Transient analysis of depressurized loss-of-forced circulation accident without scram in high temperature gas-cooled reactor

Sato, Hiroyuki  ; Yan, X. ; Tachibana, Yukio ; Kunitomi, Kazuhiko ; Kato, Yukitaka*

Transient response of HTGR to DLOFC combined with failure of all reactor trip systems is analyzed. The characteristic behavior of the reactor during the long-term conduction cooldown event is found to be shaped by several parameters that are usually not considered in the safety design of the HTGR. For example, the reactivity coefficient of temperature of the graphite moderator is found to be a critical parameter to determining the final settling temperature of the fuel. Furthermore, this study finds that the peak fuel temperature reached during this event is correlated strongly even to the initial core operating temperatures prior to the initiation of the transient event. These and other results of this study are expected to provide useful input to the development of enhanced safety design guidelines for commercial HTGR reactor in the aftermath of the Fukushima accident.