Simulation and analysis on 10-in. cold leg small break LOCA for AP1000

Abstract The AP1000 is a two-loop 3400 MWt advanced passive plant developed by the Westinghouse Electric Corporation. A series of passive safety systems are adopted to provide significant improvements in plant simplification, safety and reliability. However, thermal hydraulic characteristics of AP1000 during small break LOCAs have not been fully understood and further investigation is still required. In this study, modeling and nodalization of primary loop, necessary secondary loop and passive core cooling system (PXS) for AP1000 were conducted and a 10-in. cold leg small break LOCA was analyzed using RELAP5/MOD3.4. Some main transient parameters were obtained, including RCS pressure, break flow, passive safety injection flow and cladding temperature, etc. Further, the calculated results were compared with that of NOTRUMP code developed by Westinghouse and an acceptable agreement was obtained. Results indicated that the actuation of passive safety systems could mitigate the accidental consequence of small break LOCAs effectively. The key thermal hydraulic parameters were in the acceptable range and met the safety criterion. During the accident process, the core uncovery and fuel heat up did not occur and thus the safety of AP1000 during a 10-in. cold leg small break LOCA was proven.