Definition of workable acceptance criteria for the ITER divertor plasma facing components through systematic experimental analysis

Plasma Facing Components (PFCs) which will be installed in the ITER Divertor require a heat flux removal capability in the range 5-20 MW/m² in thermal steady-state conditions. Experience shows that the most critical part of a PFC is the armour to heat sink joint, therefore, maximum dimensions of an acceptable defect at the interfaces of bonding appeared to be a relevant criteria with regards to thermo- mechanical fatigue. A comprehensive study was thus launched in order to define acceptance criteria with regards to thermomechanical fatigue of the ITER Divertor PFCs. This study, which includes the manufacturing of samples relevant with the Divertor design with calibrated artificial defects, their non-destructive examination and their related fatigue testing is reported in this paper. As a first step, metallic samples (W armour) with calibrated defects were inspected with conventional Non Destructive Examination (NDE) technique whereas the composite ones (CFC armour) were inspected by transient infrared thermography NDE technique (so-called SATIR technique). Detection of the imperfections on CFC monoblock geometry was found reliable with a limited uncertainty. In particular it was found that defect with an extension above 30 deg could be detected at the interface CFC/copper, with a SATIR inspection on the 3 sides of each monoblock. Secondly, the samples were high heat flux tested following a program relevant with the lifetime of the Divertor PFC into the ITER machine. For each artificial defect, propagation or stability during the fatigue testing was assessed. It was observed that defects detectable with US NDE or SATIR techniques appeared to be below the threshold of propagation during fatigue experiments. This allows to be confident in the capability of commissioning components reaching the required design values of the ITER divertor PFCs. (author)