FAST NEUTRON IRRADIATION-INDUCED FAST NEUTRON IRRADIATION-INDUCED DAMAGE ON GRAPHITE AND ZIRCALOY- DAMAGE ON GRAPHITE AND ZIRCALOY-

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TSHEPO MAHAFATSHEPO MAHAFAUniversity of JohannesburgUniversity of Johannesburg

Supervisor: Dr Emanuela Carleschi (UJ)Supervisor: Dr Emanuela Carleschi (UJ)

Co-Supervisor: Dr Chris Franklyn (Necsa)Co-Supervisor: Dr Chris Franklyn (Necsa)

Energy Postgraduate Conference 2013Energy Postgraduate Conference 201311 – 14 August 201311 – 14 August 2013

iThembaLABS,Faure, Western CapeiThembaLABS,Faure, Western Cape

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

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Burnup Increase per Generation

20 - 25 GWd/tU

20 - 25 GWd/tU

To support higher burnups, improved radiation resistant materials

Need to be developed.

Gen II

Gen I

Gen III

Gen IV

50 - 60 GWd/tU

50 - 60 GWd/tU 50 - 60 GWd/tU

50 - 60 GWd/tU 100 - 200 GWd/tU

100 - 200 GWd/tU

Increase in burnup leads to:

More power generated per fresh fuel

Less fuel needed for fission and reduced fuel costs

Less spent fuel for storage and disposal

GWd/tU – GigaWatt day per ton of Uranium

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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

IAEA, 2010

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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.

GraphiteGraphite

Irradiation Hardening and

Embrittlement

Irradiation Growth

Void Swelling

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

Zircaloy-4Zircaloy-4

Hydrogen Induced Embrittlement

Irradiation Growth

Irradiation Creep

Stress Corrosion Cracking

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Experimental Approach

Sample DamageSample 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 TechniquesCharacterisation 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)

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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?

THANK YOU!THANK Y

OU!

THANK YOU! THANK YOU!

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