Validation of the THIRST Steam Generator Thermalhydraulic Code Against the Clotaire Phase II Experimental Data

Abstract

Steam generator thermalhydraulic codes are used frequently to calculate both global and local parameters inside the steam generator. The former include heat transfer output, recirculation ratio, outlet temperatures, and pressure drops for operating and abnormal conditions. The latter are used in further analyses of flow-induced vibration. fretting wear, sludge deposition, and flow- accelerated corrosion. For these purposes, detailed, three-dimensional two-phase flow and heat transfer parameters are needed. To make the predictions more accurate and reliable, the codes need to be validated in geometries representative of real conditions. One such study is an international cooperative experimental program called CLOTAIRE based in France. COG participated in the first two phases of the program; the results of the validation of Phase I were presented at the 1994 Steam Generator and Heat Exchanger Conference, and the results of the validation of Phase II are the subject of this paper. THIRST is a thermalhydraulic, finite-volume code to predict the flow and heat transfer in steam generators. The local results of CLOTAIRE Phase II have been used to validate the code. These consist of the measurements of void fraction and axial gas-phase velocity in the U-bend region. The measurements were done using bi-optical probes. A comparison of global results indicates that the THIRST predictions, with the Chisholm void fraction model, are within 2 to 3% of the experimental results. Using THIRST with the homogeneous void fraction model, the global results were less accurate but still well predicted with the greatest error of 10% for the separator pressure drop. Comparisons of the local predictions for void fraction and axial gas-phase show good agreement. The Chisholm void fraction model generally gives better agreement with the experimental data while the homogeneous model tends to overpredict the void fraction and underpredict the gas velocity.