Publication: Magyar Közlöny
Issue: MK-2006-137 (Year: 2006, Number: 137)
Era: 2004-2010
Section: 
Paragraph Index: 307

4. an efficiency of greater than 80%. Explanatory note The items listed above 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 stainless steel, aluminium, aluminium alloys, nickel or alloys containing 60% or more nickel. 5.3. Especially designed or prepared assemblies and components for use in gaseous diffusion enrichment 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 uranium hexafluoride (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 (a) Especially designed or prepared thin, porous filters, with a pore size of 100–1000 C (angstroms), a thickness of 5 mm (0,2 in) or less, and for tubular forms, a diameter of 25 mm (1 in) or less, made of metallic, polymer or ceramic materials resistant to corrosion by UF6, and (b) specially prepared compounds or powders for the manufacture of such filters. Such compounds and powders include nickel or alloys containing 60% or more nickel, aluminium oxide, or UF6-resistant fully fluorinated hydrocarbon polymers having a purity of 99,9% or more, a particle size less than 10 microns, 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 cylindrical vessels greater than 300 mm (12 in;) in diameter and greater than 900 mm (35 in) in length, or rectangular vessels of comparable dimensions, which have an inlet connection and two outlet connections all of which are greater than 50 mm (2 in) in diameter, for containing the gaseous diffusion barrier, made of or lined with UF6-resistant materials and designed for horizontal or vertical installation. 5.3.3. Compressors and gas blowers Especially designed or prepared axial, centrifugal, or positive displacement compressors, or gas blowers with a suction volume capacity of 1 m3/min. or more of UF6 and with a discharge pressure of up to several hundred kPa (100 psi), designed for long-term operation in the UF6 environment with or without an electrical motor of appropriate power, as well as separate assemblies of such compressors and gas blowers. These compressors and gas blowers have a pressure ratio between 2:1 and 6:1 and are made of, or lined with, materials resistant to UF6. 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/min (60 in3/min). 5.3.5. Heat exchangers for cooling UF6 Especially designed or prepared heat exchangers made of or lined with UF6-resistant materials (except stainless steel) or with copper or any combination of those metals, and intended for a leakage pressure change rate of less than 10 Pa (0,0015 psi) per hour under a pressure difference of 100 kPa (15 psi). 2006/137. szám 5.4. Especially designed or prepared auxiliary systems, equipment and components for use in gaseous diffusion enrichment 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 shutdown, 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 gaseous 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. 5.4.1. Feed systems/product and tails withdrawal systems Especially designed or prepared process systems, capable of operating at pressures of 300 kPa (45 psi) or less, including: – feed autoclaves (or systems), used for passing UF6 to the gaseous diffusion cascades, – desublimers (or cold traps) used to remove UF6 from diffusion cascades, – liquefaction stations where UF6 gas from the cascade is compressed and cooled to form liquid UF6, – *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. 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 large vacuum manifolds, vacuum headers and vacuum pumps having a suction capacity of 5 m3/min. (175 ft3/min.) or more. (b) Vacuum pumps especially designed for service in UF6-bearing atmospheres made of, or lined with, aluminium, nickel, or alloys bearing more than 60% nickel. 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 manual or automated shut-off and control bellows valves made of UF6-resistant materials with a diameter of 40 to 1500 mm (1,5 to 59 in) for installation in main and auxiliary systems of gaseous diffusion enrichment plants. 5.4.5. UF6 mass spectrometers/ion sources Especially designed or prepared magnetic or quadrupole mass spectrometers capable of taking on-line samples of feed, product or tails, from UF6 gas streams and having all of the following characteristics:

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