ML20010E776

Forwards LER 81-015/01T-0.Detailed Event Analysis Encl

ML20010E776
Person / Time
Site:	Oconee
Issue date:	08/25/1981
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20010E777	List: ML20010E776 ML20010E778
References
NUDOCS 8109080249
Download: ML20010E776 (4)

Text

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422 SouTn' Cnuncu STasr.T, CnAHtDTTE, N. C. coa 4a WILLIAM O. PA R M E R. J R. .

[. } ' ' ' j\ e ! I Vict Patsiotiev 7ttsp oeit: Anta 704 srt. paoevevio,. August 25, 1981 373..o.3 Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission

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f A- 4.I, Atlanta, Georgia 30303 -s U O I 19 Re: Oconee Nuclear Station Docket No. 50-269 v.,'Ag D, 3#4A i '

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Dear Mr. O'Reilly:

NCo' pro Please find attached Reportable Occurrence Report R0-269/81-15. This report is submitted pursuant to Oconee Nuclear Station Technical Specification 6.6.2.1.a(8), which concerns analyses errors which could have permitted reactor operation in a manner less conservative than assumed in the Safety Analysis Report or Technical Specification bases, and describes an incident w ich is considered to be of no significance with respect to its effect on the health and safety of the public.

Very truly yours, C7:

A Cv a.

William O. Parker, Jr

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JFK:Is Attachment l cc: . Director Mr. Bill Lavallee

! Office of Management & Program Analysis Nuclear Safety Analysis Center.

l U. S. Nuclear Regulatory Commission P. O. Box 10412 4 Washington, D. C. 20555 Palo Alto, California 94303 Mr. F. Jape Resident Inspector 1

Oconee Nuclear Station Jh% <

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8109080249 810825 PDR ADOCK 05000269 S PDR 1

'. '. DUKE POWER CO.MPANY , ,

OCONEE NUCLEAR STATION -

Report Number: RO-269/81-15 Report Date: August 25, 1981 Occurrence Date: August 11, 1981 Facility: Oconee Nuclear Station, Seneca, South Carolina Identification of Occurrence: Non-conservative Reactor Protection System instrument string errors Conditions Prior to Occurrence: Oconee 1 - Cold Shutdown Oconee 2 - 100% FP Oconee 3 - 100% FP Description of Occurrence: The NSSS vendor for Oconee (Babcock & Wilcox) indicated that, during a requalification program for the Reactor Protection System (RPS) instrumentation, it discovered that the then-current RPS instrument string errors might be non-conservative for some of the instrument strings. This incident constitutes an error in the methods used for transient and accident analyses and is thus reportable pursuant to Technical Specification 6.6.2.1.a. (8) .

Apparent Cause of Occurrence: A change in the instrument string error analysis procedure to use a more rigorous qualification standard.

Analysis of Occurrence: Beginning in 1979 Babcock & Wilcox began an RPS instrument module requalification conforming to the'IEEE standard 323-1971. Most of the equipmenc presented in BAW-10003, " Qualification Testing of Protection System Instrumentation", the licensing basis for Oconee, was still qualified and trace-able under this program and conformed to the accuracy specifications. However, some of the modules were found to have module errors larger than the originally calculated values.

The effect of these larger module errors on the RPS string error was re-evaluated for the individual RPS trip functions using a conservative error combination methodology (algebraic sum of all worst case individual module errors). The results of this re-evaluation confirmed that a reduction in the high flux trip setpoint from 105.5% FP to 104.9% FP, a reduction in the RCS outlet temperature trip setpoint from 619 F to 6180F, and certain changes in the flux-flow imbalance trip setpoint analysis, would conservatively account for these larger module errors. Further analysis ,

confirmed the present RPS power imbalance flow trip setpoints on Oconee 1 and 2 to be conservative through the end of the current cycle on each unit. The corresponding setpoints on Oconee 3 were determined to be conservative at 1r ast through 200 EFPD of the current cycle. The re-evaluation also determined new setpoints for the power imbalance flow trip string to account for the new string errors. These revised set-i points are shown in the attached figure. Due to the conservative nature of the string error calculations, no Oconee unit was operated in an unsafe condition and it has been concluded that this incident did not affect the health and safety of the public.

Corrective Action: It was determined that setpoint changes are necessary in three RPS trip strings:

(1) Overpower (2) High temperature (3) Power Imbalance Flow RPS overpower and high temperature trip setpoints on Oconee 2 and 3 will be adjusted to meet the new values by September 15, 1981. The power imbalance flow setpoints for Oconee 3 will be adjusted in accordance with the new limits by 200 EFPD (approximately October 1,1981). The upcoming reload setpoints for Oconee 1 and 2 will reflect the new RPS string errors.

4

THERMAL POWER LEVEL, 5

-- 10 (13,108.0)

(-8.0,108.0)

! I 100 M3 = .9032 l g2 = -1.864 CCEPTABLE l 4 PUMP OPERATION -- 90 l g (24,87.5)

(-39,80.0) (-8,80.8) _

(13,80.6) l I

~ ~ 80

' g l I .3 I UNACCEPTABLE I'

l CCEPTABLE ~~ 70 l OPERATION UNACCEPTABLE 3&4 PUMP l l DPERATION l OPERATION -

60 1 (24,60.1) '

l l I

(-39,52.6) (-8,52.9) . 1(13,52.9) l l -- 50 g l l I l CCEPTABLE I '

l 2,3&4 PbMP -- 40 l l

l OPERATION l

(24,32.4) 1 -- 30 l

(-39.24.9) l I I I

e l e l -- 20 go ,

jo, dI i ! 12 l%

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I -- 10 I) l+ .

Il e  ; el . ", * ,

-40 -30 -20 -10 0 10 20 30 40 s

Power localance, %

2.3-10 PROTECTIVE SYSTEM MAXiMU.'.1 ALLOWASLE SETPGINTS UNIT 3 OCONEE NUCLEAR STATICN Figure 2.3 2C