Kinetic Modeling and Analysis of Fuel Element Pneumatic Lifting System in Pebble Bed Reactors

Abstract

Thousands of fuel elements in pebble-bed reactor are lifted one by one from the bottom to the top of the core by pneumatic conveying every day. Any failure in the transportation process may lead to a safety accident. In order to ensure the safe and reliable operation of the reactor, it is important to model and analyze the motion process of the fuel element. In this paper, the kinetic modeling of the motion process of fuel elements was carried out, and the kinetic model of atypical bends was refined. Then, numerical simulation was used to analyze the motion characteristics of the fuel element in the acceleration-pipe section, vertical lifting-pipe section, and deceleration section, and it was found that with the increase in spherical/pipe-diameter ratio and pipe-inclination angle the acceleration and final velocity of the fuel-element acceleration process was larger, with the increase in spherical/pipe-diameter ratio and the decrease in recovery coefficient the collision frequency between the fuel element and pipe was reduced, and with the decrease in spherical/pipe-diameter ratio and bend radius the deceleration effect of the fuel element was more obvious. Finally, the accuracy of the model was verified on the experimental platform. This study provides several suggestions for the design and structural optimization of the pneumatic lifting system for pebble-bed-reactor fuel elements and provides a direction for subsequent research.