Tritium Transport in Poloidal Flows of a DCLL Blanket

In a Dual-Coolant Lead-Lithium (DCLL) blanket, tritium losses from the PbLi into cooling helium streams may occur when the liquid-metal breeder is moving in the poloidal ducts. Quantitative analysis of the mass transfer processes associated with the tritium transport in the breeder as well as tritium diffusion through the structural and functional materials is important for two main reasons. The first is that there can be a substantial cost in extracting tritium from helium. The second is that tritium can make its way from the helium stream into the environment. In the present study, we analyze tritium transport in the front section of the DCLL DEMO-type Outboard blanket, where PbLi moves poloidally in a rectangular duct with an insulating flow channel insert (FCI) in the presence of a strong plasma-confining magnetic field. This involves two steps, the computation of the flow field with an MHD code, followed by the solution of the mass transfer equation with a newly-developed transport code CATRYS. The analyses included a sensitivity study to investigate how uncertainties in the properties of the materials (diffusion coefficient, solubility constant) affect the results and to assess the effect of an impervious crystalline sealing layer on the FCI.