ML20126B253

Steam Generator Water Hammer Technical Evaluation for Facility. Eg&G to Id Operations Ofc,Doe,Encl

ML20126B253
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Site:	Maine Yankee
Issue date:	12/31/1979
From:	EG&G, INC.
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4 E626 Idaho, we.

P. O. Som 1625 14ano Fans, loano 83401 i

December 13, 1979 Mr. R. E. Tiller, Director Reactor Operations and Programs Oivision Idaho Operations Office - 00E 1

Idaho Falls,10 83401 MAINE YANKEE POWER STATION STEAM GENERATOR WATER HAMMER TECHNICAL EVALUATICH (A5257} - # 0-250-79 Ref:

J. A.

Dearien Ltr to R. E. Tiller,

PWR Steam Generator Water Hammer Reviews (A6257) - JAO-225-79, November 8,1979 j

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Dear Mr. Tiller:

The attachment completes the assessment of tne effectiveness of the existing means to reduce the potential for steam generator water ha=er at tne Maine Yankee Power Station (MYPS).

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l We have reviewed the operating history of the MYPS certinent to steam generator water hamer and tne related ocerational and proce-cural cnaracteristics of the feedwater system. The review has snown that conditions concucive to steam genera:ce water hac:cer nave oc:urred at the MYPS but no water ha, ner events have been b-served. The conditions have been encountered during nomal

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i ocerating transients and startup and shutdown ccerations. Such conditions would also be expected in the future during the nomal and ac:ident operating situations addressed in the review. Sased l

en enis review we have concluced that the potential for steam gen-i erator water hamer is sufficiently low to permi continued opera-tion of this facility.

This transmittal constitutes completion of the MYPS SER, Task A6257 of :ne referenced Milestone Chart.

Very truly yours, f

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um J.(A.

Dearien,

Manager Coce Assessmen and Apolications Program DOC:tn Attacnment:

As statec S. D. MacKay, NRC-COR R. W. Kienn, IGaG !dano w/o attach.

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l STEAM GENERATOR WATER HAMMER TECHNICAL EVALUATION MAINE YANKEE FOWER STAT!ON Decemoer 1979 9::aho, Inc.

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CONTENTS I.

INTRODUCTION................

1 II. MEANS TO REQUCE THE POTENTIAL FOR WATER HAMMER....... 2 III. OPERATING EXPERIENCE AND WAT'dR HAMMER SUSCEPTIBILITY.... 3 IV. CONCLUSIONS AND RECOMMENDATIONS.............. 6 V.

REFERENCES......................... 7 m

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INTRODUCTION An evaluation was performed for the Maine Yankee Preer Station (MYPS) feedwater system. The purpose of this evaluation was to assess l

the susceptibility of the feedwater system to water hamar during operating transients and situations that could result ir. conditions conducive to water hamer.

Potential steam-water slugging resulting in water hacrner in the steam generator feedrings and -adjacent feedwater pising was considered in this review. This type of water hamer is generally referred to as steam generator water hamer and is characteri:ed by ra:id steam condensation causing water slug acceleration and i cact. The impact of a water slug in the feedwater system has the potential for overstressing systec comoonents and suoports. Stern ger. erat:r water hamer was reported to have never occurred at the MYPS.

The information for this evaluation was obtained f om:

(1) discussions with the licensee, (2) licensee submittals to.iRC of l

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3 July 14,1975, November 25, 1977', and June 6, 1979, '.3) the

" Maine Yankee At:cic Pcwer Station Final Safety Analysis Re: ort"#,

(4) "An Evaluation of PWR Steam Generater Watar Hamer",

5 NUREG-0291, and (5) Westinghouse Technical Bulletin, 5

NSD-73-75-7,

The means to reduce the potential for water hamer at this f acility are presented in Section II.Section III presents descriptions of the feedwater system geometry and operation periaining l

to the susceptibility of the system to steam generat:r water hamer.

This section also cresents a description and tabulation of :cerating I

transients and situations that c:uld risult in condi ic s c:nducive to water hame. Finally, conclusions and recomenda icns.1-e ; resented in Section IV c:n=erning the suscentibility of the feecea:ar system at j

nis f acility t: steam generator water hamtr.

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II. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER The main feedwater piping geometry (original plant design) limits the horizontal lengths of piping adjacent to each steam generator.

The piping arrangement consists of a downward turning 90 elbow about 3 feet 2 inches from the outer surface of each steam generator.

This arrangement limits the horizontal length of piping connected to each steam generator feedring that could drain through the bottom discnarge holes of the feedring. By limiting this length of piping, the maximum volume which could' fill with steam during periods of feedring uncovery is also limited. Thus, limitation of the piping volumes will procortionally limit the energy of potential water hamers due to steam-water slugging.

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III. OPERATING EXPERIENCE AND WATER HAMMER SUSCEPTIBILITY-1 i

The conditiens mr. conducive to steam generator water hammer occur when the steam generator feedrings are uncovered and steam enters the feedrings and attached horizontal feedwater piping.

j Steam-water slugging and subsequent water hammer may occur when incoming cold feedwater mixes with the steam in the piping and rapid condensaticn occurs. The conditions can be avoided by keeping the This can be feedrings and associated piping full cf water.

accomplished by (1) keeping the water levels in the steam generators above the feedrings or (2) supplying feedwater at a higher flow rate than the rate at wnich feedwater drains through the discharge holes on the bottom of uncovered feedrings.

rollowing a reactor trip, the steam generator water levels drop 4

i by a cuantity aporeximately orocortional to the reactor power prior to the trip. For examcle, the greatest deco wouic occur at full power.

The drop or " shrinkage" in water level is the result of interrupted j

essure reactor power production and increased steam generator steam causing the collapse of steam veios within the secondary side of the steam generators. A si.milar situation would also be experienced during events such as loss of main feedwater, loss of offsite power, steam line break, and less-of-coolant accident.

The MYP5 has experienced 23 full power reactor tries since unit It was recortad that feedring uncovery occurred in all steam startuo.

generators as a result of each triet There have been two comolete loss of main feedwater events since initial unit startuo. The first event occurred on Novemoer la, 1972 at a reactor power level of 33%. Failure of the one coerating main feedwater pumo due to bearing problems necessitated starting of the other main feedwater pumo. The inability to coen the cischarge valve 3

r of the s*cond pump required the manual trip of the reactor and turbine. An auxiliary feedwater pump was started to restore and maintain steam generator water levels.

The second loss of main feedwater event occurred on August 31, 1978. The event was the direct result of the only loss of offsite power event to have occurred since unit startup. A fault in one of the stations's main transformers resulted in reactor and turbine trips and the loss of offsite power. As was the case for the first loss of main feedwater event, an auxiliary feedwater pump was started to restore and maintain steam generator water levels.

Information was unavailable as to whether or not feedring uncovery events occurred during startup and shutdown operations.

However, similar past reviews for other f acilities have revealed the difficulty in maintaining the steam generator water levels above the feedrings at all times during ooerating situations requiring manual feedwater control.

1 It is accarent from the review of the plant operating history that it is not always possible to avoid drainage of the feedrings and adjacent piping by keecing the feedrings covered with water. Although the drainage time (or uncovery time) varied snong the uncovery events, complete crainage of the feedrings and adjacent piping has been frecuent since the time required for complete drainage is less than one minute and the uncovery times were generally of longer duration.

The alternative to continuous coverage of the feedrings with water is to maintain sufficient feedwater flow through uncovered feedrings to keep the feedrings full of water. The ficw required for this at the MYP5 is accroximately 1800 gpm per steam generator based on static pressure drainage calculations. Since a total feedwater flow rate of. aocut 2S,000 gpm is required for full reactor :ower, the j

feedrings and feedwater piping would be kect full only witn feecwater ficw rates corresconding to power levels above aoout 150 MWe or 20% of

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full power. Thus, during startup, shutdown, and low power operation, feedwater flow requirements are insufficient to keep the feedrings I

full of water during periods of feedring uncovery. This situation l

would also be exoected during recovery from events resulting in j

reactor trips from power operation such as loss of main feedwater, loss of offsite power, steam line break, and loss of coolant accident.

Feedwater can also be supplied to the steam generators via the auxiliary feedwater system. Auxiliary feedwater can be pumped into i

cach of the three main feedwater lines at a location between the containment building and crane. wall just downstream of the last main foedwater check valve. The system consists of two motor driven and a

one turbine driven auxiliary feedwater pumps each having a cacacity of l

i 500 gpm for a total capacity of about 1500 gpm. During any j

operational phase of the plant, the cacacity of the auxiliary feedwater system would not be sufficient to '<eea uncovered feedrings l

full of water.

l The review of the operating history at the MYPS indicates that the conditions conducive to steam generator water hamer exist during normal coerating situations. However, it was reported that water hamer of this type has never occurred at this f acility nor has any feedwater system damage been found to indicate possible unobserved water hamer events. An aoparent contradiction exists between the f act that water hame" has not been observed although conditions considered conducive to water hamer frequently occur. The exclanation for this observation is not readily identifiable but probably relates to inherent characteristics of the feedwater system and/or plant operating procedures, t

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IV. CONCLUSIONS AND RECOMMENDATIONS We have reviewed the operating history of the MYPS pertinent to steam generator water hammer and the related operational and procedural characteristics of the feedwater system. The review has shown that conditions conducive to steam generator water henner have occurred at the MYPS but no water hammer events have been observed.

The conditions have been encountered during normal operating transients and startue and shutdown operations.

Such conditions would also be expected in the future.during the normal and accident operating situations addressed in the review. Based on this review we have concluded that the potential for steam generator water hammer is sufficiently low to permit continued coerstion of this facility.

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REFERENCES 1.

J. L. French, Maine Yankee Atomic Power Company (MYAPC), letter to R. A. Purple, NRC, Subject

" Response to May 13, 1975 letter on Steam Generator Water Hamer', July 14, 1975.

2.

R. H. Groce, MYAPC, letter to R. W. Reid, NRC, Subject -

"Feedline Water Hamer", Novemoer 25, 1977.

3.

C. D. Frizzle, MYAPC, letter to R. Colmar, NRC, Subject

" Maine Yankee Steam Generator Feedwater Piping", June 6,1979.

4 Final Saf e:v Analysis Recert, Maine Yankee At:cic Power Station, MYAPC, NRC Occket No. 50-309.

5.

J. A. Block, et al, An Eva'uatien of 8'e Steam 3enerator Wate-Hame*, Creare, Inc., NURE3-C291 (Decr.:er 1975).

6.

W. E. Sennett, Watarhammer in 5:eam Genera::r Fee: water _ines, Westingneuse Technical Bu'letin, N50-T5-75-7 (June 10, 1975).

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2 DISTRIBUE0N Central file J AN 1.,.gg NRC POR PSB Reading d.-

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I t'E t0RA!!DUti FOR:

R. Reid, Chief, Operating Reactors Branch 14, 00R FR0!1:

G. Lainas, Chief, Plant Systems Branch, 00R

SUBJECT:

MAINE YANKEE STEAM GENERATOR WATER HAffiER EVALUATION Plant Nane: fiaine Yankee Atomic Power Station Docket No.:

50-309 Resconsible Branch: ORE!4 Project l'anager:

M. Fairtile Reviewing Branch:

Plant Systems Branch Review Status: Complete In response to Technical Assistance Request, TAC No. 7191, regarding water hammer in the Maine Yankee feecwater systems, the Plant Systems Branch has completed its review and found that acceptable precautions are being taken to minimize the occurrence of water hammer in the feedwater piping. The basis for our conclusions are provided in the enclosed Safety Evaluation Report and our consultants' report dated December 1979.

This completes our review of steam generator water hammer under TAC No. 7191.

G.'Lainas, Chief Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated

Contact:

S. MacKay X-27111 cc w/ enclosures:

See page 2 r

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NUCLEAR REGULATORY COMMISSION

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wasmNoros. o. c. 2 ossa g, v f JAN 171960 i

l MEMORANDUM FOR:

R. Reid, Chief, Operating Reactors Branch #4, 00R FRCM:

G. Lainas, Chief, Plant Systems Branch, 00R

SUBJECT:

MAINE YANKEE STEAM GENERATCR WATER HAMMER EVALUATION l

i Plant Name: Maine Yankee Atomic Power Station Occket No.: 50-309 Responsible Branch: ORB #4 Project Manager:

M. Fairtile Reviewing Branen: Plant Systems Branch Review 5:stus: Complete In ress:ense to Technical Assistance Request, TAC No. 7191, regarding water nar=er in the Maine Yankee feedwater systems, the Plant Systems Branen nas completed its review and found that acceptacle precautions are being taken to minimite the occurrence of water hammer in the feedwater piping. The basis for our conclusions are provided in tne enclosed Safety Evaluation Report and our consultants' report cated Decemoer 1979.

This ccmoletes our review of steam generator water hammer under TAC No. 7191.

O G. Lainas, Chief Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated

Contact:

S. MacKay X-27111 c:. w/ enclosures:

See page 2

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. 1 JAN 171c80 cc w/ enclosures:

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0. Eisennut S. Hanauer B. Grimes E. Adensam W. Garmill i

M. Fairtile S. Mac.<ay

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SAFETY E'/ALUATICN REPCRT STEAM 3ENERATOR WATEP. HAMMER MA:tlE YAtlKEE ATCM C POWER STATICN DCCXET !!0. 50-3C9 DECEMBER 1979 l

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1.0 INTRODUCTION

Steam generator water hammer has occurred in certain nuclear power plants as a result of the rapid condensation of steam in a steam generator feedwater line and the consequent acceleration of a slug of water wnich ucon impact within the piping system causes undue stresses in the piping and its suoport system.

The significance of these events varies from plant to plant. Since a total loss of feedwater could affect the ability of the plant to cool down after a reactor shutdown, the NRC is concerned about these events occurring, even thougn

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an event with potentially serious consequences is unlikely to haopen.

Because of the continuing occurrence of water hammer events, the NRC, in Septemaer 1977, informed all PWR licensees that water hammer events due to the rapid condensation of steam in the feedwater lines of steam generators represented a safety concern and that further actions by licensees for Westinghouse and Combustion Engineering designed nuclear steam sucoly systems are warranted to assure thgt an acceptably low risk to public safety due to such events is maintained. Accordingly, these licensees were requested to submit proposed hardware and/or procedural modifications, if any, which would be necessary to assure that the feedwater lines and feedrings remain filled with water during normal as well as transient operating conditions. At the same time, the NRC provided each PWR licensee with a copy of its consultant's report, "An Evaluation of PWR Steam Generator Water Hammer," NUREG-0291.

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-2 The evaluation of the potential for steam generator water harmer at the Maine Yenkee plant shews that the feedwater piping adjacent,to the steam generator consists of a favoraoly short run of horizontal' piping and' that during seven years of successful operation it has experienced those conditions that might induce steam generator water hammer; but no water hanmer has oc:urred.

2.0,E]!('JA,TICN Our consultant, EG&G Idaho inc., prepared the attached evaluation of steam generator water hanter at the Maine Yankee Plant as part of our technical assistance program.

(Letter from J. A. Coarien, EG5G, to R.E. Tiller, 00E, dated Cecember 13, 1979.) We have reviewed this report together with the licensees submittals listed under item 4.0.

3.0 CONCLU5lCN, Based on our knowledge of water hammer phenomena, and our review of the licensees responses and the enclosed evaluatien report, we concur with our consultants' conclusien that the potential for steam generator water ham?.er is sufficiently low to perm,it continued operation of this facil ity. However, even though steam generator water hanner is not likely to occur, the licensee should be vigilant and nonitor for water haneers that might impose significant stresses on the piping systems or their supports. We will continue to monitor reports from this licenses for indications of possible water hammer. If

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such indications appear in the future, this matter will be reexamined and any result in additional requirements to reducs

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the probabflity of steam generator unter hamer at these facilities.

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We have concluded that steam generator water hammer is not likely to occur at this facility and, therefore, we find no undue risk to the health and safety of the public as a result of the continued operation of the Maine Yankee Atomic Power Station.

4.0 REFERENCES

4.1 J.L. French, Maine Yankee Atomic Power Company (MYAPC), letter to R. A. Pur:le, NRC.

Subject:

"Resconse to May 13, 1975 letter on Steam 3enera::e Water Hammer," July 14, 1975.

4.:

R.H. Gr:ce, MYAPC, let:er to R.W. Reid, NRC,

Subject:

"Feedline Water Hammer," November 25, 1977.

2.2

~.:. Fri::'e, MY FC, let:er R. Colmar, NRC,

Subject:

" Maine Yankee 5:eam Generator Feedwater Piping," June 6,1979.

4.4 0.E. Mcody, 9Y PC, letter to R. Reid, NRC, dated November 15,1979, in res:onse to NRC request for information regarding the potential for steam generator water hammer.

4.5 J.A. 31cck, et al, An Evaluation of PWR Steam Generator Water Han?.er, Creare, Inc., NUREG-0291 (Decameer 1976).

4.6 W.E. Bennett, Waternammer in Steam Generator Feecwater Lines, Westinghouse Technical Bulletin, NSD-TB-75-7, June 10,1975.

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EUE,6 Idaho, Inc.

P. O. Som 161s taano Falls. Iceo 3M01 December 13, 1979 Mr. R. E. Tiller, Director Reacter Operations and Programs Division Idaho Operations Office - 00E Idano Falls, ID 83401 MAINE YANKIE 80WER S~ATION STEAM GENERATOR WATER HA."MER TECHNICAL EVAL'JAT 0N (Ac257) - JAO-250-79 Ref:

J. A.

Dearien L r to R. E. Tiller,

PWR steam Genera:Or Water Hamer Reviews (A6257) - JAO-225-79, Novem:er 8,1979

Dear Mr. Tflier:

The attachmen: c mpletes one assessment of :ne ef#ectiveness Of the existing means to recuce the Octential for steam genera =r water ha=er at ne Maine Yankee Pcwer Station (MYPS).

We have reviewed the ::erning history of.he MYP5 ertinent t:

steam generat:r water hamer and One relatec c:erational and proce-cural enaracteristics of the feecwater system. The review nas snewn :na: c:nditions encucive to steam genera =r water na=er nave oc:urred a: the MYP5 but no water hamer events have been b-served. The conditions have been encountered during nomal coerating transients and s artup and shutdown 0:ernions. Suca conditions would also de expected in the fu:ure curing the nemal and at:iden =erating si.uations addressed in ne review. Sased on :nis review we have concluced that the potantial for staam gen-era:ce water namer is sufficien ly 1cw u pemi ::ntinued coera-tien of :nis facility.

Tnis transmittal constitutes ccm:letion of :ne.dYP5 SER, Task A6257 of :ne referenced Milest:ne Char.

Very truly ycurs,

_q m._

J. A. Cearien, Manager C:ce Assess:nent and Acolications P-Ogram 00C::n A::ac.-men :

as s:sted

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5. O. Mac.<ay, NRC-COR R. W. Kiehn, EG3G lcano w/c attaen.

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STEAM 3EIGATOR WATT.R HAMMER TECHNICAL r/ALUATION MAINE YANKEE POWER STAT *0N 3ecem er 1979

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e CONTENTS I.

LNTRO DU CT IO N........................ 1 II. MEANS TO REDUCE TiiE POTEYrIAL FOR WATER HAMMER....... 2 III. OPERATING EXPERIENCE AND WATER HAMMER SUSCE?TI3ILITY.... 3 IV. CONC:.USIONS ANO RECOMMENOATICNS.............. 6 V.

REFERENCIS......................... 7 9

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INTRODUCTION An evaluation was performed for the Maine Yankee P eer Station (MYPS) feedwater systen. The purpose of this evaluation was to assess the susceptibility of the feedwater system to water harcar during j

operating transients and situations that could result in conditions conducive to water hunner.

Potential steam-water slugging resulting in water hanmer in the steam generater feedrings and adjacent feedwater pising was considered in this review. This type of water hammer is generally referred to as steam generat:r wa ar han er and is characteri:ed by ra:id steam c ncensatien causing water slug acceleration anc i :act. The im ac:

Of a water slug in the feedwater system has the pe:ential for overs ressing systa= c:meonents and succcris. Steam ger. erat:r water hammer was reported to have never occurred at the MYPS.

The information for this evaluation was Obtained f 3::

(1) discussions with the licensee. (2) licensee submit:als to.iRC Of 2

3 July 14,1975, Novemcer 25, 1977, and June 6, 1979, '3) the

" Maine Yankee Atatic Power Station Final Safety Analysis Re: Ort"#,

(4) "An Evaluation of PWR Steen Generator Water Hasner",

NUREG-0291', and (5) Westinghouse Tecnnical Bulletin, a

NSD-73-75-7.

The means to reduce the potential for watar henter at this facility are cresented in Section II.Section III presants descriptions of the feedwater system geometry and opera-ion pertaining to the suscactibility of the system to steam generat:r natar hammer.

This section also scesents a description and taculation of :cerating transients and situations that could result in conditic s c:ncucive o water hanner. Finally, conclusions and rec =ninendaticns 1-e : resented in Secticn IV c:n=erning the suscectibility of tne feecea ar system at this f acility : steam generator watar hammer.

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II. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER The main feedwater piping gecmetry (criginal plant design) limits the horizontal lengths of piping adjacent to each steam generator.

U The picing arrangement c:nsists of a downward turning 90 elbow about 3 feet 2 inches from tne outer surf ace of each steam generator.

This arrangement limits the horizontal length of piping c:nnected to eacn steam generater feedring that c:uld drain through the bottsu discnarge holes of the feecring. By limiting this length of pioing, the maximum volume which could' fill with steam during periods of feedring uncovery is also limited. Thus, limitation of the piping volumes will or:cortionally limit the energy of potential water hammers eue to steam-wa:ar slugging.

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e III. OPEATING EXPGIENCE AND WATG HAMMG SUSCEPTIBILITY-The conditiens mr. conducive to steam generater water hammer cccur when the steam generator feedrings are uncovered and steam enters the feedrings and attached horizontal feedwater piping.

Steam-water slugging and subsequent water hammer may occur when inc: ming cid feedwater mixes with the stern in the piping and rapid c:ncensaticn oc:urs. The conditiens can be avoided by knecing the This can be fejdrings and associated cicing full cf water.

ac:cmolished by (1) keeping the water levels in the steam generators acave the feedrings or (2) succlying feedwater at a higner flow rate wni:n feedwater drains necugn :ne dis:nar;e holes on than :he ra:e a:

ne :ct := cf unc:vered feecrings.

Fellowing a react:r tric, the steam genera::r nater levels cr:0 by a :uantity accroximately precortional Oc :he react:r ;cwer crice to ne trip. For examcle, One greatest drce wculd oc:ur at #ull ;cwer.

The drep cr " shrinkage" in water level is the result of inter ucted essure

-eactor sewer procuction and increased steam genera:ce steam causing the OcIlacse of steam voics within the secondary side Of the A similar situation would also te ex:erienced steam generators.

during events such as loss of main feedwater, icss Of Offsite power, steam line break, and less-of-ccclant ac:ident.

The MYP5 has excerienced 23 full power reactor trics since unit It was recortad that feedring uncovery oc:urred in all steam startue.

generators as a result of each trip.-

There have been two ecmolete loss of main feedwater events since initial unit startue. The firs event oc:urred :n Novemcer la,1972 at a reactor cower level of 32%. Failure of the one :cerating main feedwater cumo due to bearing cr:blems necessitated starting of the c:Mer main feedwater cumo. The inacility to :cen One :ischarge valve l

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l of the sec:nd pumo required the manual trip of the reactor and turbine. An auxiliary feedwater pump was started to restore and maintain steam generator water levels.

The second loss of main feedwater event oc:urred on August 31, 1978. The event was the direct result of the oniv loss of offsite power event to have occurred since unit startup. A fault in one of l

the stations's main transformers resultad in reacter and turbine trips j

and the less of offsite power. As was the casa for the first loss of main feedwater event, an auxiliary feeewater pume was started to restore and maintain steam generater water levels.

Inf:rmati n was unavailable as t whether er not fetcring uncovery events oc:ur ed during startus and snutd:wn c: era:icns.

However, similar past reviews for c her f acilities have revealed One difficulty in maintaining the steam generat:r water levels a:cve :Me feedrings at all times during coerating situatiens requiring manual f ee: water ::ntrol.

It is accarent from the review of the plant cerating history that it is not always pessible to avoid drainage of the feedrings anc adj acen cicing by keecing the feedrings covered with watar. Altacugn the drainage time (er uncovery time) varied among the unc very events, c:melete crainage of the f eecrings and acjacent piping has been frecuent since the time required for e:mplete drainage is less than

ne minute and the uncovery times were generally of longer duration.

The alternative to continuous c:verage :f the feedrings with water is to maintain sufficient feedwater flow through uncovered feecrings to keep the fendrings full of water. The flew recuired for

Mis at the MYoS is accreximately 1300 gpm per staam genera::r based en static meessure crainage calculations. Since a t::a1 fencwater f1:w rate f aceut 23,000 gpm is recuired f:r full reac::r :cwer, the feecrings anc feedwater pi:ing we';1d :e kect full :nly 41:n fee:watar f* 0w estas c:r'esconding :s sewer levels acove aceu 150 MWe Or 20% :f r

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full power. Thus, during startue, shutdown, and low power operation, feedwater flow requirements are insufficient to keep the feedrings

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full of water during periods of faecting uncovery. This situation would also be excected during recevery from events resulting in reactor trics from power operation such as loss of main feedwater, loss of offsite power, steam line break, and less of coolant accident.

Feedwater can also be sucplied to the steam generators via the j

l auxiliary feedwater system. Auxiliary feedwater can be pumped into j

eacn of the tnree main feedwater lines at a location between the containment building and crane wall just dcwnstream of the last main f eedwater check valve. The system consists of two. meter driven and one turbine driven auxiliary feedwater pumps each having a cacacity of 5C0 gpm for a Octal cacacity of about 1500 gem. During any c;erational snase of the plant, the cacacity of the auxiliary f eecwater system would not be sufficient to keec uncevered feedrings full of water.

1 The review of the coerating history at the MY?S indicates tna; the conditions conducive to steam generatar water hammer exist during ncrmal coerating situatiens. However, it was recorted that watar j

hunner cf this type has never cccurred at this f acility nor nas any i

feecdater system damage been found to indicate possible unceserved watar hsnner events. An accarent contradiction exists between the f act that water harmer has not been ooserved al:ncu;n conditions considered conducive to water hsnner frequently occur. The exclanation for this coservation is not readily identifiaole but j

probably relates to inherent characteristics of the feedwatar system and/or plant coerating procedures.

5

4 IV. CONCLUSIONS AND RECOMMENDATIONS We have reviewed the coersting history of tne MYPS pertinent to steam generator water hammer and the related operational and procedursi characteristics of the feedwater system. The review has shown that conditions conducive to steam generator water hammer have occurred at the MYPS but no water hammer events have been observed.

The conditiens have been encountered during normal coerating transients and startue and shutdown ocerations. Such conditions would also be expected in the future during the normal and accident coerating situations addressed in the review. Based on this review we have concluded that the ?ctential for steam generator aatar ht :er is

- sufficiently low to permit continued coeration of this f acility.

5

V.

REFERENCES 1.

J. L. French, Maine Yani,ee At:mic Power Cs:cany (MYAPC), letter to R. A. Purple, NRC, Subject

" Response to May 13, 1975 letter on Steam Generater Water Hanmerd, July 14, 1975.

)

2.

R. H. Grece, MYAPC, letter to R. W. Reid, NRC, Subject -

"icedline Water Hammer, Novemeer 25, 1977.

d 3.

C. O. Friz:le, MYAPC, letter to R. Colmar, NRC, Subject

" Maine Yankee Steam Generator Feedwater Piping", June 6,1979.

4 Final Saf ety anaivsis Recert, Maine Yaakee A::mic P0wer 3 ati:n, MYAPC, NRC Occks: No. 50-309.

l 5.

J. A. Block, e: a', An Iva'Jatien of )WR Steam 3ene-s:ce Water Hamme, Creare, 'nc., NL'R33-C29*. (:e:rt:er 1975;.

1 5.

W. E. Bennett, Waternammer in Steam Gene-t :r Fee:wa e

ines, Westingneuse Tecnnical Eu::e-in, NSC-75-75-7 (June 10,1975).

4 l

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[0, UNITED STATES y

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'. j WASHINGTON, D. C. 20555 o

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/

JAN 171980 MEMORANDUM FOR:

R. Reid, Chief, Operating Reactors Branch #4, 00R FROM:

G. Lainas, Chief, Plant Systems Branch, DOR

SUBJECT:

MAINE YANKEE STEAM GENERATOR WATER HAMMER EVALUATION Plant Name: Maine Yankee Atomic Power Station Docket No.:

50-309 Responsible Branch: ORB #4 Project Manager:

M. Fairtile Reviewing Branch:

Plant Systems Branch Review Status: Complete l

In response to Technical Assistance Request, TAC No. 7191, regarding water hammer in the Maine Yankee feedwater systems, the Plant Systems Branch has completed its review and found that acceptable precautions are being taken to minimize the occurrence of water hammer in the feedwater piping. The basis for our conclusions are provided in the enclosed Safety Evaluation Report and our consultants' report dated December 1979.

This completes our review of steam generator water hammer under TAC 1

No. 7191.

i W

G. Lainas, Chief Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated

Contact:

S. MacKay X-27111 cc w/ enclosures:

See page 2 l

I l

' JAN I 71980 l

cc w/ enclosures:

t D. Eisenhut S. Hanauer B. Grimes E. Adensam W. Gannill M. Fairtile S. MacKay V. Noonan

1 SAFETY EVALUATION REPORT STEAM GENERATOR WATER HAMMER MAINE YANKEE ATOMIC POWER STATION 00CXET N0. 50-309 DECEMBER 1979

1.0 INTRODUCTION

Steam generator water hammer has occurred in certain nuclear power plants as a result of the rapid condensation of steam in a steam generator feedwater line and the consequent acceleration of a slug of water which upon impact within the piping system causes undue stresses in the piping and its support system.

The significance of these events varies from plant to plant. Since a total loss of feedwater could affect the ability of the plant to cool down after a reactor shutdown, the NRC is concerned about these events occurring, even though an event with potentially serious consequences is unlikely to happen.

1 Because of the continuing occurrence of water hammer events, the NRC, j

in September 1977, informed all PWR licensees that water hammer events f

due to the rapid condensation of steam in the feedwater lines of steam generators represented a safety concern and that further actions by licensees for Westinghouse and Combustion Engineering designed nuclear steam supply systems are warranted to assure that an acceptably low risk to public safety due to such events is maintained. Accordingly, these licensees were requested to submit proposed hardware and/or procedural modifications, if any, which would be necessary to assure that the feedwater lines and feedrings remain filled with water during normal as well as transient operating conditions. At the same time, the NRC provided each PWR licensee with a copy of its consultant's report, "An Evaluation of PWR Steam Generator Water Hammer," NUREG-0291.

i

4

-2 The evaluation of the potential for steam generator water hamer at the Maine Yankee plant shows that the feedwater piping adjacent s,to the steam generator consists of a favoraoly short run of horizontal

• piping and!

that du' ring seven years of successful operation it has experienced those conditions that might induce steam generator water hamer; but no water hamer has occurred.

2.0 EVALUATION Our consultant, EG&G Idaho Inc., prepared the attached evaluation of steam generator water hamer at the Maine Yankee Plant as part of our technical assistance program.

(Letter from J. A. Ocarien, EG8G, to R.E. Tiller, DOE, dated December 13, 1979.) We have reviewed this report together with the licensees submittals listed under item 4.0.

3.0 CONCLU51g l

l Based on our knowledge of water hamer phenomena, and our review of the licensees responses and the enclosed evaluation report, we concur with our consultants' conclusion that the potential for steam generator water hamer is sufficiently low to permit continued operation of this facility. However, even though steam generator water har.mer is not likely to occur, the licensee should be vigilant and monitor for water hamers that might impose significant stresses on the piping systems or their supports. We will continue to monitor reports from this licensee for indications of possible water hammer. If s'

)

such indications appear in the future, this matter will be j

-/'

reexamined and may result in additional requirements to reduce the probability of steam generator water hamer at these facilities.

e

We have concluded that steam generator water hammer is not likely to occur at this facility and, therefore, we find no undue risk to the health and safety of the public as a result of the continued operation of the Maine Yankee Atomic Power Ststion.

4.0 REFERENCES

4.1 J.L. French, Maine Yankee Atomic Power Company (MYAPC), letter to R.A. Purple, NRC,

Subject:

" Response to May 13, 1975 letter on Steam Generator Water Hammer," July 14, 1975.

4.2. R.H. Groce, MYAPC, letter to R.W. Reid NRC,

Subject:

"Feedline Water Hammer," November 25, 1977.

4.3 C.D. Frizzle, MYAPC, letter to R. Colmar, NRC,

Subject:

" Maine Yankee Steam Generator Feedwater Piping," June 6,1979.

4.4 D.E. Moody, MYAPC, letter to.R. Reid, NRC, dated November 15, 1979, in response to NRC request for information regarding the potential for steam generator water hammer.

4.5 J. A. Block, et al, An Evaluation of PWR Steam Generator Water Hamer, Creare, Inc., NUREG-0291 (December 1976).

4.6 W.E. Bennett, Waterhamer in Steam Generator Feedwater Lines, Westinghouse Technical Bulletin, NSD-TB-75-7, June 10,1975.

l

i

~

4 b

E G n 3 ie.no,inc.

p Idaho Falls, Icano 83401 December 13, 1979 Mr. R. E. Tiller, Director Reactor Operations and Programs Division Idaho Operations Office - DOE Idaho Falls,10 83401 MAINE YANKEE POWER STATION STEAM GENERATOR WATER HMMER TECHNICAL i

EVALUATION (A6257) - JAD-250-79 Ref:

J. A.

Dearien Ltr to R. E. Tiller,

PWR Steam Generator Water Hamer Reviews (A6257) - JAD-225-79, November 8,1979

Dear Mr. Tiller:

The attachment completes the assessment of the effectiveness of the existing means to reduce the potential for steam generator water hammer at the Maine Yankee Power Station (MYPS).

We have reviewed the operating history of the MYPS pertinent to steam generator water hammer and the related operational and proce-dural charheteristics of the feedwater system. The review has shown that conditions conducive to steam generator water hamer have occurred at the MYPS but no water hamer events have been :b-served. The conditions have been encountered during normal operating transients and startup and shutdown operations. Such conditions would also M expected in the future during the nomal and accident operating ;ituations addressed in the review. Based on this review we have concluded that the potential for steam gen-erator water hamnier is sufficiently low to pemit continued opera-tion of this facility.

This transmittal constitutes completion of the MYPS SER, Task A6257 of the referenced Milestone Chart.

Very truly yours, wx J. A.

Dearien,

Manager Code Assessment and Applications Program DDC:tn

Attachment:

As stated cc:

5. O. MacKay, NRC-00R R. W. Kiehn, EG&G Idaho w/o attach.

t 4

STEAM GENERATOR WATER HAMMER TECHNICAL EVALUATION MAINE YANKEE POWER STATION December 1979 EG&G Idaho, Inc.

+

9 I

l l

I l

I-CONTENTS I.

INTRODUCTION........................ 1 II. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER....... 2 III. OPERATING EXPERIENCE AND WATER HAMMER SUSCEPTIBILITY.... 3 IV. CONCLUSIONS AND RECOMMENDATIONS.............. 6 V.

REFERENCES........................ 7 O

e 9

I.

INTRODUCTION An evaluation was performed for the Maine Yankee Puer Station (MYPS) feedwater system. The purpose of this evaluatior. was to assess the susceptibility of the feedwater system to water hax:ar during operating transients and situations that could result in conditions conducive to water hamer.

Potential steam-water slugging resulting in water 5 amer in the steam generator feedrings and adjacent feedwater piping was considered in this review. This type of water hammer is generally referred to as steam generator water hamer and is characterized by ra:id steam condensation causine water slug acceleration and iroact. The impact of a water slug in th2 feedwater system has the potential for overstressing system components and supports. Stern ger. erat:r water hamer was reported to have never occurred at the MYp5.

The information for this evaluation was obtained f om:

(1) discussions with the licensee, (2) licensee submitt:Is to NRC of 1

2 3

July 14,1975, November 25, 1977, and June 6, 1979, '.3) the

" Maine Yankee Atomic Power Station Final Safety Analysis Report"#,

(4) "An Evaluation of PWR Steam Generator Water Hamer",

3 NUREG-0291, and (5) Westinghouse Technical Bulletin, 5

N50-TB-75-7,

The means to reduce the potential for water hamer at this f acility are presented in Section II.Section III presants descriptions of the feedwater system geometry and operation pertaining to the susceptibility of the system to steam generator water hamer.

This section also cresents a description and tabulation of coerating transients and situations that could result in conditic s conducive to water hamer. Finally, conclusions and recomenda: ions are presented in Section IV concerning the susceptibility of the feecea:er system at this f acility to steam generator water hamer.

1

t II. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER The main feedwater piping geometry (original plant design) limits the horizontal lengths of piping adjacent to each steam generator.

The piping arrangement consists of a downward turning 90 elbow about 3 feet 2 inches from the outer surface of each steam generator.

This arrangement limits the horizontal length of piping connected to each steam generator feedring that could drain through the bottom discharge holes of the feedring. By limiting this length of piping, the maximum volume which could' fill with steam during periods of feedring uncovery is also limited. Thus, limitation of the piping

' volumes will proportionally limit the energy of potential water hamers due to steam-water slugging.

2

.,t III. OPERATING EXPERIENCE AND WATER HAMMER SUSCEPTIBILITY-The conditions mr. conducive to steam generator water hammer occur when the steam generator feedrings are uncovered and steam enters the feedrings and attached horizontal feedwater piping.

Steam-water slugging and subsequent water hammer may occur when incoming cold feedwater mixes with the steam in the piping and rapid condensation occurs. The conditions can be avoided by keeping the This can be feedrings and associated piping full of water.

accomplished by (1) keeping the water levels in the steam generators above the feedrings or (2) supplying feedwater at a higher flow rate than the rate at which feedwater drains through the discharge holes on the bottom of uncovered feedrings.

Following a reactor trip, the steam generator water levels drop by a quantity approximately proportional to the reactor power prior to the trip. For example, the greatest drop would occur at full power.

The drop or " shrinkage" in water level is the result of interrupted essure reactor power production and increased steam generator steam causing the collapse of steam voids within the secondary side of the A similar situation would also be experienced steam generators.

during events such as loss of main feedwater, loss of offsite power, steam line break, and loss-of-coolant accident.

The MYPS has experienced 23 full power reactor trips since unit It was reported that feedring uncovery occurred in all steam startup.

generators as a result of each trip.-

There have been two complete loss of main feedwater events since initial unit startue. The first event occurred on November 14, 1972 at a reactor power level of 33%. Failure of the one operating main feedwater pumo due to bearing problems necessitated starting of the other main feedwater pump. The inability to ooen the discharge valve 3

a s

e 3

of the second pump required the manual trip of the reactor and turbine. An auxiliary feedwater pump was started to restore and maintain steam generator water levels.

The second loss of main feedwater event occurred on August 31, 1978. The event was the direct result of the only loss of offsite power event to have occurred since unit startup. A fault in one of the stations's main transformers resulted in reactor and turbine trips and the loss of offsite power. As was the case for the first loss of main feedwater event, an auxiliary feedwater pump was started to restore and maintain steam generator water levels.

Information was unavailable as to whether or not feedring uncovery events occurred during startup and shutdown operations.

However, similar past reviews for other f acilities have revealed the difficulty in maintaining the steam generator water levels above the feedrings at all times during operating situations requiring manual feedwater control.

It is apparent from the review of the plant operating history that it is not always possible to avoid drainage of the feedrings and adjacent piping by keeping the feedrings covered with water. Although the drainage time (or uncovery time) varied among the uncovery events, complete drainage of the feedrings and adjacent piping has been frequent since the time required for complete drainage is less than one minute and the uncovery times were generally of longer duration.

The alternative to continuous coverage of the feedrings with water is to maintain sufficient feedwater flow through uncovered feedrings to keep the feedrings full of water. The flow required for this at the MYPS is approximately 1800 gpm per steam generator based on static pressure drainage calculations. Since a total feedwater flow rate of about 28,000 gpm is repuired for full reactor power, the fcedrings and feedwater piping wo11d be kept full only witn feedwater flow rates corresponding to power levels above about 150 MWe or 20% of 4

1 i

4 full power. Thus, during startup, shutdown, and low power operation, feedwater flow requirements are insufficient to keep the feedrings

~

full of water during periods of feedring uncovery. This situation would also be expected during recovery from events resulting in reactor trips from power operation such as loss of main feedwater, loss of offsite power, steam line break, and loss of coolant accident.

Feedwater can also be supplied to the steam generators via the auxiliary feedwater system. Auxiliary feedwater can be pumped into each of the three main feedwater lines at a location between the containment building and crane wall just downstream of the last main feedwater check valve. The system consists of two motor driven and one turbine driven auxiliary feedwater pumps each having a capacity of 500 gpm for a total capacity of about 1500 gpm. During any operational phase of the plant, the capacity of the auxiliary feedwater system would not be sufficient to kaap uncovered feedrings full of water.

The review of the operating history at the MYP5 indicates that the conditions conducive to steam generator water hamer exist during normal operating situations. However, it was reported that water hammer of this type has never occurred at this f acility nor has any feedwater system damage been found to indicate possible unobserved water hamer events. An apparent contradiction exists between the fact that water hammer has not been observed although conditions considered conducive to water hamer frequently occur. The exalanation for this observation is not readily identifiable but probably relates to inherent characteristics of the feedwater system and/or plant operating procedures.

5

4 e

IV. CONCLUSIONS AND RECOMMENDATIONS We_have reviewed the operating history of the MYP5 pertinent to steam generator water hammer and the related operational and

. procedural characteristics of the feedwater system. The review has shown that conditions conducive to steam generator water hammer have occurred at the MYPS but no water hammer events have been observed.

The conditions have been encountered during nonnal operating transients and startup and shutdown operations.

Such conditions would also be expected in the future-during the normal and accident operating situations addressed in the review. Based on this review we 4

have concluded that the potential for steam generator water henner is sufficiently low to permit continued operation of this facility.

e f

^

4 6

J-e V.

REFERENCES 1.

J. L. French, Maine Yankee Atomic Power Company (MYAPC), letter to R. A. Purple, NRC, Subject

" Response to May 13, 1975 letter on Steam Generator Water Hanrner", July 14, 1975.

2.

R. H. Groce, MYAPC, letter to R. W. Reid, NRC, Subject -

"Feedline Water Hamer", November 25, 1977.

3.

C. O. Frizzle, MYAPC, letter to R. Colmar, NRC, Subject

" Maine Yankee Steam Generator Feedwater Piping", June 6,1979.

4 Final Safety Analysis Reoort, Maine Yankee Atomic Power Station, MYAPC, NRC Oceket No. 50-309.

5.

J. A. Block, et al, An Evaluation of PWR Steam Generator Water Hamer, Creare, Inc., NUREG-0291 (December 1976).

6.

W. E. Bennett, Waterhammer in Steam Generator Feedwater Lines, Westinghouse Technical Bulletin, NSO-To-75-7 (June 10, 1975).

7 t

l l

l

)7 DISTRIBUE0N JAN 1..g Central fil s

NRC POR PSB Reading U. f f;h %

'T10RA!!DUM FOR:

R. Reid, Chief, Operating Reactors Branch 14, 00R FR0!1:

G. Lainas, Chief, Plant Systems Branch, 00R

SUBJECT:

MAINE YANKEE STE#t GENERATOR WATER HAMMER EVALUATION Plant Name: Maine Yankee Atomic Power Station-Docket No.: 50-309 Resconsible Branch: OR2f4 Pmject !!anager:

M. Fairtile Reviewing Branch: Plant Systems Branch Review Status: Complete In response to Technical Assistance Request, TAC No. 7191, regarding water hammer in the Maine Yankee feedwater systems, the Plant Systems Branch has completed its review and found that acceptable precautions are being taken to minimize the occurrence of water hammer in the feedwater piping. The basis for our conclusions are provided in the enclosed Safety Evaluation Report and our consultants' report dated December 1979.

This completes our review of steam generator water hammer under TAC No. 7191.

G.'Lainas, Chief Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated

Contact:

S. MacKay X-27111 cc w/ enclosures:

See page 2 0

,,,,,l,

.P..S.B :

S..b..y. ES.B.1.I.D..O..R...

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UNITED STATES y

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g NUCLEAR REGULATORY COMMISSION wAswimorom. o. c. zosse g

l

%v /

JAN 171980 MEMORANDUM FOR:

R. Reid, Chief, Operating Reactors Branch #4, 00R FROM:

G. Lainas, Chief, Plant Systems Branch, 00R

SUBJECT:

MAINE YANKEE STEAM GENERATCR WATER HAMMER EVALUATION Plant Name: Maine Yankee Atomic Power Station Oceket No.: 50-309 Responsible Branch: ORB #4 Project Manager:

M. Fairtile Reviewing Branen: Plant Systems Branen Review Status: Complete In rescanse to Technical Assistance Request, TAC flo. 7191, regarding water narrer in the Maine Yankee feedwater systems, the Plant Systems' 3 ranch has completed its review and founc that acceptable precautions are being taken to minimize the occurrence of water hammer in the feedwater piping. The basis for our conclusions are provided in the enclosed Safety Evaluation Report and our consultants' report dated Decemoer 1979.

This completes our review of steam generator water hammer under TAC No. 7191.

G. Lainas, Chief Plant Systems Branch Division of Operating Reactors

Enclosures:

As stated

Contact:

5. MacKay X-27111 cc w/ enclosures:

See page 7 i

m

g t

8 e

2-JAN 171999 cc w/enciesures:

0. Eisennut S. Hanauer B. Grimes E. Adensam W. Gannill M. Fair.il e S. MacKay V. Noonan

l i

1 l

SAFETY EVALUAT CN REPORT STEAM GENEPATOR WATER HAmER MA!NE YANKEE ATOMIC POWER STATION DOCKET tt0. E0-3C9 DECEMBER 1979 l

I 1

l

)

l

1.0 INTRODUCTION

l Steam generator water hamer has occurred in certain nuclear power plants as a result of the rapid condensation of steam in a steam generator feedwater line and the consequent acceleration of a slug of water wnich upon impact within the piping system causes undue stresses in the piping and its support system. The significance of these events varies from plant to plant. Since a total loss of feedwater could affect the ability of the plant to cool down after a reactor shutcown, the NRC is concerned about these events occurring, even though an event with potentially serious consequences is unlikely to hacpen.

Because of the continuing occurrence of water hammer events, the NRC.,'

in September 1977, informed all PWR licensees that water hammer events due to the rapid condensation of steam in the feedwater lines of steam generators represented a safety concern and that further actions by licensees for Westinghouse and Combustion Engineering designed nuclear steam supply systems are warranted to assure that an acceptably low risk to public safety due to such events is maintained. Accordingly, these licensees were requested to submit proposed hardware and/or procedural modifications, if any, which would be necessary to assure that the feedwater lines and feedrings remain filled with water during normal as well as transient operating conditions. At the same time, the NRC provided each PWR licensee with a copy of its consultant's repor,, "An Evaluation of PWR Steam Generator Water Hamer," NUREG-0291.

-2 i

L.

The evaluation of the potential for steam generator water hamer at i

the Maine Yankee plant shows that the feedwater piping adjacent,to the steam generator consists of a favorsoly short run of horizontal piping and that during seven years of successful operation it has experienced those conditions that might induce steam generator water haccer; but no water hamar has occurred.

l 2.0,ElAEJAJtON 1

Our consultant, EG&G Idaho inc., prepared the attached evaluation of j

steam generator water hamer at the Maine Yankee plant as part of our technical assistance program. (Letter from J.A. Coarien, EG&G to R.E. Tiller, 00E, dated Cecember 13, 1979.) We have reviewed this report together with the licensees submittals listed under item 4.0.

3.0 CC':C'.US ION i

Based on our knowledge of water hae.ar phenomena, and our review of the licensees responses and the enclosed evalue:f on report, we c:ncar f

with our consultants' c:nclusien that the potential for steam generator water hamer is sufficiently low to perm,it continued operation of this facil ity. However, even though steam generator water hanner is not likely to occur, the licensee should be vigilant and unitor for unter hammers that afght impose significant stresses on the piping systans or their supports. We will continue to unitor reports from this licensee for indications of possible water hanner. If such indications appear in the future. this atter will,be

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reexamined irtd my result in additional requireents to reduce the probabflity of steen generator unter hatuner at these facilities.

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3-We have concluded that steam generator water hammer is not likely to occur at this facility and, therefore, we find no undue risk to the health and safety of the public as a result of the continued operation of the Maine Yankee Atomic Power Station.

4.0 REFERENCES

4.1 J.L. French, Maine Yankee Atomic Power Company (MYAPC), letter to R.A. Pur:le NRC,

Subject:

" Response to May 13, 1975 letter on Steam 3enerator Water Hammer," July 14, 1975.

• 2 R.H. Groce, MYAPC, letter to R.W. Reid, NRC,

Subject:

"Feedline Water Har=er," November 25, 1977.

a.3 0.:. Fri::'e,.*YAPC, letter to R. Colmar, NRC,

Subject:

" Maine Yankee Steam Generator Feedwater Piping," June 6,1979.

4.4 0.E. Mcody, MY'PC, letter to R. Reid, NRC, dated November 15, 1979, in res:ense to NRC request for information regarding the potential for steam generator water hammer.

4.5 J. A. 51cek, et al, An Evaluation of PWR Steam Generator Water Hammer, Creare, Inc., NUREG-0291 (Decameer 1976).

4.5 W.E. Bennett, Waternammer in Steam Generator Feedwater Lines, Westinghouse Technical Sulletin, NSD-TB-75-7, June 10,1975.

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>DE626 Idaho,Inc.

p. c. ses ists V

Haano Fans, leeno 83401 December 13, 1979 Mr. R. E. Tiller, Direc ce Reacter Ocarations and Programs Civision Idaho Operations Office - 00E

!dano Falls, IO S3401 MA;NE YANKEE 30WER STAT ON STEAM GENERATOR WATER M"MER TEC'4NICAL EVAL'JAT:CN (A6257) - JAO-250-79 Ref:

J. A.

Dearian Ltr to R. E2 Tiller,

PWR Staam Generater Water Hamer Reviews (A6257) - JAO-225-79, Novemcer 8,1979

Dear Mr. Tiller:

Tne at:achment completes :ne assessment of the effectiveness of the existing means to reduce the actential for steam genera:ce water ha=ar at :ne Maine Yanxee Pcwer Station (MYPS).

We have reviewed the ccerating history of the MYP5 certinent Oc

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stasm genenter wa:er hammer and :ne related coera:icnal and orcee -

cural enaractaristics of :ne feecwater system. Tne review nas snewn tna ccnditiens concucive to steam genera:cr water nacer have oc:urred at the MYPS but no water hamer events have been ib-served. The conditions have been encountered during nomal ccarating : ansients and starruo and shutewn ccerations. Such conditiens would also be expected in the Murt curing the ncemai and accident operating situations addressed in.ne review. Based on :nis review we have concluced that the ;ctantial for steam gen-erator water hamer is sufficiently low to permit continued coera-tion of this facility.

• his transmittal constitutes czcletien of :ne MYP5 SER, Task A6257 of :ne referenced Milestene Chart.

Very truly yours,

_ C"'

m 1 m. _ _

_ (A. Daarien, Manager J.

Code Assessment and Acclications Program 30C::n At ac=ent:

As statec

5. 2. Mac.<ay, NRC-COR R. W. Kienn, EG&G l dane w/o attaen.

s STEAW. GDGATCR WATER HAMMS TECHNICAL TIALUATION MAINE YANKEE PCWG STAT!ON Decemeer 1979

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CONTINTS I.

INTRCOUCTION........................ 1 II. MEANS TO REDUCI THE POTENTIAL FOR WATER MANNER....... 2 III. OPERATING EXPERIENCE AND WATER HAMMER SUSCEPTIBILITY.... 3 IV. CONCLUSIONS ANO RECOMMENCATICNS.............. 6 V.

REFERENCES......................... 7 4

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INTRODUCTION l

An evaluation was per omed for the Maine Yankae P:dar Station d

(MYPS) feedwater system. The purpose of this evaluation was to assess the susceptibility of the feedwater systs to water hamaa during operating transients and situations that could result ir. conditions conducive to water hanner.

Potential stem-water slugging resulting in water hame-in the steam generator feedrings and adjacent feedwater pising was considered in this review. This type of water hanner is generally referred to as steam generator wate hamer and is charactari:ed by ca:id stem concensation causing water slug acceleration and i :act. The imcact of a water slug in the feedwater system has the so ential for overstressing systa: c:moonents and succorts. Sten ;er. erat:r watar hamer was recortad to have never oc:urred at the MY75.

The information for this evaluation was Obtained f :re:

(1) discussion,s with the licensee, (2) licansee submittals to.iRC of s

3 July la,1975*, Novemeer 25, 1977', and June 6,1979, l3) the

" Maine Yankee At:r-ic P:wer Station Final Safety Analysis Recort"#,

(a) "An Evaluation of PWR Steam Generater Watar Ha:mer",

I NUREG-0291. and (5) Westinghouse Tecnnical Bulletin, j

e NSD-TB-75-7*.

1 The means to reduca the potential fer watar hamer at this facility are presented in Section II.Section III presents descriptions of the feedwater system geometry and ccaration pertaining to the suscactibility of the system to staam generat:r water hamer.

This section aisc seesants a description and taculation of :cerating t~ansients and si'uations that c:uld result in conditic s c:ncucive to natar hamer. Finally, conclusions and ete:mendaticas are tresentad in Section IV c:n:n-ning the suscsotibility of One feecea:ar systam at j

nis f acility :: staam generator watar hamer.

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II. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER The main feedwatar piping geometry (original plant design) limits the horizontal lengths of oiping adjacent to each steam generstor.

The picing arrangement consists of a downward turning 90" elbow about 3 feet 2 inches from the outer surfact of each steam generator.

This arrangement limits the hori: ental length of piping connected to eacn steam generator feedring that eculd drain througn the bottom disenarge holes of the feecring. By limiting this length of piping, the maximum volume which could fill with steam during periods of feedring uncovery is also limited. Thus, ! imitation of the pioing volumes will orcoor.icnally limit the energy of setential watar harvaers cue to steam-watar slugging.

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l III. OPERATING EXPERIENCE AND WATER HAttt!R SUSCIPTIBII.ITY-i The conditiens mr. conducive to steam generator water hammer occur when the staam generstar feedrings are uncovered and steam enters the feedrings and attached horizontal feedwater piping.

Steam-watar slugging and subsequent water hammer may occur when incoming cold feedwater mixes with the steam in the piping and rapid c:ncensation oc:urs. The conditions can be avoided by ketoing the feedrings and associated piping full cf water. This can be ac:omolished by (1) keeping the watar levels in the steam generators acove the feedrings or (2) suoplying feedwater at a higner flow rata than the cata at wnich feedwater trains thecugn the disenarge holes on

ne bott:m of uncovered feedrings.

Fellowing a reactor tris, the stamm generatsr aatar levels drce i

by a cuantity accroximately precortional t: the reactor gewer Orior to tne trip. For axamola, the greatast droo wcule oc:ur at full :ower.

The deco or " shrinkage" in water level is the result of intar-upted tactor power producif on and increased steam generator stasm essure causing the collaose of steam voies within tne seconcary side of the steam generators. A similar situation would also te ex:erienced during events such as loss of main feedwater, loss :f Offsita gewer, steam line break, and loss-of-coolant accident.

The MYPS has exoerienced 23 full power reactor tries sinca unit It was -scortad that feedring uncovery oc:urred in all staam startus.

generstars as a result of each trip.-

Tiere have been two comoleta loss of main feedwater events since initial unit startue. The first event oc:urred On November 11, 1972 at a reactor power level of 23%. Failure of the one coerating main

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feedwatar sumo due to tearing rtoisms necessitated s arting :f the other main feedwatar cumo. Tne inability to :cen tne :ischarge valve l

of the second pump required the manual trip of the reacter and turbine. An auxiliary feedwater pump was started to restore and maintain steam generator water levels.

The second loss of main feedwatar event occurred on August 31, 1978. The event was the direct result of the only loss of offsite power event to have oc:urred sinca unit startup. A fault in one of the stations's main transformers resultad in reac:cr and turbine trips and the loss of offsita power. As was the casa for the first loss of main feedwater event, an auxiliary feedwater pumo was startad to restore and maintain steam garrerator water levels.

Infcrmation was unavailable as to whether er not fetering uncovery events oc:ur ed during startup and snu:down c:eraticns.

However, similar cast eviews for other facilities have revealed the difficulty in maintaining the stanm generat:r water levels a:cve the feedrings at all times during ocerating situations requiring manual, feedwatar ::ntrol.

It is apearent fecm the review Of the plant :perating history that it is not always possible to avoid drainage of the feedrings and adjacant picing by keecing the feedrings covered with watar. A1:ncugn the drainage time (or uncove*y time) varied among the uncovery events, comolate drainage of the feedrings and adjacant piping has been frecuent since the time required for ccmcieta drainage is less than one sinute and the uncove*y times were generally of longer duration.

The alternative to continueus coverage cf the feedrings with watar is to maintain sufficient feedwater flew through uncovered feedrings to keep the feedrings full cf water. The flew required for this at the MYPS is accroximataly 1300 gpm ;er steam generat:r based on static meessure drainage calculations. Sinca a total fetcwater flew rata of accut 23,000 gpm is -scuired f:r full tact:r :cwer, the

1. eedrings and f aecwatar pising would be kact full :nly ni:n fetcwa ar flow atas ::r esconding :: Ocwer levels atove a: cut 150 %'e Or 20". :f l

,' s full power. Thus, during startue, shutdown, and low power operation, feedwater flow requirments are insufficient to keep the feedrings

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full of water during periods of fendring uncovery. This situation would also be exeected during recovery fecm events assulting in reactor trips from power ocerstion such as loss of =ain feedwater, loss of offsite power, stemn line break, and loss of coolant accident.

Feedwater can also be suoplied to the steam generators via the auxiliary feedwatar systam. Auxiliary feecwater can be pumped into each of the tnree main feedwater lines at a location between the contaimeent building and crane wall just downstream of the last main feedwater eneck valve. The system consists of two setor driven and one turbine driven auxiliary feedwater pumas each having a cacacity of 500 gpm for a total cacacity of aoout 1500 gpm. During any coerational onase of the plant, the cacacity of the auxiliary feedwater system would not be sufficient to keto un:cvered feedrings full of water.

The review of the coerating history at the MY?S indicatas that the conditions conducive to steam generator water hamar exist during normal coerating situatiens. However, it was reecrted that watar hamer cf this type has never occurred at this facility nor has any feetwater system damage been found to indicate messible unobsarted watar hamar events. An accarent contradiction exists between the f act that water hamer has not been observed althou;n =nditions considered conducive to water hamer frequently oc=r.

The exclanation for this coservation is not readily identifiaele but artbably relates to inherent characteristics of the feedwatar systam and/or plant operating procedurts.

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IV. CONC:.uSIONS AND REcomEN0ATIONS We have reviewed the operating hist:ry of tne MYPS pertinent to steam generator water hamer and the related operational and precedural characteristics of the feedwater systan. The review has i

shown that conditions conducive to staam generator water hammer have l

occurred at the MYPS but no water hamner events have been observed.

The conditions have been encountered during nomal operating transients and startue and shutdown operations. Such conditiens would also be expected in the future during the nomal and ac:1 dent ooertting situations addressed in the review. Based on this review we have concluded that the potential for staam generat:r water ha=er is sufficiently low to permit c:ntinued coeration Of this facility.

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REFERENCE.S 1.

J. L. French, Maine Yankee Atomic Power Oscany (MYAFC), letter to R. A. Purple, NRC, Subject

" Response to May 13, 1975 letter on Steam Generatcr Water Hanrnar, July 14, 1975.

d 2.

R. H. Grece, MYAPC, lettar to R. W. Reid, NRC, Subject -

"Feedline Water Hansner", Novameer 25, 1977 3.

C. O. Friz:le, MYAPC, letter to R. Colmar, NRC, Subject

" Maine Yankee Steam Generator Feedwater Piping", June 6,1979.

1 Final Safe:v Ana'vsis Reecrt, Maine Yankee Atzic Power Statien, MYAPC, NRC Occket Nc. 50-3C9.

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J. A. 31cek, et ai, An Eve'antien :! 8'A Stee 3ece-ster Wa e-Hame*, Cesare, Inc., NURE3-C29' (:ecr.:er 1975).

6.

W. E. 3annett, Watar9 amer in 3:eem Genert :e Fee water _ines, Westingneuse Tecnni:ai Ier.a-in, NSD-75-75-7 (June '.;,1375).

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