Microstructures and Properties of 304L Steel CAP1400 Fuel Bottom Nozzles Prepared by Additive Manufacturing Technology

Nozzles of fuel assembly play an important role in pressure water reactor (PWR) fuel assembly element. For a long time, ordinary processing technologies of nozzles of fuel assembly have the problems of difficult and complicated process, the low availability of material and long the development cycles of manufacturing. However, according to the study these issues can be well settled by using the additive manufacturing technology. This paper studies a nozzle of fuel assembly prepared by this additive manufacturing technology through slow-strain-rate tension (SSRT) test and microstructure observation experiment. The results of SSRT test show that yield strength of the nozzle of fuel assembly is about 401.5MPa, the extensional rigidity is about 673.5MPa and the ductility is about 45.7%. And the SEM fracture results of the SSRT sample indicate that the fracture microstructure contains a large number of dimples, and the way of fracture belongs to plastic. And the metallographic observation consequences manifest that the microstructure of nozzle of fuel assembly prepared by the additive manufacturing technology is composite tissue of both austenite and ferrite, and the grains are settled along the way of laser scanning and there are isometric with some kind of direction. This metallographic microstructure is different from the traditional morphology of the free carbide distributed in the matrix. The dual phase microstructure of austenite and ferrite can improve the mechanical properties of the matrix effectively, and avoid the free carbides which may lead to matrix fragmentation in the tensile deformation process. Moreover, the laser power could affect the microstructure and properties of nozzles of fuel assembly observably, and the high laser power could bring about the ablation of metal. Through the analysis of mechanical properties and microstructure, we have made it possible to make the laser additive manufacturing technology to be used for the fuel assembly nozzle preparation in the nuclear power area. This work not only presents the advantages of the laser additive manufacturing technology in the fuel element processing area of the nuclear power station, but also broadens the application range of the laser additive manufacturing technology. What’s more we provide the new thoughts for the fast and effective preparation of the fuel element especially for the fuel assembly nozzle in the nuclear power station.