Irradiation creep and growth of zirconium alloys: A critical review

Abstract

The fuel channels and fuel assemblies of all conventional nuclear reactors that generate power from the fission of uranium by thermal neutrons are made from zirconium alloys because of their low thermal neutron absorption cross-section. The dimensional stability, and the ability to predict dimensional changes, of components made from zirconium alloys is important to designers and operators of such reactors because deformation has a consequence for the operability or life of the reactor core. The dimensional changes in zirconium alloys due to neutron irradiation has been the subject of intense study since the inception of the thermal nuclear power reactor. During irradiation zirconium alloys behave differently from most other engineering alloys in that they resist swelling. They do exhibit anisotropic dimensional changes in the absence of an applied stress that depend on the microstructure; this process is called irradiation growth. Like any other material they also exhibit a dimensional response to an applied stress; this process is called irradiation creep. In this review the evolution in measurement methodologies (either from controlled experiments in materials test reactors or gauging of power reactor components) is described together with the results gleaned from such measurements. As measurements have improved and the amount of experimental and operational data has increased, the theoretical basis for modelling creep and growth has also evolved. The history of the evolution in understanding and the ability to predict dimensional changes in zirconium alloys over the past 60–70 years is described and discussed.