Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station
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Transcript of Measures for Reduction of Radiation Exposure at Higashidori Nuclear Power Station
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
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◎
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 化モノオキサイド
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
awa(
3)
Higa
shid
ori(
1)Coll
ecti
ve D
ose
Pers
on-
yrre
acto
r(
Sv
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)