MICROSTRUCTURE AND PROPERTIES OF A 3-LAYERS NUCLEAR FUEL CLADDING PROTOTYPE CONTAINING ... · 2013. 3. 1. · => all the hydrogen/hydrides concentrated within the intermediate Zr-Er

“MICROSTRUCTURE AND PROPERTIES

OF A 3-LAYERS NUCLEAR FUEL CLADDING

PROTOTYPE CONTAINING ERBIUM AS A

NEUTRONIC BURNABLE POISON.”

17TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY, FEB. 03-07 2013, HYDERABAD, INDIA

J.C. Brachet1, P. Olier1, V. Vandenberghe1, S. Urvoy1, D. Hamon1, T. Guilbert1, A. Mascaro1, C. Toffolon-Masclet1,

S. Doriot1, M. Tupin2, B. Bourdiliau2, C. Raepsaet3, J.M. Joubert4, J.L. Aubin51 CEA- DEN, Department for Nuclear

Materials, Section for Applied Metallurgy Research, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France.2 CEA- DEN, Department for Nuclear Materials, Section for Research on Irradiated Materials, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France3 CEA-DSM, IRAMIS/SIS2M/LEEL, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France4 Chimie Métallurgique des Terres Rares, ICMPE, CNRS, Université Paris-Est, 2-8 rue H.Dunant, F-94320 Thiais, France5 AREVA-CEZUS, BP21 44560 Paimboeuf, France.

� Introduction of neutronic burnable (solid) poisons, such as gadolinium or erbium=> to increase significantly the cycle length and/or the discharge burn-up of LWR’s nuclear fuel sub-assemblies;

� Conventionally, Gd (or Er) introduced as oxides directly into the fuel pellets=> some limitations of this concept:

- introduction into a limited number of rods per assembly => heterogeneous power distribution within the LWR core;

- potential degradation of the thermal conductivity of the fuel pellet;- for a given fuel pellet size, decrease of the overall uranium quantity available for the fission reaction- leads to a more complex quaternary (U,Pu,Gd/Er)Ox system in case of application to MOX fuel, etc…

� Alternative way: introduction of burnable poisons into the nuclear fuel cladding tubes; for such a concept, neutronic calculations (*) have shown that, compared to gadolinium, erbium is a slower burnable poison and should be particularly effective to achieve very high burnup (up to 100-120 GWj/tU !)

=> CEA prospective studies to evaluate fabricability and resultant µstructure-properties of clad materials with introduction of several % of (natural) erbium(*) C. Chabert, J.-C. Brachet, P. Olier, “Neutronic study for introduction of Erbium as a burnable poison into the fuel cladding tube to enable PWR core control”, Proceedings of ICAPP ’08, Paper 8159, Anaheim, CA USA, (June 8-12, 2008)

INTRODUCTION - MOTIVATIONS

2

- Underlying phase diagrams experimentalstudies and modelling (CALPHAD approach…),

PhD works of J. Jourdan and A. Mascaro;

- Fabricability from lab to semi-industrial

scales;

- As-received µstructure and mechanical

properties (internal pressure burst tests, tensile tests…);

- High Temperature (HT) steam oxidation &Post-Quench. (PQ) mech. behavior (LOCA);

- Effects of hydrogen up-take:* Gazeous charging (a few hundreds wt.ppm)

(to simulate hydrogen pick-up upon nominal corrosion conditions)

* Potential massive secondary hydriding(due to incidental direct access of water to the Zr-Er layer)

Main topicsstudied:

"Introduction of erbium in Zr clad...", CEA / Feb. 2013 / [email protected]

| PAGE 3

Due to lack of data/knowledgeon Zr-Er-(O,H) phase diagrams

⇒ Experimental studies and assessment of some of the relevant binary and ternaryphase diagrams;

⇒ Phase diags. modelling using« CALPHAD » methodology, i.e., « Thermo-Calc » calculations + evolution of the «CEA » « Zircobase » -thermodynamic databasefor zirconium alloys (*)

Updated version of the Zr-Er binary system compared to the previous one

(higher erbium solubility in the αZr phase, etc…)

• new proposed diagram

hcp

hcp

bcc

liquid

0 20 40 60 80 100400

0 20 40 60 80 100400

solvus measurement (µprobe)DSC measurementsDifferential Thermal AnalysisSimple Thermal Analysis

at.% Zr

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(°C)

600

800

1000

1200

1400

1600

1800

Tem

pera

ture

(°C)

• previous litterature dataPHASE

DIAGRAMSTUDIES (1)

"Introduction of erbium in Zr clad...", CEA / Feb. 2013 / [email protected] | PAGE 4

(*) N. Dupin, I. Ansara, C. Servant, C. Toffolon, C. Lemaignan, J.C. Brachet, « A Thermodynamic Database for Zirconium Alloys », JNM 275 (1999), 287-295.

PHASE DIAGRAM STUDIES (2)


Previous Er-H binary phase diag. (Mulford, 1958)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

500

1000

1500

2000

Lundin Azarkh Pebler MintzT

(K

)x(H)

ααααEr

Er liq

ErH2

ErH3

P=1e5 Pa

New calculated Er-H binary phase diag.- Comparison with experimental data

(Mascaro et al., CEA, 2010)

PHASE DIAGRAM STUDIES (3)

Zr-Er-H section at 350°C (From A. Mascaro et al., 2012)


Experimental

Calculated




scales;





(to simulate hydrogen pick-up upon nominal corrosion conditions)


Main topicsstudied:


| PAGE 7

Semi-industrial Zr-Er alloys

- wt.% Er from 1 to 10%

- Low alloyed zirconium “Grade D” or Zr-1Nb(O) alloys from Areva-Cezus have been used

(1) Arc melting (100-200g ingots) + hot & cold rolling (CEA/SRMA/LTMEX)

(2) Induction heating (« Skulls » 1-2kg) + hot forging & final cold rolling (Areva/CZ-Ugine)

Final geometry: sheets, thickness~1mm

Final heat treament:Full recristallisation at 580°C for a few hours

Pure binary/ternary Zr-Er-H/O alloys

- Dedicated to phase diagram studies

- Zr and Er of high purity used

- Synthesized by Arc melting as small buttons (a few grams) => more than 50 alloys studied !

« HOMOGENEOUS » Zr-Er ALLOYSFABRICATION ROUTES:

Reference « Grade D »

Zr(D)-4%Er


βNbEr2O3

Fig. 4-a

1µm

Thermal treatments

control has been necessary to

avoid tooimportant

coarseningof Er2O3

precipitates

Er2O3 PRECIPITATION (Ex. : Zr-1%Nb(O) MATRIX + 1,5%Er)

EPMA-WDS Er profiles (wt %):Wt.% Er

Wt.% Er

As-cast

After HT (β) thermal treatment

TEM micrographs on thin foils:


- Due to the available oxygen in solidsolution within the matrix (~500-1500 wt.ppm) and to the strong thermodynamicaffinity of erbium vs. oxygen , Er2O3 precipitation occured upon high temperature thermal treatments� consistent with Zr-Er-O phase diag.

TENSILE MECHANICAL PROPERTIES: Zr(D)-Er ALLOYS(SHEETS MATERIALS, FULLY RECRYSTALLISED CONDITIONS)

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8 9 10 11

MPa

wt. % erbium

YS UTS325°C

YS Zr1Nb

UTS Zr1Nb

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7 8 9 10 11

%

wt. % erbium

UE TE325°C

TE Zr1Nb

UE Zr1Nb


� Fabricability OK, at least up to 10 wt.% erbium

� Necessity to control the intermediate thermal treatmentsto avoid/limit coarsening of Er2O3 precipitates

� Regarding usual (tensile) mechanical properties (strength, ductility), Optimal erbium concentration range vs. reference Zr1Nb(O) alloy=> wt.% Er from ~ 3% to ~6%

� But: autoclave tests have shown very poor corrosion properties (veryfast oxidation after a few days at 360°C, 180 bar, PWR chemistry…)

⇒ Develop a 3-layers « sandwich » clad design,to protect the intermediate Zr-Er layer fromdirect outer/inner oxidising environment access,by using conventional known corrosion resistantZr alloys as inner and outer protective layers

⇒ Co-extrusion fabrication process of|Zr1Nb(O)|Zr3-6%Er|Zr1Nb(O)| clad prototypes

« HOMOGENEOUS » SEMI-INDUSTRIAL Zr-Er ALLOYSMAIN CONCLUSIONS:

Couche interne = alliage 3

Couche externe = alliage 1

Couche intermédiaire = alliage 2 (avec erbium)

Zr-1Nb(O) ~400µm

Zr(D)-5Er ~100µm

Zr-1Nb(O) ~100µmCouche interne = alliage 3



Zr-1Nb(O) ~400µm

Zr(D)-5Er ~100µm

Zr-1Nb(O) ~100µm


(1) Preliminary lab scale (non conventional) fabrication route:

- Powder Metallurgy (PM) elaboration of the intermediate Zr-Er layer + remeltingof industrial Zr1Nb(O) ingots for inner/outer clad layers (CEA);

- Hot co-extrusion + (CEA);

- Not optimised final cold working (CEA).

(2) Semi-Industrial (SI) fabrication route:

- Arc melting of both Zr1Nb(O) and Zr-Er components + cold working of the Zr-Er smallingots as thin sheets (CEA);

- Hot co-extrusion (CEA);

- Final Cold pilgering (AREVA/CZ-Paimbeuf);

In both cases: final full recristallisation heattreament for a few hours at 580°C

CLADDING TUBE (PWR) GEOMETRY - FABRICATION ROUTES (3-layers, 575µm wall thickness):

Couche interne = alliage 3



Zr-1Nb(O) ~400µm

Zr(D)-5Er ~100µm

Zr-1Nb(O) ~100µmCouche interne = alliage 3



Zr-1Nb(O) ~400µm

Zr(D)-5Er ~100µm

Zr-1Nb(O) ~100µm

"Introduction of erbium in Zr clad...", CEA / Feb. 2013 / [email protected] | PAGE 12Inner Zr1Nb(O) Liner

Outer Zr1Nb(O) Layer

Zr-4%Er thin sheets

pieceselaborated

by arc melting+ cold

rolling and final

bending

Before co-extrusion:

LINER

Zr-Er

Surface interne gaine

Inner clad surface

PM fabrication

route:

SI fabrication

route:

Image BSE cartographie X de O Ka

cartographie X de Er La cartographie X de Nb Ka

EPMA X-ray maps:

O

Er Nb

Inner clad surface

Zr1Nb(O)/Zr-4%Er/Zr1Nb(O) 3-L. TUBE – AS-RECEIVED CONDITIONS:


1µm

Er2O3

Er2O3 SIZES DISTRIBUTION WITHIN THE INTERMEDIATE Zr-4%Er LAYER OF THE SEMI-INDUSTRIAL 3-L. TUBE PROTOTYPE

FEG-SEM micrographs performed on carbon extractive replica

0

2

4

6

8

10

12

14

16

18

20

0 100 200 300 400 500 600 700 800

Er2O3 oxides diameter range (nm)

Fre

quen

cy (%

)For the « SI » cladding tube prototype:

- Er2O3 particles mean diameter ~300nm(much coarser erbium rich oxides in the previous « PM » clad prototype)

- Wall clad and layer thickness measurements performed at differentaxial and circumferential positions => Good homogeneity


Internal pressure burst tests at

Room Temperature

(Strength and ductility)

15

Internal pressure burst tests at 325°C

(Strength and ductility)

Partial conclusion: As-received strength/ductility

of the semi-industrialZr1Nb(O)/Zr-4Er/Zr1Nb(O)

clad prototype is OK"Introduction of erbium in Zr clad...", CEA / Feb. 2013 / [email protected] | PAGE 16




scales;





(to simulate hydrogen pick-up associated with nominal corrosion)


Main topicsstudied:


| PAGE 17


⇒ Limited decrease of PQ residual toughness of Zr1Nb/Zr-Er/Zr1Nb clad vs. ref. Zr1Nb(O);

⇒ Coarsening of the Er2O3 particles when increasing oxidation temperature and time,

ZrO2

α(O)

Prior-β

Zr-4%Er

One-side steamoxidation at

1000-1200°C

1mn 800°C 1mn 1200°C

ECR(BJ)=17%

D/B limit




scales;







Main topicsstudied:


| PAGE 19

Zr1Nb(O) referencecladdings

Zr1Nb/Zr-Er/Zr1Nb clad prototypes


In AR conditions, after hydrogen gaseous charging=> all the hydrogen/hydrides concentrated withinthe intermediate Zr-Er layer

=> Higher H thermodynamic affinity of Zr alloyedwith rare earth chemical elements (ex.: Yttrium)

=> Looks like the Hydrogen trapping effect of internal low-alloyed Zr liner of BWR claddings, but here, with a higher efficiency

Pre-hydriding effects(1)

« PM » fabrication route+ [H] ~ 450 ppm

« SI » fabrication route+ [H] ~650 ppm

From K. Sakamoto et al., Proceedings of the 2007 International LWR Fuel Performance Meeting, San Francisco, California, 2007

100°C/s


Pre-hydriding effects (2)Effect of cooling rate on hydrides spatial distribution

580°C (full hydrides dissolution)Temperature

Time

Cooling rates ranging from0,5°C/mn up to 100°C/s

The intermediate Zr-Er layer hydrogentrapping efficiency strongly depends on the cooling rate from the temperature range

where all the hydrides have been dissolved

[H] overall = 650 wt.ppm

10°C/s

1°C/s

10°C/mn

0,5°C/mn


Pre-hydriding effects (3)µ-ERDA / quantitative mapping of hydrogen


Pre-hydriding effects (4)Thermodynamic & kinetics considerations

I. Takagi et al., J. Nucl. Sci. & Tech., (2002)

Erbium addition:⇒ Important increase of TSS Temperature of hydrides⇒ Upon cooling, hydrides precipitation occurs earlier in

the intermediate Zr-Er layer ⇒ Zr-Er layer H enrichment due to H gradient-

diffusion from inner/outer Zr1Nb layers

Thermodynamic calculations(« Thermocalc » + « Zircobase » with

introduction of Zr-Er-H interaction parameters)

+3%Er => θ(TSS) ↑↑↑↑ �� ∆∆∆∆θ(TSS)≥100°Ccompared to ≤10°C for BWR Zry2/Zr-lined clad

α-Zr + δ-(Zr,Er)H2-x

α-Zr

650ppm


Pre-hydridingeffects (5)

Impact on mechanicalproperties at R.T.

– as received(as-prehydrided) conditions

Ring tensile testing:

Increase of H content:⇒ Limited strengthening⇒ Limited effect on

ductility parameters, except Total Elong. of Zr1Nb/Zr-Er/Zr1Nb for [H]~650ppm




scales;







Main topicsstudied:


| PAGE 25

ZrO2Zr-Er

Zr1Nb

Zr1Nb

H2O

H ?

H ?

Important issue: due to fast oxidation of the intermediate Zr-Er layer (here, fromthe clad segment ends), one could anticipatevery detrimental influence on the resultantclad mechanical properties/integrity due to potential associated massive 2ndary hydriding

Simulation of incidental direct water access to the Zr-Er layerAutoclave tests performed on the « PM » 3-layers clad prototype =>7-10 days at 360°C, 180 bar, PWR representative chemistry,

Full corrosion of ~1-2cm length (axial direction) of the Zr-Er layer after only10 days at 360°C (!) => consequences on the mechanical properties?

Fullycorroded

Zr-Er layer


POST-AUTOCLAVE RING COMPRESSION TESTS (RCT) AT RT.

Reference « PM » Zr1Nb/Zr-Er/Zr1Nb clad segment, not oxidised

« PM » Zr1Nb/Zr-Er/Zr1Nb clad segment afterautoclave test, Zr-Er layer fully oxidised

Partial conclusion: Important residual ductility after autoclave test and full oxidation of the Zr-

Er intermediate layer of the « PM » Zr1Nb(O)/Zr-4Er/Zr1Nb(O) clad prototype.=> Why ?


Local [H] content within the Zr-Er layer~ 15000 wt.ppm-mass.

~ pure hydride !

EPMA (WDS):

Nuclear microprobe (µ-ERDA) :

Mean [H] content within the inner and

outer Zr1Nb(O) layers≤≤≤≤ 150 wt.ppm.

EPMA and µ-ERDA performed on the autoclave tested « PM » Zr1Nb(O)/Zr-4Er/Zr1Nb(O) clad prototype

BSE OxygenErbium

Hydrogen

The post-corrosion preservation of the clad

ductility/integrity is due to the Zr-Er intermediate

layer, playing a « sacrificial » role, and thus avoiding anysignificant throughout wall

clad thickness hydrogenspatial redistribution…


- Erbium introduced within Zr nuclear fuel clad for neutronic purposes;

- Experimental study & modelling (CALPHAD) of Zr-Er-(O,H) phase diagrams=> Improvement of CEA « Zircobase » thermodynamic database for Zr alloys;

- Due to the detrimental influence of erbium on corrosion resistance=> Three-layers « sandwich » clad prototype, with use of corrosion resistantinner/outer Zr-1%Nb layers to protect the intermediate Zr-Er layer fromdirect water access;

- Fabrication OK (tensile prop. => optimum Er content from ~3 up to ~6 wt.%, thermal treatments have to be controlled to limit Er2O3 coarsening…);

- High hydride trapping capacity of the intermediate Zr-Er layer both for hydrogen coming from nominal outer corrosion or due to massive secondary hydriding in case of direct access of water to the Zr-Er intermediate layer (depends on the cooling rate down to RT…)

- Compared to ref. Zr-1Nb(O) alloy, slight decrease of ductility/toughness due to pre-hydriding or after high temperature steam oxidation (LOCA)

(!) Pending issue: behavior under neutron irradiation ? …


Summary…

DANSDMNSRMA

Commissariat à l’énergie atomique et aux énergies alternatives

Centre de Saclay | 91191 Gif-sur-Yvette Cedex

T. +33 (0)1 69 08 56 13 | F. +33 (0)1 69 08 71 67

Etablissement public à caractère industriel et commercial | RCS Paris B 775 685 019

Thank you for your attention


| PAGE 30

AKNOWLEDGMENTS:

From CEA labs: S. Urvoy, D. Hamon, T. Guilbert, C. Toffolon,S. Doriot, J. Jourdan, A. Mascaro, P. Olier, D. Nunès,V. Vandenberghe, C. Bernard,Ph. Bossis, M. Tupin, P. Billaud , B. Bourdiliau,X. Averty, Q. Auzoux, J. Pegaitaz, C. Raepsaet, C. Chabert, B. Gastaldi, M. Auclair, …

From Areva-Cezus: JL. Aubin, B. Guerin, P. Barberis

From EDF-R&D: M. Blat

From CNRS-ICMPE/Paris-Est: JM. Joubert

Documents

MICROSTRUCTURE AND PROPERTIES OF A 3-LAYERS NUCLEAR FUEL CLADDING PROTOTYPE CONTAINING ... · 2013. 3. 1. · => all the hydrogen/hydrides concentrated within the intermediate Zr-Er