ML092870637

Relief Request B-9 for Unit 1 and B-8 for Unit 2 to Extend the Inservice Inspection Interval for the Reactor Vessel Weld Examination

ML092870637
Person / Time
Site:	Comanche Peak
Issue date:	12/22/2009
From:	Markley M Plant Licensing Branch IV
To:	Flores R Luminant Generation Co
Singal, Balwant, 415-3016, NRR/DORL/LPL4
References
TAC ME0777, TAC ME0778
Download: ML092870637 (10)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 22, 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, UNITS 1 AND 2 - REQUEST FOR RELIEF TO EXTEND THE INSERVICE INSPECTION INTERVAL FOR THE REACTOR VESSEL WELD EXAMINATION (TAC NOS. ME0777 AND ME0778)

Dear Mr. Flores:

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed and evaluated the information provided by Luminant Generation Company LLC (the licensee) in its letter dated March 4, 2009, as supplemented by letter dated September 14, 2009. The licensee requested approval for the use of the alternative to extend the inservice inspection (lSI) interval for examinations of the reactor pressure vessel Category B-A and Category B-D welds from 10 years to 20 years for Comanche Peak Steam Electric Station (CPSES), Units 1 and 2 (Relief Request B-9 for Unit 1 and B-8 for Unit 2).

The application dated March 4, 2009, also included an amendment request to add a license condition for submittal of lSI information and analysis requested in paragraph (e) of the final Title 10 of the Code of Federal Regulations (10 CFR), Section 50.61 a, or the proposed rule (October 3, 2007; 72 FR 56275), prior to issuance of the final 10 CFR 50.61 a, following completion of each American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Category B-A and Category B-D Reactor Vessel weld inspection. By letter dated September 14, 2009, the licensee revised its application for relief request for a one-time extension only and withdrew the proposed amendment and associated license condition.

The NRC staff has completed its review of the submittals for Relief Requests B-9 and B-8 for CPSES, Units 1 and 2 and concludes that extending the current lSI interval for the identified Category B-A and Category B-D components from 10 years to 20 years results in a small and acceptable risk increase. This conclusion is based on the fact that the plant-specific information provided by the licensee is bounded by the data in the NRC-approved topical report WCAP 16168-NP, Revision 2, and the request meets all the conditions and limitations described in the approved topical report and the associated safety evaluation report. Therefore, Relief Requests B-9 and B-8 provide an acceptable level of quality and safety, and the alternative can be authorized pursuant to 10 CFR 50.55a(a)(3)(i) to extend the licensee's current second lSI interval to approximately 2020 for CPSES, Unit 1 and 2023 for CPSES, Unit 2, with the licensee performing the subject examinations in 2019 for CPSES, Unit 1 and 2021 for CPSES, Unit 2.

R. Flores -2 All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

The NRC safety evaluation is enclosed. If you have any questions, please contact Balwant K.

Singal at 301-415-3016 or bye-mail at Balwant.Singal@nrc.gov.

Sincerely, Michael 1. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-445 and 50-446

Enclosure:

As stated cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NOS. B-9 (UNIT 1) AND B-8 (UNIT 2)

SECOND 10-YEAR INSERVICE TESTING INTERVAL LUMINANT GENERATION COMPANY LLC COMANCHE PEAK STEAM ELECTRIC STATION, UNITS 1 AND 2 DOCKET NOS. 50-445 AND 50-446

1.0 INTRODUCTION

By letter dated March 4, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML090720583), as supplemented by letter dated September 14, 2009 (ADAMS Accession No. ML092650286), Luminant Generation Company, LLC (the licensee),

submitted Relief Requests (RRs) B-9 and B-8 for Comanche Peak Steam Electric Station (CPSES), Unit 1 and Unit 2, respectively. Specifically, the alternative was requested pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(a)(3)(i) for the use of the alternative to extend the inservice inspection (lSI) interval for examinations of the reactor pressure vessel (RPV) Category B-A and Category B-D welds from 10 years to 20 years. The alternative is based on the U.S. Nuclear Regulatory Commission (NRC) staff's safety evaluation report (SER), dated May 8,2008, of a topical report WCAP-16168-NP, Revision 2, "Risk Informed Extension of the Reactor Vessel In-Service Inspection Interval," dated June 2008 (ADAMS Accession No. ML082820046).

The application dated March 4, 2009, also included an amendment request to add a license condition for submittal of lSI information and analysis requested in paragraph (e) of the final Title 10 of the Code of Federal Regulations (10 CFR), Section 50.61 a, or the proposed rule (October 3, 2007; 72 FR 56275), prior to issuance of the final 10 CFR 50.61 a, following completion of each American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Category B-A and Category B-D RPV weld inspections. By letter dated September 14, 2009, the licensee revised its application for RR for a one-time extension only and withdrew the proposed amendment and associated license condition.

2.0 REGULATORY EVALUATION

In accordance with 10 CFR 50.55a(g)(4), the licensee is required to perform lSI of ASME Code,Section XI, Class 1, 2, and 3 components and system pressure tests during the first 10-year Enclosure

-2 interval and subsequent 1O-year intervals that comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR 50.55a(b),

subject to the limitations and modifications listed therein.

The current second 10-year lSI interval at CPSES, Unit 1 ends in August 2010, and the current second 1O-year lSI interval at CPSES, Unit 2 ends in August 2014. The Code of record for the inspection of Class 1, 2, and 3 components for both units isSection XI of the ASME Code 1998 Edition with the 2000 Addenda. The regulation in 10 CFR 50.55a(a)(3) states, in part, that the Director of the Office of Nuclear Reactor Regulation may authorize an alternative to the requirements of 10 CFR 50.55a(g). For an alternative to be authorized, as per 10 CFR 50.55a(a)(3), the licensee shall demonstrate that (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The licensee has requested the relief pursuant to 10 CFR 50.55a(a)(3)(i).

3.0 TECHNICAL EVALUATION

The lSI of Category B-A and Category B-D components consists of visual and ultrasonic examinations intended to discover whether flaws have initiated, whether pre-existing flaws have extended, and whether pre-existing flaws may have been missed in prior examinations. These examinations are required to be performed at regular intervals, as defined in Section XI of the ASME Code.

3.1 Summary ofWCAP-16168-NP In January 2006, the Pressurized Water Reactor Owners Group (PWROG) submitted the WCAP-16168-NP, Revision 1 (ADAMS Accession No. ML060330504) (referred to as WCAP in rest of this document), "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval," to the NRC in support of making a risk-informed assessment of extensions to the lSI intervals for Category B-A and Category B-D components. In the WCAP, the PWROG took data associated with three different pressurized-water reactor (PWR) plants (referred to as the pilot plants), designed respectively by the three main nuclear steam supply system manufacturers for nuclear power plants in the U.S., and performed the necessary studies on each of the pilot plants required to justify the proposed extension for the lSI interval for Category B-A and Category B-D components from 10 to 20 years.

The analyses in the WCAP used probabilistic fracture mechanics (PFM) methodology and inputs from the work described in the NRC's pressurized thermal shock (PTS) risk re-evaluation, specifically NUREG-1806, "Technical Basis for Revision of the Pressurized Thermal Shock (PTS) Screening Limit in the PTS Rule (10 CFR 50.61): Summary Report," (ADAMS Accession No. ML061580318), and NUREG-1874, "Recommended Screening Limits for Pressurized Thermal Shock (PTS)," (ADAMS Accession No. ML070860156). The PWROG analyses incorporated the effects of fatigue crack growth and lSI. Design-basis transient data was used as input to the fatigue crack growth evalua~ion. The effects of lSI were modeled consistently with the previously-approved PFM codes contained in WCAP-14572-NP-A, "Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report," (ADAMS Accession Nos. ML012630327, ML012630349, and ML012630313). These

-3 effects were evaluated using the Fracture Analysis of Vessels: Oak Ridge (FAVOR) computer code (ORNLlNRC/LTR04/18 (ADAMS Accession No. ML042960391)). All other inputs were identical to those used in the PTS risk re-evaluation.

From the results of the studies, the PWROG concluded that the ASME Code,Section XI 10-year inspection interval for Category B-A and Category B-D components in PWR reactor vessels can be safely extended to 20 years. The PWROG's conclusion from the results for the pilot plants was considered applicable to any plant designed by Westinghouse, Combustion Engineering, and Babcock and Wilcox as long as the critical, plant-specific parameters (defined in Appendix A of the WCAP) are bounded by the pilot plants.

In June 2008, the PWROG issued WCAP-16168-NP-A, Revision 2 (ADAMS Accession No. ML082820046), which includes the PWROG's responses to the NRC staff's request for additional information and the NRC staff's SER on the WCAP. For simplicity, the NRC staff will characterize the subject methodology as the WCAP-A methodology in the remaining of this safety evaluation.

3.2 Summary of NRC Safety Evaluation Report ofWCAP-16168-NP The NRC staff's conclusion in its SER for the WCAP indicates that the WCAP-A methodology is acceptable for referencing in requests to implement alternatives to ASME Code inspection requirements for PWR plants in accordance with the limitations and conditions in the SER (ADAMS Accession No. ML081060051). In addition to showing that the subject plant is bounded by the pilot plants' information from Appendix A in the WCAP, the key points of the SER are summarized below:

1. The dates identified in the request for alternative should be within plus or minus one refueling cycle of the dates identified in the implementation plan contained in PWROG letter, OG-06-356 (ADAMS Accession No. ML082210245), to the NRC.

Any deviations from the implementation plan should be discussed in detail in the request for alternative lSI interval. The maximum interval for proposed lSI is 20 years.

2. The request for alternative lSI interval can use any NRC-approved method to calculate the Charpy transition temperature shift at the 30 ft-Ib energy level (b.T3o )

and the fracture resistance against flaws in each RPV material X (RTMAX-X) 1 as defined in the draft and/or final alternative PTS Rule, 10 CFR 50.61 a. However, if the request uses the NUREG-1874 methodology to calculate b.T3o , then the request should include the analysis described in parqgraph (6) of subsection (f) to the voluntary PTS rule. The analysis should be done for all of the materials in the beltline area with at least three surveillance data points.

3. If the subject plant is a Babcock and Wilcox plant, licensees must 1 RTMAX stands for PTS Reference Temperature.

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• verify that the fatigue crack growth based on 12 heat-up/cool-down transients per year bounds the fatigue crack growth for all of its design basis transients, and

• identify the design basis transients that contribute to significant fatigue crack growth.

4. If the subject plant has RPV forgings that are susceptible to underclad cracking or if the RPV includes forgings with RTMAX-FO values exceeding 240 degrees Fahrenheit (OF) then the WCAP analyses are not applicable. The licensee must submit a plant-specific evaluation for any extension to the 1O-year inspection interval for ASME Code,Section XI, Category B-A and Category B-D RPV welds.

3.3 Description of Proposed Alternatives CPSES, Unit 1 In RR B-9, the licensee proposes to postpone performance of the ASME Code required Category B-A and Category B-D weld lSI for the second interval from refueling outage 1RF14 in 2010 to refueling outage 1RF20 in 2019. This schedule is consistent with the information in PWROG letter, OG-06-356.

CPSES, Unit 2 In RR B-8, the licensee proposes to postpone performance of the ASME Code required Category B-A and Category B-D weld lSI for the second interval from refueling outage 2RF13 in 2012 to refueling outage 2RF19 in 2021. This schedule is not consistent with the information in PWROG letter, OG-06-356.

3.4 Component for Which Relief is Requested The affected component is the CPSES, Units 1 and 2 RPVs. The following examination categories and item numbers from IWB-2500 and Table IWB-2500-1 of the ASME Code,Section XI, are addressed in this request:

Examination Category Item Number Description B-A B1.11 Circumferential Shell Weld B-A B1.12 Longitudinal Shell Weld B-A B1.21 Lower Head Circumferential Shell Weld B-A B1.22 Lower Head Meridional Weld B-A B1.30 Shell-to-Flange Weld B-D B3.90 Nozzle-to-Vessel Welds B-D B3.100 Nozzle Inner Radius Areas

- 5 3.5 Basis for Proposed Alternatives The methodology used to demonstrate the acceptability of extending the inspection interval for Category B-A and Category B-D welds based on an acceptably small change in risk is contained in WCAP-A. The critical parameters for demonstrating that this pilot plant analysis is applicable on a plant-specific basis, as identified in the WCAP-A, are identified in Table 1 of RRs B-9 and B-8. By demonstrating that each plant-specific parameter is bounded by the corresponding pilot plant parameter, the licensee has established the applicability of the methodology to the CPSES, Units 1 and 2 RPVs.

3.6 Duration of Proposed Alternatives As revised in the September 14, 2009, supplement, this request is applicable to the CPSES, Units 1 and 2 second RPV lSI interval.

3.7 NRC Staff Evaluation The NRC staff has reviewed RRs B-9 and B-8 for CPSES, Units 1 and 2. The "Frequency and Severity of Design Transients" of CPSES, Units 1 and 2 were found to be bounded by the information in WCAP-A. Also, the CPSES, Units 1 and 2 RPVs are single-layer clad and, therefore, bounded by the WCAP-A assumptions.

In its letter dated September 14, 2009, the licensee provided Table 2 for each RR, which includes additional information pertaining to previous RPV inspections and the schedule for future inspections. The CPSES, Unit 1 RPV has three potential beltline indications in its lSI record. However, all these indications were found to be acceptable in accordance with IWB 3500 of Section XI of the ASME Code. The CPSES, Unit 2 RPV has no recordable indications found in the latest RPV inspection.

The calculation of the 95th percentile through-wall cracking frequency (TWCF95-TOTAL) due to all relevant beltline materials was performed for each CPSES RPV, as documented in Table 3 of each request for alternative in licensee's letter dated September 14, 2009. The licensee's submittal used the methodology of RG 1.99, Revision 2, "Radiation Embrittlement of Reactor Vessel Materials," (ADAMS Accession No. ML003740284) to calculate ~T3o, The NRC staff verified these values and found the TWCF95-TOTAL of 7.51 E-15 for CPSES, Unit 1 and 2.73E-16 for CPSES, Unit 2 to be several orders of magnitude lower than the corresponding pilot plants' value of 1.76E-08, demonstrating that CPSES, Units 1 and 2 are bounded by the WCAP-A by a significant margin. It should be noted, however, that the licensee's RTMAX-AW and RTMAX-CW values 2 would create negative arguments for the logarithmic function in the TWCF 95 -AX equation for the axial weld and the TWCF 95 -CW equation for the circumferential weld. Physically, it means that if the three pilot plants' welds had the CPSES RPVs' RTMAX-AW and RTMAX-CW values, no through-wall cracking would occur in the welds. NUREG-1874 recommends use of zero for the TWCF for such a case. The licensee's approach is conservative and acceptable because its TWCF95 -AX and TWCF 95-CW values are greater than zero.

2 AW and CW stands for axial and circumferential welds

-6 Also, due to the significant margin between the CPSES Units' TWCF95-TOTAL values and the pilot plants, the NRC staff did not seek (1) resolution of the small discrepancies between the chemistry factors reported in Table 3 and those in the NRC's Reactor Vessel Integrity Database for the CPSES units, and (2) confirmation or clarification of the 60 effective full power year (EFPY) fluence used in the licensee's calculations (about 10 percent lower than the NRC staff's estimate based on a direct extrapolation from the current pressure-temperature limits for 36 EFPY).

At the time of issuance of the SER for WCAP-A, it was the NRC's intent to establish a process by which licensees could receive approval to implement 20-year lSI intervals for the subject component examinations through the end of their facility's current operating license. This objective led to the provision established in the SER that licensees submit a license condition which would require the licensee to evaluate future volumetric lSI data in accordance with the criteria in the draft and/or final alternative PTS Rule, 10 CFR 50.61 a. However, since that time, further guidance from the NRC's Office of General Counsel has resulted in a modification of this NRC position.

Based on the current guidance, the NRC staff will grant lSI interval extensions for the subject components on an interval-by-interval basis (i.e., only a facility's current lSI interval will be extended for up to 20 years). Licensees will have to submit subsequent requested alternatives, for NRC review and approval, to extend each following lSI interval from 10 years to 20 years, as needed. The requirement in the NRC staff's SER, for a license condition to address the evaluation of future lSI data, is no longer necessary. In its revised September 14, 2009, submittal, the licensee made two changes. The licensee limited the duration of the proposed alternative for CPSES, Units 1 and 2 to the second RPV lSI interval and withdrew its amendment request for adding the license condition discussed above. Subsequent alternative requests, which seek to extend additional lSI intervals from 10 to 20 years for the subject component examinations, should include the evaluation of a facility's most recent lSI data in accordance with the criteria in the final alternative PTS Rule, 10 CFR 50.61 a, in order to obtain NRC staff approval. For technical and regulatory consistency, the SER will be revised to reflect these changes in NRC position regarding the implementation of lSI interval extensions.

The NRC staff also reviewed the licensee's proposed schedule as it applies to the second lSI interval at CPSES, Units 1 and 2. The NRC staff concludes that the proposal to perform the SUbject examinations in 2019 for CPSES, Unit 1 are consistent with the information provided in the PWROG letter, OG-06-356 and, therefore, are acceptable. For CPSES, Unit 2, the licensee, in its letter dated September 14, 2009, revised its proposed date of inspection to 2021 to improve the distribution of plants performing RPV inspections per year. The NRC staff examined the overall PWROG plant examination schedules in the PWROG letter, OG-06-356, and found that there is one plant scheduled to perform RPV examinations in 2021, while there are five plants scheduled to perform RPV examinations in 2012. Therefore, performance of the CPSES, Unit 2 RPV examinations in 2021 enhances yearly distribution of PWROG RPV lSI schedule and is, therefore, acceptable.

In summary, the licensee has demonstrated in the submittal that the RPV components identified under RRs B-9 and B-8 for CPSES, Units 1 and 2 are bounded by the WCAP-A. The submittal demonstrates that the risk associated with extending the current lSI interval for Category B-A and Category B-D components from 10 years to 20 years is acceptably small.

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4.0 CONCLUSION

The NRC staff has completed its review of the submittals for RRs B-9 and B-8 for CPSES, Units 1 and 2 and concludes that extending the current lSI interval for the identified Category B-A and Category B-D components from 10 years to 20 years results in a small and acceptable risk increase. This conclusion is based on the fact that the plant-specific information provided by the licensee is bounded by the data in the NRC-approved topical report WCAP 16168-NP, Revision 2, and the request meets all the conditions and limitations described in the approved topical report and the associated safety evaluation report. Therefore, RRs B-9 and B 8 provide an acceptable level of quality and safety, and the alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) to extend the licensee's current second lSI interval to approximately 2020 for CPSES, Unit 1 and 2023 for CPSES, Unit 2, with the licensee performing the subject examinations in 2019 for CPSES, Unit 1 and 2021 for CPSES, Unit 2.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: S. Sheng Date: December 22, 2009

R. Flores -2 All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

The NRC safety evaluation is enclosed. If you have any questions, please contact Balwant K.

Singal at 301-415-3016 or bye-mail at Balwant.Singal@nrc.gov.

Sincerely, IRN Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-445 and 50-446

Enclosure:

As stated cc w/encl: Distribution via Listserv DISTRIBUTION:

PUBLIC RidsNrrPMComanchePeak Resource LPLIV Reading RidsNrrLA~IBurkhardt Resource RidsAcrsAcnw_MailCTR Resource RidsOgcRp Resource RidsNrrDciCvib Resource RidsRgn4MailCenter Resource RidsNrrDorlDpr Resource SSheng, NRRIDCI/CVIB RidsNrrDorlLpl4 Resource LTrocine, EDO RIV ADAMS Accession No: ML092870637 OFFICE NRRlLPL4/PM NRR/LPL4/LA DCI/CVIB/BC DRAlAPLAlBC NRR/LPL4/BC NRR/LPL4/PM NAME BSingal JBurkhardt MMitchell DHarrison MMarkley BSingal DATE 12/3/09 11/10109 12/3/09 12/22/09 12/22/09 12/22/09 OFFICIAL AGENCY RECORD