The paper describes a piping operational vibration problem has been resolved at the Loviisa Nuclear Power Plant main steam (RA) and feed-water (RL) lines. Excessive piping vibration occurred as the result of an increasing of working media flow in piping due to 10% upgrading of the Unit 1 and Unit 2 reactors power capacity. Piping flow induced vibration in several cases has been significantly higher codes’ recommended thresholds levels and NPPs best operational practice.

The project covers 3D vibration measurements and walkdowns of RA and RL lines with its support system, developing of dynamic finite element models of piping with vibration parameters close to obtained experimental data. In result vibration protective measures has been developed based on implementation of High Viscous Dampers Technology (HVD). An optimum minimal number and location of VES and VD high viscous dampers has been determined and then installed at the lines. Finally an essential vibration reduction of the examined systems has been achieved.