Effect of Hydrogen on ZIRLO and Zr-1.0Nb Irradiation Creep ... · – Hydrogen has no effect on the...

Westinghouse Non-Proprietary Class 3 © 2016 Westinghouse Electric Company LLC. All Rights Reserved.

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John P. Foster, Guirong Pan, Lu Cai and Andrew Atwood Westinghouse Electric Company

Effect of Hydrogen on ZIRLO® and Zr-1.0Nb Irradiation Creep and Irradiation Growth

ZIRLO® is a trademark or registered trademark of Westinghouse Electric Company LLC in the United States and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.

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Outline • Introduction • Experimental

o Test Setup o Test Conditions o Measurements o Data Analysis

• Results and Discussions o Axial Direction Summary o Axial Direction Data o Diametric Direction Summary o Diametric Direction Data o Summary

• Conclusions • Acknowledgements

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Introduction • Hydrogen effect on irradiation growth and creep is receiving

considerable attention • Out-reactor results show significant decrease in creep due

to hydrogen • Systematic evaluation of hydrogen effect on irradiation

creep is very limited. • A comprehensive evaluation will be presented, including

different alloy chemistry and microstructure: SRA (Stress Relief Annealed) ZIRLO and (Re-crystallized) RXA Zr-1.0Nb; and in both axial and diametric directions, as well as various burnup levels

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Experimental - Test Setup

• The test samples are about 168 mm long rodlets without holes

(stressed for irradiation creep) or with holes (un-stressed for irradiation growth)

• Test rodlets are combined with spacer rods to form a segmented insert rod containing a total of 7 test rodlets

Pressure relief hole for irradiation growth sample

Test Tubes of Various Alloys End Plug

Spacer Rods

Test Sample Rodlet

End Plug

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Fall 02 Spring 04 Fall 05 Spring 07 Fall 08 Spr. 10 | | | | | | Test Assembly A1 x----------------x A2 x----------------------------------------------------x A3 x----------------------------------x A4 x-----------------------------------------------------------------------x A5 x----------------x A6 x-----------------x

Experimental - Test Setup • 12 segmented insert rods are included in one test

assembly, which is inserted into fuel assembly thimble tubes

• Each test assembly contained sister test samples and were irradiated for up to 4 cycles.

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Experimental - Test Conditions • Samples include both SRA ZIRLO and RXA Zr-1.0Nb. • The samples were hydrogen pre-charged using gaseous

hydrogen and argon mixtures at temperatures well below the final annealing temperature.

• The sample diameter and length were measured using a laser micrometer prior to irradiation and after irradiation using the same facility.

• The samples were irradiated at 302-312oC. • Retrospective dosimetry measurements showed that there

were no axial or radial fast flux gradients in the sample locations.

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Experimental - Measurements

C/L

20 diameter measurements at each of 7 axial positions. Each axial position spaced 0.5" (12.7 mm)* apart (3 on each side of the capsule C/L) centre line)

32.58 mm*

1 23 4

5 6 7

Permanent standard bolted to capsule jig

• Each measured data point (diameter or length) is the averaged value of numerous repeated measurements at various locations.

• A standard is used to account for experimental setup variation

• The final value of the measurement was also adjusted for standard, temperature variations, and oxide thickness.

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Experimental - Data Analysis • The data will be presented as the strain versus the pressure

difference across the sample wall.

• The strain will be evaluated in the axial and the diametric directions o Axial Direction: The total axial strain, or split into axial irradiation growth

and axial irradiation creep components according to, ∆L/Lo(total) = ∆L/Lo(irradiation creep) + ∆L/Lo(irradiation growth)

o Diameter Direction: The total diametrical strain, or split into diametric irradiation growth and diametric irradiation creep components according to, ΔD/Do = ΔD/Do(irradiation growth) + ΔD/Do(irradiation creep)

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Results - Axial Directions Summary

– Irradiation growth is the dominating strain component in the axial direction

– For SRA ZIRLO alloy, axial irradiation growth increases with increasing hydrogen.

– For RXA Zr-1.0Nb, axial irradiation growth decreases with increasing hydrogen.

– Hydrogen has no effect on the axial irradiation creep of either SRA ZIRLO cladding or Zr-1.0Nb.

– The total strain of both Zr-1.0Nb and SRA ZIRLO cladding increases with increasing fast fluence, more significant than the hydrogen effect.

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Results - Axial Directions SRA ZIRLO Total Axial Strain

Total Axial Strain for SRA ZIRLO Increases with Increasing Hydrogen

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Conclusions • Another key takeaway: The difference of hydrogen effect on

irradiation growth between SRA ZIRLO (increase) and RXA Zr-1.0Nb (decrease) could be due to alloy chemistry or microstructure. Since SRA ZIRLO and RXA Zr-4 has the same behavior, the amount of alloy elements could be the reason.

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Results - Axial Directions SRA ZIRLO Irradiation Growth

Minor Axial Irradiation Growth Increase Due to Hydrogen; Much Smaller than Growth Due to Irradiation

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Results - Axial Directions SRA ZIRLO Irradiation Creep

Axial Irradiation Creep Strain for SRA ZIRLO the Same with Increasing Hydrogen

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Results - Axial Directions RXA Zr-1.0Nb Total Axial Strain

Axial Irradiation Growth Strain (Pi-Po=0, above) for RXA Zr-1.0 Nb Decreases with Increasing Hydrogen for All 4 Cycles

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Results - Axial Directions RXA Zr-1.0Nb Irradiation Creep

Axial Irradiation Creep Strain for Zr-1.0 Nb the Same with Increasing Hydrogen

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Results - Diametric Directions Summary

– Irradiation creep is the dominating strain component in the diameter direction.

– For both SRA ZIRLO and RXA Zr-1.0Nb samples, hydrogen has minimal effect on the total diameter strain.

– The slight decrease (if any) in the diametric irradiation creep with the addition of hydrogen is minimal.

– With hydrogen addition, the diametric growth of SRA ZIRLO slightly increase, and RXA Zr-1.0Nb slightly decrease;

– The total diameter strain behavior for the SRA ZIRLO samples and RXA Zr-1.0Nb are similar.

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Results - Diameter Directions SRA ZIRLO Total Diametric Strain

Hydrogen has Minimal Effect on Total Diametric Strain for SRA ZIRLO

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Results - Diametric Directions SRA ZIRLO Irradiation Growth

Diametric Irradiation Growth Strain for SRA ZIRLO Slightly Increases with Increasing Hydrogen

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Results – Diametric Directions SRA ZIRLO Irradiation Creep

Diametric Irradiation Creep Strain for SRA ZIRLO the Same with Increasing Hydrogen

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Results - Diametric Directions RXA Zr-1.0Nb Total Diametric Strain

Hydrogen has Minimal Effect on Total Diametric Strain for RXA Zr-1.0 Nb

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Results - Diametric Directions RXA Zr-1.0Nb Irradiation Growth

Diametric Irradiation Growth Strain for RXA Zr-1.0Nb Slightly Decrease with Increasing Hydrogen

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Results – Diametric Directions RXA Zr-1.0Nb Irradiation Creep

Diametric Irradiation Creep Strain for RXA Zr 1.0 Nb the Same with Increasing Hydrogen

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Results - Summary

• Rough Scale • Based on 1 cycle data • The total value without / with hydrogen • Pressure from -15 to +15 MPa for Creep data.

SRA ZIRLO RXA Zr-1.0Nb Axial Diametric Axial Diametric

Growth Hydrogen Effect

Increase Increase Decrease Decrease

Rough Scale (%)

0.16-0.19 (-0.03)-(-0.075)

0.09-0.06 (-0.12)-(-0.11)

Creep Hydrogen Effect

No No

No

No

Rough Scale (%)

(-0.05)-(+0.04)

(-1.5)-(+1.5)

0.02-0.03

(-1.5)-(+1.5)

Total Hydrogen Effect

Increase

No

Decrease

No

Growth is dominating in Axial Direction; Creep is dominating in Diametric Direction

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Conclusions • The key conclusion: The decrease in in-reactor creep (in

both axial and diametric direction) due to hydrogen is minimal, in contrary, hydrogen significantly decreases the out-reactor creep strain and strain rate

o The proposed mechanism: The irradiation-induced point defects could have diminished the dislocation inhibition effect of hydrides and hydrogen in the solid solution.

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Conclusions • Another key takeaway: The difference of hydrogen effect on

irradiation growth between SRA ZIRLO (increase) and RXA Zr-1.0Nb (decrease) could be due to alloy chemistry or microstructure. Since SRA ZIRLO and RXA Zr-4 has the same behavior, the amount of alloy elements could be the reason.

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Acknowledgements • The coolant temperature analysis and sample temperature calculations

were performed by John Killimayer and David Rumschlag/Westinghouse.

• Westinghouse is grateful to Southern Nuclear Operating Company for enabling irradiation of the test samples.

• The contributions of Richard Loftin, Ken Turnage and the Vogtle site staff are greatly appreciated.

• The sample diameter, length and oxide thickness measurements were performed by Frank Butcher and Allan MacCormack/AECL. The authors appreciate the assistance of Nick Christodoulou /CNSC (retired) for technical assistance during all aspects of the program including design review, experimental measurement methods, evaluation and interpretation of the data while at AECL and for reviewing the manuscript.

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Effect of Hydrogen on ZIRLO and Zr-1.0Nb Irradiation Creep ... · – Hydrogen has no effect on the...

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