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
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 Design T-hot - 618 A
9.7 EFPY at RFO 8 (May 2002) 6,L 5626 Tubes / SG - Alloy 600-TT 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
"* Straightening and Polishing
"* Thermal Treatment
"* U-Bending
"* Stress Relief 1950 F for 3 min 1320 F for 10 hrs All Rows 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
-4 Final 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 70 60 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 Residual +Pressure FPL Energy Seabrook Susceptible Microstructure Transient/Aggressive Environment 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 Grain Boundary Etch
- ASTM Grain Size 10-12
- Intragranular Carbides
-Low Carbide Density On The Grain Boundaries FPL Energy Seabrook Archive Heat 1457 Grain Boundary Etch
- ASTM Grain Size 5-7
-Fewer Intronful~ar Carbides C60Ž)
Stress Corrosion Cracking Susceptible Microstructure Residual +Pressure FPL Energy Seabiook Transient/Aggressive Environment 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 R esidual
+ r s u e FPL EZnergy 8eat~to Susceptible Microstructure "Transient/Aggressive Environment
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 FPL Energy Seabrook 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
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 Microstructure not optimum, but acceptable Ký IZPL~ Energy seihoo 0 0*,
Operating +Residual Stress Exceeds 40 Ksi On Tube Surface Chemistry Concentrated at TSP lands but not unusual
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 M e 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)
AAA y=00016X2-0 1487x + 7 9682 A A A
A R' = 0 935 A-A A
S4 A Avg-AlI Data o*
x STDEV-AJI 03 Xxxý%
,K xy, x xxxx xxxxx xx x x xx x 0
10 20 30 456 RovJ~ut*er FPL Erergy Seabtook
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 1,