ML061890003

Stations, Exemption from the Requirements of 10 CFR Part 50, Appendix G

ML061890003
Person / Time
Site:	Byron, Braidwood
Issue date:	11/22/2006
From:	Robert Kuntz NRC/NRR/ADRO/DORL/LPLF
To:	Crane C Exelon Generation Co
R. Kuntz LPL3-2
References
TAC MC8697, TAC MC8698, TAC MC8699, TAC MC8700
Download: ML061890003 (10)

Text

November 22, 2006Mr. Christopher M. Crane, President 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 - EXEMPTION FROM THE REQUIREMENTS OF 10 CFR PART 50, APPENDIX G (TAC NOS. MC8697, MC8698, MC8699, AND MC8700)

Dear Mr. Crane:

The Commission has approved the enclosed exemption from specific requirements of Title 10of the Code of Federal Regulations (10 CFR), Part 50, Appendix G, for Byron Station, Unit Nos. 1 and 2, and the Braidwood Station, Unit Nos. 1 and 2. This action is in response to your application dated October 3, 2005, which requested an exemption from the aforementioned regulations. The exemption allows the use of WCAP-16143-P in calculating certain reactor pressure vessel pressure-temperature limits in lieu of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c. A copy of the exemption is enclosed. The exemption has been forwarded to the Office of theFederal Register for publication. Sincerely,/RA/Robert F. Kuntz, Project ManagerPlant 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:

Exemptioncc w/enclosure: See next page November 22, 2006Mr. Christopher M. Crane, President 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 - EXEMPTION FROM THE REQUIREMENTS OF 10 CFR PART 50, APPENDIX G (TAC NOS. MC8697, MC8698, MC8699, AND MC8700)

Dear Mr. Crane:

The Commission has approved the enclosed exemption from specific requirements of Title 10of the Code of Federal Regulations (10 CFR), Part 50, Appendix G, for Byron Station, Unit Nos. 1 and 2, and the Braidwood Station, Unit Nos. 1 and 2. This action is in response to your application dated October 3, 2005, which requested an exemption from the aforementioned regulations. The exemption allows the use of WCAP-16143-P in calculating certain reactor pressure vessel pressure-temperature limits in lieu of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c. A copy of the exemption is enclosed. The exemption has been forwarded to the Office of theFederal Register for publication. 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:

Exemptioncc w/enclosure: See next pageDISTRIBUTION

PUBLICRidsNrrDciCvibLPL3-2 R/FRidsOgcRp RidsNrrDorlLpl3-2RidsAcrsAcnwMailCenterRidsNrrPMRKuntzRidsNrrDorl RidsNrrLADClarkeTBloomer, EDO Rgn III RidsRgn3MailCenterRidsNrrDorlDpr TWengert, NRRRidsNrrDlrRebbADAMS Accession Number: ML061890003OFFICELPL3-2/PMLPL3-2LPL3-2/LAOGCLPL3-2/BCDORL/DDNAMERKuntz:mwTWengertDClarkePMouldingDCollinsCHaneyDATE10/24/200610/20/2006 10/23/200610/19/200610/24/2006 11/22/2006OFFICIAL 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 7590-01-P UNITED STATES OF AMERICANUCLEAR REGULATORY COMMISSIONEXELON GENERATION COMPANY, LLCBYRON STATION, UNIT NOS. 1 AND 2BRAIDWOOD STATION, UNIT NOS. 1 AND 2DOCKET NOS. STN 50-454, STN 50-455, STN 50-456 AND STN 50-457EXEMPTION

1.0BACKGROUND

Exelon Generation Company, LLC (EGC, or the licensee) is the holder of FacilityOperating Licenses NPF-37, NPF-66, NPF-72, and NPF-77, which authorize operation of Byron Station, Unit Nos. 1 and 2 (Byron), and Braidwood Station, Unit Nos. 1 and 2 (Braidwood), respectively. The licenses provide, among other things, that the facilities are subject to all rules, regulations, and orders of the Nuclear Regulatory Commission (NRC, the Commission) now or hereafter in effect.The Byron facility consists of two pressurized-water reactors located in Ogle County inIllinois. The Braidwood facility consists of two pressurized-water reactors located in Will County in Illinois.

2.0REQUEST/ACTIONTitle 10 of the Code of Federal Regulations (10 CFR), Part 50, Appendix G, requiresthat pressure-temperature (P-T) limits be established for reactor pressure vessels (RPVs) during normal operating and hydrostatic or leak rate testing conditions. Specifically, 10 CFR Part 50, Appendix G states, "[t]he minimum temperature requirements...pertain to thecontrolling material, which is either the material in the closure flange or the material in the beltline region with the highest reference temperature...[T]he minimum temperaturerequirements and the controlling material depend on the operating condition (i.e., hydrostatic pressure and leak tests, or normal operation including anticipated operational occurrences), the vessel pressure, whether fuel is in the vessel, and whether the core is critical. The metal temperature of the controlling material, in the region of the controlling material which has the least favorable combination of stress and temperature, must exceed the appropriate minimum temperature requirement for the condition and pressure of the vessel specified in Table 1 [of 10 CFR Part 50, Appendix G]." Footnote 2 to Table 1 of 10 CFR Part 50, Appendix G,specifies that RPV minimum temperature requirements related to RPV closure flange considerations shall be based on "[t]he highest reference temperature of the material in the closure flange region that is highly stressed by bolt preload."In order to conform to certain provisions of proposed amendments that would modify theByron and Braidwood Technical Specifications (TS) to revise the pressure-temperature limits report (PTLR) methodology for each unit, EGC requested in its application dated October 3, 2005, that the NRC staff exempt Byron and Braidwood from the specific requirements of 10 CFR Part 50, Appendix G, as they pertain to the establishment of minimum temperature requirements, for all modes of operation addressed by 10 CFR Part 50, Appendix G, based on the material properties of the material of the RPV closure flange region that is highly stressed by the bolt preload. The requirements from which EGC requested that Byron and Braidwood be exempted shall be referred to, for the purpose of this exemption as, "those requirements related to the application of footnote (2) to Table 1 of 10 CFR Part 50, Appendix G."EGC's technical basis was submitted to the NRC by letter dated October 3, 2005, whichincluded as an attachment Westinghouse Report WCAP-16143-P, "Reactor Closure Head/Vessel Flange Requirements Evaluation for Byron/Braidwood Units 1 and 2."

WCAP-16143-P included a fracture mechanics analysis of postulated flaws in the Byron and Braidwood RPV closure flange regions under boltup, 100 F/hr heatup, 100 F/hr cooldown,and steady-state conditions, with the heatup and cooldown transients being modeled in accordance with what would be permissible using P-T limit curves based on Byron and Braidwood beltline materials. Westinghouse performed finite element modeling to calculate the stresses present at critical locations within the flange region and determined that the 100 F/hrheatup transient was the most severe condition, with the upper head-to-flange weld being the most limiting location. With these stresses, Westinghouse calculated the applied stress intensity (KI applied) for semi-elliptical, outside diameter initiated, surface breaking flaws with anaspect ratio (length vs. depth) of 6:1, and with depths ranging from 0 to 90 percent of the thickness of the component wall. The KI applied values were calculated in accordance with theAmerican Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, Appendix G, Subparagraph G-2220 requirements for the analysis of flange locations. Westinghouse then compared these KI applied values to ASME Code lower-boundstatic crack initiation fracture toughness (K IC) values determined from the nil-ductility transitionreference temperature (RT NDT) values for the Byron and Braidwood RPV closure flangematerials. Westinghouse also provided an assessment of the potential for changes in the material RT NDT values for the Byron and Braidwood RPV closure flange materials due tothermal aging resulting from exposure to the RPV operating environment.The use of ASME Code K IC as the material property for the fracture mechanics analysisrepresents the most significant change between the analysis provided in WCAP-16143-P and the analysis that was performed as the basis for establishing the minimum temperature requirements in 10 CFR Part 50, Appendix G. The minimum temperature requirements related to footnote 2 to Table 1 of 10 CFR Part 50, Appendix G were incorporated into the Code ofFederal Regulations in the early 1980s and were based on analyses that used ASME Codelower-bound crack arrest/dynamic test fracture toughness (K IA) as the parameter for characterizing a material's ability to resist crack initiation and propagation. The use of ASME Code K IA is always conservative with respect to the use of ASME Code K IC for fracturemechanics evaluations, and its use in the evaluations that established the requirements in 10 CFR Part 50, Appendix G was justified based on the limited knowledge of RPV material behavior that was available in the early 1980s. However, the use of ASME Code K IC is moreconsistent with the actual physical processes that would govern flaw initiation under conditions of normal RPV operation, including RPV heatup, cooldown, and hydrostatic and leak testing.

Based on its current understanding of the behavior of RPV materials, the NRC staff has routinely approved the use of ASME Code K IC by licensees as the basis for evaluating RPVbeltline materials; licensees have previously demonstrated compliance with the intent of 10 CFR Part 50, Appendix G through the use of the ASME Code, first as Code Cases N-640 and N-641, and now via ASME Code,Section XI, Appendix G, which has been revised to use

K IC in lieu of K IA. The minimum K IC value given in the ASME Code for RPV steel, regardless of thematerial RT NDT value or temperature, is 33.2 ksiin. This value represents the "lower shelf" ofthe ASME Code K IC curve. Based on information in WCAP-16143-P, it is apparent that the KI applied for any flaw up to 1/4 of the wall thickness (1/4 T) at the limiting location (refer toWCAP-16143-P, Figure 4-2), would not exceed 33.2 ksiin (even taking into account the NRCstaff's consideration of ASME Code structural factors) until between 1 and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> into the

100 F/hr heatup transient. The temperature at the tip of postulated flaws up to 1/4 T sizewould be adequate at that time to ensure that the limiting Byron and Braidwood flange materials would exhibit fracture toughness properties in excess of ASME Code "lower shelf" behavior. The NRC staff has determined that the analysis provided in WCAP-16143-P hasdemonstrated, for the most limiting transient addressed by 10 CFR Part 50, Appendix G, that the combination of factors that would have to exist for brittle failure to occur (high stresses in the RPV flange region along with low temperature at the metal of the flange region) can notexist simultaneously, and based on consideration of Byron and Braidwood's beltline materials,the structural integrity of the Byron and Braidwood RPV closure flange materials will not be challenged by facility operation in accordance with P-T limit curves. Therefore, the more conservative minimum temperature requirements related to footnote 2 to Table 1 of 10 CFR Part 50, Appendix G are not necessary to meet the underlying intent of 10 CFR Part 50, Appendix G, to protect the Byron and Braidwood RPVs from brittle failure during normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions.

3.0DISCUSSIONPursuant to 10 CFR 50.12, the Commission may, upon application by any interestedperson or upon its own initiative, grant exemptions from the requirements of 10 CFR Part 50, when (1) the exemptions are authorized by law, will not present an undue risk to public health or safety, and are consistent with the common defense and security; and (2) when special circumstances are present. Special circumstances are present whenever, according to 10 CFR 50.12(a)(2):(i) Application of the regulation in the particular circumstances conflicts with other rules or requirements of the Commission; or (ii) Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule; or (iii) Compliance would result in undue hardship or other costs that are significantly in excess of those contemplated when the regulation was adopted, or that are significantly in excess of those incurred by others similarly situated; or (iv) The exemption would result in benefit to the public health and safety thatcompensates for any decrease in safety that may result from the grant of the exemption;

or (v) The exemption would provide only temporary relief from the applicable regulation and the licensee or applicant has made good faith efforts to comply with the regulation;

or (vi) There is present any other material circumstance not considered when the regulation was adopted for which it would be in the public interest to grant an exemption.

If such condition is relied on exclusively for satisfying paragraph (a)(2) of this section, the exemption may not be granted until the Executive Director for Operations has consulted with the Commission.

The NRC staff finds that special circumstances exist pursuant to 10 CFR 50.12(a)(2)(ii)in that the application of the regulation is not necessary to achieve the underlying purpose of the rule. As stated in Section 2.0 above, the more conservative minimum temperature requirements related to footnote 2 to Table 1 of 10 CFR Part 50, Appendix G are not necessary to meet the underlying intent of 10 CFR Part 50, Appendix G, to protect the Byron and Braidwood RPVs from brittle failure during normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions.

Authorized by LawThis exemption would allow the use of an alternative methodology in calculating theRPV P-T limits for Byron and Braidwood in lieu of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c. As stated above, 10 CFR 50.12 allows the NRC to grant exemptions from the requirement of 10 CFR Part 50. Furthermore, Section 50.60(b) to 10 CFR Part 50 allows the use of alternatives to 10 CFR Part 50, Appendices G and H, when an exemption is granted by the NRC under 10 CFR 50.12. Therefore, this exemption is authorized by law. No Undue Risk to Public Health and SafetyThe underlying purpose of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c, is tomaintain the appropriate fracture margin in the RPV closure head region.The proposed methodology for the Byron and Braidwood P-T limits relies, in part, onASME Code,Section XI, Appendix G, which allows the use of the K IC fracture toughness curverather than the K IA curve. P-T limits developed using the K IC fracture toughness curve permit amuch higher allowable pressure through the entire range of temperatures. The benefit is negated at temperatures below RT NDT +120 F because of the additionalflange requirement of 10 CFR Part 50, Appendix G. Using the K IC fracture toughness curve, theanalyses presented in WCAP-16143-P show that there is significant margin between the applied stress intensity factor at boltup and the material fracture toughness at cracks postulated to exist in the highest stress region of the closure head/flange region. The analyses also show that the boltup temperature requirement for Byron and Braidwood could be satisfied at 60 F orhigher, easily justifying boltup at ambient temperature. Based on its review, the NRC staff finds that the results presented in WCAP-16143-Pdemonstrate that the 10 CFR Part 50, Appendix G RPV closure head flange requirement can be eliminated and appropriate fracture margins would still be maintained. Based on the above, no new accident precursors are created by using an alternativemethodology in calculating the RPV P-T limits; thus, the probability of postulated accidents is not increased. Also, based on the above, the consequences of postulated accidents are not increased. Therefore, there is no undue risk to public health and safety.

Consistent with Common Defense and SecurityThe proposed exemption would allow the use of an alternative methodology incalculating the RPV P-T limits, in lieu of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c. This change has no relation to security issues. Therefore, the common defense and security is notimpacted by this exemption.

Special CircumstancesSpecial circumstances, in accordance with 10 CFR 50.12(a)(2), are present wheneverapplication of the regulation in the particular circumstances would not be necessary to achieve the underlying purpose of the rule. The underlying purpose of 10 CFR Part 50, Appendix G, paragraph IV.A.2.c is to maintain the appropriate fracture margin in the RPV closure head region.

The NRC staff examined the licensee's rationale to support the exemption request and, based on its independent review of the information provided in WCAP-16143-P and in EGC's October 3, 2005, application, the NRC staff agrees that an acceptable technical basis has been established to exempt Byron and Braidwood from requirements related to the application of footnote 2 to Table 1 of 10 CFR Part 50, Appendix G. The NRC staff finds that the technical basis provided by EGC demonstrates that an adequate margin of safety against brittle failure would continue to be maintained for Byron and Braidwood RPVs without the application of those requirements related to the application of footnote 2 to Table 1 of 10 CFR Part 50, Appendix G, for normal operation under both core critical and core non-critical conditions and RPV hydrostatic and leak test conditions. The NRC staff concludes, pursuant to 10 CFR 50.12(a)(2)(ii), that the underlying purpose of 10 CFR Part 50, Appendix G will be achieved for Byron and Braidwood without the application of those requirements related to the application of footnote 2 to Table 1 of 10 CFR Part 50, Appendix G. Therefore, since the underlying purpose of 10 CFR Part 50, Appendix G is achieved, thespecial circumstances required by 10 CFR 50.12(a)(2) for the granting of an exemption from those requirements related to the application of footnote 2 to Table 1 of 10 CFR Part 50, Appendix G, exist.

4.0CONCLUSION

Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12(a), theexemption is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security. Also, special circumstances are present. Therefore, the Commission hereby grants EGC an exemption from those requirements related to the application of footnote 2 to Table 1 of 10 CFR Part 50, Appendix G, for Byron and Braidwood.Pursuant to 10 CFR 51.32, the Commission has determined that the granting of thisexemption will not have a significant effect on the quality of the human environment (71 FR 57577). This exemption is effective upon issuance.

Dated at Rockville, Maryland, this 22nd day of November 2006.FOR THE NUCLEAR REGULATORY COMMISSION/RA/Catherine Haney, DirectorDivision of Operating Reactor Licensing Office of Nuclear Reactor Regulation