Tritium-Related Constraints on a BPX Operation Schedule

Tritium is a very sensitive subject for public acceptance of fusion and will play a central role in the operation of a next-step experimental fusion facility, which will routinely use large amounts of tritium as fuel (e.g., 100 times more in ITER than in present experiments) in a mixture with deuterium. Tritium retention is a regulatory issue since the amount that can potentially be released in an accident sets the limits on plasma operation without removal. Fuel economy has never been an issue in deuterium-fuelled experiments and only recently have the limitations associated with the use of tritium, and its incomplete recovery in experiments in TFTR and in JET, brought the issue of fuel retention under closer scrutiny [56,57]. Table 12.3 provides a list of key quantities related to tritium in existing tokamaks and a next-step device [18,57-59]. 

With careful planning, both TFTR and JET have demonstrated safe tritium handling in a fusion machine. Special controls imposed on the handling of tritium [60-62] have required that the quantity of tritium retained in the torus be accounted for and the inventory limited [63,64] in order to permit 

Tritium is one of the main source terms in accident scenarios for ITER and to meet some of the key requirements for limitation of worker and public dose in accidents, limits need to be placed on the tritium inventory. Due to the ease of mobilization of tritium retained in co-deposited layers (co-deposited films in tokamaks start to decompose, releasing tritium, when exposed to air at temperatures 520 K, [65-69]), a limit of 350 g is currently set for the in-vessel co-deposition inventory (and 120 g in the cryo-pumps). These limits are set to allow the full release of this inventory, under hypothetical accident conditions, without the need for public evacuation under the worst weather conditions. 

Recently novel methods for tritium release relying on a laser [70,71] or flash lamp [72] have been proposed and applied to remove co-deposited layers 

---