ML071140441

Annual Steam Generator Tube Inservice Inspection Summary Report

ML071140441
Person / Time
Site:	North Anna
Issue date:	02/27/2007
From:	Funderburk C Dominion, Dominion Resources Services, Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, NRC/NRR/ADRO
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ML071140441	List: ML071140441
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07-0089
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Dominion Resources Services, Inc.

iO4)O Dominion Boulevard, Glen Allen, VA 2.3000 Wl b Address: www.dom.com February 27, 2007 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001 P Dominion" Serial No.

07-0089 NL&OS/ETS Docket Nos.

50-338 50-339 License Nos. NPF-4 N PF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNITS 1 AND 2 2006 ANNUAL STEAM GENERATOR TUBE INSERVICE INSPECTION

SUMMARY

REPORT Pursuant to Technical Specification 5.6.7.b for North Anna Power Station Units 1 and 2, Dominion is required to submit an annual steam generator tube inservice inspection report. The attachment to this letter provides the 2006 annual steam generator tube inlspection report for North Anna Unit 1. There were no inservice inspections performed on the Unit 2 steam generator tubes during 2006.

This letter does not establish any new commitments. Should you have any questions or require additional information, please contact Mr. Thomas Shaub at (804) 273-2763.

Very truly yours, C. L. ~underburk, Director Nuclear Licensing and Operations Support Dominion Resources Services, Inc.

for Virginia Electric and Power Company

Attachment:

2006 Annual Steam Generator Tube lnservice Inspection Report

Serial No. 07-0089 Docket Nos. 50-3381339 Page 2 of 2 cc::

U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. J. T. Reece NRC Senior Resident Inspector North Anna Power Station Mr. S. P. Lingam NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11 555 Rockville Pike Rockville, Maryland 20852-2738 Mr. R. E. Martin NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 1 1 555 Rockville Pike Rockville, Maryland 20852-2738 Mr. J. E. Reasor Old Dominion Electric Cooperative lnnsbrook Corporate Center 4201 Dominion Boulevard Suite 300 Glen Allen, Virginia 23060

ATTACHMENT Serial No. 07-0089 North Anna Power Station Unit 1 2006 Annual Steam Generator Tube lnservice Inspection Report Virginia Electric and Power Company (Dominion)

Serial No. 07-0089 Docket Nos. 50-3381339 Page 1 of 12 Virginia Electric and Power Company (Dominion)

North Anna Unit 1 Annual Steam Generator Report F o r t h Anna 1 1

I March 2006 1

I B

I 1 101 12007 rstation SG Inspection Program Planned Inspected lnspection Method Extent Bobbin 3592 3592 Bobbin TEC - TEH, except Outage Date Unit Design Information I!

R-1 U bends 3end RC 1

98 1

98 1

+ Point RC I

7H - 7C I

Generator Examined Number of AVBs 3

Heat Transfer Area 54,500 sq. ft.

SG Model 54 F Number of Tubes 3592 I

Date of Report I

I Exams I

I I

TSP TY pe Quatrefoil Tube Diameter 0.875" ROW 1 U-I

+ Point RC I

Various I

Hot Leg TTS RC Special Interest RC Indications of Imperfections Detected I

NDE I Row I Column / Indication I Location I Active I Measured TSP Material Type 405 SS Tube Material In 690TT 719 1

71 9

+ Point RC TSH +/- 3 Number of TSPs 7

Tube Pitch 1.225" 0

N/ A 35 I

2006 lnspection Tube Plugging Baffle Material Type 405 SS Tube Thickness 0.050

N/A SG B

Plugging Attributions AVB Material Type 405 SS Expansion Full Hydraulic SG B

PluggingIRepair Record Code NI A ReasonIMechanism N/A SG A

B C

Tubes Plugged N/A Total Tubes Plugged Row N/A NONE NONE Tubes Plugged 0

0 2

Column N/A YesINo No Tubes Repaired (Not Plugged) 0 0

0 Wall Penetration Nl A ReasonIMechanism NONE Repair Method N/A Percent Plugged 0

0 0.06 Percent Repaired (Not Plugged) 0 0

0 Percent Plugged or Repaired 0.00 0.00 0.06

Serial No. 07-0089 Docket Nos. 50-3381339 Page 2 of 12 TUBE INTEGRITY ASSESSMENT

SUMMARY

1.0 Evaluation Summary Overall condition assessments have been documented in the North Anna Steam Generator Monitoring and Inspection Plan (Reference 1) and are consistent with the requirements of the NEI 97-06 Guideline.

A Pre-Outage Assessment (POA),

Reference 2, was performed to identify any relevant condition to be considered for the North Anna Unit 1 steam generators (SG) that was not included in the referenced program document. The assessment also identified the appropriate eddy current inspection scope, probes to be utilized during the inspection, and the appropriate detection and sizing information for degradation mechanisms that may be detected during the inspection.

As required by NEI 97-06, Performance Criteria are established in three areas:

+ Structural lntegrity - Margin of 3.0 against burst under normal steady state power operation and a margin of 1.4 against burst under the most limiting design basis accident.

+ Operational Leakage - RCS operational primary-to-secondary leakage through one steam generator shall not exceed 150 gpd.

+ Accident Induced Leakage - Leakage shall not exceed 1 gpm per steam generator during Main Steam Line Break (MSLB).

The inspections performed were consistent with the Program Plan and Revision 6 of the EPRl Steam Generator Examination Guidelines, including the Interim Guidance issued by EPRl (References 3 & 4). Specific Eddy Current Analysis Guidelines (Reference 5) with inspection vendor eddy current data analysis and data acquisition technique sheets were used for system calibration and data analysis.

A condition monitoring evaluation of the SG tube bundles was performed to verify that the condition of the tubes, as reflected in the inspection results, is in compliance with plant licensing basis and meets the required performance criteria. The results of the condition monitoring evaluation were used as a basis for the operational assessment.

The operational assessment demonstrated that the anticipated performance of the SGs would not exceed the performance criteria against leakage and tube burst during the ensuing operating period.

This report summarizes the condition monitoring and operational assessment of the inspection results from the North Anna Unit 1 "6" SG. It conforms to the March 2000 EPRl Steam Generator lntegrity Assessment Guidelines, Revision 1 (Reference 6) and the requirements of NEI 97-06.

Serial No. 07-0089 Docket Nos. 50-3381339 Page3of 12 Prior to this outage there were no existing active degradation mechanisms affecting the North Anna Unit 1 SG tubes. The relevant potential degradation mechanisms identified in the POA are: Tube wear at anti-vibration bar (AVB) locations, pitting, tube wear at support plates, and tube wear caused by foreign objects.

No defective or degraded tubes were identified during this inspection.

Hence, acceptable tube integrity at the end of the current operating Cycle 18, (Replacement Cycle 9), has been demonstrated.

The absence of active tube degradation mechanisms in "B" SG and the absence of anomalous secondary side material conditions which could impact future tube integrity provide reasonable assurance that required margins of safety will be maintained through the next planned operating interval. The results of the inspection of the "B" SG confirm that the operational assessments for Unit I

" A and "C" SGs remain valid.

2.0 Condition Monitoring (CM) Assessment Summary 2.1 lnspection Results The inspections were conducted per the requirements of the EPRl PWR SG examination Guidelines, Revision 6 (Ref. 7).

2.1.I Eddy Current lnspection Results Summary No material degradation of any type was observed during this inspection on the "B" SG.

This continues to demonstrate excellent performance of the replacement generators with respect to mechanical and corrosion-induced degradation. In particular, North Anna Unit 1 has operated approximately 11.9 EFPY without any observed AVB wear, a mechanism typically observed in F-type SGs. The " 6 SG had operated for 65 EFPM since its last tube inspection.

Although not judged to be susceptible to degradation at this point in SG life, locations within the tubesheet with "over-expansions" at surface imperfections were identified with a bobbin automated analysis program. Seven (7) of these were randomly tested in the hot leg with + Point with no degradation noted. The highest reported bobbin voltage was -58 Volts.

+Point resolutions were performed on a small number of bobbin indications and sample +Point exams were performed on manufacturing dent locations.

In total, 35 of these follow-up and special interest exams were completed and no material degradation was observed.

2.1.2 Visual lnspection Results Summary The visual examinations performed during this refueling outage revealed no evidence of material degradation and no foreign objects during the upper bundle inspection. No sludge lancing was performed during this outage. No eddy current indications of foreign objects were observed during the inspection. Consequently, no top-of-tubesheet visual inspections were required.

Serial No. 07-0089 Docket Nos. 50-3381339 Page 4 of 12 Overall, no degradation of secondary side internals was identified during this outage.

Consequently, it is very unlikely that such degradation could initiate and advance to an extent that would impact tube integrity prior to the next examination.

2.1.3 Condition Monitoring Conclusion The CM is based on current inspection results. As discussed in Section 2.1.1, no indications of tube degradation were identified. In the absence of any tube degradation, it is concluded that the structural integrity performance criterion was not exceeded during the operating interval preceding this outage.

In addition, the absence of degradation exceeding this criterion provides reasonable assurance that the accident leakage performance criteria would not have been exceeded during a design basis accident. No primary-to-secondary SG tube leakage (i.e., leakage was < I gpd) was reported during the previous operating period. Therefore, the operational leakage performance criterion was also not exceeded during the operating period preceding this inspection.

3.0 Operational Assessment (OA)

The OA must demonstrate that the structural integrity performance criteria will not be exceeded prior to the next scheduled examination in any of the three North Anna Unit 1 SGs.

Although no degradation was identified during the current inspection of "B" SG or during previous inspections of the other two Unit 1 SGs, this OA will discuss the potential for foreign object wear and will evaluate the future growth of hypothetical, undetected AVB wear. Under the current chemistry control program, the initiation and development of corrosion degradation mechanisms in the North Anna Unit 1 SG tubing is not considered to be a credible event in the near-term. Future SG examinations will be conducted well in advance of the time at which degradation of this type is projected to occur.

3.1 Foreign Object Wear Tube wear resulting from tube interaction with foreign objects is by its nature random, isolated, and difficult to predict. As discussed, the SG work activities performed during this refueling outage included extensive secondary side inspections. Steam drum and upper tube bundle visual examinations were performed in SG "B". No foreign objects were identified. Extensive ECT examinations in SG "B" revealed no evidence of foreign objects or foreign object wear. As such, there is reasonable assurance that foreign objects will not cause the structural integrity performance criteria to be exceeded prior to the next tube examination in each steam generator. Because no wear exceeding the structural criteria is expected, it is reasonable to conclude that the operational leakage and accident leakage performance criteria will not be exceeded by foreign object wear.

Serial No. 07-0089 Docket Nos. 50-3381339 Page5of 12 3.2 AVB Wear Even though no AVB wear indications have been identified in the North Anna SGs to date, it could reasonably be expected to develop eventually. Industry experiences to date, on similar design steam generators have reported AVB wear. AVB wear, detected and sized with the bobbin probe, typically begins to be reported at a depth of 10% through wall (TW). Typical growth rates of 2% TW to 5% TW per fuel cycle have been experienced at Surry. The performance of the North Anna steam generators is expected to be at least equal that of Surry since close-gap AVB tolerance techniques were used during manufacture.

The following evaluation was performed to evaluate a potential undetected 10% TW AVB wear condition relative to tube integrity requirements and estimates a bounding operating time. The growth rate utilized is based upon the worst case Surry AVB growth since steam generator replacement. The upper 95%/50% AVB growth rate of 7.23% TW per operating cycle is used as the growth rate for calculating the time to reach the appropriate structural limit. Based on ETSS 96004.1 sizing performance parameters as provided in Ref. 5, the time is calculated as follows:

Best Estimate %TW:

y = 0.97 (1 O%TW) + 3.49 = 13.2% TW Total Random Uncertainty @ 90150:

10.7% TW Bounding Structural Limit For AVB Wear (Ref. 5)

Time l nterval to Reach Structural Limit (cycles):

Limit = 13.2% TW + 10.7% TW + [(7.23% TW/cycle) x (Interval)] = 61 % TW Interval = 5.1 cycles This projected time interval required for hypothetical North Anna Unit 1 AVB wear to grow to a depth equaling the most conservative structural limit (uniform thinning), far exceeds the planned maximum operating interval for any of the North Anna Unit 1 SGs.

Therefore, AVB wear does not represent a realistic concern from a tube structural integrity point of view during the next planned operating interval for SG "B", or during the current operating intervals for SGs "A" and "C". As such, no accident leakage or operational leakage concerns exist relative to AVB wear for any of the SGs.

3.3 Conclusions The North Anna Unit 1 SGs, as indicated by the results of the current condition monitoring evaluation of SG "B" and past assessments pertaining to the other steam generators, continue to satisfy the safety margin requirements with respect to structural and leakage integrity. No degradation exceeding the performance criteria was identified

Serial No. 07-0089 Docket Nos. 50-3381339 Page 6 of 12 during this or any previous North Anna Unit 1 SG inspection. This evaluation has demonstrated that there is reasonable assurance that operation of the North Anna SGs for the planned operating interval is acceptable and will not cause the tube integrity performance criteria to be exceeded.

4.0 References

1. Dominion, "North Anna Steam Generator Monitoring and Inspection Plan,"

NAPS-SGMIP-001, Rev. 0, March 2004.

2. Dominion, 'WG Monitoring Program Pre-Outage Assessment, North Anna Unit 1 - Spring 2006," February 2006.

3. EPRI, "lnterim Guidance

Letter, Rev.

6 Examination Guideline Implementation, Tube Noise Criteria, L. Womack, April 30 2003.

4. EPRI, "lnterim Guidance on Revised Structural lntegrity Performance Criterion," January 17, 2005.

5. North Anna Site Specific Eddy Current Analysis Guidelines (NAPS-SGPMS-002), Rev. 9.

6. EPRI, "SG Integrity Assessment Guidelines," TR-107621 -R1, Rev. 1, March 2000.

7. EPRI, "SG PWR Steam Generator Examination Guidelines," Revision 6, October 2002.

Serial No. 07-0089 Docket Nos. 50-3381339 Page 7 of 12 THREE LETTER CODES Locations Codes TEC - Tube End Cold TEH - Tube End Hot TSH-Tube Sheet Hot TSP - Tube Support Plate TTS - Top of Tube Sheet General Codes ANF - ANOMALY NOT FOUND - lndicates that a previously reported anomaly cannot be found within.50" of the location where the anomaly was previously called.

ANR - ANOMALY NOT REPORTABLE - lndicates that a previously reported anomaly does not meet the present reporting criteria.

AVB - Anti Vibrational Bar BDA - BAD DATA (retest) - lndicates that the data for the specified tube is not acceptable for analysis due to poor signal quality. The tube will be re-tested to the required extent.

INF - INDICATION NOT FOUND - lndicates that a previously reported INDICATION has not been found in the data being analyzed or that a tubelsignal is being re-tested for positive identification (PID) and no signal is present in the retest data.

INR - INDICATION NOT REPORTABLE - Indication called in previous inspections that are still detectable but fall below current reporting criteria.

NDD - NO DETECTABLE DISCONTINUITY - The recorded data has no signal responses meeting the criteria established in the Site Specific Analysis Guidelines for degradation, damage precursors or anomalies.

NDF - No Degradation Found - Used to address a special interest location where no signal meeting the RC criteria (MBM, DNT, etc) is present. Location of rotating coil data verses the bobbin coil shall be verified to ensure correct location was inspected.

NT - NO TEST (re-test) - lndicates that the tube ROW, COLUMN was encoded on the tape; however, no inspection data was recorded for analysis.

Serial No. 07-0089 Docket Nos. 50-3381339 Page 8 of 12 OBS - OBSTRUCTED - Blockage of a tube that prevents passage of a defined minimum size probe through the tube.

PID - POSITIVE IDENTIFICATION - Verification of a signal at the same reported ROW/COL and at the same reported tube location.

PLG - PLUG - lndicates that the tube at the specified location has been plugged.

PVN - PERMEABILITY VARIATION - Condition where the test coil impedance changes due to a change in the tubing materials inherent tendency to conduct magnetic flux lines.

PLP - POSSIBLE LOOSE PART - lndicates the possible presence of a loose part in the generator.

RST - RESTRICTED - Blockage of a tube that prevents passage of a probe beyond a specified location within the tube.

TIU - TUBE I.D. UNCERTAIN (re-test) - lndicates that the ROW and/or COL identifier for a given tube is in doubt.

LAR - Lead Analysts Review - Condition not directly covered by the guidelines, ETSS, or other documentation that the data analyst feels should be brought to the attention of the resolution and/or job lead analyst. Diagnostic testing or PID verifications that the analyst believes are not the correct tube number and/or the correct tube location shall be identified as LAR.

Bobbin Codes BLG - BULGE - An area along the tube where the diameter of the tube has been abruptly deformed in an outward direction as compared to the nominal tube diameter.

CUD - COPPER DEPOSIT - The presence of copper deposits on the outside of the tube.

DNT - DENT - An area along the tube where the diameter of the tube has been abruptly reduced compared to the nominal tube diameter.

LGV - LOCAL GEOMETRIC VARIATION - A local reduction in tube diameter usually associated with a localized change in conductivity of the tube. LGV signals are caused by dings introduced during manufacturing/installation process and do not represent a discernible wall loss. The signals must be verified by history review to be called with bobbin (See rotating probe DNG code).

MBM - MANUFACTURING BURNISH MARK - A tubing condition where localized tubing imperfections were removed by buffing and are detectable due to the effects of

Serial No. 07-0089 Docket Nos. 50-3381339 Page 9 of 12 cold working and minor localized wall thinning. The signal must be verified by history review to be called with a bobbin probe.

MMB - MULTIPLE MANUFACTURING BUFF MARK - Multiple MBM signals in close proximity over a length of tube. The signals must be verified by history review to be called with a bobbin probe.

NQI - NON-QUANTIFIABLE INDICATION - A bobbin signal requiring rotating coil examination for disposition.

NQN - NON-QUANTIFIABLE NONDEGRADED - A bobbin signal which was formally classified as NQI but has been determined to be anomalous or of a type which does not represent degradation.

PDS - POSTIVE DRIFT SIGNAL - Long (several inches to several feet) drift signals evident on absolute channels caused by variations in tube concentricity associated with the pilgring process. The signals may be located at random elevations and are generally only in one leg of the tube.

PTE - PARTIAL TUBE EXPANSION - Code used when only some portion of parent tube has been expanded into the carbon steel tube sheet. PTE shall be reported at the axial location(s)where nominal tube expansion ends and the partial begins, from the 400/100-mix channel. Bobbin and/or rotating coil data shall be carefully analyzed in the non-expanded crevice region.

NTE - NO TUBE EXPANSION - Code used when the parent tube has NOT been expanded into the carbon steel tube sheet from the top of the tube sheet to approximately 2.5" from the tube end. NTE shall be reported from the 400/100-mix channel, location as TSH +0.00. Bobbin and/or rotating coil data shall be carefully analyzed in the non-expanded crevice region.

Rotatinq Probe Codes DNG - DING - A localized inward displacement of the tube caused by a mechanical impact on the OD surface.

MAA - MULTIPLE AXIAL ANOMALY - Multiple axially oriented signals located at the top of the tube sheet that the rotating coil data shows to result from an anomalous condition in the tube.

MCA - MULTIPLE CIRCUMFERENTIALLY ORIENTED ANOMALY - Multiple circumferentially oriented signals located at the top of the tube sheet that the rotating coil data shows to result from an anomalous condition in the tube.

MA1 - MULTIPLE AXIAL INDICATION - Multiple axially oriented signals that the rotating coil data shows to result from flaws in the tube.

Serial No. 07-0089 Docket Nos. 50-3381339 Page 10 of 12 MBM - MANUFACTURING BURNISH MARK - A tubing condition where localized tubing imperfections were removed by buffing and are detectable due to the effects of cold working and minor localized wall thinning.

MCI - MULTIPLE CIRCUMFERENTIALLY ORIENTED INDICATION - Multiple circumferentially oriented signals reported from rotating probe data that the rotating coil data shows to result from flaws in the tube.

MMB - MULTIPLE MANUFACTURING BUFF MARK - Multiple MBM signals in close proximity over a length of tube.

NQN - NON-QUANTIFIABLE NONDEGRADED - A bobbin NQI signal which is determined to be anomalous or not to represent degradation.

PIT - PIT - Localized attack on tubing resulting from non-uniform corrosion rates caused by the formation of local corrosion cells. At Surry, the condition produces small volumetric indications with approximately the same axial and circumferential extent.

SAA - SINGLE AXIAL ANOMALY - A single axially oriented signal located at the top of the tube sheet that the rotating coil data shows to result from an anomalous condition in the tube.

SCA - SINGLE CIRCUMFERENTIALLY ORIENTED ANOMALY - A single circumferentially oriented signal located at the top of the tube sheet that the rotating coil data shows to result from an anomalous condition in the tube.

SAI - SINGLE AXIAL INDICATION - A single axially oriented signal that the rotating coil data shows to result from a flaw in the tube.

SCI - SINGLE CIRCUMFERENTIALLY ORIENTED INDICATION - A single circumferentially oriented signal that the rotating coil data shows to result from a flaw in the tube.

VOL - VOLUMETRIC - Indications of volumetric wall loss indicative of general localized thinning, wear or impingement.

SVVMVI - SINGLE VOLUMETRIC INDICATIONIMULTIPLE VOLUMETRIC INDICATIONS - lndications of volumetric wall loss indicative of general local inter-granular attack (IGA or IGNSCC).

Serial No. 07-0089 Docket Nos. 50-3381339 Page11 of 12

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Serial No. 07-0089 Docket Nos. 50-338/339 Page 12of12 Serial No.16-127 Request for Withholding Proprietary Information Page 2 of2