reduction of radiation exposure at aged bwr plants by water chemistry
DESCRIPTION
Reduction of Radiation Exposure at Aged BWR Plants by Water Chemistry. Nov.13 2008 Hidehiro Urata and Kenji Yamazaki Toshiba Corporation. 1/23. Content. Background and Introduction Water Chemistry Approach and Results Conclusion. Roles of Water Chemistry at Operating BWRs. - PowerPoint PPT PresentationTRANSCRIPT
1
Copyright 2008, Toshiba Corporation.CDCC-2008-100442PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Reduction of Radiation Exposure at Aged BWR Plants by Water Chemistry
Nov.13 2008
Hidehiro Urata and Kenji YamazakiToshiba Corporation
1/23
2/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Content
1. Background and Introduction2. Water Chemistry Approach and
Results3. Conclusion
3/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Roles of Water Chemistry at Operating BWRs
Increase of radiation level due to ageing and up-rating of plant and higher burn-up fuel implementation is a concern regarding roles of water chemistry at operating nuclear power plants.
Main purposes of water chemistry
– Radiation level reduction
• Improvement of work environment
• Reduction of radwaste
– Improvement of safe and reliable operation
• Structural material integrity
• Fuel integrity
Background and Introduction
4/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
At aged BWR plants, radiation dose reduction for maintenance repair works, and mitigation of SCC are most important roles of water chemistry
Optimum water chemistry
Radiation reduction
Secure and Reliable Operation
Fuel material integrity
Structural material integrity
Radwaste reduction
Radiation dose reduction
Background and Introduction
5/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
<0.5
0.5-
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1.5-
2.0
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3.5
3.5-
4.0
>4.0
J apan
02468
10
12
J apanUSA
Japan:2000.12-2003USA :2005.1
Median:0.89 mSv/h
mSv/h at PLR Piping
Num
ber o
f pla
nts
Median:1.55 mSv/h
From Y. Hayashida 2007 ISOE Asian Symposium, Seoul Korea Sep 12-14 2007
Ra
dia
tion
Exp
osu
re (
Pe
rson
S
v)
Outage (days)
Oversea BWR( Good case)
Japanese BWR
A: Reduction of works and Improvement of works
B: Improvement of radiation environment
BA
Rationale Exposure Reduction by A+B
C: Possible effects of up-rating and higher burn-up
Importance of radiation level reduction
Background and Introduction
6/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Water chemistry for control of recontamination under low ECPWater chemistry for control of recontamination under low ECP
Reduction of dose rate
Hydrogen Water Chemistry
Dos
e ra
te
Dose rate increase
Water chemistry modification
Operation
Objective
ChemistryRemedy
Mitigation of SCC
Modification of oxideIncrease of
Co-60 Conc.
Chemical Decontamination
Influence on Dose
Rate
Factors
Recontamination
Decon.
Operation
Dos
e ra
te
Factors affecting radiation level buildup at aged BWR plants
Background and Introduction
7/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Low DF Medium DF High DF
DF ( Decontamination Factor) Dose before decon/after decon)
Re-
con
tam
inat
ion
Rat
e
(arb
itra
ry u
nit
)
Re-contamination after chemical decontamination depends on “ Decontamination Factor”.
Background and Introduction
Medium Decontamination factor is preferable but not always obtained. Mechanism of the dependence should be evaluated.
8/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Water Chemistry Approach and Result
1. Issues to be evaluated(1) Dependence of Recontamination on Decon.
Factor(2) Water Chemistry for suppression of radiatio
n level build up after water chemistry modification and chemical decontamination
2. Approach(1)Experimental approach by using BWR simul
ation loop(2)Parameters
– Low ECP (ex. HWC)– TiO2, Zn (countermeasures)
9/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Water Chemistry Approach and Results
Experimental (1) Procedure
Specimen preparation
Pre-filming
Chemical decontamination
Co-60 deposition test
Measurement/Analysis
(TiO2 treatment)
Reduction (Oxalic acid)
Oxidation (ozone)
Reduction (Oxalic acid)
HClRepetition
Oxalic acid: 2000ppm, 95COzone: 3ppm,80CHydrochloric acid : 2mol/l,80C
10/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
40mm
10mm
0.3mmt
SUS316L
High Pressure Pump
Pump
Heat Ex.
PreHeater
Cooler
H2
N2
Air
DH
H2O2 Co-60
ZnDO
Con
Ion Ex.Resin
ChemistryMonitor
Filter
downstreamtest section.
upstreamtest section.
Zn Injection Line
downstreamtest section.
upstreamtest section.
High Pressure Pump
Pump
Heat Ex.
PreHeater
Cooler
H2
N2
Air
DH
H2O2 Co-60
ZnDO
Con
Ion Ex.Resin
ChemistryMonitor
Filter
downstreamtest section.
upstreamtest section.
Zn Injection Line
downstreamtest section.
upstreamtest section.
Water Chemistry Approach and Results
Experimental (2) Co-60 deposition test loop
11/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
HWC
m-HWC
• The V-shape dependency was reproduced.• Dependency is much strong under HWC.• The V-shape dependency was reproduced.• Dependency is much strong under HWC.
Co
-60
W/O Zn
W/O TiO2
Water Chemistry Approach and Results
Results (1) Dependence on decon. factor
0.0
0.5
1.0
1.5
2.0
Low DF Medium DF High DF
On
Sta
inle
ss s
teel
spe
cim
en HWC
FW DH>1.0ppm
m-HWC
FW DH<0.5ppm
12/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Low DF Medium DF High DF
After decon
Oxide removed unevenly
No residual oxide
No residual oxide
But rough
After Co-60 test Large oxide
evolved infrequently
Smallest Oxide and uniform
Large oxide evolved
No decon
Oxide deposited uniformly
Not changed
Water Chemistry Approach and Results
Results (1) Dependence on decon. factor
13/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Low DF Medium DF High DF
After decon
After Co-60 test Residual oxide causes the
irregular oxide growth and enhances Co-60 deposition and migration
Oxide film uniformly formed suppress further corrosion and Co-60 deposition
Rough surfaces causes the increase of surface area and oxide growth and enhance the Co-60 deposition
: Cr2O3: 60Co: Fe2O3: NiFe2O4
Chemical decontamination with adequate control is important to suppress re-contamination.
Chemical decontamination with adequate control is important to suppress re-contamination.
Water Chemistry Approach and Results
Results (1) Dependence on decon. factor
14/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
• Zinc is effective for suppression of recontamination under both HWC and m-HWC, even after inadequate decon.
• Zinc is effective for suppression of recontamination under both HWC and m-HWC, even after inadequate decon.
Water Chemistry Approach and Results
Co-60
0.0
0.5
1.0
1.5
2.0
Low DF Medium DF High DF
On stainless steel specimen)
HWC- W/O ZnHWC- With Znm-HWC-W/O Znm-HWC- With Zn
Results (2) Control by water chemistry - Zn -
15/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Low DF Medium DF High DF
After decon
After Co-60 test
W/O Zn
With Zn
Oxides are formed uniformly and closely packed by zinc injection.
Water Chemistry Approach and Results
Results (2) Control by water chemistry - Zn -
16/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
• TiO2 can suppress Co-60 deposition to very low level and has synergy effect with Zn.
• TiO2 can suppress Co-60 deposition to very low level and has synergy effect with Zn.
Water Chemistry Approach and Results
Co-60
*
0. 0
0. 5
1. 0
1. 5
2. 0
DF低 DF最適 DF過剰
Ref . ( )抑制対策無し
酸化チタン付着
酸化チタン付着後亜鉛注入
0.0
0.5
1.0
1.5
2.0
Low DF Medium DF High DF
On
Sta
inle
ss s
teel
spe
cim
enRef No treatment
TiO2 deposition
TiO2 deposition and Zn
Results (3) Control by water chemistry - TiO2 -
17/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Low DF Medium DF High DF Remarks
Ref.No water chemistry
counter measure
TiO2
TiO2 covers surfaces and
smaller corrosion oxides are produced.
TiO2 + Zn
Water Chemistry Approach and Results
Results (3) Control by water chemistry - TiO2 -
18/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
HWC + Zn M-HWC and TiO2
Surface morphology
Suppression effect on Co-60
deposition
Zn prevents oxide film growth.
ZnCr2O4 is formed in the inner oxide layer and prevent Co-60 migration.
(1)TiO2 layer may block the migration of Co-60 and prevent CoFe2O4 formation
(2)Radicals produced by TiO2 may oxidize Fe2+ to Fe3+ and prevent ferrite formation.
: 60Co: Fe2O3: NiFe2O4 : Cr2O3: TiO2 :Z nCr2O4
Water Chemistry Approach and Results
Results (3) Control by water chemistry - TiO2 -
19/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
• Before ferrite (CoFe2O4) formation, Fe2+ can be oxidized to Fe3+ and Fe2O3 is formed.
• Further discussion is needed to establish the mechanism for Co-60 deposition prevention.
(Cathodic reaction)2O2 + 8H+ +8e- -> 4H2O
TiO2
Heat
Excitation
h+
e-
SS
H2O + h+-> OH ・ + H+
OH- + h+ -> OH ・
O2 + e- -> O2-
(Anodic reaction)Fe ->Fe2+ + 2e-
3Fe2+ + 4H2O ->Fe3O4 + 8H+ + 8e-
SS
Possible explanation on role of TiO2
Water Chemistry Approach and Results
20/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
-0.4
-0.2
0
0.2
0 50 100 150 200 250TiO2 amount / g/cm2
ECP
/ V v
s. SH
E
○:<50W/cm2
□:50~200W/cm2
△ :>200W/cm2
Co
rro
sio
n P
ote
nti
al (
EC
P)
Current
Oxidation ofSteel
Reduction of Oxygen
Reduction of ECP
Phto-electric Current
TiO2 for SCC Mitigation
K. Takamori, International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, Aug.14-18 2005 Snowbird Utah
TiO2 technology for BWR SCC mitigation is developed by Toshiba and TEPCO.
ECP of stainless steel is decreased by TiO2 with photon, or without photon under low-HWC chemistry.
21/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Conclusion - 1
Effects of Decontamination factor on re-contamination
1. The V-shape relationship between Co-60 deposition and DF could be clearly seen, especially in case of HWC condition.
2. In case of low DF, poorly protective residual oxides accelerate the re-contamination.
3. Under HWC condition, recontamination with inadequate DF is accelerated and thus control of decontamination is particularly important.
22/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008
Water chemistry control
1. Zn injection can effectively suppress Co-60 deposition regardless of DF.
2. TiO2 can effectively suppress Co-60 deposition regardless of DF.
3. TiO2 technology is a promising candidate for simultaneous accomplishment of SCC mitigation and radiation exposure reduction.
4. Synergy effect of TiO2 and Zn can be seen.
Conclusion - 2
23/23Copyright 2008, Toshiba Corporation.CDCC-2008-100442, PSN-2008-1296
2008 ISOE International ALARA Symposium, Tsuruga Japan,13-14 Nov., 2008