[en] A theoretical model simulating the simultaneous heat and mass transfer which takes place during the desublimation of a gas to a solid is presented. Desublimer column loading profiles to experimentally verify the model were obtained using a gamma scintillation technique. The data indicate that, if the physical parameters of the desublimed frost material are known, the model can accurately predict the desublimation phenomenon. The usefulness of the model in different engineering applications is also addressed

[en] A study was conducted to obtain column concentration profiles and point buildup rates for a cold trap freezing out krypton from a nitrogen carrier gas stream and to compare those experimentally obtained profiles with profiles generated from a theoretical model. Profiles were obtained over a range of flow conditions from 0.14 to 1.06 standard cubic feet per minute, krypton feed gas concentrations varied from 5.2 to 13.5%, and cold trap operating temperatures from -281 to -312⁰F. Gamma scintillation techniques using tracer amounts of krypton-85 provided the major analytical tool employed in the investigation. Data obtained from the experiments indicate that if values for the density and thermal conductivity of the krypton frost are known, the model can accurately predict krypton loading profiles in the cold trap. The frost density and frost conductivity appear to be functions of the freeze-out temperature and condensable krypton concentration. A discussion of cold trapping theory, a description of the experimental apparatus and tests performed, and an explanation of the usefulness of the model as a design tool for engineering use are included

[en] The proposal concerns an improved gas absorption method in which a liquid absorbant (e.g. hydrocarbon fluorides) circulates continuously through a closed loop system and has gas-absorption gas-desorption zones as well as absorbant regeneration zones. The emphasized advantage is that the process can take place in a single liquid-gas apparatus which has successive contact zones working under the same pressure. The recovery of krypton 85 from a gas (N₂, O₂, ¹⁴CO₂) using dichlorofluoromethane (CCl₂F₂) is described. The apparatus can also be used in the hot cells. (RW)

[en] Recent progress in the development of a fluorocarbon adsorption process for the recovery of krypton from the off-gas of fuel reprocessing plants is reported. Three packed columns comprise the main working sections of the process. Each column is designed to exploit certain gas-liquid solubility differences that exist between the solvent and the various gas constituents that might be present. The main separation of noble gas is accomplished in the absorber. The other two columns, each fitted with a reboiler and an overhead condenser, comprise the intermediate and final stripper sections of the plant

[en] A fluorocarbon-based selective absorption process for removing krypton-85, carbon-14, and radon-222 from the off-gas of conventional light water and advanced reactor fuel reprocessing plants is being developed at the Oak Ridge Gaseous Diffusion Plant in conjunction with fuel recycle work at the Oak Ridge National Laboratory and at the Savannah River Laboratory. The process is characterized by an especially high tolerance for many other reprocessing plant off-gas components. This report presents detailed drawings and descriptions of the second generation development pilot plant as it has evolved after three years of operation. The test facility is designed on the basis of removing 99% of the feed gas krypton and 99.9% of the carbon and radon, and can handle a nominal 15 scfm (425 slm) of contaminated gas at pressures from 100 to 600 psig (7.0 to 42.2 kg/cm²) and temperatures from minus 45 to plus 25⁰F (-43 to -4⁰C). Part of the development program is devoted to identifying flowsheet options and simplifications that lead to an even more economical and reliable process. Two of these applicative flowsheets are discussed

[en] The Oak Ridge Gaseous Diffusion Plant has the primary responsibility for the development of the FASTER (Fluorocarbon Absorption System for Treating Effluents from Reprocessors) process for application to LMFBR and LWR fuel reprocessing plants. Krypton-85 removals in excess of 99.9% and carbon-14 as carbon dioxide removals greater than 99.99% have been obtained in a development pilot plant. So far, pilot plant tests show that the presence of other reprocessing plant off-gas components does not appreciably affect the general operability or removal efficiency of the process. Tests also indicate that the one process designed for krypton and carbon removal may be even more effective in removing other fission products and objectionable chemical contaminants such as nitrogen dioxide. Elemental and organic iodine removals in excess of 99.99% and nitrogen dioxide removals over 99% were recently achieved. Higher process decontaminations are possible. Trapping studies show that 13X molecular sieves are very effective in removing the fluorocarbon vapor from the process product stream

[en] In 1985, the US Department of Energy chose the Atomic Vapor Laser Isotope Separation (AVLIS) process as its advanced uranium enrichment process for the future. Since that time, the AVLIS program has advanced through various stages of development is now geared toward completing a full-scale integrated enrichment demonstration in 1992, leading to a November 1992 decision to deploy an AVLIS production plant with plant startup as early as 1997. This paper will describe the AVLIS process, discuss demonstration and deployment plans, and highlight recent technical progress. Some major accomplishments include: (1) operating the world's highest average power visible light laser system continuously at over 7,000 watts and accumulating more than 1 million hours copper vapor laser head time; (2) vaporizing metric tons of uranium in a full-scale separator unit; and (3) developing new low-cost and low waste producing methods for integrating the metal-based AVLIS system into the nuclear fuel cycle

[en] Since the late 1960s, the Oak Ridge Gaseous Diffusion Plant, in conjunction with the Oak Ridge National Laboratory, has developed a fluorocarbon-based selective absorption system for removal of ⁸⁵Kr and ¹⁴CO₂ from nuclear fuel reprocessing facilities. Process performance and reliability have been well demonstrated with over 10 years of operation using simulated reactor and reprocessing plant dissolver off-gases and three generations of pilot plant scale equipment. A major development of this work is a combination absorption and stripping column which results in a simplified process with improved reliability and lower cost. The process has shown excellent flexibility in simultaneously removing and concentrating the radioactive gases of interest, i.e., > 99% removal is easily obtainable for Kr, Xe, and CO₂. With the incoming feed gas containing around 10 ppM Kr, the product concentration of Kr from the single column is typically in the 1 to 10% range. Additional purification of the single-column product allows nearly pure components (> 90% Kr) to be obtained, thereby minimizing final storage or disposal requirements. Several alternatives for product purification have been investigated. In one system, 13X molecular sieve is used to first remove the process solvent vapor. Selective adsorption on 5A molecular sieves and silver mordenite is then used to separately remove the already concentrated CO₂ and Xe, respectively. At this point Kr, which was withdrawn from the column at the present concentration level, has now been further purified by the removal of the other components and can be collected in a cold trap. This paper summarizes the performance capabilities of the single-column and discusses product purification system options, including selective desublimation, solid sorbent, and cryogenic charcoal adsorption techniques

[en] AVLIS RD and D efforts are currently proceeding toward full-scale integrated enrichment demonstrations in the late 1980's and potential plant deployment in the mid 1990's. Since AVLIS requires a uranium metal feed and produces an enriched uranium metal product, some change in current uranium processing practices are necessitated. AVLIS could operate with a UF₆-in UF₆-out interface with little effect to the remainder of the fuel cycle. This path, however, does not allow electric utility customers to realize the full potential of low cost AVLIS enrichment. Several alternative processing methods have been identified and evaluated which appear to provide opportunities to make substantial cost savings in the overall fuel cycle. These alternatives involve varying levels of RD and D resources, calendar time, and technical risk to implement and provide these cost reduction opportunities. Both feed conversion contracts and fuel fabricator contracts are long-term entities. Because of these factors, it is not too early to start planning and making decisions on the most advantageous options so that AVLIS can be integrated cost effectively into the fuel cycle. This should offer economic opportunity to all parties involved including DOE, utilities, feed converters, and fuel fabricators. 10 refs., 11 figs., 2 tabs

[en] Dynamic simulation was used to evaluate the design of the Tails (depleted ₂₃₅U assay) Withdrawal System for an uranium enrichment plant. Desirability of a simulation to check the design was indicated by requirements for a very high system reliability (99.95% availability) over a wide range of system throughput (85:1). Objective of the simulation included: evaluate alternate compressor anti-surge schemes, identify control system sensitivities, examine start-up and shut-down procedures, identify system limitations and testing of proposed design changes, and provide an understanding of system behavior. Three levels of process complexity were modeled: (1) compressions system, (2) combined compressor and liquefaction system, and (3) parallel operation of two compression/liquefaction trains. Two compressor train configurations were evaluated with the simulation mode. A FORTRAN based simulation methodology was used to implement and solve the mathematical models and plot the time history behavior for each test run. Results included discovery that that initial process steady state design would not operate stably. A new steady state was formulated which required some modifications to equipment sizing and control system philosophy. This new design was tested and proven with the simulation. Simulation objectives were achieved. Based on the simulation results, recommendations were made regarding: best compressor configuration, most effective anti-surge control scheme, changes to enhance system reliability and operability, control system sensitivities, control system design to achieve load sharing for parallel trains, and overall system operability with existing design