ML18248A314

Relief from the Requirements of the American Society of Mechanical Engineers Code (EPID-L-2018-LLR-0035)

ML18248A314
Person / Time
Site:	Braidwood
Issue date:	09/25/2018
From:	David Wrona Plant Licensing Branch III
To:	Bryan Hanson Exelon Generation Co, Exelon Nuclear
Wiebe J
References
EPID L-2018-LLR-0035
Download: ML18248A314 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 25, 2018 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer (CNO)

Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BRAIDWOOD STATION, UNITS 1 AND 2-RELIEF FROM THE REQUIREMENTS OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE (EPID L-2018-LLR-0035)

Dear Mr. Hanson:

By letter dated March 19, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18078A185), as supplemented by letter dated June 22, 2018 (ADAMS Accession No. ML18173A012), Exelon Generation Company, LLC (Exelon, the licensee), submitted a request to the U.S. Nuclear Regulatory Commission (NRC) for the use of alternatives to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, requirements at Braidwood Station (Braidwood), Unit 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(z)(1 ), the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety.

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that Exelon has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)( 1). Therefore, the NRC staff authorizes the use of relief request 14R-05 for the fourth inservice inspection intervals at Braidwood, Units 1 and 2, currently scheduled to start on August 29, 2018, and end on August 29, 2028 (Unit 1) and start on October 17, 2018, and end on October 17, 2028 (Unit 2).

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

B. Hanson If you have any questions, please contact the Project Manager, Joel Wiebe at 301-415-6606 or via e-mail at Joel.Wiebe@nrc.gov.

Sincerely,

• , /\ ij

. "Y

() . l c___, \ /,

David J. Wrona(Chief Plant Licensing Branch Ill Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-456 and 50-457

Enclosure:

Safety Evaluation cc:

Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 14R-05 REGARDING VOLUMETRIC EXAMINATION OF REACTOR PRESSURE VESSEL THREADS IN FLANGE EXELON GENERATION COMPANY, LLC BRAIDWOOD STATION, UNITS 1 AND 2 DOCKET NOS. 50-456 AND 50-457

1.0 INTRODUCTION

By letter dated March 19, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18078A185), as supplemented by letter dated June 22, 2018 (ADAMS Accession No. ML18173A012), Exelon Generation Company, LLC (EGC, the licensee) requested relief from the requirements of the American Society of the Mechanical Engineers Boiler and Pressure Vessel (ASME Code) for Braidwood Station (Braidwood), Units 1 and 2.

The EGC proposed alternative, 14R-05, requests to eliminate the volumetric examination of the reactor pressure vessel (RPV) threads in flange (i.e., Category B-G-1 examinations) during the fourth inservice inspection (ISi) intervals at Braidwood, Units 1 and 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations ( 10 CFR) Section 50.55a(z)(1), EGC requested to use the proposed alternative on the basis it provides an acceptable level of quality and safety.

2.0 REGULATORY EVALUATION

The regulations in 10 CFR 50.55a(g)( 4) mandate that ASME Code Class 1, 2, and 3, components meet the ISi examination requirements set forth in Section XI. The ISi examinations are to 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(a), subject to the limitations and modifications listed in 10 CFR 50.55a(b). The RPV threads in flange are ASME Code Class 1 components. Therefore, per 10 CFR 50.55a(g)(4), ISi of these threads must be performed in accordance with Section XI of the applicable edition and addenda of the ASME Code.

The regulations in 10 CFR 50.55a(z) state:

Enclosure

"Alternatives to the requirements of paragraphs (b) through (h) of this section

[50.55a] or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:

( 1) Acceptable Level of Quality and Safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a Compensating Increase in Quality and Safety.

Compliance with the specified requirements of this section [50.55a] would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety."

Based on the above, and subject to the following technical evaluation, the NRG staff finds that the licensee may propose an alternative to ASME Code,Section XI, and the NRG staff has the regulatory authority to authorize the licensee's proposed alternative.

3.0 TECHNICAL EVALUATION

3.1 Licensee's Request for Alternative 3.1.1 ASME Code Components Affected Proposed alternative 14R-05 applies to the RPV threads in flange, Examination Category B-G-1, Item No. 86.40, in Section XI of the ASME Code.

Examination Examination Code Category Item No. Method Description Class B-G-1 86.40 Volumetric RPV Threads in Flange 1 3.1.2 Applicable Code Edition and Addenda The code of record for the fourth ISi interval at Braidwood, Units 1 and 2, for the inspection of ASME Code Class 1, 2, and 3, components is the ASME Code,Section XI, 2013 Edition.

3.1.3 Applicable ASME Code Requirements The ASME Code,Section XI, Table IWB-2500-1, "Examination Category B-G-1, Pressure Retaining Bolting, Greater Than 2 in. (50 mm) in Diameter," requires volumetric examination of the RPV threads in flange. The required examination area of 1-inch around each RPV stud hole is depicted in ASME Code,Section XI, Figure IWB-2500-12, "Closure Stud and Threads in Flange Stud Hole."

3. 1.4 Description of Proposed Alternative 14R-05 Proposed alternative 14R-05 is to the requirements in ASME Code,Section XI, Table IWB-2500-1. EGG proposed alternative 14R-05 requests to eliminate the volumetric examination of the Category B-G-1 RPV threads in flange during the fourth ISi interval at Braidwood, Units 1 and 2, or until the NRG approves ASME Code,Section XI, Code Case N-864 1 , "Reactor Vessel 1 ASME Section XI Code Case N-864 is available at https://www.asme.org/.

Threads in Flange Examination,"Section XI, Division 1. ASME Code Approval Date: July 28, 2017. The fourth ISi interval for Braidwood, Unit 1, is scheduled to begin on August 29, 2018.

The fourth ISi interval for Braidwood, Unit 2, is scheduled to begin on October 17, 2018.

3.1.5 Licensee's Technical Basis for Proposed Alternative 14R-05 In its March 19, 2018, letter, Attachment 5, Section 5, "Proposed Alternative and Basis for Use,"

the licensee states that the technical basis for eliminating the RPV threads in flange volumetric examinations is provide in Electric Power Research Institute (EPRI) Technical Update Report, Nondestructive Evaluation: Reactor Pressure Vessel Threads in Flange Examination Requirements (EPRI Report No. 3002007626 - ADAMS Accession No. ML16221A068).

Section 5 also states that the requirements in the relief request are based on ASME Code Case N-864, which has been approved by the ASME Board on Nuclear Codes and Standards.

Additionally, Section 5 states that Braidwood uses detailed procedures for the care and visual inspection of the PRV threads in flange and studs every time the head is removed.

In its letter dated June 22, 2018, the licensee provided a description of the maintenance activities and inspections to be performed on the RPV threads in flange and studs each time the RPV head is removed during the fourth ISi interval. Excerpts of the site-specific procedures controlling these activities were also provided. The licensee cites its plant-specific License Renewal Aging Management Program (AMP) and corrective action program (CAP) for addressing degradation of the RPV threads in flange, if detected.

In its letter dated March 19, 2018, Attachment 5, Section 4, "Reason for Request," the licensee discusses the technical information provided in EPRI report No. 3002007626, which is cited as the basis for proposed alterative 14R-05. Section 4 discusses operating experience (OE) related to the RPV threads in the flange, potential degradation mechanisms, stress analysis, flaw tolerance evaluation, and other related RPV assessments. The licensee notes that the conclusion from EPRI Report No. 3002007626, "is that the current requirements are not commensurate with the associated burden (worker exposure, personnel safety, radwaste, critical path time, and additional time at reduced water inventory) of the examination."

3.2 NRC Staff Evaluation Proposed alternative 14R-05 is based upon ASME Code Case N-864. Code Case N-864 has not been incorporated in Regulatory Guide 1.147, Revision 18, "lnservice Inspection Code Case Acceptability, ASME Code,Section XI, Division 1," dated March 2017 (ADAMS Accession No. ML16321A336). As a result, this code case is not available for application without specific NRC approval. The below evaluation provides specific approval for use at Braidwood, Units 1 and 2.

The technical basis for proposed alternative 14R-05 is provided in EPRI report No. 30020076.

The NRC staff reviewed the industry's generic stress analysis and flaw tolerance evaluation documented in Section 6 of the report and determined it to be acceptable based on the NRC evaluations in Sections 3.2.1.1 and 3.2.1.2 of the safety evaluation transmitted by letter dated January 26, 2017 (ADAMS Accession No. ML17006A109). By letter dated June 26, 2017 (ADAMS Accession No. ML17170A013), the NRC staff determined that the EPRI evaluation is applicable to Braidwood, Units 1 and 2, and the elimination of the volumetric examinations of the RPV threads in flange for a 10-year ISi interval provides an acceptable level of quality and safety. In NUREG-2190, Volumes 1 and 2, "Safety Evaluation Report, Related to the License Renewal of Byron Station, Unit Nos. 1 and 2, and Braidwood, Units 1 and 2 - Docket Nos. 50-454, 50-455, 50-456, and 50 457 - Exelon Generation Company, LLC," dated December 2015

(ADAMS Accession Nos. ML15350A038 and ML15350A041 ), the NRC staff also reviewed and approved the OE and aging management activities associated with the RPV threads in flange and related closure stud components. Therefore, the NRC staff focused its evaluation of proposed alternative 14R-05 on aspects related to maintaining reasonable assurance of adequate defense-in-depth, if volumetric inspections on the RPV threads in flange are not performed for a second sequential ISi interval during the original 40-year operating period.

Specifically, the NRC staff reviewed the maintenance and inspection activities to detect degradation of the RPV threads in flange.

The NRC staff reviewed the licensee's description of the maintenance and inspection activities associated with the RPV threads in flange and studs during the fourth ISi interval at Braidwood, Units 1 and 2. The NRC staff also reviewed the excerpts of the site-specific procedures controlling these activities. The objective of this review was to determine if the maintenance activates and inspections provide reasonable assurance that degradation of the RPV threads in flange will be detected and mitigated prior to returning the reactor to service each time the RPV head is removed during the fourth ISi interval if volumetric inspections are not performed.

The NRC staff noted that each time the RPV head is removed all studs are removed and individually cleaned, which allows access to all the RPV threads in flange on a periodic basis (i.e., each refueling outage). The licensee states that once the studs are removed care is taken to inspect the RPV threads in flange and the threads in flange are cleaned and lubricated prior to the studs being reinstalled. The plant-specific procedures state that if significant corrosion or foreign material is found in a stud hole the condition is entered into the CAP.

Maintenance and inspection activities are also performed on each RPV stud, nut, and washer each time the RPV head is removed. The condition of the mating threads and adjacent RPV closure stud components provides additional information on the condition of the RPV threads in flange. The plant-specific procedures verify that all RPV stud and nut threads have been inspected for damage, galling, and corrosion; and that adverse conditions have been entered into the CAP and corrected, if applicable. The CAP ensures that conditions adverse to quality are promptly corrected.

In summary, the NRC staff determined that the stress analysis, flaw tolerance evaluation, and OE review in the generic EPRI Report No. 3002007626 evaluation are bounding for Braidwood, Units 1 and 2. The NRC staff determined that the combination of maintenance and inspection activities of the RPV threads in flange and adjacent RPV closure stud components provide reasonable assurance that degradation of the RPV threads in flange will be detected and mitigated prior to returning the reactor to service each time the RPV head is removed during the fourth ISi interval if volumetric inspections are not performed. Therefore, there is reasonable assurance that adequate defense-in-depth will be maintained. Based on the above, the NRC staff finds that alternative 14R-05 provides an acceptable level of quality and safety.

4.0 CONCLUSION

As set forth above, the NRC staff finds that proposed alternative 14R-05 provides an acceptable level of quality and safety. Accordingly, the staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)( 1). Therefore, the NRC staff authorizes the use of relief request 14R-05 for the fourth ISi intervals at Braidwood, Units 1 and 2, currently scheduled to start on August 29, 2018, and end on August 29, 2028 (Unit 1), and start on October 17, 2018, and end on October 17, 2028 (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 lnservice Inspector.

Principal Contributor: C. Hovanec Date of issuance: September 25, 2018 t

ML18248A314 *via email OFFICE NRR/DORL/LPL3-2/PM NRR/DORL/LSPB/LA NRR/DMLR/MVIB/BC NAME JWiebe SRohrer DAIiey*

DATE 9/12/18 9/6/18 08/28/18 OFFICE NRR/DORL/LPL3/BC NAME DWrona DATE 9/25/18