Abstract
During the service lifetime of nuclear reactors, key reactor materials such as graphite and zircaloy-4
degrade under the action of fast neutrons. Fast neutrons generated in the reactor core during fission
interact with graphite and zircaloy-4 leading to the production of point defects in these materials. The
point defects transform into stable extended defects such as dislocation loops under the continual action
of fast neutrons with the passage of time. Once at this stage, the physical and mechanical properties
of the materials change, leading to a departure of the materials from their innate structural integrity.
This compromises the safe operation of reactors and results in a reduction of their lifetimes.
To overcome this limitation in key reactor materials, better radiation resistant materials are needed.
These materials need to be developed. Their development however, requires a fundamental understanding
in the mechanisms driving their degradation. Neutrons in reactor environments and ions in
accelerator environments are primarily used to gauge the radiation resistance of reactor materials with
the aim of unraveling the driving mechanisms behind their degradation. In this work, graphite and
zircaloy-4 were exposed to 2 MeV protons and 4 MeV deuterons with the aim of investigating the
e↵ects of these charged particles on these key materials. Optical microscopy (OM), Scanning Electron
Microscopy (SEM), X-Ray Di↵raction (XRD), Micro-focus X-ray Computed Tomography (μXCT), and
Raman Spectroscopy (RS) were used to characterize the e↵ects of irradiation.
Before irradiation, OM and SEM revealed that graphite is a material made up of binder and filler
particles, and it shows a porosity with random distribution in size and shape. Whilst in zircaloy-4,
OM and SEM revealed a material made up of narrow and elongated crystallites. Post irradiation SEM
revealed graphite’s microstructure to have remained relatively intact, except for a few microcracks
observed within the binder phase of the proton irradiated sample. XRD revealed in both proton and
deuteron irradiated graphite a slight decrease in the interlayer spacings, a decrease in crystallite sizes,
and relaxation of the residual stresses. With Raman analysis of proton and deuteron irradiated graphite,
the disorder peak (the so-called D band) indicative of the presence of defects was observed. The increase
in the ratio of the disorder to graphitic peaks (ID/IG) confirmed the induced damage in the materials
after irradiation. μXCT in proton irradiated graphite revealed an increase in porosity.
Post irradiation SEM in zircaloy-4 revealed a massive transformation in its microstructure. Melting and
cracking were observed in both proton and deuteron irradiated zircaloy-4. This observation suggests
that heating e↵ects on the material were dominant. While the enlargement of crystallites in proton
irradiated graphite were revealed by SEM, in deuteron irradiated zircaloy-4 the e↵ect of irradiation on
crystallite size was difficult to observe due to the melt layers presenting on the surface as ridge like
formations. With XRD however, crystallite sizes of both proton and deuteron irradiated zircaloy-4 were
shown to have increased. This was confirmed by the peaks narrowing after irradiation. The interlayer
spacings in proton irradiated zircaloy-4 increased while in deuteron irradiated zircaloy-4 decreased. XRD
unfortunately also revealed the presence of zirconium carbide (ZrC) after irradiation in zircaloy-4. It...
M.Phil. (Energy Studies)