- List
- NSG – Trigger List (Part 1) – INFCIRC/254/Rev.15/Part 1 (21 April 2026)
INTRODUCTORY NOTE
In the gaseous diffusion method of uranium isotope separation, the main technological assembly is a special porous gaseous diffusion barrier, heat exchanger for cooling the gas (which is heated by the process of compression), seal valves and control valves, and pipelines. Inasmuch as gaseous diffusion technology uses UF₆, all equipment, pipeline and instrumentation surfaces (that come in contact with the gas) must be made of materials that remain stable in contact with UF₆. A gaseous diffusion facility requires a number of these assemblies, so that quantities can provide an important indication of end use.
5.3.1. Gaseous diffusion barriers and barrier materials
(a) Especially designed or prepared thin, porous filters, with a pore size of 10 - 100 nm, a thickness of 5 mm or less, and for tubular forms, a diameter of 25 mm or less, made of metallic, polymer or ceramic materials resistant to corrosion by UF₆ (see EXPLANATORY NOTE to section 5.4.).
(b) especially prepared compounds or powders for the manufacture of such filters. Such compounds and powders include nickel or alloys containing 60% by weight or more nickel, aluminium oxide, or UF₆-resistant fully fluorinated hydrocarbon polymers having a purity of 99.9% by weight or more, a particle size less than 10 µm, and a high degree of particle size uniformity, which are especially prepared for the manufacture of gaseous diffusion barriers.
5.3.2. Diffuser housings
Especially designed or prepared hermetically sealed vessels for containing the gaseous diffusion barrier, made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to section 5.4.).
5.3.3. Compressors and gas blowers
Especially designed or prepared compressors or gas blowers with a suction volume capacity of 1 m³ per minute or more of UF₆, with a discharge pressure of up to 500 kPa, and designed for long-term operation in the UF₆ environment, as well as separate assemblies of such compressors and gas blowers. These compressors and gas blowers have a pressure ratio of 10:1 or less and are made of, or protected by, materials resistant to UF₆ (see EXPLANATORY NOTE to section 5.4.).
5.3.4. Rotary shaft seals
Especially designed or prepared vacuum seals, with seal feed and seal exhaust connections, for sealing the shaft connecting the compressor or the gas blower rotor with the driver motor so as to ensure a reliable seal against in-leaking of air into the inner chamber of the compressor or gas blower which is filled with UF₆. Such seals are normally designed for a buffer gas in-leakage rate of less than 1000 cm³ per minute.
5.3.5. Heat exchangers for cooling UF₆
Especially designed or prepared heat exchangers made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to section 5.4), and intended for a leakage pressure change rate of less than 10 Pa/h under a pressure difference of 100 kPa.
In the gaseous diffusion method of uranium isotope separation, the main technological assembly is a special porous gaseous diffusion barrier, heat exchanger for cooling the gas (which is heated by the process of compression), seal valves and control valves, and pipelines. Inasmuch as gaseous diffusion technology uses UF₆, all equipment, pipeline and instrumentation surfaces (that come in contact with the gas) must be made of materials that remain stable in contact with UF₆. A gaseous diffusion facility requires a number of these assemblies, so that quantities can provide an important indication of end use.
5.3.1. Gaseous diffusion barriers and barrier materials
(a) Especially designed or prepared thin, porous filters, with a pore size of 10 - 100 nm, a thickness of 5 mm or less, and for tubular forms, a diameter of 25 mm or less, made of metallic, polymer or ceramic materials resistant to corrosion by UF₆ (see EXPLANATORY NOTE to section 5.4.).
(b) especially prepared compounds or powders for the manufacture of such filters. Such compounds and powders include nickel or alloys containing 60% by weight or more nickel, aluminium oxide, or UF₆-resistant fully fluorinated hydrocarbon polymers having a purity of 99.9% by weight or more, a particle size less than 10 µm, and a high degree of particle size uniformity, which are especially prepared for the manufacture of gaseous diffusion barriers.
5.3.2. Diffuser housings
Especially designed or prepared hermetically sealed vessels for containing the gaseous diffusion barrier, made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to section 5.4.).
5.3.3. Compressors and gas blowers
Especially designed or prepared compressors or gas blowers with a suction volume capacity of 1 m³ per minute or more of UF₆, with a discharge pressure of up to 500 kPa, and designed for long-term operation in the UF₆ environment, as well as separate assemblies of such compressors and gas blowers. These compressors and gas blowers have a pressure ratio of 10:1 or less and are made of, or protected by, materials resistant to UF₆ (see EXPLANATORY NOTE to section 5.4.).
5.3.4. Rotary shaft seals
Especially designed or prepared vacuum seals, with seal feed and seal exhaust connections, for sealing the shaft connecting the compressor or the gas blower rotor with the driver motor so as to ensure a reliable seal against in-leaking of air into the inner chamber of the compressor or gas blower which is filled with UF₆. Such seals are normally designed for a buffer gas in-leakage rate of less than 1000 cm³ per minute.
5.3.5. Heat exchangers for cooling UF₆
Especially designed or prepared heat exchangers made of or protected by UF₆-resistant materials (see EXPLANATORY NOTE to section 5.4), and intended for a leakage pressure change rate of less than 10 Pa/h under a pressure difference of 100 kPa.