b'knowledge of material behavior and irradiation-induced phenomena helpsa) b)the prediction of its performance.Project Description:Safety and transient testing to evaluate performance under off-normal condi-tions is an essential pillar for both the development of Accident Tolerant Fuels (ATF) and the optimization of fuel operation economics beyond current discharge burnups. The knowledge of the initial microstruc- the fuel and the connections betweenFigure 2. (a) Image quality (IQ) and (b) ture of both fuel and cladding allowsthose conditions and the pre-transientinverse pole figure (IPF) maps taken a more robust interpretation of theirradiation history have hindered theat radial positions r/r0 = 0.550.60 at the interface between the central subsequent transient testing results,development of a fully mechanisticrestructured area and the non-provides validation of the physicalfragmentation and pulverizationrestructured regionphenomena underlying the modelcriterion. In this context, the scope of predictions, and eliminates the uncer- the present work is to apply a wide tainties related to the limited knowl- portfolio of advanced characterization edge of the sample status before thetechniques to determine properties test, which has been shown to havethat are relevant for safety and perfor-significant impact on the transientmance of high burnup UO 2 .testing outcomes. One example is theAccomplishments:phenomenon of fine fragmentationA fuel sample from a legacy high that occurs in UO 2light-water reactorburnup rod available at Idaho National (LWR) fuel during a Loss of CoolantLaboratory (INL) has been analyzed Accident (LOCA) [1]. The amountusing multiple experimental tech-of fine fragmentation increases withniques. Three macro-areas have been burnup, which has raised safetyinvestigated: (1) fuel microstructure concerns due to the increased likeli- including grain subdivision and hood of dispersal of such small fuelporosity distribution, (2) thermal particles after cladding burst and dueproperties and (3) micro-mechanical to the increased transient fission gasproperties. The sample had an average release [2]. Therefore, efforts havepellet burnup of 76 GWd/tHM been devoted to the assessment ofand was cut from the high-power the pulverization threshold that couldregion of the mother rod. Images of determine the conditions under whichthe entire fuel radius were collected fine fragmentation is predominantusing a Thermo Fischer Helios [37]. However, the lack of informa- Plasma Focused Ion Beam (PFIB) and tion regarding the initial conditions ofprocessed via image analysis to obtain 2021|AFC ACCOMPLISHMENTS 55'