Sensitivity analysis of APR-1400's Reactor Protection System by using RiskSpectrum PSA

Highlights: • This paper focuses on the APR-1400 and aims to improve the reliability of its RPS system. • The study was carried out using Risk Spectrum PSA. • From 171 initiating events, trends and case studies for the 3 most sensitive elements in RPS were constructed. • CCF-TCB, Operator and CC-DOP were found to be the most potent events in reducing RPS failure probability. - Abstract: The Advanced Pressurized Water Reactor (1400) offers greater power output than its predecessor, the Optimized Power Reactor (OPR-1000), hence required increased reliability and design limitations of its protection systems to be licensed for commercial operation. One of these systems is the Reactor Protection System (RPS), a set of subsystems and methods designed to fortify the integrity of the reactor. Compromise of RPS safety could stem from possible failures of subsystems, natural hazards, inadequate application of mitigation measures or human error. Probabilistic Safety Assessment is an effective and indispensable part of Nuclear Safety that is used within the assessment of RPS reliability. Alongside other techniques, it incorporates the use of fault-tree analysis to determine failure rates of top-events, but it requires input data in the form of initiating events. Unfortunately, accurate data on initiating events is hard to obtain and therefore, the use of conservative values was the norm in most studies. This signifies the importance of studying a handful of values around these conservative values. This paper focuses ontheAPR-1400 and aims to investigate the most promising elements to improve the reliability of its Reactor Protection System (RPS). The study was carried out using Risk Spectrum PSA, a tool used in more than 50% of nuclear reactors around the world. From 171 initiating events, trends and case studies for the 3 most sensitive elements in RPS were constructed and discussed. CCF-TCB, Operator and CC-DOP were found to be the most potent events in reducing RPS failure probability. This research should give an insight on how to tackle RPS-enhancements for future designs of Nuclear Power Plants.