Modelling vibration of 37-element CANDU fuel string in an aged pressure tube

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The 37-element CANDU fuel bundles are used in several nuclear generating stations in Canada, and in all CANDU 6 reactors outside Canada. With all commercial CANDU reactors at home and abroad entering into their third or fourth decade of service, the safe operation of these reactors depends upon our ability to assess how aging results in fuel string fretting and pressure tube wear. Eliminating any premature failure of pressure tubes due to fretting-induced wear in commercial nuclear power plants will reduce unnecessary reactor shutdowns, resulting in significant economic and environmental benefits to Canada. Ultimately, this research will ensure that the design of future CANDU reactors meets the wear specifications necessary for compatibility with overall reactor life and maintenance outage schedules. The results of this research will help Candu, a new Canadian-owned private company, to secure its leadership position in the nuclear power industry at home and abroad. Condition reports from nuclear generating stations indicate that fuel strings vibrate during operations, and that excessive vibration causes wear of pressure tubes, undesired amounts of debris in the coolant, and loss of fuel bundle integrity due to the failure of components. Fretting-wear damage has become a significant safety concern for nuclear fuel design engineers and analysts. Like other reactor fuels, CANDU reactor fuel is exposed to harsh thermal, mechanical, and radiation conditions during operation, yet the effects of CANDU reactor component aging are largely unknown. To date, there is no industry-wide tool to quantify fuel string vibration and pressure tube wear. The project will address this knowledge gap by developing a new state-of-the-art computer program for simulating fretting wear in a fuel channel in an aged CANDU reactor under operating conditions. This computer program will be used to assess fretting wear for actual operating conditions and will also postulate operating scenarios often required by the licensing bodies in safety analysis. The long-term objective is to have the computer program fully validated and certified for use in the nuclear industry for quantifying fuel fretting and pressure tube wear.