PTS thermal-hydraulic resoponse during a postulated MSLB accident of Kori Unit 1

The present study primarily aims to evaluate the system thermal hydraulic and thermal mixing behavior in downcomer of a postulated Main Steam Line Break (MSLB) as one of the major PTS initiators in PTS Evaluation of Kori Unit 1. For this purpose, the MSLB event sequences were reviewed and the most severe event sequence was selected based on the peer review on design and operational features. Based on the present design and operating condition of Kori Unit 1, a base calculation of the most severe sequence of MSLB events is conducted using RELAP5 and the sensitivity of the thermal-hydraulic mixing in downcomer was also investigated. The current result shows an overall downcomer fluid cooling from 558 .deg. K to 436 .deg. K. From the sensitivity analysis results, it is found that the thermal mixing could be affected by the downcomer modeling