ML20212P609

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Forwards Clarification of Item 5 in Attachment 2 of Re Pressurizer heaters-repeated Open/Close of Breakers, Per NRC 870226 Request.Actions Consistent W/Procedures to Abandon Breaker as Out of Svc on Failure to Reset
ML20212P609
Person / Time
Site: Rancho Seco
Issue date: 02/26/1987
From: Julie Ward
SACRAMENTO MUNICIPAL UTILITY DISTRICT
To: Miraglia F
Office of Nuclear Reactor Regulation
References
JEW-87-316, NUDOCS 8703160168
Download: ML20212P609 (2)


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'uj pa SACRAMENTO MUNICIPAL UTILITY DISTRICT O P. O. Box 15830, Sacramento CA 95852-1830,(9 6) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA February 26, 1987 JEW 87-316

  • Director of Nuclear Reactor Regulation Attn: Frank J. Miraglia, Jr.

Division of PWR Licensing-B U. S. Nuclear Regulatory Consnission Washington, D. C. 20S$5 Docket No. 50-312 Rancho Seco Nuclear Generating Station License No. DPR-54 PRESSURIZER HEATERS - REPEATED OPEN/CLOSE OF THE BREAKERS

Dear Mr. Miraglia:

In the District's letter of February 24, 1981, Attachment 2 contained several items for which the District would provide further clarification prior to restart. This commitment was agreed to by members on both of our staffs during a NRC/SMUD meeting held in Bethesda on february 20, 1987.

The District responded to item 4 via the B&W analysis that was included in Attachment 3 of the february 24 letter. On February 26, your staff requested the District respond as soon as possible to item 5 concerning

" clarification on the repeated open/close of the breakers" and the number of times the breakers were operated.

1he attachment to this letter provides the clarification to the breaker question. In suninary, the District's investigation of the event revealed that between 0440 hours0.00509 days <br />0.122 hours <br />7.275132e-4 weeks <br />1.6742e-4 months <br /> and 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> several heater breaker trips were experienced and an attempt to reset each breaker was made once, as permitted by procedure. The above conclusion supports the District's response to question 13 contained in the february 26 letter.

If you have any questions please contact Ray Ashley, the Manager of Nuclear Licensing, at (916) 452-3211, extension 4475.

Sincerely,

/ .

/ /

' JD n E. Ward Deputy General Manager, Nuclear Attachment cc: S. Miner, NRC, Bethesda s A. D'Angelo, NRC, Rancho Seco co' 0703160168 B70226 hs PDR ADOCK 05000312 \

P PDR RANCHO SECO NUCLEAn GENERATING STATION L 14440 Twin Cities Road. Herald, CA 95638 9799;(209) 333 2935

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ATTACHMENT Item 5 from Attachment 2 of the District's February 24, 1987 letter:

" Provide clarification on the repeated open/close of the breakers. How many times were the breakers operated?"

Clarification: The electrical distribution of the pressurizer heater is, in simplified form, as follows: The three-level bus feeds a motor control center (NCC) through a feeder breaker. The MCC contains a number of breakers,'each controlling three heater elements. The failure of a heater element will result in an alarm on the feeder breaker annunciator. Thus, all of the tripped MCC breakers appeared on a single annunciator.

During the event, the annunciator for the feeder breaker came in several times. Each time was investigated by Operations personnel. Each alarm was caused by a different MCC Breaker trip although it was on the same annunciator. The auxiliary operator responded properly by going to the MCC and observing which breaker had tripped, attempting one reset, then leaving the MCC breaker in a tripped position when it failed to reset. During the event, this sequence was repeated until eleven out of thirteen groups in the upper heater bundle had failed.

These actions were consistent with procedures and operational guidance to attempt one reclosure on a tripped breaker, and upon failure to reset, abandon the breaker as out of service.

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