A Contact Force Prediction Method for Nuclear Fuel Rod Supported by Multiple Spacers

In the field of nuclear industry, the structure with a dynamic contact can be often seen. For example, U tubes in the heat exchanger and fuel rods in the reactor are representative, and predicting the dynamic behavior of the tubes or fuel rods is critical to evaluate whether the structural integrity against wear is robust enough. For the fuel rod, due to thermal relaxation of the elastic supports and creep-down of the fuel rod cladding, the gap develops between the fuel rod and the supports. Therefore the dynamic impact caused by turbulent coolant flow is unavoidable. A degree of freedom which is free in the fuel rod becomes restrained at a certain time when the gap closes. Usually the system is modeled as a beam with extra external forces or pseudo forces which simulate a dynamic contact condition. That is when the fuel rod contacts the support, the reaction force is developed and the force is regarded as an extra external force. A time domain solution can be obtained by direct implicit integration of the governic equation using the Newmark method, but the predicted solution may not be reliable because of the unknown contact force. This paper proposes continuous and differentiable contact force model that is required to calculate its tangent stiffness