Investigation of Fission Product Interaction with the SiC Containment Layer of High Turnup TRISO Fuel Particles

Journal Article · Wed Jun 15 00:00:00 EDT 2016 · Transactions of the American Nuclear Society

OSTI ID:22992158

Seibert, Rachel L.; Terry, Jeff ^[1]; Parish, Chad M.; Terrani, Kurt ^[2]

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1. Illinois Institute of Technology, 3105 S. Dearborn St., Chicago, IL, 60616 (United States)
2. Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN, 37831 (United States)

Tri-structural Isotropic (TRISO) encapsulated fuel particles are used in high-temperature gas-cooled nuclear reactors. Fuel performance is limited by the propensity of metallic fission products to be released under high temperature testing to simulate hypothesized accident scenarios. The current particle design consists of a 350 μm or 425 μm UO{sub 2} or UCO fuel kernel surrounded by a 100μm porous carbon buffer layer, a 40μm inner pyrolytic carbon (IPyC) layer, a 35μm high-density silicon carbide (SiC) layer, and a 40μm outer pyrolytic carbon (OPyC) layer. Of interest is the fission product interaction with the SiC layer, which provides the most structural support and is the main barrier to the diffusion of fission products. Previous laboratory examination studies have indicated the release of Ag through seemingly intact particles and the localized corrosion of the SiC due to Pd. Although a number of studies have been conducted, the specifics of both the Ag and Pd reaction mechanisms, in addition to U and Pu, through SiC are currently not well understood. This work aims to understand the pathways and kinetics of these interactions under normal operation as well as accident conditions. In order to improve our understanding of this, we have the unique opportunity to examine irradiated TRISO particles to study post-irradiation effects on these materials. Experimental data is necessary to constrain the current models used to predict the behavior of fission products in the SiC layer of TRISO fuels. This work aims to understand the interaction of fission products with the SiC containment layer in TRISO particles. We have systematically examined three SiC shells from irradiated TRISO particles using XAFS, TEM, and EDS. Results indicate the formation of palladium silicides, and uranium and plutonium carbides. Additionally, silver is seen to be metallic. Preliminary microscopy results indicate fission products throughout the SiC layer of the TRISO particles, and microstructural changes have been observed between the as-irradiated and safety tested particles. These results have provided key information on the fission product transport behavior through irradiated SiC at varying temperatures. Knowledge of these reaction pathways will allow for better simulation of the long-term behavior of TRISO fuels. They may also suggest ways to modify the SiC layer to improve fuel performance and mitigate fission product release, which is critical for safety strategies required to commercialize these nuclear fuel technologies. (authors)

• OSTI ID: 22992158
• Journal Information: Transactions of the American Nuclear Society, Vol. 114, Issue 1; Conference: Annual Meeting of the American Nuclear Society. Embedded topical meeting 'Nuclear fuels and structural material for the next generation nuclear reactors', New Orleans, LA (United States), 12-16 Jun 2016; Other Information: Country of input: France; 12 refs.; Available from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 United States; ISSN 0003-018X
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
CORROSION
FINE STRUCTURE
FISSION PRODUCT RELEASE
FISSION PRODUCTS
FUEL PARTICLES
IRRADIATION
MICROSTRUCTURE
NUCLEAR FUELS
PALLADIUM SILICIDES
PYROLYTIC CARBON
REACTORS
SILICON CARBIDES
STEADY-STATE CONDITIONS
TRANSMISSION ELECTRON MICROSCOPY
URANIUM DIOXIDE
X-RAY SPECTROSCOPY