Text

Relief Request ANO2-ISI-004 to Extend Third Inservice Inspection Interval from 10 to 20 Years for Reactor Vessel Weld Examinations
	ML102450654
Person / Time
Site:	Arkansas Nuclear
Issue date:	09/21/2010
From:	Markley M; Plant Licensing Branch IV
To:	; Entergy Operations
	Kalyanam N, NRR/DORL/LPL4, 415-1480
References
	ANO2-ISI-004, TAC ME2508
	Download: ML102450654 (9)
	v • d • e

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 21. 2010 Vice President, Operations Arkansas Nuclear One Entergy Operations, Inc.

1448 S.R. 333 Russellville, AR 72802

SUBJECT:

ARKANSAS NUCLEAR ONE, UNIT 2 - REQUEST FOR ALTERNATIVE AN02-ISI-004, TO EXTEND THE THIRD 10-YEAR INSERVICE INSPECTION INTERVAL FOR REACTOR VESSEL WELD EXAMINATIONS (TAC NO. ME2508)

Dear Sir or Madam:

By letter dated October 29,2009, as supplemented by letter dated April 29, 2010, Entergy Operations, Inc. (the licensee), requested, pursuant to paragraph 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations (10 CFR), an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, paragraph IWB-2412, Inspection Program B, for Arkansas Nuclear One, Unit 2 (ANO-2). In particular, the licensee requested an extension of the existing requirement of performing volumetric examination of essentially 100 percent of the reactor vessel pressure retaining Examination Category B-A and B-D welds once each 1O-year inservice inspection (lSI) interval to an examination frequency of every 20 years.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the licensee's submittal of Request for Alternative AN02-ISI-004 regarding ANO-2 and concludes that the plant-specific information provided by the licensee is bounded by the data in the Pressurized-Water Reactor Owners Group's topical report WCAP-16168-NP-A, Revision 2, "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval" (WCAP-A), and the request meets all applicable conditions and limitations described in the WCAP-A and increasing the lSI interval for Category B-A and B-D components from 10 years to 20 years shows no appreciable increase in risk. Therefore, Request for Alternative AN02-ISI-004 provides an acceptable level of quality and safety and the alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) until the end of the third interval for Categories B-A and B-D components at ANO-2 on March 25, 2020, with the lSI examinations scheduled to occur in 2018.

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

- 2 The NRC staffs safety evaluation is enclosed. If you have any questions, please contact Kaly Kalyanam at (301) 415-1480 or via e-mail at kaly.kalyanam@nrc.gov.

Sincerely, Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-368

Enclosure:

Safety Evaluation 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 REQUEST FOR ALTERNATIVE AN02-ISI-004 REQUEST TO EXTEND THE INSERVICE INSPECTION INTERVAL FOR REACTOR VESSEL WELD EXAMINATIONS ENTERGY OPERATIONS, INC.

ARKANSAS NUCLEAR ONE, UNIT 2 DOCKET NO. 50-368

1.0 INTRODUCTION

By letter dated October 29, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML093030136), and supplemented by letter dated April 29, 2010 (ADAMS Accession No. ML101190462), Entergy Operations, Inc. (Entergy, the licensee),

requested Nuclear Regulatory Commission (NRC) approval for Arkansas Nuclear One, Unit 2 (ANO-2) to use an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Paragraph IWB-2412, Inspection Program B. The alternative was requested pursuant to Title 10 of the Code of Federal Regulations (10 CFR) paragraph 50.55a(a)(3)(i).

The licensee requested approval for the use of the alternative, AN02-ISI-004, to extend the inservice inspection (lSI) interval for examinations of the reactor pressure vessel (RPV) welds (Category B-A) as well as the nozzle-to-vessel welds and inner radius sections (Category B-D) from 10 years to 20 years.

2.0 REGULATORY EVALUATION

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

For the current (third) lSI interval at ANO-2, the Code of record for the inspection of ASME Code Class 1, 2, and 3 components is the 1992 Edition and the 1995 Edition with the 1996 Addenda of the ASME Code,Section XI. The regulations in 10 CFR 50.55a(a)(3) state, in part, that the Director of the Office of Nuclear Reactor Regulation may authorize an alternative to the Enclosure

- 2 requirements of 10 CFR 50.55a(g). For an alternative to be authorized, as per 10 CFR 50.55a(a)(3)(i), the licensee must demonstrate that the proposed alternative would provide an acceptable level of quality and safety.

2.1 Background

The lSI of Category B-A and 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. Performing all of these inspections at the same time reduces the number of times that the unit's full core and internals must be moved to gain access for the examinations.

2.2 Summary of WCAP-16168-NP, Revision 1 In 2006, the Pressurized-Water Reactor Owners Group (PWROG) submitted a topical report WCAP-16168-NP, Revision 1, "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval" (ADAMS Accession No. ML060330504),and referred to as the WCAP 16168 in the rest of this safety evaluation (SE)), to the NRC in support of making a risk-informed assessment of extensions to the lSI intervals for Category B-A and B-D components. In the report, the PWROG took data associated with three different pressurized-water reactor (PWR) plants (referred to as the pilot plants), one designed by each of the main contractors for nuclear power plants in the United States, 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 B-D components from 10 to 20 years.

The analyses in the WCAP-16168 used probabilistic fracture mechanics tools and inputs from the work described in the NRC's pressurized thermal shock (PTS) risk re-evaluation, 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 inservice inspection. Design basis transient data was used as input to the fatigue crack growth evaluation. The effects of 151 were modeled consistently with the previously-approved probabilistic fracture mechanics codes, WCAP-14572-NP-A, "Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report" (ADAMS Accession Nos. ML012630349, ML012630327, and ML012630313). These effects were used in the evaluations performed with the Fracture Analysis of Vessels - Oak Ridge (FAVOR) code, ORNLlNRC/LTR-04/18, "Electronic Archival of the Results of Pressurized Thermal Shock Analyses for Beaver Valley, Oconee, and Palisades Reactor Pressure Vessels Generated with the 04.1 version of FAVOR" (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 lSI interval for Category B-A and B-D components in PWR reactor vessels can be extended to 20 years. Their conclusion from the results for the pilot plants was considered to apply to any plant designed by the three vendors (Westinghouse Electric Corporation,

- 3 Combustion Engineering, Inc., and Babcock & Wilcox Company) as long as the critical, plant specific parameters (defined in Appendix A of the WCAP-16168) are bounded by the pilot plants.

2.3 NRC Safety Evaluation for WCAP-16168-NP, Revision 1 The NRC staff's conclusion in its SE for WCAP-16168 dated May 8, 2008 (ADAMS Accession No. ML081060045), indicates that the methodology presented in the topical report, along with the guidance provided by NRC Regulatory Guide 1.174, Revision 1," An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis" (ADAMS Accession No. ML023240437), 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 SE. In addition to showing that the subject plant is bounded by the pilot plants' information from Appendix A in the WCAP-16168, the key points of the SE 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 provided to the NRC.

Any deviations from the implementation plan (

Reference:

Letter from PWROG to the NRC, dated October 31,2006, "Plan for Plant Specific Implementation of Extended Inservice Inspection Interval per WCAP-16168-NP, Revision 1, 'Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval.' MUHP 5097-99, Task 2059,"

ADAMS Accession No. ML082210245), should be discussed in detail in the request for alternative. The maximum proposed lSI interval is 20 years.

2.

The requirements for reporting the results of ISis found in the voluntary PTS rule apply in all cases. Licensees that do not implement the voluntary PTS rule must amend their licenses to require that the information and analyses requested in the voluntary PTS rule be submitted for NRC staff review and approval. The amendment to the license shall be submitted at the same time as the request for alternative lSI interval.

3.

The request for alternative lSI interval can use any NRC-approved method to calculate

~T30 and RTMAX-X (defined in I\\lUREG-1874). However, if the request uses the NUREG-1874 methodology to calculate ~T30, then the request should include the analysis described in paragraph (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.

4.

If the subject plant is a Babcock & Wilcox-designed plant, licensees must (a) verify that the fatigue crack growth of 12 heat-up/cool-down transients per year bound the fatigue crack growth for all of its design basis transients, and (b) identify the design basis transients that contribute to significant fatigue crack growth.

5.

If the subject plant has RPV forgings that are susceptible to underclad cracking and if these forgings have RTMAx-FO(defined in NUREG-1874), values exceeding 240 of, then the WCAP-16168 analyses are not applicable. The licensee must submit a plant

- 4 specific evaluation for any extension to the 1O-year inspection interval for ASME Code,Section XI, Category B-A and B-D reactor vessel welds.

3.0 TECHNICAL EVALUATION

3.1 Description of Proposed Alternatives In the request for alternative, AN02-ISI-004, the licensee proposes to defer the ASME Code required Category B-A and B-D weld lSI of ANO-2 until 2018. This schedule is consistent with the information in the letter from PWROG to the USNRC, dated October 31,2006.

3.2 Components for Which Alternative is Requested The affected components are the subject plant RPV welds and nozzle inner radius areas. 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 Welds B-A B1.12 Longitudinal Shell Welds B-A B1.21 Circumferential Head Welds B-A B1.22 Meridional Head Welds B-A B1.30 Shell-to-Flange Weld B-D B3.90 Nozzle-to-Vessel Welds B-D B3.100 Nozzle Inner Radius Areas 3.3 Basis for Proposed Alternative The basis for the alternative, AN02-ISI-004, is found in the NRC-approved version of the WCAP-16168-NP-A, Revision 2, "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval" (ADAMS Accession No. ML082820046). This document is referred to as WCAP-A in this SE. Plant-specific parameters for the subject plant are summarized in the Attachment to the licensee's letter dated October 29, 2009. The format of the information is patterned after that found in Appendix A of the WCAP-16168.

All of the critical parameters listed in Tables 1, 2, and 3 of the Attachment to the licensee's letter of October 29, 2009, are bounded by the WCAP-A pilot plant.

3.4

NRC Staff Evaluation

The NRC staff's review of the licensee submittals determined that the "Frequency and Severity of Design Transients" of ANO-2 were bounded by the WCAP-A. The ANO-2 RPV was single layer clad and bounded by the WCAP-A.

Table 2 in the licensee's submittal dated October 27, 2009, includes additional information pertaining to previous RPV inspections and the schedule for future ones. The proposed third lSI

- 5 interval inspection for ANO-2 would be in 2018, consistent with the letter from PWROG to the NRC, dated October 31, 2006. There were a total of eight indications detected in the beltline region during the most recent lSI. All of the indications were acceptable per IWB-351 0-1 of the ASME Code,Section XI and the requirements of the proposed alternate PTS Rule (10 CFR 50.61 a), so there is no requirement for remedial action or further analysis.

The calculation ofTWCF95_ToTAddefined in NUREG-1874), was performed using Table 3 of the submittal as a basis. The request uses the methodology contained in NRC Regulatory Guide 1.99, Revision 2, "Radiation Embrittlement of Reactor Vessel Materials," dated May 1988 (ADAMS Accession No. ML003740284), to calculate ~T3o, The calculations were verified independently via NRC staff calculation and the difference between the licensee's and staff's calculations were found to be insignificant. The TWCF95-ToTAL was found to be acceptably low as calculated through the methodology prescribed in the WCAP-A and provided in Table 3 of the submittal.

At the time of issuance of the safety evaluation for WCAP-16168, it was the NRC staff'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, as discussed in Section 2.3 of this SE, 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 50.61a. The NRC staff has since determined that the appropriate process for requesting further extensions of the lSI interval, beyond authorizing this request for alternative in response to Entergy's application of October 29, 2009, is through 10 CFR 50.55a for each subsequent lSI interval. Accordingly, the NRC staff considers that a license condition such as discussed above is not necessary and that requirements for future evaluation of lSI data will be addressed as a part of the review of requests for the extension of subsequent lSI intervals for the subject components. Therefore, the staff authorizes AN02-ISI-004 for the third ANO-2 lSI interval that will now end on March 25,2020, with the lSI examinations scheduled to take place in 2018. However, in order to obtain NRC staff approval, a sUbsequent alternative that seeks to extend an lSI interval 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. For purposes of technical and regulatory consistency, the NRC's SE regarding WCAP-16168 will be revised to reflect these changes in NRC position regarding the implementation of lSI interval extensions based on WCAP-A.

In summary, the licensee has demonstrated through the submittal that the ANO-2 RPV is bounded by the WCAP-A. The NRC staff concludes that there is no significant additional risk associated with extending the lSI interval for Category B-A and B-D components from 10 years to 20 years and is, therefore, acceptable.

4.0 CONCLUSION

The NRC staff has reviewed the request for alternative, AN02-ISI-004, regarding ANO-2 and concludes that increasing the lSI interval for Category B-A and B-D components from 10 years to 20 years shows no appreciable increase in risk. The staff concludes this since the plant specific information provided by the licensee is bounded by the data in the WCAP-A and the

- 6 request meets all applicable conditions and limitations described in the WCAP-A, and Request for Alternative AN02-ISI-004 provides an acceptable level of quality and safety and the alternative can be authorized pursuant to 10 CFR 50.55a(a)(3)(i) until the end of the third interval for Categories B-A and B-D components at ANO-2 on March 25, 2020, with the lSI examinations scheduled to occur in 2018. Therefore, the NRC staff authorizes the use of Request for Alternative, AN02-ISI-004, for ANO-2.