Uncertainty and sensitivity analysis of a phenomenological dryout model implemented in DARIA system code

摘要

Uncertainties of numerical predictions play important role in assessment of safety margins in nuclear reactors. In this paper uncertainties of the predictions of the Hewitt-Govan model, which is used to determine the entrainment and deposition rates in phenomenological dryout model, are presented and discussed. Results of the global uncertainty analysis are shown in terms of trends of uncertainty values with respect to the pressure, mass flux and inlet subcooling. Regions of large and small uncertainties are identified and presented in a tabular form.Application of the global sensitivity analysis methods allowed to quantify the sources of uncertainties with high accuracy over large spectrum of experimental conditions. Since the present analysis required calculation of millions of cases, a dedicated fast-running three-field computational code called DARIA has been developed for that purpose. The analysis revealed that the uncertainties of dryout prediction are predominantly resulting from uncertainties of the coolant mass flow rate.The most obvious implication of the presented work is that, when applying the current methodology to predict dryout in rod bundles, the most important parameter, affecting the accuracy of predictions, is the distribution of coolant flow between sub-channels.