Palladium alloy membrane process for purifying hydrogen isotopes

Tritium is a radioactive isotope of hydrogen and it has a half-life of 12.3 years; it decays to He-3 by emitting a low energy beta radiation with an average energy of 5.7 keV and a maximum energy of 18.6 keV. Transfer of environmental tritiated water to humans takes place via an inhalation, diffusion through the skin and ingestion. Radioactive waste containing tritium is continuously generated by the nuclear industry in, for example, nuclear reactor operations and a radioisotope production, and in medical research. Methods for removing tritium from liquid waste provide an alternative to the control of tritium emissions and a personnel exposure. Combined electrolysis and catalytic exchange process is a very effective method to remove small quantities of tritium from light or heavy waste water streams. The process consists of three main steps: (a) A front end step that exchanges the tritium to a less toxic hydrogen phase. This can be performed either through a chemical exchange in the presence of a platinum supported catalyst or through the decomposition of water. (b) A back end process that purifies the tritiated hydrogen gas which evolved from the electrolysis. This can be performed through a palladium alloy membrane separator. (c) A means of storing the concentrated gas safely. Uranium or ZrCo metal is used if storage is temporary; titanium is mainly employed for long term storage. To have a better knowledge of the tritiated hydrogen gas purification process, a mathematical model of the palladium alloy membrane has been used. This model is described herein, and the representative results of the model calculations are presented