Thermalhydraulic Analysis of Small-Scale Tube Rupture Experiments

Abstract

Guillotine failure of a rupturing pressure tube is an accident situation currently being investigated in the safety analysis of CANDU (CANada Deuterium Uranium) reactors. One of the reasons for initiating the investigation was to determine the major factors controlling the onset of guillotine-failure. As part of this program, small-scale rupture tests using fuel sheaths have been performed and numerically simulated. The fluid dynamic aspects of rupturing fuel sheaths simulated with a multi- dimensional prototype of the two-fluid thermalhydraulic code CATHENA are described in this paper. The results of the numerical simulations were examined by observing the behaviour of pressure transients of the fluid inside the tube during the rupture. A parametric study was first performed to determine optimum model conditions for two-dimensional simulations. Results from CATHENA simulations using these conditions were then compared with experimental data. Calculations were also extended to a three-dimensional thermalhydraulic analysis. This paper describes the results of the parametric and comparative studies. The effect of varying the simulation conditions on calculated pressure transients is also described. Although agreement between simulated results and experimental data was found to be good, some discrepancies were noted and are discussed. Advantages and disadvantages of the three-dimensional study are also presented. This investigation has been successful in demonstrating a method that can be used to enhance the understanding of the behaviour of pressure-tube rupture under accident conditions. Areas in which the numerical analysis could be advanced to further the understanding of rupturing pressure tubes are provided.