NSUF 25-5279: Characterization of Pellet-Cladding Interface Damage of Spent Nuclear Fuel during Fatigue Bending
A typical light water reactor (LWR) fuel pin is composed of enriched uranium dioxide fuel pellets stacked inside a cladding tube made of zirconium alloy. In the pristine state, there exists a gap between the UO2 pellet and the cladding. However, neutron irradiation, fuel swelling and cladding creep down phenomena due to in-the-reactor conditions result in the closure of this pellet-cladding gap. Additionally, as fuel burnup increases, the chemical and mechanical bonding between the fuel and cladding results in the formation of an oxide layer. The objective of the proposed study is to investigate the role of the pellet-cladding interface in mechanical fuel rod degradation, especially under fatigue failure conditions. Under normal vibration conditions during transport to storage and disposal facilities, the spent nuclear fuel (SNF) rods experience cyclic loads, which can lead to rod failure over time. In this regard, the fatigue performance of SNF has previously been investigated at Oak Ridge National Laboratory (ORNL). The results have shown a clear indication of a non-uniform performance degradation of the fuel rods relative to cladding-only rod performance, where with increasing strain amplitudes, the fatigue performance of SNF rods approaches that of cladding only rods. This dependance on strain amplitude can be attributed to the fuel pellets inside the cladding tube which change the internal stress concentrations on the cladding at regions of pellet-pellet interfaces and intra-pellet cracks. A possible explanation could be that at high values of strain amplitudes, the pellet and the cladding are no longer bonded to each other, which in turn, decreases the stress concentrations at the pellet discontinuities. However, there is currently no qualitative analysis to substantiate this theory and no experimental evidence to show the evolution of pellet cladding bonding as a result of mechanical fuel failures. Through this proposal, we seek to elucidate the influence of pellet-cladding interface in fatigue failure by characterizing fuel rod cross-sections, failed at different strain amplitudes during fatigue testing. In addition, we propose to study different cross-section sites across the failed sample to study the evolution of pellet-cladding interface as a function of local stress/strain values for the same cycles to failure. We expect the pellet-cladding interface of the fuel rod samples failed at high strain amplitudes to show more crack damage, as compared to the samples failed at lower strain amplitude values under different cycles to failure. Optical microscopic characterization is the most efficient way to study the fuel surfaces as it involves minimal preparation (hot cell) time and yet presenting a direct method to probe fracture surfaces. The imaging steps will take around 6 months and a further 2 months will be required for data analysis.
Informações Adicionais
| Campo | Valor |
|---|---|
| Award Announced Date | 2025-08-06T10:09:36.977 |
| Awarded Institution | Oak Ridge National Laboratory |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | |
| PI | Yadukrishnan Sasikumar |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |