Unexpected steam generator tube wear has recently been discovered during in-service inspection of newly installed PWR replacement steam generators. The extent of this unexpected tube wear suggests that a new wear mechanism is emerging that is not described by current tube wear models. A key to understanding the emerging unexpected tube wear may be to better understand the effectiveness of the mechanical design for tube support (flat bars with tight clearances) with respect to preventing flow induced tube vibration, and the characteristics of hydraulic forces exerted on tubes. This paper describes the results of a non-linear, dynamic, finite element analysis of steam generator tube in-plane vibration with typical flat bar mechanical supports. Mechanical support conditions such as initial gaps between tube and supports, contact forces between the tube and the supporting flat bars, and the effect of various forces applied to the tubes by fluid flow are investigated. The analysis describes the effect of these conditions on tube in-plane vibration frequency and damping for various tube forcing functions. Computational fluid dynamics calculations that determine the unsteady forces in two-phase flow test geometries are presented. A model describing the emerging unexpected tube wear is also introduced.

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