ML14337A043
| ML14337A043 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 11/20/2014 |
| From: | Berg M South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-14003199, TAC MF4193 | |
| Download: ML14337A043 (5) | |
Text
Nuclear Operating Company South Texas Pro/ect Electric Generating Station PO. Bar 289 Wadsworth, T7eas 77483 November 20, 2014 NOC-AE-14003199 10 CFR 50.55a File No. G25 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Response to Request for Additional Information -
South Texas Project (STP), Unit 2 Steam Generator (SG) Tube Inspection Report (TAC MF4193)
References:
- 1. Letter; M. Berg to NRC Document Control Desk; "2RE16 Inspection Summary Report for Steam Generator Tubing;" NOC-AE-14003139; dated May 22, 2014 (ML14161A146)
- 2. E-mail; B. Singal to L. Sterling; "Request for Additional Information (RAI) - South Texas Project (STP), Unit 2 Steam Generator (SG) Tube Inspection Report (TAC MF4193);"
AE-NOC-14002583;dated October 29, 2014 (ML14302A821)
By Reference 1, the STP Nuclear Operating Company (STPNOC) submitted the results of the South Texas Project Unit 2 steam generator tube inspection performed during refueling outage 2RE16. By Reference 2, the NRC staff requested additional information to complete its review.
STPNOC's response to Reference 2 is provided in the attachment to this letter.
There are no commitments in this letter.
If there are any questions, please contact Drew Richards at (361) 972-7666 or me at (361) 972-7030.
Michael Berg Manager, Design Engineering Testing & Programs Engineering MJB/amr
Attachment:
Response to Request for Additional Information - STP Unit 2 Steam Generator Tube Inspection Report STI: 33992531
NOC-AE-14003199 Page 2 of 2 cc:
(paper copy)
(electronic copy)
Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 1600 East Lamar Boulevard Arlington, TX 76011-4511 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8 B1) 11555 Rockville Pike Rockville, MD 20852 NRC Resident Inspector U. S. Nuclear Regulatory Commission P. O. Box 289, Mail Code: MN116 Wadsworth, TX 77483 Steve Frantz Morgan, Lewis & Bockius LLP Balwant K. Singal U. S. Nuclear Regulatory Commission John Ragan Chris O'Hara Jim von Suskil NRG South Texas LP Kevin Polio Cris Eugster L. D. Blaylock CPS Energy Peter Nemeth Crain Caton & James, P.C.
C. Mele John Wester City of Austin Richard A. Ratliff Texas Department of State Health Services Robert Free Texas Department of State Health Services STI: 33992531
Attachment NOC-AE-14003199 Page 1 of 3 Response to Request for Additional Information -
STP Unit 2 Steam Generator Tube Inspection Report By letter dated May 22, 2014 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML14161A146), South Texas Project Nuclear Operating Company (the licensee) submitted information summarizing the results of the steam generator tube inspections performed at South Texas Project, Unit 2 during refueling outage 2RE16.
In order to complete the review, the U.S. Nuclear Regulatory Commission staff requests the following additional information; STP responses are provided below each bolded request:
- 1.
It is indicated on page 8 of the Attachment, under the "Plug Inspection Results" that "no anomalies were noted." Please clarify whether all plugs were confirmed to be present and free from degradation.
STP Response: STP confirms that all tube plugs were inspected during 2RE16. All tube plugs were present and free from degradation.
- 2.
It is indicated on page 8 of the Attachment, under the "Bowl Inspection Results" that the results were "satisfactory." Please clarify whether any degradation was noted as a result of this inspection.
STP Response: STP confirms that no steam generator channel head bowl degradation was observed during 2RE16 inspections.
- 3.
It is indicated on page 3 of the Attachment that the technical specifications require full-length bobbin inspection of all tubes. Please clarify since the technical specifications do not appear to have a specific reference to an inspection probe; rather, it requires, in part, use of probes capable of detecting degradation.
STP Response: The STP Technical Specifications do not reference any particular probe type. The Technical Specification Steam Generator Program ensures that SG tube integrity is maintained. Although not required by Technical Specifications, STP uses bobbin probe in conjunction with rotating pancake coil to satisfy Technical Specification requirements.
- 4.
The foreign object search and retrieval was performed in every fourth column in three steam generators (SGs) and every second column in one SG. Please clarify the reason for the difference in scope.
STP Response: Plant piping is configured such that loose parts tend to deposit into SG 2D because the feedwater piping for SG 2D is the last outlet on the common header.
Foreign objects tend to move down the common header until forced to enter the SG 2D feedwater connection. Typically, 50% of the loose parts deposit into SG 2D while the remaining 50% deposit in the other three steam generators. Thus, South Texas focuses foreign object search and retrieval efforts in SG 2D.
Attachment NOC-AE-14003199 Page 2 of 3
- 5.
A number of proximity signals were reported. Please discuss whether these signals have changed since SG installation. If so, discuss the reason for the changing signals. Also, please discuss whether the number of signals has increased with time.
STP Response: Until 2RE16, STP did not report proximity signals. However; South Texas has maintained a very conservative reporting criteria for dings (>2.0 voltage peak-peak), dings with rotation (>0.75 voltage peak-peak), and manufacturing burnish mark type signals (>0.50 voltage peak-peak) during previous inspection outages. Although targeted toward flaw detection and anomaly tracking (not specifically toward proximity),
this process did provide confidence that degradation associated with tube-to-tube contact would have been identified, if present.
For 2RE16, STP performed a manual evaluation, specifically for proximity signals, of all bobbin data collected. All proximity locations were rotating pancake coil tested to confirm the presence of proximity and/or the presence of low level flaw signals. Proximity was confirmed; however, no degradation was observed associated with proximity indications. A review of historical data shows that these proximity indications were present in all previous inservice inspections conducted during 2RE10 (2004) and 2RE13 (2008). The proximity indications have not changed since the first inservice inspection conducted during 2RE10.
In future inspection outages, STP plans to inspect all previously identified proximity indications with rotating pancake coil probe as well as any newly identified proximity indications identified via bobbin probe.
- 6.
A number of dings were reported. Please discuss the cause of the dings and whether the number/severity has changed with time.
STP Response: Dings in the STP Unit 2 Steam Generators occurred during fabrication.
Uneven heating during shell welding resulted in temporary support plate warping and slight tube denting at the 9 th support plate along the periphery of the bundle. These dings are relatively small, generally less than four volts. The fabrication induced dings are not growing based on a comparison of dings observed in 2RE13 (2008) and 2RE16 (2013).
Some dings indicated small growth while others appeared to be smaller. Since it is not realistic for a ding to shrink in size, it is believed that measurement technique repeatability results in slight variation of indicated dent size from inspection to inspection with some indicating larger with others indicating smaller.
A small number of new dings are reported each inspection outage. STP does not believed that new dings are developing; instead, dings that were just below the reporting criteria of two volts during previous inspections now measure just above the reporting criteria and are reported. This is corroborated by the fact that the newly reported dings are slightly greater than two volts. This phenomenon is believed to be caused by measurement technique repeatability similar to discussion of ding growth above.
STP monitors previously identified dings each time the steam generators are opened and newly observed dings greater than two volts are documented. Bobbin is the primary inspection probe with follow-up inspection with rotating pancake probe for all distorted or new dings. These small fabrication induced dings are not expected to negatively impact the performance of the steam generators over the remaining life of the plant.
Attachment NOC-AE-14003199 Page 3 of 3
- 7.
Please discuss the reason for the stud-hole gauging tests and discuss which stud holes were tested.
STP Response: Over many years of service it is possible that wear and/or galling may occur on the primary manway stud-hole threads or stud threads. The original equipment manufacturer recommends that the stud holes be gauged with "go/no-go" gauges. The purpose of the test is to ensure that no significant wear has occurred that could negatively impact the structural integrity of the bolted joint. Additionally, the studs are gauged to identify thread wear. During 2RE16, all primary manway stud holes and studs were gauged on steam generator 2C and no degradation was found. Bolting on one steam generator primary manway is gauged each inspection outage.