ML18143A981

Letter Concerning Secondary System Fluid Flow Instability

ML18143A981
Person / Time
Site:	Ginna
Issue date:	10/31/1975
From:	White L Rochester Gas & Electric Corp
To:	Purple R Office of Nuclear Reactor Regulation
References
Download: ML18143A981 (17)

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0 NRC DISTRIBUTION FOR PART 50 DOCKET MATERIAL (TEMPO RA R Y FO B MR)

CONTROL NO:

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Rochester Gas

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Leon D

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ATE OF DOC DATE R EC'D LTR TWX 10-RPT OTHER

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Robert A, Purple PROPINFO

'ESCRIPTION CLASS UNCLASS ORIG 1 Signed INPUT CC OTHER NO CYS REC'D ENCLOSURES SENTHRC PDR SENT LOCAL PDR DOCKET NO:

50-244 Ltr. re our ltr. of 5-13-75 ~ ~.Trans the follow>>

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Analysis and other relevant inforlnation con-cerning secondary system fluid flow instab-il'ities(I,'Water'anmer")., ~..With. AttaqIIments A-D.....; '.

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Director of Nuclear Reactor Regulation

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ATTN:

Robert A. Purple, Chief Branch No.

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Subject:

Secondary System Fluid Flow Instability R. E. Ginna Nuclear Power Plant Unit No.

Docket No. 50-244 6'ig'gfjp,

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Dear Mr. Purple:

This is in reply to your letter of May 13, 1975 requesting analyses and other relevant information concerning secondary system fluid flow instabilities

("water hammer").

Reviews and analyses of the potential for occurrence, and the potential consequences of, water hammer at Ginna Station have been performed.

The following information is submitted as requested by your letter:

1.

Investigations by Westinghouse of the main feedwater line "water hammer" which has occurred in PWR reactor plants have identified it as a steam-water slugging phenomenon resulting from steam entering horizontal sections of feed-water piping which are'partially filled with cold water.

In the several different plants which have experienced

".water hammer" it has been found that steam generator water levels had dropped below the feed ring and the level was being recovered (to above the feed rings) by feeding the steam generators with cold auxiliary feedwater.

In addition, it has been found that the water hammer usually occurs when the feed ring is being recovered while feedwater flows are above a threshold flow.

This threshold flow has been determined to be approximately 200 gpm.

An examination has been made of the normal,

abnormal, and accident transients which, can result in a steam generator water level below the feed ring long enough for it to drain; and which would result in feedwater flow being initiated in order to recover level. It has been determined that the following operating occurrences could cause these conditions:

ROCHESTER GAS AND ELECTRIC C P.

DATE October 31, 1975 To Mr. Robert A. Purple SHEET NO.

(2)

(3)

Load changes when steam generator level is under manual control.

Intermittent manual operation of auxiliary feedwater pumps to maintain steam generator level during hot shutdown.

Loss of Main feedwater 2.

The main feedwater piping at Ginna Station consists of two (2) lines, A and B, which run from the control valve station in the turbine building to the steam generators.

The routing of the main feedwater lines from the control valve station to the steam generators is shown on the isometrics included as attachments A and B to this letter.'he auxiliary feedwater piping at Ginna Station consists of four (4) lines, two (2) from the motor driven auxiliary feedwater pumps 1A and 1B, and two (2) from the turbine driven auxiliary feedwater pump.

The routing of the auxiliary feedwater lines from the motor driven auxiliary feedwater pumps to the main feedwater lines is shown on the isometric included as attachment.

C to this letter.

3.

Two (2) transients which could be characterized as "water hammer" experiences have occurred in the feedwater system at Ginna Station.

Neither of these transients were attributed to level control problems in the steam generators.

The first transient occurred on July 22, 1973 and was re-ported to the U. S. Atomic Energy Commission in a letter dated August 21, 1973 to Mr. John F. O'eary, Director, Directorate of Licensing.

The second occurred on June 17, 1975 and was reported to the U. S. Nuclear Regulatory Commission in a letter dated July 17, 1975 to Mr. Robert T.

Carlson, Chief, Facilities Construction and Engineering Support Branch, Region I.

) Analyses of the main feedwater piping at Ginna Station have been performed for a postulated'"water hammer" utilizing a dynamic forcing function.

These analyses assumed that a steam-water slugging process is initiated at the steam generators; that steam generator level is being recovered utilizing auxiliary feedwater; and that the main feedwater check valves are closed.

The analyses are based on the piping configuration and supports presently installed at Ginna Station.

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,D~TE October 31, 1975 Mr. Robert A. Purple SHEET NO.

The forcing function assumed in the analyses is shown in Attachment D.

The forcing function is a time dependent mathematical quantity representative of the energy released by water hammer in the feedwater piping connected to PWR steam generators.

The forcing function provides a

time history of the pressure in the piping system which results from the acoustic shock wave generated by a steam-water slug.

The forcing function shown in Attachment D

has been modified for the specific piping configuration at Ginna.

This forcing function has been derived by Westinghouse from measurements of pressure and displacement observed during a water hammer test at the Tihange site in Belgium.

Calculations performed by Westinghouse employing this forcing function for the Tihange feedwater piping resulted in displacements in fair agreement with those observed.

At this time Westinghouse considers the forcing function as preliminary and it is still under development.

The loading combinations and stress criteria used in evaluating the results of the analyses were based on the original construction

code, ANSl B31.1, Power Piping.

These criteria ~sere that the sum of the longitudinal stresses due to pressure,

weight, and water hammer not exceed 1.2 times the allowable stress in the hot condition, Sh.

Evaluation of the stresses obtained in the analyses showed that inside containment there were several locations on the A main feedwater piping and several locations on the B main feedwater piping which exceeded the stress criteria.

Outside containment there were no locations on the A main feedwater piping and several locations on the B main feedwater piping which exceeded the stress criteria.

Analyses have not been performed of the auxiliary feedwater piping systems for a postulated water hammer from the steam generators.

These analyses will be performed when the design of present. modifications to the auxiliary feedwater system is completed and the forcing function is finalized.

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4.(b)

No test programs have been carried out at Ginna Station to determine whether uncovering of the steam generator feed rings could occur, or if it did occur, whether "water hammer" would occur.

However, we have been provided the results of such tests in similar Westinghouse PWR's.

These test results confirm that there is a possibility of "water hammer" occurring under the operating conditions noted above.

The test, results also show that, certain administrative controls and steam generator modifications reduce the probability of occurrence of "water hammer";

and that certain piping configurations and supports reduce the consequences of "water hammer", if it did

'ccur.

We have not, completed our evaluation of the test results at this time since more recent tests have been per-formed for which we not yet received the results.

5.

Uncovering of a steam generator feedwater ring following a design basis loss-of-coolant accident, assuming concurrent turbine trip and loss of offsite power, is possible due to subsequent loss of main feedwater.

However, for a "water hammer" to occur the auxiliary feedwater flow would have to exceed the threshold flow during the time steam generator level is being recovered to above the ring.

6.

We are evaluating various administrative controls, steam generator modifications, and piping support, modifications to determine their effectiveness.

Such changes must be evaluated in conjunction with changes to the plant made necessary by other considerations such as postulated high energy line breaks.

We are also awaiting the evaluation of tests from other facilities pertaining to the "water hammer" transient.

Final determination of the specific changes to be made at Ginna Station, and submission of the information you require concerning these changes, will be accomplished by January 30, 1976.

In the meantime, we are prepared to discuss the alternatives being considered, and the advantages of each, at any'ime.

Very truly yours, L. D. Whi e, Jr.

Attachments

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Ginna Station Steam Generator Water Hammer Pr e luzgina ry Po rcing Func tion

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