L-05-114, Eleventh Refueling Steam Generator Condition Monitoring Report

Eleventh Refueling Steam Generator Condition Monitoring Report

ML051940281
Person / Time
Site:	Beaver Valley
Issue date:	07/05/2005
From:	Pearce L FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-05-114 NEI 97-06
Download: ML051940281 (5)

Text

r FENOC First Energy Nuclear Operating Company Beaver Valley Power Station PO. Box 4 Shippingport, PA 15077-0004 L. Wlliam Pearce Vice President 724-682-5234 Fax: 724-643-8069 July 5, 2005 L-05-1 14 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001

Subject:

Beaver Valley Power Station, Unit No. 2 Docket No. 50-412, License No. NPF-73 Eleventh Refueling Steam Generator Condition Monitoring Report In accordance with Section 3.1.7 of Nuclear Energy Institute Document, NEI 97-06, on Steam Generator Program Guidelines, enclosed is a report which provides a synopsis of the Beaver Valley Power Station (BVPS) Unit No. 2 eleventh refueling (2R1 1) steam generator condition monitoring report. This report is being submitted since the steam generator inspection results had greater than 1% of the inspected tubes in any steam generator exceeding the repair criteria.

There are no new regulatory commitments contained in this submittal. If there are any questions concerning this matter, please contact Mr. Larry R. Freeland, Manager, Regulatory Compliance at 724-682-4284.

Sincerely, Pea Uc

. illiam Pearce Attachment c:

Mr. T. G. Colburn, NRR Senior Project Manager Mr. P. C. Cataldo, NRC Sr. Resident Inspector Mr. S. J. Collins, NRC Region I Administrator Mr. D. A. Allard, Director BRP/DEP Mr. L. E. Ryan (BRP/DEP)

0

ATTACHMENT Summary of the BVPS Unit No. 2 Eleventh Refueling (2R11)

Steam Generator Condition Monitoring Report The steam generator inspection scope for 2R1 1 met or exceeded the applicable BVPS Unit No. 2 Technical Specifications, the EPRI Pressurized Water Reactor (PWR) Examination Guidelines, and was based on the 2R1 1 degradation assessment:

Initial Inspection Scope

1) 100% full length 0.720" bobbin coil examination (Rows 5 and up) and the hot and cold leg straight sections of Rows 1 through Row 4

2) 100% 0.700" bobbin examination of the U-bend region of Rows 3 and 4

3) 100% +Point inspection of tube support plate (TSP) intersections with distorted signal indications (DSI)

4) 100% +Point inspection of TSP mix residual signals > 2 volts plus a 20% +Point inspection of TSP mix residual signals > 1.5 volts but < 2 volts

5) 100% +Point inspection of TSP mix residual signals with a phase of < 550 and > 1.25 volts

6) 100% +Point inspection of dented hot leg TSP intersections Ž 5 volts

7) 100% +Point inspection of dents > 2 volts but < 5 volts at the 01 H, 02H, 03H, and 04H TSP intersections plus a 20% +Point inspection of dents > 2 volts but < 5 volts at the 05H TSP

8) 100% +Point inspection of the hot leg top-of-tubesheet (TTS) (+6.0"/-3.0")

9) 100% +Point inspection of the U-bend region in Rows 1 and 2

10) 100% +Point inspection of freespan dings > 5 volts

11) 100% +Point inspection of freespan signals that could not be resolved as Manufacturing Burnish Marks (MBM's)

12) 100% +Point inspection of dents at Anti Vibration Bar (AVB) intersections (+/- 1 inch from AVB center)

13) 100% +Point inspection of bulges within the hot and cold leg tubesheet reported above the tubesheet neutral axis and cold leg tubesheet expansions above TTS

14) 20% +Point inspection of the U-bend region in Rows 3 through 8

15) 20% +Point inspection of AVB wear indications reported from bobbin

16)

Tube plug visual inspection

17)

Steam Generator (SG) secondary side sludge lancing and Foreign Object Search & Retrieval (FOSAR)

Based on the results of the initial inspection scope, no expansion in scope was required during 2R1 1.

Degradation Mechanisms Observed During 2R11 Indications suggestive of the following degradation mechanisms were observed during the 2R1 1 inspection:

• Axial Outside Diameter Stress Corrosion Cracking (ODSCC) at non-dented TSP intersections

• Axial ODSCC in the hot leg sludge pile freespan region and expansion transition region

• Circumferential ODSCC at the hot leg TTS expansion transition

• Circumferential Primary Water Stress Corrosion Cracking (PWSCC) at the hot leg TTS expansion transition

• Wear at AVB sites

• Volumetric degradation within the expanded tubesheet region

Attachment to Letter L-05-114 Page 2 A condition monitoring evaluation of 2R1 I indications was performed by comparing the predicted burst pressure with allowance for Non-Destructive Examination (NDE) uncertainty and material properties, evaluated at probability and confidence levels consistent with the EPRI Tube Integrity Guidelines against three times normal operating pressure differential (4375 psi).

Axial ODSCC at Hot Leg Top of Tubesheet Region A total of 7 tubes were reported with axial ODSCC indications located in the historic sludge pile or the expansion transition region.

The 2R1 1 axial ODSCC +Point length and amplitude distributions were bounded by or consistent with the 2R09 and 2R10 distributions. The limiting indication with regard to burst pressure was reported in tube R21 C22 in 2RCS-SG21 B ('B' Steam Generator) with a length from profiling of 0.27 inch. The length versus depth profile is based on a regression of the +Point amplitude and maximum depth information obtained from the industry pulled tube database. This produced the largest and therefore limiting depth profile. The burst pressure of the indication at a 95% probability, 50% confidence level, is 7206 psi. This is conservative when compared to the guidance provided in the EPRI Tube Integrity Assessment Guidelines and is well above the performance criteria.

The peak +Point amplitude of 0.18 volt found in this region is below the 0.50 volt in situ proof testing threshold and is well below the in situ leakage testing threshold of 1.0 volt for expansion transitions or freespan locations. The indication was located slightly above the top of tubesheet in the historic sludge pile region.

Circumferential ODSCC at the Hot Leg Top of Tubesheet Expansion Transition A total of 44 tubes were reported with circumferential ODSCC indications in the expansion transition.

The peak +Point amplitude was 0.31 volt, while the maximum reported flaw arc angle was 1820. These values are slightly reduced compared to the observed 2R10 outage circumferential ODSCC flaw statistics of 0.43 volt and 2090 arc. As the 2R1 I circumferential ODSCC flaw parameters of +Point amplitude and arc length are bounded by the 2R10 values, it can be judged that the growth function for Cycle 11 is consistent with Cycle 10.

The peak +Point amplitude of 0.31 volt found in this region is below the 0.50 volt in situ proof testing threshold and is well below the in situ leakage testing threshold of 1.31 volts.

Tube Support Plate (TSP) Axial ODSCC A total of 622 TSP intersections with distorted signals (DSI's) were reported with amplitudes ranging from 0.11 to 2.45 volts, with one signal > 2 volts. All DSI signals were inspected with the +Point probe. Two of these 622 signals were confirmed by +Point as axial ODSCC. The DSI amplitudes of these two confirmed signals were < 1 volt. The low confirmation rate of DSI signals suggests that many of the reported DSI signals may be false reports related to deposits within the TSP crevice.

The average voltage change for 2R11 DSI signals was (-) 0.03 volt per Effective Full Power Year (EFPY) suggesting there was no change on average for the DSI population. The average DSI voltage growth for Cycle 10 was 0.01 volt per EFPY. This growth rate data suggest an essentially stagnant growth condition.

The flaw lengths from +Point data analysis for the confirmed DSI signals were 0.29 and 0.32 inch with a peak +Point amplitude of 0.17 volt.

Attachment to Letter L-05-114 Page 3 Circumferential PWSCC at the Hot Leg Top of Tubesheet Expansion Transition One tube was reported to contain a circumferential PWSCC indication at the top of tubesheet expansion transition. The peak +Point amplitude was 1.21 volts, with an arc length of 420 and a maximum depth from phase analysis of 33% through-wall (TW). A maximum depth of 59% TW can be reported for this indication when using a regression of +Point amplitude and maximum depth information obtained from the industry pulled tube database and laboratory produced flaws in doped steam.

This indication was profiled using the guidance of EPRI Examination Technique Specification Sheet (ETSS) 20510.1. The predicted burst pressure based on the depth profile at a 95% probability, 50%

confidence level, is 7528 psi, well above the performance criteria. A short, shallow circumferential ODSCC indication was also reported on this tube at the expansion transition. The indications were reported at slightly differing elevations with a clear null between the two signals indicating that the signals do not interact with each other. The presence of the ODSCC indication will not affect the burst capability of the more limiting PWSCC indication.

Tube Wear at Anti-Vibration Bar (AVB) Intersections The deepest AVB wear scar was reported at 34% TW. A total of 94 AVB wear sites are reported for all three SGs combined. Average growth of AVB wear sites for Cycle 11 was 0% TW per EFPY.

Bulges and Over-Expansions The 2R1 1 inspection program included +Point inspection of all potential bulge or over-expansion sites at the top of tubesheet (both hot and cold leg) as well as all bulge locations above the tubesheet neutral axis. No degradation was reported. The lack of degradation at these sites may be related to the application of pre-operational shot peening through the tubesheet thickness on both hot and cold leg tubes. The absence of small radius U-bend PWSCC may be related to the application of in situ U-bend heat treatment prior to operation.

Degradation Mechanisms Not Observed During the 2R11 Inspection The following degradation mechanisms were addressed by the initial inspection plan but were not observed during 2R1 1:

PWSCC at small radius U-bends PWSCC at large radius U-bends PWSCC at dented TSP intersections Axial PWSCC in the expanded tubesheet region Ding ODSCC Freespan (outside of historic sludge pile) ODSCC ODSCC at dented TSP intersections Sludge Lancing and FOSAR Sludge lancing is performed each outage to remove impurities and sludge build-up on the secondary face of the tubesheet. A total of 118.5 lbs of sludge was removed from the three SG's during 2R1. This aligns well with the average amount of sludge removed in previous outages.

FOSAR is performed each outage to visually interrogate the secondary face of the tubesheet for foreign material that may accumulate over the cycle as well as providing a means to assess the effectiveness of the sludge lancing.

Attachment to Letter L-05-114 Page 4 Conclusion Observed degradation mechanisms for the 2R1 1 outage were evaluated using methods consistent with or conservative to the EPRI Tube Integrity Assessment Guideline and EPRI In Situ Pressure Testing Guideline. The results of this evaluation show that all observed degradation satisfied the NEI 97-06 structural and leakage integrity performance criteria. The stress corrosion cracking mechanisms observed at 2R1 1 were bounded by or consistent with the flaw parameter distributions for the 2R08, 2R09, and 2R10 outages suggesting that the ODSCC growth function is consistent with, or reduced compared to previous cycles. The Cycle 11 effective length was 527.7 EFPD, which is bounded by the Cycle 10 operating period of 547.7 EFPD. The difference in operating cycle lengths is judged insignificant with regard to growth or initiation of indication distributions.

No mechanism was postulated to represent a leakage potential at end-of-cycle (EOC) 11. The indication distributions for the last several outages are essentially constant indicating that the ODSCC growth function has not changed over this period. Thus, the ODSCC distribution for 2R12 is expected to be similar to that observed for 2R1 1.

The EOC-1 2 operational assessment methodology to be applied is judged conservative compared to the observed indications during 2R1 1 and the projection of 2R1 0 indications at EOC-1 1. The projected maximum axial ODSCC amplitude of 0.43 volt and length of 0.38 inch for 2R1 1 bounds the maximum observed amplitude of 0.18 volt and maximum reported length of 0.27 inch.

The predicted circumferential ODSCC +Point amplitude and arc lengths were bounded by the observed 2R1 1 flaw parameters.

EOC-1 1 projected AVB wear depth was also bounded by the prediction.

No in situ testing was required during 2R1 1.

Therefore, it can be concluded that the prediction methodology to be applied for the EOC-12 operational assessment is conservative compared to the observed flaw parameters for EOC-1 1 and the associated predictions based on 2R10 flaw parameters.

Tubes Plugged During 2R11 The following table presents a listing of tubes plugged during 2R1 1 according to the reported degradation mechanism. In some cases one tube may contain more than one repair mechanism.

2R11 Tube RepairSummary Degradation Mechanism SG A SG B SG C Total Axial ODSCC at TTS detected by +Point 1

5 1

7 Confirmed DSI signal at TSP intersections 0

2 0

2 Circumferential ODSCC at TTS 13 26 5

44 Circumferential PWSCC at TTS 1

0 0

1 Volumetric Degradation (Not associated with a loose part) 0 1 (2) 0 1

Preventive (Large permeability signal) 0 0

1 1

Total Repairable Signals 15 34 7

56 Total Number Plugged Tubes 14 ° 34 7

55 (1): One tube contained a circ ODSCC and circ PWSCC indication at slightly different elevations at the TTS expansion transition. The signals did not intersect, a distinct null was observed between signals.

(2): Located below bottom of roll transition, judged to be an artifact of SG assembly or tube production.