Integrating STPA to NPP Systems Engineering Processes

STPA has demonstrated its usefulness in identifying hazards in NPP I&C systems. Its strengths lie in visualizing system-level control structures, uncovering interactions among technical components and human operators, and offering insights into complex feedback loops. We believe these strengths can be further leveraged by expanding the STPA method from its current focus on isolated I&C use cases to becoming a tool for broader Systems Engineering (SE) processes. By
doing so, STPA could offer valuable insights to support decision-making and planning across all SE phases.
This paper proposes enhancements to the STPA process that enable smoother integration into NPP SE, particularly within the V-model. A key contribution is the introduction of a fifth step in the STPA process, which translates loss scenarios into system requirements, connecting them to mitigation strategies and assigning responsible persons for follow-up. Additionally, we propose
establishing links to internal documentation and relevant regulatory frameworks. This should provide direct insight into for example important technical specifications of system elements and support the definition of system requirements. Further improvement suggestions include risk-based prioritization of loss scenarios, color-coded categorizations of interaction types, and grouping of common underlying risk factors in loss scenarios. These enhancements allow for more efficient analyses, targeted expert involvement, and foremost support the integration of STPA to all phases of NPP SE.