Mechanistic CHF model development based on the liquid sublayer dryout model for flow boiling phenomena under IVR-ERVC conditions

In this work a mechanistic critical heat flux (CHF) model was developed based on the liquid sublayer dryout (LSD) model, designed to predict CHF in downward-facing flow boiling conditions, particularly the operational environment of In-Vessel Retention through External Reactor Vessel Cooling (IVR-ERVC). For accurate CHF prediction using the LSD model, several key parameters were properly defined: relative velocity between liquid and vapor, slug length, liquid velocity, and liquid sublayer thickness. In this study, these parameters were interpreted from the perspective of vapor slug dynamics, which have been well characterized through prior experimental observations. The developed CHF model was validated against previous well-established experimental results, including ULPU, FIRM, MIT, and KAIST experiments, with the CHF model demonstrating excellent predictability with a root mean square error of 14.53%.