SBK-L-11193, Letter to Nextera Energy Seabrook Steam Generator Tube Inspection Report

Letter to Nextera Energy Seabrook Steam Generator Tube Inspection Report

ML11266A008
Person / Time
Site:	Seabrook
Issue date:	09/19/2011
From:	O'Keefe M NextEra Energy Seabrook
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
SBK-L-11193
Download: ML11266A008 (9)

Text

NEXTera September 19, 2011 SBK-L- 11193 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 14 in April 2011.

If you have any questions regarding this submittal, please contact me at (603) 773-7745.

Sincerely, NextEra Energy Seabrook, LLC.

Michael O'Keefe Licensing Manager Enclosure cc: NRC Region I Administrator G. E. Miller, NRC Project Manager W. J. Raymond, NRC Senior Resident Inspector NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874

Enclosure Steam Generator Tube Inspection Report

Enclosure Steam Generator Tube Inspection Report 1.0 Introduction Appendix A provides a list of acronyms.

Seabrook Station is a Westinghouse four-loop pressurized water reactor with Model F SGs.

The SGs are U-tube heat exchangers with tube bundles fabricated using thermally treated Alloy 600 tubing. A row and colunm number identifies each tube. Each SG contains 5,626 tubes arranged in 59 rows and 122 colunis. Nominal tube OD is 0.688" with a 0.040" nominal wall.

During Seabrook's thirteenth refueling outage (OR13) in October, 2009, SGs A, B, C, and D were inspected with ECT. During that inspection, one axial ODSCC indication was detected in the hot-leg tubesheet expansion transition region of a tube in SG-C. Per TS 6.7.6.k.d.3, an inspection for the damage mechanism reported was required to be performed in the next outage (OR14). The ECT inspection in OR14 was performed in accordance with Seabrook Station TS 6.7.6.k. This report presents the results of the inspection pursuant to TS 6.8.1.7, "Steam Generator Tube Inspection Report."

Seabrook Station TS 6.7.6.k and the EPRI Steam Generator Examination Guidelines, Revision 7, define the required inspection periods and their duration. For Alloy 600TT tubing, the first inspection interval is 120 EFPM; the second inspection interval is 90 EFPM; the third and subsequent inspection intervals are 60 EFPM. The requirement to complete inspection of 100% of the tubes by the end-point of the inspection interval was met by the previous inspections performed at OR13. The inspection performed during OR14 was performed to inspect for a specific degradation mechanism, expansion transition ODSCC.

2.0 Scope of Inspections Performed The inspection scope was required by Seabrook Station TS 6.7.6.k.d.3 and the EPRI Steam Generator Examination Guidelines, Revision 7. The defined inspection scope for OR14 was:

• SG-C: 100% Hot leg TTS, +/- 3", +Point examination.

• SG A, B, & D: 20% Hot leg, TTS +/- 3", +Point examination

• Visual inspection of all mechanical and weld plugs.

+Point inspection bounding the tubes exhibiting PLP signals during the inspection.

• 100% inspection of previously reported wear indications in the scope range of +/-3".

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Inspection Expansion There were no inspection expansions.

Secondary Side The following work was performed on the secondary side of the SGs:

• Top-of-Tubesheet ASCA.

• Sludge Lancing.

• FOSAR in the tube lane and annulus areas.

• SG C Nail retrieval.

3.0 Degradation Mechanisms Found The following degradation mechanism was observed in the Seabrook Station SGs during OR14:

One new volumetric indication was reported in SG-A in tube R55C70 at TSH+O. 14" (Most likely caused by transient foreign object) 4.0 NDE Techniques for Damage Mechanisms Following is a list of the EPRI ETSS used for degradation detection during the OR14 ECT inspection (with the rotating +Point coil).

• Wear due to Foreign Objects EPRI ETSS # 27901.3 through 27907.3

• Sludge Pile ODSCC EPRI ETSS # 128413

• Tubesheet Expansion ODSCC PRI ETSS #21409.1 and #21410.1

• Tubesheet Expansion PWSCC EPRI ETSS #20510.1 and #20511.1 5.0 Service Induced Flaws Volumetric Indications Volumetric indications were reported in three of the four SGs as summarized in Table 1.

One new volumetric indication was reported during OR14 in SG-A. This indication is similar to previously reported indications at the top of the tubesheet. Typically, indications of wear due to transient foreign objects exhibit no growth during subsequent operation. The previously reported indications exhibited no evidence of growth since the time when they were identified in prior inspections. Similarly, no growth of the new 2

volumetric indication attributed to a transient foreign object is expected. These indications met the performance requirements for condition monitoring and, absent growth, also meet the requirements for operational assessment. These indications are acceptable for continued operation until, at least, OR15.

Table 1 Volumetric Indications Depth (%TWD) per ETSS SG Row Col Location ECT Code 21998.1

(@OR14) ORil OR13 OR14 49 29 TSH+0.22" VOL/PCT 22% 22% 22%

A 50 29 TSH+0.22" VOL/PCT 11% 11% 15%

55 70 TSH+0.14" VOL/PCT NDD NDD 19%

B 43 96 TSH+0.05" VOL/PCT 22% 21% 19%

C 43 26 TSH+0.14" VOL/PCT 21% 23% 21%

44 26 TSH+0.16" VOL/PCT 13% 13% 9%

Foreign Objects/PLP Wear due to impingement of foreign objects on the tubes is categorized as an existing degradation mechanism due to the confirmation of loose parts in prior inspections at Seabrook. Foreign objects may be identified by both visual inspection from the secondary side and by ECT inspection from the primary side. Visual inspections result in photographic evidence of foreign objects, if any, and ECT inspection results in PLP codes.

The only new objects identified were "sludge rocks," indigenous materials that have been shown not to damage the tubes.

During the OR 11 ECT inspection, a foreign object with associated wear was detected.

The foreign object that caused the wear was subsequently identified as a metallic nail.

The nail was successfully removed from the SG during OR14 and, therefore, does not represent future potential for damage. Fourteen tubes surrounding the prior location of the nail remain plugged.

Only two known or presumed remaining foreign objects remain in the SGs.

Foreign objects known to exist in the SGs are:

• A small dumbbell-shaped object tightly captured between two plugged tubes above the top-of-tubesheet in SG-C. The object has been lodged between the two tubes since the first inspection in ORO0.

" An object just above R6C2 - 5H in SG-A. The object was identified during OR08. Seven surrounding tubes were plugged to provide a boundary against wear propagation.

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Thus, the performance criteria for operational assessment are satisfied and operation of the SGs until the next inspection at ORI 5 is justified. Sludge rocks are not considered to have the potential to damage the tubes. Further, wear on active tubes attributed to non-resident, transient foreign objects has not exhibited any growth; therefore, satisfaction of performance criteria for condition monitoring also satisfies the criteria for operational assessment. It is concluded that tubes with volumetric indications (attributed to foreign object wear) that are still in service are acceptable for continued operation until the next inspection at OR15.

Table 2 summarizes the PLP indications found in the SGs during the TTS (+/-3") +Point RPC program of the primary side ECT inspection. Also shown on Table 2 are the results of prior inspections (OR11 and OR13) at the same locations. In SG-C, a PLP call in R40C92 from the OR13 inspection was confirmed to have NDD during OR14.

Table 2 Seabrook Steam Generator Potential Foreign Objects (PLP)

SG Row Col Location (OR13) ORII OR13 OR14 1 9 TSH+O.18" NDD PLP/NDD PLP A 1 10 TSH+0.29" NDD PLP/NDD PLP 1 11 TSH+0.12" NDD PLP/NDD PLP B 3 104 TSH+0.09 NR PLP INR C 40 92 TSH+0.05" NR PLP NDD D 41 27 TSH+0.06" NR PLP PLP 42 27 TSH+0.04" NR PLP PLP 6.0 Plu22in2 There were no tubes plugged in OR 14.

The current plugging level and percentage in each steam generator is shown in table

3. This is also the effective plugging level.

Table 3 Total Tubes Plugged and Plugging Percentage SG-A SG-B SG-C SG-D Total Tubes Plugged 34 25 50 64 173 Percent 0.6% 0.4% 0.8% 1.1% 0.77%

Plugged I I I I I 4

7.0 Condition Monitoring Assessment Results.

All indications found in OR14 satisfy the condition monitoring requirements of NEI 97-06 for structural and leakage integrity. No indications were found to exceed structural limits. These conclusions are based on the evaluations included in this report as supported by the conclusions of the OR 13 condition monitoring and operational assessment and are summarized below:

a. No indications of ODSCC or PWSCC were detected during OR14. Therefore, these degradation mechanisms are not of concern for operation until OR15.

b. Volumetric indications meet the requirements for condition monitoring at 95%

probability and 50% confidence. The maximum observed indication was 22%

TWD, attributed to a transient foreign object. The structural limit for the local wear is 70% TWD. The evaluation of the observed wear indication, including all sizing uncertainties from the applicable ETSS, shows that the requirements for condition monitoring have been met.

c. No volumetric indications attributed to pitting were observed.

8.0 Observed Leak Rates The only observed operational leakage is in SG-B. The leakage fluctuates between 0.2 and 0.7 gpd. There is no observed leakage in SGs A, C, or D.

9.0 Calculated Accident Induced Leakage Seabrook operations in Cycle 13 were free from primary to secondary SG leakage in SGs-A, C and D.

Leakage between 0.2 gpd and 0.7 gpd has been reported in SG-B for a number of cycles without change. The observed leakage is well within the TS limits for Seabrook.

Because the temporary ARC approved prior to OR13 is in place until ORI 5, the leakage criteria of this ARC still apply. The maximum predicted accident induced leakage would be 1.75 gpd of it is assumed that the entire observed leakage stems from the tubesheet expansion region in SG B.

10.0 Secondary Side Inspections/Cleaning Top of tubesheet ASCA were applied to all four SGs. Approximately 98 lbs of iron were removed from all SGs during the process.

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Sludge lancing removed approximately 323 lbs from the top of tubesheet area from all four SGs.

FOSAR inspections of the annulus and tube lanes were performed in all four SGs. Other than sludge rocks and a soft, flexible item characterized as "duct tape" (which was removed), no foreign objects were found.

The foreign object located in SG-C on the FDB in OR 1I was successfuilly removed in OR14.

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Appendix A Accronyms ARC Alternate Repair Criteria ASCA Advanced Scale Conditioning Agents AVB Anti Vibration Bar DBA Design Bases Accident ECT Eddy Current Testing EFPM Effective Full Power Months EPRI Electric Power Research Institute ETSS Examination Technique FDB Flow Distribution Baffle FOSAR Foriegn Object Search and Retrieval DSI Distorted Support Indication DSS Distorted Support Signal GPD(gpd) Gallons per Day HL Hot Leg ID Inner Diameter NDD No Degradation Detectable NDF No Degradation Found NEI Nuclear Energy Institute OD Outside Diameter ODSCC Outside Diameter Stress Corrosion Cracking PCT Percent PLP Possible Loose Part PWSCC Primary Water Stress Corrosion Cracking SAI Single Axial Indication SCC Stress Corrosion Cracking SG Steam Generator TS Technical Specifications TSP Tube Support Plate TTS Top of Tube Sheet TWD Though Wall Distance VOL Volumetric 7