The influence of MHD boundary layers on tritium permeation in PbLi flows for fusion breeding blankets

•Mass transport through MHD boundary layers is increased by the magnetic field up to an asymptotic value.•Mass boundary layers affected by the thickness of the MHD boundary layers.•MHD velocity jets in the side layers increase mass transfer via advection.•The permeation regime affects weakly the mass transfer coefficient in both MHD boundary layers.•Sherwood number correlated with Hartmann number, Reynolds number and permeation number.