NL-07-0774, 1R13 Steam Generator Tube Inspection Report
| ML072480031 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/18/2007 |
| From: | George B Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-07-0774 | |
| Download: ML072480031 (13) | |
Text
Southern Nuclear Operating Company, Inc.
Post Office Box 1295 Birmingham, Alabama 35201-1295 Tel 205.992.5000 SOUTHERN COMPANY A p r i 1 18, 2007 Energy to Serve Your World" Docket No.: 50-424 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant Unit 1 1R13 Steam Generator Tube Inspection Report Ladies and Gentlemen:
In accordance with the requirements of Vogtle Electric Generating Plant Technical Specification 5.6.10, Southern Nuclear Operating Company submits this report of the steam generator (SG) tube inspections performed during the Unit 1 thirteenth maintenancelrefueling outage (1R13). Initial entry into Mode 4 occurred on October 25, 2006.
This letter contains no NRC commitments. If you have any questions, please advise.
Sincerely, ,,
B. J. ~ e 6 r ~ e Manager, Nuclear Licensing
Enclosure:
1R13 Steam Generator Tube Inspection Report cc: Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Mr. T. E. Tynan, Vice President - Vogtle Mr. D. H. Jones, Vice President - Engineering RType: CVC7000 U. S. Nuclear Regulatory Commission Dr. W. D. Travers, Regional Administrator Mr. B. K. Singal, NRR Project Manager - Vogtle Mr. G. J. McCoy, Senior Resident Inspector - Vogtle
Enclosure Vogtle Electric Generating Plant Unit 1 1 R13 Steam Generator Tube Inspection Report
Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report lR13 STEAM GENERATOR TUBE INSPECTION REPORT Introduction The 1R13 outane was conducted after cumulative service equivalent to 17 EFPY (effective full years); the Cycle 13 power generation was -1.4 EFPY. Analyses based on conservative assumptions used in the Condition Monitoring and Operational Assessments demonstrated that there were no tubes that exceeded the Reg. Guide
- 1. I 21 and NEI-97-06 Revision 2 criteria for tube integrity. The steam generator (SG) tubing eddy current inspections were performed by the Steam Generator Maintenance Services Group of the Westinghouse Nuclear Services Division. Secondary data analysis was performed by ANA'TEC under direct contract to Southern Nuclear.
1R13 Inspection S c o ~ e The base scope for 1R13 involved the scheduled inspections listed below. The inspection program addressed the known degradation mechanisms observed in Vogtle Unit 1 in prior inspections as well as those regarded as potential degradation mechanisms.
100% Bobbin examination of tubes in SGs 2 and 3, full length except for Rows 1 and 2, which are inspected from tube end to tube support plate (TSP) #7 from both hot leg side (HL) and cold leg side (CL).
50% +Point (mid-range) examination of small radius U-bends (Row 1 and Row 2) in SGs 2 and 3.
250% +Point examination (mid-range) top of tubesheet region (TTS) on HL side, k 3",
in SGs 2 and 3.
+Point tests (mid-range) of Special Interest, HL, and CL, of bobbin possible flaw locations (including U-bends). Tubes indicating Seabrook-type U-bend offset behavior in the 1R11 data and statistical review to identify the 2 sigma populations; any of these tubes with DSls (Distorted Support Indication) that are not confirmed will nonetheless be preverltively plugged.
+Point inspection of expanded tubesheet section bulges (BLGs) and overexpansions (OXPs) to include 25% of SG1 (26 tubes), SG2 (52 tubes), and SG3 (14 tubes) populations and 100% of SG4 population (78 tubes), TSH-17" to TSH+3".
100% +Point examination of dentsldings 2 5 volts in U-bends.
+Point exams for 2 tube depth around the entire periphery of the bundle at the top of the tubesheet (k3") including HL side, CL side, and down the tube lane on both sides.
Visual inspection of tube plugs in all 4 SGs.
As a result of indications found at the top of the tube sheet, the +Point examination at the top of the tube sheet was expanded from 50% of SGs 2 and 3 to 100% of all four SGs.
Damage Mechanisms Found and NDE Techniques Utilized The following damage mechanisms were discovered in the Vogtle Unit 1 SGs during 1R13:
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Outside diameter stress corrosion cracking (ODSCC) at the top of the tube sheet was found in all 4 SGs. The +Point probe was used to inspect 100% of the top of the tube sheet in all four SGs.
l Loose parts wear was found in SGs 1,2 and 3. +Point probe sizing was used to size the wear scars. Areas with potential loose parts and/or wear are identified during the bobbin inspections.
Antivibration bar (AVB) wear was found in SGs 2 and 3. AVB wear is identified during the bobbin inspection except for rows 1 and 2 which are inspected with the +Point probe.
l Oxide removal patterns on several row 1 tubes in SG 2 were identified visually at 8 to 11 inches above the top of the tube sheet. +Point examination indicated shallow wall loss, possibly as a result of ultrasonic energy cleaning which had been used in previous outages.
Service Induced Indication Descriptions Outside diameter stress corrosion cracking identified in Vogtle 1R13 is provided in the following table.
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Vogtle Electric Generating Plant Unit 1 1R13 Steam Generator Tube Inspection Report Vogtle 1 01ISCC lndica tions for 1R13 I S I Row 1 Col I Ind I Maxi- Maximum Adjusted 1 Circum- Percent 1 1 ty e fi 1 mum voltage
% Depth (Phase Sizing)
~ a x i m u m ferential
% Depth (Amplitude Extent Degraded Area (PDANDE) 6.3 Not inches Applicable (1) 'The inspection result was classified as an indication type in accordance with a convention of 3-letter codes used for grouping and tracking various types of indications.
(2) NQ - Not quantifiable.
(3) SCI - Single circumferential indication (4) MCI - Multiple circumferential indication (5) SAI - Single axial indication The circumferential ODSCC .Raws were located at the bottom of the hydraulic expansion transition at the top of the tube sheet. The axial ODSCC flaw began at the bottom of the hydraulic expansion transition and extended into the expanded section of the tube inside the tube sheet. All tubes with ODSCC flaws were removed from service.
Loose parts wear, either identified or re-confirmed in Vogtle 1R13, is provided in the following table.
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Vogtle 1 Loose Parts Wear Indications for 1R13 I SG I Row I Column I Volts I % Depth I Location 1 1 3 1 3 0 1 111 11.94 1 29 I BPH'~) I (1) TSH - Tubesheet region on HL side.
(2) 1C - 1 TSP on CL side.
(3) BPC - Flow distribution baffle plate (FDB) on CL side (4) BPH - FDB on HL side All tubes with loose parts wear were visually examined, except SG 2 row 66 column 1 and SG 2 row 39 column 46. Row 39 column 46 was plugged as a result of exceeding the 40% plugging limit. Row 6 column 1 was left in service as a result of not identifying any loose parts in inspections of tubes surrounding row 6 column 1 and its shallow 8%
depth.
AVB wear continued to be identified in Vogtle 1R13 in SGs 2 and 3. AVB wear identified is provided in the table below.
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report (1) AV# - Location of AVB intersection with the tube (there are up to 6)
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Vogtle 1 Steam Generator 2 AVB Wear Indications for 1R13 (continued)
(1) AV# - Location of AVB intersection with the tube (there are up to 6)
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report (1) AV# - Location of AVB intersection with the tube (there are up to 6)
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Repor?
Vogtle 1 Steam Generator 3 AVB Wear Indications for 1R13 (continued)
Row Column Location % Row Column Location %
(1) (1)
Depth Depth 40 102 AV2 17 47 35 AV4 15 40 102 AV6 13 47 38 AV4 27 40 104 AV4 16 47 45 AV2 15 (1) AV# - Location of AVB intersection with the tube (there are up to 6)
No tubes were plugged as a result of AVB wear.
Visual inspection in steam generator 2 identified oxide removal patterns on several tubes hypothesized to be a result of cavitation during ultrasonic energy cleaning. Wall loss information as a result of eddy current inspection is provided in the table below.
Vogtle 1 R13 Steam Generator 2 Shallow Wall Loss Row Column Volts % Location Inch1 De~th 1
~ ~p 82 1 0.05 1 5 I TSC") 1 8.31 (1) TSC - Tubesheet region on CL side.
No tubes were plugged as a result of this shallow wall loss.
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Number of Tubes Pluaaed Tubes Plugged in 1R13 SG Row Column Indication Type Description 1 1 103 SCI Circumferential ODSCC 1 1 1 3 1 103 1 SCI I Circumferential ODSCC 1 1 3 119 SCI Circumferential ODSCC 2
- 2
- 109 SCI Circumferential ODSCC 2 2 113 SCI Circumferential ODSCC 2 39 46 VOL" I Loose Parts Wear 3- 2
- 106
~ - - SCI
- - Circumferential ODSCC 3 5 118 SCI Circumferential ODSCC 3 6 112 SCI Circumferential ODSCC 1 4 1 4 1 107 1 SCI I Circumferential ODSCC I 4 5 68 SAI Axial ODSCC 4 6 105 MCI Circumferential ODSCC 4 8 106 SCI Circumferential ODSCC 1 - 1 1 4 1 8 1 108 1 MCI I Circumferential ODSCC I 4 8 113 SCI Circumferential ODSCC 4 9 107 SCI Circumferential ODSCC 4 11 115 MCI Circumferential ODSCC 4 22 84 SCI Circumferential ODSCC 1 4 1 2 5 1 51 MCI I Circumferential ODSCC 1 (1) VOL - Volumetric indication Total plugging in the SGs after 1R13 is as follows:
SG 1 - 9 tubes for a total of 0.16% tubes plugged SG 2 - 14 tubes for a total of 0.25% tubes plugged SG 3 - 25 tubes for a total of 0.44% tubes plugged SG 4 - 26 tubes for a total of 0.46% tubes plugged Chemical Cleaning The chemical cleaning process applied to the Vogtle 1 SGs during 1R13 was recognized as part of the planned maintenance activities in the 1R13 Steam Generator Degradation Assessment. The compositions of the iron removal solutions were optimized based on the anticipated sludge and tube deposits inventories. As applied, this chemical cleaning operation incorporated elements of the EPRIISGOG process and employed several phases, wherein temperature adjustments were made to facilitate dissolution in specific regions of the bundle, such as TSP crevices and the TTS sludge region. Residual iron stage chemicals were removed by multiple rinse operations prior to the copper removal phase of the cleaning process. The process was completed after similar rinse steps following the copper removal step. All 4 SGs were subjected to chemical cleaning during 1R13.
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Condition Monitorinn Results No indications were found to exceed the condition monitoring limits specified in the Degradation Assessment.
For burst of a circumferential crack at 3APNoat Vogtle 1, a percent degraded area (PDA) of 78% or a uniformly 100% through wall crack of 280" is required. The largest measured total crack angle for R8C108 is only nominally 216" or 250" at 95%
probability. The nominal PDAs for this indication range from 17.3% for the WCAP-15573 methods to 25.5% for amplitude sizing, which bound the largest PDAs for all the indications including WCAP-15573 methods at the upper 95% probability. The measured angle at 95% probability is less than the 280" required for burst under the very conservative assumption that the crack is uniformly 100% deep. Similarly, the maximum PDA of 25.5% for any indication is much less than the acceptance limit of 78% required for burst of a circumferential crack. Consequently, it can be concluded that there is a negligible probability of burst for the Vogtle 1 circumferential cracks at 3APNo. Based on the above assessments, condition monitoring requirements are satisfied for all circumferential indications found in the 1R13 inspection. Additionally, the maximum circumferential indication voltage of 0.55 volts is less than the minimum voltage threshold of 1.31 volts for in situ testing in the EPRl Steam Generator In Situ Pressure Test Guidelines. Therefore, in situ testing with respect to the circumferential indications was not performed.
The single axial tubesheet indication assessed as ODSCC similarly did not exceed the in situ screening parameters for leak testing. Based on the evaluation of R5C68 for SLB leakage with crack opening constrained by the tubesheet, the SLB leak rate at 95%
probability is 0.09 gpm (room temperature) with no leakage for the nominal estimate.
Since tube burst is prevented by the tubesheet, it can be concluded that the condition monitoring tube integrity requirements with an allowable leak rate of 0.25 gpm (RT) at 95% probability are conservatively satisfied.
A tube pull during the 1R13 outage was not practicable due to issues regarding vendor crew and equipment availability. Tube pulls of ODSCC indications in future outages are being evaluated.
The foreign object-related wear on R39C46 in SG2 exceeded the plugging criteria, but its 42% depth estimate does not exceed the Condition Monitoring limit (as provided in the Degradation Assessment for 1.5" long uniform thinning). The axial length of the wear scar (0.32") and the circumferential extent (78 degrees) indicate that there is considerable margin as compared to the uniform thinning reference. Additional margin is inherent in the result, given that the tube area affected by the wear scar is less than 10% of the area assumed in calculation of the Structural Limit.
None of the AVB wear indications in either SG2 or SG3 exceed the plugging criteria.
Therefore, they do not exceed the Condition Monitoring limits as given in the 1R13 Degradation Assessment. The growth rates are essentially negligible.
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Vogtle Electric Generating Plant - Unit 1 1R13 Steam Generator Tube Inspection Report Evaluation of the indications found in the 1R13 inspection indicate that the condition monitoring requirements for structural and leakage integrity as specified in NEI-97-06 Revision 2 are satisfied.
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