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

Abstract

A joint experimental and numerical campaign is conducted to provide validation datasets for high-fidelity fluid-structure interaction models of nuclear fuel assemblies during seismic loading. A refractive index matched flow loop is operated on a six-degree-of-freedom shake table and instrumented with non-intrusive optical diagnostics. The test section can house up to three full height 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 6×6 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 above experiments we also conducted fully coupled large-eddy 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 second order accurate, immersed boundary formulation, where the geometry is immersed in a block-structured grid with adaptive mesh refinement. To explore a wide parametric range we will consider several subsets of the experimental configuration. A typical computation involves 60K cores, on leadership high performance computing facilities (i.e. IBM Blue-Gene Q – MIRA).