Research On Key Techniques For Health Monitoring Of Steam Generator In Nuclear Power Plant

Pressure water reactor (PWR) steam generators(SG) linking the primary coolant loop and the secondary circuit have been experienced operating reliability and integrity problems during the whole servicing life of operation associated with the U-bend tube failures due to flow-induced vibration. As a result the nuclear reactor has to be shutdown as steam generators often require costly outages for inspection or plugging the failed tubes, or even more significantly, they are replaced before reaching their expectant design life-span. The causes of leakage or rupture of the steam generator tubes are mostly related to fretting wear damage resulting from impact between tube and support plate or tube and anti-vibration bar. To address these issues, some mathematical and physical models describing the dynamic characteristics and their interaction of U-bend tubes and support plate are implemented in terms of structural features, flow patterns and operation environment.The mathematical analysis methodologies and mechanical models concerning with fluid-structure interaction(FSI) to solve the modal problems of submerged circular plate are expatiated, including the establishment of the fundamental assumptions, governing equations and boundary conditions. The added virtual mass effect due to the presence of fluid on the submerged circular plate is analyzed by integral transformation technique and via the approach of separation of variables.The first and second kind of Fourier-Bessel-Hankel(F-B-H) integral transformation and the inversion formulae are firstly put forward based on the mathematic principle on second kind of generalized Fourier-Bessel series and Hankel transformation for solving encountered boundary value problems in partial differential equations deduced from above FSI problems. The F-B-H integral transformation and the inversion are utilized in conjunction with Neumann and Robbin boundary value problems in solving the nonlinear equations of plate motion submerged in liquids. The analytical solutions of the non-dimensionalized added virtual mass incremental factors for most cases of a circular plated submerged in water are obtained by means of both methods of integral transformation and separation of variables. The various boundary conditions of fluid region such as fluid domains with infinite or finite in depth and width respectively, free surface or rigid wall on top face of the fluid region, free surface or rigid wall around the circumferential surface of the fluid region, free surface or rigid wall on the circumaviate zone of the plate are performed. In particularly, the F-B-H integral transformation and the inversion are employed on the cases with finite circumferential width fluid region and corresponding theoretical solutions are deduced. The solutions of some cases concerning dual integral equations are completed, and others not as a result of present mathematical theoretical solutions restricted in some complex dual integral equations. The F-B-H integral transformation and the inversion proposed here can also be applied to solve Neumann or Robbin boundary value problems in other physical subjects like heat transfer, electromagnetics, hyperfrequency waves and radio frequency, et cetera. The empirical formulae are presented for submerged plate with different boundary conditions in fluid region based on the regression process of numerical simulation results. The coupling effect of multiplayer plates is investigated by theoretical analysis and numerical simulation. Its analytical solution is obtained by both F-B-H integral transformation technique and separation of variables approach. A dual equivalent effective principle is introduced for the first time to calculate the added virtual mass effect of a perforated plate, which the perforated plate is idealized as a homogeneous plate with effective rigidity and density and the honeycomb fluid region is idealized as a homogeneous media with effective mass. The determination procedure of non-dimensionalized added virtual mass incremental factors for perforated plate is provided.The analytical and experimental investigations on health monitoring and condition assessment of SG U-bend tubes are accomplished considering the variation of dynamic vibration parameters. The progress and trend of fault diagnosis and health monitoring technologies are summarized, and the feasibility of monitoring the health condition of key process equipments is also discussed. The signal height change of wave crest or hollow adjacent to a crack-like defect in an U-bend tube is simulated by finite element analysis. The sensitivities of the natural frequencies and the mode shape of displacement and strain are evaluated respectively. It is found that the strain mode shape is the most sensitive to a crack in U-bend tube, in consequence there is a very obvious wave crest or hollow with a signal kurtosis near a defect which can be inerrably detected by a conventional measuring instrument. It is proposed and verified that the health condition of a SG U-bend tube can be assessed by monitoring the strain change near the positions where defects likely occur.The dynamic characteristics of steam generator (SG) U-tubes counting for much with safety of an operating nuclear power plants are investigated by analytical and numerical methods. The natural frequency, corresponding mode shape and participation factor, modal analyses are performed for the U-tubes with different influencing factors and load cases. A virtual temperature method for heterogeneous mass density distribution in structural modal analysis, based on temperature dependent material properties model is presented, which is applied in SG U-tubes conveying non-uniform mass fluid flow. The method is relatively straightforward but rather effective and considerably convenient in associating with any commercial structural analysis codes. A formula considering the effects of internal and external pressures in thin-walled U-bent tubes is deduced. Many factors relating to dynamic characteristics of the U-tubes are evaluated and corresponding means are discussed. Based on the synthesis of all sorts of factors influencing the dynamic characteristics of steam generator (SG) U-tubes, the natural frequency and corresponding mode shape of the U-tubes are analyzed under practical load cases and environment by numerical simulation. The influences the of material properties, boundary constraints, supporting width, tube-support clearance, elbow tube factor, pressures in primary and secondary sides, non-uniformities of pressures and mass along the whole tube, tube deadweight and the heat expansion on the natural frequencies are then addressed. The semi-empirical regression formulae considering the effects of internal and external pressures, the non-uniform distributed mass density and pressure along tube are also deduced.Based on the elasticity theory of plates and shells, the concept of equivalent isotropic solid plate elaborated for perforated tubesheet, the new methodology to determine the effective elastic constants by modal analysis of such plates is described. The suitability of commonly used elements has been assessed in analyzing the modal of the perforated plates. The universal relationship between the effective elastic constants and the mass fraction are established, which can be used for perforated plates with arbitrary hole shape. The results of the effective elastic constants for perforated plates coming from modal approach are compared with ASME code, and the result indicates that the data given by modal approach agree well with ASME code for circular hole perforated plates. It is shown , however, that those curves for calculating effective elastic constants adopted in ASME for the design of tubesheets offer inacceptable result in non-circular hole perforated plates. The computing formulae of effective elastic constants for plates with hetero-diameter holes are given in terms of the superposition method. By modal approach, the effective elastic constants of popular used steam generators support plates with various perforation shape, such as satellitic, trefoil and quatrefoil holes are obtained. The universal relationship between the effective elastic constants and the mass fraction is established, which can be used for erforated plates with arbitrary hole shape.The natural vibration characteristics of coupling U-bend tube and support are investigated by numerical simulation, involving tube via a few kinds of perforated support plates as circular hole, satellitic, trefoil and quatrefoil holes. The varying rule between the coupling natural frequencies of vibration of integrated U-bend tube and support and the ligament efficiencies is studied. In addition, three dimensional numerical simulations are conducted to assess the effect of tube-support contact in right and incline orientation, and the non-Herzian compatible contact behavior for tube-support are analyzed in terms of complex stress functions of elasticity.