A Study of Critical Flowrate in the Integral Effect Test Facilities

In earlier studies, most of the information available in the literature was either for a saturated two-phase flow or a sub-cooled water flow at medium pressure conditions, e. g., up to about 7.0 MPa. The choking is regarded as a condition of maximum possible discharge through a given orifice and/or nozzle exit area. A critical flow rate can be achieved at a choking under the given thermo-hydraulic conditions. The critical flow phenomena were studied extensively in both single-phase and two-phase systems because of its importance in the LOCA analyses of light water reactors and in the design of other engineering areas. Park suggested a modified correlation for predicting the critical flow for sub-cooled water through a nozzle. Recently, Park et al. performed an experimental study on a two-phase critical flow with a noncondensable gas at high pressure conditions. Various experiments of critical flow using sub-cooled water were performed for a modeling of break simulators in thermohydraulic integral effect test facilities for light water reactors, e. g., an advanced power reactor 1400MWe (APR1400) and a system-integrated modular advanced reactor (SMART). For the design of break simulators of SBLOCA scenarios, the aspect ratio (L/D) is considered to be a key parameter to determine the shape of a break simulator. In this paper, an investigation of critical flow phenomena was performed especially on break simulators for LOCA scenarios in the integral effect test facilities of KAERI, such as ATLAS and FESTA. In this study, various studies on the critical flow models for sub-cooled and/or saturated water were reviewed. For a comparison among the models for the selected test data, discussions of the comparisons on the effect of the diameters, predictions of critical flow models, and break simulators for SBLOCA in the integral effect test facilities were presented