High heat flux testing of first wall mock-ups with and without neutron irradiation

•Determination of thermal performance of neutron irradiated first wall Be mock-ups.•Degradation due to decreasing thermal conductivity of degradation of joint quality.•Variation of damage location and formation for non-irradiated and irradiated mock-ups.•Detachment of neutron irradiated beryllium tiles partially at the Be/Cu interface and by crack deflection into beryllium.