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Korean Standard Nuclear Power Plant Response to Common Mode Failure of the Digital Plant Protection System

Cheol Shin Lee, Chan Eok Park, Chul Jin Choi, Jong Tae Seo

Nuclear Technology

Volume 139 / Number 1 / July 2002 / Pages 42-49


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The Korean Standard Nuclear Power Plant (KSNP) has adopted the digital plant protection system (PPS) to enhance the reliability and safety of the plant. Although the digital PPS can be designed with high reliability, it is considered to be vulnerable to common mode failure (CMF) in the system software, resulting in a total loss of the built-in hardware redundancy. Therefore, a comprehensive evaluation has been performed to demonstrate the intrinsic capability of the KSNP design in coping with the design-basis events concurrent with CMF in the digital PPS. Instead of the conservative bounding analysis methodology, a best-estimate analysis methodology has been developed and utilized since the design-basis events accompanied by CMF in the digital PPS are categorized as beyond-design-basis events. An additional reactor trip function on high containment pressure in the diverse protection system (DPS), which is totally diverse from the PPS and is not affected by the CMF in the digital PPS, has been proposed to meet the acceptance criteria of the evaluation results. A variety of diverse means such as the DPS, process control systems, and operator actions including design modification have been verified to be effective in mitigating the design-basis events with CMF in the digital PPS.

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