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Tertiary Containment Systems cont'd - hdbk1132990139
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Design Considerations - index
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Figure 12. Use of double-valved containers


DOE-HDBK-1132-99
Double-Valve Design For Transportable Containers . The use of two valves
in series on containers filled with tritium, which are to be disconnected from the
tritium apparatus on a routine basis, has been in common use for several
years. The idea behind this is straightforward. Valve seats fail and when the
failure of a single valve seat can result in the release of significant quantities of
tritium, two valves in series should be used. If a single valve is used and the
valve seat develops a leak during storage, the container should be connected
to a manifold, the container port uncapped, and the tritium released into the
containment system through the failed valve seat.
Valve seat failure is often associated with damage to the seat caused by long
exposure to tritium, especially if elastomeric seats have been used (not
recommended). Double valves should be used where the container valve seat
is exposed to tritium for long periods of time. Experienced tritium handlers
assume that valve seats can, do, and will fail, and that they have failed until
proved otherwise. Figure 12 explains how to check double valving for
leakage.
Purge Ports . A "purge port" is a capped, sealed port connected through a
valve to a potentially tritium-contaminated volume. The purpose of a purge
port is to provide a path that can be used to remove tritium-contaminated
gases from the isolation volume prior to making a line break at the component
flanges to remove a component. If the tritium-contaminated gases are not
removed from the isolation volume, they will be released into the containment
system when the flange is unsealed to remove the component and these
released gases and outgassing from the isolation volume surfaces will
contaminate the containment volume gases. Following removal and
replacement of a component, the port is used to leak-test the new component
and the new flange seals prior to placing the new component in service.
Figure 13 is an illustration of two purge ports installed to allow evacuation of
the volume and leak testing of the flanges between two sets of valves that
have been placed to allow isolation and removal of a tritium-contaminated
component. Note that the purge ports are part of the permanently installed
system and are not part of the component. The component is isolated with two
I-124


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