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.

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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

Pre-Filming Method of Reducing Metal Releasefrom 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


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Contents

  • Background

  • 2) Selective oxidation of Cr oxide for pre-filming and characterization

  • Ni release of pre-filmed alloy 690

  • 4) Conclusion

2

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Background

  • Radioactive resources are mainly released metal, Co and Ni

  • etc. from primary water structures in PWR.

  • Especially, area ofSG (Steam Generator) tubescontacting

  • with the primary water is the largest among those

  • of primary water structures.

  • Therefore, reduction of metal release from SG tubes is

  • the most effective in order to reduce exposure.

3

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Ni Release from SG Tubes

  • Radioactive nuclide that governs radiation effect is mainly 58Co which comes from

  • Ni base alloy used as SG tube.

  • It is important to study the method of reducingmetal release from SG tube from the viewpoint of reducing exposure.

Steam Generator (SG)

Ni releases from SG tube to primary water.

Primary

water

SG tube

58Ni

58Ni

(Alloy 690:

60Ni-30Cr-9Fe)

Release

Move to

reactor core.

Reactor Core

Nuclear fuel

Primary

water

58Ni

n(Neutron)

Ni is transformed

to radioactive Co.

58Co

Figure 1

Adhere to primary circuit structures.

4

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

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 release is decreasing during the early operation period because the barrier generates on the surface of SG tubes.

Ni Release from SG Tubes

Operation Cycle

Main Ni Release

Figure 2 Image of Ni Release from SG Tubes during Operation Cycle

5

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Reduction of Ni Release by Pre-Filming

on SG Tubes Surface

Pre-filming on the SG tube surface is expected to reduce

Ni release in the early operation period.

Pre-filmed barrier

Primary

water

SG tube

Ni Release

58Ni

Prevent

Ni migration.

Ni release reduction

by pre-filming

Operation Cycle

Figure 3 Image of Ni Release Reduction

6

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Commercial Application of Pre-Filming Method

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

Co Ion Concentration [ppb]

Higashidori applying

pre-filming method

Co concentration

decreased.

 EFPH (Equivalent Full Power Hours)

Figure 4 Process of Co Ion Concentration in Nuclear Reactor Water

7

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

R&D of Pre-Filming Method to Alloy 690

As different pre-filming method from below methods,

we researched oxidation at high temperature.

Released metal weight (mg/dm2)

Figure 5 Quantity of Released Metal during the Corrosion Test

( L. Guinard, EDF, Water Chemistry of Nuclear Reactor Systems 8, BNES, 2000)

8

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Possibility of Cr Oxide as Pre-Film Candidate

Cr oxide is stable

in primary water of PWR.

We considered that

Cr oxide film is suitable

as a barrier against

Ni release

from SG tubes

to primary water

during operation.

Stable region of Cr2O3

Potential (Volts vs SHE)

Primary water in PWR

pH

Figure 6 Potential-pH Diagram of Cr in 300℃ Water

9

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Cr Oxide on alloy 690

Alloy 690 contains 30% Cr.

We considered that

Cr oxide can be formed

on the surface of alloy 690

by control of oxygen

potential and temperature.

2Ni+O2=2NiO

2Fe+O2=2FeO

4/3Cr+O2=2/3Cr2O3

Partial Pressure of Oxygen

Cr is oxidized selectively

in this region.

Temperature

Figure 7 Relationship between Type of Oxide and Oxidation Condition

10

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Objective

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.

11

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Preparation of Test Specimen

Specimen : Alloy 690 sheet (60Ni-30Cr-10Fe)

Heat treatment

→Cold rolling

→Sampling test specimen

→Surface polishing

→Pre-filming

12

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Pre-Filming Method

  • Oxide film formation by oxygen at high temperature.

  • 2) H2O in H2 gas as oxygen source.

Electric furnace

Test specimen

H2O in H2 Gas

Quartz vessel

Figure 8 Pre-Filming Equipment

13

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Appearance of Oxide Film

Bare specimen

(Before pre-filming)

After pre-filming

Photo 1 Appearance of Specimen

14

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Cross Section of Oxide Film

Homogenous oxide film was formed

on the surface of the specimen.

Oxide film

Specimen

(Alloy 690)

1 μm

Photo 2 Crosse Section of Oxide Film (SEM)

15

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Composition of Oxide Film

Oxide film is mainly composed of Cr2O3.

MnCr2O4

Cr2O3

Specimen

100

120000

100000

80

Ni

O

Cr

80000

60

Proportion (%) of Constituent Metal Element

Relative Oxygen Intensity

Thickness of

oxide film

60000

40

40000

Fe

20

Mn

20000

0

0

0

500

1000

1500

2000

2500

Depth from Surface (nm)

Figure 9 Analysis of oxide film by SIMS

16

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Ni Release Test

on Various Thickness Oxide Film

17

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Ni Release Test Method

Platinum container

After immersion

in deionized water

at 320 ℃ for 1000 hrs,

Ni content in deionized

water was measured

by ICP.

Electric furnace

Deionized water

Test specimen

Figure 10 Ni Release Test Equipment

18

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

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.

Ni release decreased

Drastically

by pre-filming.

Figure 11 Effect of Oxide Film on Reduction of Ni Release

19

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Conclusion

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.

  • 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.

20

September 2009


Pre filming method of reducing metal release from alloy 690 for sg in primary water of pwr

Thank you for your attention.

21

September 2009


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