ML20207K077

Forwards Request for Addl Info Re Vessel Pressurizer Heater Failures.Use of Encl Request as Agenda for 870108 Site Meeting to Discuss Heater Failures Suggested

ML20207K077
Person / Time
Site:	Rancho Seco
Issue date:	12/31/1986
From:	Stolz J Office of Nuclear Reactor Regulation
To:	Julie Ward SACRAMENTO MUNICIPAL UTILITY DISTRICT
References
NUDOCS 8701090220
Download: ML20207K077 (6)

Text

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ocket No. 50-312 December 31, 1986 Mr. John E. Ward l Sacramento Municipal Utility District Rancho Seco Nuclear Generating Station l Post Office Box 15830, Mail Stop No. 291 Sacramento, California 95852-1830

SUBJECT:

REQUEST FOR ADDITIONAL INFOPMATION - PRESSURIZER HEATER i FAILURES AT RANCHO SEC0 NUCLEAR GENERATING STATION I We have been reviewing the recent pressurizer heater failures at Rancho Seco and find that we require additional information before we can complete the review. The information we recuire is outlined in the enclosure.

As you are aware, a meeting has been scheduled for .lanuary 8, 1986 at Rancho Seco to discuss the heater failures. We sugoest that the reouest for additional information be used as an agenda for the meeting and that verbal responses to each ouestion be provided to the NRC staff at the meetina. The schedule for providing written responses to the request for additional information can be established at the meeting.

The reportina and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.

Sincerely,

/S/

John F. Sto17 Director l PWR Proiect Directorate #6 i Division of PWR Licensing-B

Enclosure:

Request for Additional Information cc w/ enclosure:

See next page Distribution:

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((1090220 861231ADOCK 05000312 p

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l Mr. John E. Ward Rancho Seco Nuclear Generatino ,

Sacramento Municipal Utility District Station  !

cc:

Mr. David S. Kaplan, Secretary Sacramento County and General Counsel Board of Supervisors Sacramento Municipal Utility 827 7th Street, Poom 424 District Sacramento, California 95814 6201 S Street P. O. Box 15830 Ms. Helen Hubbard Sacramento, California 95813 P. O. Rox 63 Sunol, California 94586 i Thomas A. Baxter, Esq.

Shaw, Pittman, Potts & Trowbridge l 2300 N Street, N.W. -

Washinoton, D.C. 20037 l

Mr. Ron Columbo Sacramento Municipal Utility District Pancho Seco Nuclear Generating Station 4440 Twin Cities Road Herald, California 95638-9799 i Vr. Robert B. Borsum Babcock f, Vilcox Nuclear Power Generation Division Saite 220, 7910 Wondmont Avenue Rettesda, Maryland 20814 Resident Inspector / Rancho Seco c/o V. S. N. R. C.

14410 Twin Cities Road i

Herald, California 95638 Regional Administrator, Region V U.S. Nuclear Reaulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Director Eneroy Facilities Siting Division Energy Resources Conservation &

Development Commission 1516 - 9th Street Sacramento, California 95814 Mr. Joseph 0. Ward, Chief Radiolooical Health Branch State Department of Health Services 1

714 P Street, Office Building #8 Sacramento, California 95814

e REQUEST FOR ADDITIONAL INFORMATION VESSEL PRESSURIZER HEATER AT RANCHO SECO

1. Describe the measured and analyzed temperature transit in the pressurizer metal and the steam water space during the event. What was the maximum temperature reached and describe its location? Were any component's design temperature reached or exceeded? What was the temperature transient on the pressurizer PORVs and SVs? Describe how any overheating of the pressurizer or its components would effect its operation including the integrity of the pressurizer itself. Describe the relevant ASME requirements and compliance with these requirements in light of exceeding the design temperature or other aspect associated with the event.

2. Based on your evaluation of the damage to the heater bundle, describe the .

damage, extent of deformation, the maximum temperature reached by the tubes and the maximum temperature reached by the pressurizer.

3. Describe your post-event inspection and subsequent evaluation of the pressurizer interior and exterior surfaces around the heater bundle including any relevant anomalies. Compare these findings to past inspections of the pressurizer sui f"es and internals.

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! 4. Describe the bundle removal process and any unusual,or unexpected diffi-

! culties, and your evaluation thereof. l 4

5. The low level interlock prevents the heaters from being energized with

-the heaters uncovered (FSAR). Where was the problem identified in the l

level indications system (level switch, transmitter, selector switch,

! temperature compensator, the bistable)?

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! 6. First the B and C channels showed a 0 reading. After venting and " fill i

j and squeeze" the readings were 18.17 inches and 18.56 inches, respectively.

J j Why were the B and C readings ignored and the selection of channel i

j remained for A-D? Both A and D should read the same level; however, the crew saw a difference between the A and 0 readings (140 inches at A j transmitter and 150 inches at B transmitter). Why did the readings I

differ?

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7. Describe the LON and why was it issued? Was this change notice properly l

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reviewed and transformed into a field change package? After the changes j were physically incorporated was there a QA/QC sign-off?

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..-_- ~ .. . -- -. - - - - - - - - . . = _ _ - _ .

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1 l 8. What is the Kw rating of each heater element? How many elements,are i

i assigned to one MCC compartment (combination starter)?

9. The FSAR mentioned a total heater load of 126Kw supplied from Class IE buses 3A and 3B. Are the heaters distributed among each o,f the three k bundles? How is separation and isolation maintained? Do both buses j share the 126Kw or is there 126Kw per division?

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10. Each penetration circuit should have two trip devices in series to meet l

the single failure criteria. When the primary breaker tripped as indicated

{ in the report, why were the heater elements overstressed, deformed, and burnt out? Circuit breaker coordination should have been such that the

] backup breakers (main MCC and/or L.C. breakers) would trip before the i

1 equipment is destroyed. Why didn't this occur?

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{ 11. Have all cables from the MCC to the heaters been checked for their i

l insulation integrity?

J l 12. Have all the associated penetrations been tested for their design capabilities and qualified life?

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13. Were the supply cables to the heaters found to be overstressed? Have

- they been evaluated for their capabilities along with the fault current i

l effect on other cables sharing the same cable tray?

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14. If the protective devices are properly coordinated, a 225 amp rating circuit breaker should provide more conservative protection for the heater than the original 600 amp rating breaker. Why didn't this conservative protection prevent destruction of the heaters?

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