Case study on tritium inventory in the fusion DEMO plant at JAERI

Case studies on tritium inventory and permeation in a fusion demo plant designed by JAERI (DEMO(J05)) have been carried out using several data sets on the tritium transport properties of the candidate materials of the plasma facing components. The results have been compared with the design guidelines for loss of tritium into the components or coolant for tritium accountancy (1.4 kg/y) and tritium concentration in the coolant (0.37 GBq/cm3) for DEMO(J05). The results revealed that tritium concentration and inventory in the coolant attributed to permeation from the blanket (plasma facing first wall and breeding region) is expected to be much higher both of these guidelines unless designated permeation barriers are used. Therefore, permeation must be reduced by a factor of 100 in order to satisfy the guidelines. Tungsten coating on the first wall and glassy coating on the blanket cooling tubes may be good countermeasures for permeation reduction in DEMO(J05).