NSUF 13-412: STEM/LEAP Study of Fission Product Transportation in Neutron Irradiated TRISO Fuel Particles
The objective of the proposed project is to build a complete understanding of the active fission product (FP) release mechanisms from intact TRISO fuel, with a primary focus on the release of Ag, by determining the distribution of FPs in the silicon carbide (SiC) layer of irradiated TRISO fuel. TRISO fuel is the fuel of choice of the Very High Temperature Gas Reactor concept and is composed of a spherical UO2/UC fuel kernel, carbon buffer layer, and successive isotropic layers of inner pyrolytic carbon, SiC, and outer pyrolytic carbon. During operation the SiC layer serves as the main metallic fission product (FP) barrier, however during operation multiple FP have been observed to be released from intact fuel. Release of FPs limits the fuel operating lifetime, reducing the reactor economics and creates significant safety and maintenance concerns. To date little direct evidence on the responsible mechanisms for release of specific FPs have been identified. Confirming the active release mechanisms is the first step to development of engineering solutions to mitigate release, ultimately improving reactor economics and safety. This work builds off of previous work from the collaborators from the University of Wisconsin-Madison (UW) and Idaho National Laboratory (INL). The work at UW has focused on computational experiments and simulated Ag diffusion experiments and observed grain boundary (GB) fast diffusion and precipitate transport to be active transport mechanisms. The initial advanced microscopy conducted by the INL collaborators at the Electron Microscopy Laboratory (EML) at the Materials and Fuels complex (MFC) at INL has indicated similar active transport mechanisms in real irradiated fuel from the AGR-1 irradiation campaign at INL, but have not been able to identify Ag in the system due to characterization technique limitations. The proposed work will utilize the advanced analytical capabilities housed at CAES to investigate the composition of FP precipitates and the composition of FPs segregated to GBs in the SiC layer of irradiated TRISO fuel from the AGR-1 irradiation campaign. Specifically, scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) and local electrode atom probe (LEAP) will be employed. STEM-EELS will be utilized to investigate multiple features of interests providing an overview of the FP distribution throughout the SiC layer, while LEAP will be employed to gain insight on fine scale features such as precipitates < 2nm in diameter and GB concentrations where the GB width is < 0.5 nm. Insight on the chemistry of FP features decorating the SiC layer will provide insight on which mechanisms are responsible for the release of specific FPs from intact fuel. This will ultimately support the development of TRISO fuel for the advanced gas reactor fuel qualification and development project and provide direct evidence of the release mechanisms.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of the proposed project is to build a complete understanding of the active fission product (FP) release mechanisms from intact TRISO fuel, with a primary focus on the release of Ag, by determining the distribution of FPs in the silicon carbide (SiC) layer of irradiated TRISO fuel. TRISO fuel is the fuel of choice of the Very High Temperature Gas Reactor concept and is composed of a spherical UO2/UC fuel kernel, carbon buffer layer, and successive isotropic layers of inner pyrolytic carbon, SiC, and outer pyrolytic carbon. During operation the SiC layer serves as the main metallic fission product (FP) barrier, however during operation multiple FP have been observed to be released from intact fuel. Release of FPs limits the fuel operating lifetime, reducing the reactor economics and creates significant safety and maintenance concerns. To date little direct evidence on the responsible mechanisms for release of specific FPs have been identified. Confirming the active release mechanisms is the first step to development of engineering solutions to mitigate release, ultimately improving reactor economics and safety. This work builds off of previous work from the collaborators from the University of Wisconsin-Madison (UW) and Idaho National Laboratory (INL). The work at UW has focused on computational experiments and simulated Ag diffusion experiments and observed grain boundary (GB) fast diffusion and precipitate transport to be active transport mechanisms. The initial advanced microscopy conducted by the INL collaborators at the Electron Microscopy Laboratory (EML) at the Materials and Fuels complex (MFC) at INL has indicated similar active transport mechanisms in real irradiated fuel from the AGR-1 irradiation campaign at INL, but have not been able to identify Ag in the system due to characterization technique limitations. The proposed work will utilize the advanced analytical capabilities housed at CAES to investigate the composition of FP precipitates and the composition of FPs segregated to GBs in the SiC layer of irradiated TRISO fuel from the AGR-1 irradiation campaign. Specifically, scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) and local electrode atom probe (LEAP) will be employed. STEM-EELS will be utilized to investigate multiple features of interests providing an overview of the FP distribution throughout the SiC layer, while LEAP will be employed to gain insight on fine scale features such as precipitates < 2nm in diameter and GB concentrations where the GB width is < 0.5 nm. Insight on the chemistry of FP features decorating the SiC layer will provide insight on which mechanisms are responsible for the release of specific FPs from intact fuel. This will ultimately support the development of TRISO fuel for the advanced gas reactor fuel qualification and development project and provide direct evidence of the release mechanisms. |
| Award Announced Date | 2013-03-15T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Alina Zackrone, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Izabela Szlufarska |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 412 |