THERMOMECHANICAL PHYSICAL PERFORMANCES OF SIC/SI

THERMOMECHANICAL(PHYSICAL)

PERFORMANCES OF SIC/SIC COMPOSITES

FOR NUCLEAR APPLICATIONS

SEPTEMBER, 17-22 2017

| PAGE 1

F. Bourlet, C. Lorrette, T. Guilbert, C. Sauder

DEN-Section for Applied Metallurgy Research, CEA, Université Paris-Saclay,

F91191 Gif-sur-Yvette, France

And G. Vignoles

Université de Bordeaux, LCTS, Allée de la Boétie, 33600 Pessac, France

EUROMAT 2017| Thessaloniki

15 SEPTEMBRE 2017

| PAGE 2

OVERVIEW

Focus on the development of SiCf/SiC

composites

High temperature resistance : 300/550/1000°C (nominal) & 1200-2000°C (accidental)

Microstructure stability under fast neutron flux (75-150 dpa)

Neutron transparency and low activation

Corrosion resistance

Tolerance to damage (safety requirements)

Requirements to be use as material in nuclear power plant LWR, SFR and GFR-He

While preserving behavior in nominal condition

OBJECTIF ADD ADDITIONAL MARGINS (ATF – LWR)

H2 Put off

fusion

Maintain the

geometry after

water quenching

Reduce the

oxidation

exothermic

peak

Restrict gas

products

CONTEXT

F. BOURLET ET AL. | EUROMAT, SEPTEMBER 17-22, 2017 – THESSALONIKI, GREECE

INTRODUCTION

SiC/SiC composites development for actual LWR and futur GFR, SFR

Two applications compatibles with ceramic composites

Fuel cladding

FUNCTIONAL SPECIFICATIONS Stacked mixed-carbide

(U,Pu)C pellets

External diameter 10mm Wall thickness 1mm

SiCf/SiC pin Mechanical integrity

Coolant & Fission Products tightness

Heat exchanger

Patent WO 2011/042406 A1

FUNCTIONS Axial mechanical continuity of assembly

Coolant chanelling & pin-bundle protection

Mixed CMC/Metal hexagonal SA duct Motivations: No full-metallic solution (neutronic penalty)

SiCf/SiC

shrouds

Metallic

skeleton

Thickness : 3,25 mm Length: 4x250 mm

200 mm

SA head

SA foot

Fissile

height

50 mm

R&D ISSUES

| PAGE 3 F. BOURLET ET AL. | EUROMAT, SEPTEMBER 17-22, 2017 – THESSALONIKI, GREECE

First containment

barrier

Piece enclosing

fuel claddings

INTRODUCTION

SiC/SiC composite development for actual LWR and futur GFR, SFR

Two applications compatibles with ceramic composites

Fuel cladding

FUNCTIONAL SPECIFICATIONS Stacked mixed-carbide

(U,Pu)C pellets

External diameter 10mm Wall thickness 1mm

SiCf/SiC pin Mecanical integrity

Coolant & Fission Products tightness

Heat exchanger

Patent WO 2011/042406 A1

FUNCTIONS Axial mechanical continuity of assembly

Coolant chanelling & pin-bundle protection

Mixed CMC/Metal hexagonal SA duct Motivations: No full-metallic solution (neutronic penalty)

SiCf/SiC

shrouds

Metallic

skeleton

Thickness : 3,25 mm Length: 4x250 mm

200 mm

SA head

SA foot

Fissile

height

50 mm

R&D ISSUES


First containment

barrier

Piece enclosing

fuel claddings

OBJECTIVES

But prone to micro-craking beyond their elastic limit

SIC CLADDING CONCEPT : « SANDWICH » DESIGN AS A SOLUTION FOR LEAK-TIGHTNESS ISSUE

0

50

100

150

200

250

300

0 0,2 0,4 0,6 0,8 1

Str

es

s (

MP

a)

Strain (%)

Fibre damaged

Multi matrix cracks

Begining of damage

… but the liner preserves the leak-tightness

Failure limit

(F ~ 300 MPa – εF ~ 0.90 %)

Material rupture

Elastic limit

(E ~ 80 MPa – εE ~ 0.04 %) Leak-tight domain with

present-day CMC

Linear elastic

Liner SiCf/SiCm

(PyC interphase)

SiC/SiC cladding : refractory, pseudo-ductile behavior, resistant to

irradiation and low activation

| PAGE 5

Leak-tightness

preservation

beyond the elastic

limit


OBJECTIVES

Post exposure mechanical behavior

Post quenching mechanical behavior

Mechanical test realised at high

temperature under neutral atmosphere

Structure influence on thermal properties

Thermal properties

Mechanical

behavior

Internal pressure

test

Environmental

Post exposure

thermal behavior


OBJECTIVES

Post exposure mechanical behavior

Post quenching mechanical behavior

Mechanical test realised at high

temperature under neutral atmosphere

Structure influence on thermal properties

Internal pressure

test

Micro-crack

influence High

temperature

influence

Oxidation

influence

Quenching

influence

Post exposure

thermal behavior

Oxidation

influence


15 SEPTEMBRE 2017

| PAGE 8

CEA | 10 AVRIL 2012

MECHANICAL BEHAVIOR

| PAGE 9

EXPERIMENTAL PROCEDURE

TENSILE TEST

Testing method proposed to ISO Standardization :

Upper active grip

Alignment of load train insured by

structural bonding of specimen end

Tube specimen

2 contacting

extensometers

F/2 (+ Acoustic emission)

Constant crosshead displacement rate

(0.05mm/min)

Clamping

INTERNAL PRESSURE TEST

Pressurization of tubes

by oil injection into an

elastomeric bladder

Tube

Specimen

(free edges)

Strains measurement by

both DIC and gauges

2

int

2

ext

2

int1θθ

RR

RP2σ

Circonferential stress

computation (No membrane effect)

Oil input (P)

Elastomeric

bladder

ISO 21971 ISO 20323


Testing methods for mechanical behavior assessment of ceramic composites tubes

0

50

100

150

200

250

0,0 0,1 0,2 0,3 0,4 0,5

Str

es

s (

MP

a)

Strain (%)

Gauges measurement

15 SEPTEMBRE 2017

| PAGE 10

MECHANICAL BEHAVIOR (1/4)

INTERNAL PRESSURE TEST (RT)

Elastic damageable mechanical

behavior characteristic of most

ceramic composites

Greater density of microcracks

in inner surface comparatively to

the outer (Difference of curvature radius)

Hi-Nicalon type S fibers reinforcement – 30° angle

Behavior in line with longitudinal tensil tests


Significant residual strains

but possibly related to structural effect

Faciès de rupture

1400°C

NEUTRAL ENVIRONMENT : MECHANICAL TEST REALISED AT HIGH TEMPERATURE

Limitation temperature :

1600 °C !


High mechanical strength in temperature / non-zero up to 1600 ° C

Mechanical behavior stability demonstrated up to 1000 °C

Higher residual strain for mechanical test realised at 1400 °C

Weakening of mechanical poperties beyond to 1000 °C


Damage indicators

Faciès de rupture

1400°C

After 110 hours under steam at high temperature

Retention of mechanical comportment “Non-linear elastic damage” of ceramic composites Same breaking deformation / Slight decrease of young’s modulus and breaking stress

0

50

100

150

200

250

300

350

400

450

500

0 0,2 0,4 0,6

Stre

ss (M

Pa)

Strain (%)

As recieved

1400°C

1200°C

LWR - LOCA CONDITIONS : POST-EXPOSURE MECHANICAL BEHAVIOR

Breaking fracture

At 1400 °C

Interest confirmed of SiC/SiC for Accident Tolerance Fuel application



Protective comportment of silicon carbide matrix in these conditions : PyC interface stay efficient to deflect craks

QUENCHING EFFECTS : POST-EXPOSURE MECANICAL BEHAVIOR

Pyrocarbon interphase stays efficient to deviate cracks

Matrix micro-cracking saturation did not occur before ultimate failure

(singles regime of EA detected)

After high temperature treatment and quenching

Preservation of the « non-linear elastic damageable »

behavior characteristic of ceramic composites

| PAGE 13

EP (GPa) Y (MPa) m (MPa) m (%)

SiC/SiC As-received 285 ± 3 97 ± 6 252 ± 8 0,95 ± 0.03

Quenched SiC/SiC

1500°C, 200 s 280 104 283 0.95

Quenched SiC/SiC

after 1500°C, 1200 s 280 93 233 0.83



After high temperature oxidation ramp followed by water quenching

(1500°C under steam 200-1200s)

Ou

tsid

e s

urfa

ce

Insid

e s

urfa

ce

Inside surface

200 µm 200 µm

After high temperature treatment and quenching

The micro-cracks observation into the matrix

surface are deflected by PyC interphase

QUENCHING EFFECTS : METALLOGRAPHICS OBSERVATIONS



No micro-cracks

development at the heart

XPS

15 SEPTEMBRE 2017

| PAGE 15

CEA | 10 AVRIL 2012

THERMAL PROPERTIES

Originality of the measurements are based on the simultaneous treatment of both the front and rear faces of tubular specimens

(To overcome the highly anisotropic character of ceramic composites)

Pulse « Flash method » (IR thermography, periscope)

Acces to both transverse and in-plane diffusivities

Conductivity had to be higher than 10 W.m-1.K-1

THERMAL CONDUCTIVITY MEASURMENT



New testing method developed for thermal characterization of ceramic composite tubes

TubeConfig.B

Config. A

IR

Caméra

Flash

impulsion

Values would satisfy requierements for SiCf/SiC-based nuclear cladding

15 SEPTEMBRE 2017



THERMAL CONDUCTIVITY MEASURMENT New testing method developed for thermal characterization of ceramic composite tubes

Thermal properties closely dependent on the nature of the SiC fibers (TSA3 or H-NS),

the processing route for densification and the fibrous architecture…

15 SEPTEMBRE 2017

| PAGE 18

THERMAL PROPERTIES (1/2)

Measured at 25 °C on undamaged SiC/SiC exposed in dynamic conditions (Loop, AREVA Facility)

0

5

10

15

20

25

30

-10 10 30 50 70 90 110 130 150

Tran

sve

rse

th

erm

al c

on

du

ctiv

ity

(W.m

-1.K

-1)

Exposure time (days)

No changement expected for longer times… 2823 kg.m-3 / Cp 680 J.kg-1.K-1

Transverse conductivity

calculated from post-exposure

diffusivity measurments at RT


Margin reduced with temperature increase

and neutron irradiation

LWR CONDITIONS: POST-EXPOSURE MEASURMENTS

No effect of oxidation on the thermal behavior after 80 days

Conductivity stays widely higher than

the required minimal value of 10 W.m-1.K-1

Coherent with absence of damage and the very low sample recession

LWR conditions (Out of pile)

do not significant degrade

the thermal properties of SiC/SiC

15 SEPTEMBRE 2017

| PAGE 19

LIMITATION : MECHANICAL DAMAGE EFFECT ON THERMAL PROPERTIES Evaluated on tubular composite specimen submitted to a tensile loading (in-situ testing)

2,0E-06

3,0E-06

4,0E-06

5,0E-06

6,0E-06

7,0E-06

8,0E-06

0

100

200

300

400

500

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Te

ns

ile

str

es

s (

MP

a)

Tra

ns

ve

rse

th

erm

al

dif

fus

ivit

y (

m2/s

)

Longitudinal strain zz (%)

Mechanical behaviour

Thermal diffusivity

2,0E-06

3,0E-06

4,0E-06

5,0E-06

6,0E-06

7,0E-06

8,0E-06

0

100

200

300

400

500

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

Te

ns

ile

str

es

s (

MP

a)

Tra

ns

ve

rse

th

erm

al

dif

fus

ivit

y (

m2/s

)

Longitudinal strain zz (%)

Mechanical behaviour

Thermal diffusivity

Development of matrix cracking acts as a barrier to the

heat transfer in the thickness

Intra-bundle debonding – A

(normal to the heat flow direction)

Intra matrix seal-coat cracks – B

Two populations of cracks


THERMAL PROPERTIES (2/2)

Confirmation of a close relation between thermal properties and mechanical damage

15 SEPTEMBRE 2017

| PAGE 20

CONCLUSION


LWR SFR GFR

PyC interface stays efficient to deviate micro-craks (LOCA event)

Low influence of steam oxidation up to 1500°C followed by water quenching on mechanical properties

No significant influence of nominal oxidation on thermal properties

Preservation of high mechanical behavior (strength, strain) beyond the 1000/1400°C range

SiC/SiC composites are very interesting materials

…but there is still a long way to go before industrialization

Thermal properties degraded by mechanical damage

Highlighted limitation

Direction de l’énergie nucléaire

Commissariat à l’énergie atomique et aux énergies alternatives

Centre de Saclay | 91191 Gif-sur-Yvette Cedex

Etablissement public à caractère industriel et commercial | R.C.S Paris B 775 685 019

| PAGE 21

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THERMOMECHANICAL PHYSICAL PERFORMANCES OF SIC/SI