Integration issues on tritium management of the European DEMO Breeding Blanket and ancillary systems

Abstract

Within the EUROfusion framework, two reactor architectures are being developed as possible candidates for the EU DEMO. One is based on the Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) concept and the other on the Helium Cooled Pebble Bed (HCPB) BB concept. The two DEMO variants result in completely different reactor and ancillary system designs due to the use of different coolants (i.e water or helium) as well as different neutron multipliers, tritium breeders, and carriers (i.e. PbLi for the WCLL and solid ceramic and beryllide with helium as a purge gas for the HCPB). As a consequence, the definition of the tritium management systems for the extraction and the control of inventories and environmental releases also needs to be tuned for each variant. Furthermore, dedicated technologies for tritium extraction and removal must be developed and specific working points for the two architectures must be defined. It is, therefore, necessary to rely on holistic approaches for the analysis of tritium management issues of the BB, its ancillary systems and fueling systems. In this work, an overview of the tritium permeation issues and the applied mitigation measures (e.g. permeation barriers) are described. Furthermore, design limits given by tritium extraction technologies as well as experimental campaigns (e.g. determination of the Sieverts’ constant of tritium in PbLi at DEMO relevant temperatures) to substantiate the modelling approach are also reported. Finally, the impact on the fueling system due to the tritium inventories sequestered in the BB and other systems is described, providing information on the doubling time and initial tritium inventories for a given tritium breeding ratio.