Waste, radioactive

Refinement of the organic phase is necessary, because of the formation of radiolysis products. The main product of radiolysis of tributylphosphate (TBP) is dibutylphos-phoric acid (DBP) which forms very stable complexes with Pu(IV) and prohibits quantitative reduction to Pu(III). DBP is separated by washing the organic phase with an aqueous solution of Na2C03. 

The last step of reprocessing ( tail end ) is the production of compounds of U and Pu suitable for further use, e.g. uranyl nitrate hexahydrate (UNH) or a concentrated solution of U02(N03)2, and Pu02 or a solution of Pu(N03)4, respectively. 

Dry reprocessing procedures, such as volatilization of U as UFe, fusion with Na2S20v or Na0H/Na202, chemical reactions in molten salts or pyrometallurgical procedures, have also been proposed, but have not found practical application. 

The radioactive wastes originating from the operation of nuclear reactors and reprocessing plants is classified according to the activity level  

In nuclear reactors, radionuclides are produced by nuclear reactions in the coolant and in various solid materials in the reactor vessel. Furthermore, fission products or actinides may leak into the cooling system from faulty fuel elements. T, N, F and Ar are produced by a multitude of nuclear reactions with 

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Fission product distribution Radioactive waste activity distribution... 

In comparison with most other analytical techniques, radiochemical methods are usually more expensive and require more time to complete an analysis. Radiochemical methods also are subject to significant safety concerns due to the analyst s potential exposure to high-energy radiation and the need to safely dispose of radioactive waste. 

Nuclear Waste Management. Separation of radioactive wastes provides a number of relatively small scale but vitally important uses of gas-phase purification appHcations of adsorption. Such appHcations often require extremely high degrees of purification because of the high toxicity of... 

Waste Treatment. Microwave energy has been studied for the desulfurization of coal (qv) and treatment of wastes (190). Developments in microwave incinerators for medical and radioactive wastes have occurred (191,192). Even a consumer unit for consumption of sohd household waste has been proposed (193). Economic factors remain a key barrier in these developments. 

D. W. CleeUand, Proceedings of the Symposium on the Solidification and Eong-Term Storage of Highly Radioactive Wastes, USAEC, Richland, Wash., 1966. 

Chemical processing or reprocessing (39) of the fuel to extract the plutonium and uranium left a residue of radioactive waste, which was stored in underground tanks. By 1945, the reactors had produced enough plutonium for two nuclear weapons. One was tested at Alamogordo, New Mexico, in July 1945 the other was dropped at Nagasaki in August 1945. 

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). 

Classification of wastes may be according to purpose, distinguishing between defense waste related to military appHcations, and commercial waste related to civiUan appHcations. Classification may also be by the type of waste, ie, mill tailings, high level radioactive waste (HLW), spent fuel, low level radioactive waste (LLW), or transuranic waste (TRU). Alternatively, the radionucHdes and the degree of radioactivity can define the waste. Surveys of nuclear waste management (1,2) and more technical information (3—5) are available. 

Radioactive waste is characterized by volume and activity, defined as the number of disintegrations per second, known as becquerels. Each radionucHde has a unique half-life,, and corresponding decay constant, A = 0.693/tj 2 For a component radionucHde consisting of JS1 atoms, the activity, M, is defined as... 

Activities and existing and projected volumes of all types of radioactive waste are Hsted in Reference 7. 

Low Level Waste Treatment. Methods of treatment for radioactive wastes produced in a nuclear power plant include (/) evaporation (qv) of cooling water to yield radioactive sludges, (2) filtration (qv) using ion-exchange (qv) resins, (J) incineration with the release of combustion gases through filters while retaining the radioactively contaminated ashes (see Incinerators), (4) compaction by presses, and (5) solidification in cement (qv) or asphalt (qv) within metal containers. 

Nuclear utiUties have sharply reduced the volume of low level radioactive waste over the years. In addition to treating wastes, utiUties avoid contamination of bulk material by limiting the contact with radioactive materials. Decontamination of used equipment and materials is also carried out. For example, lead used for shielding can be successfully decontaminated and recycled using an abrasive mixture of low pressure air, water, and alumina. 

The disposal of radioactive waste is governed by rules of the NRC and the EPA (19). NRC regulations differ for low level waste and for high level waste, including spent fuel (20). 

Isolation of radioactive wastes for long periods to allow adequate decay is sought by the use of multiple barriers. These include the waste form itself, the primary containers made of resistant materials, overpacks as secondary layers, buffer materials, concrete vaults, and finally the host rock or sod. Barriers limit water access to the waste and minimize contamination of water suppHes. The length of time wastes must remain secure is dependent on the regulatory limit of the maximum radiation exposure of individuals in the vicinity of the disposal site. 

The geologic aspects of waste disposal (24—26), proceedings of an annual conference on high level waste management (27), and one from an annual conference on all types of radioactive waste (28) are available. An alternative to burial is to store the spent fuel against a long-term future energy demand. Uranium and plutonium contained in the fuel would be readily extracted as needed. 

Fig. 2. Volume of low level radioactive waste per U.S. nuclear power reactor (weighted industry median). The decrease over the period 1980—1994 was...

Radioactive Waste Management A.n IAEA. Source Book, International Atomic Energy Agency, Vienna, Austria, 1992. 

R. E. Berlin and C. C. Stanton, Radioactive Waste Management, John Wiley Sons, Inc., New York, 1989. 

Y. S. Tang and J. H. Saling, Radioactive Waste Management, Hemisphere, New York, 1990. 

A. A. Moghissi, H. W. Godbee, and S. A. Hobart, Radioactive Waste Technology, American Society of Mechanical Engiaeers, New York, 1986. 

The Role of the Monitored Retrievable Storage Facility in an Integrated Waste Management System, DOE/RW-0238, Office of Civihan Radioactive Waste Management, U.S. Department of Energy, Washington, D.C., 1989. 

J. E. Till and H. R. Meyer, eds.. Radiological Assessment, A Textbook on Environmental Dose Analysis, NUREG/CR-3332, U.S. Nuclear Regulatory Commission, Washiagton, D.C., 1983 Disposal of Radioactive Waste Review of S afety Assessment Methods, Nuclear Energy Agency, Paris, 1991. 

L. Carter, Nuclear Imperatives and Public Trust Dealing with Radioactive Waste, Resources for the Euture, Washiagton, D.C., 1987. 

K. B. Krauskopf, Radioactive Waste Disposal and Geology, Chapman and Had, London and New York, 1988. 

InternationalHigh-Eevel Radioactive Waste Conference, Eas Wegas, Nev., 1994, American Nuclear Society, LaGrange Park, Id., American Society of Civil Engineers, New York. 

The Shallow land Burial ofEow-Eevel Radioactively Contaminated Solid Waste, Committee on Radioactive Waste Management, National Academy of Sciences, Washiagton, D.C., 1976. 

Directions in Eow-Eevel Radioactive Waste Management A Brief History of Commercial Eow-Eevel Radioactive Waste Disposal, DOE/LLW-103, Rev. 1, The National Low-Level Waste Management Program, INEL, Idaho Eads, Idaho, Aug. 1994. 

E. L. Gershey, R. C. Kleia, E. Party, and A. Wilkerson, Eow-Eevel Radioactive Waste From Cradle to Grave, Van Nostrand Reinhold, New York, 1990. 

M. R. English, Siting Eow-Eevel Radioactive Waste Disposal Facilities The Public Poliy Dilemma, Quomm Books, New York, 1992. 

M. E. Bums, Eow-Eevel Radioactive Waste Regulation Science, Politics, andFear, Lewis Pubhshers, Chelsea, Mich., 1988. 

Historically, the Redox process was used to achieve the same purification as in the Purex process (97,129). The reagents were hexone (methyl isobutyl ketone) as the solvent, dichromate as an oxidant, and A1(N02)3 as the salting agent. The chief disadvantages of hexone are its flammability and its solubihty in water. However, because A1(N03)3 collects in the highly radioactive waste, thereby impeding the latter s further processing, the Redox process was abandoned in favor of the Purex process. 

E. P. Horwitz and W. Schulz, ia L. CeciUe, M. Casarci, and L. PietrieUi, eds.. New Separation Chemistry Techniquesfor Radioactive Waste and Other... 

The use of nuclear power has been a topic of debate for many years. Nuclear fuel represents a resource for generating energy weU into the future, whereas economically recoverable fossil fuel reserves may become depleted. Worker exposure, injuries, and fataHties in nuclear fuel mining are reportedly far less compared to those associated with recovery and handling of fossil fuels. Potential hazards associated with transporting and storing radioactive wastes do exist, however. 

Concerns over safe handling of radioactive materials and issues around the cost and disposal of low level radioactive waste has stimulated the development of nonradiometric products and technologies with the aim of replacing radioactive tracers in research and medical diagnosis (25). However, for many of the appHcations described, radioactive tracer technology is expected to continue to be widely used because of its sensitivity and specificity when compared with colorimetric, fluorescent, or chemiluminescent detection methods. 

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