Tertiary Containment Systems cont'd

DOE-HDBK-1132-99

operated in the continuous flow mode, these types of cleanup systems can

easily reduce the tritium concentration in the gas stream to the part-per-billion

level (i.e., 2.6 mCi/m3), or lower, as long as they are operated for a sufficiently

long period of time.

Although the operation of a typical catalyst/molecular sieve tritium removal

system, like that described above, can be very effective, the operation of such

systems can also have drawbacks. In the standard mode of operation, for

example, little or no gas flows through either the glovebox or the cleanup

system for relatively long periods of time because both sides of this type of

containment scheme tend to be activated on an " n demand"basis only. A

substantial drop in the catalyst bed temperature should be expected when the

system is turned on (i.e., the flow on the inside of the catalyst bed goes from a

static situation to several hundred cubic feet per minute in a matter of a few

seconds). Under such circumstances, the temperature in the bed can easily

drop below that which is required to break down tritiated methanes, and the

cleanup system will have to be run long enough to allow the system

temperatures to re-equilibrate. When cleanup systems have to run for

relatively long periods of time, leakage rates into and out of the glovebox in

question, and leakage rates into and out of the cleanup system tend to become

additional factors that must be considered in the overall design of the facility.

When the parameters are appropriately balanced, calculations indicate that the

flow rates for these types of cleanup systems (i.e., high-quality primary

containment system environments in combination with intermediate-quality

secondary system environments) should be high enough to remove the bulk of

the tritium within a few hours to a few tens of hours. Calculations further

indicate that the overall release rate to the environment will be 1 Ci for every 3

to 30 hours of operation.

When similar calculations are performed on the use of a high-quality, primary

containment system in combination with a low-quality secondary system, the

results indicate that the flow rates should be high enough to remove the bulk of

the tritium within a few minutes to a few hours.

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