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Mechanical strength testing of irradiated HTR graphite grades

Mechanical strength testing of irradiated HTR graphite grades. M.C.R. Heijna, J.A. Vreeling NRG, Petten The Netherlands INGSM-14 18 September 2013 Seattle. O utline. Introduction HTR graphite INNOGRAPH irradiation programme Tensile strength from diametric compression Why? How?

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Mechanical strength testing of irradiated HTR graphite grades

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  1. Mechanical strength testing of irradiated HTR graphite grades M.C.R. Heijna, J.A. Vreeling NRG, Petten The Netherlands INGSM-14 18 September 2013 Seattle

  2. Outline • Introduction • HTR graphite • INNOGRAPH irradiation programme • Tensile strength from diametric compression • Why? • How? • Results • Movies! • Trends for coke, grain size, production process • Conclusions

  3. HTR Graphite • Two types of (V)HTR: • pebble bed • prismatic block • Graphite as moderator • Structural material Images from Wikipedia

  4. INNOGRAPH programme • European Commission Framework Programmes: • Retain (V)HTR knowledge • Screen properties of modern graphite grades

  5. INNOGRAPH programme INNOGRAPH-1A: 750°C, 5-10 dpa

  6. INNOGRAPH programme INNOGRAPH-1B: 750°C, 10-25 dpa INNOGRAPH-2A: 950°C, 4-8 dpa INNOGRAPH-2B: 950°C, 8-15 dpa

  7. INNOGRAPH programme INNOGRAPH-1B: 750°C, 10-25 dpa INNOGRAPH-2A: 950°C, 4-8 dpa INNOGRAPH-2B: 950°C, 8-15 dpa

  8. INNOGRAPH programme INNOGRAPH-1C: 750°C, 1-2 dpa Irradiation will be concluded this month

  9. INNOGRAPH design • Selectedirradiatedsamples from“1A”and “2A” werefurtherirradiated in “1B” and “2B” • INNOGRAPH-1B and -2B have been assembled in the NRG hot-cells

  10. INNOGRAPH design • Each experiment contains 24 thermocouples and 9 dosimeter sets • Temperature controlled by gas mixture • Temperature control within ±30°C • In the order of 180-220 samples per experiment • Sample geometry: • 6 mm high, 8 mm diameter • Flat side with sample coding • Samples in inert environment

  11. Graphite grades Major grades for this programme

  12. Irradiation in HFR, Petten • Tank-in-pool type MTR • 40 MW thermal • Operated by NRG

  13. Post Irradiation Examination measurements sample recovery • Data on 800 graphite samples • Dimensional change • Density • Young’s modulus • Coefficient of Thermal Expansion • Thermal conductivity • Electrical resistivity data set

  14. Test matrix strength measurements • Irradiation temperature 750°C • Fine grains and coarse grains • Pet & pitch coke • Various production processes • Different levels of dpa’s/ volume change • Sample selection limited by: • Reloaded samples • Microscopy samples

  15. Diametric compression

  16. Why diametric compression? INNOGRAPH geometry Typical tensile test geometry

  17. Tensile strength from diametric compression Tensile strength < Compressive strength S.P. Timoshenko, J.N. Goodier, “Theory of elasticity”, 1970 H. Awaji, J. Soc. Mat. Sci. Jap. 27 (1987) C. Berre et al., unpublished

  18. Tensile strength from diametric compression z = unique direction

  19. Experiment! Coarse grain graphite

  20. Experiment! Fine grain graphite

  21. Strength vs dpa; Grain size

  22. Strength vs dpa; Grain size DV/V0

  23. Scanning Electron Microscopy Fine grain, 0 dpa Grade C Coarse grain, 0 dpa Grade A Coarse grain, 12.8 dpa Grade A Fine grain, 13.4 dpa Grade C

  24. Strength vs dpa; Coke

  25. Strength vs dpa; Process

  26. Conclusions • Successful irradiation and PIE campaign concluded by demolishing samples • Tensile strength vs. dpa trends derived from diametric compression • At turn-around, strength doubles • Regardless of grain size, coke, production process • Fine grained graphite stronger than coarse grained • Regardless of irradiation • Coke and process have negligible effect on tensile strength

  27. Conclusions • Successful irradiation and PIE campaign concluded by demolishing samples • Tensile strength vs. dpa trends derived from diametric compression • At turn-around, strength doubles • Regardless of grain size, coke, production process • Fine grained graphite stronger than coarse grained • Regardless of irradiation • Coke and process have negligible effect on tensile strength Thank you for your attention!

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