Publication: Magyar Közlöny
Issue: MK-1999-95 (Year: 1999, Number: 95)
Era: 1990-2004
Section: 
Paragraph Index: 207

4. Collector system suitable for isotopic analysis. 5.5.12. UF6/carrier gas separation systems Especially designed or prepared process systems for separating UF6 from carrier gas (hydrogen or helium). Explanatory note These systems are designed to reduce the UF6 content in the carrier gas to 1 ppm or less and may incorporate equipment such as: (a) Cryogenic heat exchangers and cryoseparators capable of temperatures of —120 ˚C or less, or (b) Cryogenic refrigeration units capable of temperatures of —120 ˚C or less, or (c) Separation nozzle or vortex tube units for the separation of UF6 from carrier gas, or (d) UF6 cold traps capable of temperatures of —20 ˚C or less. 5.6. Especially designed or prepared systems, equipment and components for use in chemical exchange or ion exchange enrichment plants Introductory note The slight difference in mass between the isotopes of uranium causes small changes in chemical reaction equilibria that can be used as a basis for separation of the isotopes. Two processes have been successfully developed: 1999/95. szám liquid-liquid chemical exchange and solid-liquid ion exchange. In the liquid-liquid chemical exchange process, immiscible liquid phases (aqueous and organic) are countercurrently contacted to give the cascading effect of thousands of separation stages. The aqueous phase consists of uranium chloride in hydrochloric acid solution; the organic phase consists of an extractant containing uranium chloride in an organic solvent. The contactors employed in the separation cascade can be liquid-liquid exchange columns (such as pulsed columns with sieve plates) or liquid centrifugal contactors. Chemical conversions (oxidation and reduction) are required at both ends of the separation cascade in order to provide for the reflux requirements at each end. A major design concern is to avoid contamination of the process streams with certain metal ions. Plastic, plastic-lined (including use of fluorocarbon polymers) and/or glass-lined columns and piping are therefore used. In the solid-liquid ion-exchange process, enrichment is accomplished by uranium adsorption/desorption on a special, very fast-acting, ion-exchange resin or adsorbent. A solution of uranium in hydrochloric acid and other chemical agents is passed through cylindrical enrichment columns containing packed beds of the adsorbent. For a continuous process, a reflux system is necessary to release the uranium from the adsorbent back into the liquid flow so that ’product’ and ’tails’ can be collected. This is accomplished with the use of suitable reduction/oxidation chemical agents that are fully regenerated in separate external circuits and that may be partially regenerated within the isotopic separation columns themselves. The presence of hot concentrated hydrochloric acid solutions in the process requires that the equipment be made of or protected by special corrosion-resistant materials. 5.6.1. Liquid-liquid exchange columns (Chemical exchange) Countercurrent liquid-liquid exchange columns having mechanical power input (i.e., pulsed columns with sieve plates, reciprocating plate columns, and columns with internal turbine mixers), especially designed or prepared for uranium enrichment using the chemical exchange process. For corrosion resistance to concentrated hydrochloric acid solutions, these columns and their internals are made of or protected by suitable plastic materials (such as fluorocarbon polymers) or glass. The stage residence time of the columns is designed to be short (30 seconds or less). 5.6.2. Liquid-liquid centrifugal contactors (Chemical exchange) Liquid-liquid centrifugal contactors especially designed or prepared for uranium enrichment using the chemical exchange process. Such contactors use rotation to achieve dispersion of the organic and aqueous streams and then centrifugal force to separate the phases. For corrosion resistance to concentrated hydrochloric acid solutions, the contactors are made of or are lined with suitable plastic materials (such as fluorocarbon polymers) or are lined with glass. The stage residence time of the centrifugal contactors is designed to be short (30 seconds or less). 5.6.3. Uranium reduction systems and equipment (Chemical exchange) (a) Especially designed or prepared electrochemical reduction cells to reduce uranium from one valence state to another for uranium enrichment using the chemical exchange process. The cell materials in contact with process solutions must be corrosion resistant to concentrated hydrochloric acid solutions. Explanatory note The cell cathodic compartment must be designed to prevent re-oxidation of uranium to its higher valence state. To keep the uranium in the cathodic compartment, the cell may have an impervious diaphragm membrane constructed of special cation exchange material. The cathode consists of a suitable solid conductor such as graphite. (b) Especially designed or prepared systems at the product end of the cascade for taking the U4+ out of the organic stream, adjusting the acid concentration and feeding to the electrochemical reduction cells. Explanatory note These systems consist of solvent extraction equipment for stripping the U4+ from the organic stream into an aqueous solution, evaporation and/or other equipment to accomplish solution pH adjustment and control, and pumps or other transfer devices for feeding to the electrochemical reduction cells. A major design concern is to avoid contamination of the aqueous stream with certain metal ions. Consequently, for those parts in contact with the process stream, the system is constructed of equipment made of or protected by suitable materials (such as glass, fluorocarbon polymers, polyphenyl sulfate, polyether sulfone, and resin-impregnated graphite). 5.6.4. Feed preparation systems (Chemical exchange) Especially designed or prepared systems for producing high-purity uranium chloride feed solutions for chemical exchange uranium isotope separation plants. Explanatory note These systems consist of dissolution, solvent extraction and/or ion exchange equipment for purification and electrolytic cells for reducing the uranium U6+ or U4+ to U 3+ . These systems produce uranium chloride solutions having only a few parts per million of metallic impurities such as chromium, iron, vanadium, molybdenum and other bivalent or higher multi-valent cations. Materials of construction for portions of the system processing high-purity U3+ include glass, fluorocarbon polymers, polyphenyl sulfate or polyether sulfone plastic-lined and resin-impregnated graphite. 1999/95. szám 5.6.5. Uranium oxidation systems (Chemical exchange) Especially designed or prepared systems for oxidation of U3+ to U 4+ for return to the uranium isotope separation cascade in the chemical exchange enrichment process. Explanatory note These systems may incorporate equipment such as: (a) Equipment for contacting chlorine and oxygen with the aqueous effluent from the isotope separation equipment and extracting the resultant U 4+ into the stripped organic stream returning from the product end of the cascade, (b) Equipment that separates water from hydrochloric acid so that the water and the concentrated hydrochloric acid may be reintroduced to the process at the proper locations. 5.6.6. Fast-reacting ion exchange resins/adsorbents (ion exchange) Fast-reacting ion-exchange resins or adsorbents especially designed or prepared for uranium enrichment using the ion exchange process, including porous macroreticular resins, and/or pellicular structures in which the active chemical exchange groups are limited to a coating on the surface of an inactive porous support structure, and other composite structures in any suitable form including particles or fibers. These ion exchange resins/adsorbents have diameters of 0.2 mm or less and must be chemically resistant to concentrated hydrochloric acid solutions as well as physically strong enough so as not to degrade in the exchange columns. The resins/adsorbents are especially designed to achieve very fast uranium isotope exchange kinetics (exchange rate half-time of less than 10 seconds) and are capable of operating at a temperature in the range of 100 ˚C to 200 ˚C. 5.6.7. Ion exchange columns (Ion exchange) Cylindrical columns greater than 1000 mm in diameter for containing and supporting packed beds of ion exchange resin/adsorbent, especially designed or prepared for uranium enrichment using the ion exchange process. These columns are made of or protected by materials (such as titanium or fluorocarbon plastics) resistant to corrosion by concentrated hydrochloric acid solutions and are capable of operating at a temperature in the range of 100 ˚C to 200 ˚C and pressures above 0.7 MPa (102 psi). 5.6.8. Ion exchange reflux systems (Ion exchange) (a) Especially designed or prepared chemical or electrochemical reduction systems for regeneration of the chemical reducing agent(s) used in ion exchange uranium enrichment cascades. (b) Especially designed or prepared chemical or electrochemical oxidation systems for regeneration of the chemical oxidizing agent(s) used in ion exchange uranium enrichment cascades. Explanatory note The ion exchange enrichment process may use, for example, trivalent titanium (Ti3+ ) as a reducing cation in which case the reduction system would regenerate Ti 3+ by reducing Ti 4+ . The process may use, for example, trivalent iron (Fe 3+ ) as an oxidant in which case the oxidation system would regenerate Fe 3+ by oxidizing Fe 2+ . 5.7. Especially designed or prepared systems, equipment and components for use in laser-based enrichment plants Introductory note Present systems for enrichment processes using lasers fall into two categories: those in which the process medium is atomic uranium vapor and those in which the process medium is the vapor of a uranium compound. Common nomenclature for such processes include: first category — atomic vapor laser isotope separation (AVLIS or SILVA); second category — molecular laser isotope separation (MLIS or MOLIS) and chemical reaction by isotope selective laser activation (CRISLA). The systems, equipment and components for laser enrichment plants embrace: (a) devices to feed uranium-metal vapor (for selective photo-ionization) or devices to feed the vapor of a uranium compound (for photo-dissociation or chemical activation); (b) devices to collect enriched and depleted uranium metal as ’product’ and ’tails’ in the first category, and devices to collect dissociated or reacted compounds as ’product’ and unaffected material as ’tails’ in the second category; (c) process laser systems to selectively excite the uranium-235 species; and (d) feed preparation and product conversion equipment. The complexity of the spectroscopy of uranium atoms and compounds may require incorporation of any of a number of available laser technologies. Explanatory note Many of the items listed in this section come into direct contact with uranium metal vapor or liquid or with process gas consisting of UF6 or a mixture of UF6 and other gases. All surfaces that come into contact with the uranium or UF 6 are wholly made of or protected by corrosion-resistant materials. For the purposes of the section relating to laser-based enrichment items, the materials resistant to corrosion by the vapor or liquid of uranium metal or uranium alloys include yttria-coated graphite and tantalum; and the materials resistant to corrosion by UF6 include copper, stainless steel, aluminium, aluminium alloys, nickel or alloys containing 60% or more nickel and UF 6-resistant fully fluorinated hydrocarbon polymers. 5.7.1. Uranium vaporization systems (AVLIS) Especially designed or prepared uranium vaporization systems which contain high-power strip or scanning electron beam guns with a delivered power on the target of more than 2.5 kW/cm. 1999/95. szám 5.7.2. Liquid uranium metal handling systems (AVLIS) Especially designed or prepared liquid metal handling systems for molten uranium or uranium alloys, consisting of crucibles and cooling equipment for the crucibles. Explanatory note The crucibles and other parts of this system that come into contact with molten uranium or uranium alloys are made of or protected by materials of suitable corrosion and heat resistance. Suitable materials include tantalum, yttria-coated graphite, graphite coated with other rare earth oxides or mixtures thereof. 5.7.3. Uranium metal ’product’ and ’tails’ collector assemblies (AVLIS) Especially designed or prepared ’product’ and ’tails’ collector assemblies for uranium metal in liquid or solid form. Explanatory note Components for these assemblies are made of or protected by materials resistant to the heat and corrosion of uranium metal vapor or liquid (such as yttria-coated graphite or tantalum) and may include pipes, valves, fittings, ’gutters’, feed-throughs, heat exchangers and collector plates for magnetic, electrostatic or other separation methods. 5.7.4. Separator module housings (AVLIS) Especially designed or prepared cylindrical or rectangular vessels for containing the uranium metal vapor source, the electron beam gun, and the ’product’ and ’tails’ collectors. Explanatory note These housings have multiplicity of ports for electrical and water feed-throughs, laser beam windows, vacuum pump connections and instrumentation diagnostics and monitoring. They have provisions for opening and closure to allow refurbishment of internal components. 5.7.5. Supersonic expansion nozzles (MLIS) Especially designed or prepared supersonic expansion nozzles for cooling mixtures of UF6 and carrier gas to 150 K or less and which are corrosion resistant to UF6. 5.7.6. Uranium pentafluoride product collectors (MLIS) Especially designed or prepared uranium pentafluoride (UF 5) solid product collectors consisting of filter, impact, or cyclone-type collectors, or combinations thereof, and which are corrosion resistant to the UF5/UF 6 environment. 5.7.7. UF6/carrier gas compressors (MLIS) Especially designed or prepared compressors for UF 6/carrier gas mixtures, designed for long term operation in a UF6 environment. The components of these compressors that come into contact with process gas are made of or protected by materials resistant to corrosion by UF 6. 5.7.8. Rotary shaft seals (MLIS) Especially designed or prepared rotary shaft seals, with seal feed and seal exhaust connections, for sealing the shaft connecting the compressor rotor with the driver motor so as to ensure a reliable seal against out-leakage of process gas or in-leakage of air or seal gas into the inner chamber of the compressor which is filled with a UF6/carrier gas mixture. 5.7.9. Fluorination systems (MLIS) Especially designed or prepared systems for fluorinating UF5 (solid) to UF6 (gas). Explanatory note These systems are designed to fluorinate the collected UF 5 powder to UF6 for subsequent collection in product containers or for transfer as feed to MLIS units for additional enrichment. In one approach, the fluorination reaction may be accomplished within the isotope separation system to react and recover directly off the ’product’ collectors. In another approach, the UF5 powder may be removed/transferred from the ’product’ collectors into a suitable reaction vessel (e.g., fluidized-bed reactor, screw reactor or flame tower) for fluorination. In both approaches, equipment for storage and transfer of fluorine (or other suitable fluorinating agents) and for collection and transfer of UF6 are used. 5.7.10. UF6 mass spectrometers/ion sources (MLIS) Especially designed or prepared magnetic or quadrupole mass spectrometers capable of taking ’on-line’ samples of feed, ’product’ or ’tails’, from UF6 gas streams and having all of the following characteristics:

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