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Hazama, Osamu; Araya, Fumimasa
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.1, p.685 - 686, 2007/09
A new concept of double-wall-tube steam generator (SG) is being introduced and investigated as an innovative technology to realize next-generation sodium-cooled Fast Breeder Reactors (FBRs) for commercialization. This new concept is posing great challenges in the engineering design of a tubesheet which must bundle over 7000 double-wall tubes under severe mechanical and thermal loads. R&D efforts concerning the development of a feasible design and establishment of design-by-analysis methods for the new-concept tubesheet structure have been begun at JAEA. As a first step, an attempt at identifying the high stress locations and their magnitudes through large-scale numerical simulations using geometrical models in accord with reality are reported.
Kasahara, Naoto; Takasho, Hideki*; Ando, Masanori
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.1, p.683 - 684, 2007/09
Tubesheet structures utilized in heat exchangers have complex perforated portions. For design analysis of these structures, axi-symmetric models with equivalent materials of perforated plate are conventionally adopted to simplify perforated portions. Double wall steam generators expected for commercial FBRs require new type of tubesheets, where conventional design methods are not applicable. Therefore, JAEA started research programs to develop a design by analysis method of these structures. This paper reports on the mechanism of thermal stress developments in new tubesheets with an associated paper.
Bubphachopt, B.*; Watanabe, Osamu*; Kawasaki, Nobuchika; Kasahara, Naoto
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.1, p.689 - 690, 2007/09
This study reports the real-time observation results on fatigue phenomena of the perforated plate and the half circular- hole notched plate made of SUS 304 stainless steel at elevated temperature. The crack initiates on the surface from the hole-side in the thickness direction and the crack initiates from the mid-surface along the thickness direction. After the crack initiation, it propagates and coalesces to fail finally. The number of micro or mini crack is summarized as a function of applied cyclic number.
Yoshida, Hiroyuki; Takase, Kazuyuki; Akimoto, Hajime
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.3, p.147 - 148, 2007/09
no abstracts in English
Zhang, W.; Yoshida, Hiroyuki; Ose, Yasuo*; Onuki, Akira; Akimoto, Hajime
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.3, p.145 - 146, 2007/09
In relation to the thermal-hydraulic design of FLWR, this study presents a statistical evaluation of numerical simulation results obtained by a detailed two-phase flow simulation code (named TPFIT). In order to clarify mechanisms of cross flow in such tight lattice rod bundles, the TPFIT was used to simulate water-steam two-phase flow in two modeled subchannels. Attention was focused on instantaneous fluctuation characteristics of cross flow. With the calculation of correlation coefficients between the differential pressure and gas/liquid mixing coefficients, the time scales of cross flow were evaluated, and the effects of mixing section length, flow pattern and gap spacing on correlation coefficients were investigated. The difference in mechanism between gas and liquid cross flows was pointed out.
Wakai, Takashi; Takahashi, Yukio*
Nihon Kikai Gakkai 2007-Nendo Nenji Taikai Koen Rombunshu, Vol.1, p.401 - 402, 2006/09
This paper describes metallurgical observation and analysis results for the aged welds made of Gr.91 and Gr.122 steels. Much more coarse carbides were observed by SEM in the fine grain heat affected zone of the welds than in the base metal and coarse carbides increased with aging. However, extracted residue analyses showed that the total amount of precipitations did not depend on regions and did not increase with aging. Therefore, the carbides which had precipitated in the early stage of aging cohered and grew mainly on the prior austenite grain boundaries, as far as the welds were subjected to stress free isothermal aging for 6,000 hours.
Yamano, Hidemasa; Muramatsu, Toshiharu; Fujii, Tadashi*
no journal, ,
A conceptual design study of a large-scale sodium-cooled fast reactor adopts a two-loop primary cooling system with large-diameter piping in order to reduce plant construction cost. In this design, one of issues is a flow-induced vibration behavior of the piping under a high Reynolds number (10
order level) condition. To investigate its basic characteristic, a 1/3-scale flow-induced vibration test simulating a hot leg piping has been carried out with water. In this study, a numerical steady-state analysis has reproduced flow characteristics, such as velocity profile in a flow separation region, of the 1/3-scale test by specifying appropriate analytical models and conditions with STAR-CD. With the validated models, the effect of the coolant viscosity and scale has been investigated as well as flow characteristics under the reactor condition involving disturbance at the inlet boundary of hot leg piping.
Watanabe, Tadashi
no journal, ,
A levitated liquid droplet is used to measure material properties of high temperature molten metals, since the effect of container wall is eliminated. Viscosity and surface tension are, respectively, obtained from the damping and the frequency of drop-shape oscillations. Three-dimensional numerical simulations of oscillations and rotations of a liquid droplet are performed in this report using the level set method, and the effects of amplitude and rotation on oscillation frequencies are studied. The oscillation frequency is shown to decrease as the initial amplitude increases, while it increases as the rotation frequency increases. It is found that the nonlinearity effect becomes notable and the effects of viscosity and surface tension appear as the amplitude or the rotation frequency exceeds 0.2.
Tsuru, Tomohito; Shibutani, Yoji*
no journal, ,
Abrupt growth of displacement observed in the relationship between indent load and indent depth in nanoindentation of crystalline materials, so-called displacement burst, has been recognized as one of the representative examples for the nanoplastic behavior. This behavior corresponds to the early stage of the plastic deformation and has greatly been influenced by the collective dislocation emission. In the present paper, we construct two models; first one is the computational model of dislocation mechanics, and second one is simplified energetic model of the first displacement burst. As the result of these models, it is found that surface step corresponding to each dislocation causes significant displacement burst and that more than one hundred high-density dislocations are emitted simultaneously.
Takeda, Tetsuaki; Tochio, Daisuke; Inaba, Yoshitomo; Ichimiya, Koichi*; Nishio, Hitoshi*
no journal, ,
Safety demonstration tests using the HTTR (High Temperature Engineering Test Reactor) are being performed to verify the inherent safety features and to validate the numerical code for the safety assessment of the VHTR (Very High Temperature Reactor). The test of loss of coolant flow as one of safety demonstration tests is carried out by tripping of the helium gas circulators. The objective of this study is to evaluate the temperature distribution of the reactor pressure vessel (RPV) and the vessel cooling system (VCS) during the loss of coolant flow. The temperature distribution of the RPV and surrounding concrete structure were obtained using a commercially available analysis code STAR-CD. The effect of thermal radiation from the RPV was evaluated using the analytical and experimental results. It was found that it is important to take account of the effect of thermal radiation in the transient analysis to evaluate the temperature change of the concrete accurately.
Uchibori, Akihiro; Ohshima, Hiroyuki; Takata, Takashi*; Yamaguchi, Akira*
no journal, ,
A numerical method for the compressible multi-phase multi-component flows with sodium-water reaction was developed. When the pressurized water leaks from a failed heat transfer tube in the steam generator of sodium cooled fast breeder reactors, the water reacts with the sodium outside the tubes. In order to simulate the multi-phase multi-component flows, the multi-fluid model and the advection-diffusion equations are used in our numerical method. Production rates of the components such as the sodium hydroxide and the hydrogen in sodium-water reaction are calculated by using a surface reaction model and a gas phase reaction model. Through the numerical analysis of a sodium-water reaction test SWAT-1R, prediction capability for the temperature field was verified. Sensitivity analysis to investigate the effect of model parameters was also performed.