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Kawasaki, Nobuchika; Watakabe, Tomoyoshi; Wakai, Takashi; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*
Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 8 Pages, 2016/07
Sodium-cooled Fast Reactors (SFRs) have components with thinner walls as compared with light water reactors, although Japan is an earthquake-prone country. Thus, seismic isolation systems have been conventionally employed in SFR system design to reduce seismic forces on the systems in Japan. Implementation of seismic design in the reactor core and buckling design in the reactor vessel requires 8 Hz (or less) vertical frequency's isolation system being applied. This paper introduces three isolation concepts to achieve the frequency. The isolation systems, which enable vertical 8 Hz natural frequency, comprise thicker laminated rubber bearings (TRBs). By combining coned disk springs with TRBs, vertical natural frequency is in a range from roughly 3 Hz to 5 Hz. Combining pneumatic springs to RBs and adding the rocking suppression system, vertical natural frequency becomes under 1 Hz. All isolation systems need horizontal damping like oil dampers. A vertical 8 Hz isolation system with TRBs and oil dampers is under development in Japan as a principal isolation concept. The reasons of choosing this system are its simplicity and the number of developing issues. Since TRBs and oil dampers are basic isolation elements, they can be applied to other isolation systems. The response acceleration of 5 Hz vertical isolation is 50% of that of 8 Hz based on the analytical survey. A series of static tests of coned disk springs was carried out to confirm design equations. Based on these knowledge, 5 Hz vertical isolation system with TRBs and the coned disk springs can be designed. The response acceleration of 1 Hz vertical isolation is 10% of that of 8 Hz. A rocking suppression system was studied in the past, and the further simplification of this system is the largest challenge for this concept. These three isolation concepts are isolation candidates for SFRs in Japan. To obtain enough seismic margins for each plant site, these isolation systems need to be developed.
Ebihara, Kenichi; Iwamoto, Takashi*; Matsubara, Yukio*; Yamada, Hiroki*; Okamura, Tsukasa*; Urushihara, Wataru*; Omura, Tomohiko*
ISIJ International, 54(1), p.153 - 159, 2014/01
Times Cited Count：13 Percentile：53.08(Metallurgy & Metallurgical Engineering)For understanding the mechanism of hydrogen embrittlement that is one cause of stress corrosion cracking, it is necessary to identify the location of hydrogen segregation (hydrogen existing state) in steels. The thermal desorption spectrum of hydrogen that is obtained by measuring hydrogen desorbing from specimens heated at a constant rate is a useful data for identifying the hydrogen existing state. In the paper, using the numerical simulation, we examined the difference of the thermal desorption spectra between two specimens of pre-strained high-strength steel, one was charged with hydrogen by the method used widely in laboratories, the other was by the method simulating hydrogen penetration in real environment. As a result, it was found that the difference results from the difference of the initial hydrogen distribution caused by the amount of charged hydrogen. If the amount of charged hydrogen is small, the thermal desorption spectrum is more sensitive to the initial distribution.
Ebihara, Kenichi; Iwamoto, Takashi*; Miwa, Noriaki*; Yamada, Hiroki*; Okamura, Tsukasa*; Urushihara, Wataru*; Omura, Tomohiko*
"Suiso Zeika Kenkyu No Kiban Kochiku" Kenkyukai Hokokusho, p.21 - 26, 2013/10
In order to explore the properly hydrogen-charging method for the estimation of hydrogen embrittlement of steels, in the workshop of Fundamental construction for hydrogen embrittlement supported by the Iron and Steel Institute of Japan of which I took part for understanding the mechanism of hydrogen embrittlement which is one cause of stress corrosion cracking, the thermal desorption spectrum of hydrogen and the amount of charged hydrogen were estimated among various kinds of steels charged with hydrogen by various methods. The presentation is a part of a series of the final report about the results obtained in the workshop. In the presentation, I talk about the numerical estimation of the desorption spectrum of low alloy steel mainly on the basis of the paper which is going to be published in the ISIJ International. Particularly, the kind of defects in the steel that capture hydrogen forming the spectrum and the experimental method for identifying the defects are explained in details.
Ishihara, Ryo*; Fujiwara, Kunio*; Harayama, Takato*; Okamura, Yusuke*; Uchiyama, Shoichiro*; Sugiyama, Mai*; Someya, Takaaki*; Amakai, Wataru*; Umino, Satoshi*; Ono, Tsubasa*; et al.
Journal of Nuclear Science and Technology, 48(10), p.1281 - 1284, 2011/10
Times Cited Count：44 Percentile：94.62(Nuclear Science & Technology)Okamura, Hiroki*; Tsuchida, Takashi*; Okada, Masao*; Yamagata, Ryohei; Seito, Hajime; Haruyama, Yasuyuki; Kaneko, Hirohisa
2011 Nen (Dai-29-Kai) Denki Setsubi Gakkai Zenkoku Taikai Koen Rombunshu, p.367 - 368, 2011/09
no abstracts in English
Isobe, Mitsutaka*; Toi, Kazuo*; Matsushita, Hiroyuki*; Goto, Kazuyuki*; Suzuki, Chihiro*; Nagaoka, Kenichi*; Nakajima, Noriyoshi*; Yamamoto, Satoshi*; Murakami, Sadayoshi*; Shimizu, Akihiro*; et al.
Nuclear Fusion, 46(10), p.S918 - S925, 2006/10
Times Cited Count：30 Percentile：69.31(Physics, Fluids & Plasmas)no abstracts in English
Tatekawa, Takayuki; Sakagami, Masaaki*; Taruya, Atsushi*; Okamura, Takashi*; Ruffo, S.*
no journal, ,
It is important to know equilibrium state of systems for analyses of relaxation process. In statistical physics, the equilibrium state corresponds to maximum entropy state. Although methods to derive the distribution function of the maximum entropy state have been studied for a long time, there was a problem with the convergence of the solution. We have developed new method which is considered the convergence of the solution. The function of the equilibrium state is derived by the maximum state of Boltzmann-Gibbs entropy. Recently several entropy models which are expected to describe the relaxation process have been proposed. Because our method can be applied to various models easily, we can inspect the validity of these models. In this study, we analyze 2-D HMF model which is known as simple long-range interacting system. By the comparison between N-body simulations and the function from various models, we have inspected the models to describe the relaxation process of the systems.
Tatekawa, Takayuki; Sakagami, Masaaki*; Taruya, Atsushi*; Okamura, Takashi*; Ruffo, S.*
no journal, ,
We will discuss relaxation processes toward thermal equilibrium in the long-range interacting system by N-body simulations. In the early stage of its evolution, the system visits quasi-equilibrium state where the value of physical quantities such as mean kinetic energy are different from equilibrium ones. Then it gradually evolves toward thermal equilibrium. We find that this transient states can be described by the polytrope which is given by the one-particle distribution of the energy 
, 
, only when the system has the negative specific heat. The relaxation processes are characterized by increase of index n to infinity which corresponds the Boltzmann distribution. For dynamical evolution, we are trying to accelerate N-body simulations with General-Purpose computation on Graphics Processing Units (GPGPU). GPGPU can accelerate the computation of 2-body interactions.
