ML092250384
| ML092250384 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 08/20/2009 |
| From: | Balwant Singal Plant Licensing Branch IV |
| To: | Flores R Luminant Generation Co |
| Singal, Balwant, 415-3016, NRR/DORL/LPL4 | |
| References | |
| TAC ME0123 | |
| Download: ML092250384 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 20, 2009 Mr. Rafael Flores Senior Vice President and Chief Nuclear Officer Luminant Generation Company LLC P.O. Box 1002 Glen Rose, TX 76043 SUB~IECT: COMANCHE PEAK STEAM ELECTRIC STATION, UNIT 2 - REVIEW OF THE 2008 STEAM GENERATOR TUBE INSPECTIONS PERFORMED DURING REFUELING OUTAGE 2RF10 (TAC NO. ME0123)
Dear Mr. Flores:
By letter dated September 18, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082690600), as supplemented by letter dated April 9, 2009 (ADAMS Accession No. ML091070586), Luminant Generation Company, LLC (the licensee),
submitted information summarizing the results of the 2008 steam generator (SG) tube inspections performed at the Comanche Peak Steam Electric Station (CPSES), Unit 2 during refueling outage 2RF1 O. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2008 SG tube inspections at CPSES, Unit 2 in a letter dated June 20,2008 (ADAMS Accession No. ML081710055).
The NRC staff has completed its review of these reports and concludes that the licensee provided the information required by the CPSES, Unit 2 Technical Specifications and no additional follow-up is required at this time. The results of the NRC staff's review of the reports submitted by the licensee are summarized in the enclosure to this letter. If you have any questions, please contact me at 301-415-3016 or via e-mail at balwant.singal@nrc.gov.
Sincerely, Po""' ILU~u..t w,~~~
Balwant K. Singal, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-446
Enclosure:
As stated cc w/encl: Distribution via Listserv
OFFICE OF NUCLEAR REACTOR REGULATION REVIEW OF INSPECTION REPORTS FOR 2008 STEAM GENERATOR TUBE INSPECTIONS PERFORMED DURING REFUELING OUTAGE 2RF10 LUMINANT GENERATION COMPANY LLC COMANCHE PEAK STEAM ELECTRIC STATION, UNIT 2 DOCKET NO. 50-446 By letter dated September 18, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082690600), as supplemented by letter dated April 9, 2009 (ADAMS Accession No. ML091070586), Luminant Generation Company LLC (the licensee),
submitted information summarizing the results of the 2008 steam generator (SG) tube inspections performed at the Comanche Peak Steam Electric Station (CPSES), Unit 2 during refueling outage 2RF1 O. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2008 SG tube inspections at CPSES, Unit 2 in a letter dated June 20, 2008 (ADAMS Accession No. ML081710055).
CPSES, Unit 2 has four Westinghouse Model D5 SGs. Each SG contains 4,570 thermally treated Alloy 600 tubes. Each tube has a nominal outside diameter of % inch and a nominal wall thickness of 0.043 inch. The tubes were hydraulically expanded at both ends for the full length of the tubesheet and are supported by a number of stainless steel 405 supports with quatrefoil-shaped holes.
The licensee provided the scope, extent, methods, and results of their SG tube inspections in the documents referenced above. In addition, the licensee described corrective actions, such as tube plugging, taken in response to the inspection findings. The tubes in all four SGs were inspected this outage.
After reviewing the information provided by the licensee, the NRC staff has the following observations and comments:
- Seventy-three tubes were identified as possibly having elevated residual stress.
Tubes with elevated residual stresses at other plants have primarily exhibited cracking at the tube support plate elevations.
- The licensee indicated that axial and circumferential indications were found in all four SGs during the +Point inspection of the hot-leg tube ends. A total of 13 tubes were identified with either axial or circumferential tube-end indications. Of these 13 tubes, one tube was identified as possibly having elevated residual stress. As a result, approximately 1.4 percent of the tubes with possibly elevated residual stresses had tube-end indications, whereas 0.07 percent of the remaining tubes had tube-end indications.
Enclosure
-2 tube-to-tubesheet contact pressure provide adequate margin against the potential for tube ejection. Using a similar justification, the licensee recently proposed a technical specification (TS) amendment to limit the extent of inspection in the tubesheet region, "License Amendment Request 09-007, Model D5 Steam Generator Alternate Repair Criteria," June 8,2009 (ADAMS Accession No. ML091670158). This amendment request is currently being reviewed by the NRC staff.
- The licensee indicated that primary water stress-corrosion cracking of the cold leg tube ends is not expected to exhibit significant cracking until cracking of the hot-leg tube ends is extensive. The NRC staff agrees that, all other factors being equal, tubes exposed to higher temperatures are generally more susceptible to stress-corrosion cracking than tubes exposed to lower temperatures. However, there are other factors that also influence a tube's susceptibility to stress corrosion cracking, such as stress and chemical effects. Operating experience has indicated that a specific tube may exhibit cracking on the cold leg before any cracking is observed in that tube on the hot leg. This suggests that there are factors other than temperature that contribute to the cracking, for example, residual stresses. In addition, flaw-like indications have been observed at the cold-leg tube ends before "extensive" cracking has been observed on the hot-leg.
- The licensee plans to implement a stretch power uprate of 4.5 percent of the original power rating during the fall 2009 refueling outage. The uprate will change the current core thermal power from 3458 megawatts (MWt) to 3612 MWt, which results in an increase of SG inlet temperature by 1.2 degrees Fahrenheit CF) over its current value of 621°F.
- The licensee provided structural limits for various types of flaws. The NRC staff did not review these limits in detail; however, the limits appear reasonable.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by the TSs. In addition, the staff concludes that there are no technical issues that warrant follow-up action at this time since the inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.
Principal Contributor: A. Obodoako Date: August 20, 2009
August 20, 2009 Mr. Rafael Flores Senior Vice President and Chief Nuclear Officer Luminant Generation Company LLC P.O. Box 1002 Glen Rose, TX 76043
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION, UNIT 2 - REVIEW OF THE 2008 STEAM GENERATOR TUBE INSPECTIONS PERFORMED DURING REFUELING OUTAGE 2RF10 (TAC NO. ME0123)
Dear Mr. Flores:
By letter dated September 18, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML082690600), as supplemented by letter dated April 9,2009 (ADAMS Accession No. ML091070586), Lurninant Generation Company, LLC (the licensee),
submitted information summarizing the results of the 2008 steam generator (SG) tube inspections performed at the Comanche Peak Steam Electric Station (CPSES), Unit 2 during refueling outage 2RF1 O. In addition to these reports, the U.S. Nuclear Regulatory Commission (NRC) staff summarized additional information concerning the 2008 SG tube inspections at CPSES, Unit 2 in a letter dated June 20,2008 (ADAMS Accession No. ML081710055).
The NRC staff has completed its review of these reports and concludes that the licensee provided the information required by the CPSES, Unit 2 Technical Specifications and no additional follow-up is required at this time. The results of the NRC staff's review of the reports submitted by the licensee are summarized in the enclosure to this letter. If you have any questions, please contact me at 301-415-3016 orvia e-mail at balwant.singal@nrc.gov.
Sincerely,
/raJ Balwant K. Singal, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-446
Enclosure:
As stated cc w/encl: Distribution via Listserv DISTRIBUTION:
PUBLIC RidsNrrDorlLpl4 Resource RidsRgn4MailCenter Resource LPLIV Reading RidsNrrPMComanchePeak Resource AObodoako, NRR/DCI/CSGB RidsAcrsAcnw_MailCTR Resource RidsNrrLAJBurkhardt Resource RidsNrrDciCsgb Resource RidsOgcRp Resource ADAMS Accession No: ML092250384 *Memo dated 7/30/09 OFFICE NRRlLPL4/PM NRRlLPL4/LA NRRlCSGB/BC (A) NRRlLPL4/BC NRRlLPL4/PM NAME BSingal JBurkhardt MGavrilas* MMarkley (MThadani for) BSingal DATE 8/17109 8/17109 6/30109 8/19/09 8/20109 OFFICIAL AGENCY RECORD