ML19241B172

Forwards Util Re Augmented Auxiliary Feedwater Provisions

ML19241B172
Person / Time
Site:	Oconee
Issue date:	04/26/1979
From:	Mattson R Office of Nuclear Reactor Regulation
To:	Hanauer S, Ross D, Tedesco R Office of Nuclear Reactor Regulation
References
FOIA-79-98 NUDOCS 7907120742
Download: ML19241B172 (1)

Text

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/****%g UNITED STATES I '.',...j, *f "1 NUCLEAR REGULATORY COMMISSION

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WASHINGTON. D. C. 20555

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April 26,1979

/D.Ross

d. Hanauer R. Tedesco er E. Case

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H. Denton D. Eisenhut The attached letter from Duke regarding augmented l

auxiliary feedwater provisions was received in I

my office while yesterday's Commission meeting l

was in progress.

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l-Roger J. Mattson,' Director - '-i.

.:s. Division of Sys tems Safety '~#5 T C5,!N -

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Dr Roger 'J Hattson, Director Divlsion of Systems D! vision U S Nuclear Regulatory Ccmission Washington, D C 20555

Dear Dr Hattson:

As a result of the recent Three Mlle Island-2 Incident. Duke Pcwer Company

'Is reviewing the design and cperation of its Dconee Nuclear Station. The review has been done both Internally and in conjunction with Babcock & Wilcox and the Nuclear Regulatory Ccmission. Among other things, this review includes the goal of Improving the reliability of the norm.al fudwater system and added assurance of emergency feedseter supply to the steam generators. We fe e l our existing design is adequate and competent; however, we have several high priority activities underway and multiple alternatives are available to achieve added margins.

A full-time,' dedicated technical teadvas organized on April 9,'1973, to N Y evaluate the Three Mlle ' Island incident and to review all Duke nuclear stations.

This team is cernposed of Duke personnel with experience in design, operation, and radiological control, along with a representative from the vendor that d*

supplied the Nuclear Steam Supply System. Among the items being reviewed are the design, equipment,' controls, and procedures associated with the tr.alfi]*I - -

condensate-feedwater and errergency feedwater systeins and the resultant system 4e11 ability. This review w!!! Identify strengths and courses of action to correct any weaknesses. Primary emphasi.s is being placed on Oconee Nuclear

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One concern of HRC has been the reliance of EFV upon the integrated Control System.. A care uf l review of the systems shows that a train of EFV exists

.which is Independent of the ICS and block valves.

An Ir:rnediate improvement in both normal feedwater reliability and assurance of emergency feedwater is availabic.

Hinor changes in existing equip: rent and procedures can be rnade to decrease the time for power to reach the main feed-water pump trains from the source of emergency pcuer, Keewe Hydro Station. This' will result in an it provement in feedwater reliability.

Also,-each unit has its own enrgency fe,e: Mater system containing a steam-driven emergency feedwater pump.

freprovement In the starting reliability of this emergency feedwater pump turbine can be achieved by improvements in the governor systee of that turbine.

This will be pursued with the turbine manufacturer.

Existing crossover iines

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April 25.,1979 g.

pemt t connections among all three Oconee units. Thus, with the addition r.c an auter atic start of all three emrgency fe4ater pumps on a demand signal from any unit and proper alignment of valves, the affected unit would have available its cwn dedicated emergency supply plus. the supplies of the two adjacent units.

The energency feedwater pumps are each sized to at least 150 percent of the required capacity, and two pumps can easily supply three units.

Changes or rnodifications In procedure, control logic, Instrumentation, and personnel assignnents can bring about these Irnprovements promptly.

In addition, consideration is being given to tr.alntaining at least one emergency feedwater pu o in the running rnede at all times during the operation of any unit.

Experience has shown that even with fel demands for Emergency Feedwater at Oconee, in no case has the crossover capability been required. Thus we have had two trains of reserve EFW available. Many of the 41 demands have occurred as a result of system testing, and the mature operation of Oconee has resulted In a large decrease In the frequency of such events.

In addi tion, our engineers are ~ pursuing the alternative--of providing an additional emergency feedwater train for each unit.

,Thus, we have it:nediate and short-term actions underway to produce alternatives.- d -

operation of Oconee Is adequate and safe, and our six years of Oconee operation

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for consideration as changes at Oconee.

In my judgment, the design and bear this out.

For the long tem, our design and operating staff has and will

, continue to perfom a comprehensive review of both nomal and emergency fee:Nater y

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Only a careful, thorough angineering review will resul.t in the proper M';

" ~1ong ~terrn modt fl cations. Ve feel this re' view will result in prudent, ef fective *? D

design and operational changes, where necessary, which can further increase the

. ;.-j. ugy;1 safety snargins and reliability of Oconce Nuclear Station.

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,s April 25, 1979

/D Mr. Harold R.

Denton Director Of fice of Nuclear Reactor Regulati U.S.

Nuclear Regulatory Commissi,ot Washington, D.C.

20555 7

Re:

Oconee)'uclear Station nn r_hef No s. 50-269, 50-270, and 50-287~

Dear Mr. Denton:

In the Nuclear Regulatory Commissioners' meeting of April 25, 1979, Duke Power Company committed to provide a three part improvement of the emergency feedwater system at Oconee Nuclear Station.

The purpose of this letter is to provide docu-mentation, design information and projected implementation schedules on each of those three parts.

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PART I.

Immediate On April 25, 19h9,DukePowerCompanyinitiatedatOconee Nuclear Station the following procedural changes to enhance the reliability of emergency feedwater system.

1.

The emergency feedwater system in the existing design for each Oconee Unit has a turbine driven emergency feedwater pump which supplies 150% of the required water to the steam generators on loss of main feedwater.

The discharges of these pumps have been tied together by alignment of manual valves such that each' and all of the pumps can supply emergency feedwater to any Oconee Unit requiring it.

2.

Operating personnel have been stationed at each emergency feedwater pump with a direct communication link to that unit's control room.

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3.

trative 1s..have been established so that in the event M 1 m or cotn main feedwaDi~q. umps on_a.

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unit, that unit's emergency feedwater pump will start.u toma ticalfy,

backed up by remote manual start from the control room.

If the" -

pump fails to start automatically the operator stationed at that pump will start the pump locally, and has been trained to do so.

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s In addition, the other two available emergency feedwater pumps will

,, be started remotely from their unit's control room or locally if

• required to provide two more redundant sources of feedwater to the affected unit.

4.

Emergency feedwater flow to the steam' generators will be assured by the control room operator who has been trained to maintain the necessary levels.

PART II. -

One Week Within a time period not to exceed seven days from April 25, 1979, the emergency feedwater system at Oconee will be revised as follows:

1.

Emergency feedwater pump control systems will be revised such that emergency feedwater pumps on all three units will start automatically whenever loss of main feedwater occurs on any unit.

2.

The emergency feedwater pump discharge flow will be connected to the interconnection headers such that each or all emergency feedwater pumps can supply water to any unit.

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PART III.

-3 to 4 Months

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Within about three to four months, two motor driven emergency feedwater pumps will be added to each unit at Oconee'

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with the following design criteria.

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The two electrically operated pumps,will provide a minimum of 100% des.gn cap ~acity for each unit.

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The design of the pumps and the associated equip-ment will be seismic.

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The controls for the electric pu=os will be. J.

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independent of the integrated control system.

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The power supply for the pumps and controls will be from the 4160 volt safety related busses.

5.

Piping and valves added will be Duke Class F (B31.1-SSE seismic design) which is of like quality to the existing turbine driven emergency feedwater pump system.

6.

The existing feedwater control valves will be utilized thereby providing four functional flow paths,to the steam generators on each unit.

A preliminary flow diagram of the revised motor driven emergency feedwater pump system is attached.

Last week we proceeded with design and procurement of these systems.

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For reliability of the Oconee emergency feedwater system, cross

. connecting the discharge headers of all three emergency feedwater pump versus single pump operation for each unit has been evaluated by the Babcock & Wilcox Company.

The approach used a WASH-1400 f ailure data for components, component mode contribution and test and maintenance contributibn.

Values utilized 'in the probability model are appropriate to the Oconee emergency feed-water rystem.

The estimates obtained we per demand for the single pump s'; stem and 2.0 x 10-ge 2.3 x 10-per demand as a conser-vati re estimate with a cross connection considered.

The incre-mental improvement f actor would then be approximately 100.

Based on a review of periodic test procedure records at Oconee Nuclear Station from June 1975 on Unit 1, from August 1977 on Unit 2 and frc= January 1977 on Unit 3 following results on emergency feedwater pump operability were derived.

In 67 tests for starting automatically the pumps successfully performed 61 times, which is 6 failures. to automatically start in 67 attempts,

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With three pumps thus aligned, the probability of ailurg of at least one pump to automatically start becomes (1/111 og 1 failure in over 1300 attempts.

As further assurance safstf, over the operating history of Oconee the emergency feed-water pumps have never failed to start manually locally.

Therefore 7,

we conclude that for the operating modes described in Parts I or II the probability of f ailure of emergency feedwater pumps to start is very remote.

Part III will provide even greater assurance.

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m m April 25, 1979 Mr. Harold R.

Denton

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Director, Office of Nuclear Reactor Regulation

! ' <l U.S. Nuclear Regulatory Commission Washington, D.C.

20555

Dear Mr. Denton:

Since my presentation to the commission this afternoon, additional commitments have been made by Duke Power Company.

These commitments have been furnished to your Staff and are presently being reviewed by them.

I am confident that, upon completion of Staff review'it will be determined that such commit-ments provide you with the necessary assurance to find that the continued operation of Oconee does not endanger the public health and safety.

I am sending copies of these commitments to you to assist you in your deliberation.

We feel these two commitments are fully responsive in this timeframe to items "a" and "c" of your Staff concerns listed on page 1-7 of the NRR Status Report to the Commission this afternoon.

With respect _to,, item "b,".,the utility industry has had years of successful experience with the ICS, first with many boilers and recently with reactors which leads us to conclude that it is the most appropriate system for this application.. We feel that further dialogue with your Staff about this c~ontrol system will result in familiarization, additional understanding and a ~% '?....

higher level of confidence in its responsiveness and value, and

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we will later provide the failure analysis just requested.

Re-garding item "d", shut-down core circulation is provided by the HPI injection, backed-up by any one of the four reactor coolant pumps, and only thereafter followed by natural circulation for which later analyses have been committed.

With respect to item "e",

we feel that the testimony of the I&E representatives today ac-curately portrayed current. control room conditions with alert, trained operators that can continue safe operation of these units.

With these commitments and comments, we feel we have been p&omptly responsive to the expressed concerns of your Staff and further commit to working closely together to assure con-tinued safe operation.

l g7l0 Sincerely yours,

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8 *-a <-;^ y April 25, 1977 Mr. Harold R. Denton, Director Office of Nuclear Regulation U.S. Nuclear Regulatory Commission

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Washington, D.C.

20555 Re:

Oconee Nuclear Station Docket Nos. 50-269, 50-270, and 50-287

Dear Mr. Denton:

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In response to the letter of April 21, 1979 from James P. O'Reilly, Director, NRC Region II Atlanta., soncerning I.E.

Eulletin No.79-05B the following information is provided.

I Duke Power Company agrees that automatic anticipatory reactor,,,

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'.-z trip on loss of main feedwater#and turbine' trip is appropriate for the Oconee Nuclear Station reactors.

The trips will be implemented as soon as practicable.

Previous reactor trips at Oconee Nuclear Station, indicate that a direct reactor trip on loss of main feedwat,er will,proside earlier reactor shutdown than

'.for the case when the reactor trips following high reactor coolant

..y syctem pressure as a result of the transient.

Based on our in-vestigation of Incident Report No. B-805 Oconee Unit One (copy of this incident report was provided to M. Fairtile of the NRC Staff

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on April 24, 1979).it is concluded that the reactor trip would occu some 50 seconds earlier when initiated by loss of mainTErff '

feedwater than if initiated by high reactor coolant system pressure.

Design information and a schedule for implementation of our committed anticipatory reactor trip will be provided to the NRC Staff by May 21, 1979 as requested in Bulletin 79-05B.

V y truly yours, Lh.

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Willic." O.

Parker, r.

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James P.

O'Reilly, Director 1

U.S.

Nucleer Regulatory Commission

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