Tritium Inventory Differences: II. Molecular Sieve Holdup

Aluminosilicate zeolite (molecular sieve) materials are employed widely to remove condensable gases from tritium-containing gas streams. By several mechanisms, the bound-tritium contents of zeolite columns can increase significantly over time, primarily as tritiated water. Attempts have previously been made to asnay the tritiated water by \"regeneration\" from the zeolite, but have encountered poor efficiency. More accurate assays have now been developed following two new approaches: controlled partial regeneration and isotopic exchange. The first method relies upcn the development of simple theoretical model of zeolite column regeneration. Water loading (in weight percent) can be described as a function of regeneration temperature and total purge throughput. From a knowledge of zeolite mass, flow rates and pressures, and the mass of delivered water and tritium, the initial masses can be derived. The second assay method is based upon the exchange of H or D gas with adsorbed HTO at temperatures around 400°C. Isotopic proportionation factors for H_0/H7 must be included in the data reduction. Both methods above have been applied to the assay of tritium in five zeolite traps at our laboratory. Results of the two approaches agree within 10%. Both methods will be useful in the future in obtaining tritium inventory estimates for zeolites.