Conceptual design of a PAV-based tritium extractor for the WCLL breeding blanket of the EU DEMO: Effects of surface-limited vs. diffusion-limited modeling

In order to close the fuel cycle, the EU DEMO will be equipped with a breeding blanket (BB) for the on-site tritium production. In the water cooled lithium lead (WCLL) BB concept, the tritium will be generated in the liquid PbLi from which it must then be extracted.The conceptual design of the tritium extraction and removal system for this BB concept is addressed here. It relies on the permeator against vacuum (PAV) technology, where the tritium dissolved in the PbLi is forced to cross a metal (Nb) membrane by pumping the vacuum on the secondary side. The proposed PAV geometrical configuration is based on the shell-and-tube concept, where the walls of the pipes in which the PbLi flows are the permeator membrane. The dimensioning of one permeator vessel for one of the PbLi loops is carried out here, adopting two different models for the tritium permeation: diffusion-limited (for the case of a non-contaminated membrane) and surface-limited (suitable for a contaminated Nb surface).The results show that in the case of a non-contaminated membrane it is possible to reach the target tritium extraction efficiency also at the PbLi nominal operating temperature, while in the case of a contaminated membrane the PbLi should be heated to enhance the permeation.