AREVA Inc. Proprietary – © AREVA – All rights reserved Presentation title – Presenter/ref. - 09 August 2015 - p.1 Presentation title – Presenter/ref. - 09 August 2015 - p.1

FRONT END BUSINESS GROUP

Hold Down Spring Failure Analysis Jacqueline N. Stevens AREVA, Inc., Lynchburg, VA, USA

Keith J. Leonard, Maxim N. Gussev Oak Ridge National Laboratory, Oak Ridge, TN, USA

Gabriel Ilevbare EPRI, Palo Alto, CA, USA

J. Lawrence Nelson JLN Consulting, Mills River, NC, USA

17th International Conference on Environmental

Degradation of Materials in Nuclear Power Systems

August 9 – 12, 2015

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Outline

Background

Examination Results

Discussion

Conclusion

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.3

AREVA Inc. Proprietary – © AREVA – All rights reserved

Outline

Background

Examination Results

Discussion

Conclusion

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.4

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Background (1/2)

Alloy 718 material to AMS 5596

HDS under high stress state during operation

PWR conditions – 2, 24-month cycles

Approximately 0.5 dpa

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.5

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Background (2/2)

Archive materials also investigated:

Archive A – Representative of HDS which failed during operation, same

manufacturing lot as irradiated samples

Archive B – Representative of HDS which completed operational life

without damage

Both archives manufactured from same alloy 718 ingot

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.6

Archive and irradiated samples examined at ORNL

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Outline

Background

Examination Results

Discussion

Conclusion

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.7

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Examination Results (1/4)

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.8

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Examination Results (2/4)

Sample surface after oxide

removal

Extensive slip lines around

major cracks

Slip line oxidation

Secondary cracks (red arrows)

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Examination Results (3/4)

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.10

Delta

phase

Twin Boundary

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Examination Results (4/4)

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.11

Archive A Archive B

Following 3.7% Bulk Strain

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Outline

Background

Examination Results

Discussion

Conclusion

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.12

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Discussion (1/2)

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.13

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Discussion (2/2)

Precipitation Heat Treat Differences

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0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1000

Te

mp

era

ture

(°C

)

Time (minutes)

Archive A / Irradiated Samples

Archive B Samples

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Outline

Background

Examination Results

Discussion

Conclusion

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.15

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Conclusion (1/1)

Failed HDS (Archive A)

2, 24-month cycles – PWR

chemistry

High Stress

Approximately 0.5 dpa

Negligible δ phase

precipitation on GBs

Hold Down Spring Failure Analysis – J. Stevens - 09 August 2015 - p.16

Non-Damaged HDS (Archive B)

3, 18-month cycles – PWR

chemistry

High Stress

Approximately 0.5 dpa

Substantial δ phase precipitation

on GBs

δ precipitates on the grain boundaries of alloy 718 produce a

PFZ which facilitates cross-slip leading to localized stress

reduction

In the absence of a PFZ, the build up of slip bands at GBs

under a high bulk stress state will initiate cracks

Cracks then readily propagate in alloy 718 in a PWR

environment

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This document and any information it contains shall not be

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and/or any person breaching the aforementioned obligations.

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