corrosion evaluation of metallic materials for long-lived hlw/spent fuel disposal containers –...

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


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


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)


Geochemical Composition of Potential Disposal Environments within various EU-Countries


Materials Selection of Candidate Container Materials within various EU-Countries


Parameters, techniques and modes of corrosion


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


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-


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


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


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)


18 mm in 106 yrs(conservative)

- - >106 yrs

Sweden/Finland1) 0.35 mm in 106 yrs


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


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.


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)



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

corrosion evaluation of metallic materials for long-lived hlw/spent fuel disposal containers –...

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