b'2.1 LWR FUEL FABRICATION AND PROPERTIESFabrication and Thermophysical Properties Evolutionin Chromium-doped UO 2Principal Investigator: Adrien J. Terricabras Team Members/ Collaborator: Joshua T. White, Scarlett Widgeon Paisner, Darrin D. BylerC hromium-doped UO 2fuels is anthe thermophysical properties. In industrially important Acci- particular, the thermal conductivity is dent Tolerant Fuel (ATF) dueof interest due to the high importance to the ability to increase the averageof this property for the safety of light grain size relative to standard UO 2 .water reactor (LWR) fuels. Although However, there is a lack of knowledgethe fabrication of the industry doped of the thermophysical properties offuel concepts is proprietary, LANL has these doped fuels, which is necessaryspent significant efforts in past years for accurately modeling the in-pileto develop a fabrication procedure performance. The work accomplishedto produce analogous samples. This this fiscal year focused on developingincludes carefully controlling the large grain Cr-doped UO 2pellets assintering atmosphere and chromium a function of Cr content and subse- content to fabricate fuels with large quently measuring the thermophys- average grain sizes, which has been ical and mechanical properties. Thefound to be 28 m and is dependent microstructural variations were alsoon the Cr concentration. The informa-investigated to evaluate chromiumtion from these measurements will formation within the microstructurebe fed into modeling efforts through of the sintered pellets. NEAMS to understand the perfor-Project Description: mance of these fuels under irradiation.Both the Nuclear Regulatory Commis- There has been particular interest on sion (NRC) and the Nuclear Energythe location of the Cr after sintering, Advanced Modeling and Simulationswhich has been hypothesized to either (NEAMS) program need thermo- accumulate at the grain boundaries physical and thermomechanical dataor may be incorporated into the UO 2of the Cr-doped UO 2system in orderlattice. The former has been inferred Figure 1. Grain morphologies of a) 750to validate information provided byfrom X-ray diffraction (XRD) patterns, ppm and b) 2500 ppm Cr-doped UO2industry. Because the data providedwhich is seen as a contraction of the as observed under SEM followingby industry is controlled as propri- lattice parameter. The Cr content, thermal etching etary information, NEAMS is notoxidation state, and location have able to use these data sets to developimplications on the fission gas release codes to study the performance. Toof the doped fuels upon irradiation. make this data widely available,The work accomplished here will be Los Alamos National Laboratoryunified into fuel performance code (LANL) is working on fabricatingsimulations of the doped fuels to Cr-doped, large grain UO 2pelletsassist in validating commercial codes and has collected measurements onprovided by industry partners.24 2022|AFC ACCOMPLISHMENTS'