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© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
The Effect of Surface Treatment on Reducing Metal Release from Alloy 690 SG Tubing
in PWR Primary Water
Yasuyoshi Hidaka, Yumi Momozono, Manabu Kanzaki Yasuhiro Masaki, Akihiro Uehira, Osamu Miyahara
Nippon Steel & Sumitomo Metal Corporation (NSSMC)
1
ISOE Asian ALARA SymposiumTokyo, Japan, September 9-11, 2015
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Outline
1) Introduction Background, Scope, Objective 2)Experimental procedure 1)Condition of Pre-film formation 2)Recirculation type metal release test 3)Results and discussion 1) Pre-film structure 2)Ni release rates 3) Physical analysis of pre-film before/after the test 4) Conclusions
2
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Alloy 690 is SG tubing material, which contains 60% Ni. Ni converts into 58Co by neutron irradiation.
reaction①:235U+n→fission product+n reaction②:58Ni+n→58Co(β decay,half life 71days)
Ni is transmuted to radioactive Co
neutron
Core
Primary water
Ni reaction① reaction②
58Co
Ni is released from inner surface of SG tubing
Ni Primary Water
Steam Generator(SG)
(TT690:60Ni-30Cr-9Fe)
SG tubes release
58Ni
58Ni
58Co
Deposit on the surface of primary tubing
fuel
Transport to the reactor core
Figure1 Ni release from SG tubing in PWR.
Background
3
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Figure 2 Image of reduction of Ni release by pre-filming.
Pre-filming on the inner surface of SG tubing is expected to reduce Ni release in the early operation period.
Operation Cycle
Scope
4
Reduction of Ni release by pre-filming
Ni r
elea
se ra
te
SG tube
Prevent Ni release
58Ni
Primary water
SG tube
Pre-filmed barrier
58Ni Primary water
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Objective
5
To simulate an actual PWR primary water environment, the recirculation type metal release test system, which mainly focused on high flow velocity, was introduced.
To clarify the effect of Pre-film on Ni release and the Ni release behavior on pre-film.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Experimental procedure
6
C Si Mn S Ni Cr Fe Cu 0.02 0.3 0.3 <0.001 59.3 29.5 10.0 <0.1
• The specimens are Alloy 690 tubing having an outer diameter of 19 mm and an inner diameter of 17 mm.
• Pre-filming: Annealed at 1100°C in hydrogen with 2000 ppm water
vapor in order to form Cr-oxide film on the surface. • Non pre-filming (as a reference): Annealed at 1100°C in dry hydrogen. • Both test tubing were thermally treated at 725°C in
vacuum for 10 h.
Table 1 Chemical composition (mass%)
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Alloy 690 contains 30% Cr. Cr-oxide can be formed on the surface of Alloy 690 by control of temperature and potential of oxidation.
Figure 3 Relationship between temperature and potential of oxidation.
7
-300
-250
-200
-150
-100
-50
0
0 500 1000 1500 2000
温度(℃)
酸化
ポテ
ンシ
ャル
ΔG
0=RTlnPO2(kcal)
Temperature (°C)
Pote
ntia
l of o
xida
tion
(kca
l)
Cr is oxidized selectively under this condition.
Forming Cr-oxide film on Alloy 690
Experimental procedure
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
[Specification] Test solutions are contacted to pure Ti or resin. Max. temp. is 330 ° C. Max. pressure is 17.5 MPa Flow rate 5 L/min (calculated to 1.7m/s(Re=22000))
Heater
High pressure pump
Circulation Pump
Water chemistry control (Con., DO, DH, pH)
Ni, Cr and Fe are free by using pure Ti and resin.
Storage tank
Ni is sampling from outer side of the specimen
Ni is sampling from Inner side of the specimen
High flow velocity (using inner bar)
Specimen (1mL)
Ni release is measured directly
Cooler
8
Figure 4 Recirculation type metal release test equipment.
Experimental procedure Recirculation type metal release test
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Experimental procedure Test condition of recirculation type metal release test
9
Test solution 1000 ppm B + 2 ppm Li Temperature 325°C
Pressure 15.5 MPa Dissolved oxygen <10 ppb
Dissolved hydrogen 2.6 ppm Flow rate 5 L/min
Flow velocity 1.7 m/s (calculated) Test time Pre-filmed: 620 h, Non Pre-filmed: 1129 h
Table 2 Test condition of recirculation type metal release test
The flow velocity in the actual plant is estimated* at approximately 5.5 m/s. * “Handbook of Water Chemistry of Nuclear Reactor System”, Atomic Energy Society of Japan, (2000), p.122
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion XRD analysis of pre-film before metal release test
10
0
50
100
150
200
250
300
350
10 20 30 40 50 60 70 80 90 100
Inte
nsity
(CP
S)
2θ (degree)
△
△
△
△△ △
○
○
○
○
○○
○
○○○
○ ○○
□
□ □
○: Cr2O3
△: MnCr2O4□: Austenite
• Cr2O3 and MnCr2O4 were detected from the pre-film. • According to Ellingham phase diagrams, it was
considered that Cr was mainly oxidized in the main elements (i.e., Ni, Cr, and Fe) of Alloy 690.
Figure 7 XRD analysis of pre-filmed Alloy 690 tubing before the metal release test.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion SEM observation and EDAX analysis of Pre-film
11
Figure SEM observation and EDAX analysis of pre-filmed Alloy 690 tubing.
SEM Cr Mn Pre-film
・Pre-film had uniform thickness with minute structure. ・Cr was distributed over the whole of the Pre-film.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion Ni release rates in simulated PWR primary water
12
0
0.0002
0.0004
0.0006
0.0008
0.001
0 500 1000 1500
Ni r
elea
se ra
te (
g/m
2 /h)
Test time (h)
Pre-filmed Alloy 690
Non Pre-filmed Alloy 690
• The Ni release rate of non pre-filmed Alloy 690 tubing decreased with test time like conventional studies.
• The Ni release rate of pre-filmed Alloy 690 tubing also decreased with test time promptly.
• The Ni release rate of pre-filmed Alloy 690 tubing is much lower than that of non pre-filmed Alloy 690 tubing.
Drastically decreased by pre-filming
Figure 6 Ni release rates in simulated PWR primary water at 1.7 m/s.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion TEM observation of Pre-film before/after the test
13
• The pre-film on Alloy 690 was stable even at a high flow velocity of 1.7 m/s.
Before metal release test After metal release test
Figure 9 Cross sectional TEM observation of pre-filmed Alloy 690 tubing.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion Ni release rates in simulated PWR primary water
14
0
0.0002
0.0004
0.0006
0.0008
0.001
0 500 1000 1500
Ni r
elea
se ra
te (
g/m
2 /h)
Test time (h)
Pre-filmed Alloy 690
Non Pre-filmed Alloy 690
• The Ni release rate of non pre-filmed Alloy 690 tubing decreased with test time like conventional studies.
• The Ni release rate of pre-filmed Alloy 690 tubing also decreased with test time promptly.
• The Ni release rate of pre-filmed Alloy 690 tubing is much lower than that of non pre-filmed Alloy 690 tubing.
Drastically decreased by pre-filming
Figure 6 Ni release rates in simulated PWR primary water at 1.7 m/s.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Results and discussion GDS analysis of Pre-film before/after the test
15
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1
Ele
men
t con
cent
ratio
n (m
ass%
)
Depth (μm)
Dashed line:Before metal release testSolid line:After metal release test
Cr
NiFeO
Mn
0123456789
10
0 0.02 0.04 0.06 0.08 0.1
Elem
ent c
once
ntra
tion
(mas
s%)
Depth (μm)
NiFe
O
Mn
• The oxide film was highly Cr enriched before and after the metal release test.
• Concentrated Ni on the surface before the test considerably decreased with the decrease of Mn, in contrast to the increase of O in the pre-film.
Figure 8 GDS depth profile of pre-filmed Alloy 690 tubing.
Decrease Decrease
Metal
Cr2O3
(Mn, Ni)Cr2O4Pre-film
Before metal release test
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Metal
Cr2O3
(Mn, Ni)Cr2O4Pre-film
Metal
Cr2O3 Pre-film
Ni Mn Cr(Mn, Ni)Cr2O4
Before metal release test After metal release test
Results and discussion Ni release behavior on pre-film
16
• A small amount of Ni was released from pre-filmed Alloy 690 at the beginning of the metal release test.
Figure 11 Schematic diagram of Ni release behavior on pre-film.
• The source of Ni released from pre-filmed Alloy 690 could be the surface layer of the pre-film.
• As shown in GDS depth profile, Ni and Mn decreased after the metal release test. It is assumed that Ni in MnCr2O4 is released.
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Conclusions (1)Physical analysis showed that the Pre-film composed
of mainly Cr2O3 layer, and the oxide layer had uniform thickness with dense structure .
(2)It was clarified that the Ni release rate of pre-filmed Alloy 690 at 1.7 m/s was much lower than that of non pre-filmed Alloy 690.
(3)However, a small amount of Ni was released from pre-filmed Alloy 690 at the beginning of the metal release test. The source of the small amount of Ni released from pre-filmed Alloy 690 could be the surface layer of the pre-film.
(4)It was also clarified that the pre-film on Alloy 690 was stable even at a high flow velocity of 1.7 m/s.
17
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Thank you for your attention.
18
© 2015 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.
Physical analysis of pre-film
19
• X-ray diffraction (XRD; RIGAKU, RINT-2500H) X-ray source: Co Kα (30 kV, 100 mA) Angle of incidence: 0.3° Scanning zone of 2θ: from 10° to 105° • Glow discharge spectroscopy (GDS; HORIBA, GD-Profiler 2) Analyzing area: 4 mm in diameter Power capacity: 35 W Pressure of Ar gas: 600 Pa • Transmission electron microscope (TEM; RIGAKU, JEM-200CX) Acceleration voltage: 200 kV