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 2

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

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

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

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

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

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

9. INNOGRAPH design Selected irradiated samples from “1A”and “2A” were further irradiated in “1B” and “2B” INNOGRAPH-1B and -2B have been assembled in the NRG hot-cells

10. INNOGRAPH design 10 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 11 Major grades for this programme

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

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

14. Test matrix strength measurements 14 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 15

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

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 Jap. 27 (1987) C. Berre et al., unpublished Tensile strength 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

18. Tensile strength from diametric compression 18 z = unique direction

19. Experiment! Coarse grain graphite 19

20. Experiment! Fine grain graphite 20

21. Strength vs dpa; Grain size 21

22. Strength vs dpa; Grain size 22  V/V 0

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

24. Strength vs dpa; Coke 24

25. Strength vs dpa; Process 25

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 26

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! 27