Development of Specific Catalysts for Detritiation of Gases by Counter Current Isotopic Swamping

The principal techniques developed by different research groups for the detritiation of primary gaseous wastes are altogether based on processes with multiple stages comprising at least one step involving heterogeneously catalyzed chemical reactions. While the permeation of hydrogen isotopes through palladium/silver membranes combined with heterogeneously catalyzed reactions were proven to be particularly suitable for highly contaminated gases, isotopic swamping in a counter current mode is the method of choice in ITER for the final detritiation and recovery of residual amounts of tritium. Since the catalyst employed to promote the isotope exchange reactions should not support methanation of carbon monoxide and carbon dioxide an attempt was made to design a highly selective exchange catalyst. Amongst the catalysts screened with methane - deuterium exchange and carbon oxide - methanation as test reactions a high temperature reduced palladium/silica (SiO₂) catalyst was found to match the selectivity requirements. However, even though the palladium/silica catalyst shows very little activity for methanation, carbon monoxide was found to obstruct the isotope exchange reaction, whereas carbon dioxide does not show this unwanted effect.