The top nozzle is an important part of the fuel assembly and is located at the core coolant outlet, which has an important impact on the uniformity of the coolant flow distribution at the core outlet and the overall pressure drop of the fuel assembly[1]. The peak stress of the top nozzle under each working condition appears at the position of the adapter plate, top nozzle and the pressure drop of the top nozzle is closely related to the flow area, height and local characteristics of the adapter plate. In this paper, the overall structure of the adapter plate is optimized to reduce the pressure drop as much as possible on the premise of ensuring that the stress meets the requirements of the standard limit. The 3D modeling software NX is used to establish the geometric model of the top nozzle, and it is transferred to ANSYS to establish a finite element model for simulation optimization design. On this basis, the key dimension parameters of the adapter plate (such as the thickness of the rib, etc.) are selected as design variables, and the law of its influence on the blocking area and stress is studied, and the structure size is further optimized.

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