Verification and validation of dynamic response simulation codes for BWR fuel assemblies under seismic loading

Abstract

The purpose of this study is to verify and validate two independently developed simulation codes for investigating dynamic response behaviors of fuel assemblies in a boiling water reactor (BWR) under seismic loading. The core of BWR consists of several hundreds of fuel assemblies. They are supported with both top guide and fuel support and are surrounded by coolant water. It is important to grasp their dynamic response behaviors under seismic loading for securing the structural integrity of the fuel assembly itself as well as for assessing control rod scrammability. For this evaluation of dynamic response behaviors, reliable simulation codes are required. In this study, we employ two different numerical simulation methods of acoustic fluid-structure interaction (AFSI) developed by the present authors independently. The one is a three-dimensional parallel finite element method for AFSI problems with solid elements based on a partitioned coupling approach, while the other is a finite element method of beam elements for fuel assemblies combining added mass matrix, which represents coupled inertia effects caused by coolant water. Both methods are implemented and applied to a problem of 368 fuel assemblies for verification and validation. The problem was set up based on the demonstration test performed by Nuclear Power Engineering Corporation in 1986. Both simulation results agreed well with each other, and the simulated results also agreed well with the experimental ones. In addition, we have discussed seismic response behaviors of fuel assemblies, which were not shown in the demonstration test. Finally, we conclude that the both developed simulation codes based on the proposed methods are powerful tools to grasp the behavior of huge number of fuel assemblies of BWR under seismic loading and to improve the seismic safety design of BWR core.