2CAN090601, Response to Request for Additional Information on ANO-2 Steam Generator Tube Inservice Inspection Report
| ML062770265 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/19/2006 |
| From: | James D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN090601 | |
| Download: ML062770265 (12) | |
Text
Entergy Operations, Inc.
Entergy 1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4619 Dale E. James Manager, Licensing 2CAN090601 September 19, 2006 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Response to Request for Additional Information on ANO-2 Steam Generator Tube Inservice Inspection Report Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6
REFERENCE:
1 Entergy letter dated March 16, 2006, Steam GeneratorTube Inservice Inspection Report (2CAN030601)
Dear Sir or Madam:
Arkansas Nuclear One, Unit 2 (ANO-2) Technical Specification 6.6.7.b requires that the complete results of ANO-2 steam generator (SG) tubing in-service inspections (ISI) be reported within 12 months following the completion of the inspection. Reference 1 provided the SG Tubing In-service Inspection Report which provided the results from ANO-2's scheduled refueling outage (2R17) inspection.
During NRC review of the ANO-2 SG Tube ISI report, the staff requested additional information to support their review. The attachment to this submittal provides the responses to the NRC requested information.
This submittal contains no commitments. Should you have any questions regarding this report, please contact Steve A. Bennett of my staff at (479) 858-4626.
Sincerely, 7DI ab c
thment: Response to NRC Request for Additional Information on Steam Generator Tubing Inservice Inspection Report AcLP7
cc: Dr. Bruce S. Mallett Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. Drew Holland Mail Stop 0-7 D1 Washington, DC 20555-0001 Arkansas Department of Health & Human Services Division of Health P.O. Box 1437 Slot H-30 Little Rock, AR 72203-1437
Attachment 2CAN090601 Arkansas Nuclear One, Unit 2 Response to NRC Request for Additional Information on Steam Generator Tubing Inservice Inspection Report
Attachment to 2CAN090601 Page 1 of 9 Response to NRC Request for Additional Information on Steam Generator Tubing Inservice Inspection Report NRC RAI 1 Discuss the scope and results of any dent and ding exams performed during the Cycle 17 steam generator(SG) tube inservice inspections. Please discuss whether any rotatingprobe exams were done and include the number of dents/dings in each SG. In addition, discuss whether there were any new dentsidingsidentified (if so, causal mechanism), whether there were changes in the dent/ding signals (if so, causal mechanism), whether any "anomalous"dent signals were identified, and the inspection criteria (e.g., greaterthan or equal to 2-volts).
ANO-2 Response:
Dents/dings are identified with the bobbin campaign. The scope from 2R17 was 54% of the tube population. A review was performed to compare the dents/dings from 2R15 (spring 2002) to 2R17 (spring 2005). 2R15 was the first inservice inspection (ISI) after one cycle of operation and included 100% of the tubing. Both generator results were consistent with steam generator A (SGA) having the largest population of dents. Therefore, for this report, SGA data is being reported. A cumulative distribution factor (CDF) of the change in voltage for dents identified in both outages was performed. The mean change was approximately 0.6 volts which is considered an insignificant change based on the technique. This is presented in the graph below:
CDF of Change in Voltage of Dents in SGA - ANO2 from 2R15 to 2R17 250 100.00%
90.00%
200 80.00%
-- 70.00%
. 150 60.o0°% Frequency 50.00%
C" 100 40.00% - Cumulative %
I.. 30.00%
50 20.00%
10.00%
Change -n Vo e 0.00%
Change in Voltage
Akttachment to 2CAN090601 Page 2 of 9 A review was performed of newly identified dents in 2R1 7. These were determined to be a function of the threshold limit of 2.0 volts as the vast majority of the newly reported dents were at this value. From the graph below, the majority of the dents remain at or near the detection threshold. Based on this data, the relative condition of the dents in the ANO-2 steam generators is not changing.
CDF of New Dent Voltages for SGA ANO2 for 2R17 60 100.00%
90.00%
50 80.00%
70.00%
40 60.00%
-0 Frequency U. 30 50.00%
--- Cumulative %
40.00%
20 30.00%
20.00%
10 10.00%
0 0.00%
Voltage NRC RAI 2 Please confirm that no otherservice induced indications other than wear at structuresand loose parts were identified during the Cycle 17 SG tube inservice inspections.
ANO-2 Response:
No other service induced indications were identified during 2R17other than wear at structures and due to loose parts.
Attachment to 2CAN090601 Page 3 of 9 NRC RAI 3 Table 3.2.1 and Table 3.2.2 in the 12-month SG tube inservice inspection report,provided the indicationsidentified in SGA and SGB for Cycle 17. Table 3.3.1 and Table 3.3.2 of the same report provided the tubes plugged in SGA and SGB during Cycle 17. There were four tubes with loose part wear indicationsin SGA and four tubes with loose part wear indicationsin SGB that were not plugged. Please discuss the basis for determining which tubes with a wear indication attributedto a loose part were plugged. In addition, discuss whether the loose parts were removed from the SGs. If the loose parts were removed, discuss the nature of the parts. If the loose parts were not removed, please discuss whether analyses were performed to ensure that tube integrity would be maintained until the next inspection of these tubes.
Several tubes with possible loose part (PLP)indications were plugged. Please confirm that all tubes with PLP indications were plugged. If they were not, discuss the rationaleused to determine which PLP indications would be plugged.
Forthe tubes that were plugged, discuss whether they were stabilized.
ANO-2 Response:
Steam Generator Tubes Not Plugged SGA Tubes R142C119, R144C119, R146C113 and R146C115 involved a wire loose part which was removed. These tubes were not plugged since the percent throughwall indications was less than the 40% tube repair limit (including projected wear through the next scheduled inspection).
2R17 SGA Tubes Having a Percent Throughwall Indication Item No. Row Column Percent Through Wall Location Mechanism 1 59 60 13 A07 AVB Wear
.2 62 13 14 A05 AVB Wear 3 63 46 11 A14 AVB Wear 4 70 169 100 TSH Loose Part Wear 5 70 169 86 TSH Loose Part Wear 6 71 170 57 TSH Loose Part Wear 7 72 169 46 TSH Loose Part Wear 8 72 169 54 TSH Loose Part Wear 9 74 15 16 A18 AVB Wear 10 87 108 17 A09 AVB Wear 11 119 76 19 A09 AVB Wear 12 121 86 21 A09 AVB Wear 13 135 78 16 TSC Loose Part Wear 14 135 102 15 A09 AVB Wear 15 135 102 14 A15 AVB Wear 16 142 119 5 TSH Loose Part Wear 17 142 119 10 TSH Loose Part Wear 18 144 119 7 TSH Loose Part Wear 19 146 113 10 TSH Loose Part Wear 20 146 115 4 TSH Loose Part Wear 21 146 115 6 TSH Loose Part Wear
Attachment to 2CAN090601 Page 4 of 9 SGA Plugged Tubes Row Column Indication Location 1 70 169 SVI TSH +0.25 2 72 169 SVI TSH +0.87 3 71 170 SVI TSH +0.92 4 135 78 SVI TSH +0.04 SGB:
Tubes R1 00C25 and R1 02C25 had a wear scar from a loose part that was removed in 2R15. Since the depth was less than 40%, the tube was left in service.
Tube R124C129 was visually inspected. The part was no longer present and the depth was less than 40% so the tube was left in service.
Tube R138C119 was visually inspected. The part was no longer present and the depth was less than 40% so the tube was left in service.
2R17 SGB Tubes Having a Percent Throughwall Indication Item No. Row Column Percent Through Wall Location Mechanism 1 52 109 7 A07 AVB Wear 2 100 25 16 TSC Loose Part Wear 3 102 25 4 TSC Loose Part Wear 4 109 92 26 All AVB Wear 5 112 149 10 A12 AVB Wear 6 112 149 14 A18 AVB Wear 7 113 92 15 A14 AVB Wear 8 113 92 7 A17 AVB Wear 9 116 99 14 A09 AVB Wear 10 116 99 13 A12 AVB Wear 11 124 129 11 TSH Loose Part Wear 12 125 92 14 A15 AVB Wear 13 133 48 13 A13 AVB Wear 14 133 48 17 A15 AVB Wear 15 133 48 8 A17 AVB Wear 16 133 48 5 A19 AVB Wear 17 138 119 8 TSH Loose Part Wear 18 138 119 10 TSH Loose Part Wear 19 139 120 43 TSH Loose Part Wear SGB Plugged Tubes Row Column Indication Location 1* 6 97 PLP TSC +0.19 2* 5 98 PLP TSC +0.13 3* 7 98 PLP TSC +0.15 4* 20 173 PLP TSC +0.11 5* 21 172 PLP TSC +0.13 6* 22 173 PLP TSC +0.09 7 139 120 SVI TSC +0.10
- These tubes did not show wear, but were preventively plugged due to a potential unconfirmed loose part.
Attachment to 2CAN090601 Page 5 of 9 Loose Parts Removed:
SGA Tubes involved Loose Part R70C169 (leaker), R71C170, Carbon steel mass - 1.25" x 0.5" R72C169 (fabrication remnant)
R142C119, R144C119, Weld Wire (fabrication)
R146C113, R146C115 R2C89, R3C90# Stainless steel screw R147C88, R149C88, R148C89# Carbon Steel fragment (fabrication)
- - The loose part at these tubes did not show wear indications SGB Tubes involved Loose Part R146C111, R145C112, Machine winding R147C112 Loose Parts Not Removed:
SGA Tubes involved Loose Part R135C78 Piece of metal wrapped around base of tube - plug & stabilized R110C137 Small wire - not retrievable - no wear SGB Tubes involved Loose Part R133C86 Small wire (needle like)- not retrievable -
no wear R142C111 Small wire (needle like)- not retrievable -
no wear R21C172, R20C173, R22C173 Small wire visible on 3 tubes - plug and stabilized R6C97, R5C98, R7C98 Unknown part on 3 tubes - plug and stabilize
Attachment to 2CAN090601 Page 6 of 9 Evaluation Criteria for Dispositioning Potential Loose Parts There were several PLPs that were evaluated and dispositioned. The following is the criteria used based on eddy current results, visual inspections and local velocities:
- 1. Identification of PLP by eddy current testing (ECT). This included full length bobbin and plus point testing at the top of the tube sheet.
- 2. Evaluation of affected area visually using remote camera equipment. Where practical, an attempt was made to perform a visual inspection. If a loose part was confirmed visually, an attempt was made to retrieve the part. To disposition any PLPs that could not be visually examined or retrieved, further evaluation was performed using the following criteria:
Wear present: Iftube wear was identified and it could not be confirmed that a PLP was not present (by removal or visual confirmation), the affected tube(s) were plugged and stabilized.
No wear present: Where there was no wear present, the PLP indication was further dispositioned considering the following:
Visual confirmation (where practical)
" If observed, depending on size and considering the other factors below, it was judged acceptable or plugging and/or stabilizing was performed.
" If it is verified that a loose part is no longer present, no further action required.
" If the area is not inspectible, additional evaluation was performed as discussed below.
ECT characterization
" Using the low frequency channel on the 0.115 pancake coil, data was reviewed for distortions, location of the indication, voltage, and adjacent signals
" Using the plus point coil, areas identified with the 0.115 pancake were analyzed for the presence of wear indications.
Fluid flow was categorized as either high or low. Any PLP in a "high" flow area was further evaluated for leaving as-is.
- If the visual inspection determines that there is no part at the tube then no further action is warranted.
- If a part is found and there is no sign of active wear on the tube and it can be concluded that the PLP is very small (e.g., the projected flow area is less than 10% of the part that caused the leak), no additional action is required.
Attachment to 2CAN090601 Page 7 of 9 If both of those criteria cannot be met, then the PLP should either be removed or the affected tube(s) is to be plugged and stabilized. A subjective dividing line of 6.5 ft/sec has been established as the cutoff between high flow and low flow areas.
Assuming the fluid density is approximately the same; the wear rate of a part would be proportional to the square of the velocity.
Example: The wear rate for a given part would be a factor of 3.0 lower in a 6.5 ft/sec flow field than in an 11.3 ft/sec flow field. Since the density decreases as the fluid enters the tube bundle, the 3.0 factor will increase farther into the tube bundle and is considered a conservative threshold. If it is assumed that the loose part wore through R70/C169 in one cycle that same loose part would take three cycles to wear through a tube in a 6.5 ft/sec flow field. Even though it cannot be determined how long a given part will wear through the tube, the 3.0 factor provides a relative basis for determining tube degradation.
Plugging and Stabilizing The following table lists the tubes that were plugged and whether they included a stabilizer. The indications identified as PLPs are for those tubes where indications were evaluated but could not be visually verified to be free of a PLP or where the part was removed. These tubes were conservatively removed from service. The breached tube (leaker) was also stabilized.
ANO SG Tubes Plugged and Stabilized Gen Row Column Indication Plug Stabilizer A 70 169 SVI Yes Yes1 A 72 169 SVI Yes No A 71 170 SVI Yes No' A 135 78 SVI Yes Yes B 6 97 PLP Yes Yes B 5 98 PLP Yes Yes B 7 98 PLP Yes Yes B 20 173 PLP Yes Yes B 21 172 PLP Yes Yes B 22 173 PLP Yes Yes B 139 120 SVI Yes No_
1 - Tube not stabilized since PLP was removed 2 - No PLP, but greater than 40% throughwall
',Attachment to 2CAN090601 Page 8 of 9 NRC RAI 4. Your report provided information about flaws in specific tubes and at specific locations within a tube. In orderfor the U.S. NuclearRegulatory Commission staff to better understand where your indications are being detected and for future reference,please provide the following information regarding the design of your replacement SGs: tube manufacturer,a tubesheet map, the tubesheet thickness (with and without the clad), the tube supportplate thickness, the smallest U-bend radiusand correspondingrow, and a descriptionof the U-bend support system, including the shape and thickness, and the tubing supportedby the various supports. In addition, discuss whetheryou have a flow distributionbaffle to distribute flow at the top of the tubesheet, including the thickness and hole shape.
ANO-2 Response:
General design details of the ANO-2 replacement steam generators are contained in Section 5.5.2 of the ANO-2 Safety Analysis Report (SAR). SAR Figure 5.5-7 provides a cutaway depiction of the ANO-2 replacement SGs. The following are specific details of the replacement SGs:
Design of replacement SG Westinghouse Delta 109 Tube Manufacturer Sandvik SG Tubes 10637 per SG Alloy 690TT 0.688" nom OD 0.04" nom wall thickness Tubesheet Map See Figure 1 (attached)
Tubesheet Thickness 31.13" for tubesheet forging 0.43" primary clad thickness Tube Support Plate Thickness 1.115 inches Smallest U-bend Radius 3.250 inches (Row 1)
Flow Distribution Baffle ANO-2 does not have a baffle U-bend Support System: Anti-Vibration Bars The SG tubes are supported on the secondary side by eight (8) tube support plates (TSPs). The TSP material is Type 405 stainless steel. The TSPs have trifoil shaped holes produced by broaching to reduce tube dryout and chemical concentration in the regions where the tubes pass through the TSPs.
Five (5) sets of staggered anti-vibration bars (AVBs) are installed to provide support for the U-bends of the tubes. The AVB assemblies are installed to staggering depths to provide enhanced flow within the central region of the tube bundle. Each AVB assembly consists of a "V" shaped bar of Type 405 SS and two (2) thermally treated (TT) Alloy 690 end caps. Each end of the AVB assemblies is secured to the
-:-.Attachment to 2CAN090601 Page 9 of 9 U-bend peripheral Alloy 690TT retaining rings by welding. Four (4) chrome plated Alloy 690TT U-shaped retainer bars are installed between several of the peripheral U-tubes. These retainer bars provide support to the AVB assemblies during seismic and postulated steam line break loads.
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