Abstract
We have investigated microstructure and microchemistry of precipitates and <c> dislocation loops in high-burnup M5® using (scanning) transmission electron microscopy ((S)TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Two (S)TEM lamellae were made by cryo-FIB from the same cladding sample. The Nb-rich native precipitates were found in the metal, in the suboxide and in the oxide. Upon diffraction analysis, most of the Nb-rich native precipitates in the metal matrix remain as β-Nb phase, while no β-Nb native precipitates were found in the oxide. Nearby the oxide and metal (O/M) interface, the native precipitates in the oxide were already oxidized into t-NbO2 phase. At further distance away from the O/M interface, the Nb-rich native precipitates were gradually oxidized and became amorphous. Besides the native precipitates, Nb-rich irradiation induced precipitates (IIPs) were found in the metal matrix. Using g = <0002> vector for imaging, the length of the IIPs was aligned with <c> dislocation loops. However, no Nb segregation to the <c> dislocation loops themselves was observed. For the first time, we report that IIPs indeed exist in the oxide but only within about 1.5 µm away from O/M interface. However, the oxidation state of the IIPs in the oxide is still unclear. The presence of both native precipitates and IIPs in the oxide may indicate the Nb concentration in the oxide solid solution remain low nearby the O/M interface, which may explain the reduced corrosion kinetics of in-pile M5®. On the other hand, no IIPs were observed in the oxide at further distance and this may indicate that they have eventually dissolved back into the oxide. A few mechanisms related to IIPs stability in the oxide are presented.
| Original language | English |
|---|---|
| Article number | 152667 |
| Journal | Journal of Nuclear Materials |
| Volume | 544 |
| DOIs | |
| State | Published - Feb 2021 |
Funding
This work was supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07- 051D14517 as part of a Nuclear Science User Facilities experiment. Support of the NRC Faculty Development program is acknowledged. The author would like to thank Kurt A. Terrani and Kory D. Linton for providing opportunities to work at ORNL, and Jesse W. Werden for his effort to make the cryo-FIB function properly. The electron microscopy was also carried out using facilities and instrumentation at the UW that are partially supported by the NSF through the Materials Research Science and Engineering Center (DMR-1121288 and DMR-1720415). We would also like to thank Michael Moorehead for the proofreading of this paper. This work was supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07- 051D14517 as part of a Nuclear Science User Facilities experiment. Support of the NRC Faculty Development program is acknowledged. The author would like to thank Kurt A. Terrani and Kory D. Linton for providing opportunities to work at ORNL, and Jesse W. Werden for his effort to make the cryo-FIB function properly. The electron microscopy was also carried out using facilities and instrumentation at the UW that are partially supported by the NSF through the Materials Research Science and Engineering Center (DMR-1121288 and DMR-1720415). We would also like to thank Michael Moorehead for the proofreading of this paper.
| Funders | Funder number |
|---|---|
| Michael Moorehead | |
| National Science Foundation | |
| U.S. Department of Energy | DE-AC07- 051D14517 |
| Office of Nuclear Energy | |
| Oak Ridge National Laboratory | |
| National Research Council | |
| Materials Research Science and Engineering Center, Harvard University | DMR-1121288, DMR-1720415 |