Corrosion Evaluation of Metallic Materials for Long-Lived HLW/Spent Fuel Disposal Containers – review of
15-20 years of research
B. KURSTEN, SCK•CEN (Mol, BELGIUM)
EURADWASTE ’04 (6th EC Conference on the Management and Disposal of Radioactive Waste)
29 March – 1 April 2004, Luxembourg
EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 2 / 15
Corrosion Evaluation of Metallic Materials for Long-Lived HLW/Spent Fuel Disposal Containers
Acknowledgements
Co-authors : E. Smailos (FZK.INE, Germany)
I. Azkarate (INASMET, Spain)
L. Werme (SKB, Sweden)
N.R. Smart (Serco Assurance, UK)
G. Marx (GNF.IUT, Germany)
M.A. Cuñado (ENRESA, Spain)
G. Santarini (CEA/SACLAY, France)
Funding : National authorities and institutions
European Commission
EURADWASTE ’04, Session VI – Waste Characterisation & Corrosion Studies, 30th March 2004 3 / 15
Corrosion Evaluation of Metallic Materials for Long-Lived HLW/Spent Fuel Disposal Containers
Background
Geochemical composition of potential disposal environments
Materials selection
Parameters, techniques, modes of corrosion
Main results Salt Clay Granite Cement
Conclusions
Future R&D
Modelling
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Background
Deep underground disposal in stable geological formations (e.g. salt, clay, granite)
favoured option that is being pursued worldwide to deal with long-lived radioactive waste in a feasible and safe manner
disposal concept varies from country to country according to type of waste
multibarrier concept : a series of natural (geosphere) and engineered (man-made) (waste matrix, metallic container, buffer) barriers that act in concert
to isolate radionuclidesto retard radionulide release from the waste to the biosphere
Metallic container is one of the principal engineered barriers
two different approaches :
corrosion-allowance concept (corrode uniformly, predictable corrosion rate, thick-walled)
corrosion-resistant concept (high corrosion resistance, low corrosion rate, thin-walled, risk for
localised attack)
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Geochemical Composition of Potential Disposal Environments within various EU-Countries
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Materials Selection of Candidate Container Materials within various EU-Countries
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Parameters, techniques and modes of corrosion
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Scientific Approach
Screening Studies
Detailed Studies
Laboratory Experiments immersion electrochemical radiochemical
In Situ Experiments
Parametric Studies T pH Conc. aggressive ions
Demonstration Tests1-1 scalewelding procedure
Modelling Natural analogues
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Main Results (1/5)Salt Environment
Carbon steel (TStE 355)
corrodes actively in MgCl2- and NaCl-brines
vCORR (µm/y)
influence of pH no significant effect on vCORR in MgCl2 (pH=3-7) and in NaCl (pH=1-5) vCORR decreased in NaCl from 50 µm/y (pH=1) to 26 µm/y (pH=10)
influence B(OH)4-, H2O2, ClO-, Fe3+ (salt impurity, radiolytic prods., corr. prod.)
90°C : 5 µm/y 236 µm/y (NaCl) 170°C : 70 µm/y 120 µm/y (MgCl2)
effect of welding (in MgCl2) reduction of corrosion resistance severe localised attack in weld region and HAZ stress relief treatment improves the corrosion resistance
slight sensitivity to SCC and loss of ductility in NaCl very low strain rates : not expected in a real repository
influence of NaCl (150°C) : no effect MgCl2 (150°C) : 47 µm/y (no ) 72 µm/y (10 Gy/h)
Ti-alloy (Ti99.8-Pd)
vCORR < 1 µm/y
not susceptible to pitting or SCC
no influence of , H2O2 and ClO-
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Main Results (2/5)Clay Environment
Two different approaches low-alloy or unalloyed steels (e.g. France) passive Fe-Ni-Cr-Mo alloys (e.g. Belgium)
Parameters risk of localised corr.: [Cl-] = 100 mg/L (Belgium) 2,700 - 7,200 mg/L (France) production of H2: enhanced transport pathways for radionuclides
Ni- and Ti-alloys vCORR < 0.1 µm/y resistant to pitting corr.: T = 140°C; [Cl-] = 50,000 mg/L; [S2O3
2-] = 200 mg/L susceptible to crevice corr.: oxic cond.; T = 140°C; [Cl-] > 20,000 mg/L
Carbon steel vCORR
Stainless steels vCORR < 0.1 µm/y resistant to pitting under ‘normal’ repository cond. ([Cl-] < 100 mg/L;
[S2O32-] = 17 mg/L)
T=140°C, oxic cond., [Cl-]>10,000 mg/L : pitting (ECORR>ENP) T=140°C, anoxic cond., [Cl-]=50,000 mg/L: no pitting (ECORR<<ENP) Effect of T:
drastic shift of ENP in the active direction (ENP << ECORR)pit depth and pit density increases with increasing T
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Main Results (3/5)Granitic Environment (Spain)
Carbon steel (TStE 355) vCORR = 6 µm/y (90°C); 14 µm/y (120°C) susceptible to pitting at 120°C (dmax = 280µm) parent and weld material are resistant to SCC at 90°C
Stainless steel (AISI 316L) resistant to SCC no loss of ductility, but isolated pits could be observed near the fracture zone
Granite
Argon
Pit
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Main Results (4/5)Granitic Environment (Sweden/Finland)
Lifetime predictions for copper canisters
Country GeneralCorrosion
LocalisedCorrosion
MicrobiallyInfluencedCorrosion
StressCorrosionCracking
PredictedLifetime
Sweden/Finland1)
0.05 mm in 106 yrs(realistic)
4 mm in 106 yrs(conservative)
0.05 mm in 106 yrs(realistic)
18 mm in 106 yrs(conservative)
- - >106 yrs
Sweden/Finland1) 0.35 mm in 106 yrs
0.35 mm in 106 yrs(realistic)
1.4 mm in 106 yrs(conservative)
SRB assumed to
reduce SO42- to HS-
Maximum possiblenitrite concentrationbelow threshlod for
SCC
>106 yrs
Sweden/Finland1) 0.33 mm in 106 yrs
0.33 mm in 106 yrs(realistic)
1.3 mm in 106 yrs(conservative)
SRB assumed to
reduce SO42- to
HS- in tunnel andgroundwater only
SCC does not occurbased on threshold
potential andconcentrations of SCC
agent, becausecreep is faster than SCC
>106 yrs
Canada2) 0.011 mm in 106 yrs 6 mm in 106 yrs
Limited impact;Maximum additional
wall loss of 1 mm
in 106 yrs
SCC not includedbecause of limited
period of stress, absenceof SCC agents, general
lack of oxidant and
inhibitive effects of Cl-
>106 yrs
1) Reference canister wall thickness of 50 mm.2) Reference canister wall thickness of 25 mm.
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Main Results (5/5)Cementitious Environment
Large amounts of concrete present in repositories (structural materials)
Carbon steel (BS4360) vCORR (µm/y)
pitting is expected to be limited (propagation only a few mm deep)
availability of water prior to re-saturationsupply of oxygen after re-saturation
Stainless steels (AISI 304L, 316L) vCORR (µm/y)
resistant to pitting corrosion
room T: [Cl-] = 100,000 mg/L45°C, 70°C: [Cl-] = 50,000 mg/L
SCC
strong synergistic effect of Cl- and S2O32-
adding 3,360 mg/L S2O32- to 17,750 mg/L Cl- led to SCC (80°C)
Conclusions
Salt environment
CARBON STEEL: corrosion-allowance concept Ti99.8-Pd: corrosion-resistant concept (negligible general corr.; high resistance to loc. corr. and SCC)
Clay environment
STAINLESS STEELS, Ni- and Ti-ALLOYS: corrosion-resistant concept CARBON STEEL: corrosion-allowance concept
Granitic environment
COPPER, CARBON STEEL: corrosion-allowance concept
Cementitious environment
CARBON STEEL: low general corrosion rates STAINLESS STEELS: very low general corrosion rates; resistant to pitting corr. (up to 50,000 mg/L Cl - at 70°C)
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Future R&D
Microbially influenced corrosion (MIC)
Atmospheric corrosion (interim storage)
Effect of fabrication aspects and container design on corrosion
Long-term metallurgical modifications
Influence of radiation effects
Influence of nitric acid on the integrity of the container
Archeological analogues
Modelling