Reduced activation ferritic steel alloys such as F82H are the candidate materials for the first wall of DEMO reactors.For self-cooled breeding blankets,the first wall will be subjected to bi-directional hydrogen isotopes permeation by two different mechanisms: in one direction by edge plasma-driven permeation(PDP)of deuterium as well as tritium into blankets,and in the other direction by bred tritium gas-driven permeation(GDP)into the edge plasma.It is important to note that deuterium PDP will lower the recovery efficiency of tritium from the breeder,and GDP,acting as fueling,will increase the particle recycling in the first wall region.