AbstractA HIP bonded DS-Cu/SS first wall (FW) with built-in circular cooling tubes was fabricated under the optimized HIP conditions. High heat flux testing of the panel was carried out on electron beam facility, JEBIS , at JAERI. The objective of this test is to examine the thermomechanical performance of the panel, including the integrity of the HIP bonded interfaces and also to examine the relation between the design fatigue curve and experimental results. Test conditions applied during these tests were 5.0–7.0 MW/m2 in average, much higher than the ITER normal operation condition of 0.5 MW/m2, to accelerate the fatigue test with a repetition cycle up to 2500 cycles in total. High heat flux tests consisted of two test campaigns. Throughout these tests, no damages such as cracks were observed and no degradation in heat removal performance was also observed from temperature responses measured with thermocouples embedded within the panel. Thermomechanical integrity of the panel was confirmed within the parameter tests and the fatigue lifetime of the panel was found to be much longer than the design fatigue curve of this material, or even beyond the raw fatigue data.