ML20028H222

Informs of Results of Investigation of Recent Instances at Plant Where Loose Fuse Holders Caused Problems of Varying Degrees W/Safeguards & non-safeguards Equipment

ML20028H222
Person / Time
Site:	Prairie Island
Issue date:	10/31/1990
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9011190062
Download: ML20028H222 (2)

Text

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U Northem States Power Company 3 m 7.

414 Nicollet Mall Minneapolis, Minnesota 55401 1027 Telephone (612) 330 5500 October 31, 1990 1.

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-1 U S Nuclear Regulatory Commission

. Attn: Document Contral Desk

]j Washington, DC.

20555 PRAIRIE ISIJD NUCLEAR GENERATING PIANT j

r Decket Nos. 50 282 License Nos. DPR 42 1

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P 50-306 DPR 60 1

Fuse Holder Decradation g

U IThsre have'been recent instances at Prairie Island where loose fuse holders.

ha've caused problems of varying degrees with safeguards and non-safeguards -

equipment..iTheLintent of'this letter is to inform you of_the results of our

.l investigation offthese events, and to.' describe our planned corrective actions.

1 Fuses are commonly removed to provide safe conditions for workers performing

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,Ltesting-and preventive or corrective maintenance, Some of the fuse holders

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iitistalled in PrairJe Island plant equipment are degrading as a result of many

. installation'and! removal cycles. 'This degradation is indicated by occasional; 1

Llosses.of continuityL from the fuse to the fuse holder. Such losses of f [?[*

continuity.have resulted in a loss of contro1' power.to a Diesel Cooling Water.

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[ Pump and/a prollemawith D2 Emergency Diesel Generator.during restoration j

.following maintenance.~ lIn both these1 instances, the;1oss ofspower was, 4

f annunciated,; and the problem-was rapidly corrected; L

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LThe-root cause of these occurrences is the-relaxaticn of the metal'in the fuse-

-:# * # " clip holder resulting from many insta11ationLand removal cycles. 'It is a

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,commonLpract-ice. for station electricians: to bond the clips to provide for more J

positive 1 electrical: contact,. This practice may accelerate the~ degradation of-

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fourirosearch of industry' standards has~ concluded that fuses'should.not be-used'

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, s for! electrical isolation'as a matter of general.practico.

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. ' fuse holders :that. have Lbeen subjected to this practice should be replaced to f' minisize the; potential'for' future equipment failures!resulting from a' loss of f

hl3 4, > continuity across fuse. holders, g

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[y N.M 9011190062 901031 a

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'- October-31, 1990 Page 2 Northem States Power Company

The following corrective actions are planned as a result of our investigation:

1. As.an interim measure, Bussman screw-on clamps that hold the fuse clips together have been applied on the fuse holders known to be weak to ensure positive contact.

2. Circuits for which fuses are regularly used for electrical isolation in safety related equipment will;be identified, and modifications will be initiated to provide other means of isolation (eg. switch, circuit breaker, etc). For key equipmer.'c such as Emergency Diesel Generators.

J, Diesel Cooling Water Pumps, Residual Heat Removal Pumps and Safety

(L Injection Pumps, modifications will be initiated by March 31, 1991.

.These modifications vill be prioritized and factored into our long term

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ql' planning.

The' renair.ing safety related equipment will be reviewed for potential modifications during the next biennial procedure review cycle.

3. Fuse holders will be inspected during regular equipment maintenance, and l worn fuse helders will be replaced when allowed by plant conditions.

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' Please contact us if you have any questions related to our investigation of fuse holder degradation or the? planned corrective actions.

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i Thomas M: Parker Manager L

Nuclear Support Services

. c.: IBr'ent' Clayton,. Region 'III, NRC_.

jRegional; Administrator III.- NRC

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_ Senior. Resident Inspector NRC' NRR Project Manager, NRC

'C Charnoff'

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