Numerical and Experimental Analysis of the Control Rod Hydraulic Deceleration Device for the Control Rod Hydraulic Drive System

Control rod hydraulic drive system (CRHDS), which is invented by INET, Tsinghua University, is a new type of internal control rod drive technology. Control rod hydraulic deceleration device (CRHDD), which consists of the plug, the hydraulic deceleration cylinder, the hydraulic buffer, etc., is one of the main components of the CRHDS. The plug is connected with the top of the control rod driving shaft and moves along with the control rod inside the hydraulic deceleration cylinder. The CRHDD performs the rod dropping deceleration function through the interworking of the plug and the deceleration cylinder which is filled with water, and reduces the rod dropping peak acceleration and the impact force acting upon the control rod to prevent the control rod cruciform blade from being deformed or damaged. The working mechanism of the CRHDD is presented and analyzed. The rod dropping performance of the CRHDS was tested experimentally under room temperature. The theoretical model of the control rod dropping process, which is composed of the three dimensional flow field analysis and flow resistance calculation of the hydraulic deceleration cylinder, the kinematics and dynamics model of the control rod, is built whose results are compared and validated by the CRHDS scram test results under room temperature. Then the model takes into account of the influence of the fuel assembly box on the control rod scram process under high temperature working conditions, and is used to analyze the influence of the key parameters, including the helical spring stiffness inside the deceleration cylinder and the working temperature on the CRHDD working performance. The research results can give guidance for the design and optimization of the CRHDD.