Year
2019
Degree Name
Master of Philosophy (Engineering)
Department
School of Mechanical, Materials and Mechatronics Engineering
Abstract
Abnormal vibration has been observed on the central cruciform shaped control rod in the Open Pool Australian Light-Water (OPAL) research reactor at the Australian Nuclear Science and Technology Organization. Increased wear in comparison to outer control rods and reactor power fluctuations have also been observed. The control rods are expected to have minimal vibration to avoid contact with the channel walls. This is presumed to be in response to the two axial coolant flows the control rod is subject to. Though minor in severity, they necessitate increased scrutiny. These activities consequently result in reduced reactor utility.
The thermal-hydraulic characteristics and flow induced vibration response of the control rod and channel were both theoretically and experimentally determined during the design and commissioning of the reactor. A review of these reports finds several deviations between the design and as-manufactured values that suggest the flow conditions have departed from the design intent.
In order to quantify the current flow conditions and to understand the vibration response of the control rod, both the theoretical and experimental validation have been reperformed. This is to ensure the control rod system is acting within design and safety margins, and to quantify the vibration response of the control plates in order to define adequate inspection periods.
The original design calculations from these reports were reviewed with updated geometries from the as-manufactured control rod and channel. A reduced length model of the control rod system was manufactured and placed into a water tunnel flow chamber for validation. The system was reviewed for pressure loss, flow rates, flow velocities, drag and vibration response under reactor operational conditions to ensure design conditions are met. A second experiment was used to examine the potential for excitation caused by the water jet used to deliver flow to one of the coolant channels.
The main conclusions from this study are:
1. The control rod experiences flow induced vibration as a result of both turbulence and leakage flow in the upper channel and shear impingement within the lower channel.
2. The operational flow values differ from the original design validation, but are still within safety margins for drag and velocity. Onset of Nucleate Boiling was not reviewed in this paper but it is suggested this be validated for the new flow conditions specified.
3. The assumption that the control rod is sufficiently damped within the channel so that the end plates can be considered fixed was confirmed.
4. The magnitude of vibration at the control plates does not cause contact with the channel wall.
5. Additional inspection frequencies are not necessary based on above findings.
Recommended Citation
Johnston, Clay, Experimental Investigation of Reactor Control Rod Flow Induced Vibration, Master of Philosophy (Engineering) thesis, School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, 2019. https://ro.uow.edu.au/theses1/834
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.