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Sumita, Junya; Shibata, Taiju; Tachibana, Yukio; Kuroda, Masatoshi*
no journal, ,
Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR) which is a graphite-moderated and helium gas-cooled reactor. The HTGR is particularly attractive due to capability of producing high temperature helium gas, and its passive and inherent safety features. The Very High Temperature Reactor (VHTR) is one of the most promising candidates as the Generation-IV nuclear reactor systems. During operation of the HTGR, the graphite structure is subjected to various loadings such as external forces and internal stresses resulted from neutron irradiation-induced dimensional and material property changes and a thermal gradient. In order to acquire the fundamental data to evaluate the integrity of the graphite structure of HTGR by fracture mechanics, it is important to investigate the fracture toughness and strain energy release rate of graphite. In this study, the fracture toughness of fine-grain and coarse-grain graphite was measured and calculated the strain energy release rate of them. Moreover, the crack propagation in these graphite and coarse-grain graphite were observed by microscope and the difference between them was discussed from the viewpoint of the grain size.
Nagaishi, Yoshihide*; Fukuda, Toshiaki*; Kondo, Akira*; Sumita, Junya; Sakaba, Nariaki
no journal, ,
Fine-Grained isotropic graphite shows higher strength making it a promising material for the graphite component of High Temperature Gas-cooled Reactor (HTGR) and Very High Temperature Reactor (VHTR). There are two kinds of considerations about lifetime of graphite components under neutron irradiation condition. One consideration is determined based on dimensional changes due to neutron irradiation. In this consideration, small dimensional change with much amount of neutron irradiation is preferable. The other consideration is determined based on a margin between the specified minimum ultimate strengths and the residual stresses induced by neutron irradiation. In this consideration, strength of graphite components is important property to decide lifetime. It is expected that development of new fine-grained isotropic nuclear grade graphite possessing higher strength will contribute toward added design margins and an extension of the lifetime of graphite components, which likely improve the reactor economy very significantly. Furthermore, from the viewpoint of graphite waste, it is also expected to decrease the exchange frequency of core components. Tokai Carbon Co., Ltd. has developed new nuclear grade graphite with higher strength and characterization of them is being carried out. This presentation shows the R&D plan and the initial results of mechanical and thermal properties of un-irradiated nuclear grade graphite.
Osaki, Hirotaka; Konishi, Takashi*; Eto, Motokuni*; Shibata, Taiju; Sumita, Junya
no journal, ,
no abstracts in English