ML041420128

Steam Generator Outage Summary Report for End of Cycle 14 Refueling Outage

ML041420128
Person / Time
Site:	Catawba
Issue date:	05/04/2004
From:	Jamil D Duke Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MC1703
Download: ML041420128 (11)

Text

• A Duke D.M. JAMIL afPower Vice President A Duke Energy Company Duke Power Catawba Nuclear Station 4800 Concord Rd. / CN01 VP York, SC 29745-9635 803 831 4251 803 831 3221 fax May 4, 2004 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Corporation Catawba Nuclear Station, Unit 1 Docket Number 50-413 Steam Generator Outage Summary Report for End of Cycle 14 Refueling Outage Reply to Request for Additional Information (TAC Number MC1703)

Reference:

Letter from NRC to Duke Energy Corporation, dated April 19, 2004 Please find attached Catawba's reply to the reference Request for Additional Information. The format of the reply is to restate the NRC question, followed by Catawba's response.

There are no regulatory commitments contained in this letter or its attachment.

If you have any questions concerning this material, please call L.J. Rudy at (803) 831-3084.

Very truly yours, Dhiaa M. Jamil LJR/s Attachment www. duke-energy, corn At

Document Control Desk Page 2 May 4, 2004 xc (with attachment):

L.A. Reyes, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, GA 30303 E.F. Guthrie, Senior Resident Inspector U.S. Nuclear Regulatory Commission Catawba Nuclear Station S.E. Peters, Project Manager (addressee only)

U.S. Nuclear Regulatory Commission Mail Stop 0-8 G9 Washington, D.C. 20555-0001

REQUEST FOR ADDITIONAL INFORMATION DUKE POWER COMPANY CATAWBA NUCLEAR STATION, UNIT 1 DOCKET NO. 50-413 The Nuclear Regulatory Commission (NRC) staff has reviewed the licensee's submittal dated December 23, 2003, forwarding the End of Core (EOC) 14 Steam Generator Tube Inspection Report for Catawba Nuclear Station (Catawba), Unit 1. The NRC staff has identified the following information that is needed to enable the continuation of its review.

1. The steam generators at Catawba, Unit 1, were replaced in 1996 with Babcock and Wilcox International CFR 80 steam generators. In several locations in your reports, you reference tube support structures (e.g., fan bar 4) and tube locations (e.g., Row 14 Column 55). In order for the NRC staff to better understand the location of the indications, please provide (1) a sketch of the Unit 1 steam generators which depicts the tube support naming conventions and (2) a tubesheet map which depict the rows and columns of the tubes. In addition, please provide the following general design information: tube manufacturer, tube material, tube outside diameter, tube wall thickness, tube support (including fan bar/anti-vibration bar) material and configuration, tube support (including fan bar) thickness, tube pitch and orientation (e.g., 1.1-inch triangular pitch), expansion method, and any other noteworthy design characteristics from a steam generator tube integrity standpoint (e.g., full length stress relief of the row 1 through row 10 tubes). Furthermore, discuss whether measurements from a tube support are from the middle of the support or the edge of the support. For example, does fan bar 5 minus 0.9 inches specify an indication 0.9 inches from the bottom edge of the fan bar?

Duke response:

Steam generators are Babcock & Wilcox International (BWI) CFR 80 vertical U-bend type, containing 6,633 tubes each. Tubing material is drawn thermally treated CrFeNi alloy (Inconel 690) with 0.688" OD and 0.040" nominal wall thickness, produced by Sumitomo. The tubes are hydraulically expanded the entire length 4

of the tubesheet in both the inlet and outlet. The tubesheet is 27.1 inches thick with the clad. The equilateral triangular tube pitch is 0.930". The tube support structures at Catawba Unit 1 are lattice grids made of 410 Stainless Steel. The lattice grid is made of a series of high bars (approximately three inches thick) oriented at thirty degrees and one hundred fifty degrees to the tube free lane and located every sixth pitch to accommodate the steam generator loading conditions. Low bars (approximately 1 inch in width) are located at every pitch between the high bars. All of the lattice grids are the same except the lowest which incorporates a differential resistance lattice grid. The difference is that the low bars on the periphery are replaced by medium bars (approximately 2.5 inches in width). There are four contact points on each tube. The connector bars (CB) are constructed of 410 Stainless Steel. The U-bend fan bars (FB) are constructed of 410 Stainless Steel. The width of the bars is 1.25 inches. The J-tabs are 316 Stainless Steel. Row 27 and less were stressed relieved full length. Each fan bar assembly is offset along the length of the tube, which means that one fan bar is touching one side of the tube, but a different axial location on the other side of the tube. The inner row tubes are offset so as to make the inner radius larger.

They are called "crossover" tubes. is a sketch of the Unit 1 steam generators which depicts the tube support naming conventions and Attachment 2 is a tubesheet map which depicts the rows and columns of the tubes. is the rotating coil characterization codes. is the bobbin coil characterization codes.

Positive direction is physically upwards in the steam generator with the positive direction stopping at the apex of the U-bend.

Measurements should be made using the nearest available landmark.

All measurements should be referenced from the center of a landmark. Measurements may be made in a positive or negative direction using the nearest available landmark.

2. For the EOC 14 inspections, please clarify the scope and extent of the inspections. For example, please discuss what probes were used during the inspection, how many tubes were inspected, and what portions of the tubes were inspected with these probes (e.g., 100 percent full-length inspection with a bobbin probe, rotating-probe inspection of the hot-leg expansion transition region (+/- 3 inches) for 100 percent of the inservice tubes, etc.).

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Duke response:

In the A and D steam generators, 100% of the tubes were inspected 100% full length with a bobbin probe. In the B and C steam generators, 100% of the tubes were inspected with the bobbin probe from the tube end through the second lattice grid. In addition, 20% of the tubes were inspected with the rotating coil probe from +2 inches to -8 inches from the top of the tubesheet.

3. Please clarify the results of your inspection. For example:

a. For the volumetric indications reported, please discuss the source and significance of these indications.

Duke response:

The volumetric indications reported are either foreign object wear or manufacturing burnish marks. The majority of VOLs reported are manufacturing burnish marks.

Manufacturing burnish marks are benign in that they just interfere with the detection of other flaws. The growth rate of loose part wear is unpredictable and can therefore be significant.

b. Please clarify the difference between an "NQI" and an "NQS" indication.

Duke response:

NQI (non quantifiable indication) is a bobbin characterization code that requires the indication in the tube to be further evaluated with another technique. In this outage, the rotating coil probe was used. NQS (non quantifiable signal) is a rotating coil probe characterization code. The signal was outside the degradation phase plane and NQS was used to track the signal.

c. Please clarify the potential and actual degradation mechanisms observed in your steam generators. For example, several wear indications have been reported.

Please briefly discuss the cause of these indications and the population of tubes susceptible to these mechanisms. In addition, several tubes were inspected/classified as "proximity" tubes in a previous 6

inspection. Please describe this categorization and the tubes potentially affected by this issue.

Duke response:

The actual degradation is support structure wear (fan bar and lattice grid) and foreign object wear. Wear is caused by the impacting of one surface against another. In the case of fan bar wear, the clearances between the fan bar and the tube are larger than design due to the stackup of tolerances. In the fan bar and lattice wear cases, the populations are small. In the case of foreign object wear, the periphery tubes at the tubesheet are most impacted.

The fan bar assembly is free floating and therefore rests on the tubes for support. During the installation of the fan bar assembly, it was observed that the J-tabs that actually rest on the most outboard tube could be pushed in too far, causing two tubes in the same column to be closer than their ideal design spacing. The tubes are therefore in

<<proximity". Five sets of tubes have been identified as being in proximity and they were inspected with the rotating coil probe for degradation. No degradation was observed.

4. Seven tubes were plugged and stabilized in steam generator C as a result of a loose part that could not be removed.

Please clarify the source and nature of this part. In addition, briefly summarize the corrective actions taken and your basis for the corrective actions (e.g., all steam generators were inspected, the part was surrounded by plugged and stabilized tubes and is not expected to move based on analysis, etc).

Duke responses The indications were located at approximately 1 inch above the tubesheet. All adjacent tubes were inspected with the rotating coil probe to determine if there were additional tubes affected.

There were no other tubes with loose part signals. There was some wear observed on two of the tubes. Retrieval was attempted, but the part could not be removed. Since the part could not be removed, it was determined that the part would not move.

However, the part is located on the periphery where the cross flow velocities are high. These tubes were conservatively removed from service and stabilized. The part was characterized as an S-hook. The source is unknown.

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5. Several indications were reported as "CHGf indications.

Please clarify the meaning of this acronym. Assuming this acronym implies the indication has changed, please discuss what signal characteristic changed and the cause of the change (or provide a description of actions that you may be planning to take to investigate the reason for the change).

For the criteria used to determine if a signal exhibits little or no change, discuss how the criteria was determined. For example, was test repeatability evaluated for these types of indications such that the criteria would identify a signal change when the change was greater than normal test repeatability?

Duke responses Since no cracking has been observed, previous indications that have been characterized by the rotating coil probe were reviewed to determine if change has occurred in the bobbin signal. If no change has occurred, then the indication would not be inspected with the rotating coil probe again. If change has occurred, then the indication would be reinspected for characterization with the rotating coil probe again.

Change is defined as an indication that changes greater than or equal to 0.50 volts or greater than or equal to 10 degrees. The values are empirically based and are within the repeatability of the eddy current test. The primary reason for a signal to change is how the analyst measures the indications.

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Attachment 1 CFR 80 Steam Generators l FB4l lFB5l

/ CFR 80O Tube Information:

No. of Tubes 6633 lCBH I lCOBC Material: Inconel 690 Nominal Dia.: 0.688" 09H 09C Nominal Wall: 0.040" Row 1 Radius: 3.973" Straight Length: 31.9'/32.7' Tube Pitch: .930" 08H 08C Roll Plug Information:

Material: Inconel 690 Nominal Dia.: 0.594" 07H 07C Nominal Wall: 0.052" Tube Support Information Type: Lattice 06H 06C Material 410 Stainless Thickness:

High: 3.150" 05H 05C Med.: 2.562" Low: 1.000" Connector Bar 04H 04C Material: 410 Stainless Fan Bars Material: 410 Stainless 03H 03C Thickness 0.110" Width 1.25" 02H 02C 01H 01C TSH TSC NOTE: Dimensions are to the TEH TEC centerline of the tube support 9

Attachment 2 Catawba Nuclear Station Unit 1 S/ A: TOTALIUSES: OM. I NOT SEELCTED TUBES: 0 PR*MARY FACE OPT OF SaRVIC~F4c KA Im

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Attachment 3 Rotating Coil Characterization Codes CODE DESCRIPTION 1

• AXI Axial Indication 2 DNT Dent 3

• L3R Level IlIl Review 4 MAI Multiple Axial Indication 5 MCI Multiple Circumferential Indication 6 MMI Mixed-Mode Indication 7 MSG Analyst Message 8 MVI Multiple Volumetric Indications 9 NDF No Defect Found 10 OBS Obstructed 11 PID Positive Identification 12 PLP Possible Loose Part 13 PVN Permeability Variation 14 RBD Retest - Bad Data 15 RIC Retest - Incomplete 16 RNC Retest - Tube Number Check 17 ROB Retest - Obstructed 18 SAI Single Axial Indication 19 SCI Single Circumferential Indication 20 SVI Single Volumetric Indication 21 VOL Volumetric 22

• WAR Wear 23 NQS Non-Quantifiable Signal

• Denotes code to be used inthe HUTIL 1"field.

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Attachment 4 Bobbin Coil Characterization Codes

1. CODE DESCRIPTION 1 ADI Absolute Drift Indication 2

• AXI Axial Indication 3 BLG Bulge 4 BOR Boron 5 CHT Chatter 7 DNT Dent 8 DWI Dent With Indication 9 FC Final Calibration 10 FCL Final Calibration Late 11 ICR Incomplete Roll 12 IC Initial Calibration 13 IV Independent Verification of tube identification 14 IDOK Tube ID Verified; This code shall be used to identify tubes acquired more than once during the current outage. Use of this code requires tube to tube comparison or fingerprinting of the affected tube(s).

15 INF Indication Not Found 16 INR Indication Not Reportable 17 IRR Irregular Roll 18 L3R Level IlIl Review 19 MSG Analyst Message 20 NEX No Expansion 21 NFC No Final Calibration 22 NQI Non-Quantifiable Indication 23 NSR Needs SGME Review 24 OBS Obstructed 25 OVR Over Roll 26 OXP Over Expansion 27 PID Positive Identification 28

• PLG Plugged Tube 29 PLP Possible Loose Parts 30 PVN Permeability Variation 31 RBD Retest - Bad Data 32 RFB Retest - Fan Bar using a wear standard for sizing 33 RIC Retest - Incomplete 34 RNC Retest - Tube Number Check 35 ROB Retest - Obstructed 36 RRC Retest - Rotating Coil 37 RPD Retest - Positive Identification 38 SAT Satisfactory 39 SLG Sludge 40 SKR Skip Roll 41

• WAR Wear 42 WTG Wetting/Leaking

• Denotes code to be used in the UUTIL 1" field 12