ML20206U305

Submits Written Rept as Required follow-up to Verbal Rept Given to NRC Regional Administrator on 990419 of SG Tube Insps Conducted,Cause of Tube Degradation & Corrective Measures Taken as Result of Insp Findings

ML20206U305
Person / Time
Site:	Calvert Cliffs
Issue date:	05/19/1999
From:	Katz P BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9905250153
Download: ML20206U305 (5)

Text

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PETER E. KATZ 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 May 19,1999 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318 Steam Generator Tube Insnection Results in the spring of 1999, Bahimore Gas and Electric Company conducted a scheduled refueling outage at Calvert Cliffs Nuclear Power Plant (CCNPP) Unit 2. An inspection of the Unit 2 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 CCNPP Technical Specification 5.5.9. In accordance with Technical Specification 5.6.9.c, Category C-3 verbal notification was made to the NRC Regional Administrator on April 19,1999. This written report is the required follow-up to the verbal report and provides a description of the inspections conducted, the cause of tube degradation, and corrective measures taken as a result of the inspection findings.

INSPECTION SCOPE The examination of Calvert Cliffs Unit 2 Steam Generators (Nos. 21 and 22) consisted of bobbin coil and motorized rotating plus point (MRPP) inspection technologies.

A. Bobbin Coll Inspections The bobbin coil examinations for Steam Generator Nos. 21 and 22 included 100 percent bobbin coil full length examination of all inservice tubes.

B. Motorized Rotating Plus Point Inspections The MRPP examinations for Steam Generator Nos. 21 and 22 inservice tubes included:

1. One hundred percent of the hot leg tubes at the top of the tube sheet (TTS), TTS+5" above to TfS-1" below.

2. One hundred percent of the cold leg tubes at the TfS + 5" through the TTS-1".

3. One hundred percent of rows 6 through 15 from the 5th hot leg tube support plate (TSP) to the 6th cold leg TSP. I I

9905250153 990519 2 PDR ADOCK 05000318 0 PDR

Docum nt Control Desk May 19,1999 Page 2

4. Twenty percent of rows 1 and 2 (U-Bend Region). The vertical extent of the exam was j from 6th hot leg TSP to the 6th cold leg TSP.

. 5. Twenty percent of the dented TSP intersections that had an eddy current response signal I greater than 5 volts. l C. Special Motorized Rotating Plus Point Inspections All MRPP inspections were performed using the "Plus Point" probe technology. All distorted l

bobbin coil indications were dispositioned with the plus point probe.

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EDDY CURRENT INSPECTION RESULTS {

Attachment (1) contains the results of the MRPC and bobbin exams for Steam Generator Nos. 21 and 22.

All steam generator tubes with axial or circumferential crack indications were plugged. Volumetric i indications that failed to confirm as non-degradation related artifacts were also plugged. No wear indications in excess of 40 percent through-wall were identified. All circumferentially oriented cracks {

and loose part indications with tube degradation present were stabilized and plugged. l 4

IN-SITU PRESSURE TEST RESULTS Two tubes from Steam Generator 22 were in-situ pressure tested. Tubes selected had the limiting axial and circumferential crack indications. The tubes tested were:

Steam Flaw Flaw Flaw Flaw Generator Ran Line Type Location Voltage length j 22 89 47 MCI TSH +0.06 0.37 1.2" 22 9 53 SAI TSH +2.34 0.84 0.7" SAI Single Axiallndication MCI Multiple Circumferential Indication TSH Tubesheet Hot The most limiting case for CCNPP is pressurization without burst to three times normal differential operating pressure. Adjustments to the three times normal differential operating pressure value considered temperature, instrumentation, and locked tube condition. Both tubes were tested to pressures in excess of the adjusted pressure values to further verify that substantial tube structural integrity margin existed. No tube leaked or burst. The steam generator tubes that were in-situ pressure tested demonstrated structural integrity per the guidance provided by Regulatory Guide 1.121.

CAUSE OF TUBE DEGRADATION AND CORRECTIVE MEASURES No new steam generator tube degradation mechanisms were identified by the 1999 Unit 2 steam generator eddy current examination. The active degradation mechanism in both steam generators is intergranular attack /intergranular stress corrosion cracking. The predominant degradation mechanism is hot leg top-of-tubesheet outside diameter stress corrosion cracking (ODSCC). Although the ODSCC remains active in this location, the size of the defects do not threaten tube integrity. Outside diameter stress corrosion cracking in other regions of the steam generators is also characterized as low voltage, short cracks. Mechanical wear is very minor in both total number and degradation rate.

Document Control Desk May 19,1999 Page 3 Future inspections will continue to: (1) focus on regions of the steam generators with known active degradation mechanisms using appropriate eddy current techniques; and (2) incorporate industry experience on steam generator degradation mechanisms.

Should you have questions regarding this matter, we will be pleased to discuss them with you.

Very truly yours, a

PEK/GT/ dim

Attachment:

(1) Results of the Motorized Plus Point and Bobbin Technologies Inspection of Steam Generators Nos. 21 And 22 cc: 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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, , ATTACHMENT (1)

RESULTS OF TIIE MOTORIZED ROTATING PLUS POINT AND ,

BOBBIN TECHNOLOGIES INSPECTION OF STEAM GENERATORS NOS. 21 AND 22 l

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Baltimore Gas and Electric Company ,

Calvert Cliffs Nuclear Power Plant May 19,1999

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ATTACHMENT (1)

RESULTS OF THE MOTORIZED ROTATING PLUS POINT AND BOBBIN TECHNOLOGIES INSPECTION OF STEAM GENERATORS NOS. 21 AND 22 l

The following outline summarizes the final results of this examination.

Location No. 21 SG Indications No. 22 SG Indications Hot Leg Top of Tubesheet 236- .180 --

axial 222 150 circumferential

• 14 30 volumetric 0 0 l

loose part

• 0 0 1

~

Upper Bundle 3 5-arc & stay dome 0 1 i steam blanket 3 4 Low Row U-bends'- 0 0~

Cold Leg Top of Tubesheet' '9 16.-

)

axial 0 4  !

circumferential

• 2 1  !

volumetric 3 10 loose part

• 4 1 Confirmed bobbin calls outside the Upper . .2- 2 Bundle -

Secondary Side Inspection ** ' ;3 98-1999 Totals 253 301 l

Total Plugged 957 (11.2 % ) 744 (8.7 % ) i l

• All tubes with circumferential cracking or loose part wear were stabilized and plugged. 1

• • Preventive plugging for operational reliability was performed on numerous peripheral tubes as a result of secondary side inspection findings.

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