Abstract

Automatic Depressurization System (ADS) is a very important part of passive core cooling system in passive safety nuclear plant AP1000. ADS have four stages with each stage having two series and only ADS4 utilizes squib valves. During the accident, emergency core injecting is realized by gravity driven passive safety injection system like makeup tank (CMT), accumulator and In-Containment Refueling Water Storage Tank (IRWST). The objective e of this study is to analyze the system response and phenomenon under part of failure of ADS in AP1000 LOCA. The plant model is built by using SCDAP/RELAP5/MOD 3.4 code. The chosen accident scenario is small and medium LOCAs followed by failure of ADS4 to open, whose location is different from the other three stages. The results indicate that long time core cooling from IRWST is postponed greatly through intentional depressurization only by ADS1, 2, 3. In addition, LOCAs with equivalent diameter 25.4 cm and 34.1 cm will not lead to core melt while 5.08 cm break LOCA will. Meanwhile, high water level in the pressurizer will appear during all of three LOCAs.

Keywords:

ADS , core melts, IRWST, LOCA, passive safety,

References

1. Bessette, D.E., 1999. Transition from depressurization to long term cooling in AP600 scaled integral test facilities. Nucl. Eng. Des., 238: 454-456.
   CrossRef    
2. Schulz, T.L., 2006. Westinghouse AP1000 advanced passive plant. Nucl. Eng. Des., 236: 1549.
   CrossRef    
3. USNRC, 2004. Final safety evaluation report to certification of the AP1000 standard design NUREG-1793, Initial Report.
   
4. Wright, R.F., 2007. Simulated AP1000 response to design basis small-break LOCA events in APEX-1000 test facility. Nucl. Eng. Technol., 39(4): 290-295.
   CrossRef    
5. Xu, Y., M. Ishii and M.A. Feltus, 2004. Safety analysis of multiple-failure of passive safety systems in ABWR-1200 SBLOCA. Nucl. Eng. Des., 230: 107-116.
   CrossRef    
6. Zhang, K., X.W. Cao, J. Deng, Z. Wang, L.C. Guo et al., 2008. Evaluation of intentional depressurization strategy in Chinese 600MWe PWR NPP. Nucl. Eng. Des., 238: 1725.
   CrossRef    

Competing interests

The authors have no competing interests.

Open Access Policy

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Copyright

The authors have no competing interests.