- List
- NSG – Trigger List (Part 1) – INFCIRC/254/Rev.15/Part 1 (21 April 2026)
INTRODUCTORY NOTE
The auxiliary systems, equipment and components for gaseous diffusion enrichment plants are the systems of plant needed to feed UF₆ to the gaseous diffusion assembly, to link the individual assemblies to each other to form cascades (or stages) to allow for progressively higher enrichments and to extract the ‘product’ and ‘tails’ UF₆ from the diffusion cascades. Because of the high inertial properties of diffusion cascades, any interruption in their operation, and especially their shut-down, leads to serious consequences. Therefore, a strict and constant maintenance of vacuum in all technological systems, automatic protection from accidents, and precise automated regulation of the gas flow is of importance in a gaseous diffusion plant. All this leads to a need to equip the plant with a large number of special measuring, regulating and controlling systems.
Normally UF₆ is evaporated from cylinders placed within autoclaves and is distributed in gaseous form to the entry point by way of cascade header pipework. The ‘product’ and ‘tails’ UF₆ gas streams flowing from exit points are passed by way of cascade header pipework to either cold traps or to compression stations where the UF₆ gas is liquefied prior to onward transfer into suitable containers for transportation or storage. Because a gaseous diffusion enrichment plant consists of a large number of gaseous diffusion assemblies arranged in cascades, there are many kilometres of cascade header pipework, incorporating thousands of welds with substantial amounts of repetition of layout. The equipment, components and piping systems are fabricated to very high vacuum and cleanliness standards.
EXPLANATORY NOTE
The items listed below either come into direct contact with the UF₆ process gas or directly control the flow within the cascade. 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.
5.4.1. 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, cold traps or pumps 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.
5.4.2. Header piping systems
Especially designed or prepared piping systems and header systems for handling UF₆ within the gaseous diffusion cascades.
EXPLANATORY NOTE
This piping network is normally of the ‘double’ header system with each cell connected to each of the headers.
5.4.3. Vacuum systems
(a) Especially designed or prepared vacuum manifolds, vacuum headers and vacuum pumps having a suction capacity of 5 m³/min or more.
(b) Vacuum pumps especially designed for service in UF₆-bearing atmospheres made of, or protected by, materials resistant to corrosion by UF₆ (see EXPLANATORY NOTE to this section). These pumps may be either rotary or positive, may have displacement and fluorocarbon seals, and may have special working fluids present.
5.4.4. 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, for installation in main and auxiliary systems of gaseous diffusion enrichment plants.
5.4.5. 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.
The auxiliary systems, equipment and components for gaseous diffusion enrichment plants are the systems of plant needed to feed UF₆ to the gaseous diffusion assembly, to link the individual assemblies to each other to form cascades (or stages) to allow for progressively higher enrichments and to extract the ‘product’ and ‘tails’ UF₆ from the diffusion cascades. Because of the high inertial properties of diffusion cascades, any interruption in their operation, and especially their shut-down, leads to serious consequences. Therefore, a strict and constant maintenance of vacuum in all technological systems, automatic protection from accidents, and precise automated regulation of the gas flow is of importance in a gaseous diffusion plant. All this leads to a need to equip the plant with a large number of special measuring, regulating and controlling systems.
Normally UF₆ is evaporated from cylinders placed within autoclaves and is distributed in gaseous form to the entry point by way of cascade header pipework. The ‘product’ and ‘tails’ UF₆ gas streams flowing from exit points are passed by way of cascade header pipework to either cold traps or to compression stations where the UF₆ gas is liquefied prior to onward transfer into suitable containers for transportation or storage. Because a gaseous diffusion enrichment plant consists of a large number of gaseous diffusion assemblies arranged in cascades, there are many kilometres of cascade header pipework, incorporating thousands of welds with substantial amounts of repetition of layout. The equipment, components and piping systems are fabricated to very high vacuum and cleanliness standards.
EXPLANATORY NOTE
The items listed below either come into direct contact with the UF₆ process gas or directly control the flow within the cascade. 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.
5.4.1. 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, cold traps or pumps 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.
5.4.2. Header piping systems
Especially designed or prepared piping systems and header systems for handling UF₆ within the gaseous diffusion cascades.
EXPLANATORY NOTE
This piping network is normally of the ‘double’ header system with each cell connected to each of the headers.
5.4.3. Vacuum systems
(a) Especially designed or prepared vacuum manifolds, vacuum headers and vacuum pumps having a suction capacity of 5 m³/min or more.
(b) Vacuum pumps especially designed for service in UF₆-bearing atmospheres made of, or protected by, materials resistant to corrosion by UF₆ (see EXPLANATORY NOTE to this section). These pumps may be either rotary or positive, may have displacement and fluorocarbon seals, and may have special working fluids present.
5.4.4. 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, for installation in main and auxiliary systems of gaseous diffusion enrichment plants.
5.4.5. 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.