Measures for Reduction of Measures for Reduction of Radiation Exposure at Higashidori Radiation Exposure at Higashidori

Nuclear Power StationNuclear Power Station

Nuclear Power Dept.Nuclear Power Dept.

Tohoku Electric Power Co.Tohoku Electric Power Co.

Tohoku Electric Power CompanyNuclear Power Plants

Onagawa MWe Type Commercial

Operation

Unit-1(O-1) 524 BWR4 1984 Unit-2(O-2) 825 BWR5 1995Unit-3(O-3) 825 BWR5 2002

Higashidori MWe Type Commercial

Operation

Unit-1(A-1) 1100 BWR5 2005

ElectricitySupply area Onagawa NPS

Higashidori NPS

Tokyo

Exposure reduction measures at Higashidori Nuclear Power Station

◎

◎

◎

保守・点検作業の省力化

作業性の改善

Improvement of equipment

Crud reduction

Cobalt reduction

Material surface treatment

Water chemistry control

Anti-adhesion

Radiation shielding

Remote handling and automation

Reliability improvement

Labor-saving in maintenance and checking

Operational improvement

Adoption of hollow fiber membrane filters for condensate cleanup system

Adoption of weather resistant steel and low-alloy steel for turbine system

Enhanced measures of storage during construction and commissioning

Oxygen injection into feed water system

Adoption of low-cobalt stainless steel

Alternative to stellite

Adoption of low-cobalt Inconel

Electropolishing

Pre-filming of feedwater heater tubes

Operation at extremely low iron concentration

Reduction of CUW pump temperature

Installation of permanent shielding

Radiation sources that control plant doses Replacement-type sources

Radioactive ions in reactor water are incorporated in the oxidized film (oxidized scale) generated on hot portions of the reactor piping system.

・ PLR/ CUW piping and components

Radioactive crud in reactor water is deposited at horizontal portions and other portions where water flow is stagnant or slow.・ CRD flanges・ Filters・ Low-temperature pipe sections, such as 　 　 those in the RHR system・ Horizontal portions of PLR/CUW 　piping・ Nozzle sleeves

Deposition-type sources

Replacement-type sources

Oxidized film

Reactor water

Reactor water

Ion

Crud

Crud

Base metal

Base

meta

l

Measures to reduce crud(Clean plant action No. 1)

① Improvement of work environment

② Protection

③ Maintenance of inner surface cleanliness

Thorough storage management and maintenance of cleanliness on inner/outer surfaces of system piping and equipment

Prevention of carried-in dust by installing air guns and jet sprays at doorways

系統試験時Purity control of test water R

eduction of carried-in crud

During system test Thorough storage management

Measures to reduce crud(Clean plant action No. 2)

★

★

★

★

During start-up test

First cycle

Primary system cleanup operation Condensate/feedwater purification operation

Condensate/feedwater swing operation Cleanup of hot well

Cleanup of residual heat removal system Control of water treatment system

Suppression of reactor water activity concentration

Measures to reduce crud(Amount of crud generated in start-up test)

2.3～2.5

220～270

Performance of existing plants for reference Higashidori unit 1

230～320255340

2.6～3.32.72.7

Other BWR units Observed Target value

2.3～2.5

220～270

Onagawa units 2 and 3

230～320255340Amount of crud

generated in condensedwater

(in kg as Fe)

2.6～3.32.72.7Amount of

carried-in crud In feedwater (in kg as Fe)

Water chemistry control (operation with extremely-low iron and high nickel concentrations)

ニッケル鉄比制御 極低鉄運転Fe

配管

① 化ﾌｪﾗｲﾄ

Ni,Co

③ Co-60 溶出

② 放射化 ,蓄積

配管

Ni,Co

① 化ﾓﾉｵｷｻｲﾄﾞ

③ Co-60 蓄積せず、即溶出

② 放射化

Fe

配管への放射能付着 疎な NiFe 2O4

Co-60

取り込まれる

密なNiFe2O4Co-60

取り込まれないｸﾛﾑﾘｯﾁ

燃料表面での挙動Behavior on fuel surface

Adhesion of radioactive

material to piping

Control of nickel/iron ratio Operation with extremely low iron concentration

(1) Ferritizing

(2)Activation and accumulation

(3) Elution of Co-60

Piping Piping

(1) Mono-oxidization

(2) Activation

(3) Immediate elution of Co-60 without accumulation

Sparse NiFe2O4

Incorporated Cr-rich

Dense NiFe2O4

Non incorporated

Water chemistry control(Progress of feed water iron concentration and

reactor water nickel concentration)

1.00E- 03

1.00E- 02

1.00E- 01

1.00E+00

1.00E+01

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000

ＥＦＰＨ

[]

クラ

ッド

鉄濃

度ｐ

ｐｂ

A- 1 FW- Fe(C)

O- 2 FW- Fe(C)

O- 3 FW- Fe(C)

1.00E- 01

1.00E+00

1.00E+01

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000

ＥＦＰＨ

[]

ニッ

ケル

イオ

ン濃

度ｐ

ｐｂ

A-1 Rx-Ni(F)

O-2 Rx-NI(F)

O-3 Rx-Ni(F)

Material surface treatment

Pre-filming of feedwater heater tubes

15214mmAverage effective length

2780Total number of heat transfer tubes

2110m / unit 2Heat transfer area

15.88×1.0mm

SUS304TB-S equivalent

Specifications of second high-pressure feedwater heater

15214mm

2780

15.88×1.0mm

【

Thermal treatment of heat transfer tubes is performed in a “hydrogen + steam” atmosphere. (conventionally, performed in a hydrogen atmosphere)

Suppression of ion elution 【 Purpose 】

【 Steam oxidation treatment 】

Reactor vessel

Condenser

Turbine

復水ろ過装置

復水脱塩装置

Low-pressure feedwater heater

Reactor recirculation pump

Condensate filtration unit

復水脱塩装置

Condensate demineralizer

Filtration demineralizer of reactor water cleanup system

Second high-pressure feedwater heater

First high-pressure feedwater heater

(first to fourth)

Material

Outer diameter x thickness

Material surface treatment (Progress of Cr ion concentration in feedwater)

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 2000 4000 6000 8000 10000 12000

EFPH（～第１サイクル末）

[ppb]

濃度

A-1

O-2

O-3

Effective full power hours (until the end of the first cycle)

Material surface treatment(Progress of Co-60 activity concentration in reactor

water)

0.0E+00

1.0E+00

2.0E+00

3.0E+00

4.0E+00

5.0E+00

0 2000 4000 6000 8000 10000 12000

EFPH（～第１サイクル末）

[Bq/cm3]

放射

能濃

度

A-1

O-2

O-3

Effective full power hours (until the end of the first cycle)

Material surface treatment(Progress of Co ion concentration in reactor water)

1.00E- 02

1.00E- 01

0 2000 4000 6000 8000 10000 12000

ＥＦＰＨ

[]

コバル

トイオ

ン濃度

ｐｐｂ

A-1 Rx-Co(F)

O-2 Rx-Co(F)

O-3 Rx-Co(F)

Effective full power hours

Effect of radiation exposure reduction measures (No. 1)

Dose rate on PLR pipingDose rate on PLR piping

Chemical decontamination performed

Domestic BWRs

Number of periodic inspections

Effect of radiation exposure reduction measures (No. 2)(Air dose rate in reactor containment vessel)

0.0

0.8

0.001

35.2

0.005

34.3

0.01

18.5

0.02

11.2

0.05

0.0

0.1

0.0

0.2

0.0

0.50 mS v/ h

%

:0.01 mS v/ h面 積 線 量 率 :0.01 mS v/ h幾 何 平 均 線 量 率 n=48

0.0

0.0

0.001

12.2

0.005

14.8

0.01

18.6

0.02

29.7

0.05

14.8

0.1

9.4

0.2

0.3

0.50 mS v/ h

%

:0.04 mS v/ h面 積 線 量 率 :0.03 mS v/ h幾 何 平 均 線 量 率 n=48

A-1 First measurement O-3 First measurement

Four days after reactor shutdown On the floor of recirculation pump motor

Geometrically averaged dose rate: 0.01 mSv/h n=48

Area dose rate: 0.01 mSv Geometrically averaged dose rate: 0.03 mSv/h n=48

Area dose rate: 0.04 mSv

SummarySummary

Surface oxidation of feedwater heater tubes was effective in suppressing carried-in Cr ions.

Suppression of carried-in Cr ions was effective in suppressing the increase of Co-60 activity concentration in the reactor water.

Dose rate on PLR piping was suppressed successfully. Air dose rate in the dry well was suppressed successfully. Total radiation exposure during periodic inspection was

reduced successfully.

Collective　Dose　in　BWR（ 2005-2007　Average ）

0.10

0.58

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Onag

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3)

Higa

shid

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Pers

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