Corrosion of aluminium-clad spent fuel in LVR-15 research reactor storage facilities

Corrosion of research reactor aluminium-clad spent fuel in water was investigated in two storage facilities. The standard racks were delivered by the IAEA and consisted of two aluminium alloys AA 6061 and Szav-1 coupons. Bimetallic couples create aluminium alloy and stainless steel 304 coupons. Rolled and extruded AA 6061 material was also tested. Single coupons, bimetallic and crevice couples were exposed in the at-reactor basin (ARB) and the high-level waste pool (HLW). The water chemistry parameters were monitored and sedimentation of impurities was measured. The content of impurities of mainly Cl and SO4 was in the range of 2 to 15 μg/l in the HLW pool; it was about one order higher in ARB. The content of Fe was below 2 μg/l for both facilities. After two years of exposure the pitting was evaluated as local corrosion damage. The occurrence of pits was evaluated predominantly on the surfaces of single coupons and on the outer and inner surfaces of bimetallic and crevice coupons. No correlation was found between the pitting initiation and the type of aluminium alloys and rolled and extruded materials. In bimetallic couples the presence of stainless coupons did not have any affect on local corrosion. The depth of pits was lower than 50 μm for considerable areas of coupons and should be compared with the results of other participating institutes. (author)