ML19269H439

Forwards Final Rept Re Potential Problem in safety-related Overcurrent Relays.Problem Was Random in Nature & Not Generic

ML19269H439
Person / Time
Site:	Catawba, McGuire
Issue date:	07/16/1980
From:	Duvall D GOULD-BROWN BOVERI
To:	Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
REF-PT21-80-196-002 NUDOCS 8007300379
Download: ML19269H439 (4)

Text

. a _ m o, _ c_,

9 GOULD-BBC'NN B'OVERI July 16, 1980 Mr. Victor Stello, Director Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Stello:

Attached is a final report on our letters to you of February 11, 1980, and April 25, 1980, on a potential problem with safety related relays. Our investigation has determined that the problem reported was random in nature and not generic.

If you need any additional information on this subject, please call Mr. E. W. Rhoads at (215) 628-7660.

Very trtdy yours,

//

/3 4 D. D. Duvall Vice President & General Manager Switchgear Systems Division Attachments copy to: J. P. O'Reilly, Director U. S. N.R.C. , Region II 101 Marietta Street, Suite 3100 Atlanta, GA.

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July 16, 1980 POTENTI4, PROBLEM IN SAFETY RELATED OVERCURRENT RELAYS On January 31, 1980, Duke Power Co. telephoned a report to the Director NRC, Region II of a potential problem in safety-related overcurrent relays fur-nished by Gould-Brown Boveri. This report indicated that a component, an SCR (Silicon Controlled Rectifier), within an overcurrent relay had failed, causing a circuit breaker to open at the Mcguire Nuclear Station.

The Gould-Brown Boveri letter of February 11, 1980 to Mr. Victor Stello, Office of Inspection & Enforcement, U.S. Nuclear Regulatory Commission, Washington, D.C. incorrectly identified the deficiency as occurring at the Catawba Nuclear Station.

The Duke Power Co. written report to the NRC dated February 29, 1980 de-scribes the deficiency detected at the Mcguire Nuclear Station as follows:

"During relay and trip device acceptance and system startup testing, it was determined that fourteen (14) relays and trip devices did not meet the time-current characteristic specifications of the relay for its application (i.e.

the relay or device would trip at a lower level of current or time than its setting). The items found to contain the deficiency were solid state relays manufactured by Gould-Brown Boveri, Horsham, PA and consists of Types ITE-5L and ITE-51Y overcurrent relays and Type SS4G (Power Shield) solid state trip devic e. The component that has been identified as cau~s ing the deficiency was Motorola, Inc. SCR's Types 1379 and 1235. Additional Gould-Brown Boveri relay Types GR-5, ground fault relay, and Type ITE-50, overcurrent relay also contain similar type SCR's."

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Prior to the initial report to the NRC by Duke Power Co., Gould-Brown Boveri had been conducting an investigation of some random failures of Motorola, Inc.

SCR's. Three units had been returned to the supplier, where they were examined by a scanning eleccron microscope. These units were determined to have failed due to the migration of copper from the top metal system into bulk silicon ma t erial . Small pin holes in a chrome metal barrier, that separate the copper from the silicon, permitted the copper to migrate into the silicon as a direct function of temperature and time, resulting in a f ailure. One of f he SCR's that had been examined in this investigation by Motorola had been returned from the Catawba Nuclear Station. The other two SCR's examined at this tire had been returned from commercial operations.

The inspection and screening methods used by Fbtorola, Inc. were thought to be sufficiently comprehensive to preclude the use of SCR's with susceptibility to this copper migration problem. As an immediate corrective action, Motorola has identified the additional high temperature screening test which is effective in identifying units that are susceptible to copper migration. This test requires baking the units at 1500 C for two weeks to identify units that would be suscep-tible.

Both Gould-Brown Boveri and Motorola, Inc. checked the then existing stock of at least 1,500 SCR;s by means of the high temperature bake and all were found to be free of copper migration.

These SCR's were then used to change out SCR's in selected devices at Duke Power Co. These changed out SCR's from Duke Power Co. were then subjected

• to a detailed examination, to accurately determine the scope of the potential pr:oblem. A total of 533 SCR's were returned for testing and evaluation at Could-Brown Boveri and Motorola. This examination showed that five SCR's had leakage above specification limits but had not failed. The leakage was due to .

various reasons such as a cracked die, a cracked weld seal or copper migration. .

9 Additionally a review of all reported SCR proPlems from Duke Power and other users was conducted to deteruine if there was any pattern or trend to indicate a generic type problem. This review shows the failure rate to be less than

.1% per year for purely random reasons.

It can be concluded that there is no generic problem with the SCR's used in the Gould-Brown Boveri relays and ' trip devices. Copper migration has been identified as a failure mechanism and the screening test previously noted will be continued to preclude this type of problem.

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