Influence of various additions to water on Zircaloy 4 corrosion in autoclave tests at 350 deg. C

The effect of different impurities or chemical compounds intentionally added into PWR primary water on the corrosion behaviour of Zircaloy-4 was studied by autoclave tests in water at 350 deg. C lasting up to 250 days. Significantly increased corrosion was only seen at high fluoride or LiOH-concentrations. A moderate increase was caused by high concentrations of chloride, chromate, cation resin, oxygen and a mixture of LiOH, KOH and boric acid. Hydrogen decreased the corrosion somewhat. Nitrides, sulfates, anion resin, hydracine and Fe3O4 had no noticeable effect. The metal oxides Cr2O3, NiO, NiFe2O3 and SiO2 caused a reduction of the time to transition but had no effect on the post-transition corrosion rate. The results indicate that the effect of alkalizing additions may be more the result of an increased pH value than derive from specific chemical species. The morphology of the oxide formed by corrosion plays an important role to understand the mechanismus of these effects. (author). 17 refs, 11 figs, 2 tabs