SBK-L-17166, Generator Tube Inspection Report

Generator Tube Inspection Report

ML17291B270
Person / Time
Site:	Seabrook
Issue date:	10/17/2017
From:	Browne K NextEra Energy Seabrook
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
SBK-L-17166
Download: ML17291B270 (7)

Text

NEXTera ENERGY ~

SEABROOK October 17, 2017 SBK-L-17166 Docket No. 50-443 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station Steam Generator Tube Inspection Report Enclosed is the Seabrook Station Steam Generator Tube Inspection Report. NextEra Energy Seabrook, LLC is submitting this report in accordance with Seabrook Station Technical Specification 6.8.1.7, Steam Generator Tube Inspection Report. This report provides the results of the steam generator tube inspections conducted during refueling outage 18 in the Spring of 2017.

This letter contains no new regulatory commitments.

If you have any questions regarding this submittal, please contact me at (603) 773-7932.

Sincerely, NextEra Energy Seabrook, LLC.

Kenneth J. Browne Licensing Manager Enclosure cc: NRC Region I Administrator R. Gladney, NRC Project Manager NRC Senior Resident Inspector NEXTERA ENERGY SEABROOK, LLC, P.O. Box 300, LAFAYEITE ROAD , SEABROOK, NH 03874

Enclosure Steam Generator Tube Inspection Report

SBK-L-17166 Enclosure Enclosure OR18 Steam Generator Tube Inspection Report

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Introduction:==

The enclosed Steam Generator Tube Inspection Report for Seabrook Unit 1 is submitted for the inspection of the SGs during refueling outage 18 (hereafter referred to as the OR18 inspection or outage), as required by Technical Specification section 6.8.1.7. Per the Seabrook Unit 1 Technical Specification section 6.7.6.k, the first inspection period is 120 EFPM; the second inspection period is 96 EFPM; the third and subsequent inspection periods are 72 EFPM. The inspection in OR18 was performed in accordance with Technical Specification 6.7.6.k, and was the fourth inspection of the SGs in the third inspection period. At unit shutdown for the OR18 inspection, the SGs had operated for approximately 23.15 EFPY (277.8 EFPM) since installation. This included operation for approximately 1.36 EFPY (16.3 EFPM) during the fuel cycle (cycle 18) leading up to the OR18 inspection. Initial entry into Mode 4 following completion of the OR18 inspection was made on April 26, 2017.

Seabrook Unit 1 is a Westinghouse 4-loop PWR with Model F steam generators. The SGs are U-tube heat exchangers with tube bundles fabricated using thermally-treated Alloy 600 tubing. Each SG contains 5,626 tubes arranged in 59 rows and 122 columns. Nominal tube OD is 0.688" with a 0.040" nominal wall thickness. The tubes have a square pitch arrangement and are supported by stainless steel, broached-hole, quatrefoil tube support plates (TSPs). The inspection of the SGs during the OR18 outage met the requirements of the Seabrook Unit 1 Tech Specs, SG Program Guidelines (NEI 97-06 Rev 3) and the EPRI SGMP: PWR Steam Generator Examination Guidelines, Rev 7.

References to Seabrook's prior SG Tube Inspection Reports in the third inspection period are tabulated in Appendix A along with a list of acronyms and abbreviations used in this report.

A. Scope of Inspections Performed on each SG The OR18 outage was originally planned to be a "skip" outage (i.e., no primary-side inspections).

Discovery of stress corrosion cracking (ODSCC, PWSCC) at the hot leg (HL) expansion transition and tube-to-tubesheet expansion regions (SG-A, SG-C) during the OR17 inspection, required an inspection of the areas of interest, in accordance with Section 6.7.6.k.d.3 of the Seabrook Unit 1 Tech Specs. There were no bulges or over-expansions (BLG/OXP) associated with any of the ODSCC/PWSCC locations in OR17. The previous (OR17) operational assessment justified continued operation until the OR19 inspection for all other degradation mechanisms in the Seabrook SGs except PWSCC/ODSCC. No bobbin probe inspection was performed in OR18. The defined OR18 inspection scope was:

Primary-side:

• +Point' probe inspection of 100% of all active tubes in the HL of SG-A and SG-C from TTS+3" to TTS-15.21" to detect SCC in the expansion transition and tube-to-tubesheet expansion regions. (The H* depth for the Seabrook SGs is TTS-15.21".)

• +Point' probe inspection of 50% of all active tubes in the HL of SG-B and SG-D from TTS+3" to TTS-15.21" to detect SCC in the expansion transition and tube-to-tubesheet expansion regions.

(Tubes not inspected in this region in OR17 were given the highest priority of the 50% sample.)

The inspection scope also included 100% of high stress (minus 2-sigma) tubes.

• +Point' probe inspection of the TTS region (TTS+/-3") of peripheral tubes (3 outermost tubes of each row) exposed to the annulus and the tube-free lane, in the cold leg (CL) of each SG to detect foreign object (FO) wear.

• Visual inspection of all mechanical and welded plugs in the HL and CL of each SG.

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SBK-L-17166 Enclosure

• Channel head visual inspection and bowl scan in the HL and CL of each SG per Westinghouse NSAL 12-1, "Steam Generator Channel Head Degradation," January 5, 2012.

Secondary-side:

• No secondary side inspections were performed during the OR18 SG inspection.

8. Degradation Mechanisms Found The following degradation mechanism was identified during the OR18 inspection:

• Historical (volumetric) wear indications in the TTS region.

The tube wear indications found during eddy-current testing (ECT) were all previously-reported, attributable to transient foreign objects (FOs), and showed no growth in percent through-wall depth

(% TWD). The list of wear indications identified is provided below in Table 2.

No PWSCC or ODSCC indications were found during the OR18 inspection. No pitting was detected. No degradation was detected during the +Point' probe inspection of high stress tubes.

No corrosion-related or other types of degradation were found during the visual inspection of the channel head bowl and tube plugs.

C. NOE Techniques utilized for each Degradation Mechanism Table 1 is a list of the NDE techniques used for degradation detection/sizing during the OR 18 inspection.

Table 1 - NDE Techniques for Degradation Mechanisms Degradation Mechanism I Detection Technique ETSS)

Location Probe Detection Sizinq Wear due to Foreign +Point' 27901.1 thru 27907.1 (latest 21998.1 Rev4 Objects at TIS +3 in. revision)

Alternate: 27901.1 thru 27907.1 (latest Rev)

PWSCC and ODSCC at +Point' ID: 20510.1 Rev 7 (Circ); 20510.1Rev7 (Circ)

TIS Expansion 20511.1 Rev 8 (Axial) 20511.1 Rev 8 (Axial)

Transition OD: 128424 Rev3 (Axial); 21410.1Rev6 (Circ) 21410.1 Rev 6 (Circ) 128431 Rev 2 (Axial) 20507.1 Rev 6 Ghent 3/4 (Circ) 20508.1 Rev 6 Ghent 3/4 (Axial)

PWSCC at Tubesheet +Point' 20510.1 Rev 7 (Circ) 20510.1 Rev 7 (Circ)

Expansion Region (TTS 20511.1 Rev 8 (Axial) 20511.1 Rev 8 (Axial) to H* depth)

D. Location, orientation (if linear), and measured sizes (if available) of service induced indications Volumetric Wear Indications at the TTS:

Wear due to impingement of foreign objects on the tubes is categorized as an existing degradation mechanism due to the confirmation of foreign objects in prior inspections at Seabrook. All volumetric indications reported during the OR18 inspection were previously reported, and were in close proximity to the TTS. These indications were attributed to transient foreign objects. No significant growth/change in depth of these indications was obseNed (beyond the accuracy of the eddy current technique), and no growth is expected of these indications since no FOs are resident at these locations. The list of volumetric wear indications identified in OR18 is provided in Table 2.

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SBK-L-17166 Enclosure Table 2 - OR18 Volumetric Indications (in %TWO)

SG Row Col Location OR17 OR18 A 49 29 TSH+0.18" 22% 23%

A 50 29 TSH+0.12" 11% 10%

B 43 96 TSH+0.07" 19% 19%

c 43 26 TSH+0.12" 23% 23%

c 44 26 TSH+0.19" 11% 9%

Foreign Objects I PLP Signals:

Possible loose part (PLP) signals were reported during the OR18 inspection (4 in SG-A, O in SG-B, 2 in SG-C, 5 in SG-D). All were previously-reported, located just above the TTS and are attributed to transient FOs. No significant changes in eddy-current response were seen using the +Point' probe, and there was no degradation/wear associated with the PLP signals. Secondary-side visual inspection performed at these locations in OR17 confirmed that these PLPs are sludge, sludge rocks or deposits, which are benign to the tubes. These tubes were left in service.

E. Number of tubes plugged during the inspection outage for each degradation mechanism No tubes were plugged during the OR18 inspection outage. The tubes that showed the degradation mechanism found (see Table 2) were not required to be plugged.

F. Number and percentage of tubes plugged to date, and the effective plugging percentage in each steam generator The number and percentage of SG tubes plugged to-date, and the effective plugging percentage in each SG are summarized in Table 3.

Table 3 - Tubes plugged to-date and effective plugging percentage SG-A SG-B SG-C SG-D Tubes Plugged 39 27 58 65 Percent Plugged 0.69% 0.48% 1.03% 1.16%

G. Results of Condition Monitoring, including the results of tube pulls and in-situ testing All indications found in OR18 met the condition monitoring (CM) requirements of NEI 97-06 for structural and leakage integrity. The largest indication (23% TWO) was much less than the structural limit (71.6%). As a result, no tube required in-situ pressure testing, and no tube pulls were required.

a. Volumetric wear indications at the TTS was the only degradation mechanism identified in OR18, and was attributed to transient foreign objects (FOs). These indications were all previously-identified and showed no growth when compared to historical data. The volumetric indications met the CM requirements for structural and leakage integrity, and are listed in Table 2.

b. PLP signals were reported during the OR18 inspection at the TTS location on some tubes in SG-A, SG-C and SG-D. All were previously reported and there were no significant changes in eddy current response with +Point' when compared with OR17 data. No wear was associated with any of the PLP signals reported during the OR18 inspection.

c. No indications of PWSCC or ODSCC were identified within the scope of tubes tested in OR18.

No pitting was observed during the inspection.

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SBK-L-17166 Enclosure

d. Except for PWSCC/ODSCC, the previous (OR17) operational assessment justified continued operation until the OR19 inspection for all other degradation mechanisms in the Seabrook SGs.

e. During the inspection of tube plugs in OR18, all installed plugs were confirmed to be in their correct location. In addition, all plugs were found to be dry; no dripping plugs were identified.

No degradation or visible signs of leakage were noted on the plugs during the visual inspection.

f. Westinghouse NSAL 12-1 recommended visual inspection of the channel head to determine if degradation of the channel head cladding, the divider plate-to-channel head weld and the weld at the top of the channel head bowl drain tube had occurred. These areas were inspected during the OR 18 outage. The observed condition during the OR 18 inspection is consistent with the manufacturing process and does not exhibit any degradation. It was concluded that a condition similar to that documented in NSAL 12-1 does not exist at Seabrook.

H. Primary-to-secondary leakage rate observed in each SG during the previous cycle Seabrook has tracked detectable normal operating primary-to-secondary leakage in SG-B that has varied between 0.14 gpd and 1.13 gpd during the fuel cycle preceding the OR 18 inspection. This low level of leakage has been detected for several cycles. No normal operating primary-to-secondary leakage has been detected in SG-A, SG-C, or SG-D.

I. Calculated accident induced leakage rate For application of H* during condition monitoring assessment, Seabrook committed (Ref. NRC ADAMS Accession No. ML12178A537) that the component of operational leakage from the prior cycle from below the H* distance will be multiplied by a leak rate factor of 2.49 and added to the total accident leakage from any other source and compared to the allowable accident induced leakage limit.

The assumed value for accident induced leakage in the Seabrook UFSAR is 500 gpd for the faulted SG and 940 gpd through the remaining three SGs, for a total leakage of 1440 gpd (=1.0 gpm). As stated in Section H, SG-B experienced leakage in the range of 0.14 gpd to 1.13 gpd in the fuel cycle preceding the OR18 inspection. Since there was no observed operational leakage from SGs A, C, and D, the predicted accident-induced leakage from the tubesheet expansion region is zero, from these three SGs.

During the OR 18 SG tube inspection, no other degradation mechanism was identified to be the source of the observed leakage in SG-B, therefore, the entire observed operational leakage is assumed to come from the tubesheet expansion region. Other than the expansion region in SG-B, there were no other sources of accident induced leakage from any of the SGs. Conservatively assuming that the operating leakage in SG-B is at the upper end of the observed range (i.e. 1.13 gpd), the predicted accident induced leakage (OosA) in SG-B is:

OosA = 2.49 X 1.13 gpd = 2.81 gpd Therefore, since the predicted accident induced leakage from SG-B (2.81 gpd) is less than the UFSAR limit (500 gpd) for leakage through any one SG, and less than the total leakage limit for all SGs (1440 gpd), the accident induced leakage performance criteria are met.

J. Results of monitoring for tube axial displacement (slippage)

A condition for licensing H* was to monitor for tube slippage within the tubesheet region. Monitoring for slippage was performed in OR18 using the motorized rotating probe coil (MRPC). No tube slippage was detected during the OR18 inspection.

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SBK-L-17166 Enclosure APPPENDIX A - Additional lnformatiion References to prior SG Tube Inspection Reports (3rd inspection period)

Inspection# EOC Outaqe NRC ADAMS Accession No.

1 EOC-15 OR15 ML13008A160 2 EOC-16 OR16 ML14297A090 3 EOC-17 OR17 ML16120A203 Abbreviations and Acronyms BLG Bulge CL Cold Leg CM Condition Monitoring OBA Design Bases Accident ECT Eddy Current Testing EFPM Effective Full Power Months EFPY Effective Full Power Years EPRI Electric Power Research Institute ETSS Examination Technique Specification Sheet FO Foreign Object GPO (gpd) Gallons per Day GPM (gpm) Gallons per Minute HL Hot Leg NEI Nuclear Energy Institute OD Outside Diameter ODSCC Outside Diameter Stress Corrosion Cracking OXP Over-expansion Per Percent Through-Wall PLP Possible Loose Part PWSCC Primary Water Stress Corrosion Cracking sec Stress Corrosion Cracking SEL Structural Equivalent Length SG Steam Generator TSC Tube Sheet Cold TSH Tube Sheet Hot TSP Tube Support Plate TTS Top of Tube Sheet TW Through Wall TWO Through Wall Depth PAGE50F5