A review of intermetallic precipitates and their influence on zircaloy corrosion in nuclear reactors

Abstract

Intermetallic precipitates are present in many aerospace and nuclear grade alloys and strongly influence their corrosion behaviors. The nuclear industry around the world uses zirconium alloys in the form of thin-walled tubing to clad radioactive fuel in light and heavy water reactors. Typical lifetimes for these fuel rods can be from 3 to 8 years depending on the reactor type and operating cycle, and corrosion is a life limiting factor of these fuel rods. In zirconium alloys, corrosion behavior is strongly tied to solute content and intermetallic precipitate size distributions. To produce a corrosion resistant alloy for service conditions it is of prime importance to have a thorough understanding of these precipitates, including their morphology and behavior during reactor operation.

Many factors influence these precipitates during fabrication as well as service exposure. Heat treatments, thermomechanical processing, and radiation exposure cause changes in the morphology of these particles. This paper summarizes current knowledge on the types of precipitates responsible for corrosion resistance, formation of these precipitates, their influence on in-reactor performance. In particular, beta quenching parameters along with heal, treatment schedules strongly influence the distribution and morphology of the precipitates. Also of importance is the effect of ahoy composition, which changes the chemistry of the predominant types of precipitates. Zirconium precipitate research is now of great interest in the nuclear industry because of the desire to increase the lifetimes of nuclear fuel to both reduce cost and waste. The formation of intermetallic particles in zirconium alloys is complex to model. While current knowledge is extensive, more research is needed to determine what the optimum types of precipitates are and how they form.