ML20198A330
| ML20198A330 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 12/23/1997 |
| From: | Abney T TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9801050351 | |
| Download: ML20198A330 (4) | |
Text
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e IUA Tennessee Vaney Authority. Post Off.ce Bon 2000, Decatur. Alabama 35009 December 23, 1997 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C. 20555 Gentlemen:
In the Matter of
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Docket Nos. 50-259 Tennessee Valley Authority
)
50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - UNITS 1, 2, AND 3 - REQUEST FOR INFORMATION REGARDING TORUS WALL THICKNESS This letter responds to NRC's letter dated October 27, 1997, regarding the staff's concern that the BFN Units 1, 2,
and 3 may not satisfy the minimum wall thickness requirements for the Mark I containment torus structure.
The staff requested TVA to provide information on results of torus wall thickness inspections in the vicinity of the torus-to-ring-girder support welds, at the air-water interface, and in submerged areas.
The staff also requested that TVA verify whether the torus wall thickness meets minimum wall thickness requirements.
TVA currently meets all regulatory requirements and maintains an inspection program for torus coatings.
While the regulatory basis on the staff's request is not apparent, TVA is voluntarily complying with the staff's request for additional torus wall inspections.
TVA has' implemented a torus inspection and coating program in ensuring that the torus wall thickness meets the American Society of Mechanical Engineers (ASME) Code requirements.
Visual inspection of the interior and exterior surfaces of the torus are conducted during.the refueling outage of each operating cycle.
Additionally, underwater visual inspections have been conducted in the torus-immersion areas for torus bays that have been desludged, 9001050351 971223
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a Nuclear Regulatory Commission Page 2 December 23, 1997 to identify any protective coatings degradation and resultant corrosion for cleaning and repair.
As part of the initial construction of BFN, a protective coating was applied as a rust inhibitor to the torus shell.
In the mid-1980's, the original protective coating in the torus for all three BFN units was removed, and a design basis accident qualified coating was applied.
TVA's inspection and coating program has been effective in preventing wall thinning from corrosion.
The effectiveness was validated earlier this year when the NRC verified the wall thickness on the Unit 3 torus to be acceptable.
The external coating on the Unit 2 and 3 torus was visually examined and found to be sound.
The findings are documented in NRC Inspection Report 50-259/97-05, 50-26C/97-05, 50-296/97-05.
This inspection report detailed an independent ultrasonic examination of the Unit 3 torus shell plates, conducted by a NRC inspector on April 24 and 25, 1997, to determine the general structural condition of the Unit 3 torus.
The inspector found the thicknese of the plates to be acceptable, and stated that the inside surface condition of the torus as revealed by volumetric examination was good.
The NRC examined plates from eight of the sixteen torus bays from the bottom center line tc sixteen feet up each side of the torus.
A total of 240 inspection locations were ultrasonically scanned to determine the minimum plate thickness.
The selection of sample locations also included several critical points where the torus structure attaches to building supports.
All ultrasonic readings were taken by the NRC inspector.
The conclusion from the NRC inspector was that the ultrasonic examinations performed on the Unit 3 Torus met the manufacturer's nominal wall thickness of.750".
Thare were, however, several plate readinge below the.750" nominal plate thickness, but these readings were acceptable in accordance with Section XI, Subsection IWE of the ASME Code.
The average minimum reading for all 240 inspection locations ultrasonically scanned was.739" with the lowest reading being.720".
Additionally, a walkdown by the NRC inspector of various external areas of the Unit 2 torus and the Unit 3 torus found
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Nuclear Regulatory _Cummission tage 3 December 23, 1997 no evidence of coating delamination on either the torus support weldments or torus surface areas.
The inspector also found the exteijal torus coatings to be sound.
TVA is voluntarily performing additional torus wall thickness inspections.
Samples in several of the torus bays from i
approximately the same areas in the Unit 1 torus and the Unit 2 torus.are being selected.
To ensure corros4.on wall thinning has l
not caused the wall thickness at critical points to fall below the allowable wall thickness, TVA is selecting plates around the torus-to-ring-girder support welds, at the air-water interface, and in submerged areas for ultrasonic examinations.
The inspections are expected to be completed on or before December 31, 1997 A summary report detailing the results will be submitted by February 13, 1990.
Unit 1 is defueled and shutdown on administrative hold with no current plans for restart.
Unit 2 and Unit 3 are in their Cycle 10 and Cycle B operating cycles, respectively.
TVA expects the wall thickness results from the Unit 1 and Unit 2 torus ultrasonic examinations to have approximately the same wall thickness values as those found by the NRC inspector in Unit 3.
This is based not only on the similarities in operating history between the units but also on the torus inspection and p otective coating program that TVA has established and maintained at BFN.
If you have any questions concerning this information, please contact me at (205) 729-2636.
Sincerely,
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Manager of censing and Indus ry Af airs cci See page w
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December 23, 1997 cc Mr. Mark S. Lesser, Branch Chief U.S. Nuclear Regulatory Commission Region II-61 Forsyth Street, S.h.
Suite 23T85 1
Atlanta, Georgia 30303 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Road Athens, Alabama 35611 Mr. Albert W. De Agazio, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Roc),ville, Maryland 20852
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