Abstract
Tests to study FluidElastic Instability (FEI) in an array of U-bend tubes were recently completed in the Multi-Span U-Bend (MSUB) test rig at Canadian Nuclear Laboratories (CNL). These tests were sponsored by the Electric Power Research Institute (EPRI) and were designed to study In-Plane (IP or streamwise) FEI of steam generator tubes in two-phase cross flow. This instability mechanism was first observed in previous research tests by Atomic Energy of Canada Limited (AECL). Although AECL planned additional research into IP FEI, this mechanism was not thought to be a serious practical concern until it recently caused severe damage to tubes in a new replacement steam-generator. The MSUB tests were conducted both with flows of air and two-phase liquid/vapour Refrigerant 134a. With 22 flexible U-bend tubes supported by a configurable flat-bar arrangement, the tests were focused on the effects of support geometry and tube-to-support interaction. Data was recorded from 33 dynamic signals from accelerometers, displacement probes, force transducers, and void-fraction probes. The paper describes the experimental test setup and reviews some of the initial test results and their implications for steam-generator users and researchers. Tests with two-phase Freon refrigerant (R-134a) are presented here.
