ML19281A562

in Response to 790209 Request,Forwards Addl Info on Feedwater Flow Instability (Steam Generator Water Hammer)

ML19281A562
Person / Time
Site:	Calvert Cliffs
Issue date:	03/15/1979
From:	Lundvall A BALTIMORE GAS & ELECTRIC CO.
To:	Reid R Office of Nuclear Reactor Regulation
Shared Package
ML19281A563	List: ML19281A562 ML19281A564
References
NUDOCS 7903210298
Download: ML19281A562 (19)

Text

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BALTIMORE GAS AN D ELECTRIC COMPANY GAS AN D ELECTRIC DUILDING B A LTI M O R E, M A R Y L A N D 21203 ARTHUR [. LUN DVALL, JR.

V+c t Pat t+ 0 t % f sans Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Co==ission Washington, D. C. 20555 Attn: Mr. Robert W. Reid, Chief Operating Reactors Branch #h Division of Operating Reactors

Subject:

Calvert Cliffs Nuclear Power Plant Units Nos. 1 & 2, Docket Nos. 50-317 & 50-318 Water Rammer; Additional Informatien

Reference:

(a) NRC letter dated 2/9/79 from Reid to Lundvall, same subject.

(b) BG&E letter dated 11/13/78 from Lundvall to Denton, Request for Amendment to Operating Licenses.

Gentlemen:

Your letter of February 9, 1979, Reference (a), requested that we provide additional information pertaining to feedvater flow instability (vater hammer) at Calvert Cliffs. This information was requested to allov you to evaluate our request for removal of License Condition 2.C.3 and to complete your review and evaluation of the entire water hammer issue.

Enclosure (1) contains our responses to your request for additional infor-mation.

The type of infor=ation requested by Reference (a) and the nature of the NRC's Safety Evaluation Report for Surry Pover Station contained in that letter have led us to conclude that our original request, Reference (b), needs some modification and clarification. In that request, we asked for the removal of the license condition restricting the stea=

generator vater level rise rate to 1.2 inches per minute based on the recent nodification to the steam generators and the subsequent satisfactory water hanner test. Eovever, ve can provide no specific assurance that the main feedvater ring would retain sufficiently filled with vater following an interruption of main feedvater flow to preclude water hamner other than that experimental evidence provided by the above-centioned test (see Response No. k in Enclosure (1)). In that case, the feedvater supply was stopped for 15 minutes and the steam generator level was reduced to -85".

This provided some opportunity for the feedring to drain through the small

(.015 .025") annular gap between the feedvater ring no::le o.d. and the steam generator nozzle 1.d.

7903210292

6. Prcvide an evaluation of the means employed to avoid water hammer that demonstrates that the feedvater lines and feedvater spargers vill remain sufficiently filled with water to preclude water hammer under normal and transient operating conditions including: a reactor trip with turbine trip, loss of main feedvater, loss of offsite power, operator error, steam line break and LOCA.

Resnonse:

a) Under normal conditions, where feedvater flow is maintained continuously, the main feed ring remains full of water, and there is no evidence that a feedvater instability (vater hammer) has or could occur.

b) A reactor / turbine trip does not cause the loss of main feedvater.

Feedvater flow is ramped down to 5% of full power flow on the bypass valves, and the main feed ring remains full.

c) Upon loss of main feedvater, the steam generator water level vill drop below the main feed ring if a main feed pump cannot be restored in time. In such cases, the main feed ring is expected to slowly drain through the no :le clearance where the feed ring nozzle fits into the steam generator feed inlet no::le. Since this is a small clearance

(.015" to .025"), the water is expected to drain slowly. However, no credit is assumed for this phenomenon, and feedvater flow vill normally be reestablished via the auxiliary feedvater system observing the license condition rise rate limit of 1.2 inches per minute until the water level reaches the main feed ring. No vater hammers have been experienced at Calvert Cliffs under these conditions.

d) A loss of offsite power would result in a loss of main feedvater. The remainder of the scenario is the same as (c) above.

e) Overator error which results in an interruption of main feedvater flow is assumed to result in a scenario similar to the loss of main feedvater, described in (c) above, f) A loss-of-coolant-accident (LOCA) which is small vould have no effect on feedvater flov and, thus, water ha==er. A large LOCA =ay affect feedvater flow if it results in a containment isolation signal or some other mechanism for interrupting main feedvater flow, g) A steam line break might result in an interruption of main feedvater flow. I it causes the turbines to tr"?, main feed would be lost. If it causes the isolation of the steam generator, water hammer is obviated.

In any of the above scenarios, if main feedvater flov is lost and there is no assurance that the main feed ring remained sufficiently filled with water to preclude water ha=mer, the steam generators vould be fed using the auxiliary feedvater system (via the auxiliary feed ring), and the maximum vater level rise rate vould be limited to 1.2 inches per minute as prescribed by License Condition 2.C.3.

5 Describe the means employed at the Calvert Cliffs Plant to reduce the potential for water hanner including a) steam generator level controls, b) top discharge ports in feedvater sparger, c ) main feedvater valve operation and d) automatic as well as e) administrative control of auxiliary feedvater flow.

Resnonse:

a) See Response No. 1 b) See Response No. 1 c) See Response No. 1 d) There is no automatic actuation or control of Auxiliary Feedvater.

See Response No. 2.

e) Auxiliary Feedvater flov is currently aiministratively controlled to produce a steam generator water level rise rate of no more than 1.2 inches per minute when filling the steam generator from an initial level below the main feedvater ring. This is in accordance with Operating License Condition 2.C.3. However, this condition is the subject of our Amendment Request dated 11/13/78 (as modified by the Cover Letter to this submittal).

Office of Nuclear Reactor Reculation November 14, 1977 While ve have not yet decided to make these nodificatiens nor conduct the associated safety analysis, nreliminary encineerine discussions have indicated that the installation of "J-tubes" or sinilar devices vould not constitutean un-reviewed safety question, and consecuently, assunine a subsequent analysis supports this preliminary indication, any modifications vould be made under the provisions of 10CFR 50.59 In summary, we vish to reiterate the following noints:

1. Auxiliary feedvater has been demonstrated to be an accentable method of refilline the main feedvater ring in the steam generators. -

2. The proper use of auxiliary feedvater precludes the occurrence of feedvater waterhamner.

3 No modifications are required to further enhance the overall safety,

h. Modifications may be desirable in that the plant could recover in less time from a plant trip.

5. The addition of "J-tubes" if economically justifiable could probably be innlemented under the provisions of 10CFR 50.59 Very truly yours, BALTIMORE GAS AND ELECTRID COMPANY I

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By:

V

', / cw[vt LC k N A. E. Ldndvall, Jr.

Vice Presiden;t - Surply AEL/CCL/dr cc: J. A. Biddison, Esquire G. F. Trowbridge, Fsquire Mr. M. Conner, NRC Mr..P. Kruse, C.E. '

bec: A. E. Lundvall, Jr. - ,

J. W. Gore, Jr.

J. 3. Bullock s R. W. Davies R. H. Kent R. F. Ash R. ". Douglass ,

C. C. Lawrence III R. C. L. Olson

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