Seismic behavior analysis of control rod dropping by vector form Intrinsic Finite-Element method

Control rod drive mechanism (CDRM) play a major role in ensuring safe operation of nuclear reactor during the earthquake, under which the dropping time of control rod is crucial for safe shutdown. Under the earthquake, Rod Cluster Control Assembly (RCCA) has contact collision with the guide tube, resulting in an increase of friction and a decrease of the speed of the falling rod. In addition, in view of the slender structure of the falling rod, the flexible deformation vibration will occur under the impact excitation, which will aggravate the collision and friction. In order to solve the nonlinear problem caused by contact collision between control rod and guide tube, we proposed a dynamic behavior analysis program of rod dropping based on vector finite element method. In order to simulate contact collision force more accurately, we proposed a conformal contact law to simulate the contact force between control rod and guide tube. The vector finite element model and simulation program are validated by comparing with a rod drop experiment. Based on the developed program, the rod dropping behavior, including rod dropping time, contact force, friction force and control rod deformation under several earthquake condition were discussed in this work.