1. Radiolysis in CANDU Coolant and its Effect on Chemistry and Materials
International Association
for the Properties of Water and Steam Workshop
May 11 & 12, 2009
Jungsook Clara Wren
Department of Chemistry
University of Western Ontario

2. Presentation Outline
Overview of NSERC/AECL Industrial Research Chair Program
Preliminary Results from -Radiolysis Induced Carbon Steel Corrosion at 150oC
Importance of Steady-State Radiolysis on Steel Corrosion 2

3. NSERC/AECL IRC Program
Water Radiolysis
H2O •OH, eaq–, H•, HO2•, H2, H2O2, O2, H+
Corrosion
Metal Oxidation/Dissolution
Catalytic Reactions
Corrosion products + Radiolysis products
Steady-State Water Radiolysis - Effects of Dissolved Impurities
H2/O2/H2O2, Transition Metals, Nitrate/Nitrite, Organic Compounds
Corrosion Kinetics
In non-irradiated but chemically-simulated radiation environments
Corrosion Kinetics under -Irradiation
Temperature Ranges: < 90oC  150oC  320oC (2nd Term ?) 3

4. 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)

5. -Radiolysis on Carbon Steel Corrosion
Coupon Studies at T  150oC
Dose Rate 6.4 kGy/ h
These studies are performed as a function of pH, T,
irradiation time, dissolved H2 and O2 (cover gas), buffer

6. Chemical Production in the Irradiated System
Aqueous and Gas Phases
Steam Radiolysis
H2, H2O2, O2, •OH, •H, •eaq, •O2
H2, O2
H2, O2
Corrosion Products
H2, Fe2+, Fe3+
Liquid Water Radiolysis
H2, H2O2, O2, •OH, •H, •eaq, •O2 6

7. Effect of pH & -Irradiation at 150oC
1 m 5x
No Rad 21 Ar
3 m
pH25=10.6
pH25= ~7 5x 5x
Rad
3 m
1 m 7

8. Effect of pH & -Irradiation at 150oC
1 m 5x
No Rad
H2 (0.6%)
H2 (0.8%) 21 Ar
3 m
pH25=10.6
pH25= ~7
H2 (2.3%)
H2 (2.2%) 5x 5x
Rad
3 m
1 m 8

9. 66 h Irradiation at 150oC, Ar pH25 = 10.6 pH25 = 7 Cross Section
Aq. Phase
Outer oxide layer
2.2 m 5x
Inner layer
3 m 9
Base metal
1 m
pH25 = 7
Cross Section
3 m
Aq. Phase
Outer oxide layer
760 nm 5x
Inner layer
3 m 9
Base metal
200 nm

10. Fe3O4 / -Fe2O3 / FeII/FeIII(OH)x
Raman Spectroscopy
Cross Section
66 h Irradiation, pH 10.6, Ar
-Fe2O3
-FeOOH
-Fe2O3
Fe3O4
Raman Intensity
Raman Shift
Irradiated Sample
A Mixed Phase ??
Fe3O4 / -Fe2O3 / FeII/FeIII(OH)x
No significant -Fe2O3
Confocal Raman Microscopy, small angle XRD for depth profile are underway

11. Steam vs Liquid 1 m 1 m 150oC pH25=7 Ar, 21 h 1 m 3 m No Rad5x 5x
1 m
1 m
No Rad
No Rad
Liquid Phase
Steam Phase
Rad
Rad
150oC
pH25=7
Ar, 21 h 5x 5x
1 m
3 m 11

12. Preliminary Conclusions
Coupon Studies at 150oC
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 pH , -irradiation appears to promote more compact oxide
Corrosion in the steam phase is more inhomogeneous
Steady-State Radiolysis affects carbon steel corrosion behaviour

13. Water Radiolysis Solvent Oriented Process Physical (chemical) Stage
Primary Radiolysis Yields (G-values)
Bulk Phase Chemistry Stage 13

14. Importance of Steady-State Radiolysis
Continuous production
Aqueous chemistry control by pH, chemical additives
Radical &
reactive species quickly decay away
Surface Oxidation
Metal Dissolution
Interfacial Transfer
Steady-State Concentrations
Steady-state concentrations determine corrosion behaviour
Different steady states in different aqueous environments 14

15. Steady-State Radiolysis Model
Aqueous Reaction Kinetics Database
~ 40 reactions
Pulse Radiolysis has been a very useful tool for obtaining G-values and rate constants of fast reactions of radicals and ions
•OH + H2
325oC
150oC
25oC
80oC
G-value (T) x water(T)

16. Steady-State Radiolysis Model
Steady-State Model Validation
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 16

17. Effect of pH on Radiolysis
Steady-State Concentrations
G-values
25oC
25oC
Without steady-state analysis
such pH dependence was not envisioned
Model sensitivity analyses to understand why such behaviour is observed 17

18. Effect of Temperature on Radiolysis
Steady-State Concentrations
G-values
pH25 = 10.6
G-value (T) x water(T)
Without steady-state analysis
such T dependence was not envisioned 18

19. 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

20. Acknowledgement Dr. Jamie Noel Dr. X John Zhang Dr. Peter Keech
Dr. Jiju Joseph
Dr. Sriya Peiris
Dr. Sergey Mitlin
Dong Fu
Sarah Pretty
Kevin Daub
Katy Yazdanfar
Pam Yakabuskie
Susan Howett

21. Thermodynamics predicts -Fe2O3 to be the most stable oxide at 150oC
Pourbaix Diagram
OLI
150oC
pH25 = 10.6
pH25 = 6
Ref: B. Beverskog, I. Puigdomenech, Corrosion 38, , 1996
Magnetite stable in a small part of water stability region
For aqueous phase, Fe(OH)4+ stable over a significant area
Copy
Thermodynamics predicts -Fe2O3 to be the most stable oxide at 150oC 21

22. Catalytic Interaction
NSERC/AECL IRC Program
Synergistic Interaction of Radiolysis & Corrosion
Water Radiolysis
Corrosion
Metal oxidation-reduction
Dissolution of metal oxides
•OH, eaq–, H•, HO2•,
H2, H2O2, H+, O2, O2•– 
H2O
Creates unusual solution conditions
A wide range in chemical reactivity, redox and transport property
Metal Oxides, MOx
Bulk Metal, M
Mn+(aq)
Catalytic Interaction
•OH, H2O2, O2
Fe2+(aq) Fe3+(aq)
Depends on surface and solution-redox conditions
•H, eaq–, •O2–
Catalytic interaction of dissolved metal and radiolysis redox species

23. Effect of Radiation 150oC 3 m pH25=10.6 Ar 3 m 3 m No Rad 21 h 66 h5*
3 m
3 m 23

24. Effect of Radiation 150oC 3 m pH25=6 1 m Ar 1 m 3 m 3 m 3 m5*
150oC
pH25=6 Ar
3 m
1 m
No Rad
21 h
66 h
Rad 5* 5* 5*
1 m
3 m
3 m
3 m 24

25. Mostly Fe3O4 + -FeOOH + possibly FeII/FeIII(OH)x
66 h Irradiation, pH 7, Ar
3 m
SEM of Cross Section
Outer oxide layer
760 nm 5x
Inner layer
3 m 25
Base metal
-Fe2O3
-FeOOH
-Fe2O3
Fe3O4
Raman Intensity
Raman Shift
Irradiated Sample
Need to compare pH 10.6 vs pH 6 cases
Mostly Fe3O4 + -FeOOH + possibly FeII/FeIII(OH)x

26. Water Radiolysis Kinetic Model
(constant radiation field)
•OH + H2
~ 40 Elementary Reactions
& Rate constants (T)
Continuous production
G-values (T)
Steady State Concentrations
water(T), Kwater(T), etc
Coupled reaction rate equations are solved using numerical integration software FACSIMILE
Input
Dose Rate
T, pH
Output
Concentrations as a function of time 26

27. Steady-State Radiolysis Database
Rate constants
Equilibrium constants
•OH + H2
325oC
150oC
25oC
80oC
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?
T dependence well established
For most reactions, it follows Arrhenius T dependence
At high T, all reaction rates approach diffusion limited
Diffusion rate  T/ 27

28. pH on Steady-State Radiolysis Behaviour
Model not validated at > 80oC
25oC
300oC
~ 3 orders of magnitude changes
at pHs around pKa of eaq + H+ = •H
pH dependence diminished due to
increase in the reaction of eaq with H+
Without steady-state analysis
such pH dependence not easily predicted 28

29. Chemical Additives/Dissolved Species
Effect of [Fe2+]o on [H2O2]SS
Ar, pH = 10.6
Effect of Radiolysis on Iron Solubility
[Fe2+]o = 0, 510-5, 110-4 M
•OH, H2O2, O2
Synergistic interaction between corrosion products and radiolysis products
Fe2+(aq) Fe3+(aq)
•H, eaq–, •O2– 29

31. Steady-State Radiolysis Model
Aqueous Reaction Kinetics Database
~ 40 reactions
Pulse Radiolysis has been a very useful tool for obtaining G-values and rate constants of fast reactions of radicals and ions
(G-value x water density) does not vary significantly with T
Solvation is important
Water vapour (dry steam) has different G-values
G-value (T) x water(T)

32. Aqueous Reaction Kinetics Database
Pulse Radiolysis has been a very useful tool for obtaining G-values and rate constants of fast reactions of radicals and ions
Rate constants
•OH + H2
325oC
150oC
25oC
80oC
T dependence well established
For most reactions, it follows Arrhenius T dependence
At high T, all reaction rates approach diffusion limits
Diffusion rate  T/