NSUF 19-1785: Microstructural characterizations of in-core molten salt irradiated TRISO particles
As a part of Integrated Research Project of fluoride salt-cooled high-temperature reactors (FHRs), surrogate (uranium-free) TRISO particles with ZrO2 kernels were tested in Li-7 enriched FLiBe salt (2LiF-BeF2) at 700°C for 1000 hours in the Massachusetts Institute of Technology research reactor (MITR) for their performance in the extreme environment similar to the FHRs. Optical microscopy observation found cracks on the outer pyrocarbon coating layer of some post-irradiation/corrosion TRISO particles. However, the effect of high-temperature molten salt in-core irradiation on the inner microstructure, particularly the coating layers, has not been analyzed due to the limited availability of high-resolution microscopes for irradiated samples on campus. The TRISO samples in this study are the surrogate TRISO (ZrO2 kernel) particles previously irradiated in molten FLiBe salt in graphite crucible in the MITR core at 700°C for 1000 hours. The overall neutron fluence was estimated 1.3E20 n/cm2 thermal and 4.3E20 n/cm2 fast (E>0.1MeV). These particles have been extracted from molten salt after irradiation, and cleaned by soaking in deionized water. The facilities of Focused Ion Beam (FIB), Electron Backscatter Diffraction (EBSD), Scanning/Transmission Electron Microscope (S/TEM, Titan Themis 200 or Talos F200X) equipped with super-X Energy Dispersive X-ray Spectroscopy (EDS) and Electron Energy Loss Spectroscopy (EELS) systems at INL-IMCL will be employed to determine the GB character, categorize high/low angle GBs, and coincident site lattices (CSL) and non-CSL GBs, and microchemistry. Four foils will be lift out from different locations of irradiated and non-irradiated particle samples, and then further milled by using FIB. The misorientation angle will be identified by EBSD. The microstructure and microchemistry at the GB will be analyzed using TEM and STEM/EDS/EELS on the lift-out lamellas. Through the PIE in this project, we will get better understanding of the TRISO fuels behavior in the accident conditions of broken pebble fuel in the FHR environment, which is critically important for the R&D of the FHRs.
Additional Info
| Field | Value |
|---|---|
| Abstract | As a part of Integrated Research Project of fluoride salt-cooled high-temperature reactors (FHRs), surrogate (uranium-free) TRISO particles with ZrO2 kernels were tested in Li-7 enriched FLiBe salt (2LiF-BeF2) at 700°C for 1000 hours in the Massachusetts Institute of Technology research reactor (MITR) for their performance in the extreme environment similar to the FHRs. Optical microscopy observation found cracks on the outer pyrocarbon coating layer of some post-irradiation/corrosion TRISO particles. However, the effect of high-temperature molten salt in-core irradiation on the inner microstructure, particularly the coating layers, has not been analyzed due to the limited availability of high-resolution microscopes for irradiated samples on campus. The TRISO samples in this study are the surrogate TRISO (ZrO2 kernel) particles previously irradiated in molten FLiBe salt in graphite crucible in the MITR core at 700°C for 1000 hours. The overall neutron fluence was estimated 1.3E20 n/cm2 thermal and 4.3E20 n/cm2 fast (E>0.1MeV). These particles have been extracted from molten salt after irradiation, and cleaned by soaking in deionized water. The facilities of Focused Ion Beam (FIB), Electron Backscatter Diffraction (EBSD), Scanning/Transmission Electron Microscope (S/TEM, Titan Themis 200 or Talos F200X) equipped with super-X Energy Dispersive X-ray Spectroscopy (EDS) and Electron Energy Loss Spectroscopy (EELS) systems at INL-IMCL will be employed to determine the GB character, categorize high/low angle GBs, and coincident site lattices (CSL) and non-CSL GBs, and microchemistry. Four foils will be lift out from different locations of irradiated and non-irradiated particle samples, and then further milled by using FIB. The misorientation angle will be identified by EBSD. The microstructure and microchemistry at the GB will be analyzed using TEM and STEM/EDS/EELS on the lift-out lamellas. Through the PIE in this project, we will get better understanding of the TRISO fuels behavior in the accident conditions of broken pebble fuel in the FHR environment, which is critically important for the R&D of the FHRs. |
| Award Announced Date | 2019-05-14T16:48:20.107 |
| Awarded Institution | Center for Advanced Energy Studies |
| Facility | Microscopy and Characterization Suite |
| Facility Tech Lead | Alina Zackrone, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Guiqiu Zheng |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1785 |