TRITIUM CONFINEMENT REQUIREMENTS FOR THE WATER-COOLED PB-17LI BLANKETFOR DEMO

In the water-cooled liquid Pb-17Li blanket concept for DEMO the limita tion of tritium permeation from the breeder material into the cooling water will be required. In order to find out on what conditions this t ritium permeation remains within reasonable limits, a 1-d FEM code was developed which evaluates the tritium partial pressure in Pb-17Li, th e tritium inventory in the blanket material, and the tritium permeatio n from the Pb-17Li into the cooling water as a function of the permeat ion reduction factor of a barrier and the efficiency of the tritium ex traction from Pb-17Li. With a parametric study the conditions were ide ntified which allow a permeation rate of as little as 1 g . d(-1) with out pushing the requirements for permeation barriers and extraction ef ficiencies excessively far. An example is a barrier with a permeation reduction factor of 75 together with an extractor efficiency of approx imately 83%. In these conditions the expected tritium inventory is att ributed to approximately one third to the martensitic blanket structur e (some ten grams) while two thirds will be found in the Pb-17Li. Thes e inventory values are two orders of magnitude lower than in solid bre eder blankets and are thus not considered a critical issue.