The Science

A missing puzzle piece for future fusion reactors is structural materials that can withstand extreme operating conditions. For example, reactors are bombarded by neutrons from fusion reactions. This weakens reactor materials over time. Using capabilities at two Department of Energy (DOE) user facilities, this research investigated the accumulated radiation damage in silicon carbide. This material shows promise for fusion reactors and other structures that are exposed to extremely high temperatures. Researchers first exposed beams of the material to physical stresses. Next, they exposed the beams to radiation at high temperatures in the High Flux Isotope Reactor (HFIR). They then examined the defects caused by radiation using high-energy X-ray diffraction at the National Synchrotron Light Source-II (NSLS-II). The results identified atomic-scale deformation in the material. This deformation was most apparent where stress had been applied.

The Impact

This is the first experimental observation of the details of the atomic structure of this material as it begins to accumulate radiation damage. Scientists could not identify these atomic-scale details in previous studies. Earlier work relied on transmission electron microscopy. At the nanoscale, many times larger than the atomic scale, scientists using transmission electron microscopy could only observe uniform clusters of defects. The X-ray diffraction analysis in this new work detects how defects are oriented due to mechanical strain and radiation. It also detects the shape of the clusters of defects that form in the crystal structure. This detailed information will help fusion scientists build models to predict how materials will perform for future fusion reactors.

Summary

The degradation of fusion reactor core structural materials as a result of energetic neutron bombardment is one of the highest hurdles to realizing a nuclear fusion reactor. Since there are currently no fusion devices for experimental materials research, the development and qualification of candidate materials requires fundamental understanding of degradation processes in simulated environments. The present results showcase an in-depth examination of radiation damage at the microscopic scale, where researchers can see the origin of material degradation.

This first-of-its-kind research finding of the anisotropic damage structure in irradiated silicon carbide was realized by a combination of unique capabilities and expertise at HFIR at Oak Ridge National Laboratory and NSLS-II at Brookhaven National Laboratory, both DOE Office of Science user facilities. In addition, the research fills the purpose of the development of materials for both nuclear fusion and fission reactors because of the common technology challenges of irradiation-induced degradation. Support from multiple research programs brought diverse expertise in irradiation experiments, X-ray diffraction analysis, and the physics of irradiation damage processes. This cross-cutting research elevates the fundamental understanding of radiation damage mechanisms in silicon carbide, an important step forward in the development of future fusion reactor core structural materials.

Funding

This research was supported by the DOE Office of Fusion Energy Sciences and the Research Foundation for the State University of New York at Stony Brook. This research was also supported by the DOE Office of Nuclear Energy, the Advanced Fuels Campaign of the Nuclear Technology R&D program at Oak Ridge National Laboratory (ORNL) and by the DOE Office of Nuclear Energy Idaho Operations Office as part of a Nuclear Science User Facilities experiment. This research used the X-ray Powder Diffraction beamline at the NSLS-II, a DOE Office of Science user facility operated by Brookhaven National Laboratory. A portion of this research used resources at the HFIR, a DOE Office of Science User Facility operated by ORNL.

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