1. Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2. Suzhou Nuclear Power Research Institute Co. , Ltd. , Suzhou 215008, China
Cite this article:
Canshuai LIU,Zhaohui TIAN,Zhiming ZHANG,Jianqiu WANG,En-Hou HAN. Corrosion Behaivour of X65 Low Carbon Steel During Redox State Transition Process of High LevelNuclear Waste Disposal. Acta Metall Sin, 2019, 55(7): 849-858.
Domestic and foreign researches on the corrosion behavior of low carbon steel canister in high level nuclear waste geological repositories focus on the initial aerobic stage and the later anaerobic stage, while few researches have been reported on the corrosion behavior during the disposal transition period. The long term electrochemical corrosion behavior of X65 low carbon steel in 80 ℃ Gaomiaozi bentonite saturated with anaerobic Beishan groundwater has been studied by electrochemical measurement system in anaerobic glovebox constructed independently. The results indicated that the open circuit potential of X65 low carbon steel decreased gradually during 150 d, while the electrochemical impedance of the corrosion film increased with immersion time. Pitting corrosion occurred at the beginning of immersion tests, and finally transformed into general corrosion. Morphologies, compositions, and phases of the corrosion film formed on the carbon steel surface were examined by SEM, EDS and μ?XRD. The results showed that the corrosion film was mainly composed of blocks, slices, rods and swellings. The elemental distribution in the corrosion film was uniform, and the phases were composed of magnetite and hematite. The average corrosion rates were detected by weight loss measurement, which decreased from 195.88 μm/a to 20.58 μm/a. The corrosion rates (V) followed a power function pattern V=8.34t-0.88, indicating that the film growth process was controlled by oxygen diffusion.
Fund: Key Research Program of Frontier Sciences, Chinese Academy of Sciences(No.QYZDY-SSWJSC012);Key Program of the Chinese Academy of Sciences(No.ZDRW-CN-2017-1)
Fig.4 Open circuit potential (OCP) variation tendency with time of X65 low carbon steel in anoxic saturated bentonite (a) and E-pH diagram of Fe-H2O system (b) at 80 ℃ (E—electrochemical potential)
Fig.5 μ-XRD spectra of corrosion products formed on X65 low carbon steel immersed in anoxic saturated bentonite at 80 ℃ for different time
Fig.6 EIS recorded on X65 low carbon steel in anoxic saturated bentonite at 80 ℃ for different time (Z—impedance, Z'—impedance real part, Z''—impedance imaginary part)
Fig.7 Equivalent circuit and physical model of EIS recorded on X65 low carbon steel in anoxic saturated bentonite at 80 ℃ for 1~40 d (a) and 60~150 d (b) (Rs—corrosion media resistance, Rct—charge transfer resistance, RL—localized corrosion resistance, Rf—film resistance, L—inductance, Qdl—constant phase angle element of electric double layer, Qf—constant phase angle element of electric double layer, W—Warburg resistance)
Time
d
Rs
Ω·cm2
Ydl
10-4·Ω-1·cm-2·s-n
ndl
Rct
Ω·cm2
L
H·cm2
RL
Ω·cm2
1
34
4.09
0.81
685
11270
3863
5
38
4.76
0.82
872
18950
7468
10
49
7.71
0.79
1392
3690
3644
20
50
5.37
0.78
1435
3094
2631
40
70
6.24
0.78
1480
2524
1568
Table 1 Fitting parameters of EIS spectra of X65 low carbon steel in anoxic saturated bentonite at 80 ℃for 1~40 d
Fig.8 Surface morphologies of X65 low carbon steel immersed in anoxic saturated bentonite at 80 ℃ for 10 d (a), 50 d (b), 100 d (c) and 150 d (d)
Fig.9 Cross sectional morphologies of X65 low carbon steel immersed in anoxic saturated bentonite at 80 ℃ for 10 d (a), 50 d (b), 100 d (c) and 150 d (d)
Time
d
Rs
Ω·cm2
Ydl
10-4·Ω-1·cm-2·s-n
ndl
Rct
Ω·cm2
Yf
10-4·Ω-1·cm-2·s-n
nf
Rf
Ω·cm2
W
60
85
6.94
0.78
1506
7.65
0.79
1036
12.82
80
88
3.89
0.79
1582
7.40
0.75
1461
9.54
100
90
5.52
0.80
1692
7.09
0.77
1878
4.62
120
111
4.28
0.77
1708
7.01
0.75
3076
3.56
150
147
5.49
0.79
1830
6.96
0.76
3374
2.87
Table 2 Fitting parameters of EIS of X65 low carbon steel in anoxic saturated bentonite at 80 ℃ for 60~150 d
Fig.10 Typical micro morphologies including blocks (a), slices (b), rods (c) and swellings (d) of corrosion products on X65 low carbon steel in saturated bentonite at 80 ℃ for 150 d
Species
O
Fe
Na
Mg
Al
Si
S
Cl
Ca
Mn
Block
42.14
54.69
0.46
0.55
0.58
0.32
0.22
0.14
0.25
0.65
Slice
56.05
39.47
0.51
1.18
0.91
0.64
0.23
0.13
0.50
0.38
Rod
56.65
40.07
0.34
0.83
1.06
0.21
0.15
0.06
0.30
0.33
Swelling
55.06
39.71
1.45
0.78
0.53
0.66
0.26
0.23
0.38
0.94
Table 3 Average elemental composition of corrosion products with typical morphologies formed on X65 low carbon steel in saturated bentonite at 80 ℃
Fig.11 Elemental distributions on cross section (selected area in Fig.9d) of corrosion products formed on X65 low carbon steel immersed in saturated bentonite at 80 ℃ for 150 d
Fig.12 Fitting results of the relationship between average corrosion rate (V) and time when X65 low carbon steel has been immersed in saturated bentonite at 80 ℃ (R2—variances between three parallel tests)
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