Abstract
Designed to contain fission products during irradiation and off-normal accident scenarios, tristructural isotropic (TRISO) particles are a robust fuel form consisting of a uranium-containing kernel surrounded by a multilayered shell. Although often overlooked as a sacrificial layer, the buffer layer's response to irradiation can affect the stress state, temperature distribution, and fission product transport throughout the other layers—potentially leading to particle failure. Therefore, it is imperative that we understand the irradiation-induced micro- and nanostructural changes that govern the fracture and densification behavior of the buffer layer. Here, we perform high-fidelity three-dimensional characterization of the buffer microstructure on several AGR-2 TRISO particles exposed to a range of irradiation conditions. We find evidence of several irradiation-condition dependent mechanisms which directly impact the buffer densification and fracture response. Densification occurs through reduction in porosity—accounting for less than ∼25 % of buffer densification—and nanostructural changes in the pyrocarbon matrix facilitated by irradiation creep. Particles exposed to higher fluences have greater proportions of densification attributed to nanostructural changes in the pyrocarbon matrix. Low-temperature particles exhibit porosity reduction near the kernel (localized densification) from compressive stresses exerted by kernel expansion. We also find evidence of irradiation condition dependent mechanisms leading to buffer fracture. The circumferential fractures close to the kernel are correlated with high concentrations of solid fission products and bands of ultra-low porosity—both observed in low-temperature particles. The high fracture fractions recorded in high-fluence, low-temperature particles are attributed to reduced fracture toughness from higher porosity and less irradiation creep than the high-fluence, high-temperature particles.
| Original language | English |
|---|---|
| Article number | 155565 |
| Journal | Journal of Nuclear Materials |
| Volume | 605 |
| DOIs | |
| State | Published - Feb 2025 |
Funding
We thank Dr. John Hunn and the AGR program for providing the samples used in this study. We also thank Dr. Grant Helmreich, Dr. Eddie Lopez, and Dr. Katherine Montoya for the useful discussions. We acknowledge the financial support from the Department of Energy, Nuclear Energy University Program (DoE-NEUP) (Grant No. DE-NE0008979). CG acknowledges support from the Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract number DE-SC0014664. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05\u201300OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). We thank Dr. John Hunn and the AGR program for providing the samples used in this study. We also thank Dr. Grant Helmreich, Dr. Eddie Lopez, and Dr. Katherine Montoya for the useful discussions. We acknowledge the financial support from the Department of Energy, Nuclear Energy University Program (DoE-NEUP) (Grant No. DE-NE0008979 ). CG acknowledges support from the Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract number DE-SC0014664 . This manuscript has been authored by UT-Battelle, LLC , under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
Keywords
- Failure
- FIB/SEM tomography
- Irradiation
- Porous carbon
- Pyrocarbon buffer
- TRISO nuclear fuel particle buffer