ONAGAWA NPS ONAGAWA NPS Dose ReductionDose Reduction

October 12, 2006　TOHOKU Electric Power Co.,Inc.

Location Miyagi Prefecture

Onagawa NPS

SpecificationsOnagawa NPS Unit 1 Unit 2 Unit 3

Commercial Operation start 1984

Jun.

1995Jul.

2002

Jan.

Reactor type BWR4 BWR5 BWR5

Electric Power(MWe) 524 825 825

Condensate Treatment CFD & CD CF & CD

RWCU(% of Feed Water) 2.8 3.0 3.0

Annual Average Dose

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Year

mSv/Y

Unit 1

Operation started

Unit2

Operation started

Unit3

Operation started

Average of

BWRs in Japan

Annual Collective Dose

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Year

person

Sv/Y

・

Unit 1

Operation started

Unit2

Operation started

　　　　　Unit3

Operation started

Onagawa NPS Outage Dose

0.01.02.03.04.05.0

#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15 #16

person

Sv

・

0.01.02.03.04.05.0

#1 #2 #3 #4 #5 #6 #7 - - - - - - - - -

person

Sv

・

0.01.02.03.04.05.0

#1 #2 #3 - - - - - - - - - - - - -

person

Sv

・

Unit 1

Unit 2

Unit 3

Our Dose Reduction Strategy

1. Measures on the design stage

2. Clean-Plant operations on the construction stage and the test run operation stage

3. Continuous Dose Reduction

Dose　 Reduction

Reducing Radiation

Shortening exposure time

CRUD　 reduction

Improvement of Working environment

Improvement of equipment Automation/Remote operation

Use of Low-Co materials

1.Dose Reduction Measures on the design stage

CRUD Generation Control

Shielding Optimization

Improvement of Water Treatment Capability

　 2.Clean-Plant operations on the construction

stage and the test run operation stage

　・　 Keep Work area clean

　・　 Use wrapping against construction dust

　・　 Introduce Water chemistry technologies

　 3. Continuous Dose Reduction

3-1. Management of Workers’ Dose Data

3-2. Monitoring of Dust & Radiation

3-3. Water Chemistry Technologies

3-4. Dose Reduction at Outages

3-1.Management of Workers’ Dose Data

Alarm Personnel Dosimeter

Work Code Input Device

Work Code

Work Code Work Code & Dose data & Dose data

Controlled area

Work Code and Dose data

3-2.Monitoring of Dust & Radiation

3-3 ． Water chemistry

Dose rate of PLR piping of our plants are remarkably low compared to other plants.

0

1

2

3

0 2 4 6 8 10 12 14 16 18Annual Outage

Dos

e R

ate

at R

ecir

cula

tion

Pip

ing

(mSv

/hr)

Unit-1Unit-2Unit-3

Typical Japanese BWRs

3-4. Dose Reduction at Outages

•　 Education program for foremen during Outage

•　 Holding “HP work Schedule meetings” periodically

•　 HP Patrol during Outage frequently

•　 Posting up the Detailed Radiation Map of D/W area

Special issue in 2005

We performed special activities for

1.　 Unit 3 Fuel Leakage …Our first experience

2.　 Earth Quake on Aug.16,2005

1 ． Unit 3 Fuel Leakage

On Jul.2,2005 We first experienced fuel leakage at Unit 3 resulted in the increasing value of OG monitor .

Main measures we took were as follows :

Surveillance of OG

Prevention from intake of I-131

2 ． Earth Quake (Aug.16,2005)

Seismic Center

Magnitude : 7.2

Depth : 42Km approx.

All Units in Operation were shut down automatically .

SCRAM triggers are set to

200 GAL: horizontal earthquake movement,

100 GAL : vertical .

2-1.Influence to electricity in 2005

0

500

1000

38443 38473.41 38503.82 38534.23 38564.64 38595.05 38625.46 38655.87 38686.28 38716.69 38747.1 38777.51 38807.92

0

500

1000

38443 38473.41 38503.82 38534.23 38564.64 38595.05 38625.46 38655.87 38686.28 38716.69 38747.1 38777.51 38807.92

0

500

1000

38443 38473.4 38503.8 38534.2 38564.6 38595 38625.4 38655.8 38686.2 38716.6 38747 38777.4 38807.8

Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar.

Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar.

Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar.

Unit 1

Unit 2

Unit 3

MW

eM

We

MW

e

Earth Quake　Aug.16

Earth Quake　Aug.16

Earth Quake　Aug.16

#3

#17

#7

2-2.Comparison of Outage Dose of Unit 3 before / after the Earth Quake

0.0

0.1

0.2

0.3

0.4

0.5

#２ #３

ma

n ・S

v

MSIV

RPV

PLR

SRV

CRD

ＩＳＩotherｓ

Before After

Jun.10/2004

　　　　　 ~　Oct.5/2004

Sep.27/2005

　　　　　 ~　Apr.18/2006

Recent Annual Average Dose

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2001 2002 2003 2004 2005

Year

mSv/Y Average of

BWRs in Japan

Unit3

Operation started

We keep going to make efforts for ALARA!