Considerations for Modeling Critical Heat Flux Behavior

During normal and accidental operations of a light water nuclear reactor, a wide range of thermal-hydraulic conditions may be encountered for which the critical heat flux (CHF) cannot be predicted by a single correlation. An encompassing model was developed for predicting the steady-state forced convective CHF for water over a wide range of thermal-hydraulic conditions. A CHF model is postulated using a conceptual CHF map to define possible CHF mechanisms for given thermal-hydraulic conditions. Existing steadystate CHF correlations, for which the primary CHF mechanism modeled can be identified, are then used in conjunction with the conceptual CHF map to construct a predictive CHF model. The CHF correlations used as the foundation of this model are the Westinghouse-3, the Biasi, and the Modified-Barnett correlations. These correlations allow coverage of a wide range of thermal-hydraulic conditions, provide favorable comparison with experimental data, and are commonly used in the nuclear industry. The parametric ranges covered by the resultant model are

0.3 < P (MPa) <16.0

6.0 <D (mm) <30.0

100.0 <G (kg/m²·s) < 8000.0

−0.3 <X (dimensionless) < 1.0,where P is pressure; D, the hydraulic diameter; G, the mass flux; and X is quality. The CHF model compares favorably with available experimental data and was used to construct specific CHF maps.