Operating Vibration Measurements of Test Fuel Assembly in Reactor Thermo-hydraulic Test Condition Kang-Hee Lee, Chang-Hwan Shin, Heung-Seok Kang, Dong-Seok Oh, Nam-Kyu Park* Korea Atomic Energy Research Institute, Innovative Nuclear Fuel Division * KEPCO Nuclear Fuel, Nuclear Fuel Design Group 1045 Daedeok-daero, Yuseong-gu, Daejeon, Korea(Ref. of), 305-353 leekh@kaeri.re.kr ABSTRACT The design verification of a newly-developed nuclear fuel assembly requires a long-term endurance test under thermo-hydraulic test condition simulating power reactor core. For this verification test, vibration of the test fuel assembly inside the simulated test core should be measured under high system temperature (over 200 °C), high system pressure (over 2.5 MPa) and fast moving coolant flow (over 5 m/s). To measure the vibration, we use specially fabricated accelerometers, various sealing techniques and conduit channel design for signal cable protection. The effects of the flow rate, coolant temperature, pre-sized support clearance on the test fuel vibration response and orbit motion were discussed. The measured data is used for fuel compatibility evaluation and a basis for endurance verification, as well as the validation tool for theoretical response prediction model. 1. Introduction Nuclear fuel assembly is a mechanical cluster of fuel rods grouped by the series of intermediate spacer grids. Fig. 1 shows a nuclear power plant with a reactor cross-cut and a typical fuel assembly. Fuel assembly absorbs the energy from the axial upward coolant flow in the power reactor core and vibrates with relatively small amplitude. Even small vibration can lead to fatal mechanical damage on the fuel cladding tube at the support point [1]. Not only does the flow-induced vibration of a fuel assembly engaged in complex fluid-structure interaction and inter-rod physical coupling through medium, the vibration responses can become more complex due to the change of support condition and the flow disturbances by intermediate spacer grids with flow mixer. Although the averaged response can be estimated with the aid of stochastic finite element analysis method combined with experimental measurement for hydrodynamic forces, results of theoretical prediction which is limited to the simple problem have large scatter [2]. Thus, experimental validation for theoretical model is essential and functional verification tests are required for each fuel assembly design. The design verification of a newly-developed nuclear fuel assembly requires a long-term endurance test under thermo-hydraulic test condition simulating power reactor core using a real scale fuel test model. Design compatibility to the neighboring fuel assembly and wear resistance capability of cladding tube can be assured by measuring a vibration response in transient test flow condition and an accumulated wear of the test rods in longterm steady-state test flow condition [3]. For this verification test, vibration of the test fuel assembly in the simulated test core has to be measured under high system temperature (over 200 °C), high system pressure (over 2.5 MPa) and fast moving coolant flow (over 5 m/s). The proper selection of the sensors based on the measurement requirements, gauge installation, signal cable protection had a key role in a successful data measurement for final test purposes. The paper deals with the flow-induced vibration measurement of test fuel assemblies in the power reactor T. Proulx (ed.), Modal Analysis Topics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series 6, 41 DOI 10.1007/978-1-4419-9299-4_4, © The Society for Experimental Mechanics, Inc. 2011
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