ML20052E262

Final Significant Deficiency Rept Re Potential for Loss of All Auxiliary Feedwater Following Small Steam Line Rupture Referenced in 801120 Ltr.Evaluation Determined That Deficiency Does Not Exist

ML20052E262
Person / Time
Site:	Millstone
Issue date:	04/26/1982
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
To:	Haynes R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
10CFR-050.55E, 10CFR-50.55E, AEC-MP3-271, B10490, NUDOCS 8205100251
Download: ML20052E262 (2)

Text

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E RECEWED( - April 26, 1982 c ..- -

I D }$N I k DOCKET No. 50-423

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Y 'A AEC-MP3-271 B10490 j

% l og \ h Mr. Ronald C. Haynes Regional Administrator Region 1 Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 10406

Reference:

(1) W. G. Counsil letter to B. H. Grier, Reportin;;

of Deficiencies in Design and Construction, dated November 20, 1980.

Gentlemen:

MILLSTONE NUCLEAR POWER STATION UNIT No. 3 FINAL REPORT ON A REPORTED POTENTIAL SIGNIFICANT DEFICIENCY CONCERNING THE POTENTIAL FOR LOSS OF ALL AUXILIARY FEEDWATER FOLLOWING A SMALL STEAM LINE RUPTURE As required by Title 10, Code of Federal Regulations Part 50, Paragraph 55 (e), Northeast Nuclear Energy Company (NNECO) reported a potential significant deficiency in the design of Millstone Unit No. 3 in Reference (1). As described in our letter, NNECO had been notified by Westinghouse Electric Corporation of a potential for blowing down more than one steam generator in the event of a pipe break in the steam supply line to the turbine-driven auxiliary feedwater pump. If the operator was unable to isolate the uncontrolled blowdown because of the adverse environment at the location of the isolation valve controller or due to a malfunction of the controller, all three steam generators that supply the header

, would depressurize. The loss of the turbine-driven auxiliary feedwater pump, due to the loss of the stcam supply line, would result in the motor-driven auxiliary feedwater pumps delivering against a back pressure corresponding to that of the blowdown steam generators. Thus, the motor-driven pumps could runout and trip due to hi.gh electrical loads.

After a detailed evaluation by Northeast Utilities Service Company, it has been determined that a potential significent deficiency does not exist for reasons stated below.

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o The Millstone Unit No. 3 design provides a normally closed valve in each of the steam supply lines from the steam genera-tors. These valves are located upstream of the common steam supply header to the turbine driven auxiliary feedwater pump.

Therefore, the common supply header is not subject to the failure described in Reference (1). Additionally an augmented inservice inspection program has been implemented for that portion of the individual steam supply lines normally pressur-ized between the containment and the above described isolation valves so these lines are not subject to the failure described in Reference (1) .

o The turbine driven auxiliary feedwater pump is required to operate when a motor driven auxiliary feedwater pump has failed. Since this failure is assumed to be the single active failure, a passive failure in the steam header piping is not postulated for short-term operation (less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />).

After 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> the plant will be in a cold shutdoen condition that would not require auxiliary feedwater, therefore, a passive failure of the steam header in the long term would not affect the ability of operators to maintain the plant in a safe condition.

The above report constitutes our final disposition of the reported significant deficiency in question. We trust it adequately discusses any concerns you may have had on the subject.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY l l Of142.dd W. G. Counsil l

Senior Vice President l

l l

l cc: Mr. James H. Sniezek, Director l Divison of Resident and Regional l Reactor Inspection i Office of Inspection and Enforcement l U. S. Nuclear Regulatory Commission l Washington, DC 20555 i

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