Analysis of critical heat flux under vertical subcooled flow boiling condition. Development and evaluation for prediction method of DNB heat flux under non-uniform axial heat flux condition

From the viewpoint of safety design of nuclear reactor and economic terms, for PWR, it is important to clear the mechanism of DNB and predict accurately the critical heat flux under vertical subcooled flow boiling condition. So, in this research, a prediction model of the CHF under vertical subcooled flow boiling condition was developed. The model is based on the vapor blanket mechanism and the homogeneous nucleation mechanism. Additionally, the model accounts for a new phenomenon called in this research as overheating phenomenon of the heated surface. The method was evaluated by comparing the prediction results with experimental data for a vertical circular tube under high pressure, subcooled flow boiling and non-uniform axial heat flux condition. It was found from the evaluation results that the method developed in this research was able to predict accurately both of the CHF and the CHF location. (author)