Double-Valve Design For Transportable 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

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