Study On Fatigue Life Analysis And Monitoring Technology Of Main Steam Isolation Valve In Nuclear Power Plants

Main steam isolation valve(MSIV) is one of the key equipment of second loop in nuclear power plants(NPPs), and its main function is that the main steam is isolated when the main steam line rupture accident occurs, to prevent the accident becoming serious. The phenomenon of larger noise and vibration were found on the main steam isolation valve in a domestic nuclear power plant during the normal operation. And various degrees of damage of isolation valve gates and safety valve components were also observed after disintegration of device during the plant overhaul. The large vibration and noise, caused by MSIV, can directly impact the safe usage of the main steam pipe, main steam isolation valves and main steam safety valve. So, it is of great significance for analyzing the fatigue of main steam isolation valves and studying the related life monitoring system. This article, based on ASME nuclear power plants operation and maintenance specifications(ASME OM-S/G 2000 PART3), has proposed the improved methods of assessing vibration stress and vibration fatigue life, and evaluated main steam isolation valve piping vibration stress and vibration fatigue life. The results showed that the calculated value of vibration alternating stress by frequency response analysis of the piping structure method was larger than the specification allowing value.Further assessing value, calculated by frequency domain method of vibration fatigue life evaluation, indicated that the fatigue life of piping vibration was higher than the design life,having the certain safety allowance.In this paper, it analyzed the nonlinear contact of the gate and the guide by using the finite element method, and calculated the stress and strain values of the risk of cross-section,contact pressure and slip of the gate and the guide. Moreover, micro-crack propagation direction and fretting fatigue life prediction are calculated by critical interface SWT method.The results showed that, the fretting fatigue crack initiation location is on the contact edge between the guide and gate. Fretting fatigue life prediction results indicated that there is a large safety margin for the main steam isolation valve operation under maximum load.Finally, the MSIV fatigue life monitoring system is designed by LabVIEW virtual instrument software. The simulation results show that the system is capable of MSIV fatigue life in real-time and off-line monitoring, and has the small collected error and high signal noise ratio(SNR) characteristics, enabled intuitive and accurate analysis of the life of the state and status display function for staff. The work of this article is that improved the MSIV piping vibration assessment methods. Fretting fatigue life prediction of MSIV gate created a precedent. Life monitoring system can provide more accurate life data for device, the aging management and life extension of nuclear power plants.