CNL-13-116, Response to NRC Request for Additional Information Related to 2012 Steam Generator Inspection Report

Response to NRC Request for Additional Information Related to 2012 Steam Generator Inspection Report

ML13333A162
Person / Time
Site:	Watts Bar
Issue date:	11/22/2013
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-13-116
Download: ML13333A162 (6)

Text

Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-13-116 November 22, 2013 10 CFR 50.4 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390

References:

Response to NRC Request for Additional Information Related to Watts Bar Nuclear Station Unit 1 - 2012 Steam Generator Inspection Report

1. Letter from TVA to NRC, "Watts Bar Nuclear Plant (WBN) Unit 1 - Cycle 11 Steam Generator Tube Inspection Report," dated April 19, 2013

[Agencywide Documents Access and Management System (ADAMS)

Accession No. ML131150048]

2. Electronic Mail from Andrew Hon (NRC) to Joseph W. Shea (TVA),

"Watts Bar Nuclear Station, Unit 1 - Request For Additional Information -

2012 Steam Generator Inspection (TAC No. MF2337)," dated October 23, 2013 [ADAMS Accession No. ML13296A712]

By letter dated April 19, 2013 (Reference 1), the Tennessee Valley Authority (TVA) submitted the Watts Bar Nuclear Plant Unit 1, Cycle 11, 2012, steam generator inspection report. On October 23, 2013, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) by electronic mail (email) (Reference 2). The due date for the RAI response is November 22, 2013. The Enclosure to this letter provides TVA's response to the NRC RAI.

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U.S. Nuclear Regulatory Commission Page 2 November 22, 2013 There are no new regulatory commitments included in this submittal. Please address any questions regarding this submittal to Edward D. Schrull at (423) 751-3850.

Respe

ully, J.

ea ic resident, Nuclear Licensing

Enclosure:

Response to NRC Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Request for Additional Information cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant, Unit 1 NRC Project Manager - Watts Bar Nuclear Plant, Unit 1

ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT I RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 2012 STEAM GENERATOR INSPECTION REPORT NRC RAI No. 1 Page 8 of the inspection report indicates that the bobbin inspection included all tubes with prior indications of degradation. Please clarify this statement, since it was our understanding that all tubes with indications were plugged during the prior outage.

TVA Response All tubes with indications were plugged during the prior inspection outage. There were no tubes with indications of prior degradation left in service at the end of Fuel Cycle 8, beginning of Fuel Cycle 9. The end of Fuel Cycle 8 was the end of the first cycle of operation since replacement of the WBN Unit 1 Steam Generators and TVA did not have sufficient growth rate information to leave degraded tubes in service. Cycle 11 was the second In-service Inspection (ISI) since the steam generators replacement.

In accordance with industry guidance (NEI 97-06 and EPRI 1013706), WVA procedures require inspection of all prior degradation to develop growth rates and evaluate tube integrity. The statement contained in the inspection report was missed during the WVA Vendor Acceptance review. This error has been entered into the WVA corrective action program.

NRC RAI No. 2 The paragraph on page 8 also indicates that the base inspection scope for the array coil was foreign objects and foreign object wear near the top of the tubesheet and support wear up to the C06 cold-leg support, but the table on page 9 seems to indicate that the base inspection scope for the array coil may have been different (e.g., either up to the C01 or C08 on the cold-leg, with some expansions in one SG up to vertical strap 2 (VS2)).

Please clarify and discuss the reason for the array coil exams up through VS2 in steam generator 1-2.

TVA Response WVA inspects as much of the tube as possible with qualified techniques. Because the array coil was qualified to detect potential degradation and was being utilized for loose part detection, there were instances where WVA could gain efficiency by testing the tube with the array probe instead of the bobbin probe. WVA was able to use the enhanced detection capability of the array probe for loose parts and also use it to inspect higher elevations e.g., VS2.

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NRC RAI No. 3 Most of the wear at the advanced tube support grids appears to be occurring on the cold-leg side. Please provide any insights on why the vast majority of the indications are on the cold-leg.

TVA Response The main Feedwater flow enters the Feedwater inlet box, which is located on the cold leg side. The recirculating "downcomer" flow (water coming from the separators and dryers or in some cases the auxiliary Feedwater system piping and flowing down the annulus between the shell and wrapper) enters the bundle above the preheater section through a "slot" or cut-out in the cold leg side wrapper. This generates cross flow, which causes wear in peripheral tubes, i.e., a few rows deep and in supports above and below the flow slot, due to the flow excitation of the tubes in the high flow regions.

Tube integrity was documented in the Operational Assessment (OA) performed for the WBN Unit 1 steam generators. Due to the combination of three cycles between outage inspections and sample inspections, tubes with wear flaws must maintain their structural integrity for up to six fuel cycles. The flaw growth projection contained in the OA was determined based on the worst-case growth rate. This growth projection was used for tubes in two separate populations: tubes inspected during the Cycle 8 outage that will be inspected during the Cycle 14 outage and tubes inspected during the Cycle 11 outage that will be inspected during the Cycle 14 outage. All tubes with flaws identified in the Cycle 11 outage and not plugged at that time will be inspected during the Cycle 14 outage, i.e., the worst case six fuel cycles. The OA is a conservative projection that ensures tube integrity will be maintained until the Cycle 14 outage when the steam generators are inspected next.

NRC RAI No. 4 Please provide a brief description of the Marmon clamp mentioned on page 10 of your report and its function in the SG.

TVA Response The function of the Marman Coupling (or clamp) is to hold the access cover (i.e., for tube bundle access) in place. It is located on the top surface of the separator support plate and is similar in concept to a drum lid clamp. The Marman Coupling is type 321 stainless steel and includes type 316 stainless steel tee-bolts and lock-nuts. Attached are two sketches taken from the Watts Bar Nuclear Plant Unit 1 Replacement Steam Generator Drawing 1001 0E36, Sheet 2 of 2, Rev.00, titled, "Separator Support Plate,"

which show the typical Marman Coupling/Access Cover assembly configuration. A photo is also attached.

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-MARMAN COUPLING ACCESS PIPE ACC SEPARATOR SUPPORT PLATE

ESS COVER MARMAN COUPLING

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