An experimental validation method for a computational approach assessing the added mass of fuel plates

Current efforts are underway to convert the fuels of high-performance research reactors (HPRRs) from a standard highly enriched uranium (HEU) fuel to a high-density low enriched uranium (LEU) fuel combined in a molybdenum alloy. The conversion process has raised a renewed interest in determining the hydro-mechanical properties of the fuel plate. Of great interest is the excitation frequency and the response frequency of the plate. Accurate determination of these frequencies is difficult and costly to perform experimentally; as such, computational methods are desired to assess the response of the plate. Current state of the art requires the use of strongly coupled computational fluid dynamics (CFD) to computational structural mechanics (CSM) simulations. These simulations require the use of large clusters in order to be performed in a reasonable time frame. Previous work conducted between the Idaho National Lab (INL) and Oregon State University (OSU) under a Nuclear Science User Facilities (NSUF) program showed promise with a new method designed to determine the frequency of a structure. The method used purely computational structural mechanics (CSM) to determine the natural frequencies of a body submersed in a fluid. The method was achieved by treating water as a pseudo-solid instead of as a fluid. The goals of this study are to (1) determine the change in the fundamental frequency of the plate when submersed in a fluid and (2) asses the ability for the pseudo-solid approach to determine the fundamental of frequency of a plate in channels. For objective (1) a small experiment, frequency identification in a fluid experiment (FIFE), has been created for the purpose of determining the change in frequency of a plate from air to fluid to fluid channels. The experiment uses sound excitation as a driving frequency and the response is measured via strain gauge, complimented with a hydrophone and microphone. Experimental results have been obtained for both air and water. The experimental results are further used to validate the pseudo-solid approach to achieve objective (2). The pseudo-solid approach has shown excellent agreement with theoretical determinations of frequencies of bodies submersed in a fluid. This paper outlines the experimental results of the FIFE as well as the validity of the pseudo-solid method.