Reliability evaluation of secondary support structure in hypothetical drop of reactor core barrel assembly

Abstract

Dynamic responses of the secondary support structure are investigated to evaluate its structural reliability in a hypothetical drop impact accident of the reactor core barrel assembly in this work. Impact analyses both in still water situation (20 °C) and dynamic water situation (289 °C) are carried out by LS-DYNA. Tensile tests in both temperature cases are conducted for the secondary support structure material (Inconel 690) in order to make the simulation results more accurate with real material properties. Various aspects of structural dynamic responses during impact are analyzed, including distributions of equivalent stress, equivalent plastic strain, and maximum principal stress as well as time histories of impact force, vertical displacement, vertical velocity, and energy. In still water situation, equivalent stress of the secondary support structure exceeds the yield strength due to the higher initial impact velocity and downward base acceleration. But in dynamic water situation, there is no plastic deformation due to the lower initial impact velocity and upward base acceleration. Peak values of the maximum principal stress distributed in the secondary support structure are less than the corresponding ultimate tensile strengths respectively in both analysis cases. Results reveal that both of the secondary support structure and the reactor pressure vessel meet the design criteria of RCC-M Code with respect to stress limits, thus the structural reliability can be ensured in this drop accident.