Fracture of Gamma and Delta Hydrides during Delayed Hydride Cracking - PowerPoint PPT Presentation

Fracture of Gamma and Delta Hydrides during Delayed Hydride Cracking 19th International Symposium on Zirconium in the Nuclear Industry S.M. Hanlon 1 , G.A. McRae 2 , C.E. Coleman 2 , and A. Buyers 1 1 Canadian Nuclear Laboratories, Chalk River, Ontario, Canada 2 Carleton University, Ottawa, Ontario, Canada May 2019 AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL -1-

Limiting Conditions for DHC • Delayed Hydride Cracking (DHC) is a mechanism responsible for extension of flaws in pressure tubes and fuel cladding • Nucleation, growth, fracture of hydrides • Chemical potential McRae, G. A., Coleman, C. E., & Leitch, B. W. (2010). The first step for delayed hydride cracking in zirconium alloys. Journal of Nuclear Materials , 396 (1), 130-143. • Leak-before-break • Limiting conditions • [H], solubility limits • Stress intensity (K IH ) • Temperature • Temperature history Mechanism: [H] in bulk and at crack tip depends on temperature history [34] UNRESTRICTED / ILLIMITÉ -2- [34] Schofield, J. S., Darby, E. C., & Gee, C. F. (2002). Temperature and hydrogen concentration limits for delayed hydride cracking in irradiated Zircaloy. In Zirconium in the Nuclear Industry: Thirteenth International Symposium . ASTM International.

Hydrides • Bulk hydrides and DHC hydrides do not necessarily form under the same conditions • X-Ray Diffraction (XRD) of fracture surfaces can reveal how DHC hydride morphology changes with test temperature • Focus on DHC hydrides rather than bulk hydrides • δ core - γ shell hydride morphology [20,21,24] Left: [29] Cann, C. D., & Sexton, E. E. (1980). An electron optical study of hydride precipitation and growth at crack tips in zirconium. Acta Metallurgica , 28 (9), 1215-1221. UNRESTRICTED / ILLIMITÉ -3- Middle, Right: [20] Root, J. H., Small, W. M., Khatamian , D., & Woo, O. T. (2003). Kinetics of the δ to γ zirconium hydride transformation in Zr -2.5 Nb. Acta Materialia, 51(7), 2041-2053. [21] Hanlon, S. M., Persaud, S. Y., Long, F., Korinek, A., & Daymond, M. R. (2019). A solution to FIB induced artefact hydrides in Zr alloys. Journal of Nuclear Materials , 515 , 122-134. [24] McRae, G. A., and C. E. Coleman. "Precipitates in metals that dissolve on cooling and form on heating: An example with hydrogen in alpha-zirconium." Journal of Nuclear Materials 499 (2018): 622-640.

Experimental • Material: Zr-2.5Nb plate (similar to pressure tube) • Cantilever beam specimens (3.2 mm width) • Axial cracking in transverse plane • K=17 MPa √m (constant load) • Test temperatures from 25 ° C to 270 ° C • Heat-up tests on quenched material • T 1 ranges from -30 ° C to 220 ° C • Over 200 tests performed • DSC on quenched material UNRESTRICTED / ILLIMITÉ -4-

Cool-down DHC Data • Cool-down data (below T6) follows Arrhenius behaviour • No effect of [H] below T6 1.E-07 100 °C 25 °C 200 °C 38 ppm 39 ppm 47 ppm 1.E-08 66 ppm DHC Velocity (m/s) 73 ppm 108 ppm Arrhenius Fit 1.E-09 1.E-10 1.E-11 UNRESTRICTED / ILLIMITÉ -5- 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 1000/T (K -1 )

Quenched ‘Conundrum’ • Slow cooling to a T test leads to similar DHCV as quenching and then heating to the same T test • Slow cooling and then heating to the same T test leads to slower DHC rates • No history effect at room temperature 1.E-07 100 °C 25 °C 200 °C Quenched 25 C Heat 1.E-08 25 C Heat DHC Velocity (m/s) 220 C Heat Arrhenius Fit 1.E-09 1.E-10 1.E-11 UNRESTRICTED / ILLIMITÉ -6- 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 1000/T (K -1 )

Quenching and DSC • Quenching is an Oven Cooled Brine Quenched ‘extreme’ temperature history • Affects bulk hydride morphology • Shifts the apparent solubility measured by DSC • Similar to removing radiation damage Second Heating Run • Shift decreases as test (Slow cool then heat) temperature increases • More hydrogen in First Heating Run solution generally means (Quench then heat) higher DHCV UNRESTRICTED / ILLIMITÉ -7-

All DHC Data • Various hydrogen concentrations • Accuracy of schematic diagram • Determine conditions under which DHC will not occur 1.E-07 Cool 100 °C 25 °C 200 °C -30 C Heat Quenched 25 C Heat 25 C Heat 1.E-08 100 C Heat DHC Velocity (m/s) 150 C Heat 180 C Heat 200 C Heat 1.E-09 220 C Heat 1.E-10 1.E-11 UNRESTRICTED / ILLIMITÉ -8- 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 1000/T (K -1 )

Stopping DHC by Heating • Good agreement with previous work (irradiated Zircaloy-2) • Quenching increases required temperature difference (empty symbols in box) • Can be used to inform reactor manoeuvering strategies • Confirm with irradiated Zr-2.5Nb data 250 Temperature Difference ( ° C) T3-T1 200 T2-T1 T3-T1 [34] 150 T2-T1 [11] T3-T1 [11] 100 50 0 -50 -30 -10 10 30 50 70 90 110 130 150 170 190 210 230 250 T1 Temperature ( ° C) UNRESTRICTED / ILLIMITÉ -9- [11] Ambler, J. F. (1984). Effect of direction of approach to temperature on the delayed hydrogen cracking behavior of cold-worked Zr-2.5 Nb. In Zirconium in the Nuclear Industry . ASTM International. [34] Schofield, J. S., Darby, E. C., & Gee, C. F. (2002). Temperature and hydrogen concentration limits for delayed hydride cracking in irradiated Zircaloy. In Zirconium in the Nuclear Industry: Thirteenth International Symposium . ASTM International.

DHC Modelling • Prediction 1 is the Diffusion First Model [10] • Accurately predicts T 5 to T 6 region • Prediction 2 is the Precipitation First Model [33] • Both models under-predict at low temperatures 1.E-06 100-140 ppm [33] 39 ppm 1.E-07 65 ppm 50 ppm DHC Velocity (m/s) Prediction 1 [10] 1.E-08 Prediction 2 [33] T 6 (39 ppm) 1.E-09 1.E-10 1.E-11 25 50 75 100 125 150 175 200 225 250 275 300 Test Temperature ( ° C) UNRESTRICTED / ILLIMITÉ -10- [10] McRae, G. A., Coleman, C. E., & Leitch, B. W. (2010). The first step for delayed hydride cracking in zirconium alloys. Journal of Nuclear Materials , 396 (1), 130-143. [33] De Las Heras, M. E., Parodi, S. A., Ponzoni, L. M. E., Mieza, J. I., Müller, S. C., Alcantar, S. D., & Domizzi, G. (2018). Effect of thermal cycles on delayed hydride cracking in Zr-2.5 Nb alloy. Journal of Nuclear Materials , 509 , 600-612

Poor DHC Model Predictions at Low Temperature • Hydrogen in solution is very low at room temperature – less than 5 ppm [18] • Very little hydrogen available to diffuse to crack tip • Diffusion is slow at room temperature • Trend in temperature maneuver plot changes around 200 ° C • DHC models either directly or indirectly assume the DHC hydride phase does not change with temperature • Ambler et al. assumed DHC hydride is always δ [11] • In-situ room temperature TEM shows γ at room temperature [29] • δ and γ have different stoichiometry, crystal structure, and morphology [11] Ambler, James FR. "Effect of direction of approach to temperature on the delayed hydrogen cracking behavior of cold-worked Zr-2.5 Nb." Zirconium in the Nuclear Industry. ASTM International, 1984. UNRESTRICTED / ILLIMITÉ -11- [18] McRae, G. A., Coleman, C. E., Nordin, H. M., Leitch, B. W., & Hanlon, S. M. (2018). Diffusivity of hydrogen isotopes in the alpha phase of zirconium alloys interpreted with the Einstein flux equation. Journal of Nuclear Materials , 510 , 337-347. [29] Cann, C. D., and E. E. Sexton. "An electron optical study of hydride precipitation and growth at crack tips in zirconium." Acta Metallurgica 28.9 (1980): 1215-1221.

DHC Hydride Phase on Fracture Surfaces • XRD spectra from δ α DHC fracture surfaces • Room temp • Top: test temperature of 240 ° C • Bottom: test γ temperature of 25 ° C • Small fraction of signal from bulk γ hydrides • No change after 1 α year at RT • Consistent with γ δ hydride stability at UNRESTRICTED / ILLIMITÉ -12- low temperature

DHC Hydride Phase on Fracture Surfaces • Fractured DHC hydride phase changes with test temperature • δ prevalent at high temperatures, γ prevalent at low temperatures • Presence of γ should be considered in future DHC models • No apparent effect of temperature history on fractured hydrides 1.0 0.9 0.8 γ Hydride Peak Fraction 0.7 0.6 0.5 0.4 0.3 Cool 0.2 Heat Quench then Heat 0.1 0.0 UNRESTRICTED / ILLIMITÉ -13- 25 50 75 100 125 150 175 200 225 250 275 Test Temperature ( ° C)

Conclusions • DHC data can be used to provide empirical guidelines and inform reactor temperature maneuvers to reduce DHC susceptibility • Quenched results reveal a ‘conundrum’ • Slow cooling to T test leads to similar DHCV as quenching then heating to T test • Slow cooling then heating leads to slower DHC rates at the same T test • Not explained/predicted by current DHC models • Observed DSC shifts provide a partial qualitative explanation for the quenched ‘conundrum’ • γ hydride is dominant on DHC fracture surfaces below about 125 ° C while δ is dominant above 225 ° C • Implications for fuel storage • The presence of γ hydride on DHC fracture surfaces may explain why DHC model predictions are poor below 150 ° C • DHC models should include DHC hydride phase temperature dependence • Follow-up with irradiated material UNRESTRICTED / ILLIMITÉ -14-

Questions? 240 ° C 25 ° C UNRESTRICTED / ILLIMITÉ -15-

Backup UNRESTRICTED / ILLIMITÉ -16-