Study on Failure Mechanism of Pressurizer Surge Line and Manhole Structure under LOCA

Pressurizer is an important equipment for pressure control and protection in nuclear reactors, and the huge shock generated by loss of coolant accident (LOCA) may cause structural failure of its critical parts. The three-dimensional transient numerical simulation of pressurizer surge line’s flow heat transfer and structural stress, the temperature distribution and sealing performance of manhole structure under the small break LOCA are carried out by the multi-field coupling method, and the failure mechanism is analyzed. The results show that the hot fluid rapidly flowing into the surge line forms a huge instantaneous load, causing a short period of strong vibration of the pipe, the middle part of the pipe deformation is the largest, which may destroy the pipe support structure; The equivalent stress of each part increases rapidly, and concentrated stress occurs at the connecting pipe part of the main pipe. Large stress fluctuation will affect its service life; The manhole structure has a large uneven temperature distribution, and the sealing performance of the gasket under the sealing structure changes the most. The contact pressure of the inner and outer sealing surfaces drops below the design sealing specific pressure before and after 100 seconds, which means leakage occurs. According to the analysis results, this paper puts forward some suggestions for improving the structure of surge line and manhole, which can provide technical reference for accident mitigation after small break LOCA in marine nuclear power plant. © 2023 Yuan Zi Neng Chuban She. All rights reserved.