Speciation of 14 C in Irradiated Graphite Mary Lou Dunzik-Gougar Idaho State University and Idaho National Laboratory

1. Speciation of 14C in Irradiated Graphite Mary Lou Dunzik-Gougar Idaho State University and Idaho National Laboratory INGSM-14, Seattle, WA, USA September 2013

2. Due recognition of student researchers, consultants and startup funding • Students • James Cleaver, MS Dec 2011 • ShiloMcCrory, MS Dec 2011 • Tara Smith, MS Dec 2012 • Dan LaBrier, PhD 2013 • Kathy Nelson, MS 2014 • Ted Pollock, MS 2014 • Consultants • Johannes Fachinger, FNAG • Will Windes, INL • Abbie Jones, U of Manchester • Tony Wickham, Nuclear Technology Consultancy

3. The Objective is to . . . . . . determine the chemical nature of 14C on irradiated graphite surfaces • Characterize unirradiated and irradiated graphite surfaces with respect to 14C • Thermally treat irradiated graphite for removal of surface 14C

4. The graphite irradiation

5. The characterization • Characterize pre- and post-irradiated graphite • Focus on 14C and precursor 14N • XPS, Raman – Bond Information • ToF-SIMS – Speciation • SEM/EDS – Morphological Features, Chemical Environment

6. Surface Analyses Completed

7. Characterization SEM and EDS

8. SEM N cluster N cluster

9. SEM Nitrogen Nucleation Poco 50000 x • Nitrogen clusters preferentially nucleate at edges and activation sites Poco 1500 x NBG-18 35000 x

10. Energy Dispersive X-Ray Carbon (red), oxygen (blue) and nitrogen (green) on surface of irradiated graphite

11. SEM: Nitrogen Clusters in Irradiated NBG-25 (FIB surface)

12. Characterization X-ray Photoelectron and Raman Spectroscopy

13. XPS Survey Scans: POCOFoam C1s O1s Unirradiated C1s O1s LN2 immersed N1s O1s C1s Irradiated C1s Thermally Treated

14. XPS Survey Scans: NBG-18 C1s O1s Unirradiated C1s O1s LN2 immersed N1s O1s C1s Irradiated C1s O1s Thermally Treated

15. XPS Survey Scans: NBG-25

16. XPS: NBG-25 Surface Scans Trace amounts of nitrogen present in unirradiatedsamples Some bound oxygen (~2%) to graphite surfaces UNIRRADIATED IRRADIATED No discernible presence of nitrogen in irradiated samples Amount of bound oxygen increases (to ~7%) due to irradiation

17. XPS: Irradiated NBG-18 & POCOFoam® Surface Scans Significant increase in the amount of surface nitrogen and oxygen present NBG-18 POCOFoam® Attributed to exposure to air and excess LN2 during irradiation

18. XPS: NBG-25 C 1s Peak Deconvolution Broadening of C 1s peak in irradiated NBG-25 (along with increased oxygen presence) suggests the formation of additional surface oxides

19. XPS: C 1s Peak for All Irradiated Graphites Significant amounts of oxides are observed on the surfaces of all graphites and are directly attributed to neutron irradiation.

20. Raman: Unirradiated vs. Irradiated NBG-25 D (sp3) peak G (sp2) peak

21. Characterization Secondary Ion Mass Spectroscopy (SIMS)

22. ToF-SIMS: Species of Interest

23. ToF-SIMS: Surface Concentration of 14C (NBG-25) Surface 14C, N 5 nm 14C, N • Sputtering of surface layers removes substantial amount (~90%) of suspected 14C • Indicates that 14C is concentrated on graphite surface

24. ToF-SIMS: Positive Ion Spectra

25. ToF-SIMS: Negative Ion Spectra

26. ToF-SIMS: m/z = 26 (CN-) Conundrum Surface 5 nm Lack of substantial surface (and sub-surface) presence of N in irradiated NBG-25 suggests m/z=26 signal is predominantly 14CC (some CN possible) Strength of sub-surface signal further suggests that 14C is bound within the graphite lattice Possible correlation between 14CC and elevated sp3 bonding just below surface

27. XPS: C 1s Analysis for All Irradiated Graphites Surface species dominated by oxides for irradiated NBG-18 & POCOFoam® Significant amount of surface oxides for irradiated NBG-25

28. XPS: C 1s Analysis for All Thermally Treated Graphites Removal of significant portions of surface oxides and sp3 bonding for all irradiated graphite Removal of 14C?

29. ToF-SIMS: Removal of 14C via Thermal Treatment of NBG-25 Pre-Thermal Treatment Pre-Thermal Treatment 14C, N Post-Thermal Treatment 14C, N • Amount of 14C on the surface of irradiated NBG-25 is reduced by 85-90% due to thermal treatment

30. ToF-SIMS: Removal of 14C via Thermal Treatment of NBG-18 Pre-Thermal Treatment 14C, N Post-Thermal Treatment 14C, N • Amount of 14C removed via thermal treatment: • NBG-18: ~95%

31. Pathways of Release for 14C • 14CO and 14CO2 are the main desorption species released during thermal treatment • Dependent on surface chemistry (C-O functional groups) • 14CO2 – dominant at lower (< 600 oC) temperatures • 14CO – dominant at higher (> 600 oC) temperatures • Complexity of species formed on surface will be affected by duration of irradiation, coolant, gamma radiation • Based on XPS results, most likely surface functional groups: • 14CO2 – aldehydes, carboxylics, lactones • 14CO – ethers, ketones, quinones

32. Temperature Dependency of 14C Removal CO2 is prominently removed at lower temperatures (with limited desorption at higher temperatures) 150-400 oC 350-650 oC 600-950 oC 600-700 oC CO is removed at higher temperatures (> 600 oC) ~700 oC 700-950 oC Figueiredo, 1999

33. Conclusions • Presence of 14C is confirmed on surfaces of irradiated graphite • Species containing 14C (or 14N) were identified using SIMS • XPS and Raman analysis eliminates substantial presence of 14N • Relative concentration of 14C is ~10 times higher on graphite surfaces than below (< 10 nm) the surface • Carbon-oxygen functional groups identified on irradiated graphite surfaces • Bond information surmised using XPS; confirmed by Raman • Chemical species identified using SIMS • Temperature dependency based on thermal treatment data

34. Thank You!

35. SEM of NBG-25 (1/2) Unirradiated(1000x) Thermally Treated (1000x) Irradiated (2000x)

36. SEM: Surface Morphology