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Tsukimori, Kazuyuki; Ando, Masanori; Yada, Hiroki; Ichimiya, Masakazu*; Anoda, Yoshinari*; Arakawa, Manabu*
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08
The analytical treatment of Multi-ply bellows behaviours is difficult compared with that of single-ply bellows, since the uncertainty of friction between plies exists. In this study verification was conducted based on experiments by comparing between two-ply and single-ply bellows test results. Following results were obtained. The spring rate of two-ply bellows is approximately twice of that of single-ply bellows, even if internal pressure is loaded. Typical buckling behaviour of bellows, in-plane squirm, was observed in both cases of two-ply and single-ply bellows. The deformation patterns were similar with each other, but the pressure levels of two-ply bellows were approximately twice of those of single-ply bellows. These means the friction force can be ignored practically. As the conclusion, two-ply bellows analyses can be replaced by the analyses of single-ply bellows model with half pressure load and the effort of numerical analysis can be reduced.
Katsuyama, Jinya; Yamaguchi, Yoshihito; Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Osaka, Masahiko
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 11 Pages, 2017/08
It is difficult to assess rupture behavior of the lower head of reactor pressure vessel in boiling-water-type nuclear power plants due to severe accident like Fukushima Daiichi because Boiling Water Reactor (BWR) lower heads have geometrically complicated structure with a lot of penetrations. Therefore, we have been developing an analysis method to predict time and location of RPV lower head rupture of BWRs considering creep damage mechanisms based on coupled analysis of three-dimensional Thermal-Hydraulics (TH) and thermal-elastic-plastic-creep analyses. In this study, we performed creep damage evaluations to investigate the effects of the debris depth and heat generation locations on failure behavior of lower head. From the analysis results, we discussed the outflow paths of the relocated molten core to the containment, and it was concluded that failure regions of BWR lower head are only the control rod guide tubes or stub tubes under simulated conditions.
Nishida, Akemi; Ota, Yoshimi*; Tsubota, Haruji; Li, Y.
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08
Many empirical formulas have been proposed for evaluating local damage to reinforced concrete structures caused by impacts of rigid missiles. Most of these formulas have been derived based on tests involving impact perpendicular to target structures. Thus far, few tests with oblique impact onto target structures have been carried out. In this study, we aim to propose a new formula for evaluating the local damage caused by oblique impact based on previous experimental and simulation results. We performed simulation analyses for evaluating the local damage to reinforced concrete panels subjected to oblique impacts by soft missiles under various impact velocities by using a simulation method that was validated using the results of previous impact experiments. Based on the results of these simulation analyses, quantitative evaluation of the reduction in local damage and the differences in energy transfer process due to the difference in impact angle and impact velocity are investigated.
Igarashi, Sayaka*; Sakamoto, Shigehiro*; Ugata, Takeshi*; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08
For the purpose of improving the precision of probabilistic seismic PRA for NPPs, the authors developed the methodology for generating hazard-consistent ground motions based on stochastic fault models which include seismic-source uncertainties by Monte Carlo Simulation. The PRA with HCGMs would require a lot of computer power. The optimization of ground-motions generations is one of the most important subjects for practical application of the PRA method. For optimizing the ground-motions generations, seismic sources for the generations should be selected effectively, and this can be conducted by utilizing optimal seismic index in the hazard analysis. In this study, the method for detecting the optimal seismic intensity index which corresponds with damage probabilities of the target equipment system was developed, and the validity of the proposed method was confirmed for some equipment systems, which has different weak equipment with each other.
Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Takada, Tsuyoshi*
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 9 Pages, 2017/08
In this research, the seismic safety of nuclear power plants (NPP) is treated as a system in which the various cliff edge effects are identified and quantified based on the concepts of risk and defense in depth. A methodology is then developed for avoiding these cliff edge effects. The first step was to carry out a preliminary elastic-plastic analysis of the NPP building system. From the analysis, some knowledge was obtained for the modeling factor dependence of cliff edge effects. Next, a preliminary fragility evaluation of the reactor vessel and piping was carried out; it was found that introducing a horizontal seismic isolation system was very effective for avoiding the cliff edge.
Choi, B.; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*
Transactions of the 24th International Conference on Structural Mechanics in Reactor Technology (SMiRT-24) (USB Flash Drive), 10 Pages, 2017/08
In order to clarify the influence of the modeling method on the result of seismic response analysis of nuclear facility, seismic response analysis using various simulated input ground motions was carried out and the uncertainty of response results were statistically analyzed. In particular, we focused on the difference of the response due to the structural modeling method (a conventional sway-rocking model and 3D FE model), and the relations among the input level, floor position, and response results were described and discussed.