1. 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. CONTEXTCONTEXT CONCLUSIONSCONCLUSIONS 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% wt O) « prior beta » ZrO 2  (O) L t (M5 ® : 0.25% wt O 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”, 14 th 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. 25-27 th, 2004, Washington-DC, USA EXPERIMENTAL 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 ~5à ZrO 2 %at. O 66,6% ~30% ~5à Clad thickness ZrO 2  (O) Prior  Optical micrography 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 calculation ZrO 2  (O) … « prior  » [2] [3] Low-tin Zy4 : 0.9% wt O Fontevraud, 18-22 September 2006 Low-tin Zy4 : 0.25% wt O Acknowledgements to AREVA NP Fuel (J.P. Mardon for supplying the alloys) and EDF/SEPTEN (A. Lesbros) <3% « Prior beta »  ZrO 2 M5 ® is a registered trade mark of AREVA NP