Research on thermal hydraulic behavior of small-break LOCAs in AP1000

In the present study, the response of AP1000 to a spectrum of cold leg small break LOCAs is simulated and analyzed using RELAP5/MOD3.4, including 2-in. break, 4-in. break, 8-in. break as well as 10-in. break which approaches the upper limit size for small break LOCAs in AP1000. Based on the calculation results, it indicates that the passive safety systems employed by AP1000, including CMTs, ACCs, IRWST, PRHRS and ADS, combine to provide continuous passive safety injection and residual heat removal. During cold leg small break LOCAs, the core uncovery and fuel heat up do not occur. The peak cladding temperatures (PCTs) during the accident process are far below the Appendix K limit value of 1478 K/2200 °F and meet the safety criterion. Results show that the accidental consequence can be mitigated effectively and thus the safety of AP1000 during cold leg small break LOCAs is proven.