ML20009B958

LER 81-007/01T-0:on 810626,during Normal Operation,Unit Tripped from Approx 80% Power Due to Loss of Instrument Bus. Caused by Performance of Backfitting Mods.Plant Contractors Reinstructed

ML20009B958
Person / Time
Site:	Point Beach
Issue date:	07/10/1981
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20009B957	List: ML20009B956 ML20009B958
References
LER-81-007-01T, LER-81-7-1T, NUDOCS 8107200080
Download: ML20009B958 (1)

Text

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NRC F ORM 366 U. S. NUCLE AR REGUL ATORY COMMISSION 177 H LICENSEE EVENT REPORT CONTROL BLOCK: l i

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7 8 60 61 DOCKET NUMBER 68 6') EVENT DATE 74 75 REPORT D ATE HQ EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h FOI2: I At 1316 hours0.0152 days <br />0.366 hours <br />0.00218 weeks <br />5.00738e-4 months <br /> on 06-26-81 Unit 1 tripped from approximately 80% power l lo l3i l due to the loss of power to the red instrument bus. The trip was l

o l4 l l induced due to the effect of the power loss on both protective and l iol3l l control systems. An additional result of the loss of power was the loss l l o l3 l l of IPT-945, Unit 1 containment pressure. The loss of this channel for 1 lO17ll less than one minute reduced the degree of redundancy to zero and is l 10181I reportable in accordance with T. S. 15.6.9.2.A.2. l C DE COOE SUSC E COMPONENT CODE St,8 CODE SU E lTJT]

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42 43 4; CAUSE DESCRIPTION AND CORRECTIVE ACTIONS l i l 0 l l The cause of the lost bus was attributed to a contractar employee per- I i i l forniing backfitting modifications required to meet new re ctul a to ry I

,, , g l requiremen ts . The contractor was working in the immediate area and i 11l3l l accidentally interrupted the bus power supply. The bus was immediatelvl i 4 l transferred to its alternate supply and the recove ry from the trip was l 7 8 9 normal . 86

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'ST A S  %;WE R OTHER STATUS ISCO RY DISCOVERY DESCRIPTION i 5 l E l@ l 0 l 8 l 0 l@l N/A l l_A_j@l Operator obse rvation l A TIVITY CO TENT RELE ASED OF RELEASE AMOUNT OF ACTivf TY LOCATION OF RELEASE 1 6 @ [ Zj@l N/A l lN/A l 7 8 9 to is 44 45 80 PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION i 7 l 0 l 0 l 0 l@[_Z_j@l N/A i l

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ATTACHMENT TO LICENSEE EVENT REPORT NO. 81-007/0lT-0 Wisconsin Electric Power Company Point Beach Nuclear Plant Unit 1 Docket No. 50-266 During normal operation, at 1316 hours0.0152 days <br />0.366 hours <br />0.00218 weeks <br />5.00738e-4 months <br /> on June 26, 1981, Unit 1 tripped from approximately 80% power due to the loss of the red instrument bus. The trip was induced due to the effect of the lost instrument bus on both protective and control systems. An additional result of the lost bus was the loss of 1PT-945, Unit 1 containment pressure. The loss of this channel for less than one minute reduced the degree of redundancy required by Technical Specification 15.3.5-3 to zero. Both sets of containment spray logic were operable at all times; one with 3 of 2, one with 2 of 3 channels available . This event of lost redundancy is reportable in accordance with Technical Specification 15.6.9.2. A.2.

The cause of the loss of power to the bus was attributed to a contractor employee performing backfitting modifications required to meet new regulatory requirements. The contractor was working in the imrediate area and accidentally opened the disconnect switch on the red bus inverter and interrupted the instrument bus power supply. The bus was immediately transferred to its alternate supply by control room operators.

The momentary power loss to the red bus caused a steam generator feed regulator valve to shut and a trip on feed flow / steam flow mismatch in coincidence with low steam generator level. All systems functioned normal af ter the trip and the unit was placed back on line approximately three hours later at 1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br />.

Plant contractors have been reinstructed to use extreme caution while working in sensitive and safety-related areas in the plant. Point Beach employee surveillance of contractors will be increased to help prevent occurrences of this type in the future.