ML17263A432

Provides Evaluation of Design Deficiency Discovered in AMSAC Sys.Power Level Time Delay lock-in Feature Not Incorporated Onto Design of Sys.Correspondence Prepared Using GL 91-18 as Guide,Although Condition Not within Scope of GL

ML17263A432
Person / Time
Site:	Ginna
Issue date:	10/22/1993
From:	Mecredy R ROCHESTER GAS & ELECTRIC CORP.
To:	Andrea Johnson NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
GL-91-18, NUDOCS 9310290172
Download: ML17263A432 (8)

Text

ACCEI ERAT DOCUMENT DISTRIBVTIONSYSTEM REGULA.

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S ACCBSS~ONsNBR'9310290172 DOC SEDATE'3/10/22 NOTARIZED NO DOCKET FACIAL:50-244 Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G

05000244 AUTH.NAME AUTHOR AFFILIATION MECREDY,R.C.

Rochester Gas a Electric Corp.

RECIP.NAME RECIPIENT AFFILIATION JOHNSON,A.R.

Project Directorate I-3

SUBJECT:

Provides evaluation of design deficiency discovered in AMSAC sys.Power level time delay lock-in feature not incorporated onto design of sys.Correspondence prepared using GL 91-18 as guide, although condition not within scope of GL.

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ROCHESTER GAS AND ELECTRIC CORPORATION o

89 EAST AVENUE, ROCHESTER N.Y. 14649-0001 ROBERT C. MECREDY Vice President Cinna Nudear Production October 22, 1993 TELEPHONE AREA cooE Tie 546-2700 U.S. Nuclear Regulatory Commission Document Control Desk Attn:

Allen R. Johnson Project Directorate I-3 Washington, D.C.

20555

Subject:

AMSAC Design Deficiency R.E. Ginna Nuclear Power Plant Docket No. 50-244

Dear Mr. Johnson:

The purpose of this letter is to provide, for your information, an evaluation of a design deficiency discovered in the Ginna Station AMSAC system.

A power level time delay lock-in feature was not incorporated into the design of this system.

The requirement for this power level lock-in was not presented as part of the Westinghouse provided design specification, but was presented in a WOG letter to the NRC.

Included in the attachment is our assessment of the effects of this deficiency, our compensatory

measures, and a schedule for incorporation of this function into the design.

This correspondence has been prepared using Generic Letter 91-18 as a guide, although this condition does not fall within the scope of the generic letter.

Very truly yours, Robert C. Mecredy Attachment REJK307 xc: Mr. Allen R. Johnson (Mail Stop 14D1)

Project Directorate I-3 Washington, D.C.

20555 U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 Ginna Senior Resident Inspector 290086 9310290172 93i022 PDR ADOCK 05000244 P

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ATTACHMENT AM A Power Level Lock-in 1.

Pr blem Descri tion The power lock-in feature portion of the AMSAC was not incorporated into the design as specified by Westinghouse.

This could affect AMSAC operational timing under certain limited plant conditions.

The AMSAClogic has a variable timer function where-by AMSACactuation (turbine trip and AFW start) is time delayed based upon plant power.

This time delay varies such that if power is high, as measured by turbine first stage pressure, AMSAC actuates sooner; and ifpower is low, AMSAC actuates later.

The AMSAC design assumed that the logic would have a power level lock-in feature which "latches" the timing value of the variable timer, for that power, at the moment that the ATWS event actuated (i.e., %

FW flow less than 25%).

As discussed in WCAP-10858-P-A, Rev.

1, "AMSAC Generic Design Package",

loss of feedwater can occur due to a malfunction in the feedwater/condensate system or in its control which may result in closure of the regulating valves or isolation valves or simultaneous trip of all main feedwater pumps.

3.

Effects RG&E has reevaluated the two conditions for which AMSAC was designed - a loss of load without reactor trip, and a complete loss of feedwater without reactor trip.

a.

Loss of Load:

As described in the generic ATWS analyses for Westinghouse PWRs (Reference

1) supporting the Final ATWS Rule (10CFR50.62) and in the AMSAC Generic Design Package (Reference 2), the loss of load transient is only a concern for ATWS due to the postulated loss of main feedwater.

The generic Westinghouse ATWS analyses for the loss of load ATWS event assume a loss of main feedwater resulting from the loss of main condenser vacuum after the initiating turbine trip.

Upon loss of the main condenser vacuum, main feedwater turbine-driven pumps that exhaust into the main condenser are tripped, thereby cutting off feedwater flow to the steam generators.

However, as described in the AMSAC Generic

'Design Package, not all Westinghouse PWRs are subject to the loss of main feedwater following turbine trip since many plants have motor-driven main feedwater pumps or they have turbine-driven pumps which do not exhaust into the main condenser.

Therefore, for these Westinghouse

PWRs, the,.loss of load ATWS event is not of concern since main feedwater is not lost.

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For Ginna Nuclear Power plant, main feedwater is supplied by motor-driven feedwater pumps.

For a loss of load ATWS event initiated by a turbine trip, the motor-driven feedwater pumps will continue to operate and provide main feedwater to the steam generators at Ginna until such time that main feedwater isolation may occur. Ifat any time the main feedwater pump breakers open or a low steam generator water level condition should occur, auxiliary feedwater would automatically initiate to maintain steam generator water inventory and RCS heat removal capability.

With both the initiating turbine'trip and either main or auxiliary feedwater availability, the function of AMSAC is satisfied since AMSAC is designed to trip the turbine and initiate auxiliary feedwater in the event of an ATWS.

Therefore, since the loss of load ATWS event with consequential loss of main feedwater is not postulated to occur for Ginna, the lack of a lock-in feature on the actuation timer in the Foxboro AMSAC is not a concern for the loss of load ATWS event at Ginna.

Hence, the concerns identified in NRC information Notice 92-06 as they relate to the loss of load ATWS event are not detrimental to the AMSAC design at Ginna.

b.

Complete loss of feedwater flow-A complete loss of feedwater flow, without feedwater pump breaker trip (which would by itself initiate auxiliary feedwater), was also analyzed.

In this scenario, although feedwater flow would be terminated, the mass inventory in the steam generators would maintain turbine first stage pressure comparable to the pre-event parameter.

Therefore, the variable time delay, although not locked in, would be expected to actuate within the time frame assumed in the design (e.g. 27 seconds from 100% power).

It should be noted that the generic Westinghouse ATWS transient analysis assumed 30 seconds for turbine trip and 90 seconds for AFW initiation.

RG&E has not analyzed all cases of complete loss of feedwater (various reactor power levels, reactivity coefficients) which could be postulated to occur.

The worst-case analysis described herein does provide us with additional confidence that the system could operate as analyzed, even without the seal-in feature on the variable timer.

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to Measures a.

Auxiliaryfeedwater willautomatically initiate at 17% lo-lo steam generator level independently of AMSAC.

b.

Both auxiliary feedwater pumps will start upon loss of both main feedwater pumps (breakers open).

c.

Existing EOPs require immediate for operator action to manually trip the reactor, trip the turbine and start the AFW pumps in order to mitigate the consequences of an ATWS.

5.

Action Plan a.

Heightened operator awareness of the degraded condition of the AMSAC system has been accomplished by the generation of A-25.1 and A-52. 12 assessment and tracking reports.

b.

Preparational (bench) testing of the new variable timer lock-in feature has been successfully accomplished.

C.

Based upon successful completion of preparational testing, installation of the modification can proceed.

Scheduling is dependent on the ability to perform the modification at power. In the event this is not feasible, installation willoccur no later than the end of the 1994 outage.

References NS-TMA-2182, "ATWS Submittal," T.M. Anderson (Westinghouse) to Dr. S.H.

Hanauer (NRC), December 30, 1979.

2.

WCAP-10858-P-A, Revision 1, "AMSACGeneric Design Package," M. Adler, July 1987.

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