General and crevice corrosion study of the materials for ITER Vacuum Vessel In-Wall Shield

摘要

Vacuum Vessel In-Wall Shield (IWS) will be inserted between the inner and outer shells of the ITER vacuum vessel and comprise of number of plates stacked together with spacers and bolts. The behavior of IWS in the vacuum vessel especially concerning the susceptibility to crevice of shielding block assemblies could cause rapid and extensive corrosion attacks. Even galvanic corrosion may be due to different metals in same electrolyte. The flow rate is locally rather low in the VV-IWS block assemblies and low flow rates generally promote local attacks on the stainless steel. In addition local accumulation of the aggressive compounds like chloride and other anions might be higher for ITER condition due to the different operational modes. IWS blocks are not accessible until life of the machine after closing of vacuum vessel. Hence, it is necessary to study the susceptibility of IWS materials to general corrosion and crevice corrosion under operations of ITER vacuum vessel. Corrosion properties of IWS materials were studied by using (i) Immersion technique and (ii) Electro-chemical Polarization techniques at normal operation condition (OC1), baking condition (OC2) and at draining and drying operations (OC3) of ITER vacuum vessel.