Calorimetry Assay cont'd

DOE-HDBK-1129-99

Physical size of the calorimeter measurement chamber,

Wattage range of the measurement system,

Precision and accuracy of the measurement for the size and wattage range of the item

to be measured,

Throughput or number of samples to be measured per day.

CHF calorimeters have been designed in many different configurations, such as over/under, and

twin. Most CHF systems in use today use digital control systems operated by a stored program

and are easy to operate. The steps in making a CHF measurement are generally as follows:

Install a dummy mass in the calorimeter container, pack steel or copper wool around the

dummy mass, and install it in the measurement chamber.

Make a zero baseline run at a wattage level (Wzbl), which is at a wattage level greater

than the unknown wattage level of the sample to be measured.

During the baseline run, the digital control system establishes a calorimeter bridge

voltage value for a known (Wzbl) wattage input.

Remove the calorimeter container from the measurement chamber, remove the dummy

sample from the container, replace it with the sample to be measured, place it back in

the measurement chamber, and make an unknown sample run.

During the unknown sample run, the digital control system decreases the power in the

calorimeter until the bridge voltage is the same as that measured in the zero baseline

run.

The power input to the calorimeter during this unknown sample run (Wusr) is measured.

The power of the sample being measured (Ws) is calculated by subtracting the wattage

value measured during the zero baseline run from the wattage measured during the

unknown sample run to find the wattage of the sample. In equation form:

Ws = Wzbl - Wusr

The calorimeter factor for tritium used at most DOE sites for the purposes of reporting

accountable quantities of tritium to DOE is 0.3240 +/- 0.0009 Watts/g of tritium.

CHF calorimetry can be used to measure tritium in solid form. CHF is the most accurate

method available for the measurement of tritium quantities if the chamber size and wattage level

of the item to be measured are well matched to the specifications of the CHF system being

used. CHF systems, however

Do not provide any information about the different gases present in a container (HT, DT

H2, D2 3He, etc.),

Only measure the quantity of tritium in the container,

Are not currently available for items larger than 11 inches in diameter and 16 inches long

Take several hours to complete a single measurement.

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