Special Radioactive Waste

In terms of special radioactive waste three radionuclides will be discussed, which are collected separately in the reprocessing plant tritium, 1, and Kr. C, as mentioned before, is presently not considered waste in the sense that attempts are made to develop techniques for recovery and final disposal. 

Spent fuel elements contain appreciable amounts of tritium, partly produced by fission, partly by other nuclear reactions. About half of the tritium is released from the fuel upon dissolution. The rest is bound to the zircaloy of the hulls and is disposed of with them. The fraction of tritium that is released exchanges with water, forming HTO. The total annual input of tritium in a 1400 MT/year reprocessing plant is about 10 Ci. In West Germany a reprocessing plant of this size is supposed to retain 75 to 80 percent. 

The fundamental problem of tritium waste management is that there is no simple way to reduce the volume of tritiated water. There are techniques available to minimize the volume generated in reprocessing, e.g., reuse of tritiated water to feed steam jets, and strict confinement of tritium in the first extraction cycle. These techniques, however, add complications to the process. If, therefore, an inexpensive way were available to dispose of untreated tritiated water, severe generation restrictions would not be appropriate. If, however, expensive methods were to be applied, such as solidification or even concentration by isotopic enrichment, the volume generated has to be limited as much as possible. 

Another approach is a suitable head-end process in the reprocessing plant, such as voloxidation (Chap. 10, Sec. 4.3). However, such a head-end process is not yet available technology but requires several more years of development. 

There are minor quantities of tritium smeared out over the whole reprocessing flow scheme that will ultimately arise as low-activity condensate with tritium concentrations of the order of 10 Ci/liter and 10 Ci/liter of other radionuclides. It is very likely that this can be released to surface waters. 

---

The main drawback to nuclear power is the production of radioactive waste. Spent fuel from a nuclear reactor is considered a high-level radioactive waste, and remains radioactive for a veiy long time. Spent fuel consists of fission products from the U-235 and Pu-239 fission process, and also from unspent U-238, Pu-240, and other heavy metals produced during the fuel cycle. That is why special programs exist for the handling and disposal of nuclear waste. 

Finally, one might note that there are concerns over problems of radioactive wastes tens of thousands of years in the future. Should there not be even more concern over the lack of needed fossil fuel supplies only a hundred or two hundred years from now. Fossil fuels are vitally needed for special energy tasks and particularly, for special non energy uses such as chemical and manufacturing production... 

The production of electricity fiom nuclear fission energy is accompanied by formation of radioactive waste, of which the larger hazard is the presence of long-lived transuranium isotopes. The problems associated with this waste are still debated, but if the transuranium isotopes could be removed by exhaustive reprocessing and transmuted in special nuclear devices, the hazard of the waste would be drastically reduced (Chapter 12). This may require new selective extractants and diluents as well as new process schemes. Research in this field is very active. 

Common hazardous wastes include (a) waste oil, (b) solvents and thinners, (c) acids and bases/alkalines, (d) toxic or flammable paint wastes, (e) nitrates, perchlorates, and peroxides, (f) abandoned or used pesticides, and (g) some wastewater treatment sludges. Special hazardous wastes include (a) industrial wastes containing the USEPA priority pollutants, (b) infectious medical wastes, (c) explosive military wastes, and (d) radioactive wastes or releases. 

The beneficial use of radiation is one of the best examples of how careful characterization of the hazard is essential for its safe use. A radioactive substance can be safely stored or transported if appropriately contained. Depending on the characteristics of the radioactive material, it can be safely handled by using appropriate shielding and safety precautions. Laboratory workers usually wear special badges that quantify radiation exposure to ensure that predetermined levels of exposure, which are considered safe, are not exceeded. Unfortunately, after more than 50 years, society has not yet been able to design and implement a safe way to dispose of radioactive waste. The hazardous properties of radiation are explored further in a subsequent chapter. 

As of March 2003, there were 26 spent fuel storage facilities in the United States located in 21 states. A total of about 160,000 spent fuel units containing about 45,000 short tons (41,000 metric tons) of radioactive waste were stored on-site at nuclear power plants and off-site at special storage areas. More than 97 percent of the wastes were still being held at on-site facilities the rest had been transported to off-site locations. 

Process economics of the GMODS are dependent on the scale of operation (D14276H, p. 5). Based on theoretical considerations (the limited number of process steps), GMODS has the potential to be a relatively low-cost process for treatment of radioactive wastes (D14276H, p. 37). In some cases, specialized equipment may be used to minimize waste volume prior to treatment, in an effort to minimize costs (D14276H, p. A-3). 

RedZone Robotics, Inc., has developed Houdini, a compact, tethered, track-driven work platform for radioactive waste retrieval operations. The vehicle is designed with a folding frame chassis that can fit through an opening as small as 22.5 inches in diameter. The unit comes with a retractable plow blade and onboard manipulator other specialized tools can be added for specific applications. 

Pretreatment is required for HTV processing. Drying and size reduction of wastes are required. Additives such as glass formers may be required. Processing of nonhazardous wastes may not be economically feasible. Treatment of radioactive wastes will produce a radioactive glass that requires special handing or treatment. 

Radionuclides constitute a special kind of environmental pollution. Their artificial production rate has increased exponentially since the development of the first nuclear reactor. They have brought us blessings in the form of power, of new research tools, and of new knowledge they have brought us problems in the form of the release of hazardous radionuclides and of the management of large quantities of radioactive waste. 

Contaminated glassware should be kept separated from uncontaminated. Contaminated beakers and flasks are placed in the special sink or other container for washing. Clean and wash all equipment with soap and water immediately after the experiment has been completed. If water-insoluble materials are being used, the first washing should be done with an organic solvent such as acetone. Soak contaminated pipets in a container filled with water. All broken glassware is disposed of in the Solid Radioactive Waste container. 

What does one do with the radioactive waste described in the previous section Clearly, the most important component of the waste is the spent fuel. Currently, most spent fuel assemblies are held in cooling ponds at the reactor sites, although one cannot do this indefinitely. In a few reactor sites, dry storage of the spent fuel is used. The fuel rods are transferred to special casks when the heat output and activity are such that air cooling will suffice. 

The statutory definitions of low-level waste apply only to radioactive waste that arises from operations of the nuclear fuel cycle i.e., to waste that contains source, special nuclear, or byproduct material as defined in AEA (see Section 4.1.2.1). This restriction, although not explicit in the definitions, is indicated by the applicability of NWPA and LLRWPAA to fuel-cycle waste only and by the reference to NRC, which can only regulate fuel-cycle waste. Thus, low-level waste does not include NARM waste. 

NRC has developed licensing criteria for near-surface disposal of waste that contains source, special nuclear, or byproduct materials in 10 CFR Part 61 (NRC, 1982a). These regulations are intended to apply primarily to disposal of commercial low-level waste. They do not include a definition of low-level waste but essentially defer to the current statutory definition in the Low-Level Radioactive Waste Policy Amendments Act of 1985. Thus, low-level waste can include wastes with high concentrations of radionuclides that are not generally acceptable for near-surface disposal in accordance with the licensing criteria in 10 CFR Part 61 (NRC, 1982a). 

Beyond these impacts, more advanced nanotechnology may allow active remediation of many environmental problems. For example, toxic wastes in contaminated aquifers may be neutralized by specially designed nano-robots (nanobots) that selectively capture undesirable molecules and then either sequester them for removal or break them down into harmless substances [114,118,119,124]. While nano-devices cannot, for example, render radioactive materials non-radioactive, they could capture molecules of radioactive waste and concentrate them into a form that would be easily removed [31-33]. 

Crown ethers are also used to remove radioactive elements from radioactive waste. For example, radioactive cesium and strontium can be extracted using specialized derivatives of 18-crown-6. 

Cell harvesters were developed to capture multiple samples of cells on membrane filters, wash away unincorporated isotopes, and prepare samples for liquid scintillation counting on special equipment developed to process and count multiple samples. Despite miniaturization and improvements in efficiency of this technique, the disadvantages of multiple liquid handling steps and increasing costs for disposal of radioactive waste materials severely limit its usefulness. Although specific applications require measuring DNA synthesis as a marker for cell proliferation, much better choices are available for detecting viable cell number for HTS. 

---