Results 1 - 10 of 105
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[en] Vibration of simulated CANDU fuel bundles induced by the coolant flow is investigated in this thesis through experiments and numerical simulations. Two simulated bundles and a hydraulic loop are built to mimic the situation of the fuel bundles located at the inlet of a fuel channel in a CANDU nuclear reactor. Fuel bundle vibration mechanism is investigated through experiments and numerical simulations. The three-dimensional turbulent flow that passes through the simulated bundles is modeled using the large eddy simulation (LES) and solved with parallel processing. The local cross flows induced by the presence of endplates at the inlet location and bundle interface location are investigated. The fluid forces are obtained as excitations for the fuel bundle vibration analysis. A finite element model of the fuel bundles is developed with the endplates modeled using the 3rd order thick plate theory. The response of the inlet fuel bundle to the fluid excitations is solved in the time and the frequency domain. The added mass and the fluid damping are approximated with the theory on the flow-induced vibration of slender bodies in a parallel flow. Measurements are obtained and used to validate the numerical prediction under various operating flow conditions. (author)
[en] Highlights: • 2D convection flow develops with internal heating and strong axial magnetic field. • Poloidal magnetic field suppresses turbulence at high Hartmann number. • Flow structure is dominated by large-scale counter-rotation vortices. • Effective heat transfer is maintained by surviving convection structures. - Abstract: We explore the effect of poloidal magnetic field on the thermal convection flow in a toroidal duct of a generic liquid metal blanket. Non-uniform strong heating (the Grashof number up to 10"1"1) arising from the interaction of high-speed neutrons with the liquid breeder, and strong magnetic field (the Hartmann number up to 10"4) corresponding to the realistic reactor conditions are considered. The study continues our earlier work , where the problem was solved for a purely toroidal magnetic field and the convection was found to result in two-dimensional turbulence and strong mixing within the duct. Here, we find that the poloidal component of the magnetic field suppresses turbulence, reduces the flow's kinetic energy and high-amplitude temperature fluctuations, and, at high values of Hartmann number, leads to a steady-state flow. At the same time, the intense mixing by the surviving convection structures remains able to maintain effective heat transfer between the liquid metal and the walls.
[en] Highlights: • 2D convection flow develops with internal heating and strong axial magnetic field. • The flow is strongly modified by the buoyancy force associated with growing T_m. • Thermal convection is suppressed at high Gr. • High temperature difference between top and bottom walls is expected at high Gr. - Abstract: The work continues the exploration of the effect of thermal convection on flows in toroidal ducts of a liquid metal blanket. This time we consider the effect of the mean flow along the duct and of the associated heat transfer diverting the heat deposited by captured neutrons. Numerical simulations are conducted for a model system with two-dimensional (streamwise-uniform) fully developed flow, purely toroidal magnetic field, and perfectly electrically and thermally insulating walls. Realistically high Grashof (up to 10"1"1) and Reynolds (up to 10"6) numbers are used. It is found that the flow develops thermal convection in the transverse plane at moderate Grashof numbers. At large Grashof numbers, the flow is dominated by the top-bottom asymmetry of the streamwise velocity and stable stratification of temperature, which are caused by the buoyancy force due to the mean temperature growing along the duct. This leads to suppression of thermal convection, weak mixing, and substantial gradients of wall temperature. Further analysis based on more realistic models is suggested.
[en] The kinetics of precipitation was investigated in the ternary Cu alloy, Cu_8_3_._5Ag_1_5W_1_._5 during irradiation with MeV Kr ions at elevated temperatures. The alloy was prepared as a solid solution by physical vapor deposition and then irradiated at room temperature to create a high density of nano-sized W precipitates. These precipitates served as effective sinks for point defects during subsequent elevated-temperature irradiation, suppressing radiation-enhanced diffusion. As a consequence the size of the Ag precipitates formed during elevated-temperature irradiation was stabilized below 20 nm, up to temperatures in excess of 300 °C, thus significantly extending the regime for “compositional patterning” above 175 °C, found for Cu_8_5Ag_1_5. For higher temperature irradiations (above 400 °C), the role of the W precipitates in stabilizing the size of the Ag precipitates switched from simply acting as point-defect sinks to serving as pinning sites for the Ag precipitates. At 500 °C, the average Ag precipitate diameter is ∼30 nm compared to ∼300 nm in the Cu_8_5Ag_1_5 binary alloy. Rate theory calculations and kinetic Monte Carlo simulations are employed to illustrate how this transition takes place
[en] This paper researches the sprout inhibition effect by irradiation on refrigerated garlic. The results shows that, the garlic is still in the period of dormancy within 7 days after taken out from the refrigerated warehouse, and irradiation have a good sprout inhibition effect on it. The irradiation dose is 40-90 Gy, the same as that of the post harvest irradiation treatment on garlic. Refrigerate the Zhongmu Garlic (at -2 degree C-0 degree C) until the middle ten days of February the next year, place it at the room temperature (10 degree C-15 degree C) for 1-7 days after taking it out of the warehouse, then use 60Co γ-ray to irradiate it until the absorbed dose reaches 40-90 Gy, the sprout inhibition effect can be realized. The test also indicates that the deposited time after taking out of the refrigerated warehouse is crucial to the sprout inhibition effect of refrigerated garlic by irradiation. (authors)
[en] This paper presents a precise approach for pose recovery of the distal locking holes using single calibrated fluoroscopic images. The problem is formulated as a model-based optimal fitting process, where the control variables are decomposed into two sets: (a) the angle between the nail axis and its projection on the imaging plane, and (b) the translation and rotation of the geometrical model of the distal locking hole around the nail axis. By using an iterative algorithm to find the optimal values of the latter set of variables from any given value of the former variable, we reduce the multiple-dimensional model-based optimal fitting problem to a one-dimensional search along a finite interval. We report the results of our laboratory as well as in-vitro experiments, which demonstrate that the accuracy of our approach is adequate for successful distal locking of intramedullary nails. (orig.)
[en] Scatter is an important problem in high-energy flash X-ray radiography. The X-ray transport of flash radiograph about FTO (French test object) was simulated by means of Monte-Carlo method to investigate the influences and the main source of side scatter. The results show that without side cone, the front cone is the main source of side scatter in the system. For any pixel, the scattered exposure from the front cone is more than 50% of the total exposure. And the side scatter has a monotony distribution in the axis direction. With side cone t he side scattered exposure is decreased, and the distribution becomes complicated with single-peak in the direction perpendicular to the axis. In addition, the increment of the distance between the recording plane and the center of the target may not lead to the reduction of the side scattered exposure. There exists an optimum distance where the side scatter is relatively uniform. (authors)
[en] A new method is proposed to simulate the scattered photons in high energy X-ray radiography fast and precisely. The problem of X-ray radiography is turned into an effective pure photon transport problem, and an iterative solution to the photon transport equation is designed. Then, the solution is turned into a discrete version and realized in a computer program. After, the Monte Carlo N-particle transport code MCNP is used to 'measure' the effective photon scattering function and other parameters needed in the discrete method. Finally, the new computer program is compared with MCNP in a radiography example as a check of the method. It is consistent with MCNP for the radiography of thin objects, but shows large deviation for thick ones. The current computer program can be used in qualitative analysis. (authors)
[en] In order to decrease the fluctuation of electron's record at imaging plane in MCNP's simulation of X-ray radiography, a new method was tried for creating virtual X-ray source with pointing probability method. The virtual X-ray source may generate the next main electrons which has contribution to the detector. This method can not only increase the possibility of the electron, but also make a history contribute pixels as much as possible. The comparison of the results whether using the proposed method or not was carried out. The results show that the using of the method could decrease the fluctuation of the electron's contribution effectively, improve the precision of the result, and develop the simulation capability of MCNP for X-ray radiography. (authors)