Appendix C to Part 110 - Illustrative List of Gaseous Diffusion Enrichment Plant Assemblies and Components Under NRC Export Licensing Authority
10:2.0.1.1.20.11.139.7.24 : Appendix C
Appendix C to Part 110 - Illustrative List of Gaseous Diffusion
Enrichment Plant Assemblies and Components Under NRC Export
Licensing Authority 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.
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 for
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 liquified 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
kilometers 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.
The items listed below 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 lined with, UF6-resistant materials. For the
purposes of this appendix, the materials resistant to corrosion by
UF6 include copper, copper alloys, stainless steel, aluminum,
aluminum oxide, aluminum alloys, nickel or alloys containing 60
percent or more nickel and fluorinated hydrocarbon polymers.
1. Assemblies and components especially designed or prepared for
use in gaseous diffusion enrichment.
1.1 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
Note in § 2 of this appendix).
(b) Especially prepared compounds or powders for the manufacture
of such filters. Such compounds and powders include nickel or
alloys containing 60 percent or more nickel, aluminum oxide, or
UF6-resistant fully fluorinated hydrocarbon polymers having a
purity of 99.9 percent 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.
1.2 Diffuser Housings
Especially designed or prepared hermetically sealed vessels for
containing the gaseous diffusion barrier, made of or protected by
UF6-resistant materials (See Note in § 2 of this appendix).
1.3 Compressors and Gas Blowers
Especially designed or prepared compressors or gas blowers with
a suction volume capacity of 1 m 3 per minute or more of UF6, and
with a discharge pressure of up to 500 kPa, 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 Note in § 2 of this
appendix).
1.4 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 cm 3 per minute.
1.5 Heat Exchangers for Cooling UF6
Especially designed or prepared heat exchangers made of or
protected by UF6 resistant materials (see Note to § 2 of this
appendix) and intended for a leakage pressure change rate of less
than 10 Pa per hour under a pressure difference of 100 kPa.
2. Auxiliary systems, equipment, and components especially
designed or prepared for use in gaseous diffusion enrichment.
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, aluminum, aluminum oxide, aluminum alloys,
nickel or alloys containing 60 percent or more nickel, and
fluorinated hydrocarbon polymers.
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:
(1) Feed autoclaves, ovens, or systems used for passing UF6 to
the enrichment process;
(2) Desublimers, cold traps, or pumps used to remove UF6 from
the enrichment process for subsequent transfer upon heating;
(3) Solidification or liquefaction stations used to remove UF6
from the enrichment process by compressing and converting UF6 to a
liquid or solid form;
(4) “Product” or “tails” stations used for transferring UF6 into
containers.
2.2 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.
2.3 Vacuum Systems
(a) Especially designed or prepared vacuum manifolds, vacuum
headers and vacuum pumps having a suction capacity of 5 m 3 per
minute 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 Note to this section). These pumps may be
either rotary or positive displacement, may have fluorocarbon
seals, and may have special working fluids present.
2.4 Special Shut-Off and Control Valves
Especially designed or prepared bellows-sealed valves, manual or
automated, shut-off or control valves, made of, or protected by,
materials resistant to corrosion by UF6, for installation in main
and auxiliary systems of gaseous diffusion enrichment plants.
2.5 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:
(a) Capable of measuring ions of 320 atomic mass units or
greater and having a resolution of better than 1 part in 320;
(b) ion sources constructed of or protected by nickel,
nickel-copper alloys with a nickel content of 60 percent or more by
weight, or nickel-chrome alloys;
(c) electron bombardment ionization sources; and
(d) having a collector system suitable for isotopic
analysis.
3. Any other components especially designed or prepared for use
in a gaseous diffusion enrichment plant or in any of the components
described in this appendix.
[79 FR 39293, July 10, 2014]