b'3.3 SCANNING ELECTRON MICROSOPY EXAMINATIONSScanning Electron Microscopy Examinationsof Advanced Metallic Fuel Forms Principal Investigators: Luca CapriottiTeam Members/ Collaborators: Tammy L. Trowbridge, Fidelma Di Lemma and Jan-Fong JueScanning electronI n sodium fast neutron spec- redistribution. Additives, such as Pd trum nuclear reactors, metallichave been suggested to bind lantha-microscopy on severaluranium-based alloys have oftennide fission products, effectively innovative fuel designsbeen chosen because of their highreducing FCCI. Sodium bonding is have revealed insightsfissile density, high thermal conduc- considered undesirable at the back on their microstructuretivity, and reactor safety benefits. Inend of the fuel cycle where sodium and have shown goodorder to address increasingly highbonded fuel must be treated to remove performance in pile atburnup / performance demands, asodium prior to geological disposi-low burnup. number of innovative fuel designstion. Helium bonded metallic fuel of are under investigation within theseveral alloys has been irradiated to Advanced Fuels Campaign (AFC). Asbetter understand the implications of part of this development, candidateremoving sodium bonding. Finally, fuel compositions and forms arelow smear density fuel is necessary irradiated in a cadmium-shroudedto enable high (30 at.%) burnup and positions at the INLs Advanced Testboth solid and annular low smear Reactor (ATR), and they are subse- density fuels have been examined.quently examined at the MaterialPostirradiation examination (PIE) Fuel and Complex (MFC) facilities. and microscopy exams such as Recent irradiation experiments havescanning electron microscopy (SEM) explored new alloys and geometrichave been completed on several forms beyond what has histori- advanced fuel forms from the AFC-3 cally been irradiated (U-10Zr, 75%series experiments to assess the smeared density, sodium bonded fuel)performance in pile, characterize to overcome two primary limitingthe microstructure evolution under performance factors: high swellingirradiation and to compare the rate at higher burnup and fuel clad- overall behavior with metallic fuel ding chemical interaction (FCCI)literature. Metallic fuel alloys investi-from lanthanides fission products. gated are U-10Zr annular fuel and Project Description:helium bonded, Pd bearing metallic The innovative fuels design, exploredfuel in solid and annular form. in these experiments, fall into variousAccomplishments: categories: alternative alloying metals,Recently performed SEM characteriza-additives, sodium bond removal, andtion on two annular metallic fuel lower smear densities. For alternativespecimens, U-10Zr irradiated to 4.3 alloys, Zr has been substituted with%FIMA (Fission per Initial Metal elements that stabilize the cubic phaseAtom) and U-13Zr-4Pd irradiated of U such as Mo to prevent constituentto 2.7 %FIMA, have provided first 134 2020|AFC ACCOMPLISHMENTS'