ML071510197

Seabrook - Steam Generator Inservice Inspection

ML071510197
Person / Time
Site:	Seabrook
Issue date:	05/23/2007
From:	St.Pierre G F Florida Power & Light Co
To:	Document Control Desk, NRC/NRR/ADRO
References
SBK-L-07088
Download: ML071510197 (6)

Text

FPL Energy Seabrook Station FPL Energy Seabrook Station P.O. Box 300 Seabrook, NH 03874 (603) 773-7000 May 23, 2007 Docket No. 50-443 SBK-L-07088 U. S. Nuclear Regulatory Commission Attention:

Document Control Desk Washington, DC 20555-0001 Seabrook Station Steam Generator Jnservice Inspection FPL Energy Seabrook, LLC encloses pursuant to Seabrook Station Technical Specification Surveillance Requirement 4.4.5.5b, a report documenting the results of inservice inspections conducted on the Steam Generators during the eleventh refueling outage that occurred in October 2006.Should you require further information regarding this matter, please contact Mr. Michael Ossing, Manager of Engineering Support, at (603) 773-7512.Very truly yours, FPL Energy Seabrook, LLC Gene St. Pierrese Site Vice President cc: S. J. Collins, NRC Region I Administrator G. E. Miller, NRC Project Manager, Project Directorate 1-2 W. J. Raymond, NRC Senior Resident Inspector 4C) 14 7 an FPL Group company ENCLOSURE TO SBK-L-07088 Steam Generator 12 Month Inservice Inspection Report 1.0 Introduction In October 2006, FPL Energy, Seabrook LLC (Seabrook Station) eleventh refueling outage, Steam Generators (SGs) A, B, C, and D were inspected.

This was accomplished in accordance with Seabrook Station Technical Specification 4.4.5. This report presents the results of the inspection pursuant to Technical Specification 4.4.5.5.b.

and NEI 97-06.Seabrook Station is a Westinghouse four-loop pressurized water reactor with Model F steam generators.

The generators are U-bend heat exchangers, with tube bundles fabricated using thermally treated alloy 600 tubing. A row and column number identifies each tube. There are 59 rows and 122 columns in each steam generator, for a total of 5,626 tubes. Nominal tube OD is 0.688" with a 0.040" nominal wall thickness.

The EPRI Steam Generator Examination Guidelines, Revision 6, defines the required inspection periods and their duration.

For alloy 600TT tubing, the first inspection interval is up to 120 Effective Full Power Months (EFPM); the second inspection interval is 90 EFPM; the third and subsequent inspection intervals are 60 EFPM. OR 1I is the approximate mid-point of the second inspection interval (90 EFPM) at Seabrook Station. The requirement to complete inspection of 50% of the tubes by the mid-point of the inspection interval is met by the inspections performed at ORI 1.2.0 Scope of Inspections Performed The inspection program required by Seabrook Station Technical Specifications and the EPRI Steam Generator Examination Guidelines, Revision 6, addresses the known degradation mechanisms observed in Seabrook in prior inspections as well as those regarded as relevant and potential degradation mechanisms.

The defined scope implemented in all 4 SGs during ORI 1 included the following, the percentages indicating the approximate inspection sample needed to satisfy the mid-period requirements of EPRI Steam Generator Examination Guidelines, Revision 6: 0 100% Bobbin examination of tubes, full length except for Rows 1 and 2, which are inspected with the bobbin from tube end to TSP#7 on both Hot Leg (HL) and Cold Leg (CL).0 30% of the U-bends in each of Rows 1 and 2 with + Point.* 30% HL Top of Tube Sheet (TTS), +/- 3", mid-range

+ Point examination to complete 50% with tubes examined in OR09.* 30% Dings and Dents > 5 Volts: HL dings/dents with the mid-range

+Point probe. The HL includes the U-bend to just above the top TSP on the CL.0 50% sample of the hot leg tubesheet expansion zone bulges (BLG) and overexpansions (OXP) in the region from the TTS to the TTS-17"; mid-range

+Point examination.

Special interest, mid-range

+Point tests at hot leg and cold leg bobbin possible flaw locations (including U-bends), including all "I-code" indications that were new or not resolved after history review.* Visual inspection of mechanical and weld plugs.* +Point inspection to bound the tubes exhibiting possible loose parts (PLP) signals during the inspection.

The NRC granted Seabrook Station a one-time technical specification change that effectively changed the definition of where a steam generator tube starts in the tube sheet. This allowed the inspection program to not consider or inspect the portion of the steam generator tubing below 17 inches from the top of the tubesheet on the hot leg side.Inspection Expansion No expansion of the inspection plan was required.

For Anti-Vibration Bar (AVB) wear, a 100%inspection of the affected tubes was performed in the base bobbin program. No other operational degradation was detected that required expansion of the inspection sample.3.0 Active Degradation Mechanisms The EPRI Steam Generator Examination guidelines Revision 6 define "Active Damage Mechanism" as: (1) A combination of 10 or more new indications of degradation

(> 20% through-wall distance[TWD]) of thinning, pitting, wear (excluding loose part wear), or impingement and previous indications that display an average growth rate > 25% of the repair limit in one inspection-to-inspection interval in any one SG.(2) Alternatively, the existence of 1 or more new or previously identified indications

(>20% through-wall) which display a growth > the repair limit in one inspection-to-inspection interval.(3) Any crack indication (outside diameter intergranular attack/stress corrosion cracking or primary side corrosion cracking).

There are no active degradation mechanisms in any of the Seabrook SGs. However, AVB wear is clearly an ongoing (relevant) degradation mechanism.

Based on the above definitions of an active degradation mechanism, for AVB wear to be an active degradation mechanism, a combination of at least ten or more new indications greater than 20%TWD and/or previously detected indication with growth rates greater than 10% would be required.4.0 NDE Techniques for Damage Mechanisms The NDE (Non Destructive Examination) techniques used met the applicable industry guidance and were qualified, also in accordance with applicable industry guidance, for site specific use.5.0 Pluein2 Twenty-one tubes were plugged during OR 1I at Seabrook.

Table 1 lists the plugged tubes and summarizes what the degradation is attributed to. No tubes were plugged in SG-A. In SG-B, a tube that was identified after restart after OR09 with potentially elevated residual stress was administratively plugged. This tube was inspected prior to plugging and was found free of any degradation.

In SGs C and D, several tubes were plugged for AVB wear that exceeded the 40% TWD Technical Specification plugging limit. Other tubes with significant AVB wear were examined for unusual wear patterns and growth rates; none was judged to have growth rates or wear patterns that indicated administrative plugging was warranted.

In SG-C, two tubes were identified initially with possible loose part (PLP) signals in an area that could not be accessed for removal of the foreign object. These tubes exhibited wear signal suggesting that the foreign object was still present; therefore they were plugged. The 14 un-degraded tubes surrounding the tubes were also plugged to create a conservative boundary for the degraded tubes.In SG-D, a tube was plugged with a volumetric (wear) indication below the 6 th TSP that was sized at 40% TWD using ETSS 29881. The location was bounded by +Point examination; no foreign objects were detected in any of the surrounding tubes.Table 1 Steam Generator Tube Plugging in ORl 1 SG Tube Attribution Notes A none NA NA B R27C97 Administrative Tube with potentially high residual stress R51 C69 AVB Wear 44% TWD at AVB5 C R51C45 AVB Wear 42% TWD at AVB3 R58C54 Foreign Object. Wear DSI,PLP,SVI,PCT 39% @ O1C+0.51 R59C57 Foreign Object. Wear DSI, SVI, PCT 48%R58C55 Administrative PLP Box R59C55 Administrative PLP Box R57C56 Administrative PLP Box R58C56 Administrative PLP Box R59C56 Administrative PLP Box R57C57 Administrative PLP Box R58C57 Administrative PLP Box R57C58 Administrative PLP Box R58C58 Administrative PLP Box R59C58 Administrative PLP Box R57C55 Administrative PLP Box R57C53 Administrative PLP Box R58C53 Administrative PLP Box R57C54 Administrative PLP Box D R52C44 AVB Wear 41% TWD at AVB4 R11C102 Volumetric SVI @ 06C-0.74; 40%TWD Note: SVI PLP DSI PCT TWD AVB Single Volumetric Indication Possible Loose Part Distorted Support Indication Percent Though Wall Distance Anti-Vibration Bar The following table (table 2) shows the total number of tubes plugged by steam generator and the effective percentage plugged in each steam generator as well as total tubes plugged and total effective plugging percentage.

Table 2 Total Tubes Plugged and Plugging Percentage S/G A S/G B S/G C S/G D Total Tubes Plugged 31 24 46 60 161 Percent lugged 0.55% 0.43% 0.81% 1.07% 0.72%6.0 Condition Monitoring Assessment Results.All indications found in OR 1I 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 and summarized below: 1. Based on the OR11 inspection results, the Seabrook Station steam generators currently meet all of the performance criteria as specified in NEI 97-06, Revision 2, "Steam Generator Program Guidelines." 2. No indications of cracking were observed at any location in all four SGs.3. The maximum observed AVB wear indication (44% TWD) meets the structural requirements of draft Reg. Guide 1.121 when the NDE uncertainties 5.3% at 95% CL (based on the use of a 0/20/40 standard) for AVB wear sizing are added to the observed wear depths.4. AVB wear, classified as a relevant (on-going) degradation mechanism in all four SGs in the pre-outage degradation assessment, is not an active degradation mechanism in any of the SGs based on the OR 1I results. The overall incidence of AVB wear in the Seabrook SGs is consistent with the Model F SG operating experience.

5. The previously reported wear at the flow distribution baffle (FDB) was reported again during OR11 at Seabrook.

Examination of the prior inspection signals shows that the signals are not changing.

FDB wear is attributed to the application of pressure pulse cleaning of the SGs and is observed in other Model F SGs at the same locations and depths. The magnitude of the wear does not challenge the requirements for condition monitoring.

6. Volumetric (wear) indications meet the requirements for Condition Monitoring at 95%probability and 50% confidence.

The maximum observed indication was 40% TWD.7. Wear due to foreign objects meets the performance requirements for Condition Monitoring.

The maximum wear observed due to foreign objects was 48% TWD; the structural limit for the local wear is 75%. The 95/50 evaluation of the observed wear flaw shows that the requirements for condition monitoring are met.8. No pitting was observed.9. No degradation indications were observed related to potential precursor signals such as dents and dings, or to interference such as permeability variations, etc.10. No degradation was observed in the tubesheet expansion zone during the BLG/OXP program from the TTS to -17 inches.