ML20027B983

Advises of Immediate Need for Imposing Specific Requirements Re Operational Restrictions for Class IE 120-volt Ac Vital Instrument Buses in Operating Plants

ML20027B983
Person / Time
Site:	Oconee, Rancho Seco, 05000000
Issue date:	07/15/1980
From:	Michelson C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:	Harold Denton Office of Nuclear Reactor Regulation
References
TASK-AE, TASK-E005, TASK-E5 AEOD-E005, AEOD-E5, NUDOCS 8210120114
Download: ML20027B983 (1)

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JUL 151980 MEMORANDUM FOR:

Harold R. Denton, Director Office of Nuclear Reactor Regulation FROM:

Carlyle Michelson, Director Office for Analysis and Evaluation of Operaticaal Data

SUBJECT:

OPERATIONAL RESTRICTIONS FOR CLASS lE 120 VAC VITAL INSTRUMENT BUSES Based on a review of the enclosed licensee event reports (80-028/0IT-0 and follow-up to R0-287/80-8), it can be generally concluded that some operating nuclear power plants do not have any specific administrative controls or technical specification requirements concerning operational restrictions for their Class 1E 120 Vac vital instrument buses and associated inverters. The lack of such restrictions would allow an instrument bus or associated inverter to be taken out of service for any length of time, leaving certain safety systems that require these power supplies to perform their functions in a position of possibly not meeting the single failure criterion. Such a conclusion was reached by the licensee of Rancho Seco Nuclear Generating Station after a review of their Safety Features Actuation System (see enclosed LER 80-028/0IT-0).

AEOD is concerned that there is an intnediate need for imposing specific require-ments concerning operational restrictions for Class 1E 120 Vac vital instrument buses in operating plants. We believe that requirements of Limiting Conditions of Operation for Class 1E 120 Vac buses (similar to that in the Standard Technical Specifications) should be applied to all operating nuclear plants that do not have them.

Carlyle Michelson, Director Office for Analysis and Evaluation of Operational Data

Enclosures:

As stated cc w/ enclosures:

C. Berlinger G. Lainas D. Brinkman T. Novak D. Eisenhut F. Rosa M, Fairtile D. Ross D. Garner V. Stello E. Jordan AEOD Members CONTACT:

M. Chiramal x29560 8210120114 000715 PDR MISC p

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y (EiSMUD SACAAF. ENTO bluN10lPAL UTILITY DISTRICT Q 6201 S Street. 8om 15833. Sacramento, Califorma 95813; (916) 452 3211

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June 19, 1980 Mr. R. H. Engelken, Director Region V Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 1990 North California Boulevard Walnut Creek Plaza, Suite 202 Walnut Creek. California 94936 4

ke: Operating I.icense DPR-54 Docket No. 50-312 Aaportaole Occurrence 60-28 6

Dear Mr. Engelken:

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t In accordance with Technical Specifications for Rancho Seco Nuclear i

j Generating Station Section 6.9.4.1h, and Regulatory Guide 1.16, Revision 4, l

j Section C.2.a(8), the Sacramento Municipal Utility District is hereby.ubmitting a fourteen-day followup report to the reportable occurrence which was initially reported to Mr. J. Zwetzig of your office on June 9,1980, and by a confirmation i

letter on the sa=a day.

i A review of the Safety Features Actuation Syste (SFAS) utilized at Rancho Seco Unit 1 revealed that under specific conditions, a single failure of an inverter.could prevent the system from actuating. The STAS is organized into i

subsystems, analog containing analog instrument strings and digital containing l

SF channels. The STAS consists of three analog subsyste=s and two independent i

digital actuation subsystems. The analog subsyste=s conitor reactor coolant i

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pressure and r'encter building pre'ssure and independently provide trip signals if preset limits are reached.

Each digital actuatien subsystem contains four actuation c.hannels that use two out of three coincidence logic on the analog 4

input signals to actuate the safety features equipcent. The digital section of the system is an " energize to actuate" system, i.e.,

requires power to actuate the output device.

If the "A" inverter were taken out cf service fer caintenance and the "B" inverter failed automatic STAS initiation could not occur.

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The inverters, although seismic and quality Cisss l', have not had i

any administrative centrols concerning operationni restrictions. As a resu2t of this review, the i nediate corrective action was the issuance of an order to' l

5 all operations personnel concerning operational restrictions. The order requires

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that if inverter "A" or."B" becomes inoperable and is not returned to service i

within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the. plant vill be placed in hot shutdovn condition. Additionally, 1

since this item may hsve u.eneric applicability, it is the District's intention I

to introdur:e this ites :t a BW Owners Group meetj.n3 j

There* vere n'a plant transients nor pcwer reductions associ:ted with

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Respectfully subnitled,

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rpT) ; is supplied by Class IA inverters. However, if one inverter was out of i

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2,3..oea Mr. Jxnes P. O'Reilly, Director r

U. S. Nuclear Regulatory Commission Region II

• 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 Re: Oconee Unit 3 Docket No. 50-287

Dear Mr. O'Reilly:

My letter of June 6, 1980 transmitted Reportable Occurrence Report R0-287/80-8 to you. That report discussed a loss of power to RPS Channel B resulting from a vital inverter failure. The report indicated that since RPS Channel C was bypassed for testing, a shutdown of Unit 3 was initiated pursuant to Technical Specification 3.5.1, which requires that a minimum of three of the four RPS channels be available. The occurrence was thus believed to be reportable under Technical Specification 6.6.2.1.b(2) because the shutdown was required by a limiting condition for operation.

t Since the submittal of that report, additional information has been reviewed l

vhich clarifies the occurrence. When the power to RPS Channel B was lost, that channel tripped and thereby reduced the logic for a reactor trip from 2 out of 3 to 1 out of 2 (with Channel C in bypass). Thus, Channel B was not inoperable, as indicated by our report, since it was still capable of performing its function, and the requirements of Technical Specificacion 3.5.1 were met. The shutdown of the unit was not initiated because power was lost to RPS Channel B, but because power was alsc lost to Channel B of the analog Engineered Safeguards (ES) channels and to the even-numbered digital ES channels. At the time of the occurrence, it was not clear that all Technical Specification requirements were i

satisfied, and the decision was made to initiate a shutdown until it could be determined whether a violation existed. Upon loss of power, Channel B of the analog ES channels tripped, thereby reducing the logic for ES actuation from 2 out of 3 to 1 out of 2.

As with the RPS, this ES channel was still operable and thus Technical Specification. 3.5.1 was satisfied. Thus, commencement of power reduction was a conservative action which was not required by Technical Specifications.

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Mr. James P. O'Reilly, Director June 20, 1980 Page Two Based upon the above information, we have determined that the loss of power discussed in R0-287/80-8 does not constitute a reportable occurrence. How-ever, the remaining information contained in that report, including the cor-rective actions, is still valid and is provided only for your information.

Very truly yours, h

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William O. Parker, Jr.

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FTP:ses cc: Director Mr. Bill Lavallee Office of Management Nuclear Safety Analysis Center and Program Analysis P. O. Box 10412 U. S. Nuclear Regulatory Coc: mission Palo Alto, California 94303 Washington, D. C.

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