ML19031B193
| ML19031B193 | |
| Person / Time | |
|---|---|
| Site: | Salem  (DPR-070, DPR-075) |
| Issue date: | 06/02/1976 |
| From: | Schwalje E Public Service Electric & Gas Co |
| To: | O'Reilly J NRC/IE, NRC Region 1 |
| References | |
| Download: ML19031B193 (4) | |
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. Public Service Electric and Gas Company 80 Park Place Newark, N.J. 07101 Phone 201 /622-7000 Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region 1 6_31 Park Avenue King of Prussia, Pennsylvania 19406
Dear Mr. O'Reilly:
- June 2, 1976 AUTOMATIC TRANSFER OF NO. l AND 2 UNITS 4KV OUTSIDE FEED.
STATION - 5'°'d-d-Z0//
SALEM NUCLEAR GENERATING
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On May 12, 1976 a verbal report was made to Region l, Office of Inspection and Enforcement advising that an unsatisfactory condition was discovered in the relay logic associated with the automatic transfer of ~ital feeds during the loss of fl exte~nal power.
This report was in accordance with the provisions of 10CFR50.55(e).
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The following is a detailed analysis and report on the subject:
DESCRIPTION OF DEFICIENCY The vital bus infeed breaker interlocks were described to the NRC in response to their question 8.6.
This response stated, the conditions which must exist in order to transfer a vital bus from its normal source to the alternate source.
In the course of reviewing settings for the relays which inititiate bus transfer and those which provide undervoltage signals to _
the Safeguards.Emergency Controls System, a condition was dis~
covered which could result in a requirement for operator action to assure that vital bus loads would sequence onto the bus.
The design criteria require fully automatic action to initiate bus transfer, to provide "blackout" signals to the SEC.
system~
and to proceed with vital bus load sequencing *.
ANALYSIS OF SAFETY IMPLICATIONS The condition which was discovered is described pelow and shown on the attached control schematic.
The Energy People 9~2001 (400M) 5*73
Mr. J. P. O'Reilly 6/2/76 ANALYSIS OF SAFETY IMPLICATIONS (Continued)
The design for vital bus transfer incorporates three rela-ys designated 27-ll, 27-12 and 83-l.
The "27" relays monitor voltage on the secondary side of Nos. ll and 12 station power transformers respectively, and the 83-1 relay monitors vital bus voltage.
If an undervoltage condition were to occur, the 83-1 relay acts to initiate a bus transfer to the transformer
- Which has not lost voltage (as determined by the "27" relays.)
This attempt to transfer is allowed prior to another relay operation which sends a vital bus undervoltage signal to all three SEC units.
The relay used for that purpose is designated 27-l and is properly coordinated with the 83-1 relay to assure that a transfer is* attempted before a blackout signal is generated.
During a postulated blackout or LOCA coincident with a blackout, the design is such that the attempted transfer would not occur and the 27-1 relay would initiate a blackout signal in the SEC units.
'The SEC, in turn, would maintain a 5 second trip signal to both bus breakers which.supply normal offsite power to the bus from the station pow~r transf-0rmers.
Since the diesel-generator breaker would be closed in another 5 seconds, a 5 second period exists during which a bus trapsfer could occur if an unlikely restoration of outside power to one station power transformer were to occur.
If one of the station power transformers were to be re-energi~ed in this specific 5 second interval, the bus breaker would close to energize the vital bus.
Such a breaker closure would then prevent closure of the diesel-generator breaker and the sequen-cing of safety loads onto the bus.
This would occur on all three vital buses and would result in a loss of all bus load sequencing.
The sequencing could be restored if the operator were to trip any breaker which closed because of the automatic transfer cir-cuits or if the 13KV breaker supplying power to the transformer were tripped.
This action would allow the diesel-generator breaker to close and the load sequence to continue.
Even thoug~ ttie conditions which will aciivate the transfer circuits and subsequent reclosing of an offsite power source within this 5 second period are considered to be highly unlikely, it would require operator action in order to continue with the automatic loading sequence.
This is unacceptable and not in accordance with our commitment.
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Mr. J. P. O'Reilly 6/2/76 CORRECTIVE ACTION The circuitry for automatic bus transfer has been redesigned to.
eliminate the possibility of a transfer any time the 27-1 relays indicate that diesel-generator loading should be initiated.
The attached control schematics show that the 27-1 relay will lock-out the automatic transfer capability when required to do so and provide adequate protection against the unacceptable condition described above.
The hardware and wiring changes will be completed by July 15, 1976.
Should you require additional information our engineers will be available to discuss the details with you.
.CC:
Dr. Ernest Volgenau Bethesda, Md.
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E. N. *-schwal.]e Manager of Quality Assurance Engineering and Construction Department
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