An operating-experience–augmented fragility framework for SiC in TRISO fuel

This study develops an operating-experience (OpE)–augmented fragility framework to evaluate silicon carbide (SiC) layer degradation in TRISO fuel for pebble bed reactors. Intrinsic SiC fragility is anchored using a normalized hybrid synthetic brittleness index (NHSBI) regression as a deterministic material-state descriptor. OpE effects, including persistent thermal exposure, transient temperature gradients, and localized cycling, are represented through physically interpretable amplification multipliers. Parametric evaluations are performed under AVR-anchored operating conditions with explicit treatment of epistemic uncertainty arising from sparse high-temperature data. Results indicate that short-duration thermal excursions typically produce modest amplification when considered in isolation, whereas persistent boundary-condition degradation and coupled mechanical–chemical processes provide plausible pathways to risk-relevant tail behavior. The framework links intrinsic material state, operating phenomena, and functional performance loss, and identifies key data and modeling requirements needed to support quantitative fuel-performance assessment and comparative and bounding evaluations of operating conditions. A demonstrative calculation is provided to illustrate framework implementation and sensitivity to operating-experience conditions.