A. Stern, J.C. Brachet, V. Maillot, L. Portier and A. Pineau

• Protocols allowing to obtain homogeneous monophased alpha and « prior beta » samples with different oxygen contents were validated for the two alloys M5® and Low-tin Zy4.

• Mechanical tests transition in the failure mode for monophased “prior ” samples depending on the test temperature and of the contents of oxygen studied (0.25 ; 0.5 ; 0.7 and 0.9wt%). • Mechanical studies by bending are in progress in order to characterize the alpha phase for the two alloys.• Fractographic studies are in progress in order to analyse more in depth the failure mode.

CONTEXTCONTEXTCONTEXTCONTEXT

CONCLUSIONSCONCLUSIONSCONCLUSIONSCONCLUSIONS

DMN/SRMA

Objective and approach: The objective is to model the HT oxidized multilayered material behaviour. The approach consists in elaborating the different homogeneous phases [1] and studying them separatly [2], then integrate all the data [3] to reinterpret the global multilayer material behaviour starting with a as-received sample in form of sheet from industrial alloys from AREVA NP Fuel: Low-tin Zy4 (Zr-1,3Sn(Fe,Cr,O)) and M5® (Zr-1Nb(O)) :

Modelisation of the global

multilayered material

Elaboration of monophased samples with different oxygen

contents

HT Homogenization in inert atmosphere to obtain

monophased samples :

[1]

Elaboration of multiphased samples: HT oxidation followed by quench, using DEZIROX

experimental device (two sides oxidation) :

(Low-tin Zy4 : 0.9%wtO)

« prior beta »

ZrO2

(O)

L

t

(M5® : 0.25%wtO homogenized at 1200°C during 3h)

« prior beta »

t

L

[1] L. PORTIER, T. BREDEL, J.C. BRACHET, V. MAILLOT, J.P. MARDON, A. LESBROS, “Influence of Long Service Exposures on the Thermal-Mechanical Behavior of Zy-4 and M5™ Alloys in LOCA Conditions”, 14th Int. ASTM Symp. on “Zr in the Nuclear Industry”, Stockholm, 13-17 June 2004,ASTM-STP

[2] JC. BRACHET, L. PORTIER, V. MAILLOT, T. FORGERON, JP MARDON, P. JACQUES, A. LESBROS, “Overview of the CEA data on the influence of hydrogen on the metallurgical and thermal-mechanical behavior of Zircaloy-4 and M5™ alloys under LOCA conditions”, proceeding of the NSRC meeting, Oct. 25-27th, 2004, Washington-DC, USA

EXPERIMENTAL APPROACH AND RESULTS OBTAINED DURING THE STUDYEXPERIMENTAL APPROACH AND RESULTS OBTAINED DURING THE STUDYEXPERIMENTAL APPROACH AND RESULTS OBTAINED DURING THE STUDYEXPERIMENTAL APPROACH AND RESULTS OBTAINED DURING THE STUDY

• The zirconium-based cladding tube, acts as the primary barrier for confinement of the radioactive fuel, and its integrity as well as its dimensional stability are key parameters during hypothetical accident scenarii.

• During a Loss of Coolant Accident (LOCA), the clad may be subject to a rapid increase of temperature (up to 800-1200°C) in steam environment, which induces accelerated oxidation until quenching during the reflooding of the core.

360°C

Coating of zirconia ~ brittle

Phase (O) ~ brittle

Phase “Prior “ ± ductile

T(°C)

time

quench

1000°C

10%

%at. O

66,6

~30

~5 à

ZrO2

%at. O

66,6%

~30%

~5 à

Clad thickness

ZrO2

(O)

Prior

Optical micrograph

y of the clad’s

thickness (after HT oxidation)

Contrary to oxidation at nominal temperatures (300-360°C): an important fraction of oxygen atoms diffuses in the suboxide metal and tends to promote embrittlement of the clad (after quench).

w

L

t

Study of each phase (here « prior beta »

phase)

Finite elements calculatio

n

ZrO2

(O)

…

« prior  » 

[2] [3]

Low-tin Zy4 : 0.9%wtO

Fontevraud, 18-22 September 2006Fontevraud, 18-22 September 2006

Low-tin Zy4 : 0.25%wtO

Acknowledgements to AREVA NP Fuel (J.P. Mardon for supplying the alloys) and EDF/SEPTEN (A. Lesbros)

<3%« Prior beta  »

ZrO2

M5® is a registered trade mark of AREVA NP