INFLUENCE OF THE HYDRIDE PRECIPITATION ON THE CORROSION KINETICS OF ZIRCALOY-4:

Transcription

1 INFLUENCE OF THE HYDRIDE PRECIPITATION ON THE CORROSION KINETICS OF ZIRCALOY-4: EFFECT OF THE NANOSTRUCTURE AND GRAIN BOUNDARY PROPERTIES OF ZIRCONIUM OXIDE LAYER ON THE OXYGEN DIFFUSION FLUX M. Jublot, G. Zumpicchiat, M. Tupin, S. Pascal, C. Berdin, C. Bisor, M. Blat ASTM : 18 th International Symposium on Zirconium in the Nuclear Industry 16 TH MAY 2016

2 BACKGROUND Pressurized Water Reactor (PWR) Fuel cladding material : ZIRCALOY-4 (Zy4) Fuel Assembly Image : Areva Primary coolant loop: liquid water - ~ 320 C; 155 bars ppm B - 2 ppm Li - [H 2 ] = 25 cc/kg Alloying elements Sn, wt% Fe, wt% Cr, wt% O, wt% Corrosion of the Zy-4 fuel cladding CEA 16 th May 2016 PAGE 2 H, wt.ppm Zircaloy

3 560 µm BACKGROUND Pressurized Water Reactor (PWR) Reaction of oxidation : Zr + 2 H 2 0 ZrO H 2 ZrO 2 Zr + ZrH x Zy-4 [Bernaudat et al., Topfuel 2009] Fuel rod Burnup Cross-section of a Zy-4 cladding oxidized in Reactor [Bossis, ASTM 2005] CEA 16 th May 2016 PAGE 3

4 BACKGROUND Pressurized Water Reactor (PWR) Potential factors of the «High Burn-Up» acceleration of Zy4 Dissolution of the Zr(Fe,Cr) 2 precipitates Tin content Li effect Irradiation impact on the microstructure Hydride accumulation at the oxide/metal interface Reaction of oxidation : Zr + 2 H 2 0 ZrO H 2 ZrO 2 Zr + ZrH x How the hydride accumulation affects the microstructure of the zirconium oxide? What is the impact on the corrosion kinetics? Zy-4 TEM investigation of the oxide with an Automated Crystal Orientation Mapping tool (ACOM-TEM) Cross-section of a Zy-4 cladding oxidized in Reactor [Bossis, ASTM 2005] Grain size distribution Grain orientations the Grain boundary misorientation CEA 16 th May 2016 PAGE 4

5 OUTLINE How the hydride accumulation affects the microstructure of the zirconium oxide? Materials & techniques Results: The oxide nanostructure The grain boundary misorientation The oxygen diffusion simulation as a function of the nanostructure Resume CEA 16 th May 2016 PAGE 5

6 MATERIALS & TECHNIQUES 2 samples Reference Zy4 (Zy4) Recrystallized sheets of Zy4 [Bisor C. Phd (2010)] Hydrided Zy4 (Zy4-h) [Blat et al. ASTM 1996 p.319] Cathodic charging technique ~ 8 µm thick 8 µm d-zrh 1,66 Oxydation in PWR conditions (Autoclave : 360 C; 190bars; Li; B) Corrosion kinetics In pre-transition phase Hydrided Zy4 Zy4 [Tupin et al., Corrosion Science 98 (2015)] dx dt X=1µm = 1,8 dx dt X=1µm Zy4 Zy4-h The oxidation rate is higher on hydrided Zy4 CEA 16 th May 2016 PAGE 6

7 MATERIALS & TECHNIQUES Cross-section analysis Fractography ZrO 2 / Hydride Fractography ZrO 2 / Hydride ZrO nm d-zrh 1,66 ZrO 2 / Zy4 ZrO nm a-zr [Bisor C. Phd (2010)] CEA 16 th May 2016 PAGE 7

8 MATERIALS & TECHNIQUES Cross-section analysis TEM Bright field ZrO 2 Fractography ZrO 2 / Hydride ZrO 2 : Columnar grains Width : nm Length : nm [De Gabory et al. JNM 456 (2015) p.272] 200 nm ZrO 2 d-zrh 1,66 TEM lamella thickness: From FIB preparation : ~100 nm ZrO 2 ZrO 2 / Zy4 ZrO nm a-zr CEA 16 th May 2016 PAGE 8 [Bisor C. Phd (2010)]

9 MATERIALS & TECHNIQUES Plan-view TEM sample preparation FIB tool ~300 nm ZrO 2 / Zy4 ZrO 2 / Hydride ZrO 2 Thickness ~ 60 nm Thickness ~ 55 nm Advantages of the plan-view analysis : - To analyse single grains through the FIB foil thickness - To investigate the properties of the grain boundaries which control the corrosion kinetics of Zy4 alloy. - To scan a wide zone of interest for a better statistic (~30 µm 2 ) CEA 16 th May 2016 PAGE 9

10 MATERIALS & TECHNIQUES Plan-view TEM analysis ACOM-TEM technique [E. Rauch et al., Microsc Anal, 22, 2008] ASTAR TM tool TEM FEI tecnai 30 G2 Automated Crystal Orientation Mapping (ACOM-TEM) To index the crystal phase To index the crystal orientation Principle e - 1 µm Acquired pattern Pre-calculated templates Orientation map Index map: highlighting the grain boundaries Reliability map: CEA 16 th May 2016 PAGE 10

11 4.2 µm 5.2 µm MATERIALS & TECHNIQUES Scanning conditions e - ZrO 2 / Zy4 ZrO 2 / Hydride 6.0 µm Beam size : 9 nm Scan step : 5 nm 1 µm 6.4 µm Scanned area: 27 µm 2 31 µm 2 Orientation maps Monoclinic phase of ZrO 2 ~300 nm Monoclinic phase of ZrO 2 (a-zro 2 ) Tetragonal phase 200 nm a-zr ZrO 2 a = 5.15 Å b = 5.21 Å c = 5.32 Å b = b y z x a a = 5.08 Å b = 5.08 Å c = 5.17 Å b = 90 b z y x a c c CEA 16 th May 2016 PAGE 11

12 RESULTS THE OXIDE NANOSTRUCTURE Orientation maps ZrO 2 / Zy4 Monoclinic phase of ZrO 2 ZrO 2 / Hydride 500 nm ~ 9000 indexed grains Euler angles ZrO 2 monoclinic F1 0 F 0 F nm ~ indexed grains CEA 16 th May 2016 PAGE

13 RESULTS THE OXIDE NANOSTRUCTURE Index map The grain size distribution ZrO 2 / Zy4 Columnar oxide grains Base shape - not a regular polygon - Spread size distribution 500 nm 100 nm CEA 16 th May 2016 PAGE 13

14 RESULTS THE OXIDE NANOSTRUCTURE The grain size distribution ZrO 2 / Zy4 ~ 9000 indexed grains Columnar oxide grains Base shape - not a regular polygon - Spread size distribution 50 % of grains Average diameter nm 34.6 nm Conditions - Base shape converted as a circular shape - Grain diameters > 15 nm - Misorientation angle between adjacent grains > 10 > 10 CEA 16 th May 2016 PAGE 14

15 RESULTS THE OXIDE NANOSTRUCTURE The grain size distribution Index map ZrO 2 / Hydride Columnar oxide grains Base shape 500 nm CEA 16 th May 2016 PAGE 15

16 RESULTS THE OXIDE NANOSTRUCTURE The grain size distribution ZrO 2 / Hydride Columnar oxide grains Base shape - ~ regular shape - Smaller size ZrO 2 / Zy4 500 nm CEA 16 th May 2016 PAGE 16

17 RESULTS THE OXIDE NANOSTRUCTURE The grain size distribution ZrO 2 / Hydride ~ indexed grains - ZrO 2 / Hydride - ZrO 2 / Zy4 Columnar oxide grains Base shape - ~ regular shape - Smaller size 50 % of grains Average diameter Ø nm 34.6 nm Ø nm 27.8 nm CEA 16 th May 2016 PAGE 17

18 RESULTS THE OXIDE NANOSTRUCTURE The grain size distribution ZrO 2 / Hydride Columnar oxide grains Base shape - ~ regular shape - Smaller size 50 % of grains Average diameter Ø nm 34.6 nm Ø nm 27.8 nm Consequences on the corrosion kinetic of Zy4 Oxygen diffuses through the grain boundaries Base size grain boundary density Surface fraction of the oxide grain boundaries f ZrO2/Hydride = 2.9 % - Base shape converted as a hexagonal shape - Intergranular space of 0.5 nm 0.5 nm f ZrO2/Zy4 = 1.8 % = + 60% CEA 16 th May 2016 PAGE 18 Partially explain the higher corrosion kinetic of the massive hydride

19 RESULTS GRAIN BOUNDARY MISORIENTATION Misorientation angles between adjacent grains [Sainfort, 1984] Consequences on the corrosion kinetic on Zy4 Base size grain boundary density 0.5 nm Oxygen diffuse through the grain boundaries Surface fraction of the oxide grain boundaries f ZrO2/Hydride = 2.9 % - Base shape converted as a hexagonal shape - Intergranular space of 0.5 nm f ZrO2/Zy4 = 1.8 % = + 60% CEA 16 th May 2016 PAGE 19 Partially explain the higher corrosion kinetic of the massive hydride

20 RESULTS GRAIN BOUNDARY MISORIENTATION Misorientation angles distribution between adjacent grains Not randomly distributed Angular range ( ) Distribution (%) on Zy4 on hydride % 29 % 20 % 9 % 15 % 19 % 28 % 9 % CEA 16 th May 2016 PAGE 20

21 b c y a z x RESULTS GRAIN BOUNDARY MISORIENTATION Misorientation angles distribution between adjacent grains Not randomly distributed 90 [001] b y z x c a a y x b z x b c a c 180 [101] z y Low coherent misorientation angles Twins tetragonal to monoclinic phase transformation Low interfacial energy Lower activation energy for the diffusion of oxygen Diffusion limited through these grain boundaries CEA 16 th May 2016 PAGE 21

22 b c y a z x RESULTS GRAIN BOUNDARY MISORIENTATION Misorientation angles distribution between adjacent grains Not randomly distributed 90 [001] b y z x c a a y x b z c a c 180 [101] x b z y Lower activation energy for the diffusion of oxygen Low coherent misorientation angles + 32 % in ZrO 2 / Hydride Twins tetragonal to monoclinic phase transformation Diffusion limited through these grain boundaries CEA 16 th May 2016 PAGE 22 Participate to the higher corrosion kinetic of the massive hydride

23 RESULTS OXYGEN DIFFUSION SIMULATION Oxygen diffusion experiments [Bisor C. Phd (2010)] ZrO 2 Isotopic exposure in H 2 18 O 6h; 360 C; 190 bars SIMS profile of 18 O After 6 h ZrO 2 / Zy4 ZrO 2 / Hydride Diffusion profile of 18 O characteristic of a diffusion through short-circuits (grain boundaries) Influence of the columnar grain width? Second Fick's law: x 18O = x s x s x 0. erf x 18O = x s for x = 0 x 18O = x 0 for x = x 2 D a t 18 O apparent diffusion coefficient Da ratio : D ZrO2/Hydride = D ZrO2/Zy4 = cm²/s cm²/s = +80% CEA 16 th May 2016 PAGE 23

24 RESULTS OXYGEN DIFFUSION SIMULATION ZrO 2 Modelisation with Voronoï cell aggregate ZrO 2 / Zy4 ZrO 2 / Hydride Conditions - Sample ZrO2 / Zy4 ZrO2 / Hydride Average grain size 34.6 nm 27.8 nm Voronoï cells aggregates - Thickness of the grain boundaries : 0.5 nm - Diffusion coefficient of oxygen in: Volume : cm²/s Grain boundaries : 4.3x10-14 cm²/s CEA 16 th May 2016 PAGE 24

25 RESULTS OXYGEN DIFFUSION SIMULATION ZrO 2 Modelisation with Voronoï cells aggregate Fickian diffusion solved with the finite element Cast3M, during 6h www-cast3m.cea.fr 18 O apparent diffusion coefficient Da ratio : D ZrO2/Hydride = D ZrO2/Zy4 = Simulated: cm²/s cm²/s = +30% Lower than experience: +80% After 6 h Num ZrO 2 / Zy4 Num ZrO 2 / hydride ZrO 2 / Zy4 ZrO 2 / hydride Experience Simulation Confirms the diffusion process occurs mainly through the grain boundaries Confirms an effect of the grain size lower ratio of diffusion coefficient CEA 16 th May 2016 PAGE 25

26 RESUME Precipitation of a massive hydride on the surface (+ 80%) Higher corrosion kinetic PWR conditions Zircaloy-4 Modification of the grains boundary components of the monoclinic oxide layer Higher (+ 60%) concentration lower grain size distribution Less coherence of the misorientation angles distribution between adjacent grains Increase the diffusion kinetics of oxygen through the oxide layer The simulation with Cast3M confirms the role of the grain boundaries associated to a lower grain size distribution To be improved ACOM-TEM Informations on the oxide microstructure - grain size - grain boundary component - grain orientation (texture) CEA 16 th May 2016 PAGE 26

27 THANK YOU PAGE 27 CEA 10 AVRIL MAI 2016 Commissariat à l énergie atomique et aux énergies alternatives Centre de Saclay Gif-sur-Yvette Cedex T. +33 (0) Etablissement public à caractère industriel et commercial RCS Paris B DEN DMN SEMI