Seawater Intrusion Event Consequence Assessment of ...
Seawater Intrusion Event ConsequenceAssessment of Vessel & Core Internals, Hamaoka Unit 5 Kouhei Kurono Maintenance Management Section, Maintenance Dept. Hamaoka Nuclear Power Station June 15, 2016
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
1
01
Overview of Facilities Unit 1
1,593
Type of Primary Containment Vessel
Generating output (MWe)
Unit 3
BWR-4
Reactor type Thermal power (MWt)
Unit 2
BWR-5 2,436
Mark-1 (540)
Unit 4
3,293
ABWR 3,293
Mark-1 modified (840)
1,100
Total power output (MWe)
Unit 5
1,137
3,926 RCCV 1,380
3,617
Construction commencement
March 1971
March 1974
November 1982
February 1989
March 1999
Operation commencement
March 1976
November 1978
August 1987
September 1993
January 2005
In outage (since November 29, 2010)
In outage* (since January 25, 2012
In outage* (since March 22, 2012)
Current status
Decommissioning (Operation terminated on January 30, 2009
Safety improvement measures being implemented
*All Units at the Hamaoka NPS halted by accepting the request from Japanese Government. (Unit-4: May 13, 2011 Unit-5: May 14, 2011) Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
2
02-1
Outline of Event
Tubes of the steam chest of the main condenser (A-1) were damaged by the jet flow, and seawater flowed into the reactor facilities. (During the process of achieving cold shutdown following the shutdown of Hamaoka Unit 5 on May 14, 2011) The jet flow were caused by dropout of the blind flange of the minimum flow pipe of the motordriven feed water pump.
Ca.90cm Ca.70cm
Ca. 14cm
Main condenser
The side view of main condenser
Damaged by jet flow
Minimum flow pipe
The blind flange
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
3
02-2
Outline of Event
Fuel pool cooling and filtering system
Reactor containment vessel Spent fuel pool
Reactor pressure vessel To gland steam converter From main steam Main steam pipe Feedwater pipe
Turbine
Generator
Grand steam converter From makeup water system Seawater
Pressure suppression chamber
Reactor coolant recirculation pump
Main condenser Hot well Minimum flow pipe
Residual heat removal system
Condensate collection tank High-pressure feedwater heater
Control rod drive mechanism
Condensate pump
Condensate demineralizer Low-pressure From main condenser superheater
High-pressure reactor core injection system
Air ejector
Turbine-driven feed water pump
Pressure suppression chamber purification system Reactor coolant purification system
Reactor core isolation and cooling system
High-pressure drain tank Water pressure control unit
To loads Condensate tank Makeup water pump
Control Rod Drive System
Motor-driven feed Condensate water pump booster pump High-pressure drain pump
Spillover Line
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Circulating water pump Condensate filter
Tube Leakage
Condensate System Off-gas system
To gland steam exhauster Gland steam condenser
: Infiltration of seawater (Including gas phase sections)
4
Outline of Event
Maximum Chloride Ion; approximately 450ppm
Maximum Temperature; approximately 240Ԩ
Dissolved Oxygen; several tens of ppb
The concentration of chloride and sodium ion（ppm） Temperature（℃）
500
▼
16:30 Alarm activation (Hig h couductivity at hot well (A) outlet)
450
2.0 The concentration of chloride ion The concentration of sodium ion Temperature
400
Dissolved oxyg en level
1.8 1.6 1.4
350 ▼
12:38 Reactor vent valve open 1.2
300 ▼
15:17 Reactor coolant purification system outag e 1.0
250
Exceeded measurement rang e (0～1ppm） 200
0.8
150
0.6
100
0.4
50
0.2
0
0.0
2011/5/14 0:00
2011/5/15 0:00
2011/5/16 0:00
2011/5/17 0:00
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
2011/5/18 0:00
2011/5/19 0:00
Dissolved oxyg en level（ppm）
02-3
2011/5/20 0:00
5
03
Concept of Assessment
Assess all affected SSCs at each level. Plant Health Assessment Monitor plant performance and trend.
System Health Assessment Confirm availability of system functions. Implement the cleanup to restart. Component Health Assessment Figure out the effects of seawater intrusion by mock-up test and inspection. Confirm availability of component functions. Determine components which need to repair or replace. Dec 15, 2015 Submit the report to NRA Based on assessment results, conduct the inspection program after restart. Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
6
04
Mock-up Test
Test condition
Test results The concentration of chloride ion Temperature
←Test Start 500
The concentration of chloride and sodium ion（ppm） Temperature（℃）
▼
16:30 Alarm activation
450 400
Chloride Ion 450ppm
350
Form of Corrosion
Results
Pitting Corrosion
Max 0.06mm
Crevice Corrosion
Max 0.20mm
SCC
Not Occurred
General Corrosion
Occurred
300 250
at Cast Stainless Steel at Stainless Steel
at LAS, CS
Temperature 250Ԩ : 3h Decrease 7Ԩ/h until 50Ԩ 50Ԩ : 54h
200 150 100
SUS403
50
SUS304
SUS316L
0
2011/5/14 0:00
2011/5/15 0:00
2011/5/16 0:00
2011/5/17 0:00
2011/5/18 0:00
2011/5/19 0:00
2011/5/20 0:00 •300 μm
SCS19A Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
SA-533 TypeB Class1
7
05-1
Inspection Scope (1. Reactor Pressure Vessel)
Inspection Scope
Top head, Shell, Bottom head Main flange Reactor internal pump penetration (N1) Main steam nozzle (N3) Feed-water nozzle (N4) Low-pressure injection nozzle (N6) Head spray/vent nozzle (N7) Reactor shutdown cooling outlet nozzle (N8) Reactor internal pump differential pressure detector nozzle (N9) Reactor shutdown cooling outlet nozzle (N10) Core plate differential pressure detector nozzle (N11) Instrument nozzle (N12，N13，N14) Drain nozzle (N15) High-pressure core injection nozzle (N16) Steam dryer hold-down bracket Steam dryer support bracket Guide rod bracket Low-pressure injection sparger bracket Feed-water sparger bracket Surveillance test piece support bracket CRD Housing ICM Housing
30 of 360 degree (VT-1) 1 1 of 10 (VT-1, Weld: MVT-1) 1 of 4 1 of 6 1 of 2 1 1 1 of 4 (VT-1, Weld: MVT-1) 1 of 2 1 of 4 (VT-1, Weld: MVT-1) each 1 of 4 (VT-1, Weld: MVT-1) 1 1 of 2 (VT-1, Bimetallic part: UT) 1 of 6 1 of 4 1 of 2 1 of 2 1 of 6 1 of 2 1 of 205 (VT-1), 16 of 205 (Weld: MVT-1) 1 of 62 (VT-1), 5 of 62 (Weld: MVT-1)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
8
05-2
Inspection Scope (2. Core Internals)
Inspection Scope Feed-water sparger Low-pressure injection sparger High-pressure core injection pipe High-pressure core injection sparger Core shroud Shroud support Top Guide Core Plate Fuel support CR guide tube ICM guide tube Steam dryer Separator/Shroud head Core plate differential pressure detector tube Reactor internal pump differential pressure detector tube Guide rod
1 of 4 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 30 of 360 degree (VT-1) 108 of 360 degree (Weld: MVT-1) 30 of 360 degree (VT-1) 108 of 360 degree (Weld: MVT-1) 30 of 360 degree (VT-1) 30 of 360 degree (VT-1) 6 of 257 (VT-1) 2 of 205 (VT-1) 1 of 62 (VT-1) 30 of 360 degree (VT-1) 30 of 360 degree (VT-1) 1 of 4 (VT-1) 1 of 4 (VT-1) 1 of 2 (VT-1)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
9
06
Inspection Results (1. Reactor Pressure Vessel)
Overview Component •Shell •Bottom head •Main steam nozzle (N3)
Results •Pitting corrosion at SUS weld metal cladding layer Some pitting corrosion penetrate through cladding layer No relevant indication was observed at base metal by UT
•Reactor internal pump penetration (N1)
•Crevice corrosion Approximately 0.35mm depth
•Surveillance test piece support bracket
•Pitting corrosion Approximately 0.14mm depth
•Others
•No relevant indication
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
10
07
Distribution of Pitting Corrosion at RPV Inner Surface
Conditions of corrosion were generally the same in circumferential direction.
Water level in operating conditions
: Weld : Area where pitting corrosion were observed at sample location of each grid : Location which grinded to determine pitting corrosion depth
Reactor internal pump Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
11
08
3D View of RPV Inner Surface Main Steam Nozzle
Guide Rod
０°
９０°
１８０°
２７０°
Guide Rod
↑RPV Main Flange
Water level in operating conditions
↓Internal Pump Deck : Location which grinded to determine pitting corrosion depth
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
12
09
Grinding to Determine the Pitting Corrosion Depth
Upper area (near guide rod bracket) Pitting corrosion didn't penetrate through cladding layer Approximately 0.3 mm depth
Lower area (near H9 weld)
Grinding area (Ca.100mm×100mm) Some pitting corrosion penetrated through cladding layer No relevant indications were observed at RPV base metal by UT from outside
Cladding Layer(SUS) Base Metal (LAS)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
13
10-1
Inspection Results (2. Core Internals)
Overview Component •Core plate
Results •Minimal pitting corrosion on upper surface •Crevice corrosion between core plate and CR guide tube Approximately 0.40mm depth
•High-pressure core injection pipe
•Minimal pitting corrosion on upper surface •Elution caused by crevice corrosion between collar and fitting
•Separator/Shroud head
•Minimal pitting corrosion •Elution caused by crevice corrosion between pin and sleeve
•Top guide •ICM guide tube •Core shroud
•Elution caused by crevice corrosion ( ex. crevice between top guide flange and sleeve crevice at ICM guide tube stabilizer crevice between core shroud lower ring and nut ) •No relevant indication
•Others
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
14
10-2
Inspection Results (2. Core Internals)
Core plate
Pitting corrosion were observed on upper surface
Remain pitting Cleaning
Crevice corrosion were observed between core plate and CR guide tube ： ： ： ：
Inspection area No relevant indications Pitting corrosion Crevice corrosion
Polishing
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Approximately 0.40mm depth
15
10-3
Inspection Results (2. Core Internals)
Separator/Shroud head
Cleaning
： ： ： ：
Inspection area No relevant indications Pitting corrosion Crevicecorrosion
Pitting corrosion were observed at stand pipe and inlet impeller blade.
Steam dryer Based on inspection results of similar equipments, steam dryer unit was evaluated to have no effects on moisture separate function. (Steam dryer unit is difficult to inspect because of accessibility. ) Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
16
10-4
Inspection Results (2. Core Internals)
Elution from crevice Water level in operating conditions
Collar and fitting (High-pressure core injection pipe)
Top guide flange and sleeve
ICM guide tube stabilizer Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
17
Distribution of Crevice Corrosion Area which may have a potential for Crevice corrosion Crevice Depth （mm）
11
Impossible to visual inspection Elution was NOT observed Elution were observed No relevant indication (disassembled) Corrosion were observed (disassembled)
Crevice Gap（mm） Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
18
12
Summary of the Assessment
RPV Pitting corrosion in SUS weld metal cladding layer did NOT intrude into RPV base metal. NO relevant indication at inconel alloy weld metal cladding layer on bottom head. There is some margin for required thickness of base material.
Core Internals The depth of pitting corrosion is within the range of design and production margin of material thickness. All crevice corrosions have NO effects on equipment function because each crevice has sufficient contact face and is firmly fixed by welding and bolts.
Others（Control rod, In-core monitor） Control rod and in-core monitor can be failed their function. Repairs/replacements are needed
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
19
13-1
Future Works
Implement repairs/replacements as needed. Conduct feasibility assessments. May need Re-cladding where grinded. Implement System Health Assessment after repairs/replacements. Continue demineralization to reduce corrosion risk (especially potential of crevice corrosion) as low as possible. Modify in-service inspection program based on the assessment.
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
20
13-2
Future Works
New NDE techniques Sizing and mapping pitting corrosion at cladding layer on RPV Visual inspection technology for the inside of the steam dryer unit May need further investigations In terms of BWRVIP-233 "Evaluation of SCC Growth in Low Alloy Steel Vessel Materials in the BWR Environment" (Nov, 2011), SCC mechanism affected by high concentration of chloride ion is unknown. Possibility of LAS SCC at RPV base metal, caused by pitting corrosion penetrate through RPV cladding layer Impact of pitting corrosion found at core internals to SCC
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
21
14-1
Development of NDE Technique
NDE Technique for pitting corrosion at RPV cladding layer 1. Issue There is a possibility that UT Inspection from the outside surface of the RPV are required as a part of the safety assurance of the soundness of the RPV. If we can`t get proper mapping and sizing of the pittings, we may need huge amount of UT Inspection as in-service inspection.
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
22
14-2
Development of NDE Technique
NDE Technique for pitting corrosion at RPV cladding layer 2. Resolution Remote Non-Destructive Test Technologies (UT, ECT) for the mapping and sizing of pittings from the inside of the vessel should be developed.
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
23
14-3
Development of NDE Technique
NDE Technique for the inside of steam dryer unit 1. Issue No visual inspection has been done for the inside of the steam dryer unit, due to inaccessibility of a camera. Considering the severe boiling of reactor water around the water line, inside the dryer might have caused the concentration of chloride.
Inside of steam dryer unit Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
24
14-4
Development of NDE Technique
NDE Technique for the inside of steam dryer unit 2. Resolution Visual inspection technology applicable for the inside of the steam dryer unit is strongly required. (The steam dryer unit is surrounded with punching metals with baffle plate being located inside the punching plates.) Any visual inspection technology or O.E. applicable for the inside of the steam dryer unit？ Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Inside of steam dryer unit
25
Any Questions?
If you have any questions, please contact us. Kouhei Kurono [email protected] Tomiyasu Imai [email protected]
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
26
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
1
01
Overview of Facilities Unit 1
1,593
Type of Primary Containment Vessel
Generating output (MWe)
Unit 3
BWR-4
Reactor type Thermal power (MWt)
Unit 2
BWR-5 2,436
Mark-1 (540)
Unit 4
3,293
ABWR 3,293
Mark-1 modified (840)
1,100
Total power output (MWe)
Unit 5
1,137
3,926 RCCV 1,380
3,617
Construction commencement
March 1971
March 1974
November 1982
February 1989
March 1999
Operation commencement
March 1976
November 1978
August 1987
September 1993
January 2005
In outage (since November 29, 2010)
In outage* (since January 25, 2012
In outage* (since March 22, 2012)
Current status
Decommissioning (Operation terminated on January 30, 2009
Safety improvement measures being implemented
*All Units at the Hamaoka NPS halted by accepting the request from Japanese Government. (Unit-4: May 13, 2011 Unit-5: May 14, 2011) Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
2
02-1
Outline of Event
Tubes of the steam chest of the main condenser (A-1) were damaged by the jet flow, and seawater flowed into the reactor facilities. (During the process of achieving cold shutdown following the shutdown of Hamaoka Unit 5 on May 14, 2011) The jet flow were caused by dropout of the blind flange of the minimum flow pipe of the motordriven feed water pump.
Ca.90cm Ca.70cm
Ca. 14cm
Main condenser
The side view of main condenser
Damaged by jet flow
Minimum flow pipe
The blind flange
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
3
02-2
Outline of Event
Fuel pool cooling and filtering system
Reactor containment vessel Spent fuel pool
Reactor pressure vessel To gland steam converter From main steam Main steam pipe Feedwater pipe
Turbine
Generator
Grand steam converter From makeup water system Seawater
Pressure suppression chamber
Reactor coolant recirculation pump
Main condenser Hot well Minimum flow pipe
Residual heat removal system
Condensate collection tank High-pressure feedwater heater
Control rod drive mechanism
Condensate pump
Condensate demineralizer Low-pressure From main condenser superheater
High-pressure reactor core injection system
Air ejector
Turbine-driven feed water pump
Pressure suppression chamber purification system Reactor coolant purification system
Reactor core isolation and cooling system
High-pressure drain tank Water pressure control unit
To loads Condensate tank Makeup water pump
Control Rod Drive System
Motor-driven feed Condensate water pump booster pump High-pressure drain pump
Spillover Line
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Circulating water pump Condensate filter
Tube Leakage
Condensate System Off-gas system
To gland steam exhauster Gland steam condenser
: Infiltration of seawater (Including gas phase sections)
4
Outline of Event
Maximum Chloride Ion; approximately 450ppm
Maximum Temperature; approximately 240Ԩ
Dissolved Oxygen; several tens of ppb
The concentration of chloride and sodium ion（ppm） Temperature（℃）
500
▼
16:30 Alarm activation (Hig h couductivity at hot well (A) outlet)
450
2.0 The concentration of chloride ion The concentration of sodium ion Temperature
400
Dissolved oxyg en level
1.8 1.6 1.4
350 ▼
12:38 Reactor vent valve open 1.2
300 ▼
15:17 Reactor coolant purification system outag e 1.0
250
Exceeded measurement rang e (0～1ppm） 200
0.8
150
0.6
100
0.4
50
0.2
0
0.0
2011/5/14 0:00
2011/5/15 0:00
2011/5/16 0:00
2011/5/17 0:00
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
2011/5/18 0:00
2011/5/19 0:00
Dissolved oxyg en level（ppm）
02-3
2011/5/20 0:00
5
03
Concept of Assessment
Assess all affected SSCs at each level. Plant Health Assessment Monitor plant performance and trend.
System Health Assessment Confirm availability of system functions. Implement the cleanup to restart. Component Health Assessment Figure out the effects of seawater intrusion by mock-up test and inspection. Confirm availability of component functions. Determine components which need to repair or replace. Dec 15, 2015 Submit the report to NRA Based on assessment results, conduct the inspection program after restart. Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
6
04
Mock-up Test
Test condition
Test results The concentration of chloride ion Temperature
←Test Start 500
The concentration of chloride and sodium ion（ppm） Temperature（℃）
▼
16:30 Alarm activation
450 400
Chloride Ion 450ppm
350
Form of Corrosion
Results
Pitting Corrosion
Max 0.06mm
Crevice Corrosion
Max 0.20mm
SCC
Not Occurred
General Corrosion
Occurred
300 250
at Cast Stainless Steel at Stainless Steel
at LAS, CS
Temperature 250Ԩ : 3h Decrease 7Ԩ/h until 50Ԩ 50Ԩ : 54h
200 150 100
SUS403
50
SUS304
SUS316L
0
2011/5/14 0:00
2011/5/15 0:00
2011/5/16 0:00
2011/5/17 0:00
2011/5/18 0:00
2011/5/19 0:00
2011/5/20 0:00 •300 μm
SCS19A Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
SA-533 TypeB Class1
7
05-1
Inspection Scope (1. Reactor Pressure Vessel)
Inspection Scope
Top head, Shell, Bottom head Main flange Reactor internal pump penetration (N1) Main steam nozzle (N3) Feed-water nozzle (N4) Low-pressure injection nozzle (N6) Head spray/vent nozzle (N7) Reactor shutdown cooling outlet nozzle (N8) Reactor internal pump differential pressure detector nozzle (N9) Reactor shutdown cooling outlet nozzle (N10) Core plate differential pressure detector nozzle (N11) Instrument nozzle (N12，N13，N14) Drain nozzle (N15) High-pressure core injection nozzle (N16) Steam dryer hold-down bracket Steam dryer support bracket Guide rod bracket Low-pressure injection sparger bracket Feed-water sparger bracket Surveillance test piece support bracket CRD Housing ICM Housing
30 of 360 degree (VT-1) 1 1 of 10 (VT-1, Weld: MVT-1) 1 of 4 1 of 6 1 of 2 1 1 1 of 4 (VT-1, Weld: MVT-1) 1 of 2 1 of 4 (VT-1, Weld: MVT-1) each 1 of 4 (VT-1, Weld: MVT-1) 1 1 of 2 (VT-1, Bimetallic part: UT) 1 of 6 1 of 4 1 of 2 1 of 2 1 of 6 1 of 2 1 of 205 (VT-1), 16 of 205 (Weld: MVT-1) 1 of 62 (VT-1), 5 of 62 (Weld: MVT-1)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
8
05-2
Inspection Scope (2. Core Internals)
Inspection Scope Feed-water sparger Low-pressure injection sparger High-pressure core injection pipe High-pressure core injection sparger Core shroud Shroud support Top Guide Core Plate Fuel support CR guide tube ICM guide tube Steam dryer Separator/Shroud head Core plate differential pressure detector tube Reactor internal pump differential pressure detector tube Guide rod
1 of 4 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 1 of 2 (VT-1, Weld: MVT-1) 30 of 360 degree (VT-1) 108 of 360 degree (Weld: MVT-1) 30 of 360 degree (VT-1) 108 of 360 degree (Weld: MVT-1) 30 of 360 degree (VT-1) 30 of 360 degree (VT-1) 6 of 257 (VT-1) 2 of 205 (VT-1) 1 of 62 (VT-1) 30 of 360 degree (VT-1) 30 of 360 degree (VT-1) 1 of 4 (VT-1) 1 of 4 (VT-1) 1 of 2 (VT-1)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
9
06
Inspection Results (1. Reactor Pressure Vessel)
Overview Component •Shell •Bottom head •Main steam nozzle (N3)
Results •Pitting corrosion at SUS weld metal cladding layer Some pitting corrosion penetrate through cladding layer No relevant indication was observed at base metal by UT
•Reactor internal pump penetration (N1)
•Crevice corrosion Approximately 0.35mm depth
•Surveillance test piece support bracket
•Pitting corrosion Approximately 0.14mm depth
•Others
•No relevant indication
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
10
07
Distribution of Pitting Corrosion at RPV Inner Surface
Conditions of corrosion were generally the same in circumferential direction.
Water level in operating conditions
: Weld : Area where pitting corrosion were observed at sample location of each grid : Location which grinded to determine pitting corrosion depth
Reactor internal pump Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
11
08
3D View of RPV Inner Surface Main Steam Nozzle
Guide Rod
０°
９０°
１８０°
２７０°
Guide Rod
↑RPV Main Flange
Water level in operating conditions
↓Internal Pump Deck : Location which grinded to determine pitting corrosion depth
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
12
09
Grinding to Determine the Pitting Corrosion Depth
Upper area (near guide rod bracket) Pitting corrosion didn't penetrate through cladding layer Approximately 0.3 mm depth
Lower area (near H9 weld)
Grinding area (Ca.100mm×100mm) Some pitting corrosion penetrated through cladding layer No relevant indications were observed at RPV base metal by UT from outside
Cladding Layer(SUS) Base Metal (LAS)
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
13
10-1
Inspection Results (2. Core Internals)
Overview Component •Core plate
Results •Minimal pitting corrosion on upper surface •Crevice corrosion between core plate and CR guide tube Approximately 0.40mm depth
•High-pressure core injection pipe
•Minimal pitting corrosion on upper surface •Elution caused by crevice corrosion between collar and fitting
•Separator/Shroud head
•Minimal pitting corrosion •Elution caused by crevice corrosion between pin and sleeve
•Top guide •ICM guide tube •Core shroud
•Elution caused by crevice corrosion ( ex. crevice between top guide flange and sleeve crevice at ICM guide tube stabilizer crevice between core shroud lower ring and nut ) •No relevant indication
•Others
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
14
10-2
Inspection Results (2. Core Internals)
Core plate
Pitting corrosion were observed on upper surface
Remain pitting Cleaning
Crevice corrosion were observed between core plate and CR guide tube ： ： ： ：
Inspection area No relevant indications Pitting corrosion Crevice corrosion
Polishing
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Approximately 0.40mm depth
15
10-3
Inspection Results (2. Core Internals)
Separator/Shroud head
Cleaning
： ： ： ：
Inspection area No relevant indications Pitting corrosion Crevicecorrosion
Pitting corrosion were observed at stand pipe and inlet impeller blade.
Steam dryer Based on inspection results of similar equipments, steam dryer unit was evaluated to have no effects on moisture separate function. (Steam dryer unit is difficult to inspect because of accessibility. ) Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
16
10-4
Inspection Results (2. Core Internals)
Elution from crevice Water level in operating conditions
Collar and fitting (High-pressure core injection pipe)
Top guide flange and sleeve
ICM guide tube stabilizer Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
17
Distribution of Crevice Corrosion Area which may have a potential for Crevice corrosion Crevice Depth （mm）
11
Impossible to visual inspection Elution was NOT observed Elution were observed No relevant indication (disassembled) Corrosion were observed (disassembled)
Crevice Gap（mm） Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
18
12
Summary of the Assessment
RPV Pitting corrosion in SUS weld metal cladding layer did NOT intrude into RPV base metal. NO relevant indication at inconel alloy weld metal cladding layer on bottom head. There is some margin for required thickness of base material.
Core Internals The depth of pitting corrosion is within the range of design and production margin of material thickness. All crevice corrosions have NO effects on equipment function because each crevice has sufficient contact face and is firmly fixed by welding and bolts.
Others（Control rod, In-core monitor） Control rod and in-core monitor can be failed their function. Repairs/replacements are needed
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
19
13-1
Future Works
Implement repairs/replacements as needed. Conduct feasibility assessments. May need Re-cladding where grinded. Implement System Health Assessment after repairs/replacements. Continue demineralization to reduce corrosion risk (especially potential of crevice corrosion) as low as possible. Modify in-service inspection program based on the assessment.
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
20
13-2
Future Works
New NDE techniques Sizing and mapping pitting corrosion at cladding layer on RPV Visual inspection technology for the inside of the steam dryer unit May need further investigations In terms of BWRVIP-233 "Evaluation of SCC Growth in Low Alloy Steel Vessel Materials in the BWR Environment" (Nov, 2011), SCC mechanism affected by high concentration of chloride ion is unknown. Possibility of LAS SCC at RPV base metal, caused by pitting corrosion penetrate through RPV cladding layer Impact of pitting corrosion found at core internals to SCC
Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
21
14-1
Development of NDE Technique
NDE Technique for pitting corrosion at RPV cladding layer 1. Issue There is a possibility that UT Inspection from the outside surface of the RPV are required as a part of the safety assurance of the soundness of the RPV. If we can`t get proper mapping and sizing of the pittings, we may need huge amount of UT Inspection as in-service inspection.
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14-2
Development of NDE Technique
NDE Technique for pitting corrosion at RPV cladding layer 2. Resolution Remote Non-Destructive Test Technologies (UT, ECT) for the mapping and sizing of pittings from the inside of the vessel should be developed.
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14-3
Development of NDE Technique
NDE Technique for the inside of steam dryer unit 1. Issue No visual inspection has been done for the inside of the steam dryer unit, due to inaccessibility of a camera. Considering the severe boiling of reactor water around the water line, inside the dryer might have caused the concentration of chloride.
Inside of steam dryer unit Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
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14-4
Development of NDE Technique
NDE Technique for the inside of steam dryer unit 2. Resolution Visual inspection technology applicable for the inside of the steam dryer unit is strongly required. (The steam dryer unit is surrounded with punching metals with baffle plate being located inside the punching plates.) Any visual inspection technology or O.E. applicable for the inside of the steam dryer unit？ Copyright © CHUBU Electric Power Co.,Inc. All Rights Reserved.
Inside of steam dryer unit
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Any Questions?
If you have any questions, please contact us. Kouhei Kurono [email protected] Tomiyasu Imai [email protected]
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