ML063400204

Byron and Braidwood, RAI Related to Application for Technical Specification Improvement Regarding Steam Generator Tube Integrity

ML063400204
Person / Time
Site:	Byron, Braidwood
Issue date:	12/13/2006
From:	Kuntz R F NRC/NRR/ADRO/DORL/LPLIII-2
To:	Crane C M Exelon Generation Co
kuntz, Robert , NRR/DORL, 415-3733
References
TAC MC8966, TAC MC8967, TAC MC8968, TAC MC8969
Download: ML063400204 (7)

Text

December 13, 2006Mr. Christopher M. CranePresident and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NOS. 1 AND 2 AND BRAIDWOOD STATION, UNITNOS. 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO APPLICATION FOR TECHNICAL SPECIFICATION IMPROVEMENT REGARDING STEAM GENERATOR TUBE INTEGRITY (TAC NOS. MC8966, MC8967, MC8968, AND MC8969)

Dear Mr. Crane:

By letter to the Nuclear Regulatory Commission (NRC) dated November 18, 2005, ExelonGeneration Company, LLC submitted an amendment request that would revise the technical specification requirements related to steam generator tube integrity, for the Byron Station, Unit Nos. 1 and 2, and Braidwood Station, Unit Nos. 1 and 2.The NRC staff is reviewing your submittal and has determined that additional information isrequired to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on December 5, 2006, it was agreed that you would provide a response within 60 days from the date of this letter. The NRC staff considers that timely responses to requests for additional information helpensure 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) 415-3733.Sincerely,/RA/Robert F. Kuntz, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket Nos. STN 50-454, STN 50-455, STN 50-456 and STN 50-457

Enclosure:

Request for Additional Informationcc w/encl: See next page Mr. Christopher M. CraneDecember 13, 2006President and Chief Nuclear Officer Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NOS. 1 AND 2, AND BRAIDWOOD STATION, UNITNOS. 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO APPLICATION FOR TECHNICAL SPECIFICATION IMPROVEMENT REGARDING STEAM GENERATOR TUBE INTEGRITY (TAC NOS. MC8966, MC8967, MC8968, AND MC8969)

Dear Mr. Crane:

By letter to the Nuclear Regulatory Commission (NRC) dated November 18, 2005, ExelonGeneration Company, LLC submitted an amendment request that would revise the technical specification requirements related to steam generator tube integrity, for the Byron Station, Unit Nos. 1 and 2, and Braidwood Station, Unit Nos. 1 and 2.The NRC staff is reviewing your submittal and has determined that additional information isrequired to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on December 5, 2006, it was agreed that you would provide a response within 60 days from the date of this letter. The NRC staff considers that timely responses to requests for additional information helpensure 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) 415-3733.Sincerely,/RA/Robert F. Kuntz, Project Manager Plant Licensing Branch III-2 Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket Nos. STN 50-454, STN 50-455, STN 50-456 and STN 50-457

Enclosure:

Request for Additional Information cc w/encl: See next page DISTRIBUTION:PUBLICLPL3-2 R/FRidsNrrDorlLpl3-2 RidsNrrPMCGrattonRidsNrrLAEWhittRidsAcrsAcnwMailCenterRidsOgcRpRidsRgn3MailCenterRidsNrrDorlDpr RidsNrrPMRKuntzRidsNrrDciCsgbADAMS Accession Number:ML063400204NRR-088 OFFICELPL3-2/PMLPL3-2/PMLPL3-2/LADCI/CSGB/BCLPL3-2/BC NAMERKuntz:mwCGrattonEWhittAHiserMMarshall DATE12/7/0612/7/0612/7/0612/11/0612/13/06OFFICIAL RECORD COPY Byron/Braidwood Stations cc:

Dwain W. Alexander, Project ManagerWestinghouse Electric Corporation Energy Systems Business Unit Post Office Box 355 Pittsburgh, PA 15230-0355Howard A. LearnerEnvironmental Law and Policy Center of the Midwest 35 East Wacker Dr., Suite 1300 Chicago, IL 60601-2110U.S. Nuclear Regulatory CommissionByron Resident Inspectors Office 4448 N. German Church Road Byron, IL 61010-9750Regional Administrator, Region IIIU.S. Nuclear Regulatory Commission Suite 210 2443 Warrenville Road Lisle, IL 60532-4351Ms. Lorraine CreekRR 1, Box 182 Manteno, IL 60950Chairman, Ogle County BoardPost Office Box 357 Oregon, IL 61061Mrs. Phillip B. Johnson1907 Stratford Lane Rockford, IL 61107Attorney General500 S. Second Street Springfield, IL 62701Illinois Emergency Management Agency Division of Disaster Assistance &

Preparedness 110 East Adams Street Springfield, IL 62701-1109Plant Manager - Byron StationExelon Generation Company, LLC 4450 N. German Church Road Byron, IL 61010-9794Site Vice President - ByronExelon Generation Company, LLC 4450 N. German Church Road Byron, IL 61010-9794U.S. Nuclear Regulatory CommissionBraidwood Resident Inspectors Office 35100 S. Rt. 53, Suite 79 Braceville, IL 60407County Executive Will County Office Building 302 N. Chicago Street Joliet, IL 60432Plant Manager - Braidwood Station Exelon Generation Company, LLC 35100 S. Rt. 53, Suite 84 Braceville, IL 60407-9619Ms. Bridget Little RoremAppleseed Coordinator 117 N. Linden Street Essex, IL 60935Document Control Desk - LicensingExelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555Site Vice President - BraidwoodExelon Generation Company, LLC 35100 S. Rt. 53, Suite 84 Braceville, IL 60407-9619Senior Vice President - Operations SupportExelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 Byron/Braidwood Stations Director - Licensing and Regulatory Affairs Exelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555Manager Regulatory Assurance - BraidwoodExelon Generation Company, LLC 35100 S. Rt. 53, Suite 84 Braceville, IL 60407-9619Manager Regulatory Assurance - ByronExelon Generation Company, LLC 4450 N. German Church Road Byron, IL 61010-9794Assistant General CounselExelon Generation Company, LLC 200 Exelon Way Kennett Square, PA 19348Vice President - Regulatory & Legal AffairsExelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555Manager Licensing - Braidwood/ByronExelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555Senior Vice President - Midwest OperationsExelon Generation Company, LLC 4300 Winfield Road Warrenville, IL 60555 ENCLOSUREREQUEST FOR ADDITIONAL INFORMATIONBYRON STATION, UNIT NOS. 1 AND 2,AND BRAIDWOOD STATION, UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454, STN 50-455,STN 50-456 AND STN 50-457In reviewing the Exelon Generation Company's (EGC) submittal dated November 18, 2005, assupplemented by letters dated August 18 and September 28, 2006, related to a proposed amendment to revise the technical specification requirements related to steam generator tube integrity, for the Byron Station, Unit Nos. 1 and 2 (Byron) and Braidwood Station, Unit Nos. 1 and 2 (Braidwood), the NRC staff has determined that the following information is needed in order to complete its review:

References:

1. EGC letter RS-05-129, "Application for Technical Specification Improvement RegardingSteam Generator Tube Integrity," dated November 18, 2005.2. EGC letter RS-06-109, "Response to Request for Additional Information RegardingApplication for Steam Generator Tube Integrity Technical Specification," dated August 18, 2006.Requested Information: 1.Regarding EGC's response to the request for information (RAI) question 8 (forByron/Braidwood, question 5 for Seabrook) in Reference 2, Attachment 6, pages 8 to 16, provide a plot of crack-opening angle for circumferential cracks located 4 inches from the bottom of the tubesheet as a function of crack length for normal operating and main steam line break conditions. Also, provide a plot of leak rate as a function of the same parameters, neglecting the effect of crevice resistance.2.Regarding EGC's response to RAI question 8 (for Byron/Braidwood, question 5 forSeabrook) in Reference 2, Attachment 6, pages 8 to 16, provide revised versions of Figures 3 and 4 to include the leak rate ratios for cracks in the range of 0.1 to 0.5 inches in length. It would seem from Figures 3 and 4, that if crack resistance dominates crevice resistance, then leakage ratios may exceed 2 for through wall crack lengths less than 0.5 inches for tubes near the periphery of the bundle, particularly for circumfrential cracks. Also, provide similar figures for the near radius and mid-radius locations.3.The discussion accompanying Figures 3 and 4 states that cracks less than 0.5 inches inlength are not expected to cause any "relative significant leakage." Please explain basis for concluding the leakage contribution from the population of circumferential cracks of through-wall length less than 0.5 inches is small, relative to the leakage contributionfrom the population of through-wall cracks greater than 0.5 inches in length such that the leakage ratio between normal operating and accident conditions is dominated by the leakage ratio (which is less than 2) exhibited by the population of cracks larger than 0.5 inches. This explanation should consider any relevant operating experience regarding the probability density function of 100 percent through wall crack lengths and, in addition, the plots provided in response to question 2 above.4.Regarding a statement in the discussion underneath Figure 4 that reads, "The resultsfrom the crack-only analyses show that in the absence of the dent the resistance to flow is increased and each crack type produces a lower leak rate ratio," please clarify what is meant by the "dent," and its impact on this statement. Additionally, please qualify what the increase in resistance to flow and lower leak ratios are relative to. 5.Reference 2, Attachment 6, page 12, Analysis of Circumferential Cracking, states thatthe circumferential crack model was developed in WCAP-15932-P, Revision 1, "Improved Justification of Partial Length RPC inspection of Tube Joints of Model F Steam Generators of Ameren-UE Callaway Plant," dated May 2003. WCAP-15932P, Appendix C states that the main loadings on a circumferential crack below the H*

distance are the pressure loads acting on the crack face. It is also stated in the WCAP that the internal pressure end cap load is not transmitted below about 1/3 the H*

distance. Assuming that H* is determined correctly, the NRC staff agrees that this statement is true for normal operating pressure provided the tube is severed immediately below the 1/3 H* distance. Similarly, the 3 delta P end cap load does notextend below the full H* distance assuming the tube is severed immediately below the H* distance. If the tube is not severed, then much of the end cap load will be transmitted below the H* distance. Taking an extreme example, the calculated H*

distance is based in part on pull out tests (on specimens that were basically severed at the bottom) where the pull out criterion was an axial displacement of 0.25 inches at the bottom of the specimen. If the tube is intact below the H* distance, then the tube must be able to stretch by 0.25 inches between the weld and the H* location which means there must be considerable force transmitted below the H* distance. For smaller end cap loads where no slippage takes place, a severed tube end would be expected to displace upward due to the accumulated strains in the tube to tubesheet joint above the severed location. If the tube is not completely severed, the tube below the crack would be expected to resist this displacement and thus resist some of the pullout load. The tube to tubesheet joint (where the tube is not severed inside the tubesheet) is a redundant structure. How much of the end cap load that gets transmitted below the crack location (assumed to be 17 inches down from the top of the tubesheet) depends on the stiffness of the friction joint above the crack relative to the stiffness of the tube below the crack. It is not clear from the NRC staff's review of the model that this effect has been evaluated. Thus, it is not clear to the NRC staff that the axial load acting on the circumferentially-cracked cross section is limited solely to the pressure acting on the crack faces and that no portion of the internal pressure end cap load is acting on the cross section. Please address this concern, including how the stiffness of the tube to tubesheet friction joint above the crack relative to the stiffness of the tube below the crack have been specifically accounted for. Has a detailed analysis (e.g., finite element analysis) been performed to determine how much of the full internal pressure end cap load is actually transmitted to the cracked cross section under normal operating andaccident conditions? If so, describe the analysis and the results. 6.The Reference 1 application included the following provision in TS 5.5.9c: "For Unit 2only, degradation found in the portion of the tube from the top of the hot leg tubesheet to 17 inches below the top of the tubesheet shall be plugged or repaired upon detection."

In the example accompanying the NRC staff's draft RAI No. 4, the NRC staff inadvertently left this sentence out. It wasn't the NRC staff's intent to suggest this sentence should be deleted. Describe your plan for re-including this sentence as part of TS 5.5.9c. Also, as a point of consistency and clarification, the word "degradation" in the above sentence and in TS5.5.9c.4.i should be replaced by the word "flaws" consistent with the rest of the technical specifications. Please describe your plan for making this change as well.7.Did any of the hydraulic expansions in the Model D5 SGs experience a stress reliefduring fabrication, directly or indirectly (e.g., as a result of stress relieving the shell to tubesheet welds)? If so, how was this reflected in the pullout and leakages tests in support of the tubesheet amendment requests? 8.The tubesheet bow analysis described in Westinghouse report, LTR-CDME-05-32-P,Rev 2, submitted as Attachment 7 to Reference 1, takes credit for resistance against bow provided by the divider plate. Cracks in the welds connecting the tubesheet and divider plate have been found by inspection at certain foreign steam generators. Please discuss how such cracks, if present at the Byron/Braidwood units, could affect the conservatism of the proposed 17-inch tubesheet inspection distance requirement for ensuring structural and leakage integrity.