EXAFS study of structural characteristics of nanocrystalline selenium with different grain sizes

Extended x-ray-absorption fine-structure measurements(EXAFS) were performed on nanocrystalline (nc) elemental Se samples with grain sizes ranging from 13 to 60 nm.Accompanied with the previous study,we concluded that,with the refinement in nc.Se.the intrachain structure (the bond length,the coordination number)is unchanged while the interchain spacing is enlarged.The grain boundary in the nc Se is found to be in a low-energy configuration that is different from the disordered gaslike grain boundary structure.     

Particle identification using CsI(Tl) crystal with three different methods

Three pulse-shape-discrimination (PSD) methods are applied to study the particle identification (PID) by using CsI(Tl) crystal, especially for identifying light charged particles. The zero-cross time method, fast and total component method and signal rise time method are used. The experiment, data analysis and results are compared. Good PID for p, α and γ can be achieved with a CsI(Tl)-photomultiplier assembly.     

电子束和热退火后处理的射频溅射沉积ZrO_2－Y_2O_3薄膜的结构特征

对射频磁控溅射沉积的ＺｒＯ２－１２ｗｔ％Ｙ２Ｏ３薄膜进行了电子束处理和热退火处理．通过ＸＲＤ、ＸＰＳ、ＳＥＭ等的微观分析，研究了薄膜的相结构组成、薄膜主要组成元素的氧化态以及薄膜的形貌特征。并对以提高薄膜增韧性为目的而进行的后处理的方式选择作了讨论。     

Numerical study of the MHD flow characteristics in a three-surface-multi-layered channel with different inlet conditions

A 3D MHD flow simulation was conducted to clarify the effects of the inlet flow conditions on the results of the validation experiment carried out previously and on the design window of the first wall using a three-surface-multi-layered channel. MHD pressure drop was largely influenced by the inlet condition. The numerical model with turbulent velocity profile showed qualitatively good agreement with the experimental result. The first wall temperature and pressure distributions obtained by the 3D simulation corresponded well to those obtained by the 2D simulation assuming fully developed flow. This suggested that complicated three-dimensional inlet flow condition generated in the L-shape elbow would not affects the existing design window.     

Thermal stresses at nozzles of nuclear steel containments under LOCA-conditions

During a loss of coolant accident (LOCA) of a PWR-nuclear power plant, a considerable heating of the containment atmosphere is expected to occur. Transient thermal stresses will appear at the containment as a consequence of a non-uniform rise of its temperature.Applying computer codes based on the finite element method, dimensionless general thermal stresses at nozzles of spherical steel containment have been calculated, varying the principal geometrical parameters and the Biot number for the containment internal surface.Atmosphere temperature and Biot number are assumed constant after the accident. Several plots of the maximum principal stresses are provided, which constitute general results applicable to stress analysis of any particular containment of this kind.     

板型元件表面结垢对堆芯最热通道流量分配影响的数值计算

运用计算流体力学程序(CFX)对板型燃料元件表面结垢对堆芯最热通道流量分配的影响进行了数值计算分析,计算结果表明．最热通道由于两边燃料板结垢,在通道间隙宽度降低10％的情况下．最热通道的流量分配系数与未结垢时相比降低18．2％。     

Descriptive characteristics of different types of test for irradiation embrittlement

Within the IAEA coordinated programme on optimizing of reactor pressure vessel surveillance programmes and their analysis, phase 3, a specially tailored radiation sensitive correlation monitor material, a Japanese steel plate with code designation JRQ, a French forging material (FFA) and a Japanese forging material (JFL) were selected for the investigations to be carried out in Finland.Based on the evaluation of the experimental results it was demonstrated that dynamic fracture toughness transition shift is equivalent to the Charpy-V shift, but the static fracture toughness transition shift may be considerably larger than the dyanamic shift. Thus, Charpy-V is not suitable for estimating the static fracture toughness transition shift.These findings have a strong impact upon the design of future surveillance programmes.     

The flow characteristics of fluid in micro-channels of different shapes

In this paper, we study hydrodynamics and thermal behaviors of micro-heat exchanger of different cross sections, with hydraulic diameters （Dh） of 0.4-0.8 mm and Reynolds numbers （Re） of 300-900. Validity of the model is proved by comparing simulation results based on classical Navier-Stokes equations with experimental data and Tuckerman correlation. Effects of dynamic viscosity, hydraulic diameter, Reynolds number and cross section of the micro-channels are investigated. The results indicate that the variable viscosity effect should be taken into account, and rod bundle micro-channels have the highest heat transfer coefficient of the three types of micro-channels.     

Discharge characteristics of different lightning air terminals under composite voltages

Different types of lightning air terminals have been designed over the years. Concern regarding the effect of different types of air terminals, especially the early streamer emission (ESE)-type, remains controversial. This paper describes the discharge characteristics of different types of air terminals, two of which are quite similar to the ESE-type dynasphere, and concludes that the tested non-standard air terminals have discharge characteristics similar to those of Franklin rods and that their lightning protection performance should be similar.     

不同通道内超临界水流动换热特性

以具有不同当量直径的矩形、圆形、三角形、环形等管道为研究对象,利用ANSYS CFX分别计算在定质量流量和定流体速度条件下,超临界水在不同通道内的流动换热特性。发现在定质量流量条件下,圆形通道换热特性最优,且小当量直径促进流体换热;在定入口流速条件下,环形通道换热特性最优,小当量直径管道促进亚临界流体换热,大当量直径管道促进超临界流体换热。     

Application and evaluation of different numerical methods for determining crack resistance curves

The engineering assessment of precracked components is frequently carried out with the help of crack resistance curves on the basis of the J-integral. Nevertheless, there are severe uncertainties regarding the validity of the J-integral in the case of large plastic deformations and unloading processes due to crack growth. Numerical and theoretical derivations are used to examine the influence of large plastic deformations and stable crack growth on the calculation of the J-integral. Numerical investigations were carried out on the example of a CT 25-specimen made of 20 MnMoNi 5 5 by means of the finite-element method. The following methods of calculations were selected:

• - Calculation of the specimen behaviour without consideration of the stable crack growth.

• - Calculation of the specimen behaviour using a J-Δa-curve as crack crack growth law.

• - Calculation of the specimen behaviour using a damage model (“ocal approach”) to compute the crack growth.

The results of the calculation carried out on the basis of the damage model makes it possible to carry out an assessment of the various methods for the experimental determination of the J-value.     

Evaluation of different Krylov subspace methods for simulation of the water faucet problem

In this study, a one-dimensional two-phase flow four-equation model was developed to simulate the water faucet problem. The performance of six different Krylov ...     

Formation and growth of cracking in feed water pipes and RPV nozzles

The observation of numerous small and large cracks in ferritic feed water pipes of boiling (BWR) and pressurized water reactors (PWR) in the last few years has led to basic research into the causes of cracking and the crack growth mechanisms.In horizontal feed water pipe sections connected to nozzles of reactor pressure vessels (RPV) of BWR's as well as of steam generators (SG) of PWR's, circumferential macro and micro cracks were detected. These cracking phenomena could be observed in base material of pipes as well as in weld seam regions. The examination of the stress state displayed that the cracked pipe regions have been exposed to a number of cyclic thermal transients (thermal shock, flow stratification) during start-up (hot stand-by) and shut-down periods of the plants. During thermal transient periods, local and global cyclic stresses in the referred pipe cross sections have been induced which in interaction with the influence from environment (in operation as well as in shut-down periods) and local geometrical imperfections led to the initiation and formation of macro and micro cracks.In the reactor water clean-up system of BWR through which reactor water is fed from the RPV to the main feed water line, two longitudinally welded elbows have been detected to be severely cracked. Both elbows have been subjected to an internal pressure corresponding to RPV and additionally to a relevant “in-plane” bending moment. These longitudinal cracks were found to be started from the inner elbow surface. In one case the longitudinal crack was situated in the base material and was enlarged to leakage. In the second elbow the longitudinal crack was located in the heat affected zone (HAZ) of a longitudinal weld. In both cases the macro cracks started either from corrosion pits located in defective areas of the magnetic protection layer or from geometrical notches (weld root). The semi-elliptic small cracks got linked to more extended shallow cracks.Formation and growth mechanism of these cracks have been studied at the MPA Stuttgart in laboratory under simulated operation conditions which were held as realistic as possible compared with those in nuclear power plants.The results of experimental studies in laboratory as well as conclusions based on the above mentioned cracking phenomena in piping have been used as basic information for a realistic design of large scale (RPV) thermal shock experiments under operation conditions. The formation and growth mechanism of these cracks and their detection by means of NDE during thermal transients at the inner surface of RPV nozzle and at the adjacent cylindrical areas of RPV shell will be described.