Effect of Chloride Concentration on the Aqueous Corrosion of a Magnesium Alloy

Abstract

AT each nuclear power station of the Central Electricity Generating Board, the spent-fuel elements will be stored under water for about one hundred days, by which time their radioactivity will have decayed sufficiently to permit them to be removed for reprocessing of the uranium fuel. The water in each cooling pond will be maintained at about pH 11.5 by adding caustic alkali to minimize corrosion of the magnesium alloy can (A12). Although corrosion should be slight, it is still, however, important, since the corrosion product is radioactive due to the presence of active isotopes developed under irradiation from impurities in the magnesium alloy. In addition, accelerated corrosion can be expected on about 50 per cent of the cans in the pond due to carbon deposited on their surface from the carbon dioxide coolant during reactor operation. This type of accelerated corrosion is very sensitive to the presence of chloride ion in the water ; the critical level for rapid attack has been estimated from corrosion tests as less than 10 p.p.m.¹. Since all the powar stations are sited near or on the coast, and most have uncovered cooling ponds, the possibility of enhanced corrosion, due to chloride pick-up, is very real, and an electro-chemical assessment of the effect of chloride and carbon on magnesium alloy corrosion is in progress.