The Cause Of Transition In Fuel Cladding Oxidation …...PowerPoint Presentation Author Swan, Helen...
1
www.nnl.co.uk The Cause Of Transition In Fuel Cladding Oxidation Rates The difficulty of monitoring active components makes predictive modelling of their degradation rates of particular value within the nuclear industry. Where models are supported by mechanistic understanding, they are more robust and more capable of extrapolation to varying material and operational conditions. The nature of the oxide on fuel cladding is very dynamic, with the grain structure, oxide phase, solute distribution, solute oxidation state, stress state, micropore and crack population all changing as a function of oxide thickness, location in the oxide and time. This poster presents the insight into the cyclic nature of fuel cladding corrosion resulting from multiple measurements made with multiple techniques on Zircaloy-4. The techniques include optical microscopy with digital image correlation (DIC) to measure strain development, standard scanning electron microscopy (SEM) and 3D SEM (3D-FIB) to follow overall morphology and crack development, transmission electron microscopy (TEM) to follow oxide grain and micropore development and to observe dislocations in the substrate, plus synchrotron X-ray diffraction (SXRD) to measure the changing stress and oxide phase distributions. The cyclic nature of corrosion is shown to be induced by stress relaxation. References [1] H. Swan, M. S. Blackmur, J. M. Hyde, A. Laferrere, S. R. Ortner, P. D. Styman, C. Staines, M. Gass, H. Hulme, A. Cole-Baker and P. Frankel, J. Nuclear Mater., vol. 479, pp. 559-575, 2016. [2] S. Ortner, H. Swan, A. Laferrere, C. English, J. Hyde, P. Styman, K. Jurkschat, H. Hulme, A. Pantelli, M. Gass, V. Allen and P. Frankel, Fontevraud 8, Avignon, France, September 2014. [3] H. Weekes, S. Ortner, A. Qaisar, M. Blackmur, S. Lozano-Perez and K. Jurkschat, submitted to J . Nuclear Mater., 2018. [4] S. Ortner, M. Blackmur, M. Fenwick, H. Weekes and M. Gass, Fontevraud 9, Avignon, France September 2018. [5] V. Allen, C. English, M. Gass, R. Howells, H. Hulme, J. Hyde, D. Ludlow, S. Ortner and H. Swan, Zirconium in the Nuclear Industry 17th Int. Symp., Hyderabad, India, February 2013. [6] P. Platt, S. Wedge, P. Frankel, M. Gass, R. Howells and M. Preuss, J. Nuclear Mater., vol. 459, pp. 166-174, 2015. Introduction S. Ortner 1 , H. Wilcox 1 , H. Swan 1 , M. Fenwick 2 , M. Blackmur 1 , M. Gass 2 , J. Smith 3 , K. Jurkschat 4 A collaborative project from: 1. 2. 3. 4. 1 2 5 3 4 6 The forward front of the inter-connected water network is located at the cracks at the delays in the oxidation front. Immediately post-transition, the oxide thickness is ~ nil at the delays, but a few hundred nm at the protrusions. This difference causes the oxide growth rate at the delay to be much greater than that at the protrusions, so the interface flattens. The flat interface prevents new in-plane cracks nucleating. The network is truncated, the protective oxide thickens and the oxidation rate decreases. Without undulations and cracks, the oxide stress has fewer relaxation modes so the compressive stress in the new oxide is again large, and can induce tension and plasticity in the metal. SXRD SEM Interface Roughness [6] 6. Stress mismatch at metal-oxide interface encourages undulations. These, and metal plasticity, reduce average oxide in-plane stresses. SXRD SEM 2. The through-plane cracks reach the inter-connected in-plane crack network, which then fills with water. The protective oxide thickness thereby drops and the corrosion rate increases. Transition ensues. The change in local stresses encourages neighbouring networks to link: transition spreads. Interfacial undulation amplitudes increase. Stress redistribution around undulations induces in-plane cracking at delays in oxidation front. This further reduces local oxide stress during 2 nd μm of oxide growth. As interface moves inward, away from individual in-plane cracks, these cracks can grow and link. 3. Metal grain to grain mismatches in plastic flow cause strain concentrations which, transmitted to contiguous oxide, produce local regions of tension in the oxide. Through- plane cracks grow in from surface. Crack growth is assisted by the presence of porosity along oxide grain boundaries. 4. DIC [4] TEM showing porosity 3D-FIB [3] SXRD SEM 5. 3D-FIB SEM [5] Cyclic growth with attendant observations and interpretations 7. Process repeats Tensile stress in metal matching large compressive stress in oxide induces plasticity in metal. TEM showing dislocations [2] 1. SXRD [1] – monoclinic stress
Transcript of The Cause Of Transition In Fuel Cladding Oxidation …...PowerPoint Presentation Author Swan, Helen...
www.nnl.co.uk
The Cause Of Transition In Fuel Cladding Oxidation Rates
The difficulty of monitoring active components makes predictive modelling of their degradation rates of particular value within the nuclear industry. Where models are supported by mechanistic understanding, they are more robust and more capable of extrapolation to varying material and operational conditions. The nature of the oxide on fuel cladding is very dynamic, with the grain structure, oxide phase, solute distribution, solute oxidation state, stress state, micropore and crack population all changing as a function of oxide thickness, location in the oxide and time. This poster presents the insight into the cyclic nature of fuel cladding corrosion resulting from multiple measurements made with multiple techniques on Zircaloy-4. The techniques include optical microscopy with digital image correlation (DIC) to measure strain development, standard scanning electron microscopy (SEM) and 3D SEM (3D-FIB) to follow overall morphology and crack development, transmission electron microscopy (TEM) to follow oxide grain and micropore development and to observe dislocations in the substrate, plus synchrotron X-ray diffraction (SXRD) to measure the changing stress and oxide phase distributions. The cyclic nature of corrosion is shown to be induced by stress relaxation.
References
[1] H. Swan, M. S. Blackmur, J. M. Hyde, A. Laferrere, S. R. Ortner, P. D. Styman, C. Staines, M. Gass, H. Hulme, A. Cole-Baker and P. Frankel, J. Nuclear Mater., vol. 479, pp. 559-575, 2016. [2] S. Ortner, H. Swan, A. Laferrere, C. English, J. Hyde, P. Styman, K. Jurkschat, H. Hulme, A. Pantelli, M. Gass, V. Allen and P. Frankel, Fontevraud 8, Avignon, France, September 2014. [3] H. Weekes, S. Ortner, A. Qaisar, M. Blackmur, S. Lozano-Perez and K. Jurkschat, submitted to J . Nuclear Mater., 2018. [4] S. Ortner, M. Blackmur, M. Fenwick, H. Weekes and M. Gass, Fontevraud 9, Avignon, France September 2018. [5] V. Allen, C. English, M. Gass, R. Howells, H. Hulme, J. Hyde, D. Ludlow, S. Ortner and H. Swan, Zirconium in the Nuclear Industry 17th Int. Symp., Hyderabad, India, February 2013. [6] P. Platt, S. Wedge, P. Frankel, M. Gass, R. Howells and M. Preuss, J. Nuclear Mater., vol. 459, pp. 166-174, 2015.
Introduction
S. Ortner1, H. Wilcox1, H. Swan1, M. Fenwick2, M. Blackmur1, M. Gass2, J. Smith3, K. Jurkschat4
A collaborative project from:
1.
2.
3.
4.
1 2
5 3
4
6
The forward front of the inter-connected water network is located at the cracks at the delays in the oxidation front. Immediately post-transition, the oxide thickness is ~ nil at the delays, but a few hundred nm at the protrusions. This difference causes the oxide growth rate at the delay to be much greater than that at the protrusions, so the interface flattens.
The flat interface prevents new in-plane cracks nucleating. The network is truncated, the protective oxide thickens and the oxidation rate decreases.
Without undulations and cracks, the oxide stress has fewer relaxation modes so the compressive stress in the new oxide is again large, and can induce tension and plasticity in the metal.
SXRD SEM Interface Roughness [6]
6.
Stress mismatch at metal-oxide interface encourages undulations. These, and metal plasticity, reduce average oxide in-plane stresses.
SXRD
SEM
2.
The through-plane cracks reach the inter-connected in-plane crack network, which then fills with water. The protective oxide thickness thereby drops and the corrosion rate increases. Transition ensues. The change in local stresses encourages neighbouring networks to link: transition spreads.
Interfacial undulation amplitudes increase. Stress redistribution around undulations induces in-plane cracking at delays in oxidation front. This further reduces local oxide stress during 2nd µm of oxide growth.
As interface moves inward, away from individual in-plane cracks, these cracks can grow and link.
3. Metal grain to grain mismatches in plastic flow cause strain concentrations which, transmitted to contiguous oxide, produce local regions of tension in the oxide. Through-plane cracks grow in from surface. Crack growth is assisted by the presence of porosity along oxide grain boundaries.
4.
DIC [4]
TEM showing porosity
3D-FIB [3]
SXRD
SEM
5.
3D-FIB
SEM [5]
Cyclic growth with attendant
observations and interpretations
7. Process repeats
Tensile stress in metal matching large compressive stress in oxide induces plasticity in metal.
TEM showing dislocations [2]
1.
SXRD [1] – monoclinic stress
