ML20199K833

Ro:On 960528,detected Abnormal Metallic Impact Sounds.Caused by Confirmed Loose Part in Sg.Removed SG 4 Hot Leg Manway & Found Loose Metal Object Inside,Performed Engineering Evaluation & Performed Insp of Guide Tube Support Pins

ML20199K833
Person / Time
Site:	Vogtle
Issue date:	11/21/1997
From:	Mccoy C SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LCV-0797-A, LCV-797-A, NUDOCS 9712010215
Download: ML20199K833 (3)

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C. K. McCoy Southern Nucleer Vice President Operating Comp:ny, lac.

Vcgtle Projer> 40 invemess Center Parkway 20 99x1295 Birmingham Alabama 35201

- Tel2059923122 fra 205 9920403 SOUTHERN COMPANY Energy to Serve Your%rld*

November 21, 1997 -

9 Docket Nos. 50-424 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 ladiec and Gentlemen:

VOGTLE ELECTRIC GENERATING PLANT CONFIRhiED LOOSE PART 14-DAY REPORT - REVISION 1 Pursuant to a commitment made in Confirmed Loose Part 14-Day Report, letter number LCV-0797, dated June 10,1996, Southern Nuclear Operating Company is submitting the enclosed revised report out!!dng follow-up actions taken since the original 14-day report was issued.

Should you have any questions regarding this request, please contact this office.

Sincere! ,

0C. K.. hicCoy

• f '

CKhiffEW

Enclosure:

Confirmed Loose Part 14 Day Repon - Revision I cc: Southern Nuclear Operatina Comoany hir. J. B. Beasley hir, hi. Sheibani NORhiS U. S. Nuclear Renulatory Commission hir L. A. Reyes,' Regional Administrator e)[

hir. L. L. Wheeler, Senior Project hianager, NRR )

NRC Senior Resident Impector, Vogtle llIlllBlRlllf8llllllIlllllll 9712010215 971121 t' POR ADOCK 05000424 s PDR

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ENCLOSURE VOGTLE ELECTRIC GENERATING PLANT CONFIRMED LODSE PART 14-DAY REPORT - REVISION 1 l A. REQUIREMENT FOR REPORT This report is required in accordance with the Vogtle Electric Generating Plant Final Safety Analysis Report, Chapter 1.9, and Regulatory Guide 1.133, Section C6. This regulatory guide requires the submittal of a follow-up report within 14 days of the initial notification of the coalirmation of a loose part. The regulatory guide requires the report to include the following information:

1) a summary of data obtained in the manual and automatic data acquisition modes;

2) a summuy of the analysis, inspections, and correlations with operating data that were pc rformed to evaluate data from the loose part detection program;

3) a sumnt ny of conclusions and a description of modifications or other actions planned or already performed to evaluate the safety implication of a loose part or to ensure that system and component safety functions are not impaired.

H. DESCRIPTION OF EVENT On May 28,1996, at 0648 EDT, a digital metal impact monitoring system (DMIMS) alarm annunciator began to continuously alarm in the control room.

Various methods were employed to confirm the existence of a loose part in steam generator (SG) # 4. After obtaining a high confidence factor that a loose part existed, the NRC Operations Center was notified at 2157 EDT, and the unit was shutdown. Information required by Regulatory Guide 1.133, Section C6, is provided as follows:

1) An audio check detected abnormal metallic impact sounds and the DMIMS system report registered a high number ofimpacts above the alarm setpoint for channel 760 (SG #4 primary side). A tape recording was made and sent to a 2

vendor for analysis. In addition, a printout from a test instrument recorded hits that resembled " textbook" examples of metal impacts. The vendor analysis concluded that a loose metal object was the cause of the impacts.

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, 16 ENCLOSURF,

- VOGTLE ELECTRIC GENERATING PLANT CONFIRMED LOOSE PART 14-DAY REPORT - REVISION 1 l

2) The SG #4 hot leg manway was removed and a loose metal object was found inside. The object was a support pin nut from a control rod guide tube --

assembly. ' The nut's locking device was found wedged into the bottom of a tube and was subsequently removed. A third object believed to be a fragment -

from the support pin nut, was found in the SG #4 cold leg side. The support pin from which the nut came was believed to be intact and captured in place in the reactor vessel. However, a portion of the pin was later found in SG #4 (see below). A dowel pin that was attached to the nut could not be located. An inspection was performed of the SG #4 reactor coolant system hot leg with no loose parts found. The SG #4 lower tubesheet on the primary supply side was impacted by the loose object and numerous indications were noted. The other 3 j SG primary supply side interior surfaces were examined with no signs of damage.

3) An engineering evaluation was performed to determine weld / pressure boundary integrity at the SG #4 lower tubesheet. The evaluation found no defects that wv.ild preclude safe operation of the SG under both normal and accident conditions and the unit is being returned to power operation. Repairs and/or modifications to both the tubesheet and the control rod guide tube assemblies were considered. l

4) Inspection of guide tube support pins during the Unit 2 Fall 1996 refueling outage found no degraded support pins. During the Unit 1 Fall 1997 refueling outage, the 31.ank of the broken support pin was found lodged in a tube of SG

1. 4. The shank was left in place and the tube was plugged. Damaged tube ends on the tubesheet were rolled. An investigation t.o determined the cause of the damaged guide tube support pin is in progress. However, all Unit I guide tube support pins were replaced, and replacement of Unit 2 support pins is scheduled for the Spring 1998 refueling outage.

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