Wastes, radioactive concentration

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]. 

The final concentrate, which includes UF and RO concentrates, should be disposed of by an authorized company, considering not only waste radioactivity levels but also chemical and biological contaminations, specially in the ultrafiltration concentrate since it contains most of the pathogens of the original waste. 

Radioactive waste is any waste material—gas, liquid, or solid—whose radioactivity exceeds certain limits. These limits have been established by governments or by local authorities, guided by the recommendations of the International Commission on Radiation Protection (ICRP). The ICRP recommendations define the maximum permissible concentration (MPC) for each individual radionuclide and for mixtures of radionuclides in water or air. The U.S. regulation defines such limiting concentration as the radioactivity concentration limit (C), which is the terminology used in this text, Values of C for selected actinides and long-lived fission products in water or air are given in App. D. 

The techniques of waste management depend largely on the type of waste to be dealt with. The criteria are the level of the radioactivity concentration in the waste, the nature of the... 

With respect to the level of radioactivity concentration, several waste classifications are in use appropriate for particular handling schemes. More basic distinctions are between waste that requires radiation shielding and that which does not and between waste that needs to be cooled and that which does not. 

In this chapter, the primary emphasis will be on HLW. Non-high-level alpha waste, tritium, 1, and Kr wiU be treated to some extent. Volumes and radioactivity concentrations of these wastes to be expected from a 1400 MT/year reprocessing plant according to a German design are given in Table 11.1 [D2]. 

As the capacity of the ion-exchanger is equally exhausted by radioactive and inactive ions, this method is suitable only for waste solutions with a high radioactivity concentration relative to the total concentrations of dissolved solids. 

Volume reduction of solid waste. Concentration of burnable solid waste can be very effectively achieved by incineration. The ashes are handled as radioactive concentrate. This is a rather costly technique because of much effort spent for off-gas filtration and safe handling of the ashes. Figure 11.21 shows an example flow sheet of an incinerator. 

The volume of natural UaOg equal to the volume of solidified waste from reprocessing 1 MT of heavy metal. This volume is assumed to be 80 liters as an average. For unreprocessed fuel 120 liters have been used. UgOg has been chosen as the standard uranium species because this is the radioactive concentrate in a uranium ore just as solidified waste is the radioactive concentrate in a waste repository. Moreover, it is a sufficiently generalized uranium species. This reference leads to a dependence of the significant period on the waste oxide concentration in the waste form. 

In principle, dispersion is only applicable for the gaseous and liquid wastes, which would need negligible pretreatment. The limitations are practical (how efficient is the dispersion into air and sea ), radiological (what radioactive concentrations are acceptable in air and sea ) and political/legal (can it be permitted ). 

Lower explosive limit—The lowest concentration of a substance that will produce a fire or fiash when an ignition source is present, expressed as a percent of vapor or gas in the air by volume. Low-level waste—Radioactively contaminated industrial or research waste such as paper, rags, plastic bags, medical waste, and water-treatment residues. 

LILW (low and intermediate level waste.- Radioactive waste in which the concentration or quantity of radionuclides is above clearance levels established by the regulatory body, but with a radionuclide content and thermal power below those of high level waste. Low and intermediate level waste are often separated into short lived and long lived wastes. Short lived waste may be disposed of in near surface disposal facilities. Plans call for the disposal of long lived waste in geological repositories [3]. 

This guide defines the principal requirements for the design and for the operation of systems and facilities for the incineration of radioactive waste. It concentrates... 

Plutonium (Pu) is an artificial element of atomic number 94 that has its main radioactive isotopes at 2 °Pu and Pu. The major sources of this element arise from the manufacture and detonation of nuclear weapons and from nuclear reactors. The fallout from detonations and discharges of nuclear waste are the major sources of plutonium contamination of the environment, where it is trapped in soils and plant or animal life. Since the contamination levels are generally very low, a sensitive technique is needed to estimate its concentration. However, not only the total amount can be estimated. Measurement of the isotope ratio provides information about its likely... 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

Nuclear Waste. NRC defines high level radioactive waste to include (/) irradiated (spent) reactor fuel (2) Hquid waste resulting from the operation of the first cycle solvent extraction system, and the concentrated wastes from subsequent extraction cycles, in a faciHty for reprocessing irradiated reactor fuel and (3) soHds into which such Hquid wastes have been converted. Approximately 23,000 metric tons of spent nuclear fuel has been stored at commercial nuclear reactors as of 1991. This amount is expected to double by the year 2001. 

If one just concentrates on the radioactive material in SNF, the volume is very small, especially compared to waste from other power production practices. However, one can only discuss the separated radioactive material if it has undergone extensive reprocessing. If SNF is to be isolated, as in a place such as Yucca Mountain, with perhaps 70 miles of tunnels, the volume is that of the interior of this minor mountain. Isolation of up to 100,000 metric tons of SNF in Yucca Mountain means that for the United States, approximately all the SNF made to date and that expected in the operating lifetime of all current reactors can be put there. Approximately 2,000 metric tons of SNF are produced each year in the United States. Waste volume and placement depend on the amount of compaction and consolidation at the sites. The plans for the Yucca Mountain present a realistic and understandable picture of the volume of SNF. 

Note that the concentrations of additive oxides differ. No attempt has been made to scale this effect with additive concentration). This curious reduction effect is not easily understood but emphasizes the complex nature of the glasses including the possible cooperative involvement of the multiple components. Similarly complex phenomena might influence leaching behavior in the complex, multicomponent glasses of interest for radioactive waste storage. 

C22-0082. A river contains a high concentration of iron cations, and environmental activists contend that an industrial manufacturing plant is the source. The manufacturer says that although the plant generates aqueous iron waste, it is processed on site and does not contaminate the river. How might this disagreement be resolved using radioactive tracers ... 

Low level waste from commercial facilities is buried on site. The Nuclear Regulatory Commission (NRC) has projected the activities and volumes of low level radioactive waste from all sources buried at commercial sites to the year 2000 using information from the Idaho National Environmental and Engineering Laboratory (INEEL) waste retrieval project and assuming that the waste disposal practices then used would continue into the future. The 20-year decayed 241Am and 243Am concentrations were estimated to be 380 and 230 pCi/m3 (14 and 8.5 Bq/m3), respectively (Kennedy et al. 1985). 

Arthur WJ, Janke DH. 1986. Radionuclide concentrations in wildlife occurring at a solid radioactive waste disposal area. Northwest Sci 60(3) 154-165. 

Waste characteristics, which may limit the effectiveness or feasibility of the remedial technologies quantity/concentration, chemical composition, acute toxicity, persistence, biodegradability, radioactivity, ignitability, reactivity/corrosivity, infectiousness, solubility, volatility, density, partition coefficient, compatibility with chemicals, and treatability... 

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