Corrosion of Structural Materials and Electrochemistry in High Temperature Water of Nuclear Power Systems Shunsuke Uchida Institute of Applied Energy 17th International Workshop on Nuclear Safety & Simulation Technology (IWNSST17) Kyoto, Japan, January 21-22, 2014
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IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.0
Corrosion of Structural Materials and Electrochemistry in High Temperature Water
of Nuclear Power Systems
Shunsuke Uchida Institute of Applied Energy
17th International Workshop on Nuclear Safety & Simulation Technology (IWNSST17)
Kyoto, Japan, January 21-22, 2014
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.1
1. Background 2. Objectives 3. Optimal water chemistry 4. Theoretical approaches towards quantifying interaction of materials and water 4.1 Electrochemistry 4.2 Electrochemical corrosion potential 5. Flow-accelerated Corrosion 6. Water radiolysis 7. Future subjects 8. Conclusions 9. Acknowledgements 10. References
Table of Contents
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.2
1. Background
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No.3 World list of nuclear power plants Countries*1 total PWR, VVER PHWR BWR GCR, AGR LWGR LMFBR USA 104 69 35 France 59 58 1 Japan 55 (49*3) 24 31 (25*3) Russia 31 13 17 1 South Korea 20 16 4 UK 19 1 18 Canada 18 18 Germany 17 11 6 India 17 15 2 Ukraine 15 15 China 11 9 2 Sweden 10 3 7 Spain 8 6 2 Belgium 7 7 Taiwan 6 2 4 Czech 6 6 Slovakia 5 5 Switzerland 5 3 2 Total*2 439 260 43 93 18 23 2 Share (%) (59) (10) (21) (4) (5) (0.5) *1: more than 5 plants Others: Finland, Hungary: 4 plants, Bulgaria, Argentina, Brazil, Mexico, Pakistan, South Africa: 2 plants, Romania, Armenia, Lithuania, Netherlands, Slovenia: 1 plant *2: 380GWe *3: after March 11 accident Version 2008 Ref.1
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.4 Major accidents and incidents at nuclear facilities Plant (reactor type) Date Causes Environmental effects Three Mile Island-2 (PWR) Mar. 1979 LOCA <1mSv Chernobyl (LGR) Apr. 1986 RIA 31 people died 16 k person Sv Surry-2 (PWR) Dec. 1986 FAC* 4 people died Fukushima Daini-3 (BWR) Jan. 1989 vibration none Mihama-2 (PWR) Feb. 1991 CF none Monju (LMFBR) Dec. 1995 parts defect none (Na leakage ) JCO (conversion Sep. 1999 critical 2 people died facility) accident 130 residents received radiation dose Hamaoka-1 (BWR) Nov. 2001 H2 explosion none Mihama-3 (PWR) Aug. 2004 FAC* 5 people died Fukushima (BWR) Mar. 2011 earthquake radioactivity release: Daiichi 1-4 + tsunami 600 PBq evacuee: 160,000 *: related to material LOCA: loss of coolant accident RIA: reactivity initiated accident FAC: flow assisted corrosion CF: corrosion fatigue Ref.2
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.5 Major problems related to structural materials in NPPs
problem reactor troubled location countermeasures type FAC PWR feed water piping material exchange water chemistry improvement BWR feed water piping water chemistry improvement heater drain piping material exchange SCC BWR primary piping material exchange, stress improvement water chemistry improvement PWSCC PWR core internals material exchange, water chemistry improvement Fuel cladding PWR fuel material improvement corrosion BWR material improvement SG tubing defects PWR SG water chemistry improvement material exchange
Ref.2
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No.6
2. Objectives
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No.7
1. Roles of materials, water and their interaction on plant safety and reliability are confirmed.
2. Optimal water chemistry control required for satisfying multi-problems related to interaction of materials and water is introduced. 3. Theoretical approaches as well as empirical ones required for quantifying the interaction of materials and water and for establishing suitable countermeasures for those problems are introduced. Electrochemistry is one of key issues to determine corrosion related problems. 4. As examples of application of theoretical electrochemistry procedures, a prediction
model for flow-accelerated corrosion (FAC) and prediction models for water radiolysis are introduced.
5. As future subjects of the theoretical models related to electrochemistry and water
radiolysis, verification and validation evaluation procedures are introduced and standardization of the procedures are introduced.
Objectives
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No.8
3. Optimal water chemistry
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No.9
BWR primary cooling water
radwaste system recirculation system main steam/ feed water systems
Major materials in primary system Their wetted surface
Ref.2
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No.11 Interaction between structural materials and cooling water
composition (impurities crystal structure local stress
temperature pH conductivity oxidant
materials water
release of metallic ions
growth of oxide film
oxide film
barrier for diffusion of oxidant and metallic ion
Ref.4
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No.12
4. Theoretical approaches towards quantifying interactions of materials and water
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No.13 Comparison of corrosion behaviors and features of major materials
Materials Carbon steel Stainless steel Zirconium alloy (nickel alloy) Corrosion rate high medium low (relatively) Oxide film magnetite/hematite Cr rich nickel ferrite zirconium oxide Application piping of secondary piping and component fuel cladding system of primary system Problems FAC IGSCC, PWSCC clad thinning radioactivity accumulation Effects of strong medium weak electrochemistry
Corrosion rates / corrosion effects should be predicted based on theoretical tools for preparing for suitable countermeasures
Ref.4
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.14 Major parameters of major corrosion induced phenomena
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No.15
4.1 Electrochemistry
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No.16 Electrochemistry Basic reaction between metal and aqueous solution
Corrosion mechanism depends on electrochemistry. Mass and charge balances between metal surface and aqueous solution. Electrode reactions => Corrosion rate Electrode potential => Electrochemical corrosion potential (ECP) Electrolysis Radiolysis Hydrogen generation reaction
2H+ + 2e- → H2
H+ e-
H2
Oxygen generation reaction 2H2O → O2 + 4H+
+ 4e- O2,H+
e- H2O
H2O
O2,H+ e-
Oxygen reduction reaction O2 + 4H+ + 4e- → 2H2O
Metal dissolution reaction Fe → Fe2+ + 2e-
Fe Fe2+ e-
Oxide film formation reaction 2Fe+3H2O → Fe2O3+6H++6e-
H+
H2O
e-
Fe Fe2O3
Ref.5
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No.17 Schematic diagram of charge balance at surface
pote
ntia
l (ar
bitr
arily
scal
e)
-1.0
-0.5
0
0.5
current density (arbitrarily scale)
10-4 100 10-1 10-3 10-2
Fe Fe2+ + e- total anodic current
with oxide film
without oxide film
total cathdic current O2 + e- O2
-
high [O2]
low [O2]
hydrogen generation
potential
H
L
b) Static charge balance
boundary layer
metal bulk
O2
H+ H2O e-
N2H4
H+
M+ e-
e-
diffusion
anodic current
cathodic current
oxide film
a) Cathodic and anodic reactions
H2
anodic reaction
cathodic reaction
Ref.6
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No.18
4.2 Electrochemical corrosion potential
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No.19 Coupled electrochemistry/oxide layer growth model for ECP evaluation
Sub-model electrochemistry model oxide layer growth model (static model) (dynamic model) Input temperature, [O2] , pH, km, temperature mass transfer coefficient (hm) anodic/cathodic current densities oxide film thickness, ECP oxide properties Output anodic/cathodic current densities oxide film thickness ECP properties (Fe2O3/Fe3O4 ratio)
coupling calculation
Ref.7
release
mass transfer
hematite particles
magnetite particles
dissolution adsorption
oxidation
flow
δ outer layer (hematite particles)
inner layer (magnetite particles)
base metal
boundary layer
bulk water
pote
ntia
l (a.
u.)
current density (a..u)
cathodic current
anodic current
oxide filn effects
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
- + 2H2 2H+ + 2e- = H2 (hydrogen generation at low potential) Current density due to the cathodic reaction is expressed by Eq. (1) Ic = fc (φ) Xs (1) fc (φ) = zc F kc
e exp(-αczcF(φ-φc0)/RT) (2)
[O2] at the metal surface is determined by its diffusion from the bulk to the surface. Da
B(Xb-XB)/δΒ = Ic/zc/F (3) Da
o(XB-Xs)/δο = Ic/zc/F (4) The current density due to the cathodic reaction is expressed by Eq. (5). Ic= fc (φ)Xb/{1+ fc (φ)/zc/F (δo/Da
o+δB/DaB}} (5)
Anodic reactions M = Mz+ + ze- Current density due to the metal release is expressed by Eq. (6). Ia = fa (φ) (Csol-Cs) (6) fa (φ) = za F ke
a exp(+αazaF(φ-φa0)/RT) (7)
The cation concentration at the metal surface is determined by its diffusion. Dc
o(Cs –CB)/δο = Ia/za/F-β(Csol-Cs) -βXs = fa (φ) (Csol-Cs)/za/F-βXs (8) Dc
B(CB -Cb)/δΒ = Ia/za/F= fa (φ) (Csol-Cs)/za/F-βXs (9) The current density due to the anodic reaction is expressed by Eq. (10). Ia = fa (φ) [Csol -{Cb+fa (φ)Csol /za/F(δο/Dc
o+δΒ/DcB)}/{1+(fa (φ)/za/F+β)(δο/Da
o+δΒ/DaB)}] (10)
Numerical expression for cathodic and anodic reactions
Ref.14
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.21 Ferrous ion release rate from base metal dM/dt= -Ia/za/F (12) dCB/dtδB=Ia/za/F -δmCBSmCmδB
water temperature: 288 C constant load: Kin/(in)1/2
Conductivity (mS/cm) :
0.3 0.2 0.1
HWC NWC
Decreasing ECP mitigates IGSCC occurrence and propagation with decreasing [O2]
Ref.16
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.37 Effects of hydrogen on PWSCC crack initiation and crack growth rate
Ni/N
iO li
ne 25
20
15
10
5
0
tube diameter 3/4 inches 7/8 inches
Nml-H2/kg-H2O (at 330 C) cr
ack
initi
atio
n tim
e (k
h)
0 5 10 15 20 25 30 35
b) Crack initiation time
0 50 100 150 [H2] (Ncm3/kg)
crac
k gr
owth
rat
e(m
ills/
day)
NiO Ni metal
2.0
1.0
0
X-750, 360C, 49 MPam1/2
a) Crack growth rate
Refs.2, 17 and 18
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.38 High Temperature G-values
molecules, atoms /100ev absorption
e-
H H+
H2
H2O2
HO2
OH OH-
species
3.50 0.90 3.50 0.60 0.55 0.00 4.50 0.00
γ rays
0.60 0.50 0.60 1.50 1.14 0.04 1.70 0.00
neutrons PWR(305ºC)
0.152 0.199 1.974 0.152 1.104 0.300 1.191 0.000
α rays
3.565 0.927 0.612 3.565 0.542 0.000 4.632 0.000
γ rays
0.662 0.453 1.278 0.662 0.836 0.050 1.849 0.000
neutrons BWR(285ºC)
Water radiolysis codes for BWR have been well developed and applied, while those for PWR have just developed with different G value sets
Ref.19
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No.39
7. Future subjects
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No.40 Calculated results of PWR radiolysis model Comparison with INCA loop experiments
Standard procedures to authorize the computer simulation codes have been based on the verification and validation (V&V) method.
The verification and validation (V&V) processes for the FAC simulation code and the corrosive condition calculation code were done in conformity with the ASME “Guide for Verification and Validation in Computational Solid Mechanics.” The definitions of V&V are as follows: 1. code verification: addressing errors in the software 2. calculation verification: estimating numerical errors due to under resolved discrete representations of the mathematical model 3. validation: assessing the degree to which the computational model is an accurate representation of the physics being modeled, based on comparison between numerical simulations and relevant experimental data (predictive capability of the model).
Ref.20
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No.41 Comparison of the calculated results with the measured Validation of FAC code based on Residual thickness
0
10
20
30
40
50
0 10 20 30 40 50 calculated (mm)
mea
sure
d (m
m) -20%
+20%
Bend (condensate water line: 146ºC)
Bend (feed water line: 222ºC)
T-junctions (drum: 190ºC)
T-junctions (pipe : 190ºC)
Ref.6
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No.42
0.2
0
-0.2
-0.4
-0.6
-0.6 -0.4 -0.2 0 0.2 measured ECP (V- SHE)
calc
ulat
ed E
CP
(V- S
HE
)
+0.05V
-0.05V
: BWR4 : BWR5
Comparison of the calculated results with the measured Validation of corrosive condition calculation code based on Residual thickness
Ref.13
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No.43
8. Conclusion
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No.44
8. Conclusions 1. Optimal water chemistry control has been established to satisfy multi-problems related to interaction of materials and water is introduced. 2. Theoretical approaches as well as empirical ones have been established to quantify the interaction of materials and water and to establish suitable countermeasures for those problems. 3. Electrochemistry procedures have been successfully applied to determine corrosion related problems. 4. As examples of application of theoretical electrochemistry procedures, a prediction model for FAC and prediction models for water radiolysis are introduced. 5. As future subjects of the theoretical models related to corrosion problems, standardization of the codes should be established based on V&V evaluation procedures
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida
No.45
9. ACKNOWLEDGEMENT
The author expresses his thanks to the members of the Institute of Applied Energy for their enthusiastic discussion and contribution to develop the FAC code.
He also expresses his thanks to the members of the HWC Standard Working Group of
the Standard Committee of the AESJ for enthusiastically discussing on the standard draft and Prof. Seiichi Koshizuka for his helpful guidance on V&V evaluation..
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No.46
[1] Nuclear Energy Institute, “World Nuclear Generation and Capacity (2007)”, web site: http://www.nei.org/resourcesandstats/documentlibrary/reliableandaffordableenergy/graphicsandcharts/worldnuclearpowerplantsinoperation/ [2] S. Uchida, “Latest Experience with Water Chemistry in Nuclear Power Plants in Japan”, Power Plant Chemistry, 8, 282 (2006) [3] S. Uchida and Y. Katsumura, “Water Chemistry Technology – one of the key technologies for safe and reliable nuclear power plant operation”, J. Nucl. Sci. Technol., 50 (4), 346 (2013). [4] S. Uchida, “Corrosion of Structural Materials and Electrochemistry in High Temperature Water of Nuclear Power Systems”, Power Plant Chemistry, 10 [11], 630, (2008) [5] H. H. Uhlig and R. W. Revie, “Corrosion and corrosion control”, Wiley-Interscience, New York, 1985. [6] S. Uchida, M. Naitoh, H. Okada, T. Ohira, S. Koshizuka and D. H. Lister, “Verification and Validation of Evaluation Procedures for Local Thinning due to Flow- accelerated Corrosion and Liquid Droplet Impingement”, Nucl. Technol., 178 280 (2012) [7] S. Uchida, M. Naitoh, Y. Uehara, H. Okada, N. Hiranuma, W. Sugino, S. Koshizuka and D. H. Lister, “Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (III), Evaluation of Pipe Wall Thinning Rate with the Coupled Model of Static Electrochemical Analysis and Dynamic Double Oxide Layer Analysis”, J. Nucl. Sci. Technol., 46 [1] , 31 (2009). [8] M. Kitamura, E. Ibe, S. Uchida, T. Honda, G. Romeo and R. L. Cowan, “Application of Pre-Oxidation Treatment to Suppress Cobalt-60 Deposition on Stainless Steel Surfaces of BWR Primary Cooling System”, Nucl. Technol., 89, 61 (1985). [9] M. Naitoh, S. Uchida, S. Koshizuka, H. Ninokata, N. Hiranuma, K. Dozaki, K. Nishida, M. Akiyama and H. Saitoh, “Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (I), Major targets and development strategies of the evaluation methods”, J. Nucl. Sci. Technol., 45 [11] , 1116 (2008). [10] H. Suzuki, S. Uchida, M. Naitoh, H. Okada, S. Koikari, K. Hasegawa, F. Kojima, S. Koshizuka, and D. H. Lister, “Risk Evaluation of Flow-Accelerated Corrosion Based on One-Dimensional FAC Code”, Nucl. Technol., 183 [2], 193 (2013). [11] S. Uchida, M. Naitoh, Y. Uehara, H. Okada, N. Hiranuma, W. Sugino and S. Koshizuka, “Evaluation Methods fo Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow (II), Evaluation of corrosive conditions in PWR secondary cooling system”, J. Nucl. Sci. Technol., 45 [12], 1275 (2008). [12] Y. Wada, S. Uchida, M. Nakamura and K. Akamine, ”Empirical Understanding of the Dependency on BWR Designs for HWC Effectiveness”, J. Nucl. Sci. Technol. 36, 169 (1999). [13] S. Uchida, Y. Wada, S. Yamamoto, J. Takagi and K. Hisamune, “Verification and validation procedures of calculation codes for determining corrosive conditions in the BWR primary cooling system based on water radiolysis and mixed potential models”, J. Nucl. Sci. Technol., 51 [1], 24 (2014). [14] S. Uchida, S. Hanawa, Y. Nishiyama, T. Nakamura, T. Satoh, T. Tsukada and J. Kysela, “Determination of Electrochemical Corrosion Potential along the JMTR In-pile Loop (I) Evaluation of ECP of Stainless Steel in High Temperature Water as a Function of Oxidant Concentrations and Exposure Time”, Nucl. Technol. 183, 119 (2013). [15] S. Uchida, T. Satoh, T. Tsukada, T. Miyazawa, Y. Satoh and K. Ishii, “Evaluation of the Effects of Oxide Film on Electrochemical Corrosion Potential of Stainless Steel in High Temperature Water”, Proc. 14th Int Conf. Environmental Degradation of Materials in Nuclear Power Systems – Water Reactors, Virginia Beach, VA, Aug. 22-27, 2009, ANS, 2009 (in CD). [16] F. P. Ford, D. F. Taylor, P. L. Andresen and R. G. Ballinger., “Corrosion-Assisted Cracking of Stainless and Low- Alloy Steels in LWR Environments”, EPRI NP-5064M Project 2006-6 Final Report, February (1987). [17] L. Wilson, J. Hickling, “Use of Primary Water chemistry in Pressurized Water Reactors to Mitigate PWSCC in Nickel Base Alloys. Proc. International Conference on Water Chemistry of Nuclear Reactor Systems”, Proc. Int. Conf. Water Chemistry of Nuclear power Systems, 2006 Oct 23-26; Jeju Island (Korea) [CD-ROM]. [18] A. Molander, A. Jenssen, M. Konig and K. Norring, “PWSCC Initiation and Crack Growth Data for Alloy 600 with Focus on Hydrogen Effects”, Proc. Int. Workshop on Optimization of Dissolved Hydrogen Content in PWR Primary Coolant; 2008 July 18-19; Sendai (Japan) [CD-ROM]. [19] H. Takiguchi, M. Ullberg, S. Uchida, “Optimization of Dissolved Hydrogen Concentration for Control of Primary Coolant Radiolysis in Pressurized Water Reactors”, J. Nucl. Sci. Technol. 41 601 (2004). [20] Performance Test Codes Standards Committee. Guide for Verification and Validation in Computational Solid Mechanics. USA: American Society of Mechanical Engineers, ASME V&V 10-2006 (2006).
10. References (1)
IWNSST17, Kyoto, Japan, Jan. 21-22, 2014 S. Uchida