ORNL is managed by UT-Battelle for the US Department of Energy Annealing Studies of Irradiated HOPG using X-ray Measurements Nidia C. Gallego Melanie J. Kirkham Tim D. Burchell Oak Ridge National Laboratory INGSM-15 Hangzhou, China – September 15-18, 2014

2 Presentation_name Irradiation-induced anisotropic dimensional changes in graphite crystal and polycrys- talline graphite Interstitial defects will cause crystallite growth perpendicular to the layer planes (c-axis direction), whereas coalescence of vacancies will cause a shrinkage parallel to the layer planes (a-axis direction) Structural and dimensional changes in polygranular graphite are a function of the crystallites dimensional change and the graphite’s texture.

3 Presentation_name Objective HOPG were included in experiment AGC-1 to provide data for the dimensional change rates of graphite crystals. These data in turn will be used in models for the dimensional change rates of polycrystalline graphites. This work is Task VHTR TDO Graphite R&D at ORNL Single crystal (HOPG) annealing studies. In support of the IAEA CRP on mechanisms in irradiation creep of graphite, a new annealing study of the d-spacings in HOPG is being conducted at both ORNL and INL. ORNL will perform annealing studies on one-half of the HOPG specimens irradiated in the AGC-1 capsule and INL will analyze the other half.

4 Presentation_name About the HOPG Samples GE Advanced Ceramics (now Momentive) Strongsville, OH Pyrolitic graphite Monochromator Grade ZYB 5mm x 5mm x 2mm HOPG samples were irradiated in the AGC-1 capsule, ATR reactor Target conditions: – T irr = 600 °C – Dose: 1.5 – 7 dpa

5 Presentation_name HOPG Samples and their Irradiation Conditions SampleT irr [°C]Dose [dpa] HOPG- unirradiated -- CPB CPB CPB CPB CPB CPB CPB CPB Irradiation conditions from Document ID ECAR-1943 (Table 1) Δ T = 240°C Δ T ~ 110°C Δ T ~ 57°C Δ T ~ 73°C ORNL received from INL 8 irradiated HOPG samples There is a significant gradient of the irradiation temperature !!

6 Presentation_name Experimental Plan Perform dimensional analysis Perform x-ray scans on irradiated HOPG samples – Monitor crystal lattice parameters and (from d 002, and d 110 ) and crystallite size parameters, L c, and L a Conduct step-wise annealing of (selected) irradiated HOPG and repeat x-ray scans after each annealing Proposed annealing temperatures – 700°C (assumed as the average irradiation temperature) – 1000, 1200, 1400 and 1600°C

7 Presentation_name Diffracted x-ray beam Experimental Setup   Incident x-ray beam (002) (004) (006)(008) (100) (110) (200) XRD was performed using PANAlytical machine using Cu-kα radiation, λ, of nm, 2 Ɵ range of 10 to 140° Calculate d 002 and L c Calculate d 110 and L a

8 Presentation_name Results to date SampleT irr [°C]Dose [dpa]Surface scanEdge scan HOPG- unirradiated -- CPB CPB CPB CPB CPB CPB CPB CPB Low dose Medium dose High dose SampleT irr [°C]Dose [dpa]Surface scanEdge scan HOPG- unirradiated -- CPB CPB CPB  CPB  CPB CPB  CPB  CPB  Additional low dose, low temp. Samples selected for annealing First 700 °C Surface scan Edge scan

9 Presentation_name Analysis of the (002) peak Sampled(002) Lc HOPG unirrad CPB CPB CPB CPB CPB CPB CPB CPB

10 Presentation_name Analysis of the (002) peak Interplanar spacing and thickness

11 Presentation_name What happens with the Lc??

12 Presentation_name Analysis of the (110) peak Sampled(110)La HOPG unirrad CPB CPB CPB CPB CPB CPB CPB CPB

13 Presentation_name Analysis of the (110) peak

14 Presentation_name What happens with the La??

15 Presentation_name How does the data compares to literature?

16 Presentation_name

17 Presentation_name T irr : 710°C. Highly oriented pyro-graphite Dimensional Change (%) Image from J-P Bonal, et al., MRS Bulletin, Vol. 34 (2009) After B.T. Kelly and Brocklehurst, Carbon 9, 783 (1971)

18 Presentation_name T irr : 710°C. Highly oriented pyro-graphite Dimensional Change (%) How does the data compares?

19 Presentation_name How about lattice parameters?

21 Presentation_name What happens after the annealing at 700°C? - Dimensions

22 Presentation_name What happens after the annealing at 700°C? – d-spacings

23 Presentation_name Summary XRD scans after irradiation have been completed: – Flat- and edge scans for all 8 irradiated HOPG 4 selected irradiated HOPG have been annealed to 700°C – Obtained flat and edge scans for all 4 annealed samples Preliminary analysis show (as expected): – Expansion on the c-axis direction – Shrinkage on the a-axis direction However, there is a huge difference in the magnitude of the changes of crystal dimension ( and ) and of ‘bulk’ dimensions of the HOPG This difference may be attributed to porosity generated during irradiation (reflected in a significant decrease in Lc and La), however additional research is needed to verify this.

24 Presentation_name Future Work Complete analysis of current XRD data Carry out step-wise annealing of 4 selected irradiated HOPG and repeat x-ray scans after each annealing Planned annealing temperatures – 700°C (assumed as the average irradiation temperature) (completed) – 1000, 1200, 1400 and 1600°C

25 Presentation_name Future Work A new set of HOPG samples are schedule to be part of AGC-4 Analysis prior to irradiation is being done for each individual HOPG sample 10 samples are at ORNL currently for XRD examination

26 Presentation_name Future Work Sample Average side1 (mm) Average side2 (mm) Average thickness (mm) Greater challenge for edge scans

27 Presentation_name THANK YOU!!