- List
- NSG – Trigger List (Part 1) – INFCIRC/254/Rev.15/Part 1 (21 April 2026)
INTRODUCTORY NOTE
The auxiliary systems, equipment and components for a gas centrifuge enrichment plant are the systems of plant needed to feed UF₆ to the centrifuges, to link the individual centrifuges to each other to form cascades (or stages) to allow for progressively higher enrichments and to extract the ‘product’ and ‘tails’ UF₆ from the centrifuges, together with the equipment required to drive the centrifuges or to control the plant.
Normally UF₆ is evaporated from the solid using heated autoclaves and is distributed in gaseous form to the centrifuges by way of cascade header pipework. The ‘product’ and ‘tails’ UF₆ gas streams flowing from the centrifuges are also passed by way of cascade header pipework to cold traps (operating at about 203 K (-70ºC)) where they are condensed prior to onward transfer into suitable containers for transportation or storage. Because an enrichment plant consists of many thousands of centrifuges arranged in cascades there are many kilometres of cascade header pipework, incorporating thousands of welds with a substantial amount of repetition of layout. The equipment, components and piping systems are fabricated to very high vacuum and cleanliness standards.
EXPLANATORY NOTE
Some of the items listed below either come into direct contact with the UF₆ process gas or directly control the centrifuges and the passage of the gas from centrifuge to centrifuge and cascade to 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.
5.2.1. 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.
5.2.2. Machine header piping systems
Especially designed or prepared piping systems and header systems for handling UF₆ within the centrifuge cascades. The piping network is normally of the ‘triple’ header system with each centrifuge connected to each of the headers. There is thus a substantial amount of repetition in its form. It is wholly made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to this section) and is fabricated to very high vacuum and cleanliness standards.
5.2.3 Special shut-off and control valves
(a) Shut-off valves especially designed or prepared to act on the feed, product or tails UF₆ gas streams of an individual gas centrifuge.
(b) Bellows-sealed valves, manual or automated, shut-off or control, made of or protected by materials resistant to corrosion by UF₆, with an inside diameter of 10 to 160 mm, especially designed or prepared for use in main or auxiliary systems of gas centrifuge enrichment plants.
EXPLANATORY NOTE
Typical especially designed or prepared valves include bellow-sealed valves, fast acting closure-types, fast acting valves and others.
5.2.4. 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 characteristics:
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.
5.2.5. Frequency changers
Frequency changers (also known as converters or inverters) especially designed or prepared to supply motor stators as defined under 5.1.2.(d), or parts, components and sub-assemblies of such frequency changers having both of the following characteristics:
1. A multiphase frequency output of 600 Hz or greater; and
2. High stability (with frequency control better than 0.2%).
The auxiliary systems, equipment and components for a gas centrifuge enrichment plant are the systems of plant needed to feed UF₆ to the centrifuges, to link the individual centrifuges to each other to form cascades (or stages) to allow for progressively higher enrichments and to extract the ‘product’ and ‘tails’ UF₆ from the centrifuges, together with the equipment required to drive the centrifuges or to control the plant.
Normally UF₆ is evaporated from the solid using heated autoclaves and is distributed in gaseous form to the centrifuges by way of cascade header pipework. The ‘product’ and ‘tails’ UF₆ gas streams flowing from the centrifuges are also passed by way of cascade header pipework to cold traps (operating at about 203 K (-70ºC)) where they are condensed prior to onward transfer into suitable containers for transportation or storage. Because an enrichment plant consists of many thousands of centrifuges arranged in cascades there are many kilometres of cascade header pipework, incorporating thousands of welds with a substantial amount of repetition of layout. The equipment, components and piping systems are fabricated to very high vacuum and cleanliness standards.
EXPLANATORY NOTE
Some of the items listed below either come into direct contact with the UF₆ process gas or directly control the centrifuges and the passage of the gas from centrifuge to centrifuge and cascade to 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.
5.2.1. 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.
5.2.2. Machine header piping systems
Especially designed or prepared piping systems and header systems for handling UF₆ within the centrifuge cascades. The piping network is normally of the ‘triple’ header system with each centrifuge connected to each of the headers. There is thus a substantial amount of repetition in its form. It is wholly made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to this section) and is fabricated to very high vacuum and cleanliness standards.
5.2.3 Special shut-off and control valves
(a) Shut-off valves especially designed or prepared to act on the feed, product or tails UF₆ gas streams of an individual gas centrifuge.
(b) Bellows-sealed valves, manual or automated, shut-off or control, made of or protected by materials resistant to corrosion by UF₆, with an inside diameter of 10 to 160 mm, especially designed or prepared for use in main or auxiliary systems of gas centrifuge enrichment plants.
EXPLANATORY NOTE
Typical especially designed or prepared valves include bellow-sealed valves, fast acting closure-types, fast acting valves and others.
5.2.4. 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 characteristics:
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.
5.2.5. Frequency changers
Frequency changers (also known as converters or inverters) especially designed or prepared to supply motor stators as defined under 5.1.2.(d), or parts, components and sub-assemblies of such frequency changers having both of the following characteristics:
1. A multiphase frequency output of 600 Hz or greater; and
2. High stability (with frequency control better than 0.2%).