Residual Stress Characterization In Zirconium Oxides Using Synchrotron XRD Manchester Materials Science Centre, The University of Manchester, Grosvenor Street, Manchester M1 7HS, United Kingdom Efthymios Polatidis, Philipp Frankel, Jianfei Wei, Michael Preuss

Uses and corrosion of Zr-Alloys Zr-alloys used as cladding materials of the fuel rods. In service environments oxidation occurs limiting their service life. OXIDE METAL

Uses and corrosion of Zr-Alloys Zr-alloys used as cladding materials of the fuel rods. In service environments oxidation occurs limiting their service life. Better understanding of the corrosion mechanisms could lead to improvement of the burn up efficiency. Residual stresses in the oxide are believed to play key role on the corrosion properties of the material.

Origin of stresses Transformation strain. Transformation of Zr-ZrO 2 is accompanied by volume dilatation. (volume of ZrO 2 is 1.56 times greater than Zr) How do stresses affect oxidation? The tetragonal phase can be stress stabilised As oxidation proceeds stresses might be reduced in the oxide away from the interface, which could lead to t m phase transformation This phase transformation is associated with a further volume increase ─ cracks─ acceleration of corrosion kinetics Stresses in Zr-alloys oxides

Synchrotron X-Ray diffraction experiment at BESSY EDDI, Berlin Residual strain (along the oxide thickness) can be extracted by altering the incident angle theta. Sin 2 psi method. Fixed angle detector Sample Diffracted beam Incoming white beam psi θ

m(-111) t(101) Zr(100) m(002) Zr(002) Zr(101) m(-211) m(211) Zr(102) m(-122) m(221) Zr(103) Synchrotron X-Ray diffraction experiment at BESSY EDDI, Berlin Increasing penetration Higher energy - greater penetration - depth profile Diffraction spectrum for each measurement angle ψ

Lowest angle= highest energy Max. Pen. greater than oxide thickness Highest angle= lowest energy Max. Pen. Only samples part of oxide thickness ≈ θ θ θ metal oxide metal oxide metal Penetration depth with 2θ

Results ZIRLO™ SR/80 days at 360 °C ZIRLO™ SR/160 days at 360 °C Maximum stress - close to the O/M interface OxideMetal Distance from outer surface (um) Distance from outer surface (um) Residual Stress (MPa)

Synchrotron XRD experiment at ESRF ID11, France Using XRD diffraction in transmission geometry and monochromatic beam, the setup allows strain characterization along the oxide thickness: Detector Sample Diffracted cones Incoming beam Residual strain (along the oxide thickness) can be extracted by comparing “strain free” samples with strained lattice spacing values. (d strained -d strain free )/d strained = strain

y z oxide 85º95º 5º -5º For each measurement point Diffraction Pattern Synchrotron XRD experiment at ESRF ID11, France

For each measurement point Diffraction pattern 85º95º 5º -5º Diffraction spectrum Synchrotron XRD experiment at ESRF ID11, France

Stress calculation Strain= (d hkl -d 0 )/d 0 Extract stress tensor using Hooke’s Law, knowing in plane (ε xx ) and out of plane (ε yy ) strain. x y oxide Metal z FE analysis suggests that the out of plane stress (σ yy ) is equal to zero, thus out of plane strain (ε yy ) occurs due to Poisson’s contraction.

Results

Compressive stresses - Oxide Balancing tensile stresses-Metal- High temperature/time-Creep FEM simulating the stress due to oxide volume expansion and relaxation due to creep High T Tension High T compression Relaxed Tension High T Relaxed compression Tension High T compression Relaxed Tension High T Relaxed compression compression Creep of the substrate

Measured Elongation by creep (M. Blat ‐ Yrieix et. al) FEM creep strain Evolution of strain versus oxide thickness Creep of the substrate Blat-Yrieix M. et. al, Toward a Better Understanding of Dimensional Changes in Zircaloy-4: What is the Impact Induced by Hydrides and Oxide Layer?, Journal of ASTM International, Vol. 5, No. 9, 2008.

Distance from O/M interface (μm) Residual Stress (Mpa) Creep of the substrate

Conclusions A stress profile exists through oxide thickness - maximum compressive stresses near the O/M interface stress decay away from interface may enable tetragonal to monoclinic phase transformation. Stress reduces with oxidation time. A stress profile may be produced by creep of substrate – however the shape of the measured profile does not match the profiles predicted by substrate creep alone. Stress profile affected by other factors such as cracks between the oxide layers.

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