OVERVIEW

Institutions have adopted several techniques to reduce waste volume and improve in the management of LLRW disposal, including:

• Increasing the capacity for onsite storage for decay.
• Increasing the use of nonradioactive alternatives.
• Limiting the number of authorized users.
• Reducing in the amount of waste shipped.

Hospitals and academic institutions have been storing radioactive materials onsite for decay for many years as access to disposal sites has become more limited. In general, these materials are stored for decay until no appreciable radioactivity is detectable (usually 10 half-lives) and then disposed of as ordinary trash. Operating such a facility means higher operation costs for user institutions: for finding and preparing space for decay storage, maintenance, training, and recordkeeping and for the use of other space for other productive purposes. Therefore, institutions must provide, adequate funds for facility management. The current policy of biomedical-LLRW disposal makes the problem of waste disposal more prominent because it exists in almost every research facility.

It is more difficult to store long-lived LLRW onsite for decay. Hospitals and academic institutions ship these materials offsite for decay. For example, the University of Iowa ships an estimated 20% of its LLRW away for treatment and disposal (Osborne, 2000).

Nonradioactive alternatives have become increasingly accepted in biomedical research as a result of the lack of access to disposal facilities, the expense associated with radioactive-waste disposal, and limitation on space for disposal by decay in storage (Castronovo, 2000; Osborne, 2000). The use of nonradioactive materials in biomedical research is one approach to waste minimization.

IMPROVED MANAGEMENT

There are three key strategies for improved management of LLRW: avoidance, consolidation, and volume reduction. They are all used to minimize the amount of LLRW that needs to be managed, treat wastes to minimize the volume of waste that ultimately need to be disposed of, and create final waste forms that are improved for long-term confinement of contained radioactive material once disposed.

Avoidance is a systematic method for the use of radioactive material that generates a minimum of waste. Careful techniques, segregation of contaminated and noncontaminated materials, and careful decontamination of materials and storage for decay followed by disposal as nonradioactive materials are all common.

In consolidation, LLRW is collected and undergoes minimal treatment before disposal. This approach might be the best for generators that produce only small amounts of waste or produce waste infrequently. Brokerage services are available to provide consolidation for small generators; many of them are in the biomedical research and academic communities. Brokers then provide more economical treatment for these larger consolidated quantities of waste, including incineration, supercompaction, and ultimate disposal.

Volume reduction focuses on reducing the volume of radioactive waste that needs to be treated and disposed. Treatment has costs, as does transportation of materials to and from processors and to disposal. The following section describes a generalized method that is commonly used to guide decision-making in the selection of treatment and disposal options.

A decision to dispose of waste directly or to process it before disposal is principally an economic decision. For the biomedical-waste generator, decisions to proceed with treatment and disposition, including disposal and recycling can be governed by simple relationships (Appendix A). For example, it might be more economical to dispose of waste directly rather than treating it first. If the treatment results in an insufficient volume decrease, the cost of treatment plus the cost of disposal of an insufficiently reduced volume might exceed the original cost of disposal of the untreated waste. Conversely, it might be necessary to treat LLRW to make it acceptable for disposal.

STORAGE PRACTICES

Storage of LLRW generated by biomedical research facilities uses specialized packaging that provides protection from radiation emitted by the waste and isolates the radioactive material from employees handling it. Storage is used to hold LLRW for decay to background levels of radioactivity before disposal as conventional nonradioactive material at conventional or industrial landfills disposal facilities or, for very small LLRW generators, to hold it until sufficient LLRW is accumulated to fill a disposal container or to warrant shipment. LLRW storage for treatment or disposal can occur at the site where the LLRW was generated, offsite at the location of a broker or processor, at a storage facility, or at an LLRW disposal facility before disposal.

Restrictions set by the US Nuclear Regulatory Commission or by individual agreement states limit the types and quantifies of radionuclides that may be stored onsite. Because the license period is confined to the time in which only short-lived material can decay to background levels of radiation, all waste contaminated with radionuclides of longer-lived material must eventually be sent to a disposal site. Because of the unavailability of regional disposal facilities throughout the country, the commission recently extended its allowance for onsite storage without a specific maximum (USNRC, SECY-94-198, 1994).

TREATMENT PRACTICES

Because of concerns over the lack of available disposal facilities in the states that do not have guaranteed long-term access to LLRW disposal sites and the costs associated with disposal, biomedical-research generators of waste continue to pursue more comprehensive and sophisticated methods of treating their LLRW and mixed waste to minimize the volumes and radioactivity of waste requiring disposal in licensed facilities. Numerous practices are used by biomedical researchers to reduce the volume of the typical waste forms generated and to reduce or eliminate radioactivity. These practices are:

1. Centrifugation. This treatment process removes suspended solids by using rotating equipment that depends on centrifugal force to separate solids from liquids.
2. Compaction and supercompaction. Compaction is one of the easiest and most effective treatment techniques in use to reduce dry solid LLRW. Depending on the type of machine, forces range from 10 tons (older, conventional compactors) to 5,000 tons (supercompactors). Resulting waste density ranges from tens to approximately a hundred pounds/ft³. Metal materials can range up to several hundred pounds/ft³.
3. Crystallization. This evaporation-related volume-reduction method precipitates solids out of liquid LLRW. The loss of water results in a more concentrated slurry of radioactive material than conventional evaporation and thereby reduces the volume of radioactive liquid waste that requires disposal. The vaporized water can be condensed and discharged or reused in the company or institution's processes.
4. Decontamination. This technique removes radioactive contaminants from the surface or near surface of objects—such as walls, floors, tools, and equipment—or from fluids. Decontamination is achieved by the transfer of contaminants to any of a number of decontamination solutions, including alkaline permanganate, detergents, mineral acids, organic acids, chelating compounds, and water or steam under high pressure. Sand blasting and electropolishing are also used successfully.
5. Dewatering. This technology uses pumps or gravity to draw water from wet solids through filer devices.
6. Drying. Various types of drying processes use heat to remove liquid and form a dry solid. Dryers include the “fluidized-bed,” “in-drum,” and “spray” types.
7. Evaporation. This frequently used volume-reduction technique removes water from radioactive material by using heat to evaporate, and thereby remove, relatively pure water. The original waste stream becomes more concentrated in waste constituents and smaller in volume, and the vaporized water can be reused or discharged.
8. Filtration. This is the process of removing solid particles from LLRW fluids by forcing the fluids through a permeable material with gravity, pressure, or vacuum. The solids suspended in the fluids can be lodged within the pores of the filter or build up on the surface as a filter “cake”.
9. Flocculation. This process gathers small particles of waste suspended in liquid waste into larger particles or clusters. Certain chemicals added to the liquid waste can aid this process.
10. Incineration. Incinerating LLRW can achieve waste volume-reduction factors ranging from 30–100 before final ash immobilization and packaging or disposal in a local landfill as provided by license conditions if the radioactivity concentration in the ash does not exceed the concentrations of 10 CFR 20 Appendix B, Table 2 Column 2. After packaging, the volume reduction continues to be up to five times greater than any other minimization technology, including supercompaction.
11. Ion exchange. The process used to separate dissolved solids from liquids by using chemical resins to exchange the atoms in the radioactive materials with the atoms attached to the resin material. This waste separation technique can reduce the level of radionuclides in liquid waste by a factor of 10–100.
12. Polymerization. This chemical process solidifies liquid and wet solid waste by encapsulating small particles or droplets of waste in an irreversibly hardened polymer matrix. Because polymeric systems do not require water to solidify, they can result in some volume reduction.
13. Precipitation. This technique removes dissolved solids from a liquid, and transforms them into a solid waste form.
14. Recycling. This volume-reduction practice is widely used to enable the repeated reuse of decontaminated or slightly contaminated materials and waste. Tools and equipment, and some radioactive sources, can be recycled for repeated use. Recycling involves a combination of other treatment technologies and practices, including segregation, filtration, ion-exchange, evaporation, crystallization, flocculation, precipitation, sedimentation, dewatering, and decontamination.
15. Sedimentation. Gravity, not chemicals, provides the vehicle to remove suspended particles from liquid through the process of sedimentation. Sedimentation, flocculation, and precipitation are often used together to produce a smaller volume of wet solids, which can be separated from any bulk liquid.
16. Segregation. Waste segregation can achieve significant decreases in the volume ultimately requiring disposal. Paper, cloths, and other waste products are frequently discarded as radioactive waste when they are not contaminated with radioactive substances. Reductions in LLRW volume can also be achieved by segregating short-lived from longer-lived waste. Before the concern over availability and cost of LLRW disposal, many research facilities sorted out their waste once before packaging and shipping it for disposal. Such a sorting procedure was able to segregate radioactive from nonradioactive waste. However, it could not segregate long-lived from short-lived waste or separate mixed waste into various treatability groups. Now that those generators in many parts of the country face the potential loss of access to disposal, research institutions are requiring additional minimization procedures of their researchers. Procedures include comprehensive and repeated training of generators, improving waste-identification procedures, reducing the quantities of radioactive materials ordered and used in research, automating procedures to enhance reproducibility, recycling chemicals where possible, repurifying for reuse, preventing the unnecessary generation of mixed waste, and planning the costs and amounts of waste disposal in the design of experiments and products.
17. Shredding. Paper, cloth, plastics, and some light metals can be shredded to aid in compaction and incineration.
18. Solidification. This process mixes materials (cement, asphalt, vinylesterstyrene, and so on) with LLRW as it is placed in disposal containers so that it becomes a solid block.
19. Stabilization. This process is accomplished by using many of the treatment technologies described here, including incineration, solidification, and polymerization. Waste stability is required by Nuclear Regulatory Commission disposal regulations [10 CFR Part 61] to ensure that the waste does “not structurally degrade and affect overall stability of the site through slumping, collapse, or other failure of the disposal unit and thereby lead to water infiltration” (Part 61.56(b)) and to ensure that it will maintain its physical dimensions and its form under disposal conditions, such as the presence of moisture and microbial activity, and activities internal to the waste package, such as radiation effects and chemical changes. Stabilizing LLRW also helps to limit exposure of anyone who inadvertently intrudes onto the disposal site after all institutional controls have ended, at least 100 years after operations cease.
20. Storage for decay. This method provides for the onsite or offsite storage of LLRW with relatively short half-lives to allow some or all of its radioactivity to decay to lower radioactivity levels. Once the activity in the waste has decayed to levels that are indistinguishable from background (at least 10 half-lives), the waste is in effect no longer radioactive and can be safely disposed of as ordinary trash. LLRW generators are building their own decay-in-storage facilities and not only are holding short-lived wastes—for example, ¹²⁵I, ⁹⁹Mo (molybdenum-99), ²⁰¹Tl, ⁶⁷Ga, ³²P and ³³P—for decay, but are holding longer-lived wastes—such as ³H, ⁶⁰Co, and ¹³⁷Cs (cesium-137)—for partial decay before they are shipped for disposal. Such partial decay can allow a generator to use the Envirocare lower-cost disposal site in Utah (Envirocare of Utah, Inc., License No. UT 2300249).

LLRW DISPOSAL PRACTICES

Disposal of waste is its isolation from the biosphere. The US Nuclear Regulatory Commission definition assumes that LLRW will be isolated by “emplacement in a land disposal facility”, meaning that it will be buried. Some states, however, define disposal slightly differently to allow for isolation in engineered vaults or above ground canisters. A number of disposal practices are used for disposal of LLRW, including that generated by biomedical research facilities. Near-surface disposal is defined in 10 CFR 61 as disposal within the upper 30 meter of the earth's surface. This type of disposal facility is operated at Barnwell, South Carolina; Richland, Washington; and Clive, Utah. It is also called engineered shallow land burial. Waste containers shipped to the Barnwell disposal site are placed into concrete overpack in engineered trenches. These concrete containers are tightly packed to minimize void spaces and to provide a stable base on which to construct a permanent cap. The cap includes a plastic cap covered by a series of barriers that are designed to retard the infiltration of precipitation down to the surface of the disposal cells. The resulting increase in surface runoff is handled through a specially designed management system. After disposal operations end and throughout the institutional control period after the site is closed, a formal post-closure-monitoring plan will be put into place by the custodial agency of South Carolina. Closure activities are fully funded by an institutional-care fund developed from fees charged to waste generators and an interest-bearing account controlled by South Carolina.

At the Richland site, with less annual rainfall, waste containers are placed in engineered trenches. The containers are backfilled to minimize void spaces and to provide a stable base on which to construct a permanent cap appropriate for the environmental conditions of the facility. The Richland site has capacity to operate through 2063 (BRER staff personal communication with Arvil Crase from US Ecology, Inc., 2000). In contrast, LLRW accepted for disposal at the Envirocare site can be removed from its packaging and mixed with soil before emplacement into a disposal cell. Other wastes and debris are controlled in size and are also placed directly into the landfill (www.envirocareutah.com).

• Case-by-case exemption. A limited exemption to allow the onsite burial of LLRW can be granted to an individual licensee, case-by-case basis, “to dispose of licensed material in a manner not otherwise authorized” in Nuclear Regulatory Commission regulations (10 CFR 20.2002). The rule requires a licensee to submit an application describing the licensed material for which the exemption is sought; kinds, and levels of radioactivity; the proposed manner and conditions of disposal; an analysis of the nature of the environment and use of groundwater and surface waters in the general area; the nature and location of other potentially affected facilities; and procedures to minimize the risk of unexpected or hazardous exposures. About 40 exemptions have been granted nationwide since this rule became effective. After the Commission promulgated its LLRW disposal regulations in 1983 (10 CFR 61), it began discouraging LLRW generators from using onsite burial.
• Disposal to sewer systems. Commission regulations prohibit the discharge of licensed material into sanitary- sewer systems except for very small quantities that are assumed to be diluted by the volume of sewage flowing through the system. The rule prohibits any licensee from using the sewer system to dispose of more than a combined total of all radioactive materials of 1 Ci/year with the exceptions of ¹⁴C and ³H. Up to 1 Ci of ¹⁴C, and up to 5 Ci of ³H per year may be released into the sanitary-sewer system (10 CFR 20.2003). An exemption within the regulation enables hospitals to use the sewer system for disposal of radioactively contaminated human waste from people undergoing medical diagnosis or treatment with radioactive materials.
• Exempt quantities. Minute quantities of certain radionuclides do not have to be disposed of in licensed LLRW disposal sites under 10 CFR 20.2005 of the regulations. This rule allows the disposal, as nonradioactive waste, up to 0.05 μCi of ³H or ¹⁴C in liquid scintillation fluids and up to 0.05 μCi of the same two radionuclides per gram of animal tissue (averaged over the weight of the entire animal).
• Release in effluents. The US Nuclear Regulatory Commission allows radionuclides in radioactive materials or LLRW to be released in effluents (air or water) as long as the release remains within the radiation dose limits allowed by Commission regulations. These limits, if inhaled or ingested continuously over the course of a year, would produce a total effective dose equivalent of 50 mrem (Appendix B of 10 CFR 20).

MINIMIZING THE USE OF RADIOACTIVE MATERIALS

Minimizing the radioactivity in LLRW before its generation by biomedical research and other users of radioactive materials is called source minimization. The biomedical research industry and other radioactive- material users have been successful in their source-minimization and waste-volume-reduction efforts and have become more knowledgeable about minimization objectives and strategies because of the economics of disposal of larger amounts of radioactive material and larger volumes of waste.

EPA also has a volume-reduction policy concerning its regulation of the hazardous components of mixed waste. EPA's requirement directs mixed-waste generators to “have a program in place to reduce the volume and toxicity of waste generated to the extent that is economically practical” (40 CFR 260–261) (USEPA, 2000).

LLRW generated as a result of biomedical research generally is disposed of as compacted trash or solids, institutional laboratory or biologic waste, absorbed liquids, animal carcasses, and sealed sources. Source- minimizing and volume-reducing technologies include compaction and supercompaction, incineration, segregation, storage for decay, and substitution.

Another incentive for the move to minimize waste has been the problem of dealing with mixed waste. Stringent requirements adopted by EPA in response to the 1985 amendments to RCRA require that all mixed waste be treated before it is disposed of (40 CFR 261, subpart C). However, treatment options are not available for all mixed waste. Some low-activity mixed waste can be treated and disposed of at the Envirocare site in Utah; some—up to 0.05 picocurie/g of material containing ³H and ¹⁴C—can be incinerated as fuel. As a result, mixedwaste generators must store this waste on site until treatment is available. But such storage is prohibited under the RCRA amendments except for the purpose of accumulating sufficient quantities to treat or dispose. EPA recently moved to modify its regulations to allow mixed waste to be stored for decay on site. Once the activity of the mixed waste has decayed, it can be disposed of as chemical waste; the legal term is “hazardous waste”. The confusion between US Nuclear Regulatory Commission and EPA regulations, as they pertain to mixed waste, has caused many generators to use various source-minimization and waste-volume reduction techniques to avoid generating mixed waste or to treat it and destroy the hazardous chemical properties so that the waste can be disposed of as LLRW.

Efforts by biomedical researchers and other users of radioactive materials to reduce LLRW volumes have been highly successful. Disposal volumes that exceeded 3.7 million cubic feet in 1980 have declined to below 0.5 million cubic feet today (National Low-Level Waste Management Program, 2000). While some LLRW generators remain hesitant to ship their LLRW to the Envirocare disposal site due to concerns over future legal liability, many other generators are shipping large volumes of low-activity LLRW to that site.

Similar efforts to minimize the radioactivity of LLRW shipped for disposal have not produced as dramatic or as consistent a decline in activity in disposed waste. For example, the total activity in all waste shipped for disposal in 1986 was 233,740 curies, which increased to 1,000,102 curies in 1992, decreased to 334,563 curies in 1998, and increased again to 1.8 million curies in 1999 (LLW Notes, 2000). The last rise was due to the disposal of high-activity LLRW from the decommissioning of nuclear power plants.

The difficulty in minimizing radioactivity in LLRW is due to the very nature of volume-reducing processes, which typically do not minimize or eliminate the radioactivity, but rather concentrate it in a smaller volume of waste.

Reducing or eliminating radioactive sources and minimizing or eliminating LLRW are not simple tasks, and complex tradeoffs are involved in designing and implementing such policies. Because the LLRWPA (Public Law 96-573, 1980) allows regional compacts to exclude waste from outside their regions and limited disposal options and because developing new disposal capacity will result in very costly disposal fees, biomedical researchers will continue to be motivated by economics and access to disposal to minimize sources and LLRW volumes. In addition, ever-increasing costs of waste treatment, storage, transportation, and disposal have had substantial impacts on volume reduction.

USE OF NONRADIOLOGICAL MATERIALS

Substituting nonradioactive materials for radioactive ones or shorter-lived materials for longer-lived ones is becoming more common. For example, biomedical researchers are substituting ³³P for ³²P and ³⁵S because of the shorter half-life and the potential for lower personnel exposure. Other substitutions involve the use of colorimetric, chemiluminescent, and bioluminescent assays for radioactive assays. And researchers are using an enzymatically catalyzed amplification process called polymerase chain reaction (PCR) to produce high- concentration gene sequences that can be detected by nonradioactive methods, such as the use of fluorescent dyes. Sensitivity, cost, and chemical hazards of the alternative need to be measured against the cost and availability of disposal of radioactive materials when substitutions are considered. Ideally, substitutes should provide equivalent or superior sensitivity, and accuracy, while not posing a greater threat to public health and safety than the radioactive material. The nonradioactive material should not make the research more expensive or labor intensive, and the cost of switching to a new methodology needs to be considered. For example, if experimental results in laboratories that have been based on use of a radioactive label are to be used as a standard, switching to a nonradioactive methodology will usually require recalibration or confirmation of the initial results and this can often be a significant financial cost to the biomedical research. Substitution of less hazardous chemicals is also used in the case of biomedical research that results in the generation of mixed waste.

Radioactive substances have several characteristics that make them attractive for laboratory investigations. They can be covalently bound to proteins, such as immunoglobulins, and provide an easily quantified product that maintains antibody activity and specificity. Radionuclides bound to ligands of various types can be used to provide an in vivo image or to deliver radioactivity to specific anatomic sites, such as a deposit of cancer cells, for therapeutic purposes.

Those characteristics are functional and useful features of radioactive materials, but there are attractive nonradioactive alternatives. The increased use of radionuclides coincides with the introduction of the radioimmunoassay (RIA). This technology allowed for the rapid and accurate measurement of small amounts of materials, such as hormones, microbial products, and antigens (Miller, 2000). RIA was often performed by radiolabeling an antibody protein with ¹²⁵I or ¹³¹I, short-half-life radionuclides readily managed in waste with storage for decay. Several years after the introduction of RIA, new variations on antibody-based quantification were introduced. A good example is the enzyme-linked immunoassay (EIA), in which the label on the antibody molecule is an enzyme, such as horseradish peroxidase, rather than a radionuclide. The assay is based on colorimetric measurement of enzymatic activity with an enzyme substrate that undergoes a color change. EIA is an attractive alternative for assays because each enzyme molecule attached to an antibody provides an amplification mechanism for detecting bound antibody. EIA replaced RIA in most uses because it is a superior technology and it avoids the costs and bother of managing radioactive materials and radioactive wastes.

A similar set of alternatives has been developed with regard to nucleic acid sequencing. DNA base sequencing was developed by using gel separations of DNA fragments internally labeled with ³²P or ³³P. Although accurate, that method was not readily adaptable to the large-scale sequencing needed to sequence the genome of an entire organism. Robots were invented that could use colorimetric assays, and these assays have facilitated the determination of the base sequence of the DNA of several microorganisms and now of most of the human genome. As in the case of EIA, the development of alternatives was based on technologic improvements rather than a need to avoid the use of radioactive materials, but the alternatives have the effect of diminishing the reliance on radioactive materials by biomedical researchers (The Scientist, 1999, 2000; Griffin and Griffin, 1993; Glazer and Mathies, 1997; Mansfield et al., 1995, Kricka, 1991; Sandhu et al., 1991, Party and Gershey, 1995).

In some cases, the alternatives are still experimental and have yet to displace radioactive materials as the materials of choice. For example, radiolabeled antibodies are used for imaging and therapy in malignant disease. Radionuclides can deliver a dose of ionizing radiation to tumor cells and are useful for diagnostic imaging. Radiomimetic drugs could be substituted for radioactive materials, and toxins, such as ricin toxin, have generated considerable interest. But those substances cannot be used for imaging. The therapeutic and diagnostic uses of monoclonal antibodies are still evolving, and radioactive materials are likely to be an important component of means to amplify the specificity of antibodies with an additional function, such as imaging or directed toxicity.

Most large research institutions make a concerted effort to find suitable and appropriate alternatives to radioactive materials for research. The National Institutes of Health (NIH), as an example of a very large research center, created a committee to explore and promote the use of alternatives. These efforts are often useful on urban campuses, where neighbors might have concerns about the local environment. Committees like the NIH Committee on Alternatives to Radioactivity can provide information to investigators who are not aware of appropriate alternatives.