Effect of cyclic heat loading on pure tungsten for the ITER divertor

Abstract The plasma facing unit (PFU) of ITER divertor is repeatedly exposed to high heat flux, and a reliable heat removal capability is crucial for its adequate performance. The cyclic high heat flux test (HHFT) that has been conducted to evaluate the reliability of PFU reveals that the surface modification and macro-crack formation in W monoblock, which is the plasma facing material, may hinder the operation of fusion reactors. Therefore, optimization of both manufacturing technology and material development is necessary for reliable operation. In this study, we investigate the dependence of material properties on the surface modification and macro-crack formation in W monoblocks. W monoblocks manufactured by two different suppliers were examined, and the results of cyclic HHFT revealed that the heat removal capability was not degraded in all the examined W monoblocks. Further, it was observed that the W monoblock exhibiting characteristic grain structure and tensile property suffered less surface modification without macro-crack formation due to cyclic heat loading.