The system effect of tritium arises from the interaction of tritium in the gas phase with water on the surface of piping materials. It has been reported that the system effect can be quantified by applying the serial reactor model to the piping system, connection of perfect mixed flow type reactors and plug flow type reactors, and that adsorption and isotope exchange reactions play the main roles in the trapping of tritium. In this study we made a calculation code of the system effect using the serial reactor model where 304SS, aluminum, copper or graphite is used for the piping material. Comparison of the calculated value using this code gives the good agreement with the experimental data taken at the cooperative experiment using a box made of stainless steel type 304 in Tritium Processing Laboratory in JAERI and that is called as the Caisson. It is observed that the isotope exchange reaction between tritiated water in the air and surface water on the 304SS surface controls the tritium trapping performance at the room temperature although HTO/HT ratio is around 0.1 in this experiment.
