(A) study of the behavior of the floating absorber for safety at transient (FAST) to improve inherent safety of a sodium-cooled fast reactor and multi-assembly-based design optimization

Abstract

The floating absorber for safety at transient (FAST) is a safety system proposed to passively enhance the inherent safety characteristics of a sodium-cooled fast reactor according to the change in coolant temperature. In this study, the physical behavior of the FAST is explained theoretically and numerically, and influential design parameters for the FAST movement are evaluated in detail. The analysis is performed through an experiment and the computational fluid dynamics code. In particular, the FAST analysis code for the velocity, position, resistance, fluid velocity profile was estabilished. The FAST can effectively contribute to the accident mitigation or can cause power and coolant temperature oscillations depending on the accident conditions. Based on the influential design parameters, the damping coefficient, this study suggests and analyzes an oscillation-damped FAST system to reduce the oscillatory behavior of the FAST under anticipated transient without scram (ATWS) events. In addition, the feasibility study for the FAST system application to the fuel assemblies is investigated considering the coolant temperature distribution along the fuel assemblies, and the design optimization of the FAST system is performed to suppress the oscillatory behavior and mitigate an accident.