All rights Reserved. Copyrights © 2004, Tohoku Electric Power Co., Inc.

Shigeru ItoShigeru ItoNuclear Power Dept.Nuclear Power Dept.

Tohoku Electric Power Co.Tohoku Electric Power Co.

Approach for reduction of Approach for reduction of radiation exposure at radiation exposure at

Tohoku Electric Power Co., Tohoku Electric Power Co., Inc.Inc.

p2Tohoku Electric Power Company Nuclear Power PlantsTohoku Electric Power Company Nuclear 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

p3Radiation sources that control plant dosesRadiation sources that control plant doses

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

Replacement-type sourcesReplacement-type sourcesRadioactive ions in reactor water are incorporated in the oxidized film generated on hot portion of the reactor piping system.・ PLR/CUW piping and components

Base metalB

ase m

etal

p4Measures to reduce crudMeasures to reduce crud 　（　（ Clean plant action No.1Clean 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 surface of system piping and equipment

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

p5Measures to reduce crudMeasures to reduce crud 　（　（ Clean plant action No.2Clean plant action No.2 ））

Purity control of test water Reduction of carried-in crud

During system test Thorough storage management

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

p6

0.0E+0

5.0E+8

1.0E+9

1.5E+9

2.0E+9

2.5E+9

EOC1 EOC2 EOC1 EOC2 EOC1 EOC2 EOC1 EOC2

A-1 O-1 O-2 O-3

LP

RM

Cru

d ra

dioa

ctiv

ity

(Bq/

LP

RM

)

Zn-65

Co-60

Fe-59

Co-58

Mn-54

Cr-51

Measures to reduce crudMeasures to reduce crud （（ LPRM Crud radioactivity)LPRM Crud radioactivity)

p7Water chemistry controlWater chemistry control （ （ Operation with extremely-low Fe high NiOperation with extremely-low Fe high Ni ））

Control of Ni/Fe ratioOperation with extremely-low

Fe high Ni

Behavior on fuel surface

Adhesion of radioactive material to piping

FeNi,Co

Co-60

Dense NiFe2O4

Sparse NiFe2O4

Fe

Ni,Co

Co-60Reduction

Incorporated Non incorporated

p8

Item ContentsEffect for

Co-60Higasidori

Unit 1Onagawa

Unit 1Onagawa

Unit 2Onagawa

Unit 3

Reactor water cleanup system (CUW) Reduction 2 ％ 2.8 ％ 3 ％ 3 ％

Adoption of low-Co materials

Reactor core internal structure

Low Concentration

● － ● ●

Feedwater heater ● ● ● ●

CR Pin and Roller ● ● ● ●

Fuel support spring ● ● ● ●

Material surfacetreatment

Electropolishing of primary looppiping

Suppresses the deposition

● － ● ●

Pre-filming of feedwaterheater tubes

Low Conc. ● － － －

Water chemistrycontrol

Fe/Ni control Low Conc. － ● － －

Ultra Low Fe High Ni control Supp. Dep. ● － ● ●

Dose rate on PLR piping at first periodic inspection (mSv/h) 0.06 0.49 0.10 0.06

Total Exposure dose during the first periodic inspection （ man-Sv ） 0.14 0.70 0.15 0.19

Exposure reduction measures at Exposure reduction measures at Tohoku Electric Power CompanyTohoku Electric Power Company

“Clean Plant Activities” have been carried out by utility and contractors since Onagawa unit 1 construction.

p9Exposure reduction measures at HigashidoriExposure reduction measures at Higashidori

Electropolishing

Pre-filming of feedwater heater tubes

Low-cobalt inconel

Remote handling and automation

Reliability improvement

Labor-saving in maintenance and checking

Operational improvement

Hollow fiber membrane filters for condensatecleanup system

Weather resistant steel and low-alloy steel forturbine system

Enhanced measures of storage during constructionand commissioning

Operation at ultra low Fe high Ni control

CUW pump at low temperature side

Permanent shieldingRadiation shielding

Anti-adhesion

Water chemistrycontrol

Improvement ofequipment

Sho

rten

ing

ofw

orki

ng h

ours

Red

ucti

on in

rad

iati

on le

vels

Material surfacetreatment

Cobalt reduction

Exp

osur

e re

duct

ion

Reactor core internal structure andfeedwater heater

CR Pin and roller

Fuel support spring

Clean Plant Activities

Crud reduction

Low-cobalt stainless steel

Alternative to stellite

Oxygen injection into feed water system

Automatic CRD substitution machine

Long life LPRM

Forged RPV

Improvement of heat insulator

p10Dose rate on PLR pipingDose rate on PLR piping

0

1

2

3

0 2 4 6 8 10 12 14 16 18 20Number of periodic inspections

Dos

e ra

te o

n P

LR

pip

ing

(mS

v/hr

)

Onagawa-1

Onagawa-2

Onagawa-3

Higashidori-1

Domestic BWRs

Chemical decontamination

p11Air dose rate in reactor containment vesselAir dose rate in reactor containment vessel

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

Higashidori Unit 1 First measurement

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 mSv/h

%

Onagawa Unit 3 First measurement

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 mSv/h

%

p12

0

1

2

3

4

5

6

7

8

9

10

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Col

lect

ive

Dos

e (m

am-S

v)

Onagawa

Higashidori

Finland

Germany

Japan

Mexico

Spain

Sweden

Switzerland

United States

Collective dose per reactor in BWRCollective dose per reactor in BWR

p13Rolling average collective dose per reactor in BWRRolling average collective dose per reactor in BWR

0

1

2

3

4

5

6

1996-1998 1997-1999 1998-2000 1999-2001 2000-2002 2001-2003 2002-2004 2003-2005 2004-2006 2005-2007 2006-2008

Year

Col

lect

ive

Dos

e (m

an-S

v)

Onagawa

Higashidori

Finland

Germany

Japan

Mexico

Spain

Sweden

Switzerland

United States