Modal analysis of tubes in a tube bundle of WWER steam generator

Vibration mode parameters of WWER steam generator tubes were measured using test stands. The objective was to determine damping characteristics for the cases with water and without water in the tubes and a water-steam mixture outside the tubes. The tests were performed using an experimental bundle of nine U-tubes of 16x1.4 mm in size; the tube mounting corresponded to the actual situation, i.e., the tubes were fitted by means of six support lattices spaced 0.7 m. The main conclusions of the tests show that water inside the tubes shifted the tube resonance frequency by about 9% towards lower values and that primary water pressure changes did affect neither the resonance frequency nor the tube damping ratio coefficient. The finding is important for dynamic tube load analysis that the presence of secondary water on the one hand increased the relative damping ratio coefficient and on the other shifted the tube resonance frequency towards lower values. (Z.M.) 5 figs