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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 : 18th International Symposium on
Zirconium in the Nuclear Industry
16TH MAY 2016
BACKGROUND
Pressurized Water Reactor (PWR)
| PAGE 2 CEA | 16th May 2016
Fuel cladding material : ZIRCALOY-4 (Zy4)
Image : Areva
Fuel Assembly
Corrosion of the Zy-4 fuel cladding
Primary coolant loop: liquid water
- ~ 320°C; 155 bars
- 1500 ppm B
- 2 ppm Li
- [H2] = 25 cc/kg
Alloying
elements Sn, wt% Fe, wt% Cr, wt% O, wt%
H,
wt.ppm
Zircaloy-4 1.46 0.22 0.11 0.13 21
[Bernaudat et al., Topfuel 2009]
Fuel rod Burnup
BACKGROUND
Pressurized Water Reactor (PWR)
| PAGE 3
ZrO2
Zr + ZrHx
Zy-4 560 µ
m
Cross-section of a Zy-4 cladding
oxidized in Reactor [Bossis, ASTM 2005]
CEA | 16th May 2016
Reaction of oxidation :
Zr + 2 H20 ZrO2 + 2 H2
BACKGROUND
Pressurized Water Reactor (PWR)
| PAGE 4
Reaction of oxidation :
Zr + 2 H20 ZrO2 + 2 H2
ZrO2
Zr + ZrHx
Zy-4
CEA | 16th May 2016
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
How the hydride accumulation affects the
microstructure of the zirconium oxide ?
► What is the impact on the corrosion kinetics ?
TEM investigation of the oxide with an Automated
Crystal Orientation Mapping tool (ACOM-TEM)
Grain size distribution the Grain boundary misorientation
Grain orientations
Cross-section of a Zy-4 cladding
oxidized in Reactor [Bossis, ASTM 2005]
OUTLINE
| PAGE 5 CEA | 16th May 2016
• Materials & techniques
• Results:
– The oxide nanostructure
– The grain boundary misorientation
– The oxygen diffusion simulation
as a function of the nanostructure
• Resume
How the hydride accumulation affects the microstructure of the zirconium oxide ?
Zy4
Zy4-h
Zy4
Hydrided Zy4 Corrosion kinetics
In pre-transition phase
MATERIALS & TECHNIQUES
| PAGE 6 CEA | 16th May 2016
Oxydation in PWR conditions
(Autoclave : 360°C; 190bars; Li; B)
2 samples Reference Zy4 (Zy4)
8 µm
d-ZrH1,66
The oxidation rate is
higher on hydrided Zy4
Hydrided Zy4 (Zy4-h)
Cathodic charging technique ~ 8 µm thick
[Blat et al. ASTM 1996 p.319]
[Tupin et al., Corrosion Science 98 (2015)]
Recrystallized sheets
of Zy4
𝑑𝑋𝑑𝑡 𝑋=1µ𝑚
𝑑𝑋𝑑𝑡 𝑋=1µ𝑚
= 1,8
[Bisor C. Phd (2010)]
MATERIALS & TECHNIQUES
| PAGE 7 CEA | 16th May 2016
Cross-section analysis
Fractography
a-Zr 200 nm
ZrO2
ZrO2 / Zy4
[Bisor C. Phd (2010)]
ZrO2 / Hydride
d-ZrH1,66 200 nm
ZrO2
ZrO2 / Hydride
Fractography
MATERIALS & TECHNIQUES
| PAGE 8 CEA | 16th May 2016
Cross-section analysis Fractography
d-ZrH1,66
a-Zr 200 nm
200 nm
ZrO2
ZrO2
ZrO2 / Hydride
ZrO2 / Zy4
TEM – Bright field
ZrO2
ZrO2
[Bisor C. Phd (2010)]
ZrO2 : Columnar grains
Width : 10-40 nm
Length : 80-300 nm [De Gabory et al. JNM 456 (2015) p.272]
TEM lamella thickness:
From FIB preparation : ~100 nm
MATERIALS & TECHNIQUES
| PAGE 9 CEA | 16th May 2016
Plan-view TEM sample preparation ►FIB tool
ZrO2
~300 nm ZrO2 / Hydride ZrO2 / Zy4
Thickness ~ 60 nm Thickness ~ 55 nm
- 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 µm2)
Advantages of the plan-view analysis :
MATERIALS & TECHNIQUES
| PAGE 10 CEA | 16th May 2016
Plan-view TEM analysis ►ACOM-TEM technique
Automated Crystal Orientation Mapping (ACOM-TEM)
To index the crystal phase
To index the crystal orientation
Orientation map
Pre-calculated
templates
Acquired pattern
ASTARTM tool
TEM FEI
tecnai 30 G2
Principle
1 µm
e-
Index map:
highlighting the
grain boundaries
Reliability map:
[E. Rauch et al., Microsc Anal, 22, 2008]
MATERIALS & TECHNIQUES
| PAGE 11 CEA | 16th May 2016
5.2
µm
6.0 µm
4.2
µm
6.4 µm
Scanning conditions
Orientation maps ► Monoclinic phase of ZrO2
~300 nm
a-Zr 200 nm
ZrO2
a
b
c
x
y
z
a = 5.15 Å
b = 5.21 Å
c = 5.32 Å
b = 99.22°
Monoclinic phase of ZrO2 (a-ZrO2)
a
b
c
x
y
z
a = 5.08 Å
b = 5.08 Å
c = 5.17 Å
b = 90°
Tetragonal phase
1 µm
e-
Beam size : 9 nm
Scan step : 5 nm
ZrO2 / Hydride ZrO2 / Zy4
Scanned area: 27 µm2
31 µm2
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 12 CEA | 16th May 2016
► Monoclinic phase of ZrO2
500 nm
500 nm
ZrO2 / Hydride
ZrO2 / Zy4
0°
0°
0°
90°
90°
180°
180°
180°
360°
45°
45°
90°
135°
135°
270°
F1
F
F2
Euler angles – ZrO2 monoclinic
~ 9000 indexed grains ~ 15000 indexed grains
Orientation maps
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 13 CEA | 16th May 2016
► The grain size distribution ZrO2 / Zy4
500 nm 100 nm
Index map
Columnar oxide grains
Base shape
- not a regular polygon
- Spread size
distribution
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 14 CEA | 16th May 2016
► The grain size distribution ZrO2 / Zy4
Columnar oxide grains
Base shape - not a regular polygon
- Spread size
distribution
Conditions
- Base shape converted as a circular shape
- Grain diameters > 15 nm
- Misorientation angle between adjacent grains > 10°
> 10°
50 % of grains Average diameter
15 - 75 nm 34.6 nm
~ 9000 indexed grains
ZrO2 / Hydride
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 15 CEA | 16th May 2016
500 nm
► The grain size distribution
Index map Columnar oxide grains
Base shape
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 16 CEA | 16th May 2016
500 nm
ZrO2 / Zy4
► The grain size distribution
Columnar oxide grains
Base shape - ~ regular shape
- Smaller size
ZrO2 / Hydride
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 17 CEA | 16th May 2016
ZrO2 / Hydride ► The grain size distribution
Columnar oxide grains
Base shape - ~ regular shape
- Smaller size
~ 15000 indexed grains
50 % of grains Average diameter
Ø 15 - 75 nm 34.6 nm
Ø 15 - 40 nm 27.8 nm
- ZrO2 / Zy4
- ZrO2 / Hydride
RESULTS – THE OXIDE NANOSTRUCTURE
| PAGE 18 CEA | 16th May 2016
ZrO2 / Hydride ► The grain size distribution
Columnar oxide grains
Base shape - ~ regular shape
- Smaller size
50 % of grains Average diameter
Ø 15 - 75 nm 34.6 nm
Ø 15 - 40 nm 27.8 nm
Consequences on the corrosion kinetic of Zy4 ◄ Oxygen diffuses through the grain boundaries
Base size grain boundary density
0.5 nm
Surface fraction of the oxide grain boundaries
- Base shape converted as a hexagonal shape
- Intergranular space of 0.5 nm
𝑓𝑍𝑟𝑂2/𝑍𝑦4 = 1.8 %
𝑓𝑍𝑟𝑂2/𝐻𝑦𝑑𝑟𝑖𝑑𝑒 = 2.9 % = + 60%
Partially explain the higher corrosion kinetic of the massive hydride
0.5 nm
| PAGE 19 CEA | 16th May 2016
Misorientation angles between adjacent grains
Consequences on the corrosion kinetic on Zy4
Base size grain boundary density
◄ Oxygen diffuse through the grain boundaries
Surface fraction of the oxide grain boundaries
- Base shape converted as a hexagonal shape
- Intergranular space of 0.5 nm
𝑓𝑍𝑟𝑂2/𝑍𝑦4 = 1.8 %
𝑓𝑍𝑟𝑂2/𝐻𝑦𝑑𝑟𝑖𝑑𝑒 = 2.9 % = + 60%
RESULTS – GRAIN BOUNDARY MISORIENTATION
[Sainfort, 1984]
Partially explain the higher corrosion kinetic of the massive hydride
RESULTS – GRAIN BOUNDARY MISORIENTATION
| PAGE 20 CEA | 16th May 2016
Misorientation angles distribution between adjacent grains
Angular range (°)
50-70
85-95
110-150
170-180
► Not randomly distributed
Angular range (°) Distribution (%)
on Zy4 on hydride
50-70 13 % 15 %
85-95 29 % 19 %
110-150 20 % 28 %
170-180 9 % 9 %
RESULTS – GRAIN BOUNDARY MISORIENTATION
CEA | 16th May 2016
Misorientation angles distribution between adjacent grains
► Not randomly distributed
Twins tetragonal to monoclinic
phase transformation
| PAGE 21
Low interfacial energy
Diffusion limited through these
grain boundaries
a
b
c
x
y
z
a
bc
x
yz
90°[001]
a
b
c
x
yz
a
b
c
x
yz
180°[101]
Lower activation energy
for the diffusion of oxygen
Low coherent misorientation angles ► 50° - 70°
110° - 150°
RESULTS – GRAIN BOUNDARY MISORIENTATION
| PAGE 22 CEA | 16th May 2016
Misorientation angles distribution between adjacent grains
► Not randomly distributed
a
b
c
x
y
z
a
bc
x
yz
90°[001]
a
b
c
x
yz
a
b
c
x
yz
180°[101]
Twins tetragonal to monoclinic
phase transformation
Diffusion limited through these
grain boundaries
Lower activation energy
for the diffusion of oxygen
Low coherent misorientation angles
+ 32 % in ZrO2 / Hydride
Participate to the higher corrosion kinetic of the massive hydride
► 50° - 70°
110° - 150°
RESULTS – OXYGEN DIFFUSION SIMULATION
ZrO2 Isotopic exposure in H2
18O
6h; 360°C; 190 bars
18O apparent diffusion coefficient Da ratio :
2.8 × 10−15𝑐𝑚²/𝑠
1.6 × 10−15𝑐𝑚²/𝑠= +𝟖𝟎%
𝐷𝑍𝑟𝑂2/𝑍𝑦4 =
𝐷𝑍𝑟𝑂2/𝐻𝑦𝑑𝑟𝑖𝑑𝑒 =
Second Fick's law:
𝑥18𝑂 = 𝑥𝑠 − 𝑥𝑠 − 𝑥0 . 𝑒𝑟𝑓𝑥
2 𝑫𝒂𝑡
𝑥18𝑂 = 𝑥𝑠 𝑓𝑜𝑟 𝑥 = 0
𝑥18𝑂 = 𝑥0 𝑓𝑜𝑟 𝑥 = ∞
SIMS profile of 18O
ZrO2 / Hydride
ZrO2 / Zy4
Diffusion profile of 18O characteristic of a diffusion
through short-circuits (grain boundaries)
After 6 h
Oxygen diffusion experiments [Bisor C. Phd (2010)]
| PAGE 23 CEA | 16th May 2016
Influence of the columnar grain width ?
RESULTS – OXYGEN DIFFUSION SIMULATION
ZrO2 Modelisation with
Voronoï cell aggregate
ZrO2 / Hydride ZrO2 / Zy4
Sample ZrO2 / Zy4 ZrO2 / Hydride
Average grain
size 34.6 nm 27.8 nm
Conditions
-
- Thickness of the grain boundaries : 0.5 nm
| PAGE 24 CEA | 16th May 2016
Voronoï cells aggregates
- Diffusion coefficient of oxygen in: Volume : 10-18 cm²/s
Grain boundaries : 4.3x10-14 cm²/s
RESULTS – OXYGEN DIFFUSION SIMULATION
ZrO2
www-cast3m.cea.fr
| PAGE 25 CEA | 16th May 2016
Fickian diffusion solved with the
finite element Cast3M, during 6h
► Confirms an effect of the grain size
► lower ratio of diffusion coefficient
► Confirms the diffusion process occurs
mainly through the grain boundaries
Num ZrO2 / hydride
Num ZrO2 / Zy4 After 6 h
ZrO2 / hydride
ZrO2 / Zy4
Modelisation with
Voronoï cells aggregate
18O apparent diffusion coefficient Da ratio :
1.3 × 10−15𝑐𝑚²/𝑠
1.0 × 10−15𝑐𝑚²/𝑠= +𝟑𝟎%
𝐷𝑍𝑟𝑂2/𝑍𝑦4 =
𝐷𝑍𝑟𝑂2/𝐻𝑦𝑑𝑟𝑖𝑑𝑒 =
Simulated:
Lower than experience: +80%
Experience
Simulation
RESUME
| PAGE 26 CEA | 16th May 2016
Higher corrosion kinetic Zircaloy-4 PWR conditions
Precipitation of a massive hydride on the surface
(+ 80%)
Increase the diffusion kinetics of oxygen through the oxide layer
► 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
► 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)
DEN
DMN
SEMI
Michael.jublot@cea.fr
Commissariat à l’énergie atomique et aux énergies alternatives
Centre de Saclay | 91191 Gif-sur-Yvette Cedex
T. +33 (0)1 69 08 88 56
Etablissement public à caractère industriel et commercial | RCS Paris B 775 685 019 25 MAI 2016
| PAGE 27
CEA | 10 AVRIL 2012
THANK YOU
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