Hiroo Osada and Kiyonobu Yamashita

Abstract Section 4.1 describes features of a fast reactor core and the procedure of the core design. The characteristics of reactivity and power distributions are explained in the nuclear design section and the reactivity control requirements are also explained in this section. The section of core thermal-hydraulic design explains the outline of the coolant flow allocation procedure and the evaluation methods of temperature distribu­tions in a fuel subassembly. The author of Sect. 4.1 is Hiroo Osada.

Section 4.2 describes design of high temperature gas-cooled reactor (HTGR). HTGR’s cores consist of graphite internals and coated particle fuels that possess high temperature resistant. Helium gas is used as coolant that has high chemical stability in any temperature. High reactor outlet coolant temperature around

1,0 °C is possible for HTGRs with the high stable characteristics of graphite, fuel and coolant. High outlet coolant temperature enables high efficiency of electricity generation and broad utilization of HTGRs not only as electricity generation but also as a heat source for chemical industry. In comparison to LWRs, the outlet coolant temperature is high and difference between inlet and outlet coolant temperature is large for HTGRs. It results in different core design philosophy for HTGRs from LWRs. The core design of the High Temperature Engineering Test Reactor (HTTR) is presented as an example of HTGRs core design. The author of Sect. 4.2 is Kiyonobu Yamashita.