[en] This paper introduces the application of damage mechanics in nuclear piping LBB analysis based on Gurson damage constitutive model. The 3D elastic-plastic damage-fracture analysis of circumferential through-wall flaws in straight pipes under pure bending has been carried out and compared with the results from the elastic-plastic fracture analysis

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[en] In the welding structure of nuclear power equipment, J-type welding is a typical welding connection form, such as the control rod drive mechanism (CRDM) seat, instrument tube and exhaust pipe connected with the top cover of reactor pressure vessel, which are connected by J-type welding on the inner surface of the upper head. Corrosion cracks and fatigue cracks are easy to occur, so it is particularly important to study the integrity of such structures. In fact, there are many influencing factors in the process of J-type welding. At present, it is difficult to obtain complete distribution of welding residual stress by means of damage or non-destructive testing. In this paper, the finite element method is used to simulate the welding process of J-type welding of typical dissimilar metals. The three-dimensional structure model and sequential coupling method are used to simulate the temperature field in the welding process, and then the temperature field is used as input condition to respond to the whole welding process. The force and deformation are simulated. Finally, the residual stress and deformation after J-type welding are analyzed, the dangerous position is found and the improvement suggestions are put forward. In this paper, J-type welding involves five kinds of materials and their thermophysical and thermoelastic-plastic parameters. The analysis software is ANSYS. The results of this paper have practical guiding significance for the design of J-type welding structure, the optimization of welding parameters and the control of residual stress and deformation after welding, and lay a foundation for the safety and reliability analysis of welding structure. (authors)

[en] There are mainly two excitation mechanisms in the vibration of the thermo-well in the main pipe of reactor coolant loop under cross flow: turbulence and vortex shedding. The natural frequencies of the G1' and G1' 1/4 thermo-well and the vortex shedding frequencies are calculated, respectively. The vortex shedding lock-in is analyzed for two different thermo-wells, and then the flow induced vibration fatigue of the thermo-well is studied using a simplified engineering approach. (authors)

[en] In order to investigate the flow induced vibration problems in tube bundles, a numerical model for fluid-structure interaction system of an in-line square tube bundle was presented. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model were solved with finite volume approach on structured grids combined with the technique of dynamic mesh. The dynamic equilibrium equation was discretized according to the finite element theory, and the properties of fluid force and responses for various elastic tube models were studied by several calculations. The results show that tube configurations have an important effect on fluid force and dynamics respond. The 5-tube model can basically represent a flexible tube bundle. The critical velocity predicted by single tube model is larger than that predicted by flexible tube bundle. Besides, it shows good qualitative agreement on flow induced vibration behaviors of square bundle with a pitch-to-diameter ratio of 1.5. (authors)

[en] The elbow is an important component in nuclear piping system, and also is the location where crack easily occurrs. To ensure the structural integrity of the nuclear piping system, a fracture mechanics analysis for the cracked elbows will be necessarily performed. In this paper, the 3-D elastic-plastic fracture mechanics methodology is used to study the elbows with a through-wall circumferential crack by using of ABAQUS software, and some numerical results for J-integral are obtained. the calculated results show that the influence of bending radius on J-integral is not associated with locations of the cracks. It is, however, intimate to sizes of the cracks. The effects on the J-integral for elbows with small size of cracks are insignificant. As to the J-integral for elbows with large size of cracks, the value of the J-integral is reduced as the R_b/R ratio of bending radii increases. In the case that the end rotating angle is kept unchanged, the relation between R/t ratio and J-integral is approximately linear, i.e., a linear interpolation can be used. (authors)

[en] Hysteretic dampers have been widely used in the reactor coolant piping system as the energy absorbing components. In the paper, the random seismic response is evaluated through the pseudo-excitation principle incorporated with stochastic equivalent linearization method without by solving the Lyapunov differential equation for which the seismic excitation at support is limited to be shot noise process. It is supposed that the structures keep elastic and the hysteretic dampers are represented by the versatile Bouc-Wen model. With the aide of assistant matrices, the unidirectional and spatial excitation vectors of three components are derived and a pseudo-excitation closed-form expression for the system random response is established. Consequently. the stationary random seismic response of two shear type structure interconnected with hysteretic dampers is analyzed. The structural root mean square displacement responses for two methods agree well. Meanwhile, the parametric studies for initial yield force of the hysteretic dampers and the optimum way to install the hysteretic damper are discussed. (authors)

[en] To calculate the stationary stochastic seismic response of coupled structures interconnected by hysteretic dampers subjected to non-uniform random seismic excitations, a pseudo excitation method based on the multi-support and multi-component was proposed. As the unknown quantity is not the dynamic relative displacement but the absolute displacement, the proposed method can be suitable for all the seismic excitation including uniform seismic excitation. Numerical research shows that: results from the proposed method, traditional pseudo excitation method based on the dynamic relative displacement and the Monte-Carlo numerical simulation method agree well, verifying the reasonableness of the proposed method, Further, parametric study of hysteretic damper about the yielding force and the yielding displacement is also developed. (authors)

[en] In order to investigate the dynamic behavior of heat transfer tube under the influence of both internal and external flows, an analytical model of the coupling system was developed. The wake oscillator model was introduced to present the analytical model. Meanwhile, the mean axial extension of the tube was also considered. The nonlinear coupled equations of motion were discretized by employing the Galerkin method. Based on numerical simulations, the effects of internal and external fluid flow velocities and nonlinear parameters on response were studied. Moreover, the bifurcation diagram and phase portrait for vibration amplitude with various external fluid velocities were constructed. The results show that the tube displays various dynamical behaviors around the post-buckling configuration such as inverse period-doubling bifurcation, periodic and chaotic motions. (authors)

[en] In order to further investigate fluid structure interaction problems, occurring in the nuclear field such as the behavior of PWR fuel rods, steam generator and other heat exchanger tubes, a numerical model was presented. It is a three-dimensional fully coupled approach with solving the fluid flow and the structure vibration simultaneously, for the tube bundles in cross flow. The unsteady three-dimensional Navier-Stokes equation and LES turbulence model were solved with finite volume approach on structured grids combined with the technique of dynamic mesh. The dynamic equilibrium equation was discretized according to the finite element theory. The vibration response of a single tube in cross flow was calculated by the numerical model. Both the amplitude and frequency were compared with experimental data and existing models in the literature. It is shown that the present model is reasonable. The flow induced vibration characteristics, for both inline and parallel sets in cross flow, were investigated by the numerical model. The dynamic response and flow characteristics, for both inline tubes and parallel tubes with pitch ratio of 1.2, 1.6, 2, 3 and 4 under different incident velocities, were studied. Critical pitch and critical velocity were obtained. (authors)