A novel approach to the study of magnetohydrodynamic effect on tritium transport in WCLL breeding blanket of DEMO

The Water-Cooled Lithium Lead (WCLL) breeding blanket is one of the European blanket designs proposed for DEMO reactor. Tritium can permeate into the different structural materials, arising potential issues concerning the fuel self-sufficiency and can be lost into the environment with consequent radiological hazard for the population. Within this frame, a tritium transport analysis is fundamental to evaluate tritium retention in LiPb (15.7 at. % Li) and in the structures and tritium permeation fluxes into the cooling water. To assess this study, a portion of the breeder unit of the outboard equatorial module of the WCLL was modelled. The buoyancy forces and the magnetohydrodynamic (MHD) effect were also included. The final system of partial differential equations was solved with a novel approach through COMSOL Multiphysics. The coupled MHD and heat transfer system of equations was solved performing a transient simulation, that was stopped when the main average variables, temperature and velocity, reached a stable condition. In this way, it was possible to determine the lithium-lead velocity field and to use it as an input for the transport analysis. Tritium transport was modelled by using the input data of tritium generation rate and volumetric power deposition coming from an ad-hoc Monte Carlo simulation realized with MCNP software. Moreover, the transport analysis included advection-diffusion of tritium into the LiPb, transfer of tritium from the liquid interface towards the steel, diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant, advection-diffusion of diatomic tritium into the coolant.