Method of Characteristics Solutions for Blowdown Involving Bubbles Break-up

A novel two-phase model was developed for evaluating coolant discharge rates from LOCA (loss-of-coolant accidents) type accidents. Of concern is the two-phase flow transient occurring in the tube section connecting the pressurized vessel to the break point. The subject is applicable for assessing and enhancing the safety of pressurized vessels containing hazardous materials. The results provide the required input data for running contaminant dispersion codes for environmental safety. The code accounts for influencing transient two-phase flow phenomena that are absent in previous codes. It indeed predicts experimental features that cannot be revealed by earlier models. Specifically, the code contains a bubble brake up model that depends on two different instability criteria. Therefore, it can be considered as a new predictive tool that can predict quite accurately discharge flow rates of fast depressurization transients. The code was successfully tested against experimental data of different cases and for various conditions. The EVUT (equal velocities unequal temperatures) two-phase model was incorporated in the code and the numerical solution is based on the method of characteristics. (author)