Radiolysis in CANDU Coolant and its Effect on Chemistry and Materials Jungsook Clara Wren Department of Chemistry University of Western Ontario 1 International

Radiolysis in CANDU Coolant and its Effect on Chemistry and Materials

Jungsook Clara Wren

Department of Chemistry

University of Western Ontario

1

International Association for the Properties of Water and Steam Workshop

May 11 & 12, 2009

2

Presentation Outline

1. Overview of NSERC/AECL Industrial Research

Chair Program

2. Preliminary Results from -Radiolysis Induced

Carbon Steel Corrosion at 150oC

3. Importance of Steady-State Radiolysis on Steel

Corrosion

3

NSERC/AECL IRC Program2006 - 2010

1. Steady-State Water Radiolysis - Effects of Dissolved Impurities

• H2/O2/H2O2, Transition Metals, Nitrate/Nitrite, Organic Compounds

2. Corrosion Kinetics• In non-irradiated but chemically-simulated radiation environments

3. Corrosion Kinetics under -Irradiation

Catalytic Reactions

Corrosion products + Radiolysis products

Corrosion

Metal Oxidation/Dissolution

Water Radiolysis

H2O •OH, eaq–, H•, HO2•, H2, H2O2, O2, H+

Temperature Ranges: < 90oC 150oC 320oC (2nd Term ?)

Experimental Techniques

Surface Analyses

(coupons/particulates)

Raman, SEM/EDX, pXRD, XRD, XPS, Auger, Reflectance FTIR, Confocal Microscopy

Electrochemistry (Ex-situ/In-Situ Spectroscopy)

Current-potential profile,

Corrosion potential,

Electrochemical Impedance spectroscopy,

Linear polarization

Chemical Analyses(gas & aqueous speciation)

GC/MS+TCD+ECD

(H2, NOx, organics, etc)

UV-Vis + chemical titration

(H2O2, NO3/NO2

, Fe2+/Fe3+)

pH

Chemical Kinetics & Transport Modelling

Interfacial Transport

COMSOL MultiPhysics

(Finite Element Method)

Water Radiolysis Kinetics

FACSIMILIE

(Differential Rate Eq Solver)

Solution Thermodynamics

OLI

(Thermo. database + solver)

-Radiolysis on Carbon Steel Corrosion Coupon Studies at T 150oC

Dose Rate 6.4 kGy/ h

5

These studies are performed as a function of pH, T,

irradiation time, dissolved H2 and O2 (cover gas), buffer

Chemical Production in the Irradiated System

6

Liquid Water Radiolysis

Steam Radiolysis

H2, O2

H2, O2

Corrosion Products

H2, Fe2+, Fe3+ H2, H2O2, O2, •OH, •H, •eaq, •O2

H2, H2O2, O2, •OH, •H, •eaq, •O2

Aqueous and Gas Phases

3 m

pH25=10.6

1 m

5x

No Rad

71 m

5x

pH25= ~7

Rad 3 m

Effect of pH & -Irradiation at 150oC

21 h @150oC

Ar

5x

3 m

pH25=10.6

1 m

5x

No Rad

81 m

5x

pH25= ~7

Rad 3 m

Effect of pH & -Irradiation at 150oC

21 h @150oC

Ar

5x

H2 (0.6%)

H2 (2.3%)

H2 (0.8%)

H2 (2.2%)

9

5x

3 m

93 m

Cross Section

3 m

5x

pH25 = 10.6

200 nm

Cross Section

66 h Irradiation at 150oC, Ar

Outer oxide layer2.2 m

Inner layer

Base metal

1 m

Aq. Phase

Aq. Phase

Outer oxide layer760 nm

Inner layer

Base metal

pH25 = 7

Raman Spectroscopy

Confocal Raman Microscopy, small angle XRD for depth profile are underway

0 500 1000 1500 20000

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Y A

xis

Titl

e

X Axis Title

Fe3O4(10 * signal) Gamma-Fe2O3 Gamma-FeOOH 150, LiOH, 66hr, liquidB Alfa-Fe2O3

-Fe2O3

-FeOOH

-Fe2O3

Fe3O4

Ram

an

Inte

nsity

Raman Shift

A Mixed Phase ??

Fe3O4 / -Fe2O3 / FeII/FeIII(OH)x

Cross Section

Irradiated Sample

No significant -Fe2O3

66 h Irradiation, pH 10.6, Ar

11

Rad

No Rad

Liquid PhaseSteam Phase

150oCpH25=7

Ar, 21 h

1 m5x

3 m

5x

1 m

Rad

No Rad

5x

1 m

5x

Steamvs

Liquid

• Kinetics is still important at 150oC

• Steady-state irradiation enhances surface oxide formation

• The type of oxide depends on the rate of oxidation and pH

• Aqueous corrosion on CS under -irradiation is uniform, and

does not show localized corrosion

• At pH25 10.6, -irradiation appears to promote more compact

oxide

• Corrosion in the steam phase is more inhomogeneous

Preliminary Conclusions Coupon Studies at 150oC

Steady-State Radiolysis affects carbon steel corrosion behaviour

Water Radiolysis

13

Primary Radiolysis Yields (G-values)

Physical (chemical) Stage

Bulk Phase Chemistry Stage

Time (s)

10-16

10-13

10-10

10-7

10-4

Non

-hom

ogen

eous

kin

etic

sHo

mog

eneo

us k

inet

ics

Time (s)

10-16

10-13

10-10

10-7

10-4

Non

-hom

ogen

eous

kin

etic

sHo

mog

eneo

us k

inet

ics

•• • •• • •••••• • •• • ••••

Tracks and Spurs

•eaq

H2O

H2O* H2O+ , e -

H + •OH •OH + H3O+ •eaq

H2 •OH H2O2 H3O+ OH H•

H2 H2O2 O2 H2O

H2O

Stable products

•eaq

H2O

H2O* H2O+ , e -

H + •OH •OH + H3O+ •eaq

H2 •OH H2O2 H3O+ OH H•

H2 H2O2 O2 H2O

H2O

Stable products

, , Solvent Oriented Process

Importance of Steady-State Radiolysis

•eaqH2 •OH H2O2 H3O+ OH H• •eaqH2 •OH H2O2 H3O+ OH H•

H2 H2O2 O2 H2O Stable productsH2 H2O2 O2 H2O Stable products

Different steady states in different aqueous environments

Steady-State Concentrations

Aqueous chemistry control by pH, chemical additives

10-4Fe2+(aq) Fe3+(aq)•H, eaq

–, •O2–

•OH, H2O2, O210-4Fe2+(aq) Fe3+(aq)•H, eaq

–, •O2–

•OH, H2O2, O2

Surface Oxidation Metal Dissolution

Interfacial Transfer

Continuous production

Radical &reactive species quickly decay away

Steady-state concentrations determine corrosion behaviour

• Pulse Radiolysis has been a very useful tool for obtaining G-values

and rate constants of fast reactions of radicals and ions

Steady-State Radiolysis ModelAqueous Reaction Kinetics Database

~ 40 reactions

0 50 100 150 200 250 300

0.5

1.0

1.5

2.0

2.5

3.0

3.5

G v

alu

e x

liq

uid

de

nsi

ty

Temperature (C)

OH

eaq

HH

2

H2O

2

G-v

alu

e (T

) x

wat

er(T

)

•OH + H2

325oC 150oC 25oC80oC

16

Steady-State Radiolysis Model

• Individual reaction components in

the database are sound

• The model as a whole has not

been validated except at room T− Missing key reactions?

− What are the rate controlling

reactions?

− Do they change with T, pH,

impurity?

Validation of the model as a function of temperature ( 150oC)

under different chemical and interfacial conditions are on-going

0 1 2 3 4 5 610-7

10-6

10-5

10-4

[H2O

2] (m

old

m-3)

Time (h)

pH6

pH8.5

pH10.6

detection limit

Steady-State Model Validation

Without steady-state analysis

such pH dependence was not envisioned

5 6 7 8 9 10 11

10-7

10-6

10-5

10-4

10-3

10-14

10-13

10-12

10-11

10-10

10-9

[H2O

2] ss, [

H2] ss

& [

O2] ss

(m

old

m-3)

pH

OH

eaq

H2

O2

H2O

2

[O

H] ss

& [e

aq

] ss (

mo

ldm

-3)

Effect of pH on Radiolysis

Steady-State Concentrations

5 6 7 8 9 10 110.00

0.06

0.12

0.18

0.24

0.30

G- v

alue

(m

ol J

-1)

pH

OHe

aq

H2O

2

H2

G-values

25oC

25oC

Model sensitivity analyses to understand why such behaviour is observed

0 50 100 150 200 250 30010-10

10-8

10-6

10-4

10-14

10-12

10-10

10-8

O2

[H2O

2] ss, [

H2] ss

, [O

2] ss &

[O

2-]ss

(m

old

m-3)

Temperature (C)

OH

eaq

H2

H2O

2

O2

pH = 10.6

[O

H] ss

& [e

aq]

ss (

mo

ldm

-3)

pH25 = 10.6

0 50 100 150 200 250 300

0.5

1.0

1.5

2.0

2.5

3.0

3.5

G v

alu

e x

liq

uid

de

nsi

ty

Temperature (C)

OH

eaq

HH

2

H2O

2

G-v

alu

e (T

) x

wa

ter(

T)

Effect of Temperature on Radiolysis

Steady-State Concentrations G-values


such T dependence was not envisioned

Summary at T 150oC

• Radiolysis affects carbon steel corrosion

– Thermodynamic considerations are not sufficient

– Steady-state concentrations of radiolytic products determine surface

oxide formation/transformation

• Steady-state radiolysis behaviour strongly depends on pH, T,

chemical additives, dose rate, etc,

– These dependences are not well established

– Pulse radiolysis studies are not sufficient

• Molecular, not radical, products are more important for aqueous

corrosion in basic solutions

– The relative importance of radical species may increase with T

– Significant implication in chemistry control

Acknowledgement

Dr. Jamie NoelDr. X John ZhangDr. Peter KeechDr. Jiju JosephDr. Sriya PeirisDr. Sergey Mitlin

Dong FuSarah PrettyKevin DaubKaty YazdanfarPam YakabuskieSusan Howett

Pourbaix Diagram

Thermodynamics predicts -Fe2O3 to be the most stable oxide at 150oC

150oC

pH25 = 10.6pH25 = 6

Ref: B. Beverskog, I. Puigdomenech, Corrosion 38, 2121-2135, 1996

Magnetite stable in a small part of water stability region

For aqueous phase, Fe(OH)4+ stable

over a significant area

Copy

OLI

• Creates unusual solution conditions• A wide range in chemical reactivity,

redox and transport property

Synergistic Interaction of Radiolysis & Corrosion

Corrosion • Metal oxidation-reduction• Dissolution of metal oxides

• Depends on surface and solution-redox conditions

•OH, eaq–, H•, HO2•,

H2, H2O2, H+, O2, O2•–

H2O

Met

al O

xide

s, M

Ox

Bul

k M

etal

, M

Mn+(aq)

Water Radiolysis

Catalytic Interaction

Fe2+(aq) Fe3+(aq)•H, eaq

–, •O2–

•OH, H2O2, O2

• Catalytic interaction of dissolved metal and radiolysis redox species

NSERC/AECL IRC Program

23

3 m150oCpH25=10.6

Ar

Rad

No Rad

5*

21 h 66 h

Effect of

Radiation

3 m3 m

24

3 m150oCpH25=6

Ar

Rad

No Rad

5*

21 h 66 h

Effect of

Radiation

3 m3 m

1 m

5*

1 m

5*

3 m

5*

66 h Irradiation, pH 7, Ar

Mostly Fe3O4 + -FeOOH +

possibly FeII/FeIII(OH)x

253 m

Outer oxide layer760 nm

Inner layer

Base metal

Irradiated Sample

SEM of Cross Section

3 m

5x

0 500 1000 1500 20000

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Y A

xis

Titl

e

X Axis Title

Fe3O4(10 * signal) Gamma-Fe2O3 Gamma-FeOOH 150, LiOH, 66hr, liquidB Alfa-Fe2O3

-Fe2O3

-FeOOH

-Fe2O3

Fe3O4

Ram

an

Inte

nsity

Raman Shift

Need to compare pH 10.6 vs pH 6 cases

26

Water Radiolysis Kinetic Model(constant radiation field)

Output

Concentrations as a function of time

Input

Dose Rate

T, pH

•OH + H2

~ 40 Elementary Reactions& Rate constants (T)

0 1 2 3 4 5 610-7

10-6

10-5

10-4

[H2O

2] (m

old

m-3)

Time (h)

pH6

pH8.5

pH10.6

detection limit

5 6 7 8 9 10 110.00

0.06

0.12

0.18

0.24

0.30

G-

valu

e (m

ol J

-1)

pH

OHe

aq

H2O

2

H2

G-values (T)

water(T), Kwater(T), etc

Coupled reaction rate equations are solved using numerical

integration software FACSIMILE

•eaqH2 •OH H2O2 H3O+ OH H• •eaqH2 •OH H2O2 H3O+ OH H•

H2 H2O2 O2 H2O Stable productsH2 H2O2 O2 H2O Stable products

Steady State Concentrations

Continuous production

27

Rate constants

Steady-State Radiolysis Database

• T dependence well established

• For most reactions, it follows

Arrhenius T dependence

• At high T, all reaction rates

approach diffusion limited

• Diffusion rate T/

0 50 100 150 200 250 300

4

5

6

7

8

9

10

11

12

H2O

2HO

2

OHO

H eaq

pK

a

Temperature (C)

HO2O

2

Equilibrium constants

• Individual rxn components are sound

• The model as a whole has not been

validated except at room T− What are the rate controlling reactions?

− Do they change with T, pH, impurity?

− Missing key reactions?

•OH + H2


~ 3 orders of magnitude changes

at pHs around pKa of eaq + H+ = •H


such pH dependence not easily predicted

Model not validated at > 80oC

25oC

5 6 7 8 9 10 11

10-7

10-6

10-5

10-4

10-3

10-14

10-13

10-12

10-11

10-10

10-9

[H2O

2] ss, [

H2] ss

& [

O2] ss

(m

old

m-3)

pH

OH

eaq

H2

O2

H2O

2

[O

H] ss

& [e

aq

] ss (

mo

ldm

-3)

300oC

5 6 7 8 9 10 11

10-10

10-9

10-8

10-7

10-6

10-12

10-11

10-10

10-9

10-8

[H2O

2] ss, [

H2] ss

& [

O2] ss

(m

old

m-3)

pH

OH

eaq

-

H2

O2

H2O

2

[O

H] ss

& [e

aq]

ss (

mo

ldm

-3)

Temperature = 300C

pH on Steady-State Radiolysis Behaviour

pH dependence diminished due to

increase in the reaction of eaq with H+

Chemical Additives/Dissolved Species

0 50 100 150 200 250 300

0.0

2.0x10-5

4.0x10-5

6.0x10-5

8.0x10-5

1.0x10-4

[H2O

2] (M

)

Time (min)

Effect of [Fe2+]o on [H2O2]SS

Ar, pH = 10.6Effect of Radiolysis on Iron Solubility

Fe2+(aq) Fe3+(aq)•H, eaq

–, •O2–

•OH, H2O2, O2

[Fe2+]o = 0, 510-5, 110-4 M

Synergistic interaction between corrosion products and radiolysis

products



Steady-State Radiolysis ModelAqueous Reaction Kinetics Database

~ 40 reactions

0 50 100 150 200 250 300

0.5

1.0

1.5

2.0

2.5

3.0

3.5

G v

alu

e x

liq

uid

de

nsi

ty

Temperature (C)

OH

eaq

HH

2

H2O

2G-v

alu

e (T

) x

wat

er(T

)

• (G-value x water density) does

not vary significantly with T

• Solvation is important− Water vapour (dry steam) has

different G-values



Aqueous Reaction Kinetics Database

Rate constants

• T dependence well established

• For most reactions, it follows

Arrhenius T dependence

• At high T, all reaction rates

approach diffusion limits

• Diffusion rate T/•OH + H2


Documents

Radiolysis in CANDU Coolant and its Effect on Chemistry and Materials Jungsook Clara Wren Department of Chemistry University of Western Ontario 1 International