Safeguards-by-design evaluation of HALEU TRISO–pebble fuel fabrication using a distribution-based modeling approach

High-assay low-enriched uranium (HALEU) fuel fabrication introduces safeguards challenges due to heterogeneous material forms and coupled process–measurement variability that are not well captured by conventional bulk accountancy approaches. This work presents a safeguards-by-design computational framework based on a distribution-based representation of material, in which stochastic process transformations and measurement realizations are propagated consistently to generate temporally resolved inventory difference (ID) and standard error of ID (SEID). The framework integrates physics, measurement, and detection layers within a unified workflow and is applied to a TRISO–pebble fuel fabrication facility based on publicly available design information. The analysis demonstrates that safeguards performance is governed by the interaction of process variability, measurement uncertainty, and accountancy structure, with key design implications for measurement placement, MBA segmentation, MBP selection, and alarm configuration under false alarm probability constraints. The results show that preserving process-level heterogeneity, prioritizing high-impact measurement points, and accounting for throughput-dependent effects are critical for maintaining detection sensitivity. Overall, the framework provides a transparent and flexible approach for evaluating and informing safeguards-by-design decisions in advanced fuel fabrication facilities.