The numerical simulation of the WWER440/V213 reactor pressure vessel internals response to maximum hypothetical Large-break Loss of Coolant Accident

Abstract

The reactor internals are designed to ensure cooling of the fuel, to ensure the movement of emergency control assemblies under all operating conditions including accidents and facilitate removal of the fuel and of the internals following an accident. This paper presents preliminary results of the numerical simulation of the WWER440/V213 reactor vessel internals (RVI) dynamic response to maximum hypothetical Large-break Loss of Coolant Accident (LOCA). The purpose of this analysis is to determine the reactor vessel internals response due to rapid depressurization and to prove no such permanent (plastic) deformations occur in the RVI which would prevent timely and proper activation of the emergency control assemblies. In the case of the LOCA accident it is assumed rapid “guillotine” break of one of the main coolant pipes and rapid depressurization of the primary circuit. The pressure wave spreads at the speed of sound, enters the reactor pressure vessel and causes deformation and stress in reactor vessel internals. The finite element model was created by MSC.Patran ( Patran, 2010) and dynamic response was solved using MSC.Dytran ( Dytran, 2008) finite element code. The model consists of reactor vessel internals (Lagrangian solid elements) and water coolant (Euler elements) inside the reactor. Arbitrary Lagrangian Eulerian ( Belytschko et al., 2003) coupling was used for simulation of the fluid-structure interaction. The calculation assumes no phase change in the water. No comparison with the experiment was performed up to now, because the required experimental data are not accessible for this type of the reactor. The most important acceptance criteria for the reactor internals demands that the movement of the emergency control assemblies under all operating conditions including accident is ensured ( BNS, 2008). The numerical simulation of the WWER440/V213 reactor internals response to a LOCA accident showed that the acceptance criteria for RVI is fulfilled and required NPP safety standards are satisfied.