Dose Rate Reduction Experiences of Piping Replacement at

Fukushima Daiichi Unit 4 and 5

Atsutoshi MakihiraALALA Mini-Workshop

Nov.9, 2005 Hamaoka NPS

Removal Work Scope of Equipment and Floor Drain Piping

4(BWR4)

Schedule

Unit

Work

Nov.22, 2002 ～ May 21,2003

Removal:415mInstallation:556m

Reactor Building Suppression Pool Area

West East

Reactor Building Suppression Pool Area

West East

5(BWR4)Jan.20, 2003 ～ Sep.26, 2003

：： Drain PipingDrain Piping：：Working AreaWorking Area

Removal:446mInstallation:446m

Dose Rate at Piping Before Replacement Work

Unit 4Unit 4

West 東側

Contact (max)Contact (max)３．５０３．５０mSv/hmSv/hField (max)Field (max)１．３０１．３０mSv/hmSv/h

RHR pipingRHR piping

Work areaWork area

East East

ContactContact（（projectionprojection））６．００６．００mSv/hmSv/h

FiledFiled（（projectionprojection））２．４０２．４０mSv/hmSv/h

Unit 5Unit 5

RHR and Drain Piping at West Part of Suppression Pool Area

Unit 4Unit 4

West East

RHR PipingRHR Piping

Drain PipingDrain Piping

(1)Filed Dose Rate and Estimated Working Time per Person-Day

(2) Estimated Working Time per Person with Annual Dose Limit <20mSv

Unit 4Unit 4

Exposure Doseat 2002

Remaining Dose at 2002

Filed Dose Rate（Geometric Ave.）

Estimated Working Hours

Estimated Working Days(4 hours/day)

Max：８．６４mSv １１．３６mSv

Min：０．００mSv ２０．００mSv

０．１５１mSv/h

7575

133133

1919

約３３日約３３日

Unit 4Unit 4 １．３０mSv/h 0.9mSv/person-day ４１分４１分

Field Dose Rate Planned Exposure Estimated Time

41min.

33

Unit 5Unit 5 ２．４０mSv/h 0.9mSv/person-day

Unit 5Unit 5Max：８．６４mSv １０．３６ mSv

Min：０．００mSv ２０．００mSv

０．３００mSv/h

3434

6666

88

約１６日約１６日16

２２分２２分22min.

Estimated Working Time for the Task

1. Work Schedule Conditioning

Proposals for Improvement

Unit 4• Increase of field dose rate (～1.3mSv/h) at west

area because RHR is used for intermediate shutdown

• Shortage of temporary shielding materials for other high radiation work– Start working at east area– Work at west area after installing temporary shielding

Unit 5• Installing scaffold and temporary shielding for the

task during operation when RHR dose rate is low

Proposals for Improvement

2. FlushingUnit 4• High dose rate at RHR-4, RHR-41, RHR-23

because of RHR operation in shutdown– Flushing RHR-4, RHR-41 by using RHR(C) pump which

circulates water in suppression pool– Flushing RHR-23 by opening MO-23 valve when RHR(C)

pump runningUnit 5• High dose rate at RHR-3, RHR-7, RHR-27 because

of RHR operation in shutdown– Flushing by using RHR pumps which circulates water in

suppression pool

RHR-Hx(B)

ＤＡ Ｂ

Ｂ Ａ

ＰＬＲポンプ ＰＬＲポンプ

PLR-5 PLR-2

ＲＨＲー２３ ＲＨＲー３

MO１５Ｃ

MO１５Ａ

MO１３Ａ

MO６５B

MO１５B

MO１５D

MO３９Ａ

MO３４Ａ

RHR-22 RHR-21RHR-1

MO１３Ｂ

MO１３Ｄ

RHR-2

MO２５Ａ

MO２７Ａ

MO２０

MO２７Ｂ

MO６６B

RHRRHR--4141

MO１２B

RHR-3

RHR-3

RHR-55RHR-53

RHR-55

RHR-1RHR-21

RHR-7

PLR-1PLR-4RHR-23

RHR-41

RHR-27

RHR-23

RHRRHR--2323

RHR-53

MO３８Ａ

MO３９Ｂ

MO３８Ｂ

RH

R-2

3R

HR

-26

RH

R-2

4

RH

R-3

RH

R-4

RH

R-6

RH

R-3

RHR-53 RH

R-3

RHR-7RHR-8

RHR-27

RHR-28

MO67MO57RHR-52

RH

R-4

4

RHR-44

RHR-47 RHR-51

RWへ

RHRRHR--33

Ｃ

MO１３Ｃ

MO６５Ａ

MO１２Ａ

MO３４Ｂ

：Flushing line

：High Dose Pipng

RPV

MO６６Ａ

Ｓ／Ｃ

MO２５Ｂ

RHR-Hx(A)

Ｃ

非常時熱負荷運転により、非常時熱負荷運転により、線量当量率上昇！！線量当量率上昇！！

残留熱除去運転により、残留熱除去運転により、線量当量率上昇！！線量当量率上昇！！Flushing by use of RHR(C)

pumps which circulate system water

Open VMO-20 valve when circulate system water

2.Flushing(example)

Proposals for Improvement

Unit 4Unit 4

3.Temporary Shielding

•Installing temporary shielding at high radiation piping after RHR flushing

［Unit 5］

［Unit 4］

•Installing temporary shielding at projected high radiation piping during operation•Installing temporary shielding at high radiation piping after RHR flushing

RW-1C（Lead covered with SS）

Equipment Drain（ Lead covered with

SS ）

RW-209（ lead blanket ）

［Installing during operation］RHR-27（ lead blanket ）

［Installing after flushing］RHR-23（lead blanket）

Proposals for Improvement

• Reactor water drained because of RRS replacement work

• High dose rate was projected at RHR-Hx, RHR pumps, suppression pool area

Proposals for Improvement4.Blow Down Water Treatment at Unit 4

R/B B floor suppression pool area R/B B floor suppression pool area R/B 1R/B 1stst floorfloor RHRRHR--HxHx roomroom R/B B floorR/B B floor RHR pump areaRHR pump area

• Planned reactor water blow down twice• First blow down water drained to

suppression pool so as to second blow down which contains higher activity can be transferred to radwaste (because of capacity)

• Removing crud deposited on RPV bottom by temporary pump and filters

• Fill up RHR-44 with water before blow down for preventing crud deposition

4.Blow Down Water Treatment at Unit 4

Proposals for Improvement

5.Remote Monitoring

２ ０．５７

１ ０．５７

Dose indicator

Wireless APDWireless APD

Remote monitoring of individual dose

TransmittanceTransmittance

Anorak

Protective cloths

Under wear

worker

Ａ

Ｐ

Ｄ

Worker

Data transmittance

ＡＰＤＩＡＰＤＩ

。

Dose indicator

Individual dose can bemonitored even on cloths

［Unit 5］ ［Unit 4 &5］

ＡＰＤＩＡＰＤＩ

Proposals for Improvement

RHR-27

N

EW

S

ＣＵＷ－１９ＣＵＷ－１９

ＲＷ－１ＣＲＷ－１Ｃ

Equipment Drain（vertical）

Equipment Drain

（horizontal）

Vertical Piping

Horizontal Piping

•CUW-19 Contact dose rate: 36.0%

•RW-1C Contact dose rate: 44.4%

•Field dose rate:20.0%

Results for Improvement

•Equipment drain piping

•Contact:66.7%

•Field:88.7%

Dose Rate Reduction Effectiveness after Installing Temporary Shielding

•RW-209 pipings

•Contact:66.7%

•Field:86.7%

Unit 4Unit 4