Peridynamic assessment of damage evolution in a full UO2 fuel pellet under RIA-like equivalent thermal-expansion loading

Reactivity-initiated accidents (RIA) in light water reactors subject UO 2 fuel pellets to rapid thermal transients that can induce fracture and fragmentation. Existing peridynamic (PD) models for nuclear fuel require coupled thermal solvers or imported temperature fields, limiting their utility for rapid parametric screening. The study does not propose a new peridynamic constitutive formulation; rather, it presents a numerically verified and sensitivity-assessed reduced-order peridynamic screening workflow for a full three-dimensional UO 2 pellet, in which the equivalent expansion magnitude and loading rate can be controlled independently. A bond-based peridynamic model with critical stretch-based bond breakage is applied to a full cylindrical pellet (radius 5 mm, height 10 mm) with a pre-existing crack. Equivalent radial thermal expansion is imposed by prescribing a radial velocity on the outer surface corresponding to target temperatures of 1000–2500 °C and loading durations of 10–80 ms, without solving the temperature field. Numerical sensitivity analyses showed that crack-extension and percentile-based local-damage measures were more robust than absolute global damaged-volume fractions, while the principal final-state metrics varied by less than approximately 3.1% over the investigated horizon-ratio range. Independent implementation-level benchmarks quantified the affine-displacement error of the baseline formulation as 10.49% and showed that the finite-width-corrected LEFM fracture stress was bracketed by microscopic first-bond failure and subsequent macro-damage onset. Uniform effective cold- and hot-side property envelopes changed the principal final-state damage metrics by no more than approximately 2.2%, while the normalized crack-extension measure remained unchanged. An axial-loading diagnostic showed that symmetric axial expansion increased the energy-corrected full-domain broken-bond fraction by 85.9%, while normalized crack extension and severe mid-plane damage remained unchanged. The results indicate that damage severity generally increases with target temperature, while loading duration modifies the damage morphology and local severity through the imposed radial velocity. The largest severe-damage fractions occur in selected high-temperature cases at shorter and intermediate loading durations. The equivalent thermal-expansion approach isolates pellet-scale damage sensitivity to prescribed displacement magnitude and loading rate, providing a preliminary screening tool for selecting cases that may require higher-fidelity multi-physics analysis. This work addresses a gap in the literature by demonstrating an equivalent-expansion damage map and computational triage methodology for RIA-like radial expansion conditions.