Validation Facility and Model Development for Nuclear Fuel Assembly Response to Seismic Loading

Abstract

A joint experimental and numerical campaign is conducted to provide validation dataset of highfidelity fluid–structure interaction (FSI) models of nuclear fuel assemblies during seismic loading. A refractive indexmatched (RIM) flow loop is operated on a sixdegreeoffreedom shake table and instrumented with nonintrusive optical diagnostics. The test section can house up to three fullheight fuel assemblies. To guarantee reproducible and controlled initial conditions, special care is given to the test section inlet plenum; in particular, it is designed to minimize secondary pulsatile flow that may arise due to ground acceleration. A single transparent surrogate 6أ—6 fuel subassembly is used near prototypical Reynolds number, Re=105 based on hydraulic diameter. To preserve dynamic similarity of the model with prototype, the main dimensionless parameters are matched and custom spacer grids are designed. Special instruments are developed to characterize fluid and structure response and to operate in this challenging shaking environment. In parallel to the earlier experiments, we also conducted fully coupled direct numerical simulations, where the equations for the fluid and the structure are simultaneously advanced in time using a partitioned scheme. To deal with the highly complex geometrical configuration, which also involves large displacements and deformations, we utilize a secondorder accurate, immersed boundary (IB) formulation, where the geometry is immersed in a blockstructured grid with adaptive mesh refinement (AMR). To explore a wide parametric range, we will consider several subsets of the experimental configuration. A typical computation involves 60,000 cores, on leadership highperformance computing facilities (i.e., IBM BlueGene Q–MIRA).