ML13316A032
| ML13316A032 | |
| Person / Time | |
|---|---|
| Site: | Salem, Indian Point, Turkey Point, Ginna, San Onofre, Cook, 05000000 |
| Issue date: | 12/22/1988 |
| From: | Johnson W WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Miraglia F Office of Nuclear Reactor Regulation |
| References | |
| REF-PT21-88, REF-PT21-88-145-000 NS-NRC-3390, PT21-88-145, PT21-88-145-000, NUDOCS 8901050342 | |
| Download: ML13316A032 (3) | |
Text
Westinghouse Energy Systems Box 355 Electric Corporation Pittsburgh Pennsylvania 15230-0355 NS-NRC-3390 December 22, 1988 Mr. F. J. Miraglia Associate Director for Inspection & Technical Assessment Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington D. C.,
20555 Dear Mr. Miraglia The following information is provided pursuant to the requirements of 10 CFR Part 21 to report the potential for the existance of a Substantial Safety Hazard as communicated by Mr. Brian A. McIntyre of my staff to Mr. Vernon Hodge of the NRC by telephone on December 16, 1988. This issue concerns the integrity of welds in secondary contact brackets of a manufacturing lot of DB-50 switchgear.
BACKGROUND Florida Power & Light notified Westinghouse on December 13, 1988 that three of four spot welds on a DB-50 reactor trip breaker secondary contact bracket at Turkey Point Unit 3 were observed to be separated. These welds are used to assemble the four bracket parts. Complete separation of welds may cause a discontinuity of the signals passing through the secondary contacts.
No report of separated welds on secondary contact brackets in DB-50 circuit breakers had been received by Westinghouse prior to the report from Florida Power & Light. In order to determine if the weld separation on this single breaker was an isolated occurrence, Westinghouse requested Florida Power &
Light to return the brackets of this type in their possession which had been manufactured in the same lot as the one which had separated. Four such brackets were returned, including the one which had separated initially.
Inspection of the welds on the returned brackets identified an increased probability of weld separation.
Examination of brackets manufactured during various time periods (including those which were returned) indicate the potential for bracket welds with an increased probability of weld separation is isolated to the single manufacturing lot as the brackets returned from Florida Power & Light. Westinghouse has determined that this lot consists of a total of 33 circuit breakers or secondary contact brackets shipped to the nuclear power plants shown on the attached list.
8901050342 8:8122 2 PDR ADOCK 05000206 PDC l
Dr. T. E. Murley NS-NRC-88-3390 Page 2 Safety Evaluation One application of DB-50 switchgear in nuclear power plants is as a reactor trip breaker. A loose secondary contact bracket in this application could lead to a loss of voltage to the breaker undervoltage trip attachment which would cause a reactor trip. This could also lead to the inability to generate a P-4 permissive signal which is used as an input to various protective functions. The inability to generate a P-4 signal would not result in accident consequences beyond those of other events analyzed in the plant FSAR.
DB-50 switchgear can be used in safety-related applications other than reactor trip. Westinghouse has no specific knowledge of such applications.
CORRECTIVE ACTIONS Westinghouse has advised the nuclear utilities which have received DB-50 circuit breakers identified in the attachment that any secondary contact bracket identified may be modified by drilling a 7/16 inch diameter hole through each of the four spot welds of the bracket. A 3/8 inch diameter bolt, SAE Grade 5 or better should be inserted through the hole. A flat washer and lock washer should be used on the side of the bolt being rotated with the flat washer against the bracket. The bolt should then be torqued to 31 ft-lbs. These bolts and torquing requirements have been selected based on a conservative estimate of breaker closing forces which also bound any forces which might be applied during a seismic event.
If you have any questions regarding this matter, please contact myself or Mr. Brian A. McIntyre of my staff at (412) 374-5282 Sincerely, Wi am
. Johnson, Manager Nucle r Safety Department BAM/wch/0218A Attachment
ATTACHMENT TO NS-NRC-88-3390 SUSPECT SECONDARY CONTACT BRACKETS FOR DB-50 SWITCHGEAR PLANT QTY SHIPPED FOR APPLICATION AS Turkey Point 5
5 - Reactor Trip Breakers D. C. Cook 3
2 - Reactor Trip Breakers 1 - Motor-Generator Set Breaker (Not a safety-related application)
Indian Point 2 18 1 - Spare Breaker 2 - Motor-Generator Set Breakers (Not a safety-related application) 15 - Bracket Assemblies Salem 2
2 - Spare Bracket Assemblies Ginna 3
3 - Spare Bracket Assemblies San Onofre 2
2 - Reactor Trip Breakers 33 Breakers and Spare Brackets