IR 05000341/1987042

Discusses 870923-24 Meetings Between Electrical Sys Branch & Licensee Re LPCI Swing Bus Design Deficiency Revealed by 870908 Operator Error.Nrr Finds Licensee Design Changes Acceptable,Affirming Conclusions of Insp Rept 50-341/87-42

ML20236Q593
Person / Time
Site:	Fermi
Issue date:	11/16/1987
From:	Stefano J Office of Nuclear Reactor Regulation
To:	Greenman E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
TAC-65603, NUDOCS 8711200159
Download: ML20236Q593 (4)

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E UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555

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Docket No. 50-341 MEMORANDUM FOR: Edward G. Greenman, Deputy Director Division of Reactor Projects Region III THRU: Martin J. Virgilio, Director LP Project Directorate III-I ]' \ b Division of Reactor Projects - III, IV, j

& Special Projects i Office of Nuclear Reactor Regulation {

FROM: John J. Stefano, Project Manager Project Directorate 111-1 i Division of Reactor Projects - III, IV, V

& Special Projects Office of Nuclear Reactor Regulation j SUBJECT:

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l ACCEPTABILITYOFLPCISWINGBUS(72CF) REDESIGN (TAC NO. 65603)

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l On Seatember 23 and 24, Messers S. Rhow and D. Tondi (Electrical Systems

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I Branc1, NRR) met the licensee (Detroit Edison Company) at the plant site to discuss the LPCI " swing Bus" design deficiency that was revealed as a result of an operator error. On September 8,1987, a reactor operator mistakenly opened a de distribution circuit breaker (2PA2-14 Pos.2) which provides de control j

power to the 72C 480 Volt bus and the 72C-3C breaker. The operator's action i resulted in a loss of power to the 72C-F swing bus which provides l Low Pressure Coolant Injection (LPCI) motor ope' rated valves (MOVs) power to all

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This event was reportable pursuant to 10 CFR 50.72/.73 since the event placed the plant beyond the analyzed conditions for the design base of Fermi-2. The event involved a LOCA coincident with a LOOP where a single failure of loss of one division of de occurs. The previously analyzed LOCA and LOOP with a loss of one division of the de system did not correctly consider the response of i motor control center MCC 72CF and its associated feeder breakers. The analysis for the loss of de systems included the loss of one division of redundant *

equipment but did not identify that the loss of MCC 72CF would result in loss of LPCI MOVs fed from the MCC 72CF with consequent loss of capability for all four LPCI pumps to inject water, given a large LOC MCC 72 CF is configured as a swing bus at Fermi-2 and is fed from the Division 1 480-volt 72C bus as the normal supply as depicted in Figure 1 attached. In the event of a loss of Division I voltage, the swing bus 72 CF transfers to the Division II 480-volt 72F bus, .its alternate supply. The event that-occurred, a loss of de control power to the 72C bus and 72C-3C breaker, prevented the transfer of the swing bus 72CF to the alternate power suppl CONTACT: J. Stefano', NRR PDR ADOCK 05000341  ;

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-2-k At the September 23 meeting, the licensee presented a proposed design change, which added a magnetic contactor (dc control) in series with the br.eaker (de control) and the existing magnetic contactor of each power feed to the MCC  !

72CF. This new magnetic contactor and its auxiliary contacts replace the  !

interlock contact functions of the de conu olled focdcr circuit breaker used in the opposite feeder breaker control and provides an effective double break ,

scheme (isolation devices to satisfy the single failure criterion) between i redundant divisions necessary when either Division I or Division 11 bus is l connected to the MCC 72C l l

The loss of de control power to the preferred feed will cause both contactors 1 on that feed to be de-energized allowing the transfer to the alternate (standby) )

feeder to re-energized swing bus MCC 72CF. On September 8, 1987, the l preferred feeder breaker remained closed and its auxiliary "b" contact l prevented transfer to the alternate feed. The redesign discussed at the  !

meeting also added an "80" relay to monitor the de power to the nomal feeder l breaker and magnetic contactor to provide an interlock to the alternate feeder control circuit to allow its closing and to also allow a second closing (reclosing) of the alternate feed breaker should LOOP in Division II occur after the transfer to Division I A partial loss of de, specifically loss of de power to the 72C bus Load i Shedding String, was also a concern as the 480V bus load shed string lacked redundancy to open the preferred feeder breaker. To address this concern, your staff also proposed to add a redundant under-voltage relay to trip this

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i breaker and thus ensure transfer of the swing bus MCC 72CF in the event of LOCA and LOOP and a single failure, i.e., partial loss of de control power to the load shed string onl During the September 23-24 meeting we discussed the need to demonstrate by l testing that the modified design functions as intended. Your staff agreed that  ;

the tests would be conducted prior to plant restart from the then maintenance outage. Operating procedures and procedures for surveillance and testing, as required by the Technical Specifications, would also be available prior to plant restart, and the operators would be trained to understand the revised design. We emphasized the importance of the protective relaying coordination, since miscoordination of the protective relaying trips could cause the upstream breaker to open on swing bus fault and result in loss of the two Core Spray pumps (CS) and LPCI injection, since such an event would violate the single failure criterion for ECC W.S. Orser's letter to the Commission dated October 8, 1987, submitting Licensee Event Report No.87-045, documented the corrective actions discussed with the staff at the September 23-24, 1987 meeting, and addresses all of the actions considered necessary to preclude recurrence of a similar even Therefore, we find that the electrical system design changes proposed will adeouately correct the single failure concern that was revealed as a result of the September 8, 1987, event and that the plant LPCI swing bus as redesigned will satisfy the licensing design basi ..,i)

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'E.'Greenman~ -3- November.16, 1987-The' Region III~ report of the LPCI Swing' Bus Design deficiency, and planned

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followup to verify. implementation of the redesign, is addressed in Inspection 1 Report No. 50-341/87-42 transmitted to the licensee by,. letter dated October 13, !

1987. This memo serves to affirm the regional inspectors' findings'and, conclusions documented in that. repor a Onginal signed by John J. Stefano, Project Manager- 1 Project Directorate III-I .

Division of Reactor Projects - III IV,' V-

& Special Projects Attachment: As stated cc: F. Rosa D. Tondi S. Rhow-W. Rogers, SRI Fermi DISTRIBUTION iDocket111ed

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