| The objective of this study is to give a best-estimate prediction of transient critical heat flux (CHF) during reactor transients and hypothetical accidents. To accomplish this task, a predictional method has been developed. Basically it involves the thermal-hydraulic calculation of the heated core with boundary conditions supplied from experimental measurements. CHF predictions were based on instantaneous "local-conditions" hypothesis and eight correlations (consisting of round-tube, rod-bundle, and transient correlations) were tested against most recent blowdown heat-transfer test data obtained in major U.S. facilities. A summary of the prediction results is presented in Table 10 where both CISE and Biasi correlations are found to be capable of predicting the early CHF of (TURN)1 s. The Griffith-Zuber correlation is credited for its prediction of the delay CHF which occurs in a more tranquil state with slowly decaying mass velocity. In many instances, the early CHF can be well correlated by the x = 1.0 criterion; this is certainly indicative of an annular-flow dryout type crisis. The delay CHF was found to occur at near or above 80% void fraction, and the success of the modified Zuber pool-boiling correlation suggests that this CHF is caused by flooding and pool-boiling type hydrodynamic crisis. |
