K

ph 7.7<pH<13.4 2

Propagation Behaviour of Lozalised Corrosion of Carbon Steel in Slightly Alkaline and Alkaline Environment (Research Document) Naoki Taniguchi*, Manabu Kawasaki**, Susumu Kawakami* and Haruo Suzuki*** Abstract In current repository concept of high-level radioactive disposal in soft rock system, concrete support will be emplaced around the buffer material, and groundwater ph will be increased by the contact with cement. In such condition, carbon steel overpack is possible to be passivated and be attacked by localized corrosion due to the breakdown of passive film. In this report, we investigated the propagation behaviour of localized corrosion of carbon steel by immersion tests in slightly alkaline and alkaline aqueous solution in which ph range was from 7.7 to 13.4. Another possible cause of non-uniform corrosion is heterogeneity of water content or porewater chemistry in buffer material around a gap between the buffer material block. In order to examine such situation, immersion tests of carbon steel were conducted in buffer material with a slit simulating the gap. Based on these experimental results, correlationship between the average corrosion depth and the pitting factor was investigated. The result indicated that any observed pitting factor was not over upper limit value estimated in second progress report by JNC. In conclusion, no severe localized corrosion enough to influence the overpack lifetime was observed in immersion test within the experimental condition in this report. The empirical model to estimate the maximum corrosion depth of carbon steel overpack under oxidizing condition was established based on our experimental data and previously reported data. * Barrier Performance Group, Waste Isolation Research Division, Waste Management and Fuel Cycle Research Center, Tokai Works ** Inspection Development Corporation ***Kokan Keisoku K.K.

1 1 2 3 2-1 3 2-2 12 3 16 3-1 16 3-2 32 4 50 5 61 62 1(1) 2 2(1) 3 3(1)

1000 1999 JNC, 1999 JNC1999 ph ph 10.5 ( 2002) ph ph 10.5 13 ( 2002) ph 13.5 ph 12.5 ph ( 1999a) (Romanoff, 1989) ph 11 ph ph 7.713.4

2-1 (1) SM400BC:0.13%, Si: 0.15%, Mn: 0.71%, P: 0.011%, S: 0.006% SFVC1C:0.22%, Si: 0.26%, Mn: 0.93%, P: 0.013%, S: 0.005% 2-1(a) 2mm 80mm 8mm 20mm 104.6cm 2 0.1M 0.027MpH10 60cm 2 1999a 20kgfcm #800 1 15 15 SM400B 2-1(b) 10mm300300mm 250250mm 625cm 2 1 5 10 (2) (Marsh et al., 1983; 1999a; 2002) 2-1 2-1 1999a No.1No.4 ph No.5No.7 ph No.8No.14 NaOH ph No.1523 80

OPC HFSC 1mm 0.5M NaCl 10 OPC: No.24 No.27HFSC: No.28No.31 2-2 80 No.8No.14 No.32No.33 No.34No.35 2-4 90 180 (3) 20kgfcm 2-2(a) 3l 5% 2 10mA/cm 2 100l 2 5% 2 Gumbel (4) x Gumbel F(x)

F(x) = exp[-exp{-(x-)/}] (2-1) y (2-2) (2-3) y=(x-)/(2-2) F(y) = exp[-exp(-y)] (2-3) y F(y) x 2-3 Gumbel Gumbel y=0 x 2-3 T S s F(y) F(y) = 1-1/T (2-4) T=S/s (2-5) 2 S=55129cm 2 s=104.6 cm 2 T=55129/104.6=527 x max i F(y) 1984 F(y) = 1- i/(n+1) 2-5 Gumbel MVLUE 1984Gumbel T X max T X max X max = lnt 2-6 Gumbel lnt a F(y)=a x P max P max = X max -ln(-ln a ) = lnt-ln(-ln a ) 2-7

P max 1-a a=0.99 P max P max 1

2mm 80mm 20mm 21(a) 300mm 10mm 250mm 300mm 250mm 21(b)

7 8 22(a) 10 22(b)

lnt a=0.99 55129cm 2 104.6cm 2 T=527 X max P max 23Gumbel

No. [HCO 3 - +CO 3 2- ] (M) [Cl - ] (M) [SO 4 2- ] (M) ph days 80 1 0.2 0.0027 0 80 90 2 0.2 0.0027 0 80 11.311.5 180 3 0.2 0.0027 0 80 10.911.2 365 4 0.2 0.0027 0 80 720 5 0.01 0.56 0.052 80 90 8.4 6 0.01 0.56 0.052 80 180 8.18.2 7 0.01 0.56 0.052 80 365 8 0.1 0.027 0 80 90 9 0.1 0.027 0 80 180 10 0.1 0.027 0 80 365 10.010.1 11 0.1 0.027 0 80 720 9.610.3 12 0.1 0.027 0 80 90 13 0.1 0.027 0 80 180 14 0.1 0.027 0 80 365 15 0.1 0.56 0 80 30 11.0 16 0.1 0.56 0 80 90 10.511.0 17 0.1 0.56 0 80 180 18 0.1 0.56 0 80 30 12.0 19 0.1 0.56 0 80 90 10.912.2 20 0.1 0.56 0 80 180 SM400B 80mm SM400B 80mm SM400B 80mm SFVC1 80mm SM400B 80mm SM400B NaOH 80mm 21 0.1 0.56 0 80 30 SM400B 13.4 NaOH 22 0.1 0.56 0 80 90 11.511.9 23 0.1 0.56 0 80 180 80mm ph No. days 80 24 OPC 0.56M NaCl 30 25 OPC 0.56M NaCl 13.013.1 90 26 OPC 0.56M NaCl 11.411.6 180 27 OPC 0.56M NaCl 365 28 HFSC 0.56M NaCl 30 29 HFSC 0.56M NaCl 10.711.0 90 30 HFSC 0.56M NaCl 9.810.0 180 31 HFSC 0.56M NaCl 365 SM400B 80mm SM400B 80mm

No. 32 2-3 ph days [HCO 3 - +CO 3 2- ]=0.1M [Cl - ]=0.027M 10.2 90 33 [HCO - 3 +CO 2-3 ]=0.1M [Cl - ]=0.027M 10.2 180 34 7.7 90 35 7.7 180 SM400B 2-4 M Mg 2+ 5.5110-2 Ca 2+ 9.2110-3 Sr 2+ 2.0910-4 Na + 5.3110-1 K + 1.1610-2 B 3.9810-4 Cl - 5.4410-1 F - 6.3210-5 Br - 8.2610-4 SO 4 2- HCO 3-2.9210-2 1.8510-3

2-2 (1) JISG3106SM400BC:0.14%, Si: 0.22%, Mn: 1.07%, P: 0.014%, S: 0.007% 226mm #800 147mm 169.6cm 2 (2) 70% 30% 146mm 50mm 1.8Mg/m 3 (3) 2-4 0.1M NaHCO 3 2-1 OPC (HFSC) 5mm 10mm 5mm 60 1440hr 150 3600hr 90 2-5 (4) 2-4 1.2mm

10mm 27mm mm Ag/AgCl (5) 90 NR1000 20 20

2-4

2-5 No. ph days 36 8.2 60 37 8.2 60 38 8.2 5mm 60 39 8.2 5mm 60 40 8.2 5mm 150 41 8.2 5mm 150 42 8.2 5mm 60 43 8.2 5mm 60 44 8.2 10mm 60 45 8.2 10mm 60 46 OPC 13.2 5mm 60 47 OPC 13.2 5mm 60 48 HFSC 10.9 5mm 60 49 HFSC 10.9 5mm 60 50 0.1M NaHCO 3 8.4 5mm 60 51 0.1M NaHCO 3 8.4 5mm 60

3-1 Gumbel 3-1 y=0 x 2 No.1No.4 3-2No.24, 26 3-3No.28, 30 3-2 30 180 3-3 30 180 No.8No.27 10-3 10-2 mm/y 3-2 No.5 7 No.2831 10-1 mm/y 3-3 3-4No.32, No.33 3-5 No.34, No.35 3-4 90 180 No.5No.14 No.32No.35 X m x max P max 3-6 X m x max P max 3-7SM400B 3-8SFVC1

X m x max P max 3-9No.32No.33 3-10No.34No.35 3-9 No.32No.33 No.8No.14 No.8No.14 80 90 1999 80 1 0.1mm/y 1995 3-11 3-16 3-20 2 SFVC1 SM400B - P max X m 3-12 ph No.15No.23 ph X m x max P max 3-13 3-15 ph11 10-3 mm ph12 ph13 10-4 mm ph ph ph 3-16 90 ph 3-17 ph11

No.24No.31 X m x max P max 3-18 3-19 OPC HFSC ph 3-20 90 OPC 180 365 HFSC 180 365 HFSC ph 9 3-21 OPC HFSC 365 ph 11 1999a 3-22 3-23 No.5No.33 No.34No.35 104.6cm 2 625.0cm 2

3-1 Gumbel No.5No.7

30 (No.24) 180 (No.26) 30 (No.24) 180 (No.26)

30 (No.28) 180 (No.30) 30 (No.28) 180 (No.30)

90 (No.32) 180 (No.33) 90 (No.32) 180 (No.33)

90 (No.34) 180 (No.35) 90 (No.34) 180 (No.35)

3-2 3-24 90 10mm 85 27mm 75 80 0.5/mm 2 0.04/mm 3-25 3-32 24.5mm 10mm 40mm 15mm 11mm38mm 3-30 No.47 +OPC 3-31 No.49 +HFSC 5001000hr No.47 +OPC 1000hr 1000hr 3-33 1500hr 3-34 100mV

3-35 500hr -700mV 1000hr 2500hr -600mV 1999b ph 1996 500hr -1100mV vs. Ag/AgCl ph 13 ph ph 12 2002 ph 2002 500hr 1995 ph Taniguchi et.al, 1998 ph 12 500hr -1100mV vs. Ag/AgCl 2002 ph 12.5 500hr ph 0.1M NaHCO 3-200-400mV vs. Ag/AgCl 1990 20%100% 0.1M NaHCO 3 Taniguchi et.al, 1998 (No.41) 3-36

ad a, b, d 3-1 No.43 0.1mm/y No.36No.45 No.46No.49 No.50No.51 NaHCO 3 No.40 No.41 5mm150 3-37

3-1

10mm 15mm 20mm 30mm 40mm 11mm 20mm 24.5mm 29mm 38mm

No.41 No.41

a b c d

4-1 ph 0.99 2 ph<11 4-1 ph <11 ph>11 1992 2 ph11 ph11 ph 2 0.31.8mm 4-2 No.36No.45 No.42 No.43 2002 150 ph ph ph NaHCO 3 ph ph 4-2 1992

Romanoff, 1989 1992131.0cm 2 Romanoff (1989)182.4cm 2 1.5inches=3.8cm 6inches=15.2cm 104.6cm 2 169.6cm 2 4-3 Marsh and Taylor, 1988; Hock et al., 1995; 1984 P t P=kt n (4-1) k : n : 0<n1 3-11 3-16 3-20 P max 0.99 t(year) (4-1) No.5No.7P max (mm) = 3.37 t 0.32 (4-2-1) No.8No.11P max (mm) = 1.01 t 0.25 (4-2-2)

No.12No.14P max (mm) = 1.06 t 0.11 (4-2-3) No.15No.17P max (mm) = 0.87 t 0.09 (4-2-4) No.18No.20P max (mm) = 0.85 t 0.13 (4-2-5) No.21No.23P max (mm) = 0.46 t 0.21 (4-2-6) No.24No.27P max (mm) = 0.91 t 0.09 (4-2-7) No.28No.31P max (mm) = 4.20 t (4-2-8) 100 1999 t=100 P max No.5No.7P max (mm) = 14.7 (4-2-9) No.8No.11P max (mm) = 3.19 (4-2-10) No.12No.14P max (mm) = 1.76 (4-2-11) No.15No.17P max (mm) = 1.32 (4-2-12) No.18No.20P max (mm) = 1.55 (4-2-13) No.21No.23P max (mm) = 1.21 (4-2-14) No.24No.27P max (mm) = 1.38 (4-2-15) No.28No.31P max (mm) = 420 (4-2-16) 100 4-2-9 4-2-16 Brossia and Cragnolino(2000)(4-1) kn 10cm 5 1992Fukuda et.al,

1994 Gumbel 4-3 X m = k 1 X m m (4-3) k 1, m : = X m k 2 X n m (4-4) k 2, n : (4-3) (4-4) (2-6) X max X max =+ lnt = X m k 2 X n m k 1 X m m lnt (4-5) a P max (2-7) (4-5) P max = X max -ln(-ln a ) = lnt-ln(-ln a ) = X m k 2 X n m k 1 X m m lnt - k 1 X m m ln(-ln a ) 4-6 (mm) (mm) k 1 = 0.45k 2 =1.5m=n=0.25 (mm) = 0.45X 0.25 m (4-7) (mm) = X m 1.5X 0.25 m (4-8) 4-5 (4-6) X max (mm)= X m 1.5 X m 0.25 0.45 X m 0.25 lnt (4-9) P max (mm)=x m 1.5 X 0.25 m 0.45 X 0.25 m lnt 0.45X 0.25 m ln(-ln a ) 4-10

T S s s s=104.6cm 2 X max (mm) = X m 1.5X 0.25 m 0.45X 0.25 m ln(s/104.6) 4-11 P max (mm)= X m 1.5X 0.25 m 0.45X 0.25 m ln(s/104.6) 0.45X 0.25 m ln(-ln a ) = X m +1.5+0.45 ln(s/104.6) 0.45ln(-ln a )X 0.25 m 4-12 P max Pf max Pf max = 1 +1.5+0.45 ln (S/104.6) 0.45ln(-ln a )X -0.75 m 4-13 X m (mm) S(cm 2 ) a (4-12) (4-13) 1992 Gumbel 3 4-4 = 0.54X 0.5 m (4-14) = X m +1.8X 0.5 m (4-15) s=131.0cm 2 X max P max Pf max X max (mm) =X m 1.8X 0.5 m 0.54X 0.5 m ln(s/131.0) 4-16 P max (mm)= X m +1.8+ 0.54 ln(s/131.0)-0.54ln(-ln a )X 0.5 m 4-17 Pf max = 1 +1.8+0.54 ln(s/131.0) -0.54 ln(-ln a )X -0.5 m 4-18 2 JNC, 1999 S=55129cm 2 a=0.99 4-12 4-17 P max (mm)= X m 6.4X 0.25 m 4-19 P max (mm)= X m 7.5X 0.5 m 4-20

4-20 2 4-13 (4-18) 4-21 2 Pf max = 16.4X -0.75 m 4-21 Pf max = 17.5X -0.5 m 4-22 4-11 4-13 (4-16 (4-18) X m X m X m a=0.99 S=55129cm 2 4-194-20 X m =0.53mm 2 0.99 0.5mm (4-17) 0.5mm (4-18) 2mm 4-5 4-1 (2) 2 0.99 (3) (1) k 1, k 2, m, n

4-1 mm P max= X m k 2 X m n k 1 X m m ln T - k 1 X m m ln(-ln a ), T=s/S P max =X m + 1.5+0.45 ln(s/104.6) 0.45ln(-ln 0.25 a )X m 0.25 P max = X m 6.4X m k 1,k 2,n,m X m s S a k 1 =0.45,k 2 =1.5, P max =X m +1.8+0.54ln n=m=0.25,s=104.6cm 2 S/131.0)-0.54ln(-ln a ) X m 0.5 P max = X m 7.5X m 0.5 S=55129cm 2 a=0.99 k 1 =0.54,k 2 =1.8, n=m=0.5, s=131.0cm 2

ph 8.413.4 ph ph>11 ph 7.7<pH<13.4 X m S a P max P max (mm)= X m +1.5+0.45ln (S/104.6)-0.45ln(-ln a )X 0.25 m P max (mm)= X m +1.8+0.54ln (S/131.0)-0.54ln(-ln a )X 0.5 m