Investigation of the Dynamic Characteristics of CANDU Fuel Bundle

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There has been a history of failures in CANDU fuel bundles and chronic cracking of fuel bundle end-plates. Most of these failures were attributed to the acoustic pressure pulsations generated by the primary system heat transport pumps. For example, in 1990, one of the fuel bundles in the Darlington nuclear power plant was damaged as a result of excessive vibration of the fuel elements. The fuel bundle endplates were found broken and subsequent inspections found severe wear marks in a few fuel channels in Units 1 and 2. The cracks in the fuel bundle endplates were caused by axial response of the fuel bundle, which was triggered by acoustic pressure pulsations generated at the primary heat transport (PHT) vane-passing frequency. More recently, endplates cracking in some fuel bundles has been observed at Bruce Power Nuclear Generating plant. The fuel bundle vibration problem that results in end plate cracking is exasperated if an external excitation frequency, such as that generated by the PHT pumps, matches one of the natural vibration frequencies of the fuel bundle. As such, the precise knowledge of the dynamic characteristics of the fuel bundle is of paramount importance to devise effective mitigation techniques that can be implemented to alleviate this issue. Up to date there is little knowledge, if any, about the dynamic characteristics of fuel bundles and the effect of radiation on their response. Therefore, the main objective of this project is to experimentally and numerically investigate the dynamic characteristics of CANDU fuel including the effect of radiation on the fuel bundles dynamics. The output of this project will provide a much needed information about the fuel bundle characteristics to aid existing CANDU operators to manage and mitigate the vibration problems and the end plate cracking issue of fuel bundles. This will not only support the increased safety and reliability of CANDU fuel bundles, which will directly benefit the Canadian economy, but could also be used in future CANDU reactors to avoid fuel bundle failures.