Analytical evaluation on dynamical response characteristics of reduced-moderation water reactor with tight-lattice core under natural circulation core cooling

Ishikawa, Nobuyuki; Okubo, Tsutomu

The time-domain analyses with TRAC-BF1 code were performed for clarifying the dynamical response characteristics of the reduced-moderation water reactor (RMWR) with tight-lattice core configuration. The response characteristics were evaluated based on the step response basically utilized for dynamical system evaluation. As for the most fundamental dynamical characteristics, the flow response characteristics of single fuel assembly concerning channel flow response characteristics were evaluated. As for a natural circulation flow response, it is clarified that the response is strongly influenced by the effect of two-phase pressure loss on account of high void fraction condition. The reactor power response with reactivity feedback shows quite stable response characteristics on account of the small absolute value of void reactivity feedback coefficient.