NSUF 17-CINR-12957: X-ray Characterization of Atomistic Defects Causing Irradiation Creep of SiC
Silicon carbide (SiC)-based accident tolerant fuel (ATF) cladding of light water reactors is continuing to undergo development at ORNL under support of the Office of Nuclear Energy’s Advanced Fuels Campaign, Fuel Cycle Research & Development program. An important task is the establishment of the thermo-mechanical analysis capability to predict in-pile performance and failure probability of the cladding. Irradiation creep is known to be a key property to model the stress state under irradiation. In short, and especially for SiC materials that possess very limited strain tolerance, irradiation creep provides an important stress mitigating function.We have experimentally evaluated neutron irradiation creep of SiC materials at 380–800°C up to 30 dpa, using a bend stress relaxation test in the HFIR. In addition, we conducted an in-pile instrumentation creep experiment of SiC at 300°C in the Halden facility. Analysis revealed that (1) irradiation creep strain was very small when compared to metals, (2) transient irradiation creep operated below ~1 dpa, and (3) secondary creep operated with a stress-normalized creep rate of ~1×10-7 [dpa MPa]-1 beyond the initial transient. Our study showed that the irradiation creep behavior could be modeled by anisotropic evolution of multi-dimensional radiation defects due to the applied stress. However, the microstructures observed by transmission electron microscopy (TEM) could not fully support this model, potentially due to the presence of atomistic defects which cannot be observed by conventional TEM. Since the creep mechanism is not physically well understood, a previous parametric thermo-mechanical analysis on SiC composites did not provided an accurate result.To better understand the radiation creep mechanism from an atomic point of view, we propose to conduct synchrotron-based X-ray diffraction (XRD) experiments on SiC neutron irradiated with and without applied stress at the National Synchrotron Light Source-II (NSLS-II). The world-class high brightness of the X-ray source and the high-resolution analysis capability at the XRD beamline enable accurate structural determination of the irradiated SiC materials. First, we will conduct powder XRD and pair distribution function (PDF) experiments in year one, followed by a small angle x-ray scattering experiment (SAXS) in year two. We expect peak shifting and/or peak broadening in the XRD patterns, depending on the magnitude of the applied stress under radiation. Analysis of such stress effects withquantitative XRD methods (such as Rietveld refinement) will provide better understanding of irradiation creep of SiC. More specifically, quantification of changes in the lattice swelling due to the applied stress will enable us to improve our proposed mechanistic creep model. The size, shape and number density of the small atomic-scale defects (0.5-2 nm in size) will be determined from the SAXS experiments. Characterization of these defects will also aid in confirming our assumption that anisotropic evolution of multi-dimensional radiation defects has a non-negligible effect on the radiation-induced creep.
Additional Info
| Field | Value |
|---|---|
| Award Announced Date | 2024-01-16T09:38:43.453 |
| Awarded Institution | Oak Ridge National Laboratory |
| Facility Tech Lead | |
| Irradiation Facility | |
| PI | Takaaki Koyanagi |
| PI Email | [email protected] |
| Project Type | CINR |
| RTE Number | 3052 |