Coupled Fluid Structure Interaction (FSI) Modeling of Parallel Plate Assemblies

As part of the Global Threat Reduction Initiative (GTRI) Reactor Conversion program, the fuel assembly at the University of Missouri Research Reactor (MURR) is undergoing a significant redesign. The proposed fuel structure is based on low-enriched uranium foils. The proposed aluminum-clad LEU foil fuel plates for the MURR core are significantly thinner than the currently used fuel plates. Further, the monolithic structure of the proposed fuel is fundamentally different than the current design based on powder metallurgy. Consequently, coolant flow reduction due to flow induced deformation of the proposed fuel plates is of concern. The goal of the current analysis is to estimate the amount of flow induced deformation of the proposed LEU-based fuel plates when subjected to coolant flow imbalance due to fuel plate assembly tolerances. Previous methods for assessing fuel plate deflection have relied heavily on analytic and experimental techniques. With the continued advancement of computational codes, new options are now available to assess structural stability. The current approach is to explicitly couple a commercial CFD code with a commercial FEM code. This paper will describe the convergence and stability criteria that were developed to obtain an accurate deflection solution. Time step management and pressure ramping strategies were effectively used as relaxation parameters to improve the computational stability. Additionally, mesh quality criterion were developed and are enforced during a simulation. Benchmarking of the numeric results to analytic calculations is also presented.