Development of numerical analysis code LEAP-III for tube failure propagation

In case pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of a sodium-cooled fast reactor, a high-velocity, high-temperature, and corrosive jet with sodium-water chemical reaction may cause tube failure propagation. In this study, a numerical analysis method to predict the occurrence of tube failure propagation by overheating rupture was developed to expand an application range of an existing computer code. This method consists of the elemental analysis models for a sodium-side temperature distribution formed by a reacting jet, water-side thermal hydraulics, heat transfer of a tube, and tube failure by internal pressure. To evaluate event progress at a shortest computation time, the elemental analysis models of this code were constructed from the experimental data, semi-theoretical correlations, or one-dimensional equations. Applicability of the method was investigated through the computation of an experiment on water vapor discharging in liquid sodium. In this experiment, one tube for water vapor discharging and the 91 target tubes were placed in a liquid sodium pool. Temperature of the target tubes increased by the effect of the reacting jet in this computation. Some of the target tubes near the initial water leak resulted in overheating rupture as with the experimental result. This computation demonstrated that the proposed method could predict the occurrence of overheating rupture and provide conservative results. (author)