Isotope Effect in Cryosorption of Tritium to Molecular Sieves and Activated Carbon at 77 K

The tritium bred in a deuterium-tritium fusion reactor is removed from its blanket by using helium sweep gas mixed with some amount of hydrogen to promote the release rate. From the viewpoint of uptake capacity at the partial pressure of tritium and ease of tritium transfer to the main fuel cycle, a cryosorption bed, which uses molecular sieves or activated carbon at the liquid nitrogen temperature, is attractive for recovery of bred tritium in the blanket sweep gas. The cryosorption bed is also applicable as a transfer pump of tritium in the fuel-handling process. Tritium cryosorbed from a certain subunit of the fuel-handling system is transferred to other subunits by an increase in temperature and the operation of valves. It is necessary to know the adsorption isotherm and the mass transfer coefficient of each hydrogen isotope for estimation of breakthrough performances of tritium in a cryosorption bed because the mixture of tritium with other hydrogen isotopes must be treated. It is observed that the isotope effects in adsorption capacity and surface diffusivity have a close connection with the quantum effect that is represented by the reduced molecular weight. The correlative equation between Langmuir constants in the adsorption isotherm with reduced molecular weight of hydrogen isotopes is proposed. The correlative equation between surface diffusivity and reduced molecular weight is also presented.