Investigation of the corrosion chemistry of hot-dip galvanized steel at LOCA condition

The loss of coolant accident (LOCA) is assumed to be one of the most severe accidents during pressurized water reactor (PWR) operation. Strainers in the reactor sump prevent the transport of fibres formed by fragmentation of insulation material to the reactor core for maintaining save cooling. Additionally, the coolant flow may be reduced or blocked by corrosion products resulting from reaction of primary circuit fluid with metallic components such as hot-dip galvanized steel gratings. The chemical behaviour of special designed galvanized steel samples was tested by means of batch experiments and in a tailored corrosion test facility under post LOCA conditions. Pure water, boric acid solution and a boric acid solution with additional LiOH for adjusting pH are used as liquid media. Only in solutions containing boric acid, the zinc ion concentration shows a significant increase within the first two days but no head loss occurred. Depending on reaction conditions, the zinc-concentration increases more slowly in the corrosion test facility than in batch experiments. At 45°C, concentrations up to 90 mg Zn/l are reached. It is remarkable that no significant amount of corrosion products of the basic material (Fe) were determined. Local damage of the outer pure zinc layer is observed especially in the trickled region of galvanized gratings.