FAST NEUTRON IRRADIATION-INDUCED DAMAGE ON GRAPHITE AND ZIRCALOY- 4

1. FAST NEUTRON IRRADIATION-INDUCED DAMAGE ON GRAPHITE AND ZIRCALOY- 4 TSHEPO MAHAFA University of Johannesburg Supervisor: Dr EmanuelaCarleschi (UJ) Co-Supervisor: Dr Chris Franklyn (Necsa) Energy Postgraduate Conference 2013 11 – 14 August 2013 iThembaLABS,Faure, Western Cape

2. 2 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.

3. 3 Reactor Technology Development T. Abram and S. Ion, Energy Policy 36(2008) 43234330

4. 4 Burnup Increase per Generation To support higher burnups, improved radiation resistant materials Need to be developed. Gen IV 100 - 200 GWd/tU Gen III 50 - 60 GWd/tU Gen II 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 50 - 60 GWd/tU Gen I 20 - 25 GWd/tU GWd/tU – GigaWatt day per ton of Uranium

5. 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 IAEA, 2010

6. Zircaloy-4 Hydrogen Induced Embrittlement Irradiation Growth Irradiation Creep Stress Corrosion Cracking 6 Radiation Damage Effects in MaterialsThe 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 • 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

7. 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. 8 Unirradiated Graphite and Zircaloy-4 Samples SEM Image of Zircaloy-4 SEM Image of Graphite

9. Reduced Lifetime of the reactor Compromised Safety Increase in downtime Increased lifecycle costs 9 Radiation Damage Impact on Nuclear Reactors

10. 10 THANK YOU! THANK YOU! ANY QUESTIONS? THANK YOU! THANK YOU!