ML023260159
| ML023260159 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 11/14/2002 |
| From: | Florida Power & Light Energy Seabrook |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| Download: ML023260159 (29) | |
Text
Seabrook Steam Generator Tube Assessment Project November 14, 2002 FPL Energy Seabrook Enclosure 2
Meeting Objectives
- Present Root Cause Evaluation Results for Axial Indications Identified in May, 2002 Inspection n Address NRC Staff Questions n Reach Agreement on Extent of Condition FPL Energy Seabrcok
Regulatory/Industry Reporting
"*Results Discussed With NRC In August 2002, and October 2002
"*I&E Notice Issued By NRC
"*INPO Event Report Issued
"*Informed Plants With Fall 2002 Inspections Of Residual Stress Signal Characteristic
"*Today's Public Meeting With NRC FPL Energy Seabrook
Investigation Process Summary
"* Removed Two Degraded Tubes For Lab Testing
"*Convened A Team Of Experts for Root Cause
"*Identified The Root Cause
>High Residual Stress Caused By Manufacturing Process In A Small Subset Of Tubes
"*Identified Extent Of Condition At Seabrook
"*Degradation Mechanism Is Not A New Generic Issue In Thermally Treated Tubing and is not an Active Damage Mechanism at Seabrook.
FL Enefy Szeabroo
Seabrook Steam Generators
"*Model F cqThermally Treated Alloy 600 Tubing
"*Recognized Industry Leader o3Primary/Secondary Side Chemistry ci3Life Cycle Management Strategies
"*Design Margin Strategies c>8% tube plugging vs. 0.5% plugged FPL Energy Seabrook.
Seabrook Model F Steam Generator 402 Commercial Operation 7/90 4 Loop System A
Design T-hot - 618 6,L 9.7 EFPY at RFO 8 (May 2002) 600-TT 5626 Tubes / SG - Alloy Full Depth Hydraulic Tubesheet Expansion Stainless Broached Tube Supports 0.5% Tubes Plugged To Date FPL Enrergy SeabrooA ,No-.I I I
Manufacturing Process Timeframe
"* Seabrook Tubes Manufactured between April 1980 and June 1980
"*Seabrook Tubes Manufactured From 376 Heats
"* Each Heat Contains Between 3,000 and 5,000 Tubes
"* Eight Other Plants Had Tubes Manufactured In Same Timeframe FPL, Energy Seabrook lu g
Key Elements Of Manufacturing Process s Tube Manufactured To Specification (0.69" OD x .040" wall) n Final Mill Anneal 1950 F for 3 min
"*Straightening and Polishing
"*Thermal Treatment 1320 F for 10 hrs
"*U-Bending All Rows
"*Stress Relief 1320 F for 2 hrs (rows 1-10)
- Desired Result - Favorable Residual Stress FPL Energjy Seabroc",
.0 Steam Generator Program Meets NEI 97-06
"*Primary Side Inspections u3Starting In RFO 5- Inspect 100% Of Two Steam Generators At Each RFO
\ "D" Generator Last Inspected RFO 6 May, 1999
"*Secondary Side Work o3Sludge Lance / FOSAR at Each RFO 03 Extensive Hydraulic Cleaning
\ UBIB, UBHB, CECIL, Pressure Pulse
"*Progressive Chemistry Program o3 Elevated pH, ETA, MPA & Reduced Hydrazi
-4Final Feedwater (1.4ppb Fe) (0.007ppb )
FPL Energy Scabroof.
OR08 Inspection Results
- A Generator- 100 % E/C Inspection
\ AVB wear-normal mechanism in model F
- D Generator- 100% EIC Inspection S15 tubes with 42 indications - all at TSPs intersections
\ All indications confined to first ten rows
\Indicative Of OD Stress Corrosion Cracking
\Confirmed by Plus Point & Ultrasonics
- Two Tubes Removed - Fourteen Segments Available
- Root Cause Team Formed e3 Lead Test Lab- Westinghouse; Independent/sting Altran + Professor Ron Ballinger (MIT)
FPL Enerpy Seabrook
Location of Degraded Tubes 60 70 50 40 30 20 10 "U4 0 20 40 60 Column FPL Energy Seabrook
Pulled Tube Testing Summary m Two Pulled Tubes Available For Testing (both from Heat 1374) n Lab test confirmed field E/C data - Tubes have Micro Cracks a Burst Test confirmed tube structural capability (i.e. Large Safety Margin) c3 Most Deeply Flawed Segment Tested To 7,000 psi- No leakage c> Non Flawed Segments Burst Tested To 13,000 psi
- Tube Chemical and Mechanical Properties Consistent w/ spec
- Fractography Confirms Cracking Mechanism Is Stress Corrosion FPL Energy Seabrook
Stress Corrosion Cracking Susceptible Microstructure Residual +Pressure Transient/Aggressive Environment FPL Energy Seabrook col
Material Susceptibility m Material Is Not Sensitized As Defined By Industry Standards m 13 ofl 5 Tubes Are From Heat 1374 (.048% C) m Two Tubes From Lower Carbon Heats (.032%C)
Heats 1456 & 1457 a Pulled Tube Micro Structure not typical of Optimum Thermally Treated Tubes c'3 Grain Structure c3 Carbide Distribution
- In-Service Performance Of This Micro ucture Has Been Excellent FPL Energy Seabrook
Pulled Tube Heat 1374 Archive Heat 1457 Grain Boundary Etch Grain Boundary Etch
- ASTM Grain Size 10-12 *ASTM Grain Size 5-7
- Intragranular Carbides -Fewer Intronful~ar Carbides
-Low Carbide Density On The Grain Boundaries FPL Energy Seabrook C60Ž)
Stress Corrosion Cracking Susceptible Microstructure Residual +Pressure Transient/Aggressive Environment FPL Energy Seabiook co5
Deposit Chemistry
"* Surface Deposits From TSP Land Areas and Crack Tip Constituents Were Analyzed
"* Deposits Contained Expected Constituents (3Very Low Concentrations Of Copper Oxide and Lead Were Present In A Limited Number Of Samples STight Crevice Between TSP Land and Tube Will Concentrate Contaminants
"* No Evidence That Chemistry Alone Dominat Cracking Process FPL Energy Seabrook
Stress Corrosion Cracking RX Susceptible Microstructure Residual
+ r s ue "Transient/Aggressive Environment FPL EZnergy 8eat~to
Operating and Residual Stress m Operating Stress - 10 Ksi (Pressure+Thermal) m Both Pulled Tubes Have An Unexpectedly High Measured Residual Hoop Stress (16-26 Ksi vs 2 Ksi) n OD Surface Residual Is Up To 2 times Higher w Low Residual Stress In Archived Tubes From The Affected Heats (1374, 1456, 1457) (1-3j*si)
FPL Energy Seabrook
Residual Stress Split Ring Test Specimen FPL Energy Seabrook
Residual Hoop Stress Results Residual Hoop Strain Calculated Residual Average Sample Description (*) Hoop Stress (psi) Residual Gage 1 Gage 2 Gage 1 Gage 2 Stress (psi)
Heat 1638 MA -240 7,464 7,464 Heat 1638 MA -378 -218 11,756 6,780 9,268 Heat 96845 MA -358 -167 11,134 5,194 8,164 Heat 96845 TT -56 -121 1,742 3,763 2,752 Pulled Tube AR -926 -762 28,799 23,698 26,248 R9C63 PulledTube AR -610 -496 18,971 15,426 17,198 TR9C63 FPL Energy Seabrook
Major Contributor to Cracking n Residual Hoop Stress c Need > 40ksi To Initiate Cracking In TT Material o High Residual + Operating Stress Exceeds 40 ksi on Tube Surface c, Potential Sources
\Cold Work After Final TT
\Improper Heat Treatment Including Stress Relief FPL Energy Seabrook
Root Cause Operating +Residual Microstructure not Stress Exceeds optimum, but acceptable 40 Ksi On Tube Surface Chemistry Concentrated Kýat TSP lands but not unusual IZPL~ Energy seihoo 0 0*,
Assessment Of Extent Of Condition m Established EPRI Eddy Current To Stress Correlation Technique Used To Characterize Residual Stress In Rows 1-10 d y C u rre n t Me a s u re s C h a n g e In C o n d u c tiv ity In d u c e d B y Cold Work In The Material c Process Is Well Established For Rows 1-10 eDistintinctive Eddy Current Offset Signal Exists In All 15 Degraded Tubes cECT Data for All Row 1-10 Tubes In All G era rs Reviewed Additional Tubes Located (N s)
\ 21 Total Affected Tube t FPL Energy Seabrook
U-bend Stress Relief Furnace Loading Zones I through 9 are heating zones in the furnace. Only zones 4, 5 and 6 were activated for stress relief of the u-bends.
FPL Energy Seatlrook
.0 Row 1-10 150 Hz Eddy Current Signal Traces (a)
(a) Normal 150 kHz Eddy Current strip chart for a Row <10 thermally treated tube (b) Seabrook degraded tube, 150 kHz Eddy Current stri chart for a Row <10 thermally treated tubg2 :
FPL Energy Seabrook
Extent Of Condition In Rows 11- 59
"*Applying The Process To Rows > 10 Is Similar c) Eddy Current Offset Values Provide Excellent Correlation With Bend Radius c3 Tubes With High Residual Stress In The Straight Length Would Be Apparent 03 There Are No Outliers - No Signal Reversals 03 Correlation Between Degraded Tubes And Offset Signal Is 100% In Rows < 10
"*Absence Of Observed Corrosion In Outer Rows Indicates That No Tubes Are Susceptible FPL Energy Seabrook
.1 U-bend Bobbin Signal Offset -CL U-bend Signafq tto Cold Leg (Bobbin Voltage)
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1, Root Cause Summary
- The Root Cause Of The Tube Cracking In Seabrook Steam Generator "D"At RFO8 Is High Residual Stress In A Subset Of Tubes Caused By Manufacturing Process
- The Extent Of Condition Is Defined
- Degradation Mechanism Is Not A New Generic Issue In Thermally Treated Tubing and is not an Active Damage Mechanism at Seabrook.
IPL Ener-gy SeabkxooL . *