© 2017 Electric Power Research Institute, Inc. All rights reserved.

Aylin Kucuk, EPRI – PI

Ioan Arimescu, AREVA – Co-PI

Yang-Pi Lin, GNF – Co-PI

Nuclear Science User Facilities FY2017

Annual Program Review, Germantown, DC

November 14-15, 2017

Improved Understanding of

Zircaloy-2 Hydrogen

Pickup Mechanism in

BWRs

2© 2017 Electric Power Research Institute, Inc. All rights reserved.

Hydrogen Impacts in Zirconium Alloy Materials

Many fuel issues are affected by hydrogen pickup of Zircaloy fuel cladding and fuel components

– Loss of Coolant Accidents (LOCA)

– Reactivity Initiated Accidents (RIA)

– Seismic Events

– BWR Channel Distortion

– PWR Fuel Assembly / Bundle Distortion

– Hydrogen Embrittlement / Hydride-induced Cracking

– Secondary Degradation

– Dry Cask Storage and Transportation

Need to better understand phenomena:

– Corrosion

– Hydrogen Pickup

Alloying Effects

– Hydrogen Diffusion, Migration & Precipitation

– Enhanced Corrosion (rims)

– Mechanical Property Changes (strength, ductility)

– Dimensional Changes

Creep; H-Assisted Irradiation Growth

– Hydride Embrittlement

– Water Chemistry Effects

– Hydride Reorientation (stress, temperature)

– Hydrogen Redistribution (thermal & stress gradients)

Oxide spallation, delamination, peeling and blistering

– Delayed Hydride Cracking

Pending Loss of Coolant Accident (50.46c) Rule

(Allowable clad corrosion during postulated accident)

0

5

10

15

20

25

0 200 400 600 800 1000

Equ

ivla

net

Cla

d R

eac

ted

(%)

Hydrogen Concentration (ppm)

DuctileBrittleLab A-DuctileLab A-BrittleNRC Proposed LimitCurrent Limit 50.46b

Forthcoming Limit 50.46c

Eq

uiv

ale

nt C

lad

Re

acte

d (

%)

More important than burnup or alloy!

3© 2017 Electric Power Research Institute, Inc. All rights reserved.

High Hydrogen Pickup and Variability at High Burnup in BWRs

Zircaloy-2 material show high hydrogen pickup and variability later in life but Zircaloy-4 does not.

– The main difference is Ni. What is the role of Ni on hydrogen pickup?

Previous Work

– EPRI NFIR and Channel Distortion Programs co-funded the HYDRanZeA project

HYDRanZeA (HYDRogen and Zr-Based Alloys)

BWR Fuel Cladding BWR Zircaloy Structural Materials

Miyashita et al., ANS LWR Fuel Performance Conference, San Francisco, 2007Geelhood et al. 2011 Water Reactor Fuel Performance Meeting, Chengdu, China, 2011

4© 2017 Electric Power Research Institute, Inc. All rights reserved.

NFIR/CDP HYDRanZeA Project Plan

GNF

Zirc-2 water rods

Zirc-2 and Zirc-4 channels

Westinghouse

Zirc-2 and Zirc-4 channels

AREVA

Zirc-2 and Zirc-4 channels

Electron

Microscopy

Pre-irradiated

Zircaloys from

BWRs

Synchrotron

techniques

Objectives:

• Determine why Zirc-4 HPUF is lower than Zirc-2 HPUF in

BWRs at high burnup

• Determine why Zirc-2 in BWRs show high hydrogen pickup at

high burnup

Scope:

• Compare pre-irradiated Zircaloy-2 and Zircaloy-4 alloy and

oxide structures at low and high fluence

3D Atom

Probe

5© 2017 Electric Power Research Institute, Inc. All rights reserved.

Irradiated BWR Chanel and Water Rod Materials in

Commercial BWRs

Zr-2 and Zr-4 channel materials Zr-2 water rod samples with various exposure and fluence

Both channel and water rod samples will be studied in the NSUF funded project. Remaining

parts of the studied samples will be donated to the NSUF material library.

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90

100

0 2 4 6 8 10 12

Hyd

roge

n P

ickup

Fra

ctio

n (

%)

Fluence (x1021 n/cm2 E>1 MeV)

Zircaloy-4 Channels Zircaloy-2 Channels

1400

1600

1800

2000

2200

2400

2600

2800

3000

0.0 5.0 10.0 15.0 20.0

Exp

osu

re T

ime

(da

ys)

Fluence (x1021 n/cm2 E>1 MeV)

Zircaloy-2 Water Rod

6© 2017 Electric Power Research Institute, Inc. All rights reserved.

Confirm or Refute the “Ni-band” Hypothesis

Developed a decision flow chart to design and focus the project

Metal

Zr2(FeNi) SPP

Ev.tetrag.oxide

Barrier

Layer

Porous

Oxide

Layer

Oxidized

SPP

a) Low burnup b) High burnup

Fe & Ni in

Forced solution

Metallic

Bands at

Oxide GB

“Ni-band” Hypothesis: After Ni

containing SPPs are dissolved under

irradiation at high burnup, metallic Ni

segregates at grain boundaries (oxide

and/or metal) and act as H window by

resulting accelerated hydrogen pickup.*

* Garzarolli et al., 16th ASTM Zr Symposium, 2010.

7© 2017 Electric Power Research Institute, Inc. All rights reserved.

HYDRanZeA Project FindingsQuestions Answers Concerns

Are Ni containing SPPs

dissolved in Zr-2 showing high

HPUF?

(TEM & 3DAP)

Yes. SPPs dissolve as a function of fast

fluence. Ni dissolves slower than Fe. 3DAP

showed high Ni content in metal matrix in

high HPUF materials.

TEM results were too qualitative with poor

statistics. 3DAP results were quantitative but too

localized. Need more examinations to confirm the

correlation.

Any segregation of Ni at grain

boundaries or other defects in

the metal?

(TEM & 3DAP)

Yes. Ni and Fe nano segregations observed

in irradiated metal matrix.

What happens to these nano segregations when

they are incorporated into the oxide? Stay metallic?

Any segregation of Ni at oxide

grain boundaries?

(TEM & 3DAP)

No. Conflicts with the previous findings.

Does Ni stay metallic in the

oxide?

(XANES)

Yes. High HPUF materials show up metallic

Ni up to 5-10 micron in the oxide while low

HPUF materials do not.*

More measurements are needed to strengthed the

correlation. Is high HPUF caused by metallic Ni or

metallic Ni is caused by high H content in the

oxide?

“Ni band” hypothesis could not be confirmed systematically. • Many supporting evidences were observed but no “Ni bands” are found in the oxide.

• A different form of the hypothesis may be in play.

• More measurements should be performed to fully understand the role of Ni in HPUF.

* A. Shivprasad et al., 18th ASTM Zr Symposium, 2016

8© 2017 Electric Power Research Institute, Inc. All rights reserved.

Oxide Resistivity vs. Hydrogen Pickup

Is this correlation also valid for irradiated Zircaloy-2

materials?

– How about the metallic Ni measured in high hydrogen

pickup Zircaloy-2?

1. It is verified that experimentally

𝜌ZrO2

EIS (ZrNb) < 𝜌ZrO2

EIS (Zr4)

2. There is a clear correlation between

𝜌𝑍𝑟𝑂2EIS and 𝑓𝐻

𝑖

Couet et al., 18th ASTM Zr Symposium, 2016

9© 2017 Electric Power Research Institute, Inc. All rights reserved.

Project Objective and Approach

Objective To understand why Zircaloy-2 material exhibit high

hydrogen pickup and a large variability in BWR environments by investigating a correlation between the irradiated Zircaloy-2 oxide layer resistivity and hydrogen pickup.

Approach Perform in-situ EIS measurements on pre-

irradiated BWR channel and water rod samples

– Focus tests on determining if the irradiated Zircaloy-2 oxide layer resistivity is correlated to the hydrogen pickup.

Perform PIE of same materials using TEM and SEM

– To complement the electrochemistry measurements, detailed oxide microstructure of the tested materials such as cracks and porosity will be determined.

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20

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40

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80

90

100

0 2 4 6 8 10 12

Hyd

roge

n P

ickup

Fra

ctio

n (

%)

Fluence (x1021 n/cm2 E>1 MeV)

Zircaloy-4 Channels Zircaloy-2 Channels

1400

1600

1800

2000

2200

2400

2600

2800

3000

0.0 5.0 10.0 15.0 20.0

Exp

osu

re T

ime

(da

ys)

Fluence (x1021 n/cm2 E>1 MeV)

Zircaloy-2 Water Rod

10© 2017 Electric Power Research Institute, Inc. All rights reserved.

Industry Activities on Hydrogen Pickup Issue

FRP

SHIZAM

NFIR-7

HYDRanZeA

Phase 2

MUZIC-3

Utilities

• Many PhDs on characterization of irradiated

Zircaloy materials and testing to understand the

HPU mechanism (PWRs and BWRs)

• In-situ EIS measurements in-reactor on

irradiated cladding (BWR and PWR)

• Advanced Modelling

• Hot cell examination

• Test Reactor experiments

• NDE method development

• Funds MUZIC-3

• Funds HYDRanZeA Phase 2

• Coordinates the interaction between MUZIC-3

and HYDRanZeA Phase 2

Same materials tested in the

HYDRanZeA project will be

characterized in the MUZIC-3

program.

DOE

NSUF

11© 2017 Electric Power Research Institute, Inc. All rights reserved.

Project Collaborators

Roles Responsible Party

Lead PI Aylin Kucuk, EPRI

Co-PIs Ioan Arimescu, AREVA

Yang-Pi Lin, GNF

PNNL NSUF Technical Lead Dave Senor, PNNL

Technical Staff at PNNL

NSUF

Olga Marina, PNNL

Dan Edwards, PNNL

3 year program

Complementary test program to

the HYDRanZeA Phase 2 project

– Focused on the irradiated Zircaloy-2

and Zircaloy-4 non-heat transfer

materials

Some key industry experts will

review progress through NFIR-VII

steering committee

12© 2017 Electric Power Research Institute, Inc. All rights reserved.

Benefits of HYDRanZeA Phase 2 Tests to Industry

Empirical hydrogen pickup models have been developed for forthcoming NRC LOCA rulemaking

– Especially challenging for BWR Zircaloy-2 due to significant HPU variability at later in life

Empirical models are only valid for conditions that they are benchmarked to

Any mechnanistic understanding of the hydrogen pickup phenomenon would be a supporting basis

of these empirical models

– May facilitate regulators’ timely licensing of new materials (e.g., HPU models)

0

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Equ

ivla

net

Cla

d R

eac

ted

(%)

Hydrogen Concentration (ppm)

DuctileBrittleLab A-DuctileLab A-BrittleNRC Proposed LimitCurrent Limit

50.46b

Proposed Limit

50.46c

New LOCA rule

requires industry

to develop HPU

models

AREVA’s HPU Model Results on Zircaloy-2 in BWRs

Equiv

ale

nt C

lad R

eacte

d (

%)

13© 2017 Electric Power Research Institute, Inc. All rights reserved.

Project Status and Plan

Channel sample selection is completed.

Water rod samples will be transferred from ORNL to PNNL by the end of the year.

– Paperwork is in-progress

Project team will meet in Charlotte on November 16 to discuss about the testing details.

FY18 FY19 FY20

Select fuel channel samples X

Transfer water rod samples from ORNL to PNNL X X

Setup EIS measurements for various irradiated materials X X

SEM/TEM characterization of irradiated materials X X X X X

Begin autoclave testing and EIS measurements X X X X X

SEM/TEM of autoclave samples X X X X

Complete autoclave testing and EIS measurements X X

Finish characterization of tested materials and EIS data analysis X X X

Final report X X

14© 2017 Electric Power Research Institute, Inc. All rights reserved.

Together…Shaping the Future of Electricity