Apparatus for a steam generator that employs tube support plates within a shroud that is in turn disposed within a shell. The tube support plates are made of a material having a coefficient of thermal expansion lower than that of the shroud. The tube support plates are aligned during fabrication, with minimal clearances between components. Using a tube support displacement system, a controlled misalignment is then imposed on one or more tube support plates, as the steam generator heats up. The tube support plate displacement system has only one part, a push rod, which is internal to the steam generator shroud, thereby minimizing the potential of loose parts. The tube support plate displacement system can be used to provide controlled misalignments on one or more tube support plates, in the same or varying amounts and directions, and with one or more apparatus for each individual tube support plate.