- List
- NSG – Trigger List (Part 1) – INFCIRC/254/Rev.15/Part 1 (21 April 2026)
INTRODUCTORY 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 include 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. Since 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.
EXPLANATORY NOTE
The items listed in this section either come into direct contact with the UF₆ process gas or directly control the flow within the cascade. All surfaces which come into contact with the process gas are wholly made of or protected by UF₆-resistant materials. For the purposes of the section relating to aerodynamic enrichment items, the materials resistant to corrosion by UF₆ include copper, copper alloys, stainless steel, aluminium, aluminium oxide, aluminium alloys, nickel or alloys containing 60% by weight or more nickel and fluorinated hydrocarbon polymers.
5.5.1. Separation nozzles
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.
5.5.2. Vortex tubes
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 nozzletype appendages at either or both ends.
EXPLANATORY NOTE
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.
5.5.3. 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.
5.5.4. 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 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 or gas blower which is filled with a UF₆/carrier gas mixture.
5.5.5. Heat exchangers for gas cooling
Especially designed or prepared heat exchangers made of or protected by materials resistant to corrosion by UF₆.
5.5.6. 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.
5.5.7. 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:
(a) Feed autoclaves, ovens, or systems used for passing UF₆ to the enrichment process;
(b) Desublimers (or cold traps) used to remove UF₆ from the enrichment process for subsequent transfer upon heating;
(c) Solidification or liquefaction stations used to remove UF₆ from the enrichment process by compressing and converting UF₆ to a liquid or solid form;
(d) ‘Product’ or ‘tails’ stations used for transferring UF₆ into containers.
5.5.8. 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. This piping network is normally of the ‘double’ header design with each stage or group of stages connected to each of the headers.
5.5.9. Vacuum systems and pumps
(a) Especially designed or prepared vacuum systems consisting of vacuum manifolds, vacuum headers and vacuum pumps, and designed for service in UF₆-bearing atmospheres,
(b) Vacuum pumps especially designed or prepared 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.
5.5.10. Special shut-off and control valves
Especially designed or prepared bellows-sealed valves, manual or automated, shut-off or control, 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.
5.5.11. 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:
1. Capable of measuring ions of 320 atomic mass units or greater and having a resolution of better than 1 part in 320;
2. Ion sources constructed of or protected by nickel, nickel-copper alloys with a nickel content of 60% by weight or more, or nickel-chrome alloys;
3. Electron bombardment ionisation sources; and
4. Having a 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 153 K (120°C) or less;
(b) Cryogenic refrigeration units capable of temperatures of 153 K (-120°C) or less;
(c) Separation nozzle or vortex tube units for the separation of UF₆ from carrier gas; or
(d) UF₆ cold traps capable of freezing out UF₆.
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 include 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. Since 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.
EXPLANATORY NOTE
The items listed in this section either come into direct contact with the UF₆ process gas or directly control the flow within the cascade. All surfaces which come into contact with the process gas are wholly made of or protected by UF₆-resistant materials. For the purposes of the section relating to aerodynamic enrichment items, the materials resistant to corrosion by UF₆ include copper, copper alloys, stainless steel, aluminium, aluminium oxide, aluminium alloys, nickel or alloys containing 60% by weight or more nickel and fluorinated hydrocarbon polymers.
5.5.1. Separation nozzles
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.
5.5.2. Vortex tubes
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 nozzletype appendages at either or both ends.
EXPLANATORY NOTE
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.
5.5.3. 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.
5.5.4. 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 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 or gas blower which is filled with a UF₆/carrier gas mixture.
5.5.5. Heat exchangers for gas cooling
Especially designed or prepared heat exchangers made of or protected by materials resistant to corrosion by UF₆.
5.5.6. 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.
5.5.7. 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:
(a) Feed autoclaves, ovens, or systems used for passing UF₆ to the enrichment process;
(b) Desublimers (or cold traps) used to remove UF₆ from the enrichment process for subsequent transfer upon heating;
(c) Solidification or liquefaction stations used to remove UF₆ from the enrichment process by compressing and converting UF₆ to a liquid or solid form;
(d) ‘Product’ or ‘tails’ stations used for transferring UF₆ into containers.
5.5.8. 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. This piping network is normally of the ‘double’ header design with each stage or group of stages connected to each of the headers.
5.5.9. Vacuum systems and pumps
(a) Especially designed or prepared vacuum systems consisting of vacuum manifolds, vacuum headers and vacuum pumps, and designed for service in UF₆-bearing atmospheres,
(b) Vacuum pumps especially designed or prepared 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.
5.5.10. Special shut-off and control valves
Especially designed or prepared bellows-sealed valves, manual or automated, shut-off or control, 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.
5.5.11. 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:
1. Capable of measuring ions of 320 atomic mass units or greater and having a resolution of better than 1 part in 320;
2. Ion sources constructed of or protected by nickel, nickel-copper alloys with a nickel content of 60% by weight or more, or nickel-chrome alloys;
3. Electron bombardment ionisation sources; and
4. Having a 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 153 K (120°C) or less;
(b) Cryogenic refrigeration units capable of temperatures of 153 K (-120°C) or less;
(c) Separation nozzle or vortex tube units for the separation of UF₆ from carrier gas; or
(d) UF₆ cold traps capable of freezing out UF₆.