Recent observations at operating plants and subsequent U.S.NRC requirements have identified flow stratification in surge lines as a phenomenon that must be considered in the design basis of surge lines. During YGN(Younggwang Nuclear) unit 3 pre-core hot functional testing, surge line pipe wall temperatures and pipe displacements were measured to determine the degree of surge line flow stratification. Test data from YGN Unit 3 indicate that stratified flow exists in the surge during heatup and cooldown. This paper presents the circumferential and axial temperature distributions and the pipe movements measured from surge line stratification testing performed during the YGN Unit 3 pre-core hot functional test.
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