approach for reduction of radiation exposure at tohoku electric power co., inc
DESCRIPTION
Approach for reduction of radiation exposure at Tohoku Electric Power Co., Inc. Shigeru Ito Nuclear Power Dept. Tohoku Electric Power Co. Higashidori NPS. Onagawa NPS. Tokyo. Tohoku Electric Power Company Nuclear Power Plants. Electricity Supply area. Onagawa - PowerPoint PPT PresentationTRANSCRIPT
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