Corrosion of steels in liquid metals

1 | Vorname Nachname | Mid-term Review NUKLEAR | February 5-6, 20071 | C. Fazio | MATGEN IV.2 | February 2009

KIT - Die Kooperation von

Forschungszentrum Karlsruhe GmbH

und Universität Karlsruhe (TH)

Corrosion of steels in liquid metals

Concetta FazioProgram Nuclear Safety Research

MATGEN IV.2February 2- 8, 2009Stockholm – Kiruna, Sweden





Outline• Motivation

– The role of Nuclear Energy in an Energy Mix– The Fast Reactor System and its fuel cycle– Transmutation objectives and Scenarios

• Fast Reactor Systems and the role of liquid metals as coolant– Examples

• Loop type Na cooled FR• Pool Type Pb cooled FR• ADS

• Corrosion of steels in liquid metals– What is corrosion?– Parameters affecting corrosion– Corrosion mechanisms in HLM and Na– Experimental evaluation of corrosion mechanisms and rate– Models– Practical applications

• Summary and Perspectives





The role of Nuclear Energy in an Energy Mix

0

5

10

15

20

25

30

1990 2000 2010 2020 2030 2040 2050

Wo

rld

Pri

ma

ry E

ne

rgy

So

urc

es

(Gto

e)

6

6,5

7

7,5

8

8,5

9

Wor

ld P

opul

atio

n (B

illio

ns)

Other Renewable

Biomass

Nuclear

Gas

Oil

Coal

Population

Source IEA : Energy to 2050 -Scenarios for a Sustainable Future





- Economic Competitiveness- Safety and Reliability- Environment Protection - Proliferation Resistance

Fast Breeder Reactor

MOX+MA Fuel

Geological Disposal

Low Decontaminated Fuel

Reprocessing

Fuel Fabrication

U/Pu/MA Mixed Product

Fission Product

Spent Fuel

Global Concept of Future FBR CycleGlobal Concept of Future FBR Cycle

Objectives of future implementation of FR in a power park (starting from ~ 2040)





Optimal resources utilisation ….

G. Koch, Radiochimica Acta 37 (1984) 205





Transmutation Objectives and Scenarios

• Generic objectives of P/T strategies: – reduce the burden on a geological storage in terms of waste mass

minimization, reduction of the heat load and of the source of potential radiotoxicity.

Radiotoxicity of 1 ton Spent FuelSeparation of Pu and MA

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08

1E+09

1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07

Time after Discharge [years]

Ra

dio

tox

icit

y [

Sv

/ t

HM

]

without

99,9%Pu

99,9%Pu,MA

Nat-U






• More specific objectives can be defined according to the specific policy adopted towards nuclear energy and according to specific strategies of reactor development.

• Three categories of specific objectives:– Waste minimization and sustainable development of nuclear energy

and increased proliferation resistance of the fuel cycle. A transition from a LWR fleet to a FR fleet is foreseen.

– Reduction of MA inventory and use of Pu as a resource in LWRs, in the hypothesis of a delayed deployment of fast reactors. Use of dedicated burners (ADS or FR)

– Reduction of TRU inventory as unloaded from LWRs: Management of spent fuel inventories, as a legacy of previous operation of nuclear power plants in ADS.

It is a generally agreed conclusion that fast neutron spectrum systems are more appropriate for transmutation of TRU






DEDICATED FUEL REPROCESSINGAqueous (A) vsPyro (P)

REACTOR TYPE

High CR CRITICAL FR

ADS

RECYCLE MODE

Homogeneous

FUEL (target)MOX

3-5 % b)

REPROCESSING (MA recovery)

Full TRU

Cm Separa-

tion

Umatrix

Inert matrix

MA content ~ 50 % c)

MA/Puseparation

A A or P

?

?

?

CONVERSION RATIO (CR)

High CR Low (or zero) CR

Heterogeneous

Umatrix

Inert matrix

MA/PuSepara

-tion

10-20 % a)

Cm/Am/Puseparation

A or P

?

?

Low CR CRITICAL FR

HomogeneousHomogeneous

Umatrix

Sustainable nuclear energy development

Double strata and TRU legacy inventory reduction

?

?

a) MA/(MA+Matrix) b) MA/(U+TRU) c) MA/TRU





Among the 6 preferred Gen IV systems, 3 are FRs

Very High Temperature Reactor

Sodium Fast reactor

Supercritical Water Reactor Molten Salt Reactor

Lead Fast ReactorGas Fast Reactor





Examples - Loop type Na cooled FR: JSFR

Ref. SMINS, 2007





Loop type Na cooled FR: JSFR

Operational conditions

K. Mukai, Int. Seminar on coolants and Innovative Reactor Technologies, CEA Cadarache Nov. 2006

Parameters to be considered for material assessment





Examples - Pool type Pb cooled FR: ELSY

L. Cinotti, Int. Seminar on coolants and Innovative Reactor Technologies, CEA Cadarache Nov. 2006

PumpImpellerAlternative materials for pump impeller under investigationMaxthal, SiSiC, Noriloy

HX - T91 or AISi 316L

Vessel – AISI 316LCladding – T91





Pool type Pb cooled FR: ELSY

L. Cinotti, Int. Seminar on coolants and Innovative Reactor Technologies, CEA Cadarache Nov. 2006

Operational conditions

Parameters to be considered for material assessment





ADS

EFIT XT-ADS





ADS: Operational conditions

XT-ADS (LBE) EFIT (Pb)

Core components: mechanical stresses: e.g. Hoop stress on cladding

T 300 – 500 °C 400 – 530 °C

dpa Up to 160 Up to 100

flow ~ 2m/s ~ 2m/s

Reactor Vessel T 300 – 400 °C 400 – 430 °C

dpa < 0.02 < 0.003

flow ~ 1 m/s ~ 0.1 m/s

stress 50-150 MPa 80-150 MPa

Heat exchanger T 300 – 400 °C 400 – 480 °C

dpa < 0.02 < 0.03

flow ~ 1 m/s ~ 1 m/s

stress ~100 MPa 125-190 MPa

Spallation target T 240 - 340 °C 400 – 480 °C

dpa/yr Up to 40 Up to 30

flow ~ 3 m/s ~ 1.5 m/s

stress ~100 MPa + 40 fatigue cycles/yr n.a.

EFIT Pump: T= 480 °C; dpa < 0.03; flow = 10 m/s (on impeller)





Liquid Metals

Fast reactors have:- Hard neutron spectrum (i.e. limited neutron thermalisation and

as small neutron capture as possible)- High power density: need for effective coolant with high

thermal exchange capability.

Therefore: liquid metals as coolant. Historically Na and, at a lesser extent, Heavy Liquid Metals (HLM) have been the preferred choices.





Liquid Metals Properties

Property Unit Na Pb LBE

Atomic Number - 11 82 -

Atomic Mass amu 23 207 -

Melting Temperature °C 98 327 125

Boiling Temperature °C 883 1745 1670

Density at 450°C kg/m3 845 10520 10150

Thermal Conductivity at 450 °C

W/mK 69 17 14

Chemical reactivity - High Moderate as dust Moderate as dust

Toxicity - High High High





Corrosion of steels in liquid metals

What is Corrosion?Why it is important to study it?





„The word corrosion denotes the destruction of metal by chemical or electrochemical action; a familiar example is the rusting of iron” U. R. Evans

Pitting Corrosion: Corrosion Pits are the primary source of leaks in water handling systems

Liquid metal corrosionLecor impeller (presented at the ELSY Meeting by ENEA)

Active Corrosion on Carbon Steel Manhole





Why it is important to study it

- Ensure Integrity of structures- Avoid Plugging of systems with corrosion products - Ensure thermal conductivity of fuel cladding and functional

components

An example for HLM cooled FR:• Stringent safety requirement on the integrity of the cladding

material has been put for design basis operating conditions and design extension conditions.

• For the chosen temperature regime, the selected cladding material should withstand the combined effect of neutron irradiation, corrosion and mechanical stresses in order to comply with the safety requirements.





Factors affecting liquid metal corrosion

Temperature Temperature gradient (mass transfer) Cyclic temperature fluctuations Surface area to volume ratio Chemical purity of the liquid metal (wetting) Flow velocity (Reynolds number) Surface conditioning (surface films) Number of materials in contact with the same liquid metal

(dissimilar mass transfer) Condition of the container material (carbides or nitrides at the

grain boundary)





Liquid metal corrosion mechanism

Alloying between liquid and solid metals: for this type of mechanism there must be some solubility of the liquid metal in the solid metal. In some cases the liquid metal dissolves considerably in the solid metal with the formation of an intermetallic compound (e.g. V in Pb at 1000°C).

Scheme of the simple dissolution mechanism

Simple solution attack: Removal of the metal from the surface to saturate the liquid metal.

Concentration gradient mass transfer dissimilar metals, e.g: Mo samples tested in Na contained in a Ni crucible at 1000°C: Ni had transferred through the Na and deposited on the Mo surface to produce Ni-Mo compounds





Liquid metal corrosion mechanism

Temperature gradient mass transfer: the most damaging type of liquid metal corrosion is temperature gradient mass transfer. The driving force for temperature gradient mass transfer is the difference in solubility of the dissolved metal at the temperature extremes of the heat transfer system. By knowing the solubility limit of the solid in the liquid metal the driving force of these phenomena can be determined

1. Solution2. Diffusion3. Transport of dissolved metal

4. Nucleation5. Transport of crystallites6. Crystal growth and sintering (plug formation)

Pulg in an Inconel-Pb loop





Part 2: Factors affecting liquid metal corrosion

Temperature Temperature gradient (mass transfer) Cyclic temperature fluctuations Surface area to volume ratio Chemical purity of the liquid metal (wetting) Flow velocity (Reynolds number) Surface conditioning (surface films) Number of materials in contact with the same liquid metal

(dissimilar mass transfer) Condition of the container material (carbides or nitrides at the

grain boundary)





Liquid metal quality: Sources and type of impurities

• At installation start up and in normal operating conditions

– From Cover gas and adsorbed gases on structures (O2, H2O)

– From neutron reaction and from spallation (e.g. Po, Hg, other activation products)

– Corrosion products from structural material (e.g. Fe, Cr, Ni, etc.)– Intrinsic impurities (Ag, Cu, Sn, etc.)

• Off normal conditions– From Fuel cladding failure (Pu, U, MA, etc.)

– Air entrance (N2, O2, H2O, ..)

– Steam entrance (H2O)





HLM quality control: the case of Oxygen

Above solubility limit lead and bismuth oxide formation

Solubility of Oxygen in LBE

Solubility of Oxygen in Pb

Oxides floating on the liquid metal





Na quality control: the case of Oxygen

10

100

1000

10000

250 300 350 400 450 500 550 600 650

Temperature, °C

So

lub

ilit

y, p

pm





Solubility of metallic elements

1,0E-05

1,0E-04

1,0E-03

1,0E-02

1,0E-01

1,0E+00

1,0E+01

1,0E+02

1,0E+03

1,0E+04

1,0E+05

1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8

Temperature 1000/T [K]

So

lub

ility

[w

pp

m]

Ni(Pb)

Ni (Pb-Bi)

Cr (Pb)

Cr (Pb-Bi)

Fe(Pb)

Fe(Pb-Bi)

In Na

In HLM





From liquid metal quality to corrosion

Liquid metal corrosion depends from the solubility of the solid metal in the liquid metal and its solution rate.• Solution rate and extent of solubility are affected by

– formation of surface intermetallic compounds (among the liquid and the solid)

– oxide or nitride films formation (due to the presence of oxygen / nitrogen in the liquid metal)

– Other impurities present in the liquid metal can increase the solution rate

– Temperature gradients and multimetallic systems





Results from screening experiments: HLM

10000 h

20 m

PbBi

ferriteferritelayerlayer

20 m

PbBi

Case 1) oxygen content in LBE < 10-9 wt.% T=400 °C

Dissolution of solid metal in the liquid metal

Uniform dissolutionTransgranular and intergranular

Leaching of Ni and ferritisation

AISI 316L

T91

Case 2) [O2]LBE > 10-8 wt.% and < 400 °C < T < 550 °C

(PbO)GΔ O2

Impurities in LBE forming simple or complex substances on the

metal surface

Under controlled O2 content

and T: the oxide can be considered as a corrosion protection layer

AISI 316L

2)

1)

Corrosion mechanism in HLM depends from:Temperature – oxygen content in the liquid metal – composition of steel





Results from experiments: Na

Low Oxygen High Oxygen

Similar mechanism is observed with Cr (Na-Cr-O are more stable than Na-Fe-O)

Formation of ternary oxides increased corrosion rate

In austenitic steels ferritisation can be observed (Ni solubility highest)





Experimental Programs to address Corrosion mechanism and rate





Choice and characterisation of reference structural materials: the case of HLM systems• Materials selected

– Ferritic Martensitic steel T91 for the highly loaded parts (e.g. cladding, spallation target)

– Austentic steel AISI 316L for e.g. Vessel

– Fe, Al based corrosion protection barrier

Element Cr Mo Nb N C V

wt. % 8-9,5 0.85-1.05 0.06-0.1 0.03-0.07 0.08-0.12 0.18-0.25

Element Mn P Si Ni Al S

wt. % 0.30-0.60

<0.02 0.2-0.5 <0.4 <0.04 <0.01

T91

Element Cr Mo Nb N C V

wt. % 16-18 2-3 - 0.1 0.03 -

Element Mn P Si Ni Al S

wt. % 2 0.045 0.75 10-14 - 0.03

AISI 316L





Materials qualification program for HLM systems

0

1

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450 500 550 600

Temperature [°C]

HLM

flow

[m/s

]

FZK

CEA

NRI

ENEA

CIEMAT FZK/IPPE

100

200

300

400

500

600

0 20 40 60 80 100

BR2/SHFR/SBOR60/S

BR2/DHFR/DPX/D

Irra

dia

tion

Te

mpe

ratu

re (

°C)

Dose (dpa)

Temperature and Dose of Irradiation Experiments

PHENIX

BOR60

BR2

HFR

HFR

BR2

BR2

HFR

SPIRE (red symbols) DEMETRA (green)

Conditions foreseen for ADS Components

Target window

Clad tubesTarget structuresSINQ

SINQ

+ He

(LBE)

(LBE)

Irradiation studiesCorrosion studies

Corrosion / n-irradiation combined effect





Corrosion studies in HLM

Dissolution (uniform or transgranular) of the steel elements in the liquid metal

Oxidation of the steel surface. The oxide layer can act as a protection barrier against a direct corrosive attack of the liquid metal

HLM oxides precipitates causing hydraulics problems (e.g. plugging)

Ellingham Diagram

For the operating condition of XT-ADS (300 – 400°C) and EFIT (480 – 530 °C) respectively an appropriate oxygen potential can be selected to avoid HLM oxides formation and to promote oxidation of the steel surface.

These are thermo-chemical statements, which enables to identify the corrosion mechanism. However, no information are available on the corrosion rate and the hydraulics effect.





Corrosion studies: experimental results

Loop Experimental conditions 2.000 h Oxide scale/LM attack

Up to 10.000 h Oxide scale/LM attack

T91 316 T91 316

CORRIDA (FZK)LBE

550°C; 10-6 wt.-%O flow= 2 m/s

Oxide: 20-25 m Oxide : few Oxide: 45 m(data dispersion)

LM attack up to 350 m

CU2 (IPPE/FZK) LBE 550°C; 10-6 wt.-%O flow= 1.3 m/s

Oxide: 39 m _____ 6600 hOxide: 36-45 m (data dispersion)

_____

CHEOPE III (ENEA) Pb

500°C; 10-6wt%; flow = 1 m/s

20 m (non homog.)

Oxide: few 5000/10000 hOxide: 25 m / scale spall off

5000/10000 hOxide: thin/thin and compact

LINCE (CIEMAT) LBE 450 °C; 10-8 wt.-%O (probl. on sensor)

1700 h T91: 4 m (non homog. oxide)

Unaffected Corrosion attack up to 350 m

Corrosion attack up to 200 m

LECOR (ENEA) LBE 450°C;10-10-10-8 wt%

LM attack less evident LM attack

_____ _____






CORRIDA FZKOxide: 25 m

550°C; 10-6 wt.-%O flow= 2 m/sNo magnetite detected (higher velocity)

550°C , 10-6 wt.-%O flow= 1.3 m/sOxide thickness: spinel+ internal oxidation = 22 µm Magnetite thickness: 17 µm

CU2 IPPE/FZKOxide: 39 m

Results after 2000h in LBE at 550°C and Pb at 500°C performed with a controlled oxygen potential

500°C , ~10-6 wt.-%O flow ~ 1 m/s1. Lower temperature2. Different oxygen potential3. “low” flow velocity

CHEOPE /ENEAOxide: ~ 20 m

1. Oxide scale is formed by three layers: outer magnetite – intermediate Fe, Cr spinel oxide – inner oxygen diffusion zone

2. However, oxide scale tested in Corrida do not has the outer magnetite layer: Hydraulics effect (see next slide)?

3. After 2000h oxidation rate in Pb at 500°C is lower with respect to LBE at 550°C: temperature effect






100mm 50mm 100mm 50mm 50mm 100mm

V=1 м/s V=2 м/s V=3 м/s

АА

Confirmation of hydraulics effects on the oxide scale formation: Experiment performed with different flow velocities

550 °C, 2000 h, ~10-6 wt.% O

At 1m/s outer magnetite scale, at 1,75 m/s small rests are visible, at 3m/s magnetite scale entirely eroded.

FZK-IHM/IPPE collaboration

Fe3O4

V = 1 m/s V = 1,75 m/s V = 3,0 m/s

(Fe, Cr)3O4

Internal oxidation

Fe3O4

(Fe, Cr)3O4

Internal oxidation Internal oxidation

(Fe, Cr)3O4





Corrosion studies experimental results

10-6 wt.-%O flow= 1 m/s t=2000h 550°C

Pressurised tube in HLM





Example of application of corrosion results to Design

(D. Struwe, W. Pfrang, IRS/FZK)

Oxide layer thickness should be limited to less than 20-30 m in order to keep margin on the maximum allowable temperature for the T91 steel.

Control of oxidation process in a reactor system might not be applicable

GESA surface alloyed steel can be seen as a solution

Axial profiles of clad inner temperature modified calculation with different additional oxide layers





Corrosion studies: Fe, Al corrosion protection barrier

600°C

Up to 600°C and 10000 h no corrosion attack and no visible oxidation.

Thin alumina scales protect the surface alloyed steel.

1. LPPS of Fe, Al

FeC

rAlY

coat

ing

FeC

rAlY

coat

ing

FeC

rAlY

coat

ing

FeC

rAlY

coat

ing

2. GESA treatment on the LPPS coating

1. Enhance metallic bonding with substrate

2. Smoother surface3. Reduced Al content

500°C550 °C

3. GESA treated samples tested for 10000 h in flowing LBE at three different temperatures, flow rate 1 m/s and oxygen ptential equivalent to 10-6 wt%





Corrosion studies: Fe, Al corrosion protection barrier

100mm 50mm 100mm 50mm 50mm 100mm

V=1 м/s V=2 м/s V=3 м/s

АА

Confirmation of hydraulics effects on the Fe, Al GESA treated samples: Experiment performed with different flow velocities

550 °C, 2000 h, ~10-6 wt.% O

Samples with proper LPPS coating and proper GESA treatment: no flow velocity effect on surface appearance, no dissolution attack, no severe oxidation, no erosion.

FZK-IHM/IPPE collaboration

V = 1 m/s V = 1,75 m/s V = 3,0 m/s





• Oxygen activity: oxidation/dissolution• Time, Temperature• Flow rate: high flow rate erosion of Fe3O4 • Steel composition: high Cr content increased oxidation resistance. • Stresses: hoop stress enhances Fe diffusion

Parameters affecting corrosion of steels and modelling

Effect of temperature, oxygen content and steel composition Effect of flow velocity





Corrosion modelling: Example Na – steel system

Oxygen content in Na and flow velocity have been identified as the two main variables affecting the corrosion rate. The corrosion mechanism is the dissolution. From experimental results two semi-empirical equations have been determined:

For v ≤ 4m/s - the corrosion rate depends from the velocity

For v ≥ 4m/s – the corrosion rate depends only from the oxygen concentration





• Structural material corrosion in a closed an-isothermal system as a nuclear reactor, 2 kinds of model are needed:– Mechanistic model: give the structural material life time hox(t) or kp,

hdiss(t), jox, jdiss, using the physical-chemical data characteristic of the mechanism (Dox, DLM, S…)

– Mass transfer model: give the system life time Vcorr/prec(x) (prediction of plugging in the loop), using the output of the mechanistic model (kp, kpr, jox, jdiss…)

• Data needed:– Mechanistic model is based on numerous specific experiments which can

be partly performed in static conditions– Mass transfer model is based on long term experiments in LM closed

loop– To develop these models, need of physical-chemical data as: Dox, DLM,

SLM, kpr, kdiss which are very difficult to obtain and important lack of data to supply the corrosion model

jox oxygen flux in steel; Jdiss Fe flux in steel, hox oxide thickness, hdiss dissolution thickness, D diffusion coefficient, S solubility limit, kox oxidation constant kpr precipitation rate

Corrosion modelling: Example Steel-HLM





Corrosion modelling

• Example: Pb-Bi eutectic – steel system





Perspectives

•Advantages of F/M steels with respect to austenitic steel:

• Better thermal properties: 1. higher thermal conductivity 2. lower thermal expansion

(can have impact on the dimensioning, see e.g. Japanese Sodium Fast Reactor, JSFR)

• Lower Swelling

•However, experience on austenitic steels for the nuclear use is available

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15

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19

50 100 150 200 250 300 350 400

Temperature, °C

Me

an

Th

erm

al

Ex

pa

ns

ion

, 1

0-6

/K

AISI316L

T91

5

10

15

20

25

30

0 100 200 300 400 500 600

Temperature, °C

Th

erm

al

Co

nd

uc

tiv

ity

(l )

, W

/mK

AISI 316L

T91

Data AISI316L from AAA handbook; Data T91 from RCC-MR





Perspectives• Advantages of ODS alloys, with respect to F/M steels

• 9% Cr ODS RAFM steel has been developed for future fusion reactors and has shown very promising mechanical properties at high temperature

R. Lindau et al., FZK

…..but what about corrosion resistance of ODS steels?





Summary

• For the development of nuclear energy, FRs provide solution to the key issues of sustainability and waste minimisation;

• Among the preferred systems of Gen IV three types of FRs and two among them are liquid metal cooled;

• In this respect corrosion issues have to be considered due to safety requirements;

• The corrosion control in HLM is more challenging when compared to Na;

• Current programs allow to consolidate and extend corrosion understanding and modelling;

• In future, new type of steels (e.g. ODS) can provide improved performances. These materials need to be characterised also for their corrosion resistance





Selected ReferencesNa• H.U. Borgstedt, C.K. Mathews, Applied Chemistry of Alkali Metals, Plenum, New York, 1987.• K. Fink, L. Leibowitz, “Thermodynamic and Transport Properties of Sodium Liquid and

Vapor” ANL/RE-95-2, January 1995 (www.insc.anl.gov)• M. Konomura, M. Ichimiya „Design challenges for sodium cooled fast reactors“ J. Nucl. Mat.

371 (2007) 250–269HLM• “Handbook on Lead-bismuth Eutectic Alloy and Lead Properties, Materials Compatibility,

Thermal-hydraulics and Technologies” issued by the OECD-NEA and available at the following link: http://www.nea.fr/html/science/reports/2007/nea6195-handbook.html

• Nuclear Technology September 2004 – Vol. 147, No3• Several Issues of J. Nucl. Mater (Vol. 296 (2001); Vol. 301 (2002);Vol. 318 (2003); Vol. 335

(2004), etc.)Comparative assessment HLM - Na• „Comparative assessment of thermo-physical and thermohydraulic characteristics of Pb,

LBE and Na coolants for fast reactors“, IAEA TECDOC – 1289, June 2002F/M Steels• High-Chromium Ferritic and Martensitic Steels for Nuclear applications, Ronald L. Klueh and

Donald R. Harries, ASTM, MONO3





Thank you for your attention

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Corrosion of steels in liquid metals