An Assessment of Void Fraction Data with COBRA-IE

COBRA-IE is a three-field subchannel analysis code under development at the Bettis Atomic Power Laboratory. The analysis code is being developed as a general-purpose thermal-hydraulic analysis tool with an emphasis on use in an integrated code system for analyzing postulated large-break loss-of-coolant accidents.

The overall accuracy of programs such as COBRA-IE is tied to the ability to predict void fraction. As such, a comprehensive assessment has been made using one-dimensional void fraction data. The results of this assessment are provided in this paper. The assessment utilizes data from nine different experimental facilities. It includes data from air-water and steam-water facilities, heated flow, adiabatic flow, subcooled boiling, saturated boiling, cocurrent upflow, and cocurrent downflow. Approximately 1100 data points are evaluated and included in this assessment. Overall, COBRA-IE was able to predict the void fraction with an average error (predicted − experimental) of less than 0.04. Plots describing the relationship between the error in the prediction and parameters such as pressure and flow are also provided.