共查询到20条相似文献,搜索用时 12 毫秒
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《同步辐射装置用户科技论文集》1999,(1):30-33
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. 相似文献
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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. 相似文献
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《Fusion Engineering and Design》2014,89(7-8):1227-1231
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. 相似文献
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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. 相似文献
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Kim Wallin Matti Valo Rauno Rintamaa Kari Trrnen Ralf Ahlstrand 《Nuclear Engineering and Design》1995,159(1)
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. 相似文献
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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. 相似文献
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Chijie ZHUANG 《等离子体科学和技术》2019,21(5):51001-4
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. 相似文献
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E. Roos M. Seidenfuss D. Kra mer S. Krolop U. Eisele U. Hindenlang 《Nuclear Engineering and Design》1991,130(3):297-308
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. 相似文献
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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 ... 相似文献
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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. 相似文献