pre-filming method of reducing metal release from alloy 690 for sg in primary water of pwr
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Pre-Filming Method of Reducing Metal Release from Alloy 690 for SG in Primary Water of PWR. 2009 ISOE Asian ALARA Symposium Aomori September 9, 2009 Sumitomo Metal Industries, Ltd. Akihiro Uehira Manabu Kanzaki Kazuyuki Kitamura Hiroyuki Anada. 1. September 2009. Contents. - PowerPoint PPT PresentationTRANSCRIPT
Pre-Filming Method of Reducing Metal ReleasePre-Filming Method of Reducing Metal Release
from Alloy 690 for SG in Primary Water of PWRfrom Alloy 690 for SG in Primary Water of PWR
2009 ISOE Asian ALARA Symposium Aomori
September 9, 2009
Sumitomo Metal Industries, Ltd.Akihiro Uehira
Manabu KanzakiKazuyuki Kitamura
Hiroyuki Anada
September 2009 1
Contents
1) Background
2) Selective oxidation of Cr oxide for pre-filming and characterization
3) Ni release of pre-filmed alloy 690
4) Conclusion
September 2009 2
Background
1) Radioactive resources are mainly released metal, Co and Ni etc. from primary water structures in PWR.
2) Especially, area of SG (Steam Generator) tubes contacting with the primary water is the largest among those of primary water structures.
3) Therefore, reduction of metal release from SG tubes is the most effective in order to reduce exposure.
September 2009 3
Ni Release from SG Tubes
Reactor Core
58Ni
58Co
Ni releases from SG tube to primary water.
58NiPrimary water
Steam Generator (SG)
(Alloy 690 :60Ni-30Cr-9Fe)
SG tube
Release
Adhere to primary circuit structures.
1) Radioactive nuclide that governs radiation effect is mainly 58Co which comes from
Ni base alloy used as SG tube.
2) It is important to study the method of reducing metal release from SG tube from the viewpoint of reducing exposure.
Move to reactor core.
Nuclear fuel Primary water
Ni is transformedto radioactive Co.
Figure 1
September 2009 4
n(Neutron)
58Ni
Figure 2 Image of Ni Release from SG Tubes during Operation Cycle
Main Ni release from SG tubes occurs in the early operation period. In order to reduce total Ni release, reduction of Ni release in the early operation period is the most effective.
Ni R
elea
se f
rom
SG
Tu
bes
Operation Cycle
Ni Release from SG Tubes during Operation Cycle
Ni release is decreasing during the early operation period because the barrier generates on the surface of SG tubes.
Main Ni Release
September 2009 5
Figure 3 Image of Ni Release Reduction
Pre-filming on the SG tube surface is expected to reduce Ni release in the early operation period.
Ni Release
Operation Cycle
Reduction of Ni Release by Pre-Filming on SG Tubes Surface
SG tube
Pre-filmed barrier
Prevent Ni migration.
58Ni
Primary water
Ni release reductionby pre-filming
September 2009 6
Co release in Higashidori Nuclear Power Station, BWR, decreased by pre-filming on the surface of feed water heater tube, about 1/2 compared with other plant without pre-filming method. (*)Sato, Tohoku Electric Power Company, The thermal and nuclear power generation convention 2008 Sendai
Commercial Application of Pre-Filming MethodC
o Io
n C
once
ntra
tion
[pp
b]
EFPH (Equivalent Full Power Hours)
Figure 4 Process of Co Ion Concentration in Nuclear Reactor Water
Higashidori applying pre-filming method
September 2009 7
Co concentration decreased.
( L. Guinard, EDF, Water Chemistry of Nuclear Reactor Systems 8, BNES, 2000)
R&D of Pre-Filming Method to Alloy 690R
elea
sed
met
al w
eigh
t (m
g/dm
2 )
0
24
68
10
Untreate
d
Picklin
g
Electro
polishin
g
Aqueous o
xidati
on, O2
Aqueous o
xidati
on, Zn
Chromiza
tion
Gaseo
us oxid
ation
Post-disc
harge o
xidati
on
(72)
September 2009 8
As different pre-filming method from below methods, we researched oxidation at high temperature.
Figure 5 Quantity of Released Metal during the Corrosion Test
Cr oxide is stable in primary water of PWR.
We considered thatCr oxide film is suitableas a barrier against Ni release from SG tubes to primary waterduring operation.
Stable region of Cr2O3
Primary water in PWR
Figure 6 Potential-pH Diagram of Cr in 300 ℃ Water
Pot
entia
l (V
olts
vs
SH
E)
pH
September 2009 9
Possibility of Cr Oxide as Pre-Film Candidate
Alloy 690 contains 30% Cr.
We considered that Cr oxide can be formed on the surface of alloy 690by control of oxygen potential and temperature.
Cr Oxide on alloy 690
4/3Cr+O2
=2/3Cr2O3
2Ni+O 2
=2NiO
2Fe+O2=2Fe
O
Figure 7 Relationship between Type of Oxide and Oxidation Condition
Temperature
Par
tial P
ress
ure
of O
xyge
n
September 2009 10
Cr is oxidized selectively in this region.
1) Clarify the possibility of selective oxidation of Cr in alloy 690 by controlling oxygen partial pressure and temperature.
2) Clarify the effectiveness of pre-filming on Ni release reduction from alloy 690.
Objective
September 2009 11
Specimen : Alloy 690 sheet (60Ni-30Cr-10Fe)
Heat treatment→Cold rolling→Sampling test specimen→Surface polishing→Pre-filming
Preparation of Test Specimen
September 2009 12
Pre-Filming Method
H2O in H2 Gas
Quartz vessel
Electric furnace
Test specimen
Figure 8 Pre-Filming Equipment
September 2009 13
1) Oxide film formation by oxygen at high temperature.2) H2O in H2 gas as oxygen source.
Appearance of Oxide Film
After pre-filmingBare specimen(Before pre-filming)
Photo 1 Appearance of Specimen
September 2009 14
Cross Section of Oxide Film
Oxide film
Homogenous oxide film was formed on the surface of the specimen.
Specimen (Alloy 690)
Photo 2 Crosse Section of Oxide Film (SEM)
September 2009 15
1 μm
Oxide film is mainly composed of Cr2O3.
Depth from Surface (nm)
Rel
ativ
e O
xyge
n I
nte
nsi
ty
Pro
por
tion
(%
) of
Con
stit
uen
t M
etal
Ele
men
t
Thickness ofoxide film
Composition of Oxide Film
NiCrO
Mn Fe
120000
100000
80000
60000
40000
20000
0
100
80
60
40
20
0
0 500 1000 1500 2000 2500
SpecimenCr2O3
MnCr2O4
September 2009 16
Figure 9 Analysis of oxide film by SIMS
Ni Release Teston Various Thickness Oxide Film
September 2009 17
Ni Release Test Method
Test specimen
Platinum container
Electric furnace
Deionized water
After immersion in deionized water at 320 ℃ for 1000 hrs, Ni content in deionized water was measured by ICP.
Figure 10 Ni Release Test Equipment
September 2009 18
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500
Thickness of Oxide Film (nm)
Ni C
onte
nts
(ppm
)Ni Release Test Result of Pre-Filmed Specimen
Ni release decreased from 0.9 ppm to 0.01 ppm by pre-filming, regardless of oxide film thickness.
Figure 11 Effect of Oxide Film on Reduction of Ni Release
Ni release decreased Drastically by pre-filming.
September 2009 19
Following results were obtained.
1) Cr oxide film can be formed on the surface of alloy 690 by using H2O in H2 gas at high temperature.
2) The oxide film is mainly composed of Cr2O3.
3) Pre-filming of Cr2O3 decreased Ni release from alloy 690 by a factor of 0.1.
4) Ni release from SG tubes in PWR can be expected to reduce by this pre-filming.
Conclusion
September 2009 20
Thank you for your attention.
September 2009 21