Advanced scattering techniques for the investigation of radiation-induced damage in nuclear materials

Young, Ela (2022). Advanced scattering techniques for the investigation of radiation-induced damage in nuclear materials. University of Birmingham. Ph.D.

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Abstract

Harsh fission and fusion reactor environments lead to radiation damage in nuclear materials in the form of nanoscale precipitation events. Such microstructural changes can ultimately compromise macroscopic material properties. Understanding the evolution of nuclear material properties over their operational lifetime is crucial for the provision of safe, reliable nuclear power generation.

This thesis aims to demonstrate how advanced scattering techniques can contribute to the understanding of nanoscale transitions in nuclear materials systems. It focuses on materials of interest in the current nuclear landscape where knowledge gaps and contradictions exist on the structural and compositional properties of both thermal ageing induced and irradiation induced precipitates. Specifically, it presents novel applications of small angle scattering (SAS) techniques to the study of both thermal ageing induced and irradiation induced precipitation damage to showcase the versatility of SAS for characterising the differences between the two mechanisms of precipitation damage. The systems of interest are
life-limiting nuclear materials such as low alloy reactor pressure vessel (RPV) steels and tungsten as a fusion plasma-facing material. These material systems were chosen as they are critical for the future of nuclear power generation (advanced light water fission reactors and commercial fusion reactors) where there is an industry requirement to increase the understanding of how thermal ageing induced and irradiation induced precipitation damage can lead to adverse material property evolution.

A high Ni RPV weld thermally aged for 100 000 hours at 330 ◦C was studied using SAS to complement previous findings from other investigative techniques. Magnetic precipitates with mean radius 2.01 ± 0.06 nm were observed using small angle neutron scattering. The first use of anomalous small angle x-ray scattering on this RPV material system allowed for the explicit consideration of the role of iron and vacancies on thermal ageing induced precipitation which is often omitted in literature.

A series of model Fe-Cu-Mn-Ni RPV alloys were thermally aged to elucidate the role of alloying elements on precipitate nucleation and growth. SAS was used to extract precipitate properties and also for a novel in-situ ageing study on the kinetics of precipitation. The structure and likely composition of thermal ageing induced precipitates was confirmed. It was found that Mn suppresses precipitate growth in the presence of Cu and Ni during thermal ageing. A comparison between the mechanisms of thermal ageing and irradiation induced precipitation was made.

A novel proton irradiation configuration was used to investigate transmutation reactions and precipitation damage in pure tungsten. Displacement damage up to 0.414 dpa was reached, with small fractions of rhenium, osmium and tantalum transmuted during irradiation. Due to the limited transmutation, the matrix damage was identified, using SANS, as a network of spherical nanoscale voids that increase in size and volume fraction with increasing damage in irradiated tungsten.

Material hardening and embrittlement due to the presence of nanoscale precipitates has been quantified for each material system using microindentation and nanoindentation hardness techniques.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):