1. Vacancy type defects in oxide dispersion strengthened steels V. Slugeň, J. Veterníková, V. Sabelová, J. Degmová, R. Hinca, M. Petriska and S. Sojak Institute of Nuclear and Physical Engineering Faculty of Electrical Engineering and Information Technology Slovak University of Technology Bratislava, Slovakia

2. Available techniques for material studies: Positron Annihilation Spectroscopy: Conventional PALS 2-det. or 3-det. Set- ups (for irradiated materials), digital Doppler Broadening set-up, access and experiences with PLEPS measurements at FRM-II in Garching Moessbauer spectroscopy, Atomic force microscopy, Alfa, beta, gamma spectroscopy including low/background chamber, X-ray diffraction, Barkhausen Noises measurements, TEM, SEM, Operating cascade accelerator for simulation of radiation induced defects via ion implantation Institute of Nuclear and Physical Engineering Slovak University of Technology

3. What kind of information we can obtain from Positron Annihilation Spectroscopy? Report: EUR 22468 EN Vladimír Slugeň JRC-Petten, 30.8.2006 Defects density Annealing effectiveness Precipitation Types of defects Near surface region study Microstructural changes due to irradiation, ageing,...

4. Neutron-irradiation –Defect production Self-interstitial atom (SIA) & vacancy (V) rich regions –Matrix damage SIA-clusters, SIA-loops Micro voids –Solute atom diffusion Precipitates Complex defect-solute configurations GB segregation Irradiation-induced changes of microstructure x x x x x x x x x x x

5. Depth profile of the helium implantation, E=250keV (SRIM simulation 10 5 ions) Experiment Radiation treatment Dose [ions/cm 2 ] (C/cm 2 ) 6,24.10 17 (0.1) 1,25.10 18 (0.2) 1,87.10 18 (0.3) 2,5.10 18 (0.4) 3,12.10 18 (0.5) DPA PALS 0,150,300,450,600,74 DPA PLEPS 18.5537.1055.6474.1992.74 DPA (average) calculation for different level of implantation in first 100  m layer (DPA PALS ) and 800nm (DPA PLEPS ) of studied Fe-Cr alloys To obtain cascade collisions in the microstructure of studied materials without neutron activation, accelerated helium ions have been used

7. Complementary techniques results Experiment SEM x Z SEM confirms the PLEPS results of large voids in the depth >500nm which correspondent to the helium implantation profile maxima. 1m1m

8. Technical specification Total accelerating voltage: 0 - 1 MV Ripple factor: < 1% Energy range for singly charged particles: 5 keV to 1 MeV Energy spread: 70 keV – 1 MeV:  2 keV < 70 keV:< 0,1% Beam current:1 - 100  A Cascade accelerator, laboratory of ion beams, Slovak University of Technology Radiation treatment Experiment

9. PALS equipment

10. Pulsed low energy positron system (PLEPS) remoderated positrons [1] P. Sperr, W. Egger, G. Kögel, G. Dollinger, Ch. Hugenschmidt, R. Repper, C. Piochacz, Applied Surface Science 255 (2008) 35–38 [2] Hugenschmidt C., Dollinger G., Egger W., Kögel G.,Löwe B., Mayer J., Pikart P., Piochacz C., Repper R., Schreckenbach K., Sperr P., Stadlbauer M., Applied Surface Science, Volume 255, Issue 1, p. 29-32

11. SLUGEŇ, V. et al., Nuclear Fusion 44, 2004, 93. Defects depth profiling study and studies of near-surface region. PAS and TEM results are useable for microstructural evaluation of new materials

12. HV10 PAS MS 020406080100 120 140 160 180 200  [% fracture strain]  [ps]  0 50 100 150 200 250  [N/mm 2 ]  2 ]  Stress-strain experiments on Fe  Distinct positron trapping after 80% Hooks range (fully elastic region)  Early stage of fatigue Stress-strain diagram of pure Fe Average positron LT in Fe after tensile strain PAS parameters in comparison to results from other techniques (TEM, SEM, HV10, MS, XRD). SLUGEŇ, V., MAGULA, V.: Nuclear engineering and design 186/3, 1998

13. Lattice parameter vs. positron lifetime in defects in helium implanted Fe-Cr alloys. a.) Fe2.56%Cr; b.) Fe11.62%Cr a.) b.) KRSJAK, V.: PhD Thesis, STU Bratislava, 2008

14. PAS Results - Annealing temperature for WWER-steels at 475 °C is acceptable, but PAS gives more information. The 3D presentation of PLEPS results (Tau1) of irradiated (1.25x10E24m -2 ) and annealed Sv-10KhMFT steel (WWER-440 weld). The effectiveness of the annealing process to removing of small defects (mono/di-vacancies or Frenkel pairs) can be followed via significant decrease of parameter tau1. This figure also shows rapid increase of mentioned small defects in WWER type of RPV steels after about 480 ºC. Slugen et al: NTD&E Int. 37 (2004) 651

15. 15 The EPR pressure vessel in Olkiluoto 3 (Finland) – 2009 VVER-440 annealing facility VVER-440 V-213 Pressure vessel

16. Corrosion reistance, Radiation resistance – negligible radiation swelling, small ΔDBTT (RT NDT, NDTT) and upper shelf energy (USE) decrease Thermal resistance, Reduced activated steel – with eliminated content of long-term radiactive Ni, C, Cu and Co replaced by V, Mn, Cr, Ti, W. How should the ideal WWER-reactor steel look like and why? Optimization of all factors affected on properties

17. Difficulties with irradiated RPV steels and advantages for implantation Radioactivity ―> special rules for handling, transport, polishing, storage... (PROBLEMS), –Reducing of volume, –Reducing of number of samples, –Application of other techniques if possible. PAS disturbing 60 Co contribution (photopiks 1.17 and 1.33 MeV) –1. Measurement using PLEPS (very thin samples of about 20 μm are necessary), –2. Measurement using 3 detector set-up in coincidence mode (takes about 2 weeks), –3. To wait... (T 1/2 (Co-60)=5.27 a). Ion implantation – none transmutations = none 60 Co, very short half-time of decay for radionuclides, only 2 detectors measurement equipment for PAS In ODS steels – 0 Co content (theory)

18. Chemical composition of studied ODS steels (in % wt.). CMnNiCrMoTiAlSiWY2O3Y2O3 MA 9560.070.120.07200.10.33.40.04-0.5 ODM 7510.07 0.02161.740.73.80.06-0.5 ODS Eurofer0.10.44-90.01-- 1.10.3 Addition of stable oxides (Al 2 O 3, Cr 2 O 3, Y 2 O 3 ) Better mechanical properties – strength, toughness Better corrosion resistance and resistance to thermal loading Candidate materials for fuel cladding in new reactors (fast reactors) Oxide Dispersion Strengthening might improve the swelling resistance of F/M steels

19. 19 ODS 14%Cr ferritic steels: MA957 Less hardening than conventional and low activation F/M Steels J. L. Boutard, J. L. Boutard, IAEA Technical Meeting, Vienna, 27-29 June 2011

20. Experimental techniques Positron annihilation lifetime spectroscopy (PALS) − Slovak University of Technology, Slovakia Doppler Broadening Spectroscopy (DBS) − Aalto University, Finland Magnetic Barkhausen Noise (MBN) − JRC, Petten, Netherland

21. PALS meaurement – MLT

22. Results of Positron Annihilation Lifetime Spectroscopy: Lifetimes (a); Intensities (b). ODM 751 had visible higher values – 250 ps. This signifies that MA 956 and ODS Eurofer contain defects probably with the similar size of di-vacancies, although the lifetime of MA 956 has much higher deviation. According to ΔLT2, MA 956 can also contains three-vacancies. ODM 751 has three- and four-vacancy clusters. The intensities (percentages) of positron annihilation in the defects (I2) differ significantly for investigated steels, i.e. for MA 956 ~ 60%, ODM 751 - 51% and ODS Eurofer – over 70%. Observed defects are categorical and they are formed during manufacture. a)b)

23. DBS results

24. Behavior of S- W parameters. The highest gradient ODM 751. ODM 751 is probably by the lowest defect presence.

25. The signal envelope of Magnetic Barkhausen noise for frequency up to 50 Hz (depth ~ 1 mm). The highest signal amplitude – BNA: ODM751, which demonstrates the lowest concentration of all structural defects (vacancies, precipitations, grain boundaries) than in ODS Eurofer and MA 957. It can also denote lower hardness or lower level of residual stress in ODM 751. The highest residual stress belongs to ODS Eurofer. The smallest grains were found in MA 956. The highest Hpeak as well as the coarsest grains were detected for ODM 751.

26. Conclusion ODM 751 – the lowest defect concentration, but the largest defects, ODS Eurofer – the higher defect concentration as well as hardness. No relation to chromium content as was assumed HHardness (residual stress) increases with defect concentration growth, no with defect size growth (precipitation vs dislocation) Defect concentration, defet size (PALS) Defect concentration, defet size (DBS) Hardness = residual stress (MBN) SSame or similar results Influence of Cr + Mo + W and aslo Al on hardness (creation of precipitates

27. Thank you! Vladimir.Slugen@stuba.sk Vladimir.Slugen@stuba.sk