Preliminary Study on the Torque Coefficient and Filtering Coefficient for Threaded Fasteners in Fuel Assembly

As an important element of non-permanent connection, threaded fasteners are commonly used in Pressurized Water Reactor (PWR) fuel assembly connections. The relationship between applied torque and preload of screw is always estimated based on the engineering experience, because the friction coefficient between screw and nut is complicated. The threaded fasteners in fuel assembly under Nuclear Power Plants (NPPs) operational conditions are subjected to external tensile or compressive loads, and when the external load is applied to the threaded fastener, the load is distributed between the members of fastener, the ratio between increased preload of screw and the external load is difficult to predict because of the complexity among the connection members. In order to understand the behavior of each member in threaded fasteners, it is necessary to investigate the relationship between torque and preload of the screw, and also the axial load distribution of threaded connections. In this paper, the torque coefficient and filtering coefficient of the threaded connection among fuel assembly components are studied. The torque coefficient results are compared with the theoretical calculation, and the fastener members are connected by preload screw, when the external load is applied to the connection, the filtering coefficient are obtained via FEM simulation, which is compared with the reference value. The comparison has shown very good agreements between referenced test and calculation.