Tritium Monitoring

Tritium Primer

DOE-HDBK-1079-94

TRITIUM MONITORING

TRITIUM MONITORING

The tritium monitoring system at a tritium handling facility is critically important to its safe

operation. Operators and others at the facility need to be informed of the status of the processes,

the development of any leaks in the primary or secondary containments, or of any releases to the

room or environment so that protective measures and corrective action may be taken quickly.

The location and degree of surface contamination are equally important to prevent accidental

uptakes of tritium by personnel.

In this section, the various techniques used to monitor for tritium in gases (including air), in

liquids, and on surfaces will be discussed.

Air Monitoring

Fixed ionization chamber instruments are the most widely used instruments for measuring

gaseous forms of tritium in laboratory and process monitoring applications. Portable ionization

chamber instruments are also used to control contamination and to supplement fixed instrument

measurements. Such simple devices require only an electrically polarized ionization chamber,

suitable electronics, and a method for moving the gas sample through the chamber--usually a

pump. Chamber volumes typically range from a tenth to a few tens of liters, depending on the

required sensitivity. The output is usually given in units of concentration (typically Ci/m3) or,

if a commercial electrometer or picoammeter is used, in current units that must be converted to

those of tritium concentration. The following rule-of-thumb can be used to convert current to

concentration: 1015 current (amps)/chamber volume (liters) = concentration (Ci/m3). For

real-time tritium monitoring, the practical lower limits of sensitivity range from 0.1 to 10 Ci/m3.

External background radiation or the presence of radon can lower the sensitivity of the

instrument.

For measurements of low concentrations, sensitive electrometers are needed. For higher

concentrations (>1 mCi/m3 for example), the requirements on the electronics can be relaxed,

and smaller ion chambers may be used. Smaller chambers also need less applied voltage.

Because of a greater ratio of surface area to volume, residual contamination in the chamber is

more likely and is called "memory." This residual contamination elevates the background

chamber current. Response times for higher level measurements can be made correspondingly

shorter. However, because small chambers and chambers operated at low pressures may have

significant wall effects, the above rule-of-thumb may not apply. Such instruments would have

to be calibrated to determine their response.

Although most ionization chambers are the flow-through type that require a pump to provide

the flow, a number of facilities use "open window" or "perforated wall" chambers. These

chambers, which employ a dust cover to protect the chamber from particulates, allow the air

or gas to penetrate through the wall to the inside chamber without the need for a pump. These

instruments are used as single point monitors to monitor rooms, hoods, gloveboxes, and ducts.

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Tritium