Measurement of Leakage Flow Induced Vibrations of Cylinder

For development of a two-phase flow analysis code by use of two-velocity two-temperature (2V2T) model, six basic equations completely independent and consistent with one another are derived for several possible types of thermodynamical unequilibrium conditions. Characteristic of the basic equations is that evaporation and condensation take place in the saturated water and saturated vapor separately. These phase change equations in the saturated state are rigorously derived using the thermodynamical law.

The energy conservation equation of each phase is derived from the well known total two-phase flow energy equation, using the first law of thermodynamics and conservation equations of mass and momentum of each phase. This derivation method will give assurance that all conservation equations are consistent with one another.

To form simplest 2V2T model, the terms of wall and interphase friction, and heat transfer to the two-phase flow and between phases are considered in this paper.     

A New Principle for Radiation Dosimetry and Control

A new principle which can be used for radiation dosimetry and control is described. It is based on the behaviour of a moving electrode subjected to two opposite forces ; one of them is created by the field of an electret, which decreases during irradiation the other force, of mechanical or magnetic origin for instance, is independent of the irradiation dose. A small, light weight, individual dosimeter is described ; it gives a sound alarm when a pretedermined dose is reached ; preliminary experimental results are presented.     

A New Static and Dynamic One-Point Equation and Analytic and Numerical Calculations for a Subcritical System

In this study we derived a new one-point equation based on the balance of fission neutrons. The equation has the same form as the conventional equation using k _eff which represents the neutron balance in the whole core. The variables of the new equation are the number of fission neutrons and delayed neutron precursors, and the coefficients are the multiplication rates of prompt fission neutrons, delayed neutrons and source neutrons. In the conventional equation, the variables are weighted by the adjoint flux; in other words, they are adjusted to the critical state. The variables in the new equation correspond to actual values even in a deep subcritical state; hence, the physical meaning of each term is clear.

The dynamic behavior of a slab core with an external source was analyzed through calculations based on the new equation. Deterministic and probabilistic calculations of the equation were performed for a typical accelerator-driven system in the static state.     

Radial and Vertical Displacement Events of Plasma in the Damavand Tokamak

The plasma current in tokamak is under the influence of forces in such a way it tents toward the radial expansion. The forces resulting from external self-induced, internal inductance, thermal energy, and magnetic field fluctuations on the plasma column, cause radial expansion. To keep plasma in its position, the Lorentz force should be applied by vertical magnetic field to balance these forces. Control of the plasma position in the radial direction is very complicated. Poloidal beta, β_θ, and the internal inductance parameter depend on plasma current where plasma current parameters themselves are not steady in tokamak. The experimental data of Damavand tokamak is used to compare radial displacement with theoretical prediction. Temporal variation of plasma current along with time variation of R and Z positions of the plasma column is studied. The vertical displacement event takes place because of the elongated cross section of plasma column. Theoretical and experimental results show reasonable agreement.     

CANDU堆热工水力设计方法和计算机软件

ＣＡＮＤＵ堆热工水力设计采用目前一些典型的分析方法，并通过一些重要的实验研究计划对这些典型的分析方法进行强化支持。这些研究计划是为了发展和验证数学模型。主要针对ＣＡＤＵ堆特有的热工水力学。本文介绍了ＣＡＮＤＵ堆设计所用的计算机模型，以及为确认其     

On a simplified inelastic analysis of structures

In this paper two main problems are considered: the derivation of cyclic constitutive relations during inelastic regime where hardening, softening and creep can occur, and the development of the eventual periodical state in the structure during cyclic thermodynamical loadings.We give a very simple and practical framework to solve these problems in one unique manner.Its essential feature consists in the introduction of a family of internal parameters which characterize local inelastic mechanisms and the family of transformed internal parameters which are linearly linked to the previous ones through a symmetrical non-negative matrix and are indeed the opposite of the associated residual stresses. Thanks to that, the treatment of the local plastic or viscoplastic yield conditions can be easily made from only the classical simple purely elastic (or viscoelastic) analysis.This property allows important results during cyclic loadings: conditions for elastic shakedown, plastic shakedown, ratcheting and bounds for the limiting state.Several examples are given in the text.     

304不锈钢的非饱和循环硬化行为及其本构描述

针对循环硬化行为的应变幅值依赖性和相对大应变幅值下的非饱和特性．建立了新的粘塑性循环本构模型,在本构模型中．引入新的变量来表征材料的循环硬化特性,该变量的演变方程中引入一个临界状态来反映循环硬化对应变幅值的依赖性：同时,将该变量分解为2个具有不同演变规律的分量．以此来描述相对大应变幅值下的非饱和循环硬化特性．结果表明．新建模型能够很好地描述304不锈钢循环硬化行为的应变幅值依赖性和非饱和特性．     

Anisotropic creep damage in the framework of continuum damage mechanics

For some years various works have shown the possibility of applying continuum mechanics to model the evolution of the damage variable, initially introduced by Kachanov. Of interest here are the complex problems posed by the anisotropy which affects both the elastic behaviour and the viscoplastic one, and also the rupture phenomenon.The main concepts of the Continuum Damage Mechanics are briefly reviewed together with some classical ways to introduce anisotropy of damage in the particular case of proportional loadings. Based on previous works, two generalizations are presented and discussed, which use different kinds of tensors to describe the anisotropy of creep damage:

• - The first one, by Murakami and Ohno introduces a second-rank damage tensor and a net stress tensor through a net area definition. The effective stress-strain behaviour is then obtained by a fourth-rank tensor.

• - The second theory, by Chaboche, uses one effective stress tensor only, defined in terms of the macroscopic strain behaviour, through a fourth-order non-symmetrical damage tensor.

The two theories are compared at several levels: differences and similarities are pointed out for the damage evolution during tensile creep as well as for anisotropy effects. The possibilities are discussed and compared on the basis of some existing experimental results, especially for creep under tension-torsion, which leads to a partial validation of the two approaches.     

两类钒基合金的辐照硬化研究

钒合金(V-Cr-Ti系列)是重要的聚变堆结构候选材料,但是相比于铁素体/马氏体钢等其他候选材料,有关钒合金(V-Cr-Ti)的辐照损伤研究较为缺乏。利用载能离子束模拟聚变堆中子辐照条件,对V-4Cr-4Ti和V-5Cr-5Ti两种样品进行了载能He离子和重离子辐照实验。实验采用离子束梯度减能方法在样品中产生辐照损伤的坪区,利用纳米压痕技术测试材料的辐照硬化效应。结果表明,样品纳米硬度的深度递减现象可以用Nix-Gao模型很好描述,高能重离子辐照的样品中软基体效应可以有效避免;在He离子辐照情形,He浓度(以原子百万分率计(Atomic parts per million,APPM))/位移损伤(以每原子平均离位数计(Displacement per atom,DPA))大于4 200/0.2时,两种钒合金样品出现硬化饱和现象;相近位移损伤水平下,He与空位的结合导致缺陷集团的加速长大,致使材料的辐照硬化远大于重离子辐照情形。     

Shakedown and ratchetting under tension–torsion loadings: analysis and experiments

Structural design analyses are conducted with the aim of verifying the exclusion of ratchetting. To this end it is important to make a clear distinction between the shakedown range and the ratchetting range. The performed experiment comprised a hollow tension specimen which was subjected to alternating axial forces, superimposed with constant moments. First, a series of uniaxial tests has been carried out in order to calibrate a bounded kinematic hardening rule. The load parameters have been selected on the basis of previous shakedown analyses with the PERMAS code using a kinematic hardening material model. It is shown that this shakedown analysis gives reasonable agreement between the experimental and the numerical results. A linear and a nonlinear kinematic hardening model of two-surface plasticity are compared in material shakedown analysis.     

CUPIDON-code decrivant le comportement thermique et mecanique d'un crayon combustible de reacteur a eau sous pression au cours d'un accident de depressurisation

In the scope of the PHEBUS experimental program to be performed in Cadarache on the behaviour of PWR's fuel assemblies under loss of coolant accidental conditions, a computer code has been developed to help designing the experimental rods and to contribute to the definition of the test runs.This code, dubbed CUPIDON, deals only with the thermal and mechanical behaviour of the rods as well as the oxidation of the cladding outside surface; it does not include any thermohydraulic subroutine. Rather, it is coupled with the RELAP code for providing necessary input data such as coolant temperatures and pressures and cladding-to-coolant heat transfer coefficients. It is restricted to a single, non irradiated, rod of short length as representing the PHEBUS experimental conditions.It is a two dimensional code, using a finite difference resolving technique. It calculates the radial thermal profile across each section of the rod, the stress and creep rate to which the cladding is submitted and the rate of formation of the oxide layer on the surface of the cladding under steady state and transient conditions. As cladding plastic strain input data, it is using the EDGAR-ZY experimental results.     

Identification and modeling of nonlinear systems

A nonparametric identification technique is presented for use with discrete multidegree of freedom nonlinear dynamic systems of the type encountered in nuclear reactor technology. The method requires information regarding the system response and estimates of its pertinent “mode shapes” to determine, by means of regression techniques involving the use of two-dimensional orthogonal functions, an approximate expression for the system generalized restoring forces in terms of the corresponding generalized system state variables. For the special class of nonlinear systems that have chain-like characteristics, drastic simplifications in the procedure are realized, and the identification task can be easily and accurately accomplished without using any information regarding estimated “mode shapes”. The technique is applied to several example systems. The method can be used with deterministic or random excitation to identify dynamic systems with arbitrary nonlinearities, including those with hysteretic characteristics. It is also shown that the method is easy to implement and needs much less computer time and storage requirements compared to the Wiener-Kernel approach.     

Strain estimation for external event loads

It is common knowledge that structural design on the basis of stress limitation leads to an overestimation of the damage potential of low cycle dynamic loads (e.g. seismic events).Until now the high effort needed for step-by-step numerical evaluation of nonlinear dynamic structural response is a serious obstacle for a more realistic design based on strain limitation.The concept of energy dissipation and structural hardening as functions of strain range leads to the definition of a set of 1-DOF-substitute structures gained by a limited number of quasi-static non linear computations or by a certain knowledge of the yield behaviour of structural members. Step-by-step numerical computations are restricted to the substitutes and thus the effort for a strain limitation design is reduced to a bearable level.     

Deformation and microstructure of neutron irradiated stainless steels with different stacking fault energy

The influence of the stacking fault energy (SFE) on the microstructure, mechanical property and deformation behaviour of stainless steels before and after irradiation was investigated. The mechanical properties, such as strength, ductility, strain hardening and irradiation induced hardening behaviours of 3 alloys with various SFEs are quite different. Such significant variations of mechanical properties must result from the different microstructures, deformation mechanisms and defects accumulation behaviours. Thus, the microstructures, deformation mechanisms and irradiation induced small defect clusters (including their types, natures, densities and size distributions) of 3 alloys are determined in detail by transmission electron microscopy. It indicated that before irradiation, alloy with low SFE has more localised deformation behaviour than alloy with high SFE. After irradiation, in the samples with low SFE, the irradiation induced stacking fault tetrahedral was observed, while in the ones with high SFE, the dominant defects are Frank loops. All the results shown that, SFE has a strong effect on both the deformation mechanism and irradiation induced defect accumulation behaviour of stainless steels.     

In situ dynamic tests and seismic records on the RHR system building enel IV nuclear plant/caorso (Italy)

The tests on the RHR Building of the Caorso Nuclear Plant are part of a program of dynamic tests on large structures sponsored by ENEL, which ISMES is presently carrying out.The main purposes of this program are:

• - to collect information on the effectiveness of different excitation methods;

• - to set up the most suitable recording and processing technique;

• - to compare the experimental results with the computed ones, in view of the validation of the adopted computing schemes.

The structure has been excited by a mechanical vibrator delivering sinusoidal forces in a frequency range 2 to 20 cps, in conditions of empty, , and completely full pools. The response, recorded by 36 velocity transducers was digitally processed by means of a Fourier Analyzer. Moreover, a number of Friuli earthquake aftershocks could be picked up, and the building response recorded in many points.More than ten natural frequencies could be detected, and the related damping and mode shapes determined, in a frequency range from 3 to 16 cps.The structure frequencies determined by tests are lower than the computed ones.The energy content of the seismic excitation, due to the large distance from the epicentral area, is confined within very low frequencies. Some data on the behaviour of the RHR and Reactor buildings could however be obtained.The testing technique adopted, which does not require long testing time and high costs, supplies a large amount of reliable data in case of excitation within the linear range. To account for non-linearities, different testing methods should be used, such as blasting or strong forced vibrations of the foundation. Moreover, the adopted method can fully describe the higher vibration modes, which are of noticeable importance as to the behaviour of mechanical and electric equipment installed in the structure.     

矩形小尺度加热通道流型构成及过渡准则研究

基于可视化实验系统研究了矩形小尺度加热通道内主要流型构成，从微观角度深入研究气-液两相在流型过渡临界状态下的受力情况，构建了基于力学模型假定的流型过渡准则，并采用可视化实验数据对该模型进行了验证。结果表明，泡沫流-受限气泡流过渡准则预测准确度为93.94%，受限气泡流-环状流过渡准则预测准确度为94.07%，模型预测结果与实验数据基本吻合。