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isotopes of helium. Both of these techniques can be used for real-time measurements.
For the mass spectrometer system a sample is bled to a high vacuum system for mea-
surement. The RAMAN system is easily adopted to real-time measurements. The gas
stream at atmospheric pressure is passed through an optical cell. The spectrum for a
mixture hydrogen isotopes can be determined in ~1 min. The total accuracy of these
measurements is ~3 to 5%. The mass spectrometer technique has been the standard
method that DOE facilities have used for the determination of the tritium inventory. It is
a proven system although it requires an expensive spectrometer ($200K) and accurate
determination of the temperature, pressure, and volume. The RAMAN system has not
been accepted. Experiments are currently being performed to demonstrate that this will
be an acceptable technique.
b. Thermal Methods. The primary method to inventory large quantities of tritium in the
liquid or solid form is to use a calorimeter. The sample is placed in a thermally iso-
lated container. The power required to maintain the temperature of the container is
then a measure of the amount of tritium in the sample. Containers can accept sam-
ples that vary from several inches in diameter up to a 55-gal drum. The lower limit
of accuracy can be as low as 100 Ci. Calorimeters are expensive ($200K+). They
require high-tech electronics. They are the primary methods used to measure tritium
in waste such as HTO on molecular sieve. They have not been used to measure
process tritium except in a very specific application. For example, solid tritium storage
beds that can be disconnected and moved have been placed in a calorimeter
designed to accept the bed. New methods are being developed to allow for the deter-
mination of the amount of tritium stored on a solid storage bed, When tritium is stored
on a uranium bed the temperature increase of the bed can be used to determine the
amount of tritium stored on the bed. When tritium is stored on a material such as
LaAlNi, usually gas is passed through the secondary containment to maintain the
temperature. The temperature rise of the gas as it passes through the bed can then
be used to determine the amount of tritium. Both of these methods are being pro-
posed for tritium accountability. Their acceptance is now based on a case-by-case
system, and they are not used widely. Development of these methods will be impor-
tant for the operation of fusion facilities. They offer potential savings in time and effort
to account for the tritium in a facility.
c. Tritium Concentration Measurement. A Beta scintillation counter has been used for
tritium measurement if only the total tritium composition is required. In this instrument,
the gas is passed over a crystal that will scintillate with the beta from the tritium decay.
A photomultiplier tube is used to detect the light. The tritium concentration can then be
determined from the signal from the photomultiplier tube. This method is commonly
used for gas inventory requirements. Liquid scintillation is commonly used to
determine small concentrations of tritium. The tritium liquid or compounds containing
tritium are placed in a scintillation liquid. The liquid is then placed in a counter that
determines the amount of tritium by the light emitted from the sample. Ion chambers
are commonly used to determine environmental tritium releases and to monitor the
atmosphere for personnel safety. Process ion chambers are used for determining
tritium concentrations in secondary containment. Specially designed ion chambers

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