富山大学水素同位体科学研究センター研究報告29 ･ 30 : 45‑49, 2010.

Preliminary Study on Electrochemical Corrosion Behavior of F82H SteelM. Oyaidzu and T. Yamanishi
Tritium Process Laboratoyy, Japan Atomic Energy Agency, Ibaraki 319‑2295, JapanA study on the corrosion behavior of F82H steel and the effects oftritium on ituslng
the electrochemical techniques of Tafel extrapolation and anodic polarization has just been
started and the preliminary results without the use of tritiated water were introduced in thepresent report･ Using Tafel extrapolation, the corrosion rate of F82H steel in 5W%
H2SO4/H20 Could be estimated as approximately 2 cm year‑1, which was approximately 2Orders or magnitude larger than that or SUS 304. 1n anodic polarization cuⅣe, the reglOnSof passivation, passive layer sustention and transpassivation could be obseⅣed under thesame circumstance as Tafel extrapolation experiment and the quantum of electricity for
F82日steel to passivate was approximately 100 C cm‑2, which was approximately 3 Ordersof magnitude larger than that of SUS304･ Therefわre it was expected that the co汀OSion rateof F82H steel could far higher than that of SUS304, even though only a preliminary

experiments under the highly corrosive circumstance has been perfbmed･Keywords : tritium, radiochemistry, electrochemistry, corrosion

Could be induced by tritiated water. Indeed, itⅠ. Introductiom

has been reported that pH changes in highly
ln且ISion reactors, much more tritium thanconcentrated tritiated water ll]. Therefore in
ever

befわrewillbeused,generated

andtritiated water, such exotic co汀OSion behavior

processed. Therefわre, the establishment of thedue to tritium and/or radiolysIS products are

tritium confinement technique is one of the mostexpectedasenhancement

orco汀OSion,

important issues to realize RlSion reactors, anddistraction of passive layer, local co汀OSionwideィanglng Studies have been perfb‑ed toincluding plttlng CO汀OSion, and so on･understand the behavior of tritium, especially inOn the other hand, F82H steel, one of thefunctional materials for fusion reactors. In

reduced activation fTemitic/martensitic steels wasalmost all of these studies, however, tritium wasdeveloped as one of the most promlSlng
treated only as one or hydrogen isotopes,

although some radiochemical effects on thecandidate structural materials for fusion reactor,
and therefわre, Will be used f♭r the stmctural

materials should be also taken into consideration,
especially on the boundary between a material

and tritiated water l1]. The effects of tritiatedmaterial of water cooled solid breeder (WCSB)
test blanket module (TBM) for ITER l216]. It isimperative to clarify the effects of tritiated water

water on the materials have not beenon co汀OSion of F82H steel, since the data on

well‑understood, while in some facilities, theinner surface of piplng Or Vessel which had
contact with tritiated water co汀Oded more than

F82H steel is limited and rupture of WCSB
TBM will bring not only destmction or tritium
confinement but also serious accidents such as

expected, indicatlng that change in water
explosion due to hydrogen generated by thecondition and/or local equilibrium collapse
reaction between neutron multiplier of beryllium

45

M̲

Oyaidzu and T. Yamanishiand cooling water.

Therefore, the study on the effects of

1‑Ieo+誓‑e 雪(3,tritium on the corrosion behavior or F82H steel
has Just been started uslng electrochemical
technique･ In this report, preliminary study about

where I, a; F, R and T mean the current, thethe electrochemical co汀OSion behavior of F82H

transfer coefficient (usually 0.5), Faraday

steel

constant, gas constant and absolute temperature,inco汀OSivewater

circumstanceisintroduced.

respectively. q lS Called overpotential that canexpressed as fbllowlng;

ⅠⅠ･ Theory

ln the present study, two electrochemical

71‑ E‑ Ec.,r(4)experiments of Tafel extrapolation and anode

where E means applied potential. When the rate
polarization were employed to obtain theof either reaction is negligible, Eq. (4) gives:co汀OSion current which derives the corrosion
rate, and to obseⅣe the passivation behavior,

E‑a+blogI

re spe c tive ly.

II･ A･ Tafel extrapolation l7](5)where α and ∂ are constants･ This equation is

It is wellknOwn that the electrochemistry ofcalled Tafel's law, and the basis of the Tafel
extrapolation is to extrapolate Eq. (5) toward

co汀Oding metals involves two or more half cell

Econ. so as to obtain Ieo,,･ The intersection polnt Of

reactions as fbllowlngS;

Eq. (5) for both cathodic and anodic reactions
should be theoretically on the Eco,r. The
M‑Mn++ne(1)

corrosion rate could be estimated using Ieo,,I
2H++2e

‑

H2,

(2)

II･ B･ Anodic polarization
where n means the valence number or half celllt is well known that the anodic polarization
reaction, and M is metal or co汀Oding material.

These half cell reactions are expected as themost probable electrochemical reactions on thesample surface in the present experiment. Since
the main constituent elements of the samples or

the present study were Fe, Cr and Ni, M waseach of them and n could be assumed as 2. For

the dissolution or M of F82H steel in acidsolutions, the anodic rate (indicating thecorrosion of the sample) and the cathodic rateis one of the best methods to elucidate suchelectrochemical behavior as dissolution,passivation and transpassivation [8,9]. In an
anodic polarization experiment, the applied

potential was swept from equilibrium potential(usually Ec.,,) toward anodic side up totranspassivation reglOn With a certain sweep rate･
An anodic polarization spectmm fわr a stainlesssteel or the other passivatlng metal under 5wt.%
sulfuric acid solution usually consists of three(indicating the generation of H2) should be thesame at the equilibrium potential. Therefわre,corrosion current, leo,,, resulting ln corrosion rate,

Could be estimated at equilibrium potential (thesame as corrosion potential, Ec.r,) by applying

Butler‑Vblmer equation as fbllowlng;

parts; (i) passivating region, (ii) passive layer
sustention region and (iii) transpassivation

reglOn･ If the passivation is affected by tritium, it
will appear in the passivatlng reglOn, and ir thepassive layer is affected, it will be observed in
the passive layer sustention reglOn･46

Preliminary Study on Electrochemical Corrosion Behavior of F82H SteelⅠH. Experimental

W: Working electrode (sample)

III. A. Sample preparation

C: Counter electrode (Pt)

The materials used in the present s山dy

R: Reference electrodewere a disc ofF82H steel with 8 mm in diameter(Ag/AgCl(sat. KCl))and a sheet ofSUS304 with its size of 10 x 10G.: Purge gas lnlet

mm2 as a reference･ Both of samples wereG｡: Purge gas outlet

insulated

uslng

epOXy

resin

exceptfわrmeasurement surface, polished uslng lけm

Fig. 1 Conceptual diagram of electrochemical
experimental set‑up.

alumina polisher and ultrasonically cleaned inpure water f♭r 30 min sequentially.

polarization from corrosion potential up to 2.0 V
III. B. Experimental procedure

with the sweeplng rate Of O･33 mV s‑1 tounderstand the passivation behavior.

Thesample

wassetinthecellfわrelectrochemical measurement as working

IV. Results

electrode with the other accessories or counter

IV. A. Tafel extrapolationelectrode, reference electrode, and gas purge

In the spectra for Tafel sweeplng Of bothlines as indicated in Fig. 1. The solvent of 5W%

samples, the linear reglOnS Of both cathodic andH2SO4 aqueous solution was poured to soak theanodic sides were extrapolated. From theelectrodes･ After the cell was made airtight, Arintersection of both extrapolated lines, thegas was purged fわr 1 h to remove the dissolved

corrosion rate could be derived as shown in Fig.

oxygen. Cathode treatment at 0.7 V vs. reference

2, where two results f♭r both experiments wereelectrodewasperformedfor

20minandplotted to obtain the deviation. The co汀OSion

thereafter the electric circuit was kept opened fわrrate of F82H steel and SUS304 in 5W% H2SO440 min to reach equilibrium potential (co汀OSionaqueous solution were estimated as 9.l上o.2 andpotential). Two types of electrochemicalo･038 ± 0･003 cm year‑1, respectively, indicatlng

measurements were performed: one is Tafelthat the co汀OSion rate of F82H steel wassweeplng from corrosion potential to j: 0.2 V

approximately 2 Orders of magnitude larger thanwith the sweeplng rate Of 1 mV s‑1 to obtain thethat of SUS304.
co汀OSionrateandtheotherisanodic〜∈3く＼^)!SuaP一U心ヒnC)〜LJ 31, '^1!SUaPIUaJ nU

ヽﾂヽ

′

""

"

"

""

c09595g

‑0.50

‑0.45

‑0.40

Applied vc>ltage A V vs AgIAgCl(sat.KCl)
Fig. 2‑0̲35

‑0.30

‑0.25

‑0̲20‑0.15Applied voltage ･: V vs AgIAgCIくsat.KCl)

Tafel extrapolation views for F82H steel and SUS304. Solid curves, dotted lines andbroken lines mean experimental results, Ecm and Tafel extrapolation, respectively.

47

M. Oyaidzu and T. Yamanishi

luJUVr'^1!SUaP7uaJ nO〜∈OV＼^)!SUaP一uaJ nC)･.1‑. 紬

独00

油00

ヽ.

‑LO5

0.0

0.5

1.0

1.5

2.0

0.0

voltage : V (A8 I AgCl)

0.2

0.4

0.6

0̲8

1.0

volbge., V (^名I A8CF)

Fig. 3 Anodic polarization cuⅣes fわr F82H steel and SUS304.

IV. B. Anodic polarization
The spectra of anodic polarization

V. Sammaryln the present study, the corrosion behavior

measurements of F82H steel and SUS304 areof F82H steel and SUS304

shown in Fig. 3. In this figure, both spectra

highly co汀OSive circumstance ofcould be consist of three reglOnS aS the same as

H2SO4/Ii,o were observed by means of thean usual stainless steel: (i) passivation (or active)

e lectrochemi c al techn i que s o f TafTelreglOn Where peaks of cu汀ent denslty Wereextrapolation and anodic polarization, asobseⅣed in lower applied potential region, (ii)pre‑experiments to investlgate the effects ofpassive layer sustention (or simply, passive)

tritium on the corrosion of F82H steel. As thereglOn Where low and approximately constantresults, the corrosion rates of F82H steel andcurrent denslty Was Observed in the applied

SUS304 stainless steel were estimated as 9.1土

potential region between (i) and (iii), and (iii)o･2 and O･038士0･003 cm year｣, respectively･transpassive reglOn Where sharp increase or

From the deviation, lt Was expected that Tafel

current density was obseⅣed in higher叩plied

extrapolation method would be able to apply thepotential reglOn, and the other is passive reglOnexperiments to see the effects of tritiated waterwhere small and steady cun･ent denslty COuld beon corrosion rate. On the other hand of anodic

obseⅣed between passivation and transpassive

polarization

as a reference inmeasurement,

three5W%

reglOnSregion. The quantum of electricity to passivate(passivation, passive and transpassive regions)

F82H steel and SUS304 were approximately 100

could be obseⅣed in both samples of F82H steel

c cm12 and O･04 c cm‑2, respectively. Theseand SUS304 stainless steel. Therefore, it was

results indicate that F82H steel would be

expected that the effects of tritiated water on

reluctant to passivate, ir compared with SUS304

passivation and/Or passive layer could be

stainless steel.

observed.

48

Preliminary Study on Electrochemical Corrosion Behavior of F82H SteelVI. Future workrates measured by the Tafel extrapolationmethod'', Co汀OSion S°i. 47

3202‑3215

Befbre the experiments in tritiated water,(2005).

pH dependence experiments, especially ln less

[8] L Felloni, S. Sostero Traverso G L

co汀OSive circumstance than the present study,

Zucchini, "Investlgation on the secondand dissolved oxygen concentration dependence

to understand its effects on passivation andpassive layer will be perfTormed. Thereafter, theano di c current maximum on thepolarization cuⅣes of commercial stainlesssteels in sulphuric acid", Corrosion S°i. 13

experiments in tritiated water will be perf♭medto investlgate the effects of tritium on thecorrosion behavior or F82H steel.

773‑789 (1973).

[9] JIS G 0579, "Method or anodic
polarization

curvesmeasurement

fわrstainless steelsM, (2007).

Referen ces[1] T. Hayashi, T. Itoh, 良. Kobayashi, K. Isobe,

M･ Nishi,.TSafety handling characteristics
of high‑level tritiated water'‑, Fusion Eng.

Design 81 1365‑1369 (2006).

[2] K. Shiba, M. Enoeda, S. Jitsukawa,''Reduced activation martensitic steels as astmctural material fわr ITER test blanket'‑, ∫.

Nucl. Mater. 329‑333 2431247 (2004).
[3] M. Oda, T. Kurasawa, T. Kuroda, T. Hatano,
H. Takatsu, ''Development or HIP bonding
procedure and mechanical properties of HIP

bonded joints for reduced activation femitic
steel F82H'', JAERI‑Tech 97‑013, (1997).
[4] T. Hirose, K. Shiba, T. Sawai, S. Jitsukawa,

M. Akiba, "Effects of heat treatment
process for blanket fabrication onmechanical properties of F82H'', J. Nucl.

Mater. 3291333 3241327 (2004).
[5] T. Hirose, K. Shiba, M. Ando, M. Enoeda,
M. Akiba,.'Joinlng teChnologleS Of reduced
activation felTitic/martensitic steel forblanket fabrication", Fusion Eng. Design 81
645‑65 1 (2006).

[6] T. Hirose, K. Shiba, M. Enoeda, M. Akiba''Corrosion and stress corrosion cracking offerritic/martensitic steel in super criticalpressurized water'', J. Nucl. Mater. 367‑370
1185‑1189 (2007).

[7] E. McCafferty, "Validation of corrosion

49