LAUSR

Abstract To predict the performance of the Safety Injection Tank (SIT) with Fluidic Device (FD) of APR1400 (Advance Power Reactor 1400) and its effect on Large Break Loss-of-Coolant Accident (LBLOCA) of APR1400, a model using two flow paths within the SIT is developed such that a flow path along the standpipe and a flow path through the connecting holes to mixing chamber of the FD can be simulated. A method to determine the hydraulic resistance of each flow path based on the hydrodynamic consideration is also developed. Since the method requires overall K-factor during high SIT flow phase and one during low SIT flow phase, the similarity of the hydrodynamics along the initial SIT pressure is evaluated assuming a simple isentropic process. The transition in those hydraulic resistances from the high flow phase to low flow phase are also considered in terms of K-factor of each flow path. From the course of estimating the overall K-factors, the modeling uncertainties are estimated. A good agreement with the test data and validity of the estimated uncertainty range are found from the calculation of the actual test using MARS-KS code and the present modeling. A LBLOCA of APR1400 plant is calculated using the present modeling scheme and the uncertainties of hydraulic resistance. Effect of nitrogen on cladding thermal response is discussed.