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Cr and Co release reduction from stainless steels in PWR and BWR. 2009 ISOE Asia ALARA Symposium Aomori EPRI Radiation Protection Conference September 9, 2009 Sumitomo Metal Industries, Ltd. Hiroyuki ANADA Kiyoko TAKEDA Tetsuo YOKOYAMA. Contents. Background Conventional Technologies - PowerPoint PPT Presentation
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Cr and Co release reduction from stainless steels in PWR and BWR
2009 ISOE Asia ALARA Symposium Aomori
EPRI Radiation Protection Conference
September 9, 2009
Sumitomo Metal Industries, Ltd.
Hiroyuki ANADA
Kiyoko TAKEDA
Tetsuo YOKOYAMA
September 2009 2
Contents
• Background• Conventional Technologies• New Method of Co Release Reduction• New Method of Cr Release Reduction• Experimental Procedure• Results• Application• Conclusion
September 2009 3
Background
• Co release・ Co content in stainless steels from contamination in
raw material
・ Co release to coolant
・ Co raise the dose rate in coolant
・ 60Co has long half-life, 5.7 years
EPRI; Restricted less than 0.05%
Influence of metallic ion release from stainless steels on the dose rate
September 2009 4
Background
pH
Co
Ab
sorb
ed
ra
tio
, %Increasing Cr
・ Cr release
・ Corrosion of the stainless steels release Cr into coolant
・ Decrease pH in the coolant with increasing Cr content inCoolant
・ Absorbed Co ion on the surface resolved into the coolant
September 2009 5
Conventional Technologies
1. Reduction of Co release・ Pure raw material selection; Scraps
・ Min. 0.05 – 0.20%・ High cost
2. Reduction of Cr release・ No commercial productions for stainless
steels
September 2009 6
New Method of Co Release Reduction
1. Reduction of Co releasePure raw material selection;
・ Hot metal; Pure Fe
・ A little selected scraps
・ Less than 0.02%
・ Low cost
September 2009 7
New Method of Cr Release Reduction
2. Reduction of Cr release Pre-filming technique
Cr oxide film by control oxygen content
during a heat treatment
Protective Cr oxide film for Cr release into coolant
September 2009 8
New Method of Cr Release Reduction
0 1000 2000
Temperature, degree C
Free
ene
rgie
s of
for
mat
ion
of o
xide
s (
Δ-
G0 =
RT ln
Po 2
), k
J/m
ol O
2
100
500
1000
Po 2
, atm
10-10
1
10-20
10-30 10-50 10-100
4/3Cr + O2 = 2/3Cr2O3
2Ni + O2 = 2NiO2
2Fe + O2 = 2FeO2
2. Reduction of Cr release
・ Control of oxygen content during heat treatment in manufacturing process
・ Selective oxidation of Cr in stainless steel
September 2009 9
Experimental Procedure -Material-
• Material TP304L; Raw material selection, hot metal in addition
to scraps
• Pre-filming on inner surface of the tube, 15.9 mm dia.1. Laboratory test
• Heat treatment in H2 with slight amount of O2 content controlled by dew point; -10 to -50 deg. C in H2
2. Application to feed water heater tube for BWRCold draw
15.9 mm diaPre-filming; Solution treatment >1000degCH2 environment adding H2OSelective oxidation of Cr
Melting
September 2009 10
Experimental Procedure
• Characterization of pre-filming oxide
1. Color and Oxide morphology • Naked eyes and SEM
2. Oxide structure identified by XPS• Depth profile of the chemistries by Ar sputtering• Chemical state analysis
September 2009 11
Experimental Procedure
• Cr and Co release from the pre-filmed tube to coolant
Corrosion test in pure water– Refreshed type autoclave at 215 deg. C for 450 hr. – Cr and Co content in the test water was analyzed.
September 2009 12
Result -Co content-
New method Conventional method
Melting ・ Small amount of selected scraps
・ Hot metal, pure Fe from blast furnace
・ Selected pure scraps
Large cost impact
Facility ・ Combination of blast furnace and electric furnace
・ Suitable mixing, small cost impact
・ Electric furnace
Co Less than 0.02% 0.05%
September 2009 13
Result - Pre-filming oxide in the lab. test
DP, O2 ; Low High⇒
SEM imagesSurface pre-filmed at -25deg. C
• Thin oxide formed by heat treatment under controlled dew point in H2
September 2009 14
Result -Depth profile of the pre-filming oxide
September 2009 15
Result - Application of pre-filming
Application of pre-filming for feed water heater tube
・ Specification; TP304L ・ 15.9mm dia. ・ Pre-filming condition
Atmosphere ; In H2, DP= - 25deg.C Temperature; 1060deg.C
September 2009 16
Result - Application of pre-filming
September 2009 17
Result - Cr release from the tube
・ Pre-filming reduced 25% of Cr release
Autoclave test; 215deg.C
0.0000.0020.0040.0060.0080.0100.0120.014
0 200 400 600Time, hr.
Cr
rele
ase,
g/m
2
Pre-filmingTube
Bare Tube - 25%
September 2009 18
Result - Experience of Japanese BWR
Radioactivity, Bq/cm3100
Onagawa
Higashidori; Pre-filming Tube applied
0 10,000 20,000EFPH (Equivalent Full Power Hours)
Jun-ichi Satoh, Proceedings of Thermal and nuclear power engineering society, p72-p73 October 23 2008, Sendai Japan
10
1
0.1
0.01
0.001
September 2009 19
Conclusion
• New Method of Co & Cr release reduction from stainless steel tubes to coolant :
(1) reduces Co content in stainless steels less than 0.02% without large cost impact.
(2) reduces 25% of Cr release from stainless steels tubes
(3) is applied for Higashi-dori BWR plant, and contributed to reduce the dose rate and to be No.1 plant in whole BWR
September 2009 20
Future work
• Challenge to reduction of Ni release from steam generator tube for PWR.– Pre-filming technique using by oxygen potential control
Thank you for your attention!
September 2009 21
Co release into coolant
September 2009 22
Depth profile of the pre-filming oxide
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
0 10 20 30 40 50 60 70 80 90 100Depth,nm
Com
positio
n, a
t%
C1sO1sSi2sCr-OMet.CrMn2p1Fe2p3Ni2p3
DP= - 30C
Surface
September 2009 23
Structure of the pre-filming oxide
• Cr-Mn mixed oxide layer formed adjacent to the matrix.• Fe2O3 or Fe3O4 layer formed at the surface of the oxide
Fe
DP=-20
C
DP=-30
C
Intensity, Arb. Unit
DP=-25
C
Fe2O3
Binding Energy,
eV Figure 4 Fe2O3 formed on the surface,
showing effectiveness of dew point
Fe2O3
Cr-Mn oxide(mainly)
(FeO and Fe, Ni)
TP304 matrix
Figure 5 Multi-oxide layers in the
pre-filming on TP304
September 2009 24
Thickness of pre-filming
• Thickness of the pre-filming increase with increasing DP.• Suitable pre-film thickness for will be selected easily.• This might contribute to the effectiveness of the barrier layer
0
10
20
30
40
50
60
70
- 35 - 30 - 25 - 20 - 15
Dew point, degree C
Thi
ckne
ss, n
m
September 2009 25
Diffusion of Co in oxide
• Diffusion coefficient of Co decrease with increasing Cr content in oxide.
• This suggests that Cr rich layer adjacent to the matrix acts as a protective film.
Cr in Cr2O3
Co in Feo.8Cr0.2O3
Fe in Fe0.8Cr0.2O3
Fe in Fe2O3
Fe2O3
Cr-Mn oxide(mainly)
(FeO and Fe, Ni)
TP304 matrix
Figure 5 Multi-oxide layers in the
pre-filming on TP304