ML20126D112
| ML20126D112 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/15/1980 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Rubenstein L Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20126D115 | List: |
| References | |
| NUDOCS 8004170148 | |
| Download: ML20126D112 (2) | |
Text
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400 Chestnut Street Iower II April 15, 1980 Director of Nuclea. Reactor Regulation Attention:
Mr. L. S. Rubenstein, Acting Chief Light Water Reactors Branch No. 4 Division of Project Management U.S. Nuclear Regulatory Commission Washington, DC 20555 Dear Mr. ~ib.1 in:
In the h Application of
)
Docket No. 50-327 j
Tennersee crity
)
Technical an 9.3 for Sequoyah Nuclear Plant (SNP) unit 1 requires t
- -pressure turbines be subjected to a preservice inspection.
int;ection should consist of a visual examination of all accessibiu surfaces of the rotors, discs, and blading and a volumetric examination, using ultrasonic techniques, of the bore and keyway region of the discs.
TVA has completed the visual and volumetric examinations for SNP unit 1 low-pressure turbines.
The results of the visual inspection are included as an enclosure.
The volumetric examination revealed a single disc indication during the tangential aim technique on dise number 5 of the generator end of low-pressure turbine number 1.
However, this indication could not be confirmed with the radial aim technique.
The tangential aim technique is very sensitive and will pick up very shallow surface irregularities.
Previous Westinghouse experience has shown that indica-tions as small as 19 mils have been found.
Westinghouse is confident that the radial aim technique has the capability of reliably detecting cracks as shallow as 60 mils.
Therefore, TVA and Westinghouse have concluded that the indication is below that normal detectable depth and is probably a surface discontinuity.
Even though experience leads TVA to believe that this indication is not a crack, a minimum service life for the disc can be calculated by conservatively assuming that the indication is a crack with a depth I
equal to 60 mils.
Such a calculation yields the following data:
l 800417"lN t
2 Director of Nuclear Reactor Resci d ion April 15, 1980 Critical Flaw Size (a )
= 6.496 in Temperature at Inlet of Disc
= 150 F
-7 Crack Growth Rate
= 3.0 x 10 1n/hr Using the above information, TVA would expect the disc to operate reliably throughout the entire life of the unit.
Very truly yours, TENNESSEE VALLEY AUTHORITY k.
L.
M'.
- Mills, nager Nuclear Regulation and Safety Enclosure (10) l ll
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