Investigation of various floating absorber for safety at transient (FAST) designs

Floating absorber for safety at transient (FAST) is a device to support negative reactivity feedback and enhance coolant temperature coefficient (CTC) and coolant void reactivity (CVR) values in a sodium-cooled fast reactor (SFR). The absorber region of the FAST passively inserts negative reactivity into the active core region when the buoyance acting on the FAST is smaller than gravity and vice versa. Since the FAST moves upward and downward inside the pin depending on the coolant density, the resistance applied to the FAST body determines the velocity and ultimately the reactivity of the reactor system. In this study, resistance acting on various FAST designs is presented using computational fluid dynamics code (CFD) STAR CCM+ [1].