压水堆核容器密封分析(英文)

本文作为核容器密封性能综合研究中心课题之一,给出容器密封分析基本方程及程序系统。经多种试验校核证实程序可信。根据多个容器分析计算,提出了就密封性能而言的压力容器类型概念,这对容器设计选定合宜预紧系数、保证密封并改善主螺栓疲劳性能有重要意义。     

Stress analysis of a nuclear reactor grid plenum assembly and its application to the EBR-II

A structural model is presented to predict the stress and deformation of a nuclear reactor grid plenum assembly. The model consists of two circular grid plates on top of one another which are interconnected by a large number of tubes, a perforated cylindrical shell and a cylinder at the outer edge of the plates. During normal reactor operation and shutdown the grid plenum assembly is subjected to both external and internal loads, in which the external load is due to the dead weight of the subassemblies resting on the upper grid plate and the coolant pressure, while the internal load is due to the temperature gradient and irradiation swelling in the grid plates accumulated through the life of the reactor.The structure is divided into many annular regions implying an axisymmetric treatment. The solution of the structural system is obtained by solving the equilibrium equations of the individual tubes, plates and shells, and satisfying the compatibility condition at the boundary of each region. The swelling strain in the grid plates is treated analogously to that of thermal strain in the elastic region. The numerical results of the problem are obtained by means of a computer code which uses a matrix-inversion technique to solve the simultaneous algebraic equations involved.     

Seismic model of the gas cooled fast breeder reactor core support structure

The modelling technique for the seismic analysis of the core support structure of a gas-cooled fast breeder reactor is developed. The core support structure consists of the support cylinder and a perforated grid plate to which 265 fuel and blanket elements are clamped as cantilevered beams. The analysis of the core support structure consists of three steps: (1) analysis of the grid plate, (2) analysis of the core elements, and (3) modal synthesis.The first step in developing a solution to the problem is to assume that the core elements (fuel and blanket) are attached to the grid plate as rigid rods. In this case the influence of the rigid rods can be represented by their masses and rotary inertias. The solution of this problem was developed by applying the dynamic theory of grid plates. This was accomplished by generalizing the Reissner-Mindlin thick-plate theory with orthotropic constants and then modifying the formulations of the rotary inertia expressions to include the rotary inertia effects of the core elements. The numerical results showed that the grid plate's fundamental frequency is in the range of the fundamental frequencies of the core elements so that a dynamic coupling effect exists. Because of this dynamic coupling effect the elastic properties of the grid plate must be included in the seismic analysis of the GCFR'The second step was to develop a mathematical model of the grid-plate core-element system using the method of Rayleigh-Ritz. In this model the elastic coupling effect of the core elements was included.For the final application of the theory, the exact solution of the elastic plate with rigid rods was simulated on the computer by applying the elastic rotary inertias of the core elements to the model of the grid plate. With this technique it is possible to model the grid plate with a reasonable number of fuel and blanket elements and to replace the missing core elements with their equivalent effective rotary inertias. The method includes the capability of modeling the different mass, damping and elastic properties of the fuel and blanket elements.Comparing the results of the present analysis with the preliminary simple spring-mass core model, the amplitudes of vibration obtained, in some cases in the present analysis, are a factor of ten smaller than was previously computed. Applying this more elaborate analysis will lead to a simpler and less expensive design.     

Similarity aspects for closure systems in reduced scale package drop testing

Abstract

An exact scaling of all structural components of a package for radioactive materials and their mechanical characteristics is not always possible in drop tests with reduced scale models. This has to be especially considered for bolted closure systems. On the one hand, the sizes of the bolts cannot be scaled with the same geometrical scale factor. On the other hand, the possibilities of an accurate scaling of seal characteristics are very limited. Owing to non-linearity of the force–compression relationship of a gasket, it is, for instance, impossible to simulate the maximum compression force and permissible elastic decompression of a metallic gasket simultaneously on the same scale model. Additional problems can also result from a dispersion of friction conditions in the bolted joints (at threads and under bolt heads). This dispersion, as well as an imprecise bolt tightening technique, leads to more or less considerable scatter of the bolt pretension. The minimum pretension creates more severe conditions in a drop test with regard to the seal function (higher probability of the lid opening and sliding). The maximum pretension is usually conservative for the total bolt stress (the sum of the initial tension and additional load due to the drop test). These circumstances should be considered in planning drop tests as well as regarding the interpretation and transfer of test results to the original package design. In this paper some recommendations are described concerning the modelling of closure systems based on Federal Institute for Materials Research and Testing (BAM) experience in the approval assessment of transport casks for radioactive materials.     

Influence of irradiation temperature and dose gradients on the microstructural evolution in neutron-irradiated 316SS

A cold worked 316SS baffle bolt was extracted from the Tihange pressurized water reactor and sectioned at three different positions. The temperature and dose at the 1-mm bolt head position were 593 K and 19.5 dpa respectively, whereas at two shank positions the temperature and dose was 616 K and 12.2 dpa at the 25-mm position and 606 K and 7.5 dpa at the 55-mm position. Microstructural characterization revealed that small faulted dislocation loops and cavities were visible at each position, but the cavities were most prominent at the two shank positions. Measurable swelling exists in the shank portions of this particular bolt, and accompanying this swelling is the retention of very high levels of hydrogen absorbed from the environment. The observation of cavities in the CW 316SS at temperatures and doses relevant to LWR conditions has important implications for pressurized water reactors since SA 304SS plates surround the bolts, a steel that usually swells earlier due to its lower incubation period for swelling.     

主螺栓断裂对压力容器密封性能、应力及疲劳的影响分析

Base on the mechanics theory and numerical simulation technique, a method to analyze the effect of the main bolt break on the stress, fatigue and seal is studied in this paper, and is adopted to evaluate and analyze the fracture influence of main bolt. The results show that this method is applicable for the analysis of the RPV safety performance induced by one bolt break or several bolts break accident, and for the determination if the nuclear reactor can be operated when similar problems occur.     

主螺栓断裂对压力容器密封性能、应力及疲劳的影响分析

在理论分析和数值仿真技术基础上,研究并提出了一种主螺栓断裂对反应堆压力容器(RPV)密封性能、螺栓应力及疲劳的影响分析方法,采用该方法对主螺栓断裂影响进行了评价分析。结果表明,该方法适用于分析1根或多根主螺栓断裂情况对压力容器安全性能的影响,可以用于核电厂在运行中发生类似问题时判断反应堆能否继续运行。     

Three-dimensional transient sealing analysis of the bolted flange connections of reactor pressure vessel

The failure of sealing system of the bolt flange connections is the primary failure mode of the nuclear reactor pressure vessel (RPV). For the safety and integrity of RPV, it is important to predict the sealing behaviour of the bolt flange connections under various loading conditions. Based on the finite element (FE) method for coupled thermal elastoplastic contact problems, a three-dimensional (3D) transient sealing analysis program of nuclear reactor pressure vessels is developed with the consideration of the non-linearity from both surface and material, transient heat transfer and multiple coupled effects. A contact correction approach is proposed to simulate the loading of the bolt connection under the condition of pre-stressing. An automatic pre-processing program is developed for FE modelling of RPVs. Using these programs, a 1:4 scaled model of a 300 MW RPV is analyzed under the loading conditions including pre-stressing, pressurization, heating and cooling. The computational results obtained are in a good agreement with the data of experimental tests. These programs are also successfully used in analyzing the full-scale model of the RPV in a nuclear power plant.     

Finite element analysis of moving contact in mechanically fastened joints

The Finite Element Method (FEM) has made a number of otherwise intractable problems solvable. An important aspect for achieving an economical and accurate solution through FEM is matching the formulation and the computational organisation to the problem. This was realised forcefully in the present case of the solution of a class of moving contact boundary value problems of fastener joints.This paper deals with the problem of changing contact at the pin-hole interface of a fastener joint. Due to moving contact, the stresses and displacements are nonlinear with load. This would, in general, need an interactive-incremental approach for solution. However, by posing the problem in an inverse way, a solution is sought for obtaining loads to suit given contact configuration.Numerical results are given for typical isotropic and composite plates with rigid pins. Two cases of loading are considered: (i) load applied only at the edges of the plate and (ii) load applied at the pin and reacted at a part of the edge of the plate. Load-contact relationships, compliance and stress-patterns are investigated.This paper clearly demonstrates the simplification achieved by a suitable formulation of the problem. The results are of significance to the design and analysis of fastener joints.     

Nonlinear vibrations of elastically restrained rectangular orthotropic plates

The influence of large amplitudes on the flexural vibrations of elastically restrained rectangular orthotropic plates is considered in this paper. The basic equations used are those due to Von Karman. Galerkin's averaging technique is used to reduce the original equation to an ordinary nonlinear differential equation in modal function, the solution of which is given in terms of elliptic functions.     

Mechanical and temperature contact in fuel rod and cladding

This paper presents a method of analysis for nuclear fuel rods. The paper concentrates on the interaction between fuel and cladding and between cracked surfaces. Both temperature and mechanical contact are considered. For the temperature contact an analysis model for the heat transfer conditions at fuel and cladding is presented. The most attention of the interaction problem is focused on the constitutive modelling of the mechanical interaction. A constitutive relation between contact stresses and the slip between fuel and cladding is presented. The paper presents a finite element solution of the proposed model. For assumed elastic material properties results from the proposed interaction models are presented. The effect of different contact conditions on contact stresses, stress intensities, etc. are presented.     

On the finite element solution of the three-dimensional tire contact problem

Starting from a theoretical analysis of the static contact problem “deformable body-rigid object” various solutions including the three-dimensional pneumatic tire contact problem are being discussed. The computed shapes and sizes of the footprint area as well as the load-deflection response are in good agreement with experimental results. The following approaches for a numerical solution are presented in this paper:

1. (1) Elimination method: This method is based on using the influence coefficient technique to compute the nodal forces as well as the footprint area by iteration applying a geometrical linear or nonlinear FE technique.

2. (2) ‘Nonlinear Programming’ technique: Recent developments in the theory of nonlinear optimization in abstract spaces suggest to describe the contact problem by a constrained optimization problem in function spaces. The minimization of the potential energy of the elastic body, the rigid obstacle being replaced by an operator constraint depending on the displacement functions, leads to three necessary conditions determining completely the equations of equilibrium, the contact zone and the pressure distributions in the contact zone. This result justifies the use of a nonlinear programming code to solve the discrete problem approximated by the method of finite elements.

3. (3) Variation of boundary conditions: This method is based on an incremental formulation including nonlinear geometry and variable boundary conditions.

Resolution of flat bottom tank outlier

This paper contains the results of an outlier resolution evaluation for a large flat bottom tank, 40 ft 6 in. in diameter and 32 ft 8 in. in height. The tank was an outlier in both the USI A-46 and IPEEE programs due to insufficient strength of the bolt chair to transfer the bolt load to the side of the tank. The bolt chair evaluation resulting in the outlier was linear elastic. A more sophisticated non-linear analysis was performed of the bolt chair using the program ANSYS. The evaluation resulted in the conclusion that the bolt chair was able to transfer almost the entire yield strength of the bolt without excessive deformation that could ultimately cause overall tank failure. This evaluation tremendously increased the seismic capacity of the tank and resolved the outlier for both programs. The tank outlier evaluation also included a evaluation of soil–structure interaction (SSI) effects on the seismic demand on the tank. However, the formal consideration of SSI had a small effect on the overall seismic demand.     

Three dimensional analysis of thermally loaded thick plates

A mixed three dimensional formulation is presented for the analysis of thermally loaded thick plates. The method developed follows the guidelines furnished by the Vlasov-Iyengar technique applicable to the analysis of mechanically loaded thick plates, in which the three dimensional governing equations are derived from the elasticity equations by using a MacLaurin series approach. The expressions for the components of displacement, stress, and heat flux as well as the temperature are obtained in a series form in terms of the linear partial differential operators operating on a set of initial functions, which are the solutions to the governing equations. The procedure to be followed in arriving at the solution is illustrated by solving the problem of the thermal bending of a clamped-supported thick square plate; it is found that the present solution deviates significantly from those of the lower order theories for large values of the thickness ratio.     

The use of analytic continuation in solutions of plane thermal stresses in an orthotropic elastic medium

This paper describes a general method for plane thermoelasticity in an orthotropic elastic medium of doubly-connected shape. The analysis is based upon the complex variable method and the analytic continuation is effectively employed. Numerical calculations are carried out for orthotropic rectangular plates with an elliptical hole subjected to heat flow and results illustrating the influence of geometry and orthotropy of the plates are obtained.     

Thermal stress waves with applications to laser fusion reactors

A closed-form solution is developed for stress waves in a solid resulting from volumetric energy deposition. The material is linear elastic and the geometry a plate or slab-like component. One dimensional waves perpendicular to the surface are considered. Such a model can be used to describe the response for plates or thin shells. The problem is relevant to the design of liners and first wall structure of laser fusion reactors. For demonstration purposes, examples are presented based upon the University of Wisconsin SOLASE conceptual power plant. It is shown that X-rays and reflected long wavelength laser light produce relatively small amplitude waves but short wavelength reflected laser light can produce stresses of significant amplitude.     

Thermal flexure of an infinite plate with a doubly periodic array of holes

A theoretical method is presented for bending problems of perforated plates. The method is illustrated by giving the solution for an infinite plate with a doubly periodic set of circular holes having a square or triangular pattern under a uniform temperature difference between upper and lower faces of the plate within the framework of the Poisson-Kirchhoff theory of thin plates. Numerical results are given for the bending moment around holes and curves of stress concentration factors. The results show the power and flexibility of the technique. The solution obtained here can be used, just as it is, for a plate with holes of arbitrary shape and array. Also the extension of the method to a plate under a class of loads other than thermal load, e.g. uniform bending or twisting moment, is quite straightforward.     

Smearing in an axisymmetric finite element structural analysis application to the GCFR steam generator cavity closure plug

A methodical technique for smearing material properties in an elastic finite element analysis to derive an approximate axisymmetric model of a structure is presented. In this process, material properties are smeared circumferentially about an axis of symmetry in the structure's outline. Attention is given to the subsequent problem of unsmearing the results to obtain an estimate of circumferential variation in the solution. The scheme is illustrated with an application to an analysis of a GCFR steam generator cavity closure plug.     

Application of conformal mapping to the determination of unsteady temperature distribution in thermally orthotropic plates

Very few papers and reports are available on the solution of heat conduction problems in anisotropic solids. This situation is of particular interest in some nuclear engineering applications (for instance, fuel elements possess, in general, anisotropic characteristics). The present study deals with the solution of an unsteady heat conduction problem in domains of complicated boundary shape, considering a particular case of anisotropy: a thermally orthotropic material. It is shown that the conformal mapping technique coupled with the Ritz method leads to a unified solution of the title problem for an arbitrary orientation for the axes of orthotropy with respect to the directions of the sides of the plates.