3Forschungszentrum Karlsruhe, TLK, PO Box 3640, 76021 Karlsruhe, Germany

A catalytic isotope exchange facility is being operated at the Tritium Laboratory Karlsruhe (TLK) in order to investigate the simultaneous transfer of tritium and deuterium between various molecular hydrogen isotopes and water in a catalytic isotope exchange column. To allow visual inspection, a glass column with an active height of 900 mm and a diameter of 40 mm is being used initially. Experiments have been performed to determine the equivalent height of theoretical plate (HETP) and the mass transfer coefficients during simultaneous deuterium and tritium exchange between deuterated and tritiated water and gaseous hydrogen isotopes. A mathematical model and the corresponding codes are presently being verified by experiments aimed to provide the data required for the design of large isotopic exchange columns needed for the recovery of tritium from waste water generated during the operation of the tritium facilities of fusion machines.

Four catalyst/packing combinations from different manufacturers (SCK-CEN Belgium, Mendeleev University Russia, ICIT Romania, Showa Eng. Japan) are currently being tested. The working temperatures are as recommended by these suppliers, i.e. between 40°C and 80°C. The investigated gas flow rates correspond to linear gas velocities in the range between 0.1 and 0.2 m× s^-1 and different molar gas/liquid ratios were used.

Pre-heated water at the working temperature is fed into the column from the top and tritium-deuterium-hydrogen mixture saturated with water vapor from the bottom. The vapor is condensed and returned together with the column feed. Hydrogen depleted of deuterium and tritium is removed from the top of the column.

The isotopic compositions of the liquid phases are analyzed with an on-line infrared spectrometer and a liquid scintillation counter. For the gaseous phases, a quadrupole and an Omegatron mass photospectrometer as well as ionization chambers are employed.

To describe the performance of the separation process, an analytical approach solving the transport equations for the isotopic exchange process is considered. To make the developed model broadly applicable, both tritium and deuterium isotopic exchange was included. To increase the degree of information with respect to the isotopic transfer from gas to liquid, the contribution of water vapor is also included in the model. The three-phase system (gas-liquid-vapor) is examined taking into account all molecular species involved in the process. The input data to establish the catalyst performances are the isotopic concentrations in both gas and liquid phase at the inlet and outlet of the column, the flow rates and the geometric dimensions of the column.

The model, the experimental results, the HETP and also the gas/vapor mass transfer coefficients for deuterium and tritium of each catalyst are presented.