ML20081B359
| ML20081B359 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 03/07/1995 |
| From: | James Fisicaro ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| RBF1-95-0070, RBF1-95-70, NUDOCS 9503160146 | |
| Download: ML20081B359 (3) | |
Text
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Entergy operations,inc.
River Bend Station 5485 U S. Highway 61 w ENTERGY LFe%"A m ons Tel 504 336 6225 Fax 504 635 5068
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James J. Fisicaro Dwector -
Nuclear Safety March 7,' 1995 i
U.S. Nuclear Regulatory Commission Document Control Desk 1
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Mail Stop PI-37 Washington, DC 20555
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Subject:
River Bend Station - Unit 1 Docket No. 50-458 Supplemental Special Report - Failure of Division II EDG Exhaust Bolts Li
Reference:
Letter from J. J. Fisicaro to NRC, "Special Report - Failum of Division II EDG Exhaust Bolts," dated January 20,1995 (RBG-41166).
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File No.:
G9.5, G9.25.1.3 RBF1-95-0070 RBG-41269 Gentlemen:
t This repoit supplements the mferenced Special Report which described a December 21,1994 invalid failure of the Division II Emergency Diesel Generator (EDG). During this event, the 4
monthly surveillance run was conservatively terminated due to the discovery of two broken l
bolts in an exhaust manifold flange. This supplement provides the final msults of our t
investigation of the bolt failure.
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The root cause of the bolt failum was determined to be bending and cyclic fatigue. This
.l determination was based on visual examination, laboratory tests and a metallurgical analysis.
' As discussed below, it is believed that these bolts were exposed to abnonnal stresses during a Refueling Outage (RF) 4 maintenance activity during which the EDG was run with this l
connection assembled slightly out of square.
An investigation was conducted to determine whether the design of the bolted joint or a maintenance activity was the primary contributor to the failure. This investigation concluded that the design was adequate. A myiew of maintenance records identified a 1992 maintenance i
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Supplemerdal Special Repon - Failure of Division II EDG Exhaust Bolts March 7,1995 RBG-41269 RBF1-95-0070 Page 2 of 3 -
activity on the #8 cylinder of the Division II EDG as the likely initiating event.'.Our investigation identified that an exhaust leak was observed on the #8 cylinder during a post-maintenance run in RF-4. During the investigation'of this leak, it was noted that this joint had ~
been assembled slightly out of square, apparently due to a poorly aligned gasket. Our
-investigation concluded that this shon maintenance mn (approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />) subjected these bolts to abnormal bending and cyclic stmsses. The leak was corrected by mplacing the gasket and reassembling the joint pmperly. However, the same bolts wem used for the reassembly. At that time, it was not suspected that this condition could have caused fatigue in the bolts or initiated a crack. This condition was limited to this one cylinder and as such was an isolated occurrence. As discussed in the initial Special Report on this condition, all four of the #8 cylinder exhaust manifold bolts were replaced immediately following the December, 1994 event. In addition the tightness of the mmaining exhaust manifold bolts on both the
- Division I and II EDGs was checked.. While no specific corrective action for this causal factor (i.e., poor maintenance practices) has been deemed necessary, EOI does have ongoing programs for enhancing current maintenance practices and contractor oversight. These generic activities should adequately serve to pmvent recurrence.
The statistics for valid EDG failures at River Bend were not impacted by this event. These -
statistics were provided in the initial Special Report.
If there are any questions concerning this issue please contact M. K. Brandon at (504) 381-4506.
Sincerely, hd" JJF/MKB/kym
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Supplemental Special Report - Failure of Division II EDG Exhaust Bolts L
March 7,1995 RBG-41269
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RBF1-95-0070 i
Page 3 of 3 1
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U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 i
Arlington, TX 76011 l
NRC Sr. Resident Inspector P.O. Box 1051 St. Francisville, LA 70775
. INPO Records Center 700 Galleria Parkway Atlanta, GA 30339-3064 Mr. C.R. Oberg i
Public Utility Commission of Texas 7800 Shoal Creek Blvd., Suite 400 North Austin, TX 78757 I.ouisiana Depanment of Environmental Quality
-l Radiation Protection Division P.O. Box 82135.
Baton Rouge, LA 70884-2135 ATTN: Administrator 8
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