An Investigation into the Accuracy of CHF Modelling in One-Dimensional Two-Phase Flow Analyses

Abstract

The accuracy of empirical CHF prediction models and two-phase pressure drop correlations, recently introduced in the SOPHT computer code, is investigated in comparisons of the code model to the experimental results, measured in a full-scale 37-element bundle simulated fuel string. Since predicted thermohydraulic parameters (i.e., pressure, mass flux and quality) are used as correlation parameters in the CHF prediction methodology, the uncertainties of the CHF and pressure drop predictions can not be considered independent in estimating the code uncertainty: estimation of the actual accuracy of dryout predictions should include comparisons of the code model to the experimental results. The choice of the two-phase pressure drop model is shown to have an appreciable impact on the accuracy of the prediction of critical conditions. Results show that the representation of the extent the subcooled boiling region is the most important factor in the accuracy of the predictions. This should be taken in consideration in the calculation of the experimental dryout pressures used in the derivation of CHF models.