Numerical study of tube bundle vibrations in an N4 standardized nuclear plant series steam generator

Nuclear power plant operators are concerned with flow-induced vibrations of Steam Generator (SG) tube bundles. They have to make sure that changes affecting, either the SG itself, or its operating conditions, will not create the conditions for the vibrations of any tube in the bundle to become unstable. French operator EDF has therefore developed GEVIBUS, a dedicated, user-friendly software, that allows one to evaluate the stability of any tube in an SG bundle, by comparing its critical velocity to actual velocity. In addition, most recent French standardized nuclear N4 series is fitted with a new SG model that differs from previous ones by the kind of arrangement of its bundle, which is triangular instead of square. In preparation for tube stability studies that could be required in the future in case of whatever change that could affect the N4 SG bundle, GEVIBUS was recently updated and tested by applying it to some tubes of that bundle. In that context, the paper first points out the main specific design characteristics of the N4 SG bundle. It afterwards focuses on the physics principles that have been developed and are available for use in the frame of GE VIB US. The updates applied to GEVIBUS for making possible the study of the N4 SG tube bundle are then described. Some results obtained on r110c69, the tube with the largest radius in the bundle, are finally displayed. (authors)