Risk-Informed Optimization of Equipment Fragility Under Ship Collision Accident in Floating Nuclear Power Plant

Abstract

Inspired by seismic probabilistic safety analysis, a systematic methodology for assessing the equipment fragility of floating nuclear power plants (FNPPs) under ship collision has been proposed for the first time. External event and fault tree models have been developed for FNPPs, and a comprehensive risk assessment has been performed to optimize equipment fragility, emphasizing safety and economy. The fragility analysis revealed similarities in valve fragility curves between seismic and ship collision scenarios. Under the current design, the FNPP exhibits an average core damage frequency (CDF) of $ 3.2 \times 10^{-9}$. Dominating the core damage sequences are off-site power failure superimposed on core makeup tank (CMT) failure and instrument and control (IC) system failure—findings corroborated by sensitivity analysis. Optimization analysis, focusing on equipment fragility parameters, demonstrated that evolutionary algorithms effectively assessed the disparity between the current design and licensing basis events (LBEs) regulatory limitings at both the cut-set and LBE levels. Simultaneously, the optimization framework enhanced safety and economic margins based on predefined objectives, providing valuable insights for correcting design deviations. As an integral part of the iterative risk-informed design, the proposed assessment and optimization will unfold as a multi-iteration process, progressively providing more refined risk insights to guide the ongoing design evolution.

Keywords: Risk-informed, FNPP, Ship collision, Fragility assessment, Multi-objective optimization