Numerical Simulation and Mechanics Analysis of Structural and Equipment Components with Random Defects in Power Plants

• Main Authors: Sue-Ray Lin, 林書睿
• Other Authors: Wen-Fang Wu
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/zq3839

博士 === 國立臺灣大學 === 機械工程學研究所 === 106 === As random defects presenting in a system or electronic components, it is indeed quite difficult to solve such structural integrity and mechanical problems. Reviewing the anchor-bolt failure event of reactor pressure vessel support skirt in a domestic nuclear power plant in 2012, at that time there were doubts about the reoccurrence of similar incidents thereafter although the loosen bolts have been replaced. If the failure event of anchor bolts reoccurred, the question whether there is still enough tightening capacity to ensure safety of the whole system remains. Aiming to convince the public in an appropriate and quantitative manner that is not extremely conservative, this research begins with a proposed finite element model that handles a large number of random events and improves the efficiency of the analysis. Statistical tests and other related assessments to deal with such a random problem are also proposed. In fact, such a problem also appears in guidelines issued by the Electric Power Research Institute (EPRI), which is aimed at analyzing the undetectable area of the reactor pressure vessel shourd support (the two inner and outer circular weldments aside the support plate). However, the overall assessment is merely based on the assumption of symmetric through-wall cracks to reduce the structural strength for conservative reasons. The possible issue on random events is not explored. In this study, an improved analysis in consideration of random fracture anchor bolts is proposed to improve the treatment of cracked support plate. The efficiency method is verified with a large number of random events. It also shows in this dissertation that the proposed analysis for the discrete structures can also be applied to the continuous structures. In the viewpoint of safety assessment on power plants, the random defects problem not only belongs to the mechanical issue of systems, structures and components, but also occurs on safety related electrical and electronic equipment. In fact, the US Nuclear Regulatory Commission (USNRC) has issued guidelines for environmental qualification for electrical and electronic equipment, but with little mentioning about the microprocessor-based equipment, despite a few studies on the physical failure of semiconductor-based equipment have been carried out in non-nuclear industry. Those guidelines considered that even under mild environments, such equipment should function normally without affecting the safe operation of power plants. However, the new type of microprocessor-based equipment, especially those used for monitoring and instrumentation continues to develop but its failure only relies on the testing or analyzing data from semiconductor manufacturers. Most reliability studies of the electronic packaging are based on assuming integrated structures, and the evaluation of fatigue life often ignores defects induced in production process. To improve the shortcomings, the concept of rational model proposed in the first part of this dissertation is adopted, and an equivalent general formula for use in the simulation of lead-free solder ball containing void is derived in the second part of the dissertation. The formula results in simplified equivalent cylinders to replace sloder balls containing random voids for use in the finite element simulation of packages. The fatigue life distribution of a package used in electrical or electronic equipment is determined under an accelerated environment. Its life under the normal operation of power plant can also be obtained. The result is also helpful for the maintenance of a power plant.