The Effect of Irradiation on Ni-Containing Components in CANDU® Reactor Cores: A Review

Abstract

For nickel-containing alloys irradiated in thermalized neutron fluxes, the formation and reaction of 59 Ni with thermal neutrons can lead to time-varying changes in displacement damage rate, expressed as displacements per atom per second (dpa.s -1 ), gas formation and nuclear heating. Ni-rich alloys are used in PWR and BWR reactors as spacers within fuel assemblies but also as tensioning springs for these same assemblies. Flux thimbles have also been made from Ni-rich alloys in the past but are gradually being replaced by thimbles made from other alloys containing substantially less Ni. In a CANDU® reactor, Ni-alloys are used as tensioning springs, fuel channel spacers (in the form of garter springs) and as cable sheathing and core wires in flux-detector assemblies. Prediction of the irradiation processes that affect the functionality of these CANDU internals, such as irradiation embrittlement and irradiation creep, especially under conditions of extended operation, necessitates a consideration of the effect of the transmutation of Ni. Over the past 10 years, there has been a considerable increase in the understanding of the effects of irradiation on the properties of components made from Ni-rich alloys. The nuclear processes and the effects of irradiation damage on the performance of components made from these alloys will be described.