Characterization of new nuclear-grade graphites for HTGR/VHTR

Nagaishi, Yoshihide*; Fukuda, Toshiaki*; Kondo, Akira*; Sumita, Junya ; Sakaba, Nariaki 

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.