INFLUENCE OF THE HYDRIDE PRECIPITATION ON THE … · influence of the hydride precipitation on the...

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


| 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


| 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


• 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


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)]



Cross-section analysis

Fractography

a-Zr 200 nm

ZrO2

ZrO2 / Zy4


ZrO2 / Hydride

d-ZrH1,66 200 nm

ZrO2

ZrO2 / Hydride

Fractography



Cross-section analysis Fractography

d-ZrH1,66

a-Zr 200 nm

200 nm

ZrO2

ZrO2

ZrO2 / Hydride

ZrO2 / Zy4

TEM – Bright field

ZrO2

ZrO2


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



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 :



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]



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


► 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



► The grain size distribution ZrO2 / Zy4

500 nm 100 nm

Index map

Columnar oxide grains

Base shape

- not a regular polygon

- Spread size

distribution



► The grain size distribution ZrO2 / Zy4


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



500 nm

► The grain size distribution

Index map Columnar oxide grains

Base shape



500 nm

ZrO2 / Zy4

► The grain size distribution


Base shape - ~ regular shape

- Smaller size

ZrO2 / Hydride



ZrO2 / Hydride ► The grain size distribution



- Smaller size

~ 15000 indexed grains


Ø 15 - 75 nm 34.6 nm

Ø 15 - 40 nm 27.8 nm

- ZrO2 / Zy4

- ZrO2 / Hydride



ZrO2 / Hydride ► The grain size distribution



- Smaller size


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


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



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 %


CEA | 16th May 2016



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°





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)]


Influence of the columnar grain width ?


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


Voronoï cells aggregates

- Diffusion coefficient of oxygen in: Volume : 10-18 cm²/s

Grain boundaries : 4.3x10-14 cm²/s


ZrO2

www-cast3m.cea.fr


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


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

[email protected]

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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