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

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Fracture of Gamma and Delta Hydrides during Delayed Hydride Cracking

19th International Symposium on Zirconium in the Nuclear Industry S.M. Hanlon1, G.A. McRae2, C.E. Coleman2, and A. Buyers1

1Canadian Nuclear Laboratories, Chalk River, Ontario, Canada 2Carleton University, Ottawa, Ontario, Canada

May 2019

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• 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
• Leak-before-break
• Limiting conditions
• [H], solubility limits
• Stress intensity (KIH)
• Temperature
• Temperature history

Mechanism: [H] in bulk and at crack tip depends on temperature history [34]

Limiting Conditions for DHC

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.

[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.

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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. 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.

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• 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
• T1 ranges from -30 °C to 220 °C
• Over 200 tests performed
• DSC on quenched material

Experimental

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Cool-down DHC Data

• Cool-down data (below T6) follows Arrhenius

behaviour

• No effect of [H] below T6

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 DHC Velocity (m/s) 1000/T (K-1) 38 ppm 39 ppm 47 ppm 66 ppm 73 ppm 108 ppm Arrhenius Fit

200 °C 100 °C 25 °C

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Quenched ‘Conundrum’

• Slow cooling to a Ttest leads to similar DHCV as quenching and then heating to the same Ttest
• Slow cooling and then heating to the same Ttestleads to slower DHC rates
• No history effect at room temperature

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 DHC Velocity (m/s) 1000/T (K-1) Quenched 25 C Heat 25 C Heat 220 C Heat Arrhenius Fit

200 °C 100 °C 25 °C

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Quenching and DSC

• Quenching is an

‘extreme’ temperature history

• Affects bulk hydride

morphology

• Shifts the apparent

solubility measured by DSC

• Similar to removing radiation

damage

• Shift decreases as test

temperature increases

• More hydrogen in

solution generally means higher DHCV

First Heating Run (Quench then heat) Second Heating Run (Slow cool then heat)

Oven Cooled Brine Quenched

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All DHC Data

• Various hydrogen concentrations
• Accuracy of schematic diagram
• Determine conditions under which DHC will not occur

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.70 1.90 2.10 2.30 2.50 2.70 2.90 3.10 3.30 DHC Velocity (m/s) 1000/T (K-1) Cool

• 30 C Heat

Quenched 25 C Heat 25 C Heat 100 C Heat 150 C Heat 180 C Heat 200 C Heat 220 C Heat

200 °C 100 °C 25 °C

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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

50 100 150 200 250

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10 30 50 70 90 110 130 150 170 190 210 230 250 Temperature Difference (°C) T1 Temperature (°C) T3-T1 T2-T1 T3-T1 [34] T2-T1 [11] T3-T1 [11]

[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.

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DHC Modelling

• Prediction 1 is the Diffusion First Model [10]
• Accurately predicts T5 to T6 region
• Prediction 2 is the Precipitation First Model [33]
• Both models under-predict at low temperatures

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 25 50 75 100 125 150 175 200 225 250 275 300 DHC Velocity (m/s) Test Temperature (°C) 100-140 ppm [33] 39 ppm 65 ppm 50 ppm Prediction 1 [10] Prediction 2 [33]

[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

T6 (39 ppm)

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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. [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.

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DHC Hydride Phase on Fracture Surfaces

• XRD spectra from

DHC fracture surfaces

• Room temp
• Top: test temperature
• f 240 °C
• Bottom: test

temperature of 25 °C

• Small fraction of

signal from bulk hydrides

• No change after 1

year at RT

• Consistent with γ

hydride stability at low temperature

γ γ α α δ δ

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• 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

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 25 50 75 100 125 150 175 200 225 250 275 γ Hydride Peak Fraction Test Temperature (°C) Cool Heat Quench then Heat

DHC Hydride Phase on Fracture Surfaces

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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 Ttest leads to similar DHCV as quenching then heating to Ttest
• Slow cooling then heating leads to slower DHC rates at the same Ttest
• 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

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Questions?

240 °C 25 °C

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