A Mechanics-Based Sensitivity Analysis of Nuclear Piping Stress Under Design-Parameter Uncertainty

Design deviations introduced during the fabrication and installation of nuclear-grade piping systems can alter structural response and substantially increase reanalysis effort. This study develops a mechanics-based framework to identify critical parameters controlling the code-stress ratio of a representative nuclear piping system. Finite-element analysis, Monte Carlo sampling, and Sobol global sensitivity analysis were combined to evaluate the effects of gravity, thermal-pressure loading, and seismic excitation. The results show that parameter sensitivity is strongly load-dependent. Under Level-A conditions, the response is governed mainly by constrained thermal deformation, and the dominant parameters are support locations that control deformation compatibility and the redistribution of secondary stress. By contrast, structural and weight-related parameters have only limited influence in this regime. Under Level-D conditions, however, the governing mechanism shifts to inertia-driven amplification. The dominant variables then become those associated with dynamic constraint, concentrated mass, and eccentric loading, including key support positions, valve eccentricity, and valve weight. Multi-parameter analyses further reveal clear interaction effects, showing that simultaneous deviations in critical supports, concentrated masses, or eccentricities can significantly amplify the stress response and, in some cases, drive the stress ratio beyond the allowable limit. These results show that the mechanical importance of design parameters depends on both the loading regime and system-level parameter interactions, and they provide a quantitative basis for condition-specific tolerance allocation in nuclear piping design.