Influence of chemical composition of zirconium alloy E110 on embrittlement under LOCA conditions – Part 1: Oxidation kinetics and macrocharacteristics of structure and fracture

Exploratory investigations of the influence of alloying and impurity content in the E110 alloy cladding tubes on the behavior under conditions of Loss of Coolant Accidents (LOCA) has been performed. Three alloys of E110 type have been tested: E110 alloy of nominal composition Zr–1%Nb (E110), E110 alloy of modified composition Zr–1%Nb–0.12%Fe–0.13%O (E110M), E110 alloy of nominal composition Zr–1%Nb with reduced impurity content (E110G). Alloys E110 and E110M were manufactured on the electrolytic basis and alloy E110G was manufactured on the basis of zirconium sponge. The high temperature oxidation tests in steam (T = 1100 °C, 18% of equivalent cladding reacted (ECR)) have been conducted, kinetics of oxidation was investigated. Quantitative research of structure and fracture macrocharacteristics was performed by means of optical and electron microscopy. The results received were compared with the residual ductility of specimens. The results of the investigation showed the existence of “breakaway oxidation” kinetics and white spalling oxide in E110 and E110M alloys while the specimen oxidation kinetics in E110G alloy was characterized by a parabolic law and specimens had a dense black oxide. Oxygen and iron alloying in the E110 alloy positively changed the macrocharacteristics of structure and fracture. However, in general, it did not improve the resistance to embrittlement in LOCA conditions apparently because of a strong impurity influence caused by electrolytic process of zirconium production.

► Breakaway oxidation effect in electrolytic-based alloys E110 and E110M was observed.
► No breakaway oxidation was observed in E110G alloy produced on a sponge basis.
► Electrolytic-based alloys had a zero residual ductility and brittle fracture surface.
► Oxygen and iron alloying of E110 alloy positively changed macrostructure.
► Oxygen and iron alloying of E110 alloy did not improve the residual ductility.