b'Thermophysical and Mechanical Property Assessment of UB 2and UB 4 ; Constituent Phases for Advanced LWR FuelsPrincipal Investigator: Erofili Kardoulaki, LANLTeam Members/ Collaborators: Josh White, Darrin Byler, David Frazer, Adi Shivprasad and Tarik Saleh (LANL),Tiankai Yao, Bowen Gong, Jie Lian (Rensselaer Polytechnic Institute)This highlight marksU ranium diboride (UB2) andAccomplishments 2and two uranium tetraboride (UB4)Four uranium boride samples were the completion of theare candidate constituentsanalyzed using RUS: two UBbaseline thermophysicalfor multi-phase accident tolerant fuelUB 4 . RUS measurements were made at and mechanical property(ATF) due to their anticipated highconstant amplitude using a National assessment for uraniumthermal conductivity. These fuels haveInstruments NI, PXIe 1075 function boride phases, candidatehigh uranium density that contributesgenerator. Frequency generation and phases for LWR fuels. to fission, and by tailoring the ratio ofspectra acquisition were managed by 10B/11B, can also act as an integratedthe Resonance Inspection Techniques burnable poison. Understandingand Analysis (RITA) software package the thermophysical and mechanicaldeveloped at Los Alamos National properties of uranium borides, forLaboratory (LANL)[1]. The elastic which only limited data are availableconstants were calculated from a spec-in the literature, is of importance totrum using the Rayleigh-Ritz method determine their accident tolerance. from the resonance frequencies [24]. Project description Assuming each sample was comprised This highlight outlines the completionof a polycrystalline, isotropic mate-of the thermophysical and mechanicalrial, the independent moduli are C11 property assessment of UB2 andand C44 and macroscopic quantities, UB4 synthesized via arc melting andsuch as bulk (K), shear (G), and sintered to high densities via sparkYoungs (E) moduli, as well as Poissons plasma sintering (SPS). The highratio, were calculated as was done in density SPS samples were used toprevious work [36]. From the RUS measure the thermal diffusivity viaresults, the Debye temperatures of laser flash analysis (LFA) and thermalthe uranium borides were calculated expansion via dilatometry of UB2 andusing methods detailed in the literature UB4 and, in conjunction with specific[7]. Nanoindentation was performed heat literature data, their thermalwith a Hysitron TM Triboindenter TM conductivities were calculated from(Minneapolis, USA) in load-controlled 298 to 1773 K. Finally, resonancemode with an indent load of 15 mN. ultrasound spectroscopy (RUS) andThe indents were performed with nanoindentation (NI) were performeda diamond Berkovich tip that was to investigate the mechanical propertiescalibrated with fused silica prior of the uranium borides, thus giving ato indentation on the UB 2and UB 4complete picture on their propertiesspecimens. The nanoindentation curves and sufficient data to assess them aswere analyzed using the Oliver and candidate fuel phase constituents forPharr method [8] and measuring the light water reactors (LWRs).reduced modulus and hardness of the specimens. The elastic modulus of the 60 2019|AFC ACCOMPLISHMENTS'