ML20248L264
| ML20248L264 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/04/1998 |
| From: | Katz P BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9806110049 | |
| Download: ML20248L264 (5) | |
Text
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PETER E. Kurz Baltimore Gas and Electric Company Plant General Manager Calven Cliffs Nuclear Power Plant Calvert Cliffs Nuclear Power Plant 1650 Calven Cliffs Parkway Lusby. Maryland 20657 410 495-4101 June 4,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No.1; Docket No. 50-317 Steam Generator Tube Inspection Results
REFERENCE:
(a)
Calvert Cliffs Unit 1 Technical Specifications In the spring of 1998, Baltimore Gas and Electric Company conducted a scheduled refueling outage at Calvert Cliffs Nuclear Power Plarit Unit 1. An inspection of the Unit I steam generator tubes was performed during the outage. The results of the Steam Generator Tube Inspection fell into the C-3 category, as described in Technical Specification 4.4.5.2 (Reference a).
In accordance with Reference (a), a verbal notification was made to the Nuclear Regulatory Commission Region I office on May 13,1998. The required written follow-up report, providing a description of the investigations conducted to determine the cause of the tube degradation and corrective measures taken as a result of the inspection findings, is provided below.
INSPECTION SCOPE The examination of Calvert Cliffs Unit 1 Steam Generators (Nos. I1 and 12) consisted of bobbin, motorized rotating pancake coil, and motorized rotating plus point (MRPP) inspection technologies.
A.
Bobbin Coil Inspections The bobbin cail examinations for Steam Generator Nos.11 and 12 included 100 percent bobbin coil full length examination of all inservice tubes.
B.
MRPP Inspections
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The MRPP examinations for Steam Generator Nos. I1 and 12 inservice tubes included:
1.
One-hundred percent of the hot leg tubes at the top of the tube sheet (TTS), TTS+5" above to TTS-1" below.
,hO) 9806110049 900604 PDR ADOCK 05000317 P
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Document Control Desk June 4,1998 i
i Page 2 2.
Twenty percent of rows 1 and 2 (U-Bend Region). The vertical extent of the exam was from 6th hot leg tube support plate (TSP) to the 6th cold leg TSP.
3.
One-hundred percent of rows 6 through 13 from the 5th hot leg TSP to the 6th cold leg TSP.
4.
Fifty 1,ercent of the upper bundle Stay Dome Region tubes from rows 35 through 64, lines 55 through 120. These inspections were conducted from the 6th hot leg TSP to the vertical middle support.
5.
Fifty percent of the upper bundle Arc Region tubes from rows 65 though 135. These inspections were conducted from the 6th hot leg TSP to the vertical middle support.
j 6.
Fifty percent of the 9th hot leg TSP intersection from rows 90 through 135.
7.
One-hundred percent of the cold leg tubes at the TTS + 5" through the TTS -1" in Steam Generator No.12.
8.
Thirty-nine percent of the cold leg tubes at the TTS +5" through the TTS -1" in Steam Generator No.11, which consisted of a twenty percent programmatic sample and a periphery sample for loose part degradation.
9.
Twenty percent of the dents, excluding the ninth hot leg solid drilled TSP, that had an eddy current response signal greater than or equal to five volts.
10.
One-hundred percent of the ninth hot leg TSP dented intersections that had an eddy current response signal greater than or equal to five volts.
I 1.
Twenty percent of the rolled mechanical plugs in the hot leg were examined using a motorized rotating pancake coil probe.
C.
.Special MRPP Inspections All MRPP tube inspections were performed using the "Plus Point" probe technology. All distorted bobbin coil indications were dispositioned with the plus point probe, l
EDDY CURRENT INSPECTION RESULTS
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Attachment (1) contains the results of the MRPP and bobbin exams for Steam Generator Nos. I1 and 12.
All steam generator tubes with crack-like indications and volumetric indications that are not wear indications were removed from service. No wear indications in excess of 40 percent through-wall or j
. degraded tube plugs were identified.
CAUSE OF TUBE DEGRADATION AND CORRECTIVE MEASURES No new steam generator tube degradation mechanisms were identified by the 1998 Unit I steam generator eddy curmnt examination. flhe active degradation mechanism in both steam generators is outside' diameter'intergranular attack /intergranular stress corrosion cracking. Mechanical wear is present, but the' depth growth rate is small. and is managed in accordance with the Technical Specifications, i.e., tubes with through-wall wear degradation greater than or equal to 40 percent are
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plugged.
Documsnt Control Desk June 4,1998 Page 3 1
The sizes of sne eddy current flaw indications are best characterized as low voltage and short length. The 1998 Unit 1 examination voltage and length distribution compared favorably to that found during the
- 1996 Unit I steam generator eddy current exam. The mean flaw voltage and length were equal to or less 1
than the 1996 values, while the extremes of the distributions were much less severe. Both the 1996 and 1998 examinations used "Plus Point" technology. The TTS degradation mechanism is significantly less active than the 1996 result indicated, suggesting that the indications identified in 1996 developed over greater than one operating cycle. The upper tube bundle eddy current examination indicated that upper bundle free span tube degradation continues, but the indications are small and their depth growth rates are low. All Unit I steam generator tubes with crack-like indications and volumetric indications that are not wear indications were removed from service. No wear indications greater than or equal to 40 percent through-wall or degraded tube plugs were identified. Future inspections will continue to: (1) focus on regions of the steam generators with known active degradation mechanisms, (2) incorporate industry experience on steam generator degradation mechanisms, and (3) remove from service or repair degraded tubes as required by plant Technical Specifications.
Should you have questions regarding this matter, we will be pleased to discuss them with you.
I Very truly yours,
[&
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r for P. E. Katz Plant General Manager PEK/GT/bjd
Attachment:
(1)
Results 'of the Motorized Plus Point and Bobbin Technologies Inspection of '
l Steam Generators Nos.11 and 12
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~ R. S. Fleishman, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident inspector,NRC S. S. Bajwa, NRC R. I. McLean, DNR A. W. Dromerick, NRC J. H. Walter, PSC i
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4 ATTACHMENT (1)
RESULTS OF THE MOTORIZED PLUS POINT AND BOBBIN TECHNOLOGIES INSPECTION OF STEAM GENERATOR NOS.11 AND 12 l
l 1
i Baltimore Gas and Electric Company Calvert Cliffs Nuclear Power Plant June 4,1998 l
i
ATTACHMENT (1)
RESULTS OF TIIE MOTORIZED PLUS POINT AND BOBBIN TECIINOLOGIES INSPECTION OF STEAM GENERATOR NOS.11 AND 12 The following outline summarizes the final results of this examination.
STEAM STEAM Indications by Tube GENERATOR GENERATOR NO.11 NO.12 TotalHot LogTapffTubeshsstll
[291 f331 axial 16 24 circumferential 9
6 volumetric 3
3 loose part*
1 0
Total [Uppsr)TaliBusdid[Mc[asd StapDsise
!;55#
195j RikiossiE axial 54 86 volumetric 1
9 T6tilSiism Blanket Rssi6n?
if3)(
W pil axial 3
2 volumetric 0
0 TofalC61dlijT6pOfTubeshseG 110 s (19?
axial 0
1 circumferential 0
9 volumetric 8
8 loose part*
2 1
Othofrsgiossy,
4 (17e B20s
!ToialTulies Plugjedis11998jQ ill4j it169;!! +
Total Tubes Plugged 604 776 Total Percent Plugged 7.1%
9.1%
- All tubes with loose part indications were plugged and staked.
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