Note: In aerodynamic enrichment processes, a mixture of gaseous UF6 and light gas (hydrogen or helium) is compressed and then passed through separating elements wherein isotopic separation is accomplished by the generation of high centrifugal forces over a curved-wall geometry. Two processes of this type have been successfully developed: The separation nozzle process and the vortex tube process. For both processes, the main components of a separation stage included cylindrical vessels housing the special separation elements (nozzles or vortex tubes), gas compressors, and heat exchangers to remove the heat of compression. An aerodynamic plant requires a number of these stages, so that quantities can provide an important indication of end use. Because aerodynamic processes use UF6, all equipment, pipeline and instrumentation surfaces (that come in contact with the gas) must be made of, or protected by, materials that remain stable in contact with UF6. All surfaces which come into contact with the process gas are made of, or protected by, UF6-resistant materials; including copper, copper alloys, stainless steel, aluminum, aluminum oxide, aluminum alloys, nickel or alloys containing 60 percent or more nickel by weight, and fluorinated hydrocarbon polymers.
The following items either come into direct contact with the UF6 process gas or directly control the flow within the cascade:
(1) Separation nozzles and assemblies.
Especially designed or prepared separation nozzles and assemblies thereof. The separation nozzles consist of slit-shaped, curved channels having a radius of curvature less than 1 mm, resistant to corrosion by UF6 and having a knife-edge within the nozzle that separates the gas flowing through the nozzle into two fractions.
(2) Vortex tubes and assemblies.
Especially designed or prepared vortex tubes and assemblies thereof. The vortex tubes are cylindrical or tapered, made of, or protected by, materials resistant to corrosion by UF6, and with one or more tangential inlets. The tubes may be equipped with nozzle-type appendages at either or both ends.
The feed gas enters the vortex tube tangentially at one end or through swirl vanes or at numerous tangential positions along the periphery of the tube.
(3) Compressors and gas blowers.
Especially designed or prepared compressors or gas blowers made of, or protected by, materials resistant to corrosion by the UF6/carrier gas (hydrogen or helium) mixture.
(4) Rotary shaft seals.
Especially designed or prepared rotary shaft seals, with seal feed and seal exhaust connections, for sealing the shaft connecting the compressor rotor or the gas blower rotor with the driver motor 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 or gas blower which is filled with a UF6/carrier gas mixture.
(5) Heat exchangers for gas cooling.
Especially designed or prepared heat exchangers, made of, or protected by, materials resistant to corrosion by UF6.
(6) Separation element housings.
Especially designed or prepared separation element housings, made of, or protected by, materials resistant to corrosion by UF6, for containing vortex tubes or separation nozzles.
(7) Feed systems/product and tails withdrawal systems.
Especially designed or prepared process systems or equipment for enrichment plants made of, or protected by, materials resistant to corrosion by UF6, including:
(i) Feed autoclaves, ovens, or systems used for passing UF6 to the enrichment process;
(ii) Desublimers (or cold traps) used to remove UF6 from the enrichment process for subsequent transfer upon heating;
(iii) Solidification or liquefaction stations used to remove UF6 from the enrichment process by compressing and converting UF6 to a liquid or solid form; and
(iv) “Product” or “tails” stations used for transferring UF6 into containers.
(8) Header piping systems.
Especially designed or prepared header piping systems, made of or protected by materials resistant to corrosion by UF6, for handling UF6 within the aerodynamic cascades. The piping network is normally of the “double” header design with each stage or group of stages connected to each of the headers.
(9) Vacuum systems and pumps.
(i) Especially designed or prepared vacuum systems consisting of vacuum manifolds, vacuum headers and vacuum pumps, and designed for service in UF6-bearing atmospheres.
(ii) Especially designed or prepared vacuum pumps for service in UF6-bearing atmospheres and made of, or protected by, materials resistant to corrosion by UF6. These pumps may use fluorocarbon seals and special working fluids.
(10) Special shut-off and control valves.
Especially designed or prepared bellows-sealed valves, manual or automated, shut-off or control valves made of, or protected by, materials resistant to corrosion by UF6 with a diameter of 40 mm or greater for installation in main and auxiliary systems of aerodynamic enrichment plants.
(11) UF6 mass spectrometers/ion sources.
Especially designed or prepared mass spectrometers capable of taking on-line samples from UF6 gas streams and having all of the following:
(i) Capable of measuring ions of 320 atomic mass units or greater and having a resolution of better than 1 part in 320;
(ii) Ion sources constructed of or protected by nickel, nickel-copper alloys with a nickel content of 60 percent or more by weight, or nickel-chrome alloys;
(iii) Electron bombardment ionization sources; and
(iv) Collector system suitable for isotopic analysis.
(12) UF6/carrier gas separation systems.
Especially designed or prepared process systems for separating UF6 from carrier gas (hydrogen or helium).
These systems are designed to reduce the UF6 content in the carrier gas to 1 ppm or less and may incorporate equipment such as:
(i) Cryogenic heat exchangers and cryoseparators capable of temperatures of 153 K (-120 °C) or less;
(ii) Cryogenic refrigeration units capable of temperatures of 153 K (-120 °C) or less;
(iii) Separation nozzle or vortex tube units for the separation of UF6 from carrier gas; or
(iv) UF6 cold traps capable of freezing out UF6.
(13) Any other components especially designed or prepared for use in an aerodynamic enrichment plant or in any of the components described in this appendix.
[79 FR 39294, July 10, 2014]
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