ML20058G811

Special Rept:During Feb 1989,inservice Insp of SG Tubes Found Defects Greater than Repair Limit

ML20058G811
Person / Time
Site:	Millstone
Issue date:	11/05/1990
From:	Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9011140011
Download: ML20058G811 (2)

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YsI."nI[aIsIeNEttNec E. I $ t N O D cNn7 pany P.O. box 270 HARTFORD. CONNECTICUT 06414-0270' Northeast Nuclear Energy Company (203)665-6000-

November 5,'1990 MP-90-Il80 Re: Millstone Unit 2 .

Technical Specification 4.4.5.1.5.c -

U. S. Nuclear Regulatory Commission Document Control . Desk Washington, D. C. 20555

Reference:

Facility Operating License No. DPR-65 Docket No. 50-336-

- Gentlemen:

This letter provides information required by Millstone Unit 2 Technical Specification 4.4.5.1.5.c and constitutes the Spec,al i Report required by4 hat. Specification.

Durine the inservice inspection of steam generator tubes cotiducted in February 1989,

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defects greater than the repair limit (40% through wall penetration) were identified in 20-tubes in No.1 Steam GeneratorLand 41 tubes in No. 2 Steam Generator.LSix. tubes could not be adequately examined because they were obstructed. Three tubes had distorted signals which could not be resolved. Both the defective tubes and the tubes which could. '

not be adequately examined or resolved were repaired by plugging. One other tube was inadvertently plugged; All tubes with circumferential cracks were stabilized as well-as -

being plugged. This will prevent any contact with adjacent tubes in the unlikely event that cracking continues to tube separation after plugging.

During the inspection,8589 unsleeved tube ends were examined with 'a narrow groove, high frequency bobbin coil probe in the region near the top of the tubesheet. All tube-

- ends in the region susceptible to cracking (8148 tube ends) were examined with a multi-coil rotating probe. Approximately 977 sleeved tube ends were examined with special probes. In addition 5952 tubes were examined full length with conventional bobbin coil eddy current probes.

Two defect types accounted for all of the observed defects. Circumferential cracks at the -

top of the tubesheet were identified in 7 tube ends. Pit type defects exceeding the repair -

limit were identified, in'a region extending several inches above the top of the tubesheet in 54 tube ends.

Circumferential cracking was first identified in February 1987, and confirmed during the '

1988 inservice inspection. Boric acid addition was initiated in April 1988 to mitigate the causes of this cracking. Subsequent examinations have shown declining numbers of '

cracked tubes.

9o11140011 9o1105 7 w p .

j.  :-. 2 Pit type defects have been identified in the steam generators since 1981c These defects-

. have been limited to a recion of the steam cenerator associated with the location of the 3 sludge pile prior to chedlical cleaninc in i985. ;This corrosion process is essentially-arrested, improved inspection conditions and normal test variability rather than corro L sion progression account for essentially all-the pit type defects. identified during this O]

examination.

These actions meet all Millstone Unit 2 Technical Specification requirements and when 1 combined with a continuing program of proper chemistry control provide assurance that-  !

the Millstone Unit 2 steam generators can be safely operated during the upcoming oper-ating cycle.

The licensee contact for this Special Report is R. Thomas Blanchard Jr., wiio may be contacted at (203) 444-5350.

Very truly yours, NORTHEAST-NUCLEAR ENERG COMPANY

.g) e Steph n E. Scace i Director, Millstone Station a I

SES/RTB i,

cc: T. T. Martin, Region 1 Administrator 1 G. S. Vissing, NRC Project Manacer, Millstone Unit No.- 2 ;. .

W. J. Raymond, Senior Resident [nspector, Millstone. Units No.1, 2 and 3.

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