Measures for Reduction of
Radiation Exposure at Higashidori
Nuclear Power Station
Nuclear Power Dept.
Tohoku Electric Power Co.
Tohoku Electric Power Company
Nuclear Power Plants
Higashidori NPS
Electricity
Supply area
Onagawa NPS
Tokyo
Onagawa
MWe
Unit-1(O-1) 524
Unit-2(O-2) 825
Unit-3(O-3) 825
Type
BWR4
BWR5
BWR5
Higashidori
Commercial
Operation
1984
1995
2002
MWe
Type
Unit-1(A-1) 1100 BWR5
Commercial
Operation
2005
Exposure reduction measures at Higashidori
Nuclear Power Station
Remote handling and automation
Improvement
of equipment
Reliability improvement
Labor-saving
in maintenance and checking
保守・点検作業の省力化
Operational
improvement
作業性の改善
◎
Adoption of hollow fiber membrane filters for condensate cleanup system
Crud
reduction
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
Cobalt
reduction
Adoption of low-cobalt Inconel
◎
◎
Alternative to stellite
Electropolishing
Material
surface
treatment
Pre-filming of feedwater heater tubes
Water chemistry
control
Operation at extremely low iron concentration
Anti-adhesion
Reduction of CUW pump temperature
Radiation
shielding
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.
Oxidized film
Base metal
・PLR/ CUW piping and components
Reactor water
Ion
Crud
Replacement-type sources
Reactor water
Crud
Base metal
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
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
Measures to reduce crud
(Clean plant action No. 2)
During
system test
系統試験時
Thorough storage management ★
During start-up test
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
First cycle
Reduction of carried-in crud
Purity control of test water
Suppression of reactor water activity
concentration
Measures to reduce crud
(Amount of crud generated in start-up test)
Higashidori unit 1
Target value Observed
Performance of existing plants for reference
Onagawa units 2 and 3
Other BWR units
Amount of crud
generated in
condensedwater
(in kg as Fe)
340
255
220～270
230～320
Amount of
carried-in crud
In feedwater
(in kg as Fe)
2.7
2.7
2.3～2.5
2.6～3.3
Water chemistry control (operation with extremely-low
iron and high nickel concentrations)
Control
of nickel/iron ratio
ニッケル鉄比制御
Operation with extremely low
iron concentration
極低鉄運転
Fe
燃料表面on
Behavior
fuel
surface
での挙動
Fe
(1)
Ferritizing
①ﾌｪﾗｲﾄ化
(1)
Mono-oxidization
①ﾓﾉｵｷｻｲﾄﾞ化
(2)Activation and accumulation
②放射化
(3) Elution of Co-60
③
Co-60
, 蓄積
Ni,Co
Ni,Co
(2)
Activation
②放射化
溶出
(3)
of Co③ Immediate
Co-60 elution
蓄積
60 without accumulation
せず、即溶出
配管
Piping
Adhesion of
配管への
radioactive
material
to piping
放射能付着
配管
Piping
Co-60
Sparse
NiFe22OO4 4
疎な NiFe
Incorporated
取り込まれる
Co-60
ｸﾛﾑﾘｯﾁ
Cr-rich
Dense
NiFe22OO
密な NiFe
44
Non
incorporated
取り込まれない
Water chemistry control
(Progress of feed water iron concentration and
reactor water nickel concentration)
1.00E+01
A -1 FW -Fe(C )
O -2 FW -Fe(C )
クラッド鉄濃度[ｐｐｂ]
1.00E+00
O -3 FW -Fe(C )
1.00E-01
1.00E-02
1.00E-03
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
22000
24000
ＥＦ
ＰＨ
1.00E+01
A -1 R x-N i(F )
ニッケルイオン濃度[ｐｐｂ]
O -2 R x-N I(F )
O -3 R x-N i(F )
1.00E+00
1.00E-01
0
2000
4000
6000
8000
10000
12000
ＥＦ
ＰＨ
14000
16000
18000
20000
22000
24000
Material surface treatment
 Pre-filming of feedwater heater tubes
Specifications of second high-pressure feedwater heater
Material
Second high-pressure
feedwater heater
Reactor
vessel
Outer diameter x thickness
15.88×1.0mm
Average effective length
15214mm
Turbine
First high-pressure feedwater heater
Condenser
Total number of heat transfer tubes
Heat transfer area
Low-pressure
feedwater heater
(first to fourth)
Reactor recirculation pump
Filtration demineralizer of
reactor water cleanup system
復水
Condensate
脱塩
demineralizer
装置
SUS304TB-S equivalent
復水
Condensate
ろ過
filtration unit
装置
2780
2
2110m / unit
【Steam oxidation treatment】
Thermal treatment of heat transfer tubes is performed
in a “hydrogen + steam” atmosphere.
(conventionally, performed in a hydrogen atmosphere)
【【Purpose】
Suppression of ion elution
Material surface treatment
(Progress of Cr ion concentration in feedwater)
1.0E+00
A -1
O -2
O -3
濃度[ ppb]
1.0E-01
1.0E-02
1.0E-03
1.0E-04
0
2000
4000
6000
8000
10000
Effective full power EFPH（
hours～第１
(until
end of the first cycle)
サイthe
ク ル末）
12000
Material surface treatment
(Progress of Co-60 activity concentration in reactor
water)
5.0E+00
A -1
O -2
O -3
放射能濃度[ Bq/cm3]
4.0E+00
3.0E+00
2.0E+00
1.0E+00
0.0E+00
0
2000
4000
6000
8000
Effective full power
hours
(untilサイ
theクend
of the first cycle)
EFPH（
～第１
ル末）
10000
12000
Material surface treatment
(Progress of Co ion concentration in reactor water)
1.00E-01
A -1 R x-C o(F)
O -2 R x-C o(F)
コバルト
イオン濃度[ｐ
ｐ
ｂ
]
O -3 R x-C o(F)
1.00E-02
0
2000
4000
6000
Effective fullＥＦ
power
ＰＨ hours
8000
10000
12000
Effect of radiation exposure reduction measures (No. 1)
 Dose 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
0.001
0.8
0.005
35.2
0.01
34.3
0.02
18.5
Geometrically
averaged dose rate: 0.01mSv/h
mSv/h
幾何平均線量率:0.01
n=48
n=48
0.05
11.2
0.1
0.0
0.2
0.0
0.50 mSv/h
0.0
%
Area
dose rate: 0.01 mSvmSv/h
面積線量率:0.01
A-1 First measurement
0.0
0.001
0.0
0.005
12.2
0.01
14.8
0.02
18.6
0.05
29.7
0.1
14.8
Geometrically averaged dose rate: 0.03 mSv/h
幾何平均線量率:0.03 mSv/h
n=48 n=48
0.2
9.4
0.50 mSv/h
0.3
%
Area dose rate: 0.04 mSv
面積線量率:0.04
mSv/h
O-3 First measurement
Four days after reactor shutdown
On the floor of recirculation pump motor
Summary
 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.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.58
0.5
0.0
Higashidori(1)
0.10
Onagawa(3)
Collective Dose（Person-Ｓｖ／（yr・reactor））
Collective Dose in BWR
（2005-2007 Average）