Atomic-energy processes

As a substitute for chonical methods Chemical methods consume reagents and frequently lead to expensive disposal problems for chemical by-products. Liquid extraction, which incurs no chemical consumption or by-product production, can be less costly. Metal separations such as uranium-vanadium, hafnium-zirconium, and tungsten-molybdenum and the fission products of atomic-energy processes are more economical by liquid extraction. Even lower-cost metals such as copper and inorganic chemicals such as phosphoric acid, boric acid, and the like are economically purified by liquid extraction, despite the fact that the cost of solvent recovery must be included in the final reckoning. 

For several years, the French Atomic Energy Commission (CEA) has developed modelling tools for ultrasonic NDT configurations. Implemented within the CIVA software for multiple technique NDT data acquisition and processing [1,2], these models are not only devoted to laboratory uses but also dedicated to ultrasonic operators without special training in simulation techniques. This approach has led us to develop approximate models carrying out the compromise between as accurate as possible quantitative predictions and simplicity, speed and intensive use in an industrial context. 

The defects generated in ion—soHd interactions influence the kinetic processes that occur both inside and outside the cascade volume. At times long after the cascade lifetime (t > 10 s), the remaining vacancy—interstitial pairs can contribute to atomic diffusion processes. This process, commonly called radiation enhanced diffusion (RED), can be described by rate equations and an analytical approach (27). Within the cascade itself, under conditions of high defect densities, local energy depositions exceed 1 eV/atom and local kinetic processes can be described on the basis of ahquid-like diffusion formalism (28,29). 

To examine the soUd as it approaches equUibrium (atom energies of 0.025 eV) requires molecular dynamic simulations. Molecular dynamic (MD) simulations foUow the spatial and temporal evolution of atoms in a cascade as the atoms regain thermal equiUbrium in about 10 ps. By use of MD, one can foUow the physical and chemical effects that induence the final cascade state. Molecular dynamics have been used to study a variety of cascade phenomena. These include defect evolution, recombination dynamics, Hquid-like core effects, and final defect states. MD programs have also been used to model sputtering processes. 

F. J. Hurst, D. J. Crouse, and K. B. Brown, Solvent Extraction of Craniumfrom Wet Process Phosphoric Acid, ORNL-TM-2522, U.S. Atomic Energy Commission, Washington, D.C., 1969. 

H. J. Neubetg, J. E. Atheriey, and L. G. Walker, Girdler-Sulfde Process Physical Properties, Atomic Energy of Canada Report AECL-5702, Chalk Rivet Nuclear Laboratories, Chalk Rivet, Ontario, Canada, 1977. 

The X-ray emission process followii the excitation is the same in all three cases, as it is also for the electron-induced X-ray emission methods (EDS and EMPA) described in Chapter 3. The electron core hole produced by the excitation is filled by an electron falling from a shallower level, the excess energy produced being released as an emitted X ray with a wavelength characteristic of the atomic energy levels involved. Thus elemental identification is provided and quantification can be obtained from intensities. The practical differences between the techniques come from the consequences of using the different excitation sources. 

Table 5. Energy requirements of four industrial desalination processes. (Source International Atomic Energy Agency 1992.)...

Short Guide to Reducing Human Error in Process Operation (United Kingdom Atomic Energy Authority, 1987)... 

There are a number of differences between interstitial and substitutional solid solutions, one of the most important of which is the mechanism by which diffusion occurs. In substitutional solid solutions diffusion occurs by the vacancy mechanism already discussed. Since the vacancy concentration and the frequency of vacancy jumps are very low at ambient temperatures, diffusion in substitutional solid solutions is usually negligible at room temperature and only becomes appreciable at temperatures above about 0.5T where is the melting point of the solvent metal (K). In interstitial solid solutions, however, diffusion of the solute atoms occurs by jumps between adjacent interstitial positions. This is a much lower energy process which does not involve vacancies and it therefore occurs at much lower temperatures. Thus hydrogen is mobile in steel at room temperature, while carbon diffuses quite rapidly in steel at temperatures above about 370 K. 

Amplitude of a process, 114. Andrew s diagram, 173 Anisotropic bodies, 193 Aphorism of Clausius, 83, 92 Arrhenius theory of electrolytic dissociation, 301 Aschistic process, 31, 36, 51 Atmosphere, 39 Atomic energy, 26 Availability, 65, 66 Available energy, 66, 77, 80, 98, 101... 

The energy produced in a nuclear reactor vessel is the result of a nuclear fission (atom splitting) process that occurs when sufficient nuclear material is brought together (critical mass). Under these circumstances, a chain reaction occurs and an external supply of neutrons is not required. A nuclear fuel control rod system raises or lowers the nuclear fuel (which is contained within fuel rods) inside the reactor vessel. 

Zircaloy Cladding by the Zirflex Process, Report A/ Conf. 15/2429, June 1958, "Second United Nations International Conference on Peaceful Uses of Atomic Energy,"... 

Pulsed source techniques have been used to study thermal energy ion-molecule reactions. For most of the proton and H atom transfer reactions studied k thermal) /k 10.5 volts /cm.) is approximately unity in apparent agreement with predictions from the simple ion-induced dipole model. However, the rate constants calculated on this basis are considerably higher than the experimental rate constants indicating reaction channels other than the atom transfer process. Thus, in some cases at least, the relationship of k thermal) to k 10.5 volts/cm.) may be determined by the variation of the relative importance of the atom transfer process with ion energy rather than by the interaction potential between the ion and the neutral. For most of the condensation ion-molecule reactions studied k thermal) is considerably greater than k 10.5 volts/cm.). 

Since it thus appears that reactions other than the atom transfer process are occurring, one must consider the possibility that the low k (thermal)/ (10.5 volts/cm.) ratios may result from a variation of the relative importance of the atom transfer reaction channel with ion energy. Similarly, in some of the cases where (thermal) = (10.5 volts/cm.) the relative importance of the atom transfer process may also change with ion energy. Thus the value of k(thermal)// (10.5 volts/cm.) does not necessarily provide conclusive evidence for the interaction potential between the ion and the neutral molecules. 

The authors wish to express their appreciation for the grants-in-aid made by the Texas Gulf Sulphur Company in the early stages of this work, without which it could not have been undertaken. The authors are also indebted to J. T. Middleton for the samples of muskmelon leaves. The radioactive sulfur 35 as H2S 04 was obtained from the Atomic Energy Commission, Oak Ridge, Tenn., and subsequently processed by Tracerlab, Boston, Mass. 

Bakstad, P, and K. O. Solberg, 1967, A Model for the Dynamics of Nuclear Reactors with Boiling Coolant with a New Approach to the Vapor Generation Process, KR-121, U.K. Atomic Energy Research Establishment, Harwell, England. (3)... 

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