Supply and set-up of an on-line tritium monitoring

Tritium (3H or T) is the only radioactive isotope of hydrogen and it is used to fuel fusion reactions at JET. In materials containing hydrogen, present tritium atoms will exchange with hydrogen atoms to form tritiated molecules of the material. This property of tritium is used for trapping tritium in water from the gas passing through the water. However, trapping of gaseous tritium (HT/T2) in such way is more difficult than tritiated water molecules. Therefore, oxidation of the sampled air has to take place during the sampling stage, so it is ensured that all tritium is sampled. The main exposure route to tritium is via inhalation. If tritium in gaseous form (HT, DT, T2) is inhaled, only small fraction of it is not exhaled, but dissolved in the blood stream and then exhaled after a few minutes. Tritium in form of water (HTO, DTO, T2O) is adsorbed through the skin and in the lungs from inhaled gases. Tritiated water is retained in the body for ~10 days which is its biological half-life. Therefore, exposure to tritiated water in air is up to 25000 times more hazardous than exposure to gaseous tritium. UKAEA's research on detritiation of fusion materials requires on-line monitoring of tritium released during various experimental activities in order to correctly identify optimal parameters of the experimental set-up.