ML080070454

Request for Additional Information Regarding the 2007 Steam Generator Tube Inspections

ML080070454
Person / Time
Site:	Byron
Issue date:	01/17/2008
From:	Thorpe-Kavanaugh M NRC/NRR/ADRO/DORL/LPLIII-2
To:	Pardee C Exelon Generation Co
Thorpe-Kavanaugh, Meghan, LPL3-1
References
TAC MD6203
Download: ML080070454 (6)

Text

January 17, 2008 Mr. Charles G. Pardee Chief Nuclear Officer and Senior Vice President Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO. 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING THE 2007 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD6203)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated July 31, 2007, Exelon Generation Company, LLC (the licensee) submitted information pertaining to the 2007 steam generator tube inspection performed at Byron Station, Unit No. 2 during refueling outage 13.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on January 3, 2008, it was agreed that you would provide a response within 30 days from the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC=s goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-5735.

Sincerely,

/RA/

Meghan M. Thorpe-Kavanaugh, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosure:

Request for Additional Information cc w/encl: See next page

Mr. Charles G. Pardee January 17, 2008 Chief Nuclear Officer and Senior Vice President Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO. 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING THE 2007 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. MD6203)

Dear Mr. Pardee:

By letter to the Nuclear Regulatory Commission (NRC) dated July 31, 2007, Exelon Generation Company, LLC (the licensee) submitted information pertaining to the 2007 steam generator tube inspection performed at Byron Station, Unit No. 2 during refueling outage 13.

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on January 3, 2008, it was agreed that you would provide a response within 30 days from the date of this letter.

The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC=s goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-5735.

Sincerely,

/RA/

Meghan M. Thorpe-Kavanaugh, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosure:

Request for Additional Information cc w/encl: See next page DISTRIBUTION:

PUBLIC LPL3-2 R/F RidsNrrDorlLpl3-2 RidsNrrPMMThorpe-Kavanaugh RidsNrrPMCGoodwin RidsNrrLAEWhitt RidsAcrsAcnwMailCenter RidsOgcRp RidsRgn3MailCenter RidsNrrDorlDpr EWong, NRR ADAMS Accession Number: ML080070454 NRR-088 OFFICE LPL3-2/PM LPL3-2/PM LPL3-2/LA LPL3-2/BC NAME CGoodwin:sp MThorpe-Kavanaugh EWhitt RGibbs DATE 1/14/08 1/16/08 1/14/08 1/17/08 OFFICIAL RECORD COPY

Byron Station, Unit Nos. 1 and 2 Byron Resident Inspectors U. S. Nuclear Regulatory Commission cc: via e-mail Corporate Distribution Ms. Lorraine Creek Exelon Generation Company, LLC RR 1, Box 182 via e-mail Manteno, IL 60950 Byron Distribution Chairman, Ogle County Board Exelon Generation Company, LLC P.O. Box 357 via e-mail Oregon, IL 61061 Illinois Emergency Management Agency Mrs. Phillip B. Johnson Division of Disaster Assistance & 1907 Stratford Lane Preparedness Rockford, IL 61107 via e-mail Attorney General Mr. Dwain W. Alexander, Project Manager 500 S. Second Street Westinghouse Electric Corporation Springfield, IL 62701 via e-mail Chairman Howard A. Learner Will County Board of Supervisors Environmental Law and Policy Will County Board Courthouse Center of the Midwest Joliet, IL 60434 via e-mail Mr. Barry Quigley Byron Senior Resident Inspector 3512 Louisiana U.S. Nuclear Regulatory Commission Rockford, IL 61108 via e-mail

REQUEST FOR ADDITIONAL INFORMATION STEAM GENERATOR TUBE INSPECTIONS 2007 BYRON STATION, UNIT NO. 2 DOCKET NO. 50-455 In reviewing the Exelon Generation Company=s (Exelon=s) submittal dated July 31, 2007 (Agencywide Documents Access and Management System Accession No. ML072120520),

related to the 2007 steam generator tube (SG) inspection, for the Byron Station, Unit No. 2 (Byron), the NRC staff has determined that the following information is needed in order to complete its review:

1. For each refueling outage or SG tube inspection since installation of the SGs, please provide the cumulative effective full power months that the SGs have operated.

2. The +PointTM coil was used to inspect the U-bend region of 25 percent of the SG tubes in rows 1 and 2. Please discuss when the last time the U-bend region of the remaining 75 percent of the row 1 and 2 tubes was inspected. In addition, please confirm that you have inspected 50 percent of the portions of the tubes (with the objective of detecting flaws that may satisfy the tube repair criteria) susceptible to cracking (e.g.,bulges/overexpansions, dents, etc.) by the refueling outage nearest the midpoint of your current sequential period and the remaining 50 percent by the refueling outage nearest the end of your current sequential period, whichever is applicable given your response to Question 1.

3. Twenty five percent of the dents and dings whose voltages were greater than 5 volts were inspected with a rotating probe, and 50-percent of the dents and dings whose voltages were between 3 and 5 volts were inspected with a rotating probe. Given the limited ability of the bobbin probe to detect any forms of degradation in dents whose voltages are greater than 5 volts, please discuss why more inspections were performed in the lower voltage dents than in the higher voltage dents.

4. In evaluating the SG tube examination techniques in Table 4.1, it does not appear that the SG tubes were inspected for axially oriented outside diameter stress corrosion cracking in dents and dings. In addition, it does not appear that the SG tubes were inspected for axially and circumferentially oriented outside diameter stress corrosion cracking in the U-bend region. Please confirm that the techniques used were capable of finding these degradation mechanisms.

5. Please clarify the last sentence in section 4.2.3, Tubes containing bulges and overexpansions within the initial sample were inspected from the top of the hot leg tubesheet +3 inches to -17 inches below the top of the tubesheet. For example, is the sentence indicating that the 30 percent sample of bulges and overexpansions was a subset of the 30 percent sample of tubes inspected from 3 inches above the top of the tubesheet to 17 inches below the top of the tubesheet?

Enclosure

6. Additional pre-heater baffle plate expansion transitions were inspected in three of the SGs. Please discuss the reason for expanding the sample, the final scope of examination (e.g., 35 percent of the expansions), and the results of the inspection.

Please discuss the purpose and nature of the flow block. Please discuss the results of the visual inspection of the preheater expansion transitions in SG 2D and discuss why a visual inspection was only necessary. In Attachment B.5, tubesheet maps for only SGs 2A and 2B were provided. Please clarify whether the preheater baffle expansion transitions were inspected in SG 2C.

7. Please clarify the number of tubes that have expansion transition and bulges that are significantly outside the tubesheet.

8. In Section 5.1.2, it is stated that, two adjacent tubes that contained possible loose part (PLP) signals with no detectable degradation (R33-54 and R34-C64) located at the 8th TSP and in Section 5.2.4 it states, Tubes R33-C64 and R34-C65 in SG 2C were preventively plugged and stabilized because they contained a possible loose part signal. Please clarify which tubes contained a possible loose part signal and which were plugged.

9. In Section 5.1.2, it is stated, Additionally, the foreign object is adjacent to two tubes that were plugged during Refueling Outages 2 and 7 that were not stabilized due to what was believed at the time to be pitting degradation at TSP 08H. Is it now believed that the degradation is now due to foreign object wear instead of pitting? If so, please discuss whether the eddy current data of these previously plugged tubes is consistent with eddy current data from wear indications attributed to loose parts.

10. In Section 5.2.4, it is stated, a large 139.4 volt bulge located at . Please discuss whether this bulge has been present since the steam generators were installed or whether it has changed with time. If it has not been present since manufacture or has changed with time, please discuss the nature of this bulge and/or the reason for any change with time.

11. Please clarify the following statement in Section 6.0: Satisfying the structural limit ensures that the SG tube integrity performance criteria for structural integrity, accident induced leakage and operational leakage will be maintained. Is this statement implying that a tube that has structural integrity would not leak at a rate that is in excess of the accident induced or normal operational leakage limit? If so, please provide the technical basis.

12. Please discuss the scope and results of any foreign object search and retrieval. If any loose parts/foreign objects were left in the steam generators (other than those discussed in your July 31, 2007, letter), please discuss the basis for leaving these parts in service (e.g., engineering analysis supports leaving part in service from a tube integrity perspective).