Quantification of the ααα(O) and Prior-ββββ phase ... · contents of ααα(O) and...

1J.C. Brachet et al., CEA-Saclay, DEN/DMN/SRMA, 91191 Gif-Sur-Yvette, France

e-mail : [email protected]

Nuclear Energy Division

Quantification of the αααα(O) and Prior-ββββ phase fractions

and their oxygen contents

in high temperature (HT) oxidised Zr alloys (Zy-4, M5™)

Outlines : to be able to quantify the local « ECR » of HT oxidised cladding

tubes (i.e. to characterize locally the resultant clad microstructure after a

LOCA test leading to a non homogeneous oxidation of the cladding tube,

for examples : due to azimuthal and/or axial thermal gradients along the

tube, due to secondary oxidation in the vicinity of a failure, etc…)

• illustration of application of the methodology to study the influence of :

(1) Conventional Furnace Heating (FH) vs. Induction Heating (IH)

(2) Single Face (SF) vs. Double Face (DF) oxidation mode

on M5™ oxidised at 1000°C (before/after «break-away» occurrence)

J.C. Brachet, L. Portier, D. Hamon, Ph. Trouslard, S. Urvoy, V. Rabeau

CEA - Saclay (France)

+ A. Lesbros (EDF-Septen) and J.P. Mardon (FRA-ANP)




Parameters influencing the αααα(O) and Prior-ββββ

phases thickness and morphology of HT oxidised

clads and their local oxygen contents :

(1) Temperature transient conditions : that is,

heating/cooling rate, time & temperature of the HT

oxidation (as an example, the increase of the

oxidation temperature => increase of the oxygen

solubility in Prior-β phase) ;

(2) Alloy types (Zircaloy’s, Niobium containing,…);

(3) Hydriding (due to nominal in-service oxidation)

(4) Other…




The experimental methodology has been developed and applied to

HT oxidised Zy-4 and M5™ cladding tubes :

(1) Quantification of the α(O) and Prior-β phases thickness by

Scanning Electron Microscopy (SEM) in back-scattered

electron imaging mode coupled with image analysis

procedure

=> illustration on M5™ oxidised at 1000°C

– influence of the heating mode (furnace vs. induction)

and Single-Face vs. Double-Face oxidation modes

(2) Measurements of the local oxygen content by Electron Probe

Micro Analysis (EPMA) and thanks to the use of Nuclear

Reaction Analysis (NRA) to take into account the influence

of « surface contamination » (nanometric ZrO2 layer formed

on the sample surfaces during the preparation)

+ Vickers microhardness (50-100 g) measurements




M5 après essai d’oxydation

à 1200°C pendant 1422s

dans Dézirox

Micrographie optique Micrographie électronique (rétro-diffusés)

Image de départ en niveau de gris obtenue en microscopie

électronique Image binaire obtenue après traitement de la micrographie

MEB (seuillage, érosion, dilation, fermeture, ouverture, ...)

Ex-ββββ

αααα-Zr(O) αααα-Zr(O)

Ex-ββββ

Ex-ββββ

αααα-Zr(O) après

binarisation

(1) Experimental procedure for the quantification of the α(O) and

Prior-β phase thickness – illustration on the M5TM alloy

Optical micrograph

(polarised light)

Electron (SEM) micrograph

Electron (SEM) micrograph

(backscattered electron mode)

Binarisation (Image Analysis)

M5TM

SF oxidation

for 1422 s.

at 1200°C

α(O) after image

binarisation

Prior-β

Prior-βPrior-β

α(O) α(O)




N°3

0

10

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60

70

80

90

100

110

0 50 100 150 200 250 300 350 400 450 500

epaisseur en µm

% phase

Clad thickness (µm)

α(O) %

Image analysis measurement of

the α(O) fraction evolution

within the thickness of a SF

oxidised M5™ clad

ZrO2/αααα(O)

interface

Internal clad

surface

Continuous

αααα(O) layer

αααα(O) +

Prior-ββββContinuous

Prior-ββββ layer

8 fields per

tube section

are considered




Evolution of the αααα(O) and Prior-ββββ phase phase thickness

as a function of the oxidation time at 1000°C of M5TM

{Single Face (SF) – Furnace Heating (FH)} - « Dezirox » facility

vs. {Double Face (DF) – Induction Heating (IH)} – « Cinog » Facility

0 20 40 60 80 100 1200

5

10

15

20

25Measurements performed

for 4 typical oxidation times

M5™

SF oxidised

at 1000°C




0 20 40 60 80 100 120 1400

50

100

150 DF - IH (Ext. + Int.)

SF - FH (Ext.)

Parabolic growth kinetics (diffusion controlled)

5-6 min

21-24 min

55 min

3h45min-4hbeginning of "breakaway" (5000s)

1/2

M5™ SF & DF

oxidised at 1000°C




0

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120

0 10 20 30 40 50 60 70 80 90 100

Relative distance (%) / clad metal thickness

% of Alpha(O)

SF/FH - 3270s

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80

100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O)

DF/IH - 3270s

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O

)

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60

80

100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O)

Direct comparison of the Alpha(O) phase fraction spatial distributions

within the thickness of M5™ oxidised tubes for the both oxidation modes




Direct comparison of the Alpha(O) phase fraction spatial distributions

within the thickness of M5™ oxidised tubes for the both oxidation modes

SF/FH - 14550s

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O

)

DF/IH - 13500s

0

20

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100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O)

0

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40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O

)

0

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60

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120

0 10 20 30 40 50 60 70 80 90 100


% of Alpha(O)




No significant influence on M5TM oxidised at 1000°C :

of the heating mode (FH vs. IH)

nor of the oxidation mode (SF vs. DF)

on the αααα(O) thickness evolution vs. oxidation time

- and thus, no significant influence on the « Breakaway » (this last

point has been also confirmed by post-test hydrogen analysis and by

the observation of the ZrO2 morphology evolution, which gave similar

results for the two heating-oxidation conditions applied in CEA)

- the α(O) growth kinetics seems to be parabolic even after

breakaway occurrence (up to 4 hours of oxidation at 1000°C)

Partial conclusions




(2) Measurements of the local oxygen content by :

• Electron Probe Micro Analysis (EPMA)

=> CAMECA « Microbeam », 15kV, ~10 nA

=> Volume analysed ~1µm3

• Nuclear Reaction Analysis (NRA) :

⇒ HVEE AN-2000 Van de Graaff

(2A & 2F) positive in accelerator [*]

=> nuclear reaction 16O(d,p1)17O

=> 900 keV deuteron beam

=> incident current = 150 nA (take angle = 150°)

=> spot diameter ~ 0.5 mm - resolution in depth ~ 1µm

[*] L. Beck, A. de Château-Thierry, J.-P. Frontier, S. Pellegrino, Ph.Trouslard,

Twenty five years of IBA teaching experience at the National Inst. For

Nuclear Science and Technology, France, Nucl. Instr. and Meth. B (in press)




Problem with EPMA measurements :

Overestimation of the oxygen content due to surface

contamination (contribution of the surface oxide layer)

Incident

electron

beam

X-Ray (WDS analysis of oxygen)

~1µm3

«Native» nanometric oxyde

layer on the sample surface

Polished sample




Solutions to the EPMA oxygen overestimation problem :

(1) Systematic use of calibration samples consisting of a

Zy-4 or a Zr-1%Nb matrix with a very low oxygen

content (100-200 wt-ppm)

=> assumption that the surface nanometric oxide layer has

the same contribution on the global oxygen WDS analysis

on both low oxygen and highly oxidised Zr alloys (?)

(2) Use of NRA measurements which allows to

deconvolute the contribution of the oxygem atoms

near the sample surface from that of the oxygen atoms

in the bulk




Sample preparation for NRA measurements of the oxygen

content within the Prior-Beta phase internal layer of High

Temperature SF oxidised cladding tubes :

before polish after polish

Internal cladding

tube surface

Prior-ββββ

αααα (O)

ZrO2

NRA spot

~ 200µm2



Nuclear Energy Division16O(d,p1)

17O

0

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120

140

160

180

200

0 200 400 600 800 1000 1200 1400

Energie [keV]

Contenu

Expérimental

Simulé

Oxygène en profondeur

Oxygène en surface

Condutions expérimentales

Ed 900 keV

Ξη��&�� 150°

i 250 nA

q 400 µC12 µm Mylar

O in the bulk

O in the

sample surface

Typical NRA oxygen

spectrum obtained within the

Prior-ββββ phase internal layer

of a HT SF oxidised sample

=> It is possible to deconvolute the contribution of the oxygen atoms at the sample surface

c

o

u

n

t

s

Energy (keV)

experimental

simulation




Comparison between oxygen content measurements performed

by EPMA and NRA on the internal Prior-β phase layer

0 0,2 0,4 0,6 0,8 1 1,20

0,2

0,4

0,6

0,8

1

1,2




Microhardness evolution of the internal Prior-Beta phase layer

vs. oxygen content measured by NRA

(SF oxidations performed for different times at 1000-1200°C)

⇒Scattering of the µhardness

values (especially for Zy-4

alloy) - probably due to the

coarse grain sizes and local

crystallographic texture effects

+ α(O) phase penetrations within

the internal Prior-β phase layer

⇒ µhardness measurements

can only give semi-quantitative

information on the local

oxygen concentration ; they

should depend also on the

alloy, on the quenching rate, …

0 0,2 0,4 0,6 0,8 1 1,2200

250

300

350

400

450

500




CONCLUSIONS

• Because of the strong influence on quenching behavior and on the post-quench

mechanical properties of HT oxidised Zr base cladding tubes, a methodology has

been developped and applied to quantify the fractions and the local oxygen

contents of αααα(O) and prior-ββββ phases in the thickness of HT oxidised tubes.

• The methodology is able to quantify locally the ECR and thus can be applied on

cladding tubes wich have been subjected to a non homogeneous HT oxydation

=> validation of the methodology by comparing (re)calculated ECR v.s. «realistic

ECR» derived from weight measurements on homogeneously HT oxidised tubes is

in progress

• The methodology can be transposed to irradiated samples (thanks to the avaibility

of SEM, EPMA & NRA in CEA-Saclay hot cells)

• An application of the methodology to M5™ alloy oxidised at 1000°C has shown

no significant influences of the heating (FH vs. IH) and of the oxidation (SF vs.

DF) modes on the αααα(o)/prior-ββββ thickness evolution and thus on the breakaway

occurrence => check the consistency between the two main HT-oxidation

facilities used in CEA on non-irradiated clads (“Dezirox” & “Cinog” facilities)




Zy-4:

(3)

(2)

(1)

(1) Brittle failure of α(O)

(2) Incursions of brittle

α(O) in ex-β zone

(3) Ex-β zone with flatdimples indicating a quite

low residual ductility

No ZrO2 (delamination)EPMA X-ray maps of oxygen (+ Fe, Cr) and

typical fractographs of an impact tested Zy-4

specimen failed at R. T. (Single Face oxidation

for ~3000s at 1100°C)

(from Halden IAEA meeting, J.C. Brachet, 2001);

Zy-4:

O-Kα

Fe-Kα Cr-Kα

ZrO2 αααα(O) Ex-ββββ

=> Illustration of the strong influence

of the α (O) and Prior-β phase

characteristics (morphology : i.e.

spatial repartition and thickness,

oxygen contents…) on the post-

quench mechanical properties




Electron Probe X-ray maps -ECR=17%

Zy-4:

M5TM:

O-Kα

Fe-Kα Cr-Kα

Nb-KαO-Kα

ZrO2 αααα(O) Ex-ββββ

Illustration of the influence of alloy type on the α/Prior-β phases :

EPMA X-ray maps of Zy-4 and M5TM oxidised up to ~17%-ECR at 1100°C

(from Halden IAEA meeting, J.C. Brachet et al., 2001)




M5TM –– 1000°C

323 sec. 360 sec.

M5 Dé zyrox Essa i 190

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0 20 40 60 80 100 120

Dis tanc e en % épais s eur gaine

% phase a form

é

Moyenne M5 DC 3

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90.00

100.00

0.00 20.00 40.00 60.00 80.00 100.00

Distance en % epaisseur gaine

% phase a form

é

SF + FH DF + IH% α(O)

Relative distance (%) / clad metal thickness Relative distance (%) / clad metal thickness

% α(O)



Nuclear Energy DivisionMicrographies MEB-rétrodiffusé comparatives (épaisseur métal.)

M5TM – Dezirox/Cinog –1000°C 1290 sec. 1450 sec.

M5 Dézyrox Essai 159

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0 20 40 60 80 100

Distance en % épaisseur gaine

% de phase a form

é

M5 DC 9

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120

0 20 40 60 80 100

Distance en % épaisseur

% phase a formé

M5TM –– 1000°C

% α(O)SF + FH

% α(O)DF + IH






M5 Dézyrox Essa i 192

0

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0 20 40 60 80 100

Dis tance en % épaisseur gaine

% phase a form

é

M5 Cinog DC20

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0 20 40 60 80 100

Dis tance en % épaisseur gaine

% phase a form

é

% α(O)

M5TM –– 1000°C

SF + FH % α(O) DF + IH






M5 Cinog essai NT3

0

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0 20 40 60 80 100Distance en % épaisseur gaine

% phase form

é

M5 Dézirox Essai 152

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0 20 40 60 80 100Distance en % épaisseur gaine

% phase a form

é

Ep.métal ~530µm Ep.métal ~520µm

% α(O)

M5TM –– 1000°C

SF + FH % α(O)DF + IH


Quantification of the ααα(O) and Prior-ββββ phase ... · contents of ααα(O) and...

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Transcript of Quantification of the ααα(O) and Prior-ββββ phase ... · contents of ααα(O) and...