Evaluation on thermal conductivity of fine-grain isotropic graphite on the basis of its porosity

Sumita, Junya ; Shibata, Taiju ; Muto, Takenori*; Mihashi, Masahiko*; Sato, Masahiro*; Yamashita, Ryo*; Sakaba, Nariaki 

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. Since the thermal conductivity of graphite is one of important properties to evaluate the maximum core temperature of the VHTR, many researchers investigated and reported it. Graphite material is porous material containing 20% of porosity and the thermal conductivity strongly depends on shape and volume distribution of pore. It is important to evaluate the thermal conductivity as a function of them. In the presentation, the evaluation results of the thermal conductivity for fine-grain isotropic graphite as a function of open pores and closed pores measured by a mercury porosimeter were reported. Moreover, the prediction method for the thermal conductivity considering the amount of open and closed pore was discussed.