Determining the Factors Causing Resonant Vibrations in Main Steam Pipelines of Novovoronezh NPP-2 Unit 1

The problem of the occurrence of increased levels of operational vibrations in the main steam pipelines of the VVER-1200 power unit and ways to reduce them are considered using the example of power unit no. 1 of the Novovoronezh NPP-2. For the first time, this problem was identified during the commissioning of power unit no. 1 of the Zaporizhzhya NPP (VVER-1000) at the stage of commissioning and power development and remained relevant for all power units with VVER-1000 series reactors. Increased vibrations of the steam pipelines of the main steam system led to various damages—the appearance of fistulas, breakage of auxiliary pipelines for fittings, etc.—and also caused a multiple decrease in the cyclic strength of the main steam pipelines and an increase in the likelihood of their cyclic destruction. In order to study the resonant vibration frequencies of the main steam pipelines of the 10LBA system and pipelines of the high-pressure bypass pipes of the 10MAA system of NVNPP-2 power unit no. 1, their mathematical model was developed. Comparison of the data obtained by measuring the natural frequencies in the course of the experimental modal analysis of the identified resonant frequencies during the vibration survey with the calculated natural frequencies of the pipelines of these systems using the developed model of the ANSYS program showed their satisfactory convergence, which made it possible to verify this ANSYS model. As a result of the modal analysis (analysis of natural forms and natural frequencies of vibrations) of the 10LBA and 10MAA systems, all natural frequencies of the systems in the range of 0–100 Hz were determined. A method is proposed to reduce the vibration of main steam pipelines of the 10LBA system and pipelines of high-pressure bypass pipes 10MAA, based on the shift of the identified natural frequencies to the high-frequency region by selecting and installing additional dampers on the pipelines of the systems at the places of maximum displacement.