[en] The need for design criterion to limit amplitudes of liquid cross flow induced vibration of tube bundles took on great significance with the development of the current generation of heavy water cooled and moderated Canadian Nuclear Power Reactors. Associated with the primary coolant circuits of the reactors are large inverted U-tube steam generators which transfer heat from the primary circuit, tube side, to the boiling light water, shell side. Vibration induced damage to the tubes, with ensuing mingling of heavy and light water is not acceptable. The research described is confined to the lower portion of the steam generators where liquid cross flow of the light water occurs. There exist two significant modes of tube excitation which can lead to large amplitude vibration. These are the Connors type excitation, sometimes known as Connors instability, which permeates the entire bundle, and the vortex shedding phenomenon found here to be significant only at the first and second rows of tubes leading into the bundle. This latter observation is of particular importance because, to the authors' knowledge, it has not been heretofore discussed in the technical literature. The possibility of adding mid-span support to the inlet tubes is discussed. The main parameters which have been studied in this work are tube diameters, pitch-to-diameter ratios, flow directions, and liquid velocities, etc. Both equilateral triangular and square pitch tube arrays have been studied. (Auth.)