Dynamic analysis and performance evaluation of CPS-AR insertion into VVER-1000 fuel assemblies under normal and accident reactor conditions

• Dynamic Analysis of CPS-AR insertion into VVER-1000 Fuel Assemblies is presented. • Control rod movement of a VVER-1000 reactor is simulated via ABAQUS software. • Both dynamic and static forces acting on the CPS-AR are modeled and calculated. • Deflection of the guide tube with spacer grids under seismic events is modeled. • Results show that spacer grids cause smaller falling time for accident condition. The objective of this research is to investigate the performance and insertion time of Control and Protection System - Absorber Rods (CPS-ARs) into the fuel assembly under normal reactor operating conditions, as well as under reactor accident conditions (seismic events), considering both dynamic and static forces acting upon them. In this study, a MATLAB Simulink model was first developed to simulate the control rod movement of a VVER-1000 reactor. This model generated several outputs, including the control rod's velocity profile, which was limited to 1.7 m/s, as well as the buoyancy force (constant at 1.63 N), shear stress, and pressure stress. These outputs were then used as input parameters for ABAQUS software. Then, a single control rod from a VVER-1000 reactor control rod cluster, along with its corresponding guide tube, is modeled and simulated using the ABAQUS software. This simulation is then subjected to both dynamic forces (from the coolant fluid and seismic loads) and static forces (including the control rod’s weight, fluid buoyant force, and the weight of components above the fuel assembly). The resulting bending of the guide tube is subsequently calculated based on the application of these forces. Following the dynamic and static analyses, and determination of guide tube displacement and deflection, the insertion conditions of the CPS-ARs into the fuel assembly are investigated under distinct scenarios. In normal reactor conditions, the forces acting on the control rod encompass its weight, the buoyant force from the fluid, the shear stress force from the fluid, the pressure stress force from the fluid, and the friction between the control rod and the guide channel walls. And the fall time is 2.192s. During a seismic event, the reactor's geometry is subjected to vibrational forces from the earthquake, which act in addition to the normal operational forces. This comprehensive assessment effectively evaluates the feasibility of control rod insertion into the reactor core across various operational and accident conditions. Results show greater falling time for earthquake condition (falling time for Bam earthquake = 2.26s) than that of normal condition (2.192s). Also, spacer grids cause to smaller falling time for earthquake condition (time for Bam earthquake with spacer grid = 2.15s) than that of normal condition.