Corrosion Optimized Zircaloy for Boiling Water Reactor (BWR) Fuel Elements

A corrosion optimized Zircaloy has to be based primarily on in-boiling water reactor (in-BWR) results. Therefore, the material parameters affecting corrosion were deduced from results of experimental fuel rod irradiation with systematic variations and from a large variety of material coupons exposed in water rods up to four cycles. The major material effect is the size and distribution of precipitates. For optimizing both early and late corrosion, the size has to stay in a small range. In the case of material quenched in the final stage, the quenching rate appears to be an important parameter. As far as material chemistry is concerned, the in-BWR results indicate that corrosion in BWRs is influenced by the alloying elements tin, chromium, and the impurity silicon. In addition to corrosion optimization, hydriding is also considered. A large variation from lot to lot under identical coolant condition has been found. The available data indicate that the chromium content is the most important material parameter for hydrogen pickup.