Advanced Nuclear Structural Materials Development for the Next Generation Reactor Applications

Advanced structural materials for the next generation nuclear reactors are facingenormous challenges from the crucial environments including very high operatingtemperature, higher neutron radiation damage and corrosive environment. Over the pastdecades, remarkable efforts have been devoted to find the promising candidate materials forthe various challenging new design of the advanced nuclear reactor systems.SiC has been one of the most promising and potential nuclear structural materials inboth fission and fusion reactors for it has numerous attractive properties, including resistanceto high neutron damage, low activation characteristics, excellent mechanical property andchemical resistance at high irradiation temperatures. Because large amount of radiationleakage during Fukushima Daiichi disaster was caused by hydrogen explosion induced fromthe oxidation of zircoloy cladding under high temperature, SiC is considered as thealternative candidate for the accident-tolerant fuel cladding materials in current commercialoperating light water reactors. However, the accumulation of irradiation induced defects canlead to unwanted microstructural changes such as crystalline-to-amorphous transformation,extrinsic and intrinsic stacking faults, void swelling at high temperature irradiation, as well aslattice expansion at low temperature irradiation. A 2% homogeneous lattice expansioninduced by large density of point defects is inevitable and thus should include inconsideration for the degradation of the cladding capability and mechanical properties of SiC.Therefore, a fundamental understanding of the production and evolution of radiation damagein SiC is crucial.Having been one of the worldwide leading research group in studying radiationdamage using high resolution TEM, we have successfully observed two types of irradiation-inducedplanar defects at high temperature by the annular bright-field (ABF) imagesincluding the extrinsic stacking fault loop with two offset SiC bilayers and the intrinsicstacking fault loop with one offset SiC bilayer. In this proposal, we intend to develop ascientific scheme to bridge the lattice expansion dynamic process and the atomic structure ofthe radiation-induced point defects and defect clusters through a combination of the state-of-the-art experimental techniques and theoretical calculations. Based on the experimental andsimulation outcomes from the ion-irradiated single crystal SiC material, we plan to establish aunique radiation-induced lattice expansion theory of this material at low temperatureirradiation and to explore the fundamental physical mechanism of SiC defect clusters andswelling phenomena.Coordinating the spherical aberration corrected scanning TEM (Cs-corrected STEM)by ABF method and Synchrotron based X-ray diffraction (XRD) analysis at glancing angle tocharacterize the lattice expansion, void swelling behavior and accurately determine the defectclusters under atomic scale TEM images for ion irradiated SiC to high dose at varioustemperature conditions. High resolution TEM will provide a direct visualization of the defectmicrostructures and XRD provides a larger regime of average information and quantitativelyresults. Besides the systematic experimental studies, molecular dynamic simulationperformed by LAMMPS as well as ab-initio model calculating the defect distribution intarget material will also be integrated into this research to probe the atomic-scale defectstructural evolution during irradiation. This thorough investigation coupled with our previousresults will allow us to approach the physical origin of the lattice expansion and defectclusters formation and lead to a profound understanding of irradiation effects on SiC.?