246
H. T. Sessions Jr. and S. E. H. Murph
Results and Discussion
Initial Hydrogen Isotope Separation
The Thermal Cycling Absorption Process developed by Savannah River National
Laboratory is based on a modified gas chromatography technique to separate
hydrogen isotopes. The purpose of the Thermal Cycling Absorption Process system
is to not only separate tritium from other hydrogen isotopes but also to minimize environmental releases of tritium. Environmental releases of less than 5 ppm of tritium
can be achieved. The operational principle of a Thermal Cycling Absorption Process
is based on the heating and cooling of hydride material, namely palladium-coated
kieselguhr that is housed in a column. Palladium is the material of interest in this
process as it readily absorbs hydrogen and provides an Isotopic effect as it preferentially absorbs the lighter hydrogen isotope [12]. A second column containing
kieselguhr only assists with the pressure profiles. The temperature cycling generates
the pressure gradients that provide the driving force to move and separate hydrogen
isotopes.
A residual gas analyzer, a gas chromatograph, and a helium leak detector were
used to monitor the Thermal Cycling Absorption Process during initial field testing.
Each instrument has unique capabilities and limitations such as sensitivity, detection,
quantification, specificity, and reproducibility. However, when used in conjunction,
although cumbersome, these three instruments can trend the operation of the Thermal
Cycling Absorption Process and demonstrate that it separates protium and deuterium.
An ion chamber can be used to monitor the Thermal Cycling Absorption Process
during normal tritium operation. It is relatively inexpensive, easy to operate, and has
sensitivity equivalent to less than 1 ppm. Theoretically, an ion chamber can detect
the decay of one tritium atom. Therefore, monitoring for small quantities of tritium
in the final product is relatively simple. Raffinate term refers to the component which
had a component removed from its mixture (Fig. 1).
One could monitor a decrease in concentration of deuterium in the column raffinate, while in the same time an increasing concentration of deuterium in the column
product. Final determination of Thermal Cycling Absorption Process performance
was accomplished by collecting data from the column raffinate and column product
and analyzing them using a low mass high-resolution mass spectrometer. While
successful, this process is operational complex and requires a number of steps that
may add uncertainty to the accuracy of the final result.
Moreover, when tritium was substituted with deuterium, monitoring the column’s
raffinate and product for isotope separation and differentiation of small amounts of
deuterium in protium posed a significant analytical challenge. To further complicate matters the Thermal Cycling Absorption Process will also produce hydrogendeuterium (HD) which could contaminate either the raffinate or product (Fig. 2).
Therefore, the analytical challenge for the test was to provide instrumentation to
measure both total deuterium in the column raffinate, and total hydrogen (protium)
in the column product.
H. T. Sessions Jr. and S. E. H. Murph
Results and Discussion
Initial Hydrogen Isotope Separation
The Thermal Cycling Absorption Process developed by Savannah River National
Laboratory is based on a modified gas chromatography technique to separate
hydrogen isotopes. The purpose of the Thermal Cycling Absorption Process system
is to not only separate tritium from other hydrogen isotopes but also to minimize environmental releases of tritium. Environmental releases of less than 5 ppm of tritium
can be achieved. The operational principle of a Thermal Cycling Absorption Process
is based on the heating and cooling of hydride material, namely palladium-coated
kieselguhr that is housed in a column. Palladium is the material of interest in this
process as it readily absorbs hydrogen and provides an Isotopic effect as it preferentially absorbs the lighter hydrogen isotope [12]. A second column containing
kieselguhr only assists with the pressure profiles. The temperature cycling generates
the pressure gradients that provide the driving force to move and separate hydrogen
isotopes.
A residual gas analyzer, a gas chromatograph, and a helium leak detector were
used to monitor the Thermal Cycling Absorption Process during initial field testing.
Each instrument has unique capabilities and limitations such as sensitivity, detection,
quantification, specificity, and reproducibility. However, when used in conjunction,
although cumbersome, these three instruments can trend the operation of the Thermal
Cycling Absorption Process and demonstrate that it separates protium and deuterium.
An ion chamber can be used to monitor the Thermal Cycling Absorption Process
during normal tritium operation. It is relatively inexpensive, easy to operate, and has
sensitivity equivalent to less than 1 ppm. Theoretically, an ion chamber can detect
the decay of one tritium atom. Therefore, monitoring for small quantities of tritium
in the final product is relatively simple. Raffinate term refers to the component which
had a component removed from its mixture (Fig. 1).
One could monitor a decrease in concentration of deuterium in the column raffinate, while in the same time an increasing concentration of deuterium in the column
product. Final determination of Thermal Cycling Absorption Process performance
was accomplished by collecting data from the column raffinate and column product
and analyzing them using a low mass high-resolution mass spectrometer. While
successful, this process is operational complex and requires a number of steps that
may add uncertainty to the accuracy of the final result.
Moreover, when tritium was substituted with deuterium, monitoring the column’s
raffinate and product for isotope separation and differentiation of small amounts of
deuterium in protium posed a significant analytical challenge. To further complicate matters the Thermal Cycling Absorption Process will also produce hydrogendeuterium (HD) which could contaminate either the raffinate or product (Fig. 2).
Therefore, the analytical challenge for the test was to provide instrumentation to
measure both total deuterium in the column raffinate, and total hydrogen (protium)
in the column product.