Qinshan Phase Ⅱ Nuclear Power Plant Main Steam Isolation Valve Vibration And Noise Analysis

During the commissioning of the main steam isolation valves it is found that the noise and the vibration are very strong. The internal parts of MSIV and MSSV are found damaged during the first outage. The noise is a pollution to the environment and the vibration damaged the valve internal parts of MSIV(Main Steam Isolation Valve) and MSSV(Main Steam Safety Valve). The MSSV setting value is floated which result in opened accidentally and leakage.After investigation on the valves situation in the reference power plant Daya Bay, it is found that there is same problem in Daya Bay and in nuclear power plant with the similar MSIV in France. In the analysis report they suggest that the vibration and the valve disc damage will not affect the safety and the operation of the MSIV and there is no analysis of the cause and recommended solution.A series of research such as vibration measurement, CFD analysis, abrasion and corrosion analysis is done to find out the reason of the problem. The result concludes that because of the contraction of the valve throat, the steam velocity reaches 87m/s. It is much over the speed of 40~60m/s recommended by electricity power standard. The contraction of throat also form of sonic resonance cavity, which causes the big vibration and noise. The vibration result in the jiggle corrosion and the fatigue damage, which is reason of the contact surface damage of the disc and the disc guide.The inlet and outlet pipe size is 739mm and the valve throat is 465mm. This essay recommend that by modification of the valve throat from 465mm to 489mm, the calculated speed will be slowed from 87m/s to 71.8m/s.According to the research of the Canadian Atomic Company, by modification of the specific shape of the valve seat will improve the valve noise and vibration.