ML20116E593

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Forwards Addl Info Re Design Features Incorporated to Minimize Potential for Water Hammer in Main Feedwater Sys. Encls Provide Technical Justification for Elimination of Main Feedwater Arbitrary Intermediate Pipe Breaks
ML20116E593
Person / Time
Site: Vogtle  Southern Nuclear icon.png
Issue date: 04/24/1985
From: Foster D
GEORGIA POWER CO.
To: Adensam E
Office of Nuclear Reactor Regulation
References
GN-589, NUDOCS 8504300339
Download: ML20116E593 (6)
v • d • e


Text

Georgia Power Company Route 2. Bu 299A Waynesboro. Georgia 30830 .

Telephone 404 554 9961, Est 3360 404 724-8114. Ext. 3360 D. o. Foster April 24, 1985 Georgia Power i yP ta Propc1 g

tresoutten dewc system Vogtfe Project Director of Nuclear Reactor Regulation File: X4AK01 Attention: Ms. Elinor G. Adensam, Chief X4BA17 Licensing Branch #4 Log: GN-589 Division of Licensing.

U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

1. Letter from D. O. Foster (GPC) to H. Denton (NRC) dated April 26, 1985 (Leg: GN-352)
2. Letter from T. Novak (NRC) to D. O. Foster (GPC) dated June 28,1984(Docket 50-424,50-425)

NRC DOCKET NUMBERS 50-424 AND 50-425 CONSTRUCTION PERMIT NUMBERS CPPR-108 AND CPPR-109 V0GTLE ELECTRIC GENERATING PLANT - UNITS 1 AND 2 ARBITRARY INTERMEDIATE PIPE BREAKS

Dear Mr. Denton:

In reference 1, GPC requested your approval for the application of alternatiave pipe break criteria which would eliminate the need to postulate arbitrary intermediate pipe breaks. In reference 2, the NRC approved that request, with the exception of breaks in the main feedwater piping. This exception was based on the susceptibility of the main feedwater. system to water hammer.

-In this submittal, we are providing additional technical information regarding the design features which have been incorporated into the design of the Vogtle' Electric Generating Plant (VEGP) to minimize the potential for water hammer in the main feedwater system. Also addresssed are the stress analyses performed to determine the effects of water hammer, should it occur, and the ability of the piping system to with-l- stand such a transient (see Attachment a).

The attached information is intended to supplement the technical informa-tion provided in reference 1. Together, these submittals provide techni-cal justification for the elimination of the main feedwater arbitrary intermediate pipe breaks. The application of this proposed criteria change would result in the elimination of 11 break locations and 24 pipe whip restraints, per unit, as identified in Attachment b.

i We would appreciate your expeditious review and approval of this submittal.

Yours truly, f 8504300339 850424 -

I ;I PD? ADOCK 05000424 i A PDR  !~ < *

. O. Foster

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Director of Nuclear Reactor Regulation File: X4AK01 April 24,1985 X4BA17 Page 2 Log: GN-589 D0F/sw Attachments: a. Potential for Water Hammer in the Main Feedwater System

b. Postulated Pipe Breaks / Whip Restraints to be Eliminated xc: R. A. Thomas J. A. Bailey B. Churchill, Esq.

J. E. Joiner, Esq.

T. Johnson D. Teper L. Fowler M. A. Miller B. Jones, Esq.

L. T. Gucwa G. Bockhold, Jr.

O. Batum

Attachment a POTENTIAL FOR WATER HAMER IN MAIN FEEDWATER PIPING DESIGN FEATURES WHICH MINIMIZE WATER HAMMER POTENTIAL The routing of the 16-inch main feedwater piping and the 6-inch bypass feedwater piping is in compliance with the Westinghouse criteria for functional requirements, arrangement and layout require-ments, instrumentation and control requirements, and operational procedures and constraints to minimize or eliminate water hammer.

Plant Vogtle has Westinghouse Model F (feedring type) steam genera-tors. During normal power operation, approximately 92 percent of the feedwater is supplied through the 16-inch main feedwater line. The remaining 8 percent is supplied through the 6-inch bypass (auxiliary) feedwater line. This split flow scheme provides a continuous flow through the bypass piping to the bypass nozzle which effectively prevents the backflow of steam or hot water from the steam generator.

During heatup, cooldown, and hot standby (flow less than 15% of rated flow and temperature less than 250 F) feedwater is supplied only through the 6-inch bypass (auxiliary) nozzle.

The feasibility of replacing the main feedwater check valve with a slow closing type valve was evaluated and the decision was made to retain the tilting disc design. The features of the tilting disc type check valve design which resulted in its selection at Plant Vogtle are as follows:

1. The valve can withstand the pressure pulses resulting from fast closure and remain functional.
2. Its fast closure minimizes the magnitude of the resultant pulse pressures and reverse flow characteristics of other slow closing check valves (swing or lift plug).
3. Tilting disc check valves are of simple design and have had more than 50 years of successful operating history in the power industry.
4. Maintenance experience is available on this type of check valve from operating plants and valve manufacturers.

DESIGN FEATURES WHICH PREVENT DRAINAGE INTO THE STEAM GENERATOR The steam generator feedring will be provided with Inconel J-tube discharge nozzles on the top surface of the feedring.

The annular flow path between the thermal sleeve and the inlet feedwater nozzle, which was present in earlier steam generator designs, has been eliminated for Vogtle.

The length of the horizontal flow path at the main feedwater nozzle elevation is minimized by welding a downward directed elbow close to the nozzle.

An upwardly-inclined pipe section is connected to the 6-inch bypass (auxiliary) nozzle inside the steam generator.

The length of the horizontal flow path at the 6-inch bypass (auxiliary) nozzle elevation outside the steam generator is minimized by welding a downward directed elbow close to the nozzle.

DESIGN FEATURES WHICH PREVENT OR MONITOR BACKLEAKAGE A check valve is located between the main feedwater isolation valve (MFIV) and the main feedwater nozzle.

When not in use, the main feedwater nozzle will be isolated by closing the feedwater isolation valve.

The main feedwater system piping is provided with temperature sensors close to the nozzle which alarm and alert the operator of backleakage so that corrective action can be taken.

Four check valves in series are provided between the 6-inch bypass (auxilary) nozzle and the auxiliary feedwater system pump recircula-tion lines which will minimize backleakage from the nozzle into the auxiliary feedwater system.

Forward flow will be maintained through the 6-inch bypass (auxiliary) nozzle as much as possible even during heatup, hot standby, and cooldown.

The bypass (auxiliary) feedwater system piping is provided with temperature sensors close to the nozzle which alarm and alert the operator of backleakage so that corrective action can be taken.

Temperature sensors are provided on the discharge piping close to each auxiliary feedwater pump to alarm and alert the operator of backleakage so that corrective action can be taken.

pm CORRECTIVE ACTION TO ADDRESS BACKLEAKAGE DETECTION

.If backleakage of steam or hot water into either the 16-inch main or 6-inch bypass feedwater lines does occur, as determined from the temperature sensors installed in the feed lines, the lines may be slowly refilled.

For the 16-inch main feedwater line, flow control would be with the 4-inch bypass feedwater control valve and the flowrate maintained at a value of less than 150 gpm per steam generator.

For the 6-inch bypass (auxiliary) feedwater line, the flow wo'uld be provided by the . auxiliary feedwater system controlling with the < auxiliary feedwater system flow control valves. A flowrate of 15 gpm -or less would not result in water hammer in the 6-inch bypass line.

WATER HAMER ANALYSIS DUE TO POSTULATED PIPE BREAK An analysis was performed to evaluate the classical water hamer effects due to a feedwater line break in the non-safety portion of the feedwater piping (upstrea'n of the safety grade feedwater check valve and isolation valve). Stress analysis for the tilting disc check valve in the main feedwater piping confirmed that this valve would not fail and would provide its closure function for the faulted feedwater line break operating condition.

The effect of pipe break induced water hammer on the main feedwater piping was also analyzed. Resultant pipe stresses were determined to be well within ASME code _ allowables. This provides assurance that a main feedwater line break outside containment will not result in additional piping failure inside containment.

An evaluation of the internal piping - for the auxiliary feedwater-nozzle was performed for one postulated bubble collapse water hanner event. A maximum inelastic stress of 50 ksi was computed, compared to a 64 ksi allowable per ASME Section III.

SUMARY A special effort has been made to prevent bubble collapse water hammer associated with either the main or auxiliary feedwater nozzles by implementing a variety of features. As a consequence, bubble collapse water hammer is not an anticipated event.

_ Based on the close adherance to the Westinghouse. Steam System Design Criteria and -the results of the analysis of pipe breaks and check valve slam, it is concluded that the possibility of water hanner in the main and bypass feedwater piping has been essentially eliminated.

F .]

a.

Attachment b MAIN FEEDWATER BREAKS / RESTRAINTS TO BE ELIMINATED RESTRAINT SYSTEM EVENT NUMBER NUMBER Inside Containment - Loop 1 P-1108-C 38, 41, 120 P-1109-C 43, 45 Inside Containment.- Loop 2 P-llll-C 55, 57, 121 P-lll2-C 60, 54 Inside Containment - Loop 3 P-1101-C 46, 49, 122 P-1102-C 51 , 53 Inside Containment - Loop 4 P-1105-C 8, 5, 123 P-1106-C 3, 1 Outside Containment - Loops 2 & 3 P-lll9-C 249 P-lll8-C 247 Outside Containment - Loops 1 & 4 P-ll40-C 234, 263.

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