FAST NEUTRON IRRADIATION-INDUCED
DAMAGE ON GRAPHITE AND ZIRCALOY- 4
TSHEPO MAHAFA
University of Johannesburg
Supervisor: Dr Emanuela Carleschi (UJ)
Co-Supervisor: Dr Chris Franklyn (Necsa)
Energy Postgraduate Conference 2013
11 – 14 August 2013
iThembaLABS,Faure, Western Cape
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Basic Nature of Radiation Damage



The interaction of fast
neutrons with atoms of the
material
results
in
the
displacement of atoms from
their positions.
The initial atom to be
displaced from its lattice site,
the PKA (primary knock-on
atom) continues along the
lattice path knocking more
atoms off their sites.
This in essence leads to the
creation of a cascade of
displaced atoms.
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Reactor Technology Development
T. Abram and S. Ion, Energy Policy 36(2008) 43234330
4
Burnup Increase per Generation
GWd/tU – GigaWatt day per ton of Uranium
5
Reactor Operating Regime as a function of
Temperature and Radiation Dose
Thermal Reactors – Gen II and III
reactors
OPERATING ON A LOWER
RADIATION AND
TEMPERATURE RANGE
High Temperature Reactor (HTR)
and Fast Reactor – Gen IV
OPERATING ON A HIGHER
RADIATION AND
TEMPERATURE RANGE
6
Radiation Damage Effects in Materials
The continual irradiation of materials by fast neutrons translates into the evolution of the materials
microstructure that leads eventually to the physical property changes seen in those materials.
Graphite

Irradiation Hardening and
Embrittlement
Zircaloy-4

Hydrogen Induced Embrittlement
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Irradiation Growth
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Irradiation Growth
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Irradiation Creep
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Void Swelling
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Stress Corrosion Cracking
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Irradiation Creep
The main object of the project is to understand the underlying mechanism that govern the
radiation damage that leads to these effects that are very damaging to the nuclear power
reactors
7
Experimental Approach
Sample Damage


The Graphite and Zircaloy-4
samples would be exposed to
fast neutrons to induce the
damage in a Radio-Frequency
Quadropole accelerator located
at Necsa.
The accelerator delivers a flux of
1012 neutrons per seconds, within
an energy range of 1-10MeV's.
Characterisation Techniques

Pre
and
post
irradiation
examination of the samples
would be carried out.
The following techniques will be
used:

Scanning Electron Microscopy
(SEM)

X-Ray Diffraction (XRD)

Raman Spectroscopy

Focussed Ion-Beam and
Scanning Electron Microscopy
(FIB-SEM)
8
Unirradiated Graphite and Zircaloy-4 Samples
SEM Image of Graphite
SEM Image of Zircaloy-4
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Radiation Damage Impact on Nuclear Reactors

Reduced Lifetime of the reactor

Compromised Safety

Increase in downtime

Increased lifecycle costs
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ANY QUESTIONS?