ML20308A656

Request for Additional Information Traveler TSTF-577, Revision 0, Revised Frequencies for Steam Generator Tube Inspections

ML20308A656
Person / Time
Site:	Technical Specifications Task Force
Issue date:	11/06/2020
From:	Michelle Honcharik NRC/NRR/DSS/STSB
To:	Technical Specifications Task Force
Honcharik, M., NRR/DSS, 301-415-1774
References
EPID L-2020-PMP-005
Download: ML20308A656 (7)

Text

November 6, 2020 Technical Specifications Task Force 11921 Rockville Pike, Suite 100 Rockville, MD 20852

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION RE: TRAVELER TSTF-577, REVISION 0, "REVISED FREQUENCIES FOR STEAM GENERATOR TUBE INSPECTIONS (EPID L-2020-PMP-0005)

Dear Members of the Technical Specifications Task Force:

By letter dated June 8, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20160A359), you submitted to the U.S. Nuclear Regulatory Commission (NRC) a request to incorporate Traveler TSTF-577, Revision 0, "Revised Frequencies for Steam Generator Tube Inspections.

Upon review of the information provided, the NRC staff has determined that additional information is needed to complete the review. Mr. Brian Mann, Vice President of Industry Programs, EXCEL Services Corporation, agreed that the NRC staff will receive your response to the enclosed request for additional information questions within 30 calendar days of the date of this letter.

The review schedule that was provided in the acceptance letter dated August 6, 2020 (ADAMS Accession No. ML20211L766), has not changed.

MILESTONE SCHEDULE DATE Issue Draft Safety Evaluation March 24, 2021 Issue Final Safety Evaluation June 5, 2021 If you have any questions, please contact me at (301) 415-1774 or via e-mail to Michelle.Honcharik@nrc.gov.

Sincerely, Digitally signed by Michelle C. Michelle C. Honcharik Date: 2020.11.06 Honcharik 09:17:57 -05'00' Michelle C. Honcharik, Senior Project Manager Technical Specifications Branch Division of Safety Systems Office of Nuclear Reactor Regulation Project No. 753

Enclosure:

Request for Additional Information cc: See next page

Technical Specifications Task Force cc:

Technical Specifications Task Force c/o EXCEL Services Corporation 11921 Rockville Pike, Suite 100 Rockville, MD 20852 Attention: Brian D. Mann E-mail: brian.mann@excelservices.com James P. Miksa Entergy Nuclear Operations, Inc.

Palisades Nuclear Power Plant 27780 Blue Star Memorial Highway Covert, MI 49043 Email: jmiksa@entergy.com Jordan L. Vaughan Duke Energy EC07C / P.O. Box 1006 Charlotte, NC 28202 Email: jordan.vaughan@duke-energy.com Ryan Joyce Southern Nuclear Operating Company 3535 Colondate Parkway / Bin N-274-EC Birmingham, AL 35243 Email: rmjoyce@southern.com Dwi Murray Exelon Generation 4300 Winfield Road Warrenville IL 60555 Email: Putri.Kusumawatimurray@exeloncorp.com Wesley Sparkman Southern Nuclear Operating Company 3535 Colonnade Parkway / Bin N-226-EC Birmingham, AL 35242 Email: wasparkm@southernco.com

ML20308A656 *concurred via e-mail NRR-106 OFFICE NRR/DSS/STSB/PM* NRR/DNRL/NCSG/BC* NRR/DSS/STSB/BC*

NAME MHoncharik SBloom VCusumano DATE 11/3/2020 10/15/2020 11/5/2020 OFFICE NRR/DSS/STSB/PM*

NAME MHoncharik DATE 11/6/2020 REQUEST FOR ADDITIONAL INFORMATION TECHNICAL SPECIFICATIONS TASK FORCE TSTF-577, "REVISED FREQUENCIES FOR STEAM GENERATOR TUBE INSPECTIONS (EPID L-2020-PMP-0005)

By letter dated June 8, 2020 (Agencywide Documents Access and Management System Accession No. ML20160A359), the Technical Specifications Task Force (TSTF) submitted TSTF-577, Revision 0, Revised Frequencies for Steam Generator Tube Inspections, to the U.S. Nuclear Regulatory Commission (NRC) for review. TSTF-577 would revise the technical specifications (TS) related to steam generator (SG) tube inspections to extend the inspection interval for thermally treated Alloy 600 (Alloy 600TT) and thermally treated Alloy 690 (Alloy 690TT) SG tubing.

The general design criteria (GDCs) in Appendix A to Part 50 of Title 10 of the Code of Federal Regulations (10 CFR) provide regulatory requirements that state the reactor coolant pressure boundary (RCPB) shall have an extremely low probability of abnormal leakage and of gross rupture (GDC 14), shall be designed with sufficient margin (GDCs 15 and 31), shall be of the highest quality standards practical (GDC 30), and shall be designed to permit periodic inspection and testingto assess structural and leak tight integrity (GDC 32).

In 10 CFR 50.36, Technical specifications, NRC regulatory requirements related to the content of the TS are established. The TS for all current primary water reactor (PWR) licenses require that an SG Program be established and implemented to ensure that SG tube integrity is maintained. Programs established by the licensee, including the SG Program, are listed in the administrative controls section of the TS to operate the facility in a safe manner.

SG tube integrity is maintained by meeting the performance criteria specified in the TS for structural and leakage integrity, consistent with the plant design and licensing basis. The TS require that a condition monitoring assessment be performed during each outage in which the SG tubes are inspected, to confirm that the performance criteria are being met. The TS include provisions regarding the scope, frequency, and methods of SG tube inspections. These provisions require that the inspections be performed with the objective of detecting flaws of any type that may be present along the length of a tube and that may satisfy the applicable tube plugging criteria. The applicable tube plugging criteria, specified in the TS, are that tubes found during in-service inspection to contain flaws with a depth equal to or exceeding 40 percent of the nominal wall thickness shall be plugged, unless the tubes are permitted to remain in service through application of alternate repair criteria provided in the TS. The TS include a limit on operational primary-to-secondary leakage, beyond which the plant must be promptly shut down.

Should an existing flaw that exceeds the tube integrity repair limit not be detected during the periodic tube surveillance required by the plant TS, the operational leakage limit provides added assurance of timely plant shutdown before SG tube structural and leakage integrity are impaired, consistent with the design and licensing bases.

As part of the plants licensing basis, applicants for PWR licenses are required to analyze the consequences of postulated design-basis accidents (DBAs), such as a SG tube rupture and a steam line break. These analyses consider primary-to-secondary leakage that may occur during these events and must show that the offsite radiological consequences do not exceed the applicable limits of 10 CFR 50.67 or 10 CFR 100.11 for offsite doses; GDC 19 of 10 CFR Part 50, Appendix A, for control room operator doses (or some fraction thereof as appropriate to the accident); or the NRC-approved licensing basis (e.g., a small fraction of these limits).

Enclosure

REQUESTED ADDITIONAL INFORMATION While the following questions are based on the NRC staffs review of TSTF-577, the NRC staff notes there is a parallel effort in reviewing the technical basis for the proposed Alloy 600TT SG tubing inspection interval. The NRC staff recently completed an audit of the feasibility studies that support the proposed changes for Alloy 600TT tubing material. The Audit Plan for the Regulatory Audit of Electric Power Research Institute [EPRI] for Steam Generator Task Force Information Related to [TSTF]-577, Revised Frequencies for Steam Generator Tube Inspections, is available in ADAMS under Accession No. ML20216A676. These preliminary feasibility studies are expected to be finalized and submitted in 2020. The NRC staff expects additional technical discussions with industry on topics of importance to TSTF-577, such as how the probability of crack detection from the Alloy 600TT fleet compare to the values determined from eddy current technique development, how sizing errors could influence the crack growth rates determined from plant eddy current data, and on a template for the TSTF-577 TS reporting requirements. It is possible, but not certain, that additional questions could arise from these activities.

1) In Section 2.4.4., Editorial Improvements, it is stated that, The model application states that on implementation of the license amendment request the current inspection period will begin at the last 100 percent inspection of each SG. During the recent NRC staff audit, an industry slide discussing lessons learned to be applied in future SG inspections stated that a 100 percent inspection of the region of interest would be performed at the beginning of TSTF-577 implementation.

a) Please clarify if the implementation of TSTF-577 would be considered at the next 100 percent inspection of all SG tubes in a unit.

b) Upon implementation of TSTF-577, how is the starting point of the new current inspection period determined if units performed SG inspections on only a portion of the SGs in alternating refueling outages (e.g., SGs A and C in one outage and then SGs B and D in the next outage)?

c) Upon implementation of TSTF-577, how is the starting point of the new current inspection period determined if units performed partial SG inspections of all SGs in alternating refueling outages (e.g., 50 percent inspections of SGs A, B, C, and D in two outages)?

2) Section 3.1.3., Technical Evaluation of Alloy 600TT Tubing Material Inspection Frequency, states:

Operating experience for nearly forty years has shown no propensity for rapidly increasing crack initiation rates in Alloy 600TT SG tubes, as was observed for Alloy 600MA [mil annealed Alloy 600] SG tubes. The proposed change of inspection frequency from 48 EFPM [effective full power months] to 72 EFPM has been demonstrated to meet the structural integrity and accident induced leakage performance criteria even for SGs that have experienced cracking. However, the proposed change maintains the existing requirement to inspect each affected and potentially affected SG at the next refueling outage after identifying a definitive crack indication. Based on this operating

experience, the proposed TS change to require inspection of the tubing at least every 72 EFPM is acceptable.

The NRC staff agrees that the operational experience of SGs with Alloy 600TT tubing is significantly improved over that demonstrated by SGs with Alloy 600MA tubing. The NRC staff notes, however, the proposed change to increase inspection intervals of Alloy 600TT tubing is supported by industry modeling performed using the Operational Assessment (OA) methodology contained in the EPRI Steam Generator Management Program: Steam Generator Integrity Assessment Guidelines, not actual operating experience since the current TS do not permit the longer intervals. The NRC staff also notes that the technical bases documents reviewed by the NRC staff in the audit performed in September 2020 were preliminary and that changes were expected to be made in the final documents.

Please submit the final feasibility study documents, as discussed in the audit exit meeting on September 24, 2020, since the NRC staff may rely on portions of this material during the regulatory evaluation process.

3) Section 3.1.4., Technical Evaluation of Alloy 690TT Tubing Material Inspection Frequency, states that the Advanced Passive 1000 (AP1000) SGs are fundamentally the same as other Westinghouse SG designs utilizing Alloy 690TT tubing. The TSTF goes on to state that, recent international operating experience indicates the only damage mechanism is wear, which is consistent with other SGs with Alloy 690TT tubing. Please confirm that this statement is specific to international operating experience for AP1000 SGs and provide the international operating experience. In addition, the NRC staff requests that Section 3.1.4.

be revised to clearly describe how the AP1000 SG design, operating conditions, and international experience is bounded by the U.S. Alloy 690TT SG tubing operating experience.

4) Section 3.1.5., Consideration of Inspection Techniques, states that, the TS will continue to require robust inspections to support the proposed inspection intervals. In general, licensees have demonstrated the ability to detect stress corrosion cracking (SCC) before tube integrity is challenged, demonstrated the ability to conservatively manage loose parts once they are detected, and have managed tube wear while maintaining tube integrity. This good operational experience, however, was developed within the inspection frequency of the existing TS.

The proposed SG tube inspection frequencies will increase the amount of time that SCC can initiate and grow and will increase the amount of time that wear can occur from loose parts and at support structures between inspections. The NRC staff notes that some assumptions made in the OA modeling, such as consistent secondary side conditions, have greater uncertainty with increasing time between inspections. In addition, detection of early stages of SCC can be challenging, particularly in the presence of masking signals caused by local tube changes, for example at dents/dings, manufacturing marks, and under deposits. The NRC staff notes that the enhanced detection achieved by inspection with advanced probes could be expected to provide one mitigating factor to increased operational time between inspections, by providing a more accurate assessment of the current tube condition.

The NRC staff believes that such inspections are an important element of an inspection program supporting an increased interval between inspections. Regardless of the specific tubing alloy in a SG, detection of existing loose parts is enhanced by using advanced probes, such as the combination bobbin and array coil probe or other equivalent (or better) probes. Use of enhanced probes would also provide earlier detection of corrosion, should it

occur during future operation. Therefore, the NRC staff supports the widespread use of advanced probes in future inspections.

In light of the preceding discussion, discuss how strategies for greater use of advanced probes will support longer inspection intervals on a tube material basis or provide justification for not incorporating enhanced inspections equivalent to or better than array probe technology into the SG TS (e.g., in Section 5.5.9.d.2). Alternatively, revise the SG TS to incorporate enhanced inspections equivalent to or better than array probe technology or provide revisions that will ensure enhanced inspections equivalent to or better than array probe technology will be performed during the SG inspections.

5) The model application states that the TS Bases are not affected by the proposed changes.

TSTF-577 proposes to incorporate TSTF-510, which affected the TSTF-449 TS Bases.

Therefore, this statement will be incorrect for units currently using TSTF-449 and proposing to incorporate TSTF-577. Please revise the sentence to be applicable to units using either TSTF-449 or TSTF-510.

6) Please provide details for any changes that are planned to the EPRI SG Guidelines in support of longer inspection intervals.