PLA-1812, Final Deficiency Rept Re Water Hammer in Essential Svc Water Sys.Initially Reported on 830505.Vacuum Breakers Will Be Installed During First Refueling Outage.Also Reported Per Part 21

Final Deficiency Rept Re Water Hammer in Essential Svc Water Sys.Initially Reported on 830505.Vacuum Breakers Will Be Installed During First Refueling Outage.Also Reported Per Part 21

ML20090H409
Person / Time
Site:	Susquehanna
Issue date:	09/22/1983
From:	Curtis N PENNSYLVANIA POWER & LIGHT CO.
To:	Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
REF-PT21-83 10CFR-050.55E, 10CFR-50.55E, PLA-1812, NUDOCS 8310280130
Download: ML20090H409 (7)

Text

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PPat Pennsylvania Power & Light Company Two North Ninth Street

• Allentown, PA 18101

• 2151770L5151 Norman W. Curtis Vice President-Engineering & Construction-Nuclear 215/770-7501 Septaber 22, 1983 Dr. 'Ihmas E. Murley Regional Administrator, Region I U.S. Nuclear Regulatory Ca mission 631 Park Avenue King of Prussia, PA 19406 SUSQUEHANNA STEAM ELECTRIC STATICH FINAL REPORT CF A DEFICIENCY INVOLVING ENERGENCY SERVICE WATER (ESW) SYSTEM WATER HAbEER ERs 100450/100508 FILE 821-10 DOCKEP NOS. 50-387 PIA-1812 AND 50-388

References:

PIA-15258 dated 8/27/82 PIA-1604 dated 4/12/83

Dear Dr. Murley:

This letter serves to provide the Camission with a final report on a deficiency involving Water Hamner in the ESW System.

This deficiency was originally reported by telephone to Mr. S. Ebneter of NBC Region I by Mr. A. R. Sabol of PP&L on May 5, 1982. The referenced PIA-1604 provided the Cmmission with a third interim report on the subject deficiency.

l In PIA-1604 PP&L indicated that we anticipated subnitting a final report in June, 1983. During subsequent discussions with NBC Resident Inspectors G. Rhoads and J. McCann on the ESW Water Hanmer concerns, including project schedules for systs analysis and corrective action determination, PP&L was granted an extension for subnitting the final report.

The attachment to this letter contains a description of the deficiency, its cause, an analysis of safety inplications and the corrective action taken and planned. This information is furnished pursuant to the provisions of i

10CFR50.55 (e).

Since the details of this report provide information relevant to the reporting requirements of 10CFR21, this correspondence is considered to also discharge I

any fonnal responsibility PP&L may have in capliance thereto.

h0g%[o DR h

f eh a

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Septaber 22, 1983 -

SSES PIA-1812 ERs 100450/100508 File 821-10 Dr. 'Ihcanas E. Murley We trust.the Camission will find this report to be satisfactory.

Very truly yours,

-- s N. W. Curtis Vice President-Engineering & Construction-Nuclear JS:sab Attachment js/lt/1/124/a

Septenber 22, 1983 SSES PIA-1612 ERs 100450/

File 821-10 100508 Dr. Thomas E. Murley Copy to:

Mr. Richard C. DeYcnng (15)

Director-Office of Inspection & Enforcenent U.S. Nuclear Regulatory Ccmnission Washington, D.C. 20555 Mr. G. Mcdonald, Director Office of Management Information & Program Control U.S. Nuclear Regulatory Ccunission Washington, D.C. 20555 Mr. Gary Rhoads U.S. Nuclear Regulatory Conmission P.O. Box 52 Shickshinny, PA'18655 Records Center

-Institute of Nuclear Power Operations 1100 Circle 75 Parkway, Suite 1500 Atlanta, GA 30339 Mr. Robert L. Perch Nuclear Regulatory Cm mission 7920 Norfolk Avenue Bethesda, MD 20014

s I

SSES PLA-1812 ERs 100450/100508 FILE 821-10 l

SUSQUEHANNA STEAM ELECTRIC STATION WATER HAMMER IN *d

'MERGENCY SERVICE WATER SYSTEM FINAL REPORT PURPOSE This report supplements our previous Interim Report transmitted in our letter PLA-1604, dated April 12,-1983.

DESCRIPTION OF DEFICIENCY During preoperational testing at Susquehanna Steam Electric Station, water hammer occurred in the ESW System, which resulted in damage to three pipe hangers. An investigation into the cause of the hanger failures revealed that there are certain operating and test conditions under which the ESW system could be subjected to water hammer.

The water hammer occurs as a result of the following sequence of events:

(1) ESW System in operation - ESW pumps are on and the 36" Motor Operated

. Bypass Valves to the spray pond are open.

(2) Loss of Offsite Power (LOOP) occurs - ESW pumps trip; 36" MOVs remain open; ESW piping begins to drain down to spray pond.

(3) Power supply transfers from offsite source to onsite emergency diesel generators.

(4) Approximately 10 seconds after the diesel generators receive a start signal, the 36" bypass valves begin to close. The ESW System continues to drain down to the spray pond during the nominal 30-second closure time of the valves.

(5) 55 seconds.after the start of the diesel generators, the ESW pumps restart simultaneously.

The restart of the ESW pumps causes water to be accelerated through partially emptied ESW piping, resulting in water hammer.

It was also determined that the potential for water hammer exists on ESW (loop A only) due to an inadequate 1" keep fill crosstie with service water.

As a result of the above-described events, the potential exists for the ESW System to experience stresses which exceed the design allowables during a water hammer event.

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'PAGE 2 SSES PLA-1812 ERs 100450/100508 FILE 821-10

-CAUSE-Non-simultaneous'LOCA/ LOOP was not a. design basis for the plant.

Also..the water hammer can be caused from having ESW in service and experiencing a LOOP.

SAFETY IMPACT Water hammer may cause degradation of the ESW System. If the ESW System degrades, the safe shutdown of the plant could be compromised. The safety function of'the ESW System is the removal of heat from the ECCS equipment and the diesel generators. The loss of heat removal capability has an adverse affect on plant safety.

' INTERIM FIX See PLA 1604:for a description of the interim fix. The inadequate 1" keep fill crosstie has been corrected by modifying valve arrangements to allow for an additional 4" crosstie. Subsequently test'0P-TY-054, "ESW Operability Test", was parformed and no water hammer was observed.

CORRECTIVE ACTION

-PP&L.has evaluated vacuum breakers, a slow refill system, head tanks, check valves on ESW supply lines to -the control structure chillers, accumulators, motor operated isolation valves on the lines'to the control structure chillers and hanger modifications as possible solutions to the ESW water hammer problem. PP&L's evaluation of these alternatives indicated that the vacuum

. breaker alternative will yield acceptable stress levels, meet the cooling requirements for ESW and not overly complicate the control of ESW. The vacuum breakers.will be installed during the first refueling outage on Unit 1.

The initial computer generated forcing function run for the vacuum breaker solution indicates that this case produces only a fraction of the unbalanced force that would exist without vacuum breakers. The addition of vacuum breakers' introduces air into the piping system when the high points begin to drain. :When the ESW pumps restart, the air is compressed by the water thus reducing the velocity of the two water interfaces.

.The. pressure-spike that results from this scenario is caused by an overshooting of system pressure to dissipate the momentum of the water. This pressure. spike rises very slowly (seconds) compared to the water hammer event without vacuum breakers (milliseconds). Accordingly, the unbalanced forces on the. piping system are significantly reduced since the pressure difference from

.oneLand of a segment to the other end will be small. Actually the " water

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PAGE 3-

-SSES

-PLA-1812 ERs'100450/100508

. FILE 821-10 P

hammer" - the meeting of the two water interfaces - is eliminated by the introduction of air into the. system since the two' water interfaces don't meet 5

during the transient.-

. 0ther' utilities' contacted that have used vacuum breakers as a water hammer fix have not found it necessary to incorporate air relief valves. PP&L is

. investigating any Susquehanna unique features that may make air reliefs

~ necessary.

- COMMITMENT COMPLIANCE PP&L letter PLA-1258 delineates the criteria for operation until the first

-refueling outage on Unit l'and the criteria for the long term fix.

lFor operation until the Unit 1 f'irst refueling outage..PP&L demonstrated by test that the piping stresses were below the allowables during the transient.

The-long term fix commits PP&L to demonstrating that_all piping. hanger and anchor: bolt loads ~for this event are withinL code and NRC allowables either by analysis or testing.

After the installation of the vacuum breakers water hammer related concerns are dismissed since the two water interfaces do not meet during the transient.

.However,:to demonstrate that the vacuum breakers do eliminate water hammer concerns, an analysis is being done for "A"' loop of ESW in the control structure. chiller area. This analysis _will calculate the piping, hanger and anchor bolt loads. PP&L expects that all these loads will be within code and NRC.allowables for the~ existing piping and support system. PP&L will review the results of this analytical effort for ESW loop A and decide if further analyses must be performed for ESW loop B and for the ESW piping for the two direct' expansion units on Unit 2.

This decision will be made by October 31, 1983.

JUSTIFICATION FOR TWO UNIT OPERATION r

Operation of Unit 2 until the startup of Unit i following its first refueling outage will be justified by demonstrating by test that the piping stresses do not exceed-the allowables during the transient (the interim water hammer fix will be used during this period). The_ locations where high water hammer stresses are expected to occur on Unit 2 will be inctrumented with pressure transducers and tests conducted prior to fuel load to show compliance with our

. piping stress commitment.

The control structure chiller area will not have any instrumented tests

}

conducted on it.

Acceptable water hammer loads were achieved in this area

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when'the system was started in'the following sequence:

oEAn ESW pump starts.

T g-e y

.,. r y

e--

w

-+-e,wver ww-,,,w w-

--g vgw yv.--+=,

-m y-

,-vv,.er+q 3,y,,.,s-,y-,*wv,w,,e e,

, - ---,.n..

-,--v-r-v..ww--w-ew-+-

g-

--,,-+

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PAGE 4 SSES PLA-1812 ERs 100450/100508 FILE 821-10 o The ESW. pump. discharge valve remains throttled until the system is

' filled.

o.The ESW pump' discharge valve is fully open before.the bypass. valve begins to open.

7 Acceptable loa'ds were achieved before (TP-54-001 and BLP-24025) with this sequence'of events-(Unit _1 only). Piping loads in this area will continue to be acceptable when it is shown this starting sequence still occurs after Unit 2 is tied in.-

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