Development and heat load experiments of graphite brazed to stainless steel for the first wall structure of FER

Abstract

A guard limiter concept with graphite brazed to a stainless steel base plate has been proposed in FER. The bonding of graphite and stainless steel was successfully done by vacuum brazing with an interlayer material of Mo or Cu. Mechanical strengths were measured by tensile and shear tests. Fatigue tests up to approximately 107 cycles were done. Heat load experiments were performed with electron beam equipment. Brazed materials with a Mo interlayer were subjected to a heat load up to 60 MJ/m2 (6 kJ/cm2). No complete failures were observed in every condition, but cracks were generated by heat loads greater than 40 MJ/m2 (4 kJ/cm2). The failures were generated in graphite near to the interface. Mechanical strength and thermal shock resistance were improved by the change from 1 to 3 mm in thickness of Mo interlayer. Residual stresses due to brazing and cool-down were analyzed with an FEM code, and the results were compared with strain measurements on the test specimen. A comparison study on interlayer materials is continuing, and heat load cycle tests are now underway for 10 MJ/m2(1 kJ/cm2), which is a target value based on the FER design.