Development of Primary Coolant Piping for AP1000 Pressurized Water Reactor

Nuclear power is increasing rapidly as an important substitute for coal-fired electricity power in China. Four 3rd generation AP1000 nuclear reactors are under construction. The primary piping is one of the key components for reactor coolant system pressure boundary, which provides a barrier against the release of radioactivity generated within the reactor and is designed to provide a high degree of integrity throughout operation of the plant. Manufacturing of the world first AP1000 primary piping is a big challenge. According to Westinghouse design, it is forged integrally with nozzles. Ultra-low carbon-nitrogen alloyed stainless steel AISI 316LN is selected. Microstructure and precision shape control are two major goals to fulfill in manufacturing. A number of investigations on the materials and process have been carried out both in lab and full scale. Solidification sequence was observed in-suit to optimize the microstructure of ingot. Hot deformation behavior was studied by a large number of tensile and compression experiments. Constitutional model for flow stress was established. Recrystallization was observed and physical based models for microstructure evolution was obtained. Full scale 3D FEM simulations on forging and bending were performed to optimize grain size and its distribution, as well to ensure the final shape precision. Based on the laboratory results, full-size hot leg and cold leg piping were trail-manufactured. Both microstructure and property requirements are fulfilled. The final product was granted by authorities.