Jiang, Menghan
(2023)
Radiation effects in pyrochlore-based
glass-ceramics.
PhD thesis, University of Liverpool.
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Abstract
Safe and reliable management of nuclear waste is one of the key components if energy from nuclear is to become a primary energy source. The current strategy involves immobilizing high-level nuclear waste from spent nuclear fuel in a glass or ceramic wasteform. Nuclear wasteforms used to immobilize the actinides must remain stable for long geological timescales. Pyrochlore-based glass-ceramics have the potential to be the novel nuclear wasteforms. In order to evaluate the performance of glass-ceramic wasteforms during long-term storage and compare with pure ceramics wasteforms, in this thesis, radiation effects from α-decay events have been investigated in Gd2Ti2O7 and Y2Ti2O7 glass-ceramic composites using accelerated ion beams. Separate effect of He accumulation was studied in Gd2Ti2O7 glass-ceramics, showing that the helium bubbles with an average bubble size of 1.2 nm were formed within the ceramic ma trix at 1.1 × 1017 He/cm2 (15 at.%). While no helium bubbles were observed in glass phase due to their higher diffusion coefficient. Besides, helium bubbles preferred to nucleate near glass-ceramic interfaces and accumulate along ceramic grain boundaries. Separate effect of α-recoil damage was also studied in Y2Ti2O7 glass-ceramics, showing that the fully amorphization of pyrochlores occurred at 5 × 1014 Au/cm2, indicating Y2Ti2O7 glass-ceramics retain comparable radiation tolerance as Y2Ti2O7 ceramics. The phase transformation to the defect-fluorite structure was observed at the interface between pristine and irradiated regions. In relevant geological environments, the waste forms will experience modifications due to synergistic effects produced by α-recoil’s displacive damage and He accumulation. Combined effects of α-recoil damage and He accumulation were studied in pre-damaged Y2Ti2O7 glass-ceramics, showing that the accumulation of He can lead to the nucleation of helium bubbles within the amorphous Y2Ti2O7 ceramic phase at a critical concentration of 3.4 at.%, corresponding to 45,000 years of 20 wt.% 239Pu loading. Hence, amorphization caused by α-recoil damage may occur before helium bubble nucleation. To the best of our knowledge, the works related to the radiation damage in glass-ceramics are very limited, and this being the first one to present radiation damage and He accumulation in pyrochlore-based glass-ceramics.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Engineering |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 23 Aug 2023 15:25 |
| Last Modified: | 23 Aug 2023 15:25 |
| DOI: | 10.17638/03170943 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3170943 |
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