자유낙하에 의한 경수로용 핵연료집합체의 동적 거동 해석

The objective of this research is to propose the methodology that could predict the dynamic failure behavior on the pressurized water reactor (PWR) fuel assembly structure for the reactor coolant pump (RCP) over-speed transient event. To perform this objective, the finite element analysis method for predicting the axial impact behavior on the fuel structure is established by a commercial finite element codes ANSYS and DYNA-3D. In this FE analysis method, appropriate boundary conditions and impact loading conditions are applied to simulate the actual core conditions. The drop impact analysis of a fuel assembly for PWR power plant is executed by the finite element analysis method. The analysis results are compared with the previous experimental results. The impact force results differed from the analysis condition depending on how many fuel rods slipped down to the bottom nozzle. And the joint and connection parts between components of a fuel assembly are very important for determining the stiffness of it. In the analysis, the fuel assembly experienced an impact force of approximately 111.53 kN when dropped from a height 25 mm with the fuel rods on the bottom nozzle. The secondary peak value is about 57.55 kN and the duration is about 6 milliseconds. After comparing with the previous test results, the developed finite element model and analysis procedure will be useful tool for evaluating the dynamic stiffness and strength of a fuel assembly. It is found that the joint and connection characteristics among parts are dominant factor which determine the non-linear behavior of a fuel during free fall event.