ML20246F487

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Advises That 4,160-volt Breakers for Charging/Hpsi Pumps, Equipped w/anti-pumping Feature Might Inhibit auto-start of Standby Pump Under Certain Accident Conditions.Redesign of Breaker Control Circuitry Will Be Completed by 890915
ML20246F487
Person / Time
Site: Maine Yankee
Issue date: 08/23/1989
From: Whittier G
Maine Yankee
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GDW-89-273, MN-89-108, NUDOCS 8908310016
Download: ML20246F487 (2)


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MaineYankee i; EDISON DRIVE . AUGUSTA, MAINE 04330 . (207) 622-4868 August 23, 1989 MN-89-108 GDH-89-273 UNITED STATES NUCLEAR REGULATORY COMMISSION

. Attention: Document Control Desk-

/ Washington, D.LC.s 20555

References:

(a) -License No. DPR-36.(Docket No. 50-309)

Subject:

-Maine-Yankee Charging /HPSI Pump Protective Circuitry

' Gentlemen:

The'.4160V. breakers for Maine Yankee's charging /HPSI pumps are equipped

-with an anti-pumping feature that is designed to protect the breaker and pump motor in the event.of simultaneous start /stop signals on the circuit. It has recently been postulated that this feature might also inhibit auto start of the standby pump under certain accident conditions. The running charging /HPSI pump is unaffected.

~

Maine Yankee's standby charging pump'is wired to start on either low charging pump header pressure or low pressurizer level. It is also wired to trip on ;either high charging pump header pressure or high pressurizer level.

Following a. reactor trip when no accident is in progress, the charging pump header pressure can remain above 2400 psig while the pressurizer level drops due to post-trip shrink. Under these circumstances the standby charging pump is locked out by the anti-pumping feature. This lockout of the standby pump ,

has:been observed on plant trips at nominal system' operating pressure. For a j reactor trip which involves a low pressure accident condition requiring HPSI, the charging header pressure could be postulated-to remain high enough to engage' the high header pressure trip despite the simultaneous existence of low

system pressure. We cannot easily confirm this condition by analysis and therefore are uncertain as to whether the hydraulic characteristics of the RCS and charging system would result in a lockout of the standby charging pump.

However, we cannot ignore that the possibility exists. Therefore, in lieu of deterministic' analysis, we plan to redesign the breaker control circuitry to eliminate any possibility of standby pump lockout due to simultaneous high level or high' discharge pressure and a safety injection actuation signal.

This modification will be completed by September 15, 1989.

8908310016 890823 i- I PDR ADOCK 05000309:

P PNV; 04761-SEN-00061 i p i

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l '* dnitedStatesNuclearRegulatoryCommission MN-89-108 Attentjon:

  • Document Control Desk Page two i

' Using Probabilistic-Risk Assessment techniques, we have determined 'that

-this postulated condition would not significantly affect the calculated core damage frequency._ Further, verification of HPSI actuation is currently required by plant emergency operating procedures and manually starting the pumps as called for in these procedures bypasses the postulated lockout.

1 Please do not hesitate to call should you have any questions.

Very truly yours, HAINE YANKEE t

bhW G. D. Whittier, Manager Nuclear Engineering and Licensing GDH:BPB c: Mr. Richard H. Hessman Mr. Hilliam T. Russell Mr. Eric J. Leeds Mr. Cornelius F. Holden 1

I I

I 04761-SEN-00061 <

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