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Microstructural characterisation of Irradiated Nuclear Graphite using FE Analysis A. T. Bakenne , A. N. Jones, B. J. Marsden and G. N. Hall Nuclear Graphite Research Group, The University of Manchester. Background. Graphite is an allotrope of carbon.

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  1. Microstructural characterisation of Irradiated Nuclear Graphite using FE Analysis A. T. Bakenne, A. N. Jones, B. J. Marsden and G. N. HallNuclear Graphite Research Group, The University of Manchester UNTF 2010 University of Salford 14th - 16th April 2010

  2. Background • Graphite is an allotrope of carbon. • Nuclear graphite is used within a reactor as a moderator and reflector material. • NBG-10 and PCEA - new nuclear graphites, candidates for Gen-IV technology reactor components. • During operation graphite will experience significant property changes such as dimensional change and Young’s modulus. • Property changes occur as a function of fast neutron irradiation and temperature can lead to component distortion and high internal stresses. UNTF 2010 University of Salford 14th - 16th April 2010

  3. Project aim • To characterise the structure of two grades of graphite; NBG-10 (SGL-carbon group) and PCEA (GrafTech). Using high resolution X-ray tomography to provide an input for FE modelling. Changes in material properties before and after irradiation will then be validated using DIC technique UNTF 2010 University of Salford 14th - 16th April 2010

  4. Manufacturing process UNTF 2010 University of Salford 14th - 16th April 2010

  5. Porosity in Virgin NBG10 and PCEA Polarised light micrograph SEM of virgin nuclear graphite: A) NBG-10 and B) PCEA UNTF 2010 University of Salford 14th - 16th April 2010

  6. Bulk physical properties of NBG-10 and PCEA PCEA NBG-10 • Irradiated in materials test reactor (MTR) programmes (Raphael project) • courtesy of NRG Petten. PCEA and NBG-10 samples have been irradiated • to 8.66 and 9.16dpa respectively UNTF 2010 University of Salford 14th - 16th April 2010

  7. Methodology UNTF 2010 University of Salford 14th - 16th April 2010

  8. Finite Element Modelling (Ongoing work) UNTF 2010 University of Salford 14th - 16th April 2010

  9. Effect of porosity shape and size on Young’s modulus using simple model • 2D meshes will be created, each mesh with different porosity shape (circle, oblate spheroid) and size (20- 40% porosity). • The mesh will be given isotropic properties (i.e HOPG properties), each mesh will be loaded, the behaviour will be checked and validated. The same procedure will be repeated for 3D mesh UNTF 2010 University of Salford 14th - 16th April 2010

  10. Finite element predictions • A linear displacement is expected in the Finite element analysis due to the elastic property input. • The Young’s modulus results obtained from small models size will be more scattered (variation) than those obtained with larger models. • The effective Young’s modulus calculation in different areas of a virgin specimen should highlight some differences across the specimen, since pore volume fractions can differ slightly between the 8mm3 models. • The Young’s modulus of irradiated graphite will be higher than virgin graphite due to the closure of porosity during irradiation and pinning. UNTF 2010 University of Salford 14th - 16th April 2010

  11. Microstructural characterisation of Virgin PCEA and NBG10 Optical microscopy images PCEA (B and D) NBG-10 (A and C) UNTF 2010 University of Salford 14th - 16th April 2010

  12. PCEA 4th baked 8.66DPA Virgin UNTF 2010 University of Salford 14th - 16th April 2010

  13. NBG-10 Virgin 9.16 DPA UNTF 2010 University of Salford 14th - 16th April 2010

  14. SEM at low resolution NBG-10 (A and C) PCEA (B and D) UNTF 2010 University of Salford 14th - 16th April 2010

  15. SEM at high resolution NBG-10 (A and C) PCEA (B and D) UNTF 2010 University of Salford 14th - 16th April 2010

  16. X- ray diffractometer Crystallite dimensions Xrd Analysis UNTF 2010 University of Salford 14th - 16th April 2010

  17. Future work • Young’s modulus of sub-models at different areas in both graphites will be calculated and compared with each other. The numeric Young’s modulus will be compared with experimental Young’s modulus (12.8GPa and 11GPa for NBG-10 and PCEA respectively). Effect of mesh density, model length and X- ray Tomography resolution on Young’s modulus will be examined. • Eventually in this project, the plan is to validate the Abaqus modelling by using DaVis codes which can be also be used to make the strain analysis and failure prediction of nuclear graphite components in HTR/VHTR. • More secondary validation characterisation techniques for PCEA and NBG10 will be carried out using scanning electron microscopy (SEM), optical microscopy and X-ray diffraction (XRD). UNTF 2010 University of Salford 14th - 16th April 2010

  18. Acknowledgement • NRG @ Petten for completing the irradiation of this graphite within the • Raphael Program and making these samples available to Manchester • SGL and GrafTech for supplying the graphite and helpful discussions • The author will also like to acknowledge KNOO for their support UNTF 2010 University of Salford 14th - 16th April 2010

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