Vibro-impact dynamics of complex engineering structures with applications to fretting of nuclear fuel bundles

在核反应堆中，燃料束的过度振动是导致支撑结构或压力管异常磨损的原因。反应堆部件的故障可能导致部分生产损失甚至完全停产。维护和更换严重磨损的部件可能非常昂贵。在操作过程中，一串燃料束被放置在燃料通道内，并受到多种激励源的影响，包括声压脉动、流动诱导的动力等。由于燃料束结构和压力管之间的间隙很小，即使是小振幅的振动（微动）也会引起周期性的冲击和滑动。本文将对典型CANDU燃料束在不同工况下的微动结构和接触冲击力进行建模。尽管已经进行了大量的研究来研究微动的机制，但对于新燃料或现有燃料在运行条件变化时的燃料束微动机制仍然缺乏全面的了解。无论哪种情况，燃料束振动的量化都很重要。加拿大核工业对开发一种全面的微动模型很感兴趣。这样的模型一旦得到验证，将对未来监管机构对新燃料设计的认证具有不可估量的价值。由于燃料束的复杂结构及其与流体流动的耦合，微动的预测需要专门的研究、严格的建模和实验验证。主要目标是促进对流体流动管道中结构动态行为的理解，研究设计变化的影响，帮助核工业制定微动规范和标准。模拟结果可用于评估压力管材料在所有关键位置的磨损率。这项研究提案的完成将有助于加拿大核工业取得进一步的技术成功和新的CANDU核燃料的认证。

In a nuclear reactor, presence of excessive vibrations of fuel bundles was found responsible for abnormal wear of the supporting structures or pressure tube. Failures of reactor components may lead to the partial loss of production or even complete shutdowns. Maintenance and replacement of severely worn components can be very costly. During operations, a string of fuel bundles are placed inside a fuel channel and are subjected to several sources of excitations including acoustic pressure pulsations, flow induced dynamic forces, etc.  Because of small clearances between fuel bundles structures and the pressure tube, even small amplitude vibrations (fretting) can cause impact and sliding periodically.   In this proposal, fretting of fuel bundle structures and contact-impact forces will be modeled for typical CANDU fuel bundles under various operating conditions. Although significant amount of research has been conducted to investigate the mechanisms of fretting, there is still a lack of a comprehensive understanding of fuel bundle fretting mechanisms for new fuel or existing fuel when operating conditions change. Quantification of fuel bundle vibrations is important for either case.  The Canadian nuclear industry is interested in developing a comprehensive fretting model. Such a model, once validated, will be invaluable for future certifications of new fuel designs by the regulatory authorities. Because of the complex configuration of fuel bundles, and their coupling with fluid flow, prediction of fretting requires dedicated research, rigorous modeling and experimental validation.  The main objectives are to advance understanding of the dynamic behaviors of structures, confined in liquid-flowing pipe, to study the effects of design changes, to aid the nuclear industry in developing a code and standard for fretting. Simulation results can be used to assess wear rate of pressure tube materials at all critical locations. Completion of this research proposal will assist the Canadian nuclear industry in achieving further technical success and certification of new CANDU nuclear fuel.