ML20010C877

Interim Deficiency Rept Re accident-induced Neutron Flux Errors,Originally Reported on 801029.Problem Will Be Investigated & NRC Will Be Notified of Mods.Also Reportable Per Part 21

ML20010C877
Person / Time
Site:	North Anna
Issue date:	01/08/1981
From:	Spencer W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
REF-PT21-81 1000, 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8108210156
Download: ML20010C877 (2)

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6m' 3gg [l8 j ,' q m: to Mr. James P. O'Reilly, Directer Serial No. 10C0' t, <

'Of fice of Inspection & Enforeccent PSE&C/WBR:vnl: wang O. S. truclear heculatory Cei.nission /% .ia Region II Docket Nos. 50-404 2-101 Marietta Street, Suite 3100 50-405 Atlanta, Cecrgia 30303 6

Dear Mr. O'Reilly:

On Decamoer 9,1920, a report was tr. ace under the previsions of 10CFR50.M(c) anc 10CFR21, concerning accinent induced neturen flux errors.

Tnis concern was pr::viously rescrted to Mr. Victor Stello of the NRC in a e&w letter of Octcoer 29, 1980.

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Recent stueles perfctmod by 04W for 177FA 8. 205FA plants indicate that for certain transients and accicents, a decreasing downcocer reactor coolant temperature or power distribution anocalles, will result in larger neutron flux measurement errors than assumed in previous acciocnt analyses.

The tyoe of transients and accicents of ccncern are snell cvarcoolino transients, small steam line breaks, large steam line breaks in containtmnt 6nd rco ejecticn accicents. These transients ano their potential conseceences .

are discusseo Delow: .

Saall overcooling transients and steam line breaks result in increased primary to seconcary heat transfer. This increased hest transfer lcwers the reactor coolant inlet ternerature. This lower te.ronrature causes a neutron flux neasurement error by increasing neutrcn moceration which reduces the nurNer of neutrons tm out-of-ccre cetectors wculd detect for any given power level. Since H1' flux signals are recuired to initiate reactor trip in a timely fasalon, this flur error in combination with the afcrementlened events has tne following consequenct:s as aetermineo by Sw.

(1) Flux errors exceed tncse assumeo in previous accicent ar.alyses.

l 8108210156 810108 PDR ADOCK 05000404 PDR 4[3 S

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(2) Reactor power safety limits are exceeded. Note that Reactor Power could re.ach a steady state level above the f establisned trip envelope. 4 i

(3) DNER anu KW/ft Safety limits may be excerced with possible ,

centerline fuel relt. t

' (4) For a large steam line break (205FA plants only) the i reactor builcing pressure limits ciculd be exceedec.  !

For th" tJC ejection acticent, tne concern is with reds having a relatively small worth, for this ente fB5 has postulated a lecclized positive reactivity insertion wnich tray not be larce encur,h to ce seen ny the

' out-of-core cetectors (assuming a failure of one detector) to initiste reactor trip when reouireo. Here B&W is concerned that peak fuel enthalpy acceptance

- criterion may oe exceeced.

While plant scecific analyses have not been performed for our 145FA unit, it's epparent that the accicent incuceo flux errors will te larger than those assuned in previous accicent analyses and that sinilar consecuences may be expected.

Vesco,' S&W Uic B&W will be investigating this problen in the future. The NRC will be notifleo of any modifications which are found necessary in order to eliminate this potential safety concern. ,

Very truly yours, '

- onginal S180ed DY-W. C. SPENCER W. C. Soencer Vice Presic:ent - Power Station

• Engineering and constructicn -

Tervices cc:

bc: Mr. J. H. Ferguson Mr. E. G. Lifrage Mr. J. I. Oatts Ms. P. C. Cover (2)

Pr. S. C. Brown, Jr. Mr. W. R. Cartwright H . W. C. Spencer Mr. 8. R. Sylvia Mr. W. N. Thomac Mr. J. N. Christman - H&W Mr. J. W. Waddill Mr. P. G. Perry i. ,

Mr. E. A. Baum Mr. H. J. Fortune, Jr.

Mr. W. L. Stewart Mr. E. H. Webster, NRC (N.A.)

Mr. H. B. Wessinger Mr. E. R. Smith Mr. J. McFarland - B&W Mr. W. B. Rodill Mr. J. V. Harrison .

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