invisible to the human eye. Commercial state-of-the-art hyperspectral imaging systems operate across up to 220 wavelengths to record precise images of an otherwise hidden world. Where a standard sensor with fewer than 10 bands is capable of differentiating only between gross classes of vegetation, a hyperspectral imager can discriminate between plants and is sensitive enough to separate healthy from unhealthy growth. Hyperspectral sensors and imaging offer many attractive features for long-term, remote monitoring applications.20 Current and advanced technologies include the following: 20   See http://www.techexpo.com/WWW/opto-knowledge/hyperspectrum/index.html.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes remote sensing of earth resources, chemical detection and cloud tracking, medical photodiagnosis, and positional radionuclide concentrations. A better way to monitor large, remote sites may be from airborne or satellite platforms.21 Overflight monitoring of nuclear power plants and other nuclear facilities for radionuclide emission is commonly practiced today. Mineral and oil prospecting is also done from the air. Research Opportunities There are research opportunities for developing remote, distributed sensor systems to achieve self-monitoring “smart” drums and in monitoring TM repositories to achieve more fundamental knowledge of physical, chemical, and biological processes that govern their behavior. Remote Sensing Smart sensors can dramatically improve the monitoring of waste storage and waste disposal in near-surface (RCRA) landfills by creating smart drums that self-analyze and report their content and location. Smart filters could monitor and control (i.e., vent or getter) the gas produced in the drum. The Internet and wireless technologies can monitor these and other distributed sensors remotely during all phases of waste disposition, including storage, transportation, and disposal. The availability of inexpensive and reliable sensors for chemical and radiological hazards in the drums would also be beneficial. To be cost-effective, the sensors must be small and mass produced like today’s MicroElectroMechanical Systems (MEMS) and tomorrow’s Nano-ElectroMechanical Systems (NEMS). To be practical, the sensors must be self-sufficient, harvesting their energy from the environment or from the waste itself. Research on hyperspectral-imaging methods coupled with image-processing algorithms could lead to advanced remote-sensing technologies that would be well suited to monitor large, remote sites from airborne or satellite platforms. 21   See, for example, the International Journal of Remote Sensing.

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes Repository Behavior If WIPP is used only as a geological repository for the disposal of TRU wastes, then a scientific opportunity to advance our understanding of this unique major facility will be missed. In addition to being a repository, WIPP can be an important laboratory for geoscience and sensor technology. Scientific research could be done in conjunction with measures to ensure WIPP’s long-term safety. The results will be indispensable if WIPP is enlarged or if a new salt repository is needed. A previous NRC WIPP study recommended pre-closure monitoring to gain information on the following: room deformation, healing of the disturbed zone around the rooms, and performance of shaft seals; brine migration and moisture access to the repository; gas generation rates and volumes; and effectiveness of materials placed around the waste (e.g., MgO) to modify its chemical environment (NRC, 2001d). Sensors developed and tested at WIPP could then be used for long-term monitoring of other repositories, landfills, and burial sites. These sensors must be robust and have a lifetime of at least 10 years to monitor room closure. They should be controlled remotely and monitored by the Internet and wireless technologies, and they must be self-sufficient, harvesting their energy from the salt or the waste itself. Microbes are likely to exist and evolve in wastes in the WIPP and in RCRA landfills. A better understanding of these microbes and their activities will help predict the long-term fate of the different waste forms and their components. Microbial activity may destroy or immobilize some waste components while increasing the motility or toxicity of others. Research should focus on specific processes, including biodegradation of the various organic components of the waste and reactions altering the geochemistry of the inorganic components. Research should evaluate biogeochemical factors that can affect the leaching or migration of toxic and radioactive materials in the environment and the effect of physical conditions (e.g., pH, temperature) and chemical composition (e.g., organic and inorganic components, oxygen or other electron acceptor availability) on biogeochemical processes occurring in the waste. Near-Term and Longer-Term Research Accelerating site closure, a key feature of Office of Environmental Management (EM) planning since the 1990s, has been emphasized by

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Research Opportunities for Managing the Department of Energy’s Transuranic and Mixed Wastes EM’s recent top-to-bottom review. Among the areas for EMSP research recommended by the committee, research in characterization that would expedite shipping wastes for off-site disposal is most likely to provide immediate payoffs. Research toward methods for treating wastes that do not meet shipping or disposal criteria might provide similar near-term payoffs. Nevertheless, closing the larger DOE sites will require decades. Problems that are not foreseen or appreciated today are likely to be encountered in buried waste retrievals. Monitoring the WIPP during its operational period is a unique scientific opportunity. Demonstration that WIPP behaves as expected could be invaluable as DOE seeks to open other geological waste repositories. These opportunities for the long-term, breakthrough research envisioned by Congress should not be overlooked in the rush to meet short-term needs.