Performance assessment of safety injection tank with fluidic device during LBLOCA

Safety Injection Tank (SIT) with Fluidic Device (FD) has been developed for APR1400 nuclear power plants to improve a safety performance during Large Break Loss-of-Coolant Accident (LBLOCA). The mixing chamber inside the FD was designed to control the flow resistance and combine the flow through the supply port of the stand pipe and the control port of the FD. It enabled to achieve a longer passive safety injection than the existing accumulator by its characteristic flow phases, such as the high flow injection phase, the subsequent low flow injection phase and the transition flow one between them. During the review process of APR1400 plants, the performance and uncertainty of the SIT safety injection, the possibility of nitrogen intrusion of the SIT into the reactor core and the comprehensive impact of the aforementioned factors on the LBLOCA have been highlighted. In this study, a pipe component model for the SIT with FD was developed for MARS-KS 1.4 calculation and the flow resistance ranges of the model to cover the measurement data from the Shin Kori Unit 3 test was derived. The performance and uncertainty issues of the SIT with FD raised during the review process of APR1400 plants has been assessed in the present study. A pipe component model was developed to simulate variable hydraulic resistance changes of the SIT with FD. The local K-factor for the stand pipe and the connecting holes were determined based on the SIT discharge test performed at Shin Kori Unit 3.