ML15091A306
| ML15091A306 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/23/2015 |
| From: | Katzman E Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2015-089 | |
| Download: ML15091A306 (7) | |
Text
VMarch 23, 2015FPL. L-2015-089 10 CFR 50.410 CFR 50.55aU.S. Nuclear Regulatory Commission Document Control DeskWashington, D.C. 20555-0001 Re: St. Lucie Unit 2Docket No. 50-3 89Response to Request for Additional Information Regarding the Spring 2014 SteamGenerator Tube Inspections
References:
- 1. FPL letter L-2014-291 dated September 18, 2014: Steam Generator Tube Inspection Report (NRC ADAMS Ascension
- 2. NRC Email Letter dated January 27, 2015: St. Lucie Plant, Unit 2 -Request forAdditional Information (RAI) Regarding the Spring 2014 Steam Generator TubeInspections.
(NRC ADAMS Ascension
Per Reference 1 above, Florida Power and Light Company (FPL) submitted information summarizing the results of the spring 2014 steam generator tube inspections performed at St.Lucie, Unit 2. These inspections were performed during refueling outage 21.By email dated January 27, 2015 (Reference 2), the NRC Staff requested additional information regarding the spring 2014 steam generator tube inspections.
The attachment to this letterprovides the detailed response to the requests for additional information.
Please contact Richard Sciscente at (772) 467-7156 if there are any questions about thissubmittal.
Sincerely, Eric KatzmanLicensing ManagerSt. Lucie PlantESK/rcsAttachment cc: USNRC Regional Administrator, Region IIUSNRC Senior Resident Inspector, St. Lucie Units 1 and 2Florida Power & Light Company6501 S. Ocean Drive, Jensen Beach, FL 34957 L-2015-089 Attachment Page 1 of 6RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE SPRING 2014 STEAM GENERATOR TUBEINSPECTIONS By letter dated September 18, 2014 (Agencywide Documents Access and Management System(ADAMS) Accession No. ML14279A237),
Florida Power & Light Company submitted information summarizing the results of the Spring 2014 steam generator tube inspections performed at St. Lucie, Unit 2. These inspections were performed during refueling outage 21.The NRC staff has reviewed the information the licensee provided and determined that thefollowing additional information is needed in order to complete the review.RAI-1Clarify whether the U-bends of rows 1 and 2 were inspected with the bobbin probe.RESPONSEYes, all Row 1 and 2 tubes were inspected full length with the bobbin probe.RAI-2Discuss the results of the Plug Visual Inspections.
Were all plugs confinned to be present andfree of degradation?
RESPONSEPrior to starting the eddy current examination at the End-of-Cycle 20 (EOC-20) refueling outagein 2014, all of the previously installed hot-leg and cold-leg plugs in Steam Generator 2A andSteam Generator 2B were confirmed to be present in their correct locations.
In addition, all ofthe hot-leg and cold-leg plugs were confirmed to be free from degradation and visible signs ofleakage based on the visual examination.
L-2015-089 Attachment Page 2 of 6RAI-3Discuss the results of the Supplemental Primary Side Inspections to address Westinghouse NSAL 12-01. Was any degradation of the channel head cladding detected?
RESPONSEVisual inspection of the steam generators (SGs) at a Westinghouse designed plant showedindications of degradation in the cladding and/or divider plate-io-channel head weld, withexposure and wastage of the channel head base. Westinghouse issued NSAL 12-01 "SteamGenerator Channel Head Degradation" on January 5, 2012 and included recommended actionsfor the visual inspection at other plants. Although the degradation described in NSAL 12-01 isnot directly applicable to St. Lucie Unit 2 (per Table 1 of NSAL 12-01), a visual inspection ofthe primary side channel head bowl (in both SGs) was performed in accordance with therequirements presented in Westinghouse NSAL 12-01. No channel head degradation related toNSAL 12-01 was detected.
RAI-4Discuss the results of the following Secondary Side Inspection and cleaning activities:
- a. Upper Bundle Flushb. Sludge Lancec. Foreign object search and retrieval
- d. Upper internals visual inspection RESPONSEUpper Bundle Flush and Sludge Lancing were performed in both SGs. A total of 89.5 lbs ofsludge was removed from the SGs; 36 lbs. from SG 2A and 53.5 lbs. from SG 2B.Foreign Object Search and Retrieval (FOSAR) was performed on both SGs at the top-of-tubesheet location.
One small piece of foreign material was removed from SGA H/L top-of-tubesheet; no tube wear was associated with the foreign object. The lens and cover from anindexing camera were discovered to be missing during dis-mounting of the water lancingequipment used in SG 2B. A search was performed within and outside of the steam generator but the lens and cover were not found. These parts collectively weigh 4.05 grams and wereconservatively assumed to be inside the SG; their impact on SG tube integrity has been evaluated within the corrective action program.
L-2015-089 Attachment Page 3 of 6The upper steam drum components listed below were visually examined (in both SGs):* Stabilizers and Water Level Taps" Recirculation Pipe Flange Assembly* Feedring inspection port covers* Wrapper Room Hatches" Manway Hatch to Top of Dryers* SG-B Lower Separator Support Stuck Studs* SG-A Lower Separator Support Stuck Studs* Loose Parts Trapping SystemAdditional inspections included a sample of primary separators, secondary separator perforated plates, drain pipes, the feedring
- nozzles, other access hatches and inspection ports, and supportstructures.
The loose part trapping system screens were examined for foreign objects in both SGs. TheLoose Parts Trapping Systems remain structurally sound with no signs of structural damage.Three foreign objects were retrieved from the screens.
One retrieved foreign object (in SG 2B)was a piece of gasket material of unknown origin. The other two retrieved foreign objects (onein each SG) were determined to be part of the support system for the feedrings.
Additional inspections identified that the feedring supports for both SGs had been damaged due to a waterhammer event caused by a steam void in the feedring system. Denting to a j-tube stiffener andsome j-tubes was also identified.
The damaged supports were repaired during the outage. Thefunction of the feedring was not impacted.
The St. Lucie Unit 2 feedrings have a split design(not a full donut) and had bolted inspection ports installed at the ends of each pipe section.
Thefour feedring inspection port covers were found to be loose. All four inspection port covers werereplaced with welded end caps during SL2-2 1 to prevent loosening during future operation.
Noother abnormalities were observed during the Upper Internals visual inspection.
L-2015-089 Attachment Page 4 of 6RAI-5Summarize the number of tubes and the number of indications associated with the tube supportstructures (anti-vibration bars, tube support plates, V-shaped pads, apex of anti-vibration bars).RESPONSEEOC-20 Number of Affected Tubes at associated Tube Support Structures Location Mechanism SIG 2A SIG 25 TotalAnti-Vibration Bars Wear 2523 1788 4311U-Bend Apex (AV4/5) Wear 16 6 22AVB -Transition Tube WearNolumetric 1 0 1V-Shaped Support Pads Wear 1 1 2V-Shaped Support Bar Wear 1 0 1Tube Support Plates Wear 97 107 204Foreign Objects Volumetric 0 0 0EOC-20 Number of Indications at associated Tube Support Structures Location Mechanism SIG 2A SIG 2B TotalAnti-Vibration Bars Wear 8734 5061 13795U-Bend Apex (AV4/5) Wear 16 6 22AVB -Transition Tube WearNolumetric 1 0 1V-Shaped Support Pads Wear 1 1 2V-Shaped Support Bar Wear 1 0 1Tube Support Plates Wear 127 122 249Foreign Objects Volumetric 0 0 0SIG Total: 8880 5190 14070Note: In the above tables," The Location listed as "AVB -Transition Tube" refers to the wear indication in SG-A, inRow 41 Column 154, which is discussed in RAI # 7.* The Location listed as "V-Shaped Support Bar" refers to the wear indication in SG-A, inRow 91 Column 24, which is discussed in RAI # 6.
L-2015-089 Attachment Page 5 of 6RAI-6One tube was plugged since it had wear associated with a neighboring tube's V-shaped supportpad. Has this phenomenon been observed in the past? Are the V-shaped support pads in closeproximity to the neighboring tubes? Would this occurrence be expected given the design(rigidity) of the anti-vibration bar support structure and the spacing between the tubes?RESPONSEThe tube discussed in the RAI is in Row 91 Column 24 (R91C24) in SG-A of the St. Lucie 2RSGs and had a wear indication created by contact with the side of the adjacent (neighboring)
V-shaped support pad at AV7+18.38, which is in close proximity to the AV8 location.
The tubethat is supported by the V-shaped support pad is Row 90 Column 23 (R90C23).
This indication (R91C24) is the first reported occurrence of this type of wear. The V-shapedsupport pads are designed to be in very close proximity to the adjacent tubes (i.e. neighboring tubes). The AVB bars and V-shaped support pads are located at different axial elevations.
Contact between a V-shaped support pad and the adjacent tubes is not expected by design. Thecontact between the V-shaped support pad and the neighboring tube is most likely due to amisalignment of the V-shaped support pad during manufacturing.
With this misalignment, it isthen possible that the V-shaped pad that is supporting tube R90C23 to induce wear on theadjacent tube (R91C24).
L-2015-089 Attachment Page 6 of 6RAI-7One tube was plugged since the length of the indication associated with the anti-vibration barwas shorter than most anti-vibration bar wear indications.
Discuss any insights on thisoccurrence.
RESPONSEThe indication referred to in RAI-7 is located in the St Lucie Unit-2, steam generator A (SG-A),tube Row 41 Column 154. To clarify, note that the tube was plugged because the indicated depth measurement using the +Point probe was 41% TW, as discussed in Note 4 of Section "e"of the SL2-21 SG Tube Inspection Report (ML 14279A237),
not because it had a short axiallength. The indication was reported as a single volumetric indication (SVI) at location AV3+2.02".This indication is at a location where the top of the U-bend is in close proximity to the bottom ofthe AVB bar. This location is referred to as the "crossover region" as shown in the sketch below.AVB Support, Crossover RegionThe SVI is due to mechanically-induced wear occurring between the tube and AVB support.Normally, this indication would be reported and sized as a wear indication, but it wasconservatively reported as an "SVI" to give it a unique reporting code in the database.
The shortaxial length of the indication (0.15") is most likely attributed to tube-to-AVB contact over a shortspan in the "crossover region" as shown in the sketch above.