NSUF 15-581: STEM/EELS Study of Fission Product Transport in Neutron Irradiated TRISO Fuel Particles
The proposed study aims to obtain local charge states of fission products and irradiated SiC through scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and to ascertain the influence of such charge states on fission product transport in the irradiated SiC layer of TRISO coated particles. During neutron irradiation, point defects are generated in SiC and these point defects can have effective charge. In addition, the accumulation of charged point defects in the matrix leads to the formation of an internal effective electrical field. In such a locally charged matrix, the fission products may also carry an effective charge. The internal electrical field in the matrix may affect the diffusion process of charged fission products. Different mechanisms have been proposed for transport of fission products (especially Ag) through the SiC layer of TRISO coated fuel particles. However, the possible effect of effective charge has not been considered or studied. Our proposed project will be the first effort to study the possible effect of charge state on fission product transport, and new mechanisms for fission product transport may be identified. This project is anticipated to significantly contribute to enhancing the understanding of the mechanisms of fission product transport in irradiated SiC layer of the TRISO particles. The project will include three sets of samples, i.e., unirradiated TRISO particles, irradiated TRISO particles with low Ag release, and irradiated TRISO particles with high Ag release. The STEM/EELS study on unirradiated SiC will provide a reference for the charge states in SiC. STEM/EDS studies will also be performed on irradiated TRISO particles to first locate Ag-containing fission products, since EDS is more advantageous than EELS for studying heavy elements such as Ag and Pd. After identifying the Ag fission products, EELS will be implemented on those fission products and the irradiated SiC matrix immediately surrounding and far way from them. EELS will also be performed on areas in the SiC matrix without Ag containing fission products, to establish any differences in charge states between the areas in the SiC matrix with and without Ag. Attention will also be given to the potential differences in charge states between GBs and grain interiors. Furthermore, the comparisons between irradiated TRISO particles with low and high Ag release will establish potential link between the different transport behavior and the potential differences in charge states. STEM samples of unirradiated TRISO particles and irradiated TRISO particles with low and high Ag release have all been prepared and the samples are currently stored at MaCS, CAES. Significant amount of STEM/EDS studies have been performed on irradiated TRISO particles with low and high Ag release. STEM/EELS will be performed on unirradiated TRISO particles, and STEM/EDS/EELS will be executed on irradiated TRISO particles, using FEI Tecnai G2 F30 FEG (S)TEM at MaCS, CAES. The proposed research will be performed at MaCS, CAES in ten work days in Aug 2015 and Sep 2015.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed study aims to obtain local charge states of fission products and irradiated SiC through scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and to ascertain the influence of such charge states on fission product transport in the irradiated SiC layer of TRISO coated particles. During neutron irradiation, point defects are generated in SiC and these point defects can have effective charge. In addition, the accumulation of charged point defects in the matrix leads to the formation of an internal effective electrical field. In such a locally charged matrix, the fission products may also carry an effective charge. The internal electrical field in the matrix may affect the diffusion process of charged fission products. Different mechanisms have been proposed for transport of fission products (especially Ag) through the SiC layer of TRISO coated fuel particles. However, the possible effect of effective charge has not been considered or studied. Our proposed project will be the first effort to study the possible effect of charge state on fission product transport, and new mechanisms for fission product transport may be identified. This project is anticipated to significantly contribute to enhancing the understanding of the mechanisms of fission product transport in irradiated SiC layer of the TRISO particles. The project will include three sets of samples, i.e., unirradiated TRISO particles, irradiated TRISO particles with low Ag release, and irradiated TRISO particles with high Ag release. The STEM/EELS study on unirradiated SiC will provide a reference for the charge states in SiC. STEM/EDS studies will also be performed on irradiated TRISO particles to first locate Ag-containing fission products, since EDS is more advantageous than EELS for studying heavy elements such as Ag and Pd. After identifying the Ag fission products, EELS will be implemented on those fission products and the irradiated SiC matrix immediately surrounding and far way from them. EELS will also be performed on areas in the SiC matrix without Ag containing fission products, to establish any differences in charge states between the areas in the SiC matrix with and without Ag. Attention will also be given to the potential differences in charge states between GBs and grain interiors. Furthermore, the comparisons between irradiated TRISO particles with low and high Ag release will establish potential link between the different transport behavior and the potential differences in charge states. STEM samples of unirradiated TRISO particles and irradiated TRISO particles with low and high Ag release have all been prepared and the samples are currently stored at MaCS, CAES. Significant amount of STEM/EDS studies have been performed on irradiated TRISO particles with low and high Ag release. STEM/EELS will be performed on unirradiated TRISO particles, and STEM/EDS/EELS will be executed on irradiated TRISO particles, using FEI Tecnai G2 F30 FEG (S)TEM at MaCS, CAES. The proposed research will be performed at MaCS, CAES in ten work days in Aug 2015 and Sep 2015. |
| Award Announced Date | 2015-08-10T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Haiming Wen |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 581 |