This report provides the understanding of the mechanisms of dimensional instability (including irradiation creep and growth) in the aggressive environment of the nuclear core and the potential effects on fuel performance.
The objective of this Report is to provide a better understanding of the mechanisms behind the dimensional changes of structural materials in LWRs and CANDUs. Such improved understanding may improve both fuel reliability and reactor safety.
In this Report we have attempted to summarize data and mechanisms by addressing the variables that are known to affect irradiation creep. A number of conclusions are reached which give insight into the uses of creep data, mechanisms and models to assess in-service performance of reactor components.
In the past ten years approximately half of the 35 BWRs in the United States have reported Control Blade interference due to channel distortion, primarily channel bow. Channels fabricated by all vendors have been affected. This Report is primarily focused on channel distortion; that is, change of shape during in-reactor service: length, bow, bulge and twist. This Report addresses a broad range of channel features which can contribute to normal and problematic performance. In particular, the so-called “shadow corrosioninduced” channel bow phenomena are analyzed.
The ability of reactor engineers to predict changes in the dimensions of the reactor core components during service is crucial to the safety and efficiency of reactor operation. Successful core design anticipates dimensional changes due to thermal expansion, stress-induced elastic deformation and, to some extent, large stress plastic deformation of core components. Of greater difficulty is predicting dimensional changes due to the effects of the intense irradiation environment, mainly due to high energy neutrons produced by the fission process. Fuel rods, spacers/grids, channels, guide tubes, tie rods, other structural components, etc. – all undergo irradiation-induced dimensional changes due to irradiation growth, irradiation creep, irradiation-altered plastic deformation, and irradiation-influenced corrosion and hydriding of the zirconium alloy components. These topics and process are routinely covered by the ZIRAT Programmes. This Report reviews the effect of ion irradiation (or ion bombardment, used interchangeably in this report) on not only the standard dimensional stability topics but also the full range of properties that can be influenced by ion irradiation. The primary questions addressed are: What properties of zirconium alloys can ion irradiated simulate (emulate or substitute for) neutron irradiation? How, or to what extent, can ion bombardment complement neutron irradiation?
In this STR review, aimed specifically at irradiation growth, addressed are conditions of direct interest to LWRs and CANDUs, including information that has mechanistic implications. Irradiation creep was covered earlier by ZIRAT14 Special Topic Report: In-reactor Creep of Zirconium Alloys, authored by Ron Adamson, Friedrich Garzarolli and Charles Patterson, 2009.
The STR addresses all data deemed relevant to understanding irradiation growth, including a broad review of growth mechanisms, and a summary of practical effects of growth on component performance.