Prediction of performance of Safety Injection Tank with Fluidic Device using a model of two flow paths and its effect on LBLOCA

- A model of the Safety Injection Tank with Fluidic Device was developed for analysis of LBLOCA of APR1400.
- Both the standpipe and the connecting holes to mixing chamber of Fluidic Device were simulated to be appropriate to MARS-KS code.
- A variable hydraulic resistance was determined at each flow path based on the hydrodynamic consideration.
- Introduction of the Nitrogen gas into the reactor core and its effect on cladding thermal response was discussed.

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.