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