Advanced characterisation of stress corrosion cracking in long-term aqueous storage of 20-25Nb AGR cladding
Lead Research Organisation:
University of Bristol
Department Name: Physics
Abstract
"This PhD project funded by Sellafield and the UKRI iCase scheme will use advanced microscopy to characterise the corrosion behaviour of 20-25Nb steels used in advanced gas cooled reactor (AGR) fuel cladding during long-term storage. The student would be based in the Interface Analysis Centre (IAC) at the University of Bristol, within the Materials Degradation research group of Dr Tomas Martin.
Following its lifetime in-reactor, AGR fuel is discharged and stored pending a decision on the disposition route. Presently, Sellafield store AGR fuel within a caustic dosed pond until future routes, such as geological disposal, may be carried out. During storage, the 20-25Nb steel AGR cladding provides the primary containment for the radioactivity within the fuel. Intergranular attack (IGA) of the fuel cladding does not occur whilst in-reactor as it is too hot and dry, however, during storage within aqueous environments IGA may occur if chromium depletion due to irradiation and/or thermal annealing becomes severe enough. This can lead to intergranular stress corrosion cracking (IGSCC) and eventual cracking of the clad material.
The aim of the proposed work is to both characterise AGR fuel cladding to support long term storage of AGR fuel, as well as to evaluate the suitability of a thermally sensitised proxy material (such as 304 steel) for the study of corrosion mechanisms and behaviours. The project would build on recent work that has utilised the power of the high-speed atomic force microscope (HS-AFM) developed at Bristol IAC to observe the evolution of stress corrosion cracking of steel alloys in real time. SCC observations will be performed by HS-AFM at the University of Bristol on proxy material and irradiated clad. This will allow us to compare the two materials corrosion behaviour in real-time in-situ observations, to better predict SCC behaviour,
We will also compare irradiated ex-service AGR 20-25Nb steel cladding samples to thermally sensitised proxy samples using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques including electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS). The project will also take advantage of the newly funded plasma focused ion beam (PFIB) at Bristol to characterise crystallography and chemistry in 3D. "
Following its lifetime in-reactor, AGR fuel is discharged and stored pending a decision on the disposition route. Presently, Sellafield store AGR fuel within a caustic dosed pond until future routes, such as geological disposal, may be carried out. During storage, the 20-25Nb steel AGR cladding provides the primary containment for the radioactivity within the fuel. Intergranular attack (IGA) of the fuel cladding does not occur whilst in-reactor as it is too hot and dry, however, during storage within aqueous environments IGA may occur if chromium depletion due to irradiation and/or thermal annealing becomes severe enough. This can lead to intergranular stress corrosion cracking (IGSCC) and eventual cracking of the clad material.
The aim of the proposed work is to both characterise AGR fuel cladding to support long term storage of AGR fuel, as well as to evaluate the suitability of a thermally sensitised proxy material (such as 304 steel) for the study of corrosion mechanisms and behaviours. The project would build on recent work that has utilised the power of the high-speed atomic force microscope (HS-AFM) developed at Bristol IAC to observe the evolution of stress corrosion cracking of steel alloys in real time. SCC observations will be performed by HS-AFM at the University of Bristol on proxy material and irradiated clad. This will allow us to compare the two materials corrosion behaviour in real-time in-situ observations, to better predict SCC behaviour,
We will also compare irradiated ex-service AGR 20-25Nb steel cladding samples to thermally sensitised proxy samples using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques including electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS). The project will also take advantage of the newly funded plasma focused ion beam (PFIB) at Bristol to characterise crystallography and chemistry in 3D. "
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/Y528687/1 | 30/09/2023 | 29/09/2028 | |||
| 2919795 | Studentship | EP/Y528687/1 | 02/06/2024 | 01/06/2028 | KAMIL ULATOWSKI |