05000272/LER-1976-004, Supplemental LER 76-004/03L:on 760902,during Transfer of 1A Vital Instrument Bus to Alternate Power source,1RH2 Closed,Resulting in Loss of RHR Flow to Rcs.Caused by tagged-open Supply Breakers

Supplemental LER 76-004/03L:on 760902,during Transfer of 1A Vital Instrument Bus to Alternate Power source,1RH2 Closed,Resulting in Loss of RHR Flow to Rcs.Caused by tagged-open Supply Breakers

ML20086B810
Person / Time
Site:	Salem
Issue date:	01/28/1977
From:	Schneider F, Spencer T Public Service Enterprise Group
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20086B813	List: 05000272/LER-1976-004, Supplemental LER 76-004/03L:on 760902,during Transfer of 1A Vital Instrument Bus to Alternate Power source,1RH2 Closed,Resulting in Loss of RHR Flow to Rcs.Caused by tagged-open Supply Breakers
References
LER-76-004-03L, LER-76-4-3L, NUDOCS 8311210429
Download: ML20086B810 (4)

LER-2076-004, Supplemental LER 76-004/03L:on 760902,during Transfer of 1A Vital Instrument Bus to Alternate Power source,1RH2 Closed,Resulting in Loss of RHR Flow to Rcs.Caused by tagged-open Supply Breakers

Event date:
Report date:
2722076004R00 - NRC Website

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SUPPLEMENTAL REPORT TO

- *- LER 76-04/3L - 9/15/76 LICENSEE EVENT RE CoNrpoL atocx l I I I I I I i e .

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l O l 01 -10101010101 -101oQ) .Tsl4111111111Jo 01 9 14 15 EVENT oATE REpomfoAtt CATEGoRv P Ou E oOCKET NUMSER

{ccN r Q g ljl 5101-l 012! 712} s 0191012171 101112181717J EVENT DESCRIPTION o7 l During Mode 6 operation, RHR System in service. the 1A Vital Instrtment l ao 7 ss a3 [ Bus t as being transferred to an alternate source of power to allow ao I

7 as gl the 1A Vital Instrument Bus Inverter to be deenergized. During the so 1

7 as g j lA Vital Instrument Bus transfer, 1RH2 closed resulting in a loss of ao I

7 es g ; RHR flow to the RCS. No redundant system was available during this I esI:'s" %?a" com.oMeNrcaos "fu a a u.fu",7cYu"n's = vios.arioN o7 MB_J LEl 7 A3 io a4 12 12 12 12 I2 12 I 12 17 LIf 4

INIoIoIoI 44 47 Wed CAUSE DESCRIPTION fois l The 115 VAC vital instrument busses are nomn11v bd thronch ebf r -

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7 89 l associated inverters. These inverters are equipped with automatic So l

81 load transfer switches which transfer the load to the backup power I 7 89 N

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PERSONNEL EXPOSURES NuMSE A TYPE otsCAl8TfoM Qis101010i L7J l N/A I 7 d9 at 12 13 ao PERSONNEL INJURIES NuM9(R otScalpfloN E os1010101u 7.

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cre$lfs :cNSEcutNcES i l N/A I n'15is sa LOSS OR DA84 AGE TO FACILITY tves oascnierioN s Z l N/A I

e 10 au PUBLICITY 17l M/A l 7 as ao AOof floNAL F ACTORS 31 7 as Supolemental Reoort to 76-04/3L

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,, l EVENT DESCRIPTION & CAUSE DESCRIPTION (Continued on Page 2) l 7 89 So l NAwE: T. I;. Spencer ,ucu,; ( 6 09 ) 3 65'-7000 Ext. Salem- 52 khD S

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9 9 Pagi 2 EVENT DESCRIPTION (Continued) occurrence. Corrective action for this event was to establish administrative controls as follows:

A. When operating at or below 10% reactor power:

i

1. Will not allow maintenance or calibration of the 1A-lD inverters.

B. When operating above 10% reactor power:

1. Will not transfer 1D Vital Instrument Bus as a reactor trip signal will result due to the " General Warning" trip in the SSPS.

i C. At any reactor power level, will not transfer any vital bus if another protective channel bistable is in a tripped condition since the protective -

logic for the function would then be complete.

This is the first occurrence of this type (76-04/3L).

CAUSE DESCRIPTION (Contioned) source only when both the inverter output voltage and current are zero (0).

However, due to NRC requirements, the supply breakers for the backup source for the vital instrument busses must be tagged open.

PROBLEMS:

A. When transferring the 1A vital instrument bus to back-up power, 1RH2 valve closes due to an arroneous HIGH pressure signal caused by an 8-cycle (approx.)

loss of voltage during the transfer. Also, a P-7 reactor trip signal is '

generated if the reactor is below 10% power due to de-energization of turbine first stage pressure bistables.

B. When transferring the 1B vital instrument bus, the loss of voltage due to the switching causes the 1RH1 valve to close, also, one source range channel is lost, resulting in a reactor trip signal "HIGH neutron flux-source-range."

C. When transferring the 1C vital instrument bus, the Reactor Protection Channel III trips, initiating a P-10 permissive and a resultant de-energization of both No. 31 and 32 source range channels, -

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LicinzaEvantReporth04/3L O Page 3 CAUSE DESCRIPTION (Continued)

ANALYSIS OF PROBLEMS:

On September 23, 1976, a test was made on the 1A vital instrument bus. transfer switch. It was shown that there exists an 8 1/2 - 9 cycle loss of voltage from the instant the 1A inverter's output breaker was opened to the time the transfer switch's contacts closed on the backup supply. After investigation, it is apparent that modification of the transfer switch to obtain a minimal loss of voltage period is not feasible. Because of the 1-2 millisecond operating time of the bistable comparators used in the protection racks, even the 1/4 cycle transfer time of static switches would still trip these bistables. Therefore, administrative control is necessary to minimize the impact of vital instrument bua transfers on the plant.

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, i l FradIrick W. Sch.1 eider Public Service Electnc and Gas Company 80 Park Piace Newark. N J 07101 201/622-7000 Vice President Production i.

February 17, 1977 15,MW '

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Mr. James P. O'Reilly e m i O g[

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Director of USNRC Wg 7 n Office of Inspections and Enforcements l.#'e ' [t Region 1  ;., u.53P,g gjggg p[' f.'y 631 Park Avenue ,, ti/ \

King of Prussia, Pennsylvania 19406 N Qi s CV N L41 We wt./

Dear Mr. O'Reilly:

LICENSE NO. DPR-70 DOCKET NO. 50-272 REPORTABLE OCCURRENCE 76-04/3L SUPPLEMENTAL REPORT Pursuant to the requirements of Salem Generating Station Unit No. 1 Technical Specifications, Section 6.9.1, we are submitting a Supplemental Report to 76-04/3L dated 9/15/76.

Sincerely yours, CC: Director, Office of Inspection and Enforcement (30 copies) 207G Director, Office of Management Information and Program Control (3 copies) l l

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