Tritium Cleanup and Removal Systems cont'd

DOE-HDBK-1129-99

There are several considerations in determining the adequacy of the tritium removal system. First

is the volume: the larger the volume, the longer it will take to remove tritium from the gases.

Second is the tritium removal system flow rate. This rate affects the time required to remove

tritium from the gases. The lower the flow rate, the longer it will take to remove tritium from the

volume.

Third is the cleanup rate of the tritium removal system. This system is typically operated in a

recirculating mode, but may also be operated in a single-pass mode. The tritium-contaminated

gases are pumped through the tritium removal system, and the cleaned gases are either returned

to the volume or released to the environment.

In a large complex system filled with equipment, it is difficult to know exactly how the returned or

make-up gases will mix with gas in the system. The gas exit port should be spaced several feet

away from the return port. It could be assumed that gas flows through in a slug, like a piston, and

that only a single pass would be required to remove all of the tritium from the gases. Slug or piston

displacement flow, however, is unlikely, and a more common assumption is to assume that the

incoming tritium free gases exponentially dilute the gases.

Employing the standard assumption of exponential dilution (which has been experimentally verified

in the DOE complex [23]), the quantity of tritium in the system Qt is expressed by

Qi e -t(F/V)

Qt =

where Qi =

initial quantity of tritium released

time after starting the tritium removal system

volume of the system

flow rate of the tritium removal system

A simple way of using the equation is to calculate the time it will take to reduce the system tritium

concentration by a factor of 10. That is:

Qt/Qi = 1/10 = e -t(F/V)

This implies:

-t(F/V) = ln 1/10 = -2.3

2.3 x (F/V)

Therefore, assuming exponential dilution, the tritium concentration of the gas will be reduced by a

factor of 10 for every 2.3 time constants determined by F/V. Similar calculations show that the

concentration will be reduced by a factor of 100 and 1000 for every 4.6 and 6.9 time constants,

respectively. Figure 4-6 is the plot of the relationship between the percent of tritium remaining in

the volume with time.