ML20234F526

Followup Part 21 Rept Re Defective MIS-5 Actuating Fuses. Initially Reported on 870620.All Defective Fuses Will Be Replaced W/Fuses from Subsequent Lots Before Mode 4

ML20234F526
Person / Time
Site:	Sequoyah
Issue date:	09/16/1987
From:	Gridley R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
REF-PT21-87, REF-PT21-87-173-000 PT21-87-173, PT21-87-173-000, NUDOCS 8709230157
Download: ML20234F526 (5)

Text

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e TENNESSEE VALLEY AUTHORITY CH ATTANOOGA, TENNESSEE 374o1 SN 157B Lookout Place SEP 161987 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, D.C.

20555 Gentlemen:

In the Matter of

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Docket Nos. 50-327 Tennessee Valley Authority

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50-328 SEQUOYAH NUCLEAR PLANT (SQN) - FOLLOW-UP TO THE PART 21 REPORT ON BUSSMANN CORPORATION MIS-5 FUSES Enclosed is a follow-up to the Part 21 report submitted to NRC on October 29, 1986 (enclosure 1). is a list of commitments in enclosure 1.

This submittal provides an up-to-date status of the TVA resolution of the fuse problems at SQN.

The enclosed report identifies the corrective actions TVA will take for SQN restart. This information should allow NRC to close this issue.

If you have any questions, please telephone M. R. Harding at 615/870-6422.

Very truly yours, TENNESSEE VALLEY AUTHORITY R. Gridley, D rector Nuclear Safe y and Licensing Enclosures cc:

See page 2 8709230157 870916 PDR ADOCK 0500 7

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An Equal Opportunity Employer

.. SEP 161987 U.S. Nuclear Regulatory Commission cc'(Enclosures):

Mr. G. G. Zech, Assistant Director for Inspection Programs office of Special Projects U.S. Nuclear Regulatory Commission 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. J. A. Zwolinski, Assistant Director

. for Projects Division of TVA Projects office of Special Projects U.S. Nuclear Regulatory Commission 4350 East-West Highway EWW 322 Bethesda, Maryland 20814 Sequoyah Resident Inspector Sequoyah Nuclear Plant

.2600 Igou Ferry Road Soddy Daisy Tennessee 37379 l

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ENCLOSURE 1 SEQUOYAM NUCLEAR PLANT (SQN) UNITS 1 AND 2 FOLLOW-Up REPORT ON BUSSMANN CORPORATION MIS-5 ACTUATING FUSES This is a follow-up to the part 21 report on defective MIS-5 indicating fuses submitted on October 29, 1986.

In early 1972, because of miscommunication or misunderstanding between TVA and Bussmann, TVA concluded that KAZ actuators cuuld be used as fuses in 6 ampere or lower rated 125-V de circuits and 600-V ac circuit application and decided to use them in class 1E circuits.

Subsequently, in 1986 additional communication between TVA Division of Nuclear Engineering (DNE) and Bussmann established that the KAZ actuating device cannot be used as a fuse.

The device can only be used in parallel with a higher rated fuse so that when the higher rated fuse blows, the KAZ also blows; and the indicator pin actuates the annunciation circuit.

In June 1965. TVA decided to change out the KAZ actuator devices with MIS-5 indicating fuses that are also manufactured by Bussmann.

Bussmann could not provide MIS-5 fuses with the seismic qualification required for class 1E application; therefore, TVA contracted with Nutherm International, Inc., to supply MIS-5 fuses with a seismic qualification report.

Nutherm delivered approximately 4.300 MIS-5 fuses with seismic qualifications to SQN during August and September 1986. As of October 1986. TVA had replaced approximately 2,540 KAZ actuators with MIS-5 actuating fuses.

The MIS-5 actuating fuse consists of two wires in a sand-like filler.

One of the wires, which is approximately 96-percent silver, acts as a retaining wire for a spring-loaded indicator pin located at one end of the fuse assembly.

Even though seismic tests were performed by Nutherm and passed, the MIS-5 fuses were very fragile and some fuses were damaged during handling and transportation.

In some cases, the indicator pin was fully ejected because of a minor impact while others have exhibited partial actuation that was not discernable through visual inspection.

In early October 1986, SQN management suspected MIS-5 fuses were defective and suspended installation of MIS-5 fuses. A part 21 report was submitted to NRC as specified above.

The MIS-5 fuses that were installed in safety-related systems, which were required for mode 5 operation, were tested and verified operable.

In November 1986, TVA i

decided to replace all MIS-5 indicating fuses with more reliable indicating i

fuses.

I In January 1987, a contract was awarded to Littelfuse, Inc., to supply 15,000 indicating fuses (Model No. FLAS-5).

Rigorous test requirements were specified in the contract document to overcome the problems experienced with MIS-5 fuses.

The seismic qualification of the FLAS-5 fuse was performed by Wyle Laboratory under a separate contract.

The FLAS-5 fuse consists of a fuse wire, 560-ohm resistor, spring-loaded indicator pin, and sand-like filler.

The indicator pin is mechanically attached to the spring.

At the end of the spring, the resistor and the fuse wire are soldered together. The solder material used is a eutectic alloy that has a low melting point.

During overcurrent or f ault conditions, the solder joint melts and releases the I

indicator pin.

The indicator pin serves to cause annunciation only and does I

not trigger any safety features.

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. I Littelfuse, Inc., delivered six lots of FLAS-5 fuses to SQN as follows:

LOT OUANTITY DATE SHIPPED 1.

3 1,000 Februa'ry 23, 1987

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2.

2 845 March 7, 1987 3.

4 857 March 13, 1987 4.

6 1,000 March 31, 1987 5.

10 1,000 August 19, 1987 6.

11 1,000 August 31, 1987 Total - 5,702 On June 20, 1987, an FLAS-5 fuse blew in a diesel generator (D/G) remote emergency start circuit that started all four D/Gs. No maintenance or modification activity was in progress that would have caused a short circuit or overcurrent, and no operational basis could be found for the failure.

FLAS-5 blown fuse los maintained by SQN Operations personnel indicated that FLAS-5 fuses of Lot Nos. 2 and 3 were inadvertently blowing since installation began in March 1987. The log also indicated that the fuses have blown without the component in service or any other activity in progress. A telephone conversation on June 29, 1987, with Littelfuse, Inc., revealed that they believed this to be a creep failure problem introduced during the manufacturing of fuses in Lot Nos. 2 and 3.

The problem was believed to be corrected by changing the solder material and soldering process during the manufacturing of subsequent lots.

Littelfuse, Inc., did not notify TVA with regard to the creep problem with FLAS-5 (Lot Nos. 2 and 3) fuses; however, it appears that the changes in the solder material and soldering process have made the subsequent lots of FLAS-5 more reliable.

Installation records indicate that approximately 1,683 FLAS-5 (Lot Nos. 2 and 3) fuses are installed.

A Part 21 report on defective FLAS-5 (Lot Nos. 2 and 3) fuses was submitted as part of Licensee Event Report (LER) SQRO-50-327/87030 dated July 20, 1987.

FLAS-5 (Lot Nos. 2 and 3) fuses belonging to D/G-related circuits were replaced by FLAS-5 Lot No. 6 fuses on hand to ensure D/G operability.

The replacement fuses (Lot Nos. 10 and 11) were delivered on August 19 and 31, 1987, respectively. The defective FLAS-5 fuses (Lot Nos. 2 and 3) will be replaced with fuses from Lot Nos. 10 and 11 by mode 4.

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i ENCLOSURE 2 LIST OF COMMITMENTS 1.

All defective fuses (FLAS-5, Lot Nos. 2 and 3) will be replaced with fuses from subsequent lots before mode 4.

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