THE BEHAVIOR OF CR-COATED ZIRCONIUM ALLOY CLADDING … · Cr diffusion in the substrate to form solid solution Eutectic transformation Under steam Cr oxidation is added as a third

THE BEHAVIOR OF CR-COATED ZIRCONIUM ALLOY CLADDING TUBES AT HIGH TEMPERATURES

N. Chaari, J. Bischoff, Ch. Delafoy, P. Barberis, K. Nimishakavi

Manchester, UK, May 20, 2019

Property of Framatome and partners- © FramatomeAll rights reserved

The behavior of Cr coated zirconium alloy cladding tubes at high temperatures – N. ChaariManchester 2019 - Mai 20th

p.2

Framatome E-ATF solutions: PROtect programBenefits during

severe accidents

Time of deployment (years)10 15 20

Development of new fuel rod concept for the E-ATF irradiation

program

Associated with Cr2O3 doped UO2

fuel as full fuel rod E-ATF solution

Evolutionary solution Revolutionary Solution

SiC/SiCcladdingCr-coating on

M5Framatome

cladding

M5Framatome


p.3

PROtect: Framatome’s evolutionary E-ATF solution

Cr2O3-doped UO2 Fuel

Large grain microstructure Improved fission gas retention

Enhanced viscoplasticity Improved PCI

performance

100µm

Cr-coated M5Framatome cladding

Thin coating (5-20µm)

No modification of the underlying Zr substrate microstructure

Dense coating

• Improved oxidation resistance

• Improved wear resistance

M5Framatome



p.4

Focus on the Cr-coating upon M5Framatome cladding: Project scheme

Material Characterization

Cr-

Coate

dZ

r C

laddin

gD

eve

lopm

ent

Material Irradiation

Cr-coating Manufacturing

Full Length Cr-coated Tube Fabrication

- Normal operating conditions- Accidental conditions

LT

R/L

FA

Irr

ad

iati

on

Fuel Performance Modelling

Licensing and Implementation



p.5

1. CR-COATING MANUFACTURING

Fabrication process and coating microstructure



p.6

Development of PVD process for the coating of full length Cr-Coated Tubes

Demonstrates the feasibility of full

length Cr deposition by PVD process

Fabrication of full length prototype completed in 2017

Began production of 4m long tubes for LFRs in 2018

Qualification completed in 2018 LFRs irradiation in commercial

reactor started already!



p.7

Development of PVD process for the coating of full length Cr-Coated Tubes

General characteristics of the coating:

Uniform visual aspects

Uniform thickness of the coating in axial and radial directions

Dense coating with no porosity

Smooth interface between the coating and the substrate with no porosity very good adherence with no modification of the substrate!

+/- 2µm over 4m length

M5Framatome



p.8

2. MATERIAL CHARACTERIZATION

Focus on the Cr coating behavior inaccidental conditions



p.9

Cr-coated cladding behavior at high temperatures: LOCA conditions T≤ 1200°C

0

10

20

30

40

50

0 5000 10000 15000 20000

We

igh

t g

ain

(m

g/c

m2)

Time (s)

Steam oxidation at 1100°C

Cr-coated cladding (10-15µm)

Uncoated Reference M5

ruptured during quench

Significantly reduced oxidation kinetic

Steam oxidation at 1100°C followed by quench in water

M5Framatome

Uncoated M5Framatome reference sample

Cr-coated M5Framatome sample



M5Framatome 15µm Cr

p.10


SEM after oxidation at 1000°C during 18000s (V=25°C/s)

Cr2O3

Residual Cr

ZrCr2


Focus on the involved mechanism during high temperature oxidation:

No oxygen diffusion in the substrate

M5Framatome

Cr2O3

Residual Cr

ZrCr2

SEM after oxidation at 1000°C during 5000s (V=25°C/s)

M5Framatome



p.11

Two mechanisms of Cr consumption during high temperature oxidation:

Cr diffusion in the substrate

Cr oxidation

SEM-EDX profile for Zr and Cr after oxidation at 1000°C during 18000s (V=25°C/s)

Cr2O3

Residual Cr

ZrCr2

A

B

M5 15µm Cr

Focus on the involved mechanism during high temperature oxidation:

M5Framatome

15µm Cr

Cr diffusion

Zr diffusion

A B

(µm)

Log(C)

ZrCr2 Cr

Limited Cr diffusion in the substrate


M5Framatome

M5Framatome



p.12

Cr-coated cladding behavior under high temperatures: LOCA conditions T≤ 1200°C

Significantly reduced oxidation kinetic

Steam oxidation at 1100°C followed by quench in water

Significantly reduced oxygen diffusion in the sample (no alpha (o) layer)

Significantly reduced hydrogen production and hydrogen pick up

Improved post-quench ductility

Improved safety

0

10

20

30

40

50

0 5000 10000 15000 20000

We

igh

t g

ain

(m

g/c

m2)

Time (s)

Steam oxidation at 1100°C

Cr-coated cladding (10-15µm)

Uncoated Reference M5

ruptured during quench

M5Framatome

Cr-coated M5Framatome sample

Uncoated M5Framatome reference sample



p.13

Cr-coated cladding behavior under high temperatures: Beyond LOCA conditions T>1200°C

Eutectic transformation: wrinkled crocodile-like skin

No down Flow of the eutectic liquid phase

No cracks or delamination observed

Cladding integrity perfectly maintained

Zr-Cr Eutectic transformation

1330°C

Steam oxidation at 1400°C for 100s

(V=1°C/s)




Heating at 20°C/min up to 1400°C under argon

p.14

Different visual aspect:

5µm Cr: Visible coarse beta grains

15µm Cr: Uniform golden surface

Differential Scanning Calorimetry : Determination of the Zr-Cr Eutectic Temperature

Eutectic temperature: T (5µm of Cr) = 1320°CT (15µm of Cr) = 1328°C


M5Framatome 5µm CrM5Framatome 15µm Cr



Zone 1

Zone 2

p.15

Zone 1

Zone 2

Zone 3

Zr(o)

ZrCr2

precipitates

Fine precipitates

Thick precipitates


Differential Scanning Calorimetry : Resulting microstructure Only two zones are distinguished:

Zone 1: External Cr-rich zone with ZrCr2 precipitates

Zone 2: Internal zone with less Cr in solid solution

Three zones distinguished:

Zone 1: Zr-Cr eutectic layer

Zone 2: Cr-rich zone with ZrCr2 precipitates

Zone 3: Internal zone with no precipitates

M5Framatome

5µm CrM5Framatome

15µm Cr



p.16


Differential Scanning Calorimetry :Cr diffusion profile

Three zones distinguished:

Zone 1: External Zr-Cr eutectic layer (around 27at% Cr)

Zone 2: Cr-rich zone

Zone 3: Internal zone with decreasing Cr content

Only two zones can be distinguished:

Zone 1: External Cr-rich zone (around 2 at%)

Zone 2: Internal zone with decreasing Cr content gradually to 0 at the internal surface of the cladding tube

log

M5Framatome

5µm Cr

M5Framatome

15µm Cr



p.17


Eutectic temperature T= 1320°C to 1330°C

In case of sharp temperature rise T>1330°C the eutectic melting is restricted to the external surface of the tube

After eutectic transformation, the resulting microstructure depends on:

The thickness of the initial Cr layer: thicker Cr layer would result on more available residual Cr to form thicker eutectic layer.

Partial conclusion



Zone 2: quench microstructure

Zone 1: eutectic microstructure

Porosity

p.18


Heating tests at higher heating rate (25°C/s and 100°C/s) under argon: investigate heating rate effectM5Framatome 15µm Cr

Heating rate: 25°C/s Heating rate: 100°C/s

External eutectic layer is observed in both samples: its thickness is around 60µm at 25°C/s and around 80µm at 100°C/s

The eutectic layer is characterized by a dendritic microstructure with fine ZrCr2 precipitates (dark phase) in alpha-Zr (light phase)

Beta grains in the sample heated at 25°C/s seem to be larger and more connected: lower heating rate enhances Cr diffusion in beta grains



p.19


Eutectic temperature T= 1320°C to 1330°C

In case of sharp temperature rise T>1330°C the eutectic melting is restricted to the external surface of the tube

After eutectic transformation, the resulting microstructure depends on:

The thickness of the initial Cr layer: thicker Cr layer would result on more available residual Cr to form thicker eutectic layer.

The heating rate: lower heating rate enhances Cr diffusion and thus results on thinner eutectic layer

At high temperature and under inert atmosphere two mechanisms of Cr consumption are in competition controlling the resulting microstructure:

Cr diffusion in the substrate to form solid solution

Eutectic transformation

Under steam Cr oxidation is added as a third mechanism that would affect the final microstructure

Conclusion



p.20

Steam oxidation at 1400°C for 100s

(V=1°C/s)

After eutectic transformation Cr-coated cladding manifests an improved post-quench ductility

Cr-coated or not

T(°C) of steam

introduction upon heating

at 1°C/s

Temperature range achieved

(*) (°C)

Oxidation time (s)

Failed or not upon quenching?

No

600°C

1300-1320 600 No

Yes 1300-1320 600 No

No 1400-1420 100 NoYes 1400-1450 100 No

No 1500-1530 50 No

Yes 1500-1550 50 NoNo

1300°C

1300-1350 600 YesYes 1300-1310 600 NoNo 1400-1450 100 YesYes 1400-1450 100 No

M5Framatome

15µm Cr




p.21

3.MATERIAL IRRADIATION

Overview of Framatome irradiationprogram for Cr-coated cladding



p.22

Framatome Irradiation programs in both Europe and USA



p.23

Cr-coated cladding samples exhibit excellent irradiation feedback

IMAGO-2016Visual inspection of Cr-coated cladding after

2 cycles of irradiation in Gösgen reactor

No defects or delamination observedNo changes between cycle 1 and 2

Slight golden color = very thin oxide layer (<1µm)

Unirradiatedreference

Irradiated sample

Cr-coating Zy4 substrate

Distance (µm)0 20 40 60 80

Negligible inter-diffusion at the Cr-Zrinterface due to irradiation

OSIRIS irradiation (1.5dpa) - 2015

Cr

(%)

0

0,5

1

4

3

5

2,5

3,5

4,5

M5Framatome



Framatome is developing both evolutionary and revolutionary E-ATF solution

p.24

Take away message!

Evolutionary solution

Cr-coated M5Framatome

cladding

Cr2O3-doped UO2 Fuel

Normal operating conditions- Reduced corrosion and H pickup- Reduced cladding wear

Accidental conditions- Reduced HT steam oxidation- Reduced HT creep and ballooning- Increased post quench ductility

- Reduced fission gas release- Improved PCI behavior- Reduced Fuel Fragmentation

- Improved reliability- Increased safety- Flexible operation- Economic benefits



p.25

Take away message!

First LTRs irradiation started in commercial reactor!

On track for LTAs irradiation in 2021!

Excellent Out of Pile Characterization results

First Commercial Irradiation feedback ok!

Fabrication of Full Length Coating Prototype Completed !



The authors would especially like to thank Kernkraftwerk Gösgen-Däniken AG for their collaboration in the irradiation of E-ATF samples in the Gösgen reactor and to Southern Nuclear for supporting LTRs irradiation in USA.

The authors would like to thank the CEA for contributing to the development of the full length tubes coating process.

The authors would like to mention also that part of the in-pile and out of pile characterizations of Cr-coated cladding is performed in the frame of the I3P collaboration (Framatome, CEA and EDF).

This work is partially supported by the U.S. Department of Energy under Award Number DE-NE0008220 with Framatome Inc.

p.26

Acknowledgements



Any reproduction, alteration, transmission to any third party orpublication in whole or in part of this document and/or its content isprohibited unless Framatome has provided its prior and writtenconsent.

This document and any information it contains shall not be used forany other purpose than the one for which they were provided. Legalaction may be taken against any infringer and/or any personbreaching the aforementioned obligations.

M5 and PROtect are trademarks or registered trademarks of Framatome or its affiliates, inthe United States or other countries

p.27The behavior of Cr coated zirconium alloy cladding tubes at high temperatures – N. ChaariManchester 2019 - Mai 20th

Documents

THE BEHAVIOR OF CR-COATED ZIRCONIUM ALLOY CLADDING … · Cr diffusion in the substrate to form solid solution Eutectic transformation Under steam Cr oxidation is added as a third