Tritium recovery from the TFTR vessel

The Tokamak Fusion Test Reactor (TFTR) was supplied over 7.5×10⁵ Curies combined through the vacuum vessel and Neutral Beam (NB) tritium gas injectors. Out of this quantity approximately 29,530 Curies (Ci) has entered the vacuum vessel as neutral atoms, including cold streaming gas and 20,270 Ci as direct vessel injection. TFTR has had two short term outages during DT operations Outage 1(´95) and 2(´96), plus the final shutdown, Outage 3 (´97), after DT operations in which tritium held up in the vessel and NB´s has been actively recovered. The respective recovery values are: Outage (No.1) 8,257 Ci, (No.2) 4,668 Ci and (No.3 final shutdown) 3965 Ci. The methods for recovering this included: 1. Vessel baking to 150°C during Deuterium Glow Discharge Cleaning (DGDC), 2. Helium/Oxygen GDC (HeOGDC), 3. Pulse Discharge Cleaning (PDC), 4. Continuous moist air purges and 5. Dry air, moist air (40% RH), and deuterium vent/soak/pump. The processes showing equivalent efficiency are the GDC, HeOGDC, and moist air purges at elevated temperatures. A small amount of tritium is introduced in the vessel at high energy through the NE ~3% relative to that supplied to the beam lines and ~1/2 of this is essentially buried in the carbon composite tiles and has a longer time constant for removal than the direct vessel injected tritium. Data shows that the bulk of surface tritium is removed by active cleaning methods and in the presence of moist air purges (room air at ~40% relative humidity) combined with elevated temperatures which accelerates its removal. Continuous outgassing at low levels in the presence of moist air (750 Torr) follows the active tritium removal processes and moist air purges. The TFTR tritium removal processes and their corresponding removal rates and quantities are reported. An ion chamber is used to measure the tritium accumulated in the Gas Holding Tanks (GHT) from the vessel throughout all the active and passive processes. The ion chamber compensation for varying gas mixtures was found to be critical in accurate measurement of this recovery and is discussed