ML17317B041
| ML17317B041 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 01/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17317B040 | List: |
| References | |
| NUDOCS 7903300519 | |
| Download: ML17317B041 (25) | |
Text
Wisconsin Public Service Corporation 2
cc:
Steven E.
- Keane, Esquire Foley and Lardner 777 East Wisconsin Avenue Milwaukee, Wisconsin 53202 Kewaunee Public Library 314 Milwaukee Street
- Kewaunee, Wisconsin 54216 Stanley LaCrosse
- Chairman, Town of Carlton Route 1
- Kewaunee, Wisconsin 54216
~
~
SALTY PTALUAVZON BsPGRT ST&A G~TCR VA~ HAPKZ, DONALD C, COG'UCLM PLANT UNIT NO+
3.
JANUAPZ 1979
1 0 yi'i~0 UCTION Steam gen rator water hamme has occ e" ~-. cer'.~". nuc" a
"owe" plants as a result cf the rapid cordensa=ic". of steam in a st ~
ger. ra.or feedwater
~~'
and the consecn.ant acceleraticn of a s "-
of water which upon itrioact w'~". the p~=.'"~ syste= causes
"-." e s
esses in the piping and its support system.
T'"~ si~ 'cance of h se events varies from plant, to plant,.
Since the t"ta loss of feedwat,er could affect the ability of the plant to cool i~-.. a ter a "eactor si". tdowx, the NRC is concerned about these events ccc"~,
even though an event with potentiaLly ser"'ous consecuenc s is ur'-'eely to happen.
Because of the contirnSg occurrence of water hamm events>
the NRC, in Septemoer 1977, informed a3~
FHR licensees that, water hamm r events due to the rapid condensation of earn in the feedwater ~~" s of steam generators represented.
a safety ccncern
="".d that fu~¹r actions by Licensees for Mestinghouse anc C"mousticn Engineer='".g designed nuclear steam suoply systems are durante" to assure t:".at ar.
acceptably low risk to pubLic safety due to such ever s is m~.ta=.ed.
Accor~~ gly, these licensees were recuest d to sub 'ro"ose" hardware and/or procedural moo'f=cations, i
- any,
."'h auld be rec-essary to assure that the feedwate Lines a.-.d feec mgs remai-..
i~Wed with water during normal as we32 as tran 'e..-'perat~".g conc"='crs.
At,'e same time, the NRC provided each
.=riP. Licensee ith a copy of "ts consultant's report,,
"An Evaluation of Fn~ S'earn C neraur
'elate Homer, "
NUKED-0291.
The means employed at the Donald C.
Ccok.'nuclear c~ant, Ur~t Ho (Cook-1) to reduce the potential fo stew -eneratcr wa.er."~er include loop seals,
'J-tubes, autcma ic ~"- =ation c auxiLia..
e d-water flow and an adz>strative
~~~~t o" the flow of auiL~ay feedwater in the event that, a eedwater."".e might contain st ~
2,0 ZVALUII.TION Our consultant, ERcG Idaho, Inc., prepare the attach d evaluation of steam generator water hammer a
Cook-1 as pert of cu" tec&Xcal assistance program.
Ve have rev'ewed th='s =epor'ogether with the licensee's submittals 3'sted under it m 4 0.
3,0 CONCLUSION Based on our knowledge of water hammer phenomena, and our rm ew c the Licensees responses and the enclosed evaluation report, we concur with ou corsultants conc" usion
-.'.".e the means cr r c"'""
he potential for steam ge..erator wate
.""-=- r at
=.=-'=- ac':y a=e adecuate.
T.".ese means are, there o"e, aces=-.able
=" =.".e sta "cticn:s recuired o
the
-'ens=e;- t'-. "~-"--'"
Ot Ce
~
A4 6
4
'5~0%
~
~
~
1.
Lette" from R S. Hunter to K. Kr~e', Subject - "S ean Genera="r Mater ihmm r", July ~, 1975.
2.
Letter from G. P. Maloney to E. G. Case, Subject "Steam Generator Mater Hardener,"
June 7, 1978.
TECHNICAL EYALUATIOH D.
C.
COOK UNIT NO.
1 JANUARY 1979 EGEG IDAHO, INC.
CONTENTS INTRODUCTION........................
'1 II.
FEEDWATER SYSTEM.
2 1.
DESCRIPTION.....................
2 2.
GENERAL OPERATION...................
3 3.
WATER HAWSER EXPERIENCE................
4.
III.
MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER.~....
6 1.
DESCRIPTION....................
~ '
6 2.
EFFECTIVFHESS DURING TRANSIENTS AND CONDITIONS CONDUCIVE TO WATER HAMMER..........
7 2.1 Reactor Trip.
2.2 Loss of Main Feedwater Pumps 2.3 Loss of Off-Site Power 2.4 Operator Error..
2.5 Steam Line 8reak
~
~
7 8
~
~
~
~
~
~
~ "~
~
~
~
9
~
~
~
~
~
~
~
~
10
'2. 6 Loss-of-Coolant Accident....
~
~
~
~
~
~
~
~
10 IY.
CONCLUSIONS AHD RECOMMENDATIONS.........
12 V.. REFERENCES..........................
13
I.
INTRODUCTIOH An evaluation was performed for the Donald C.
Cook Unit Ho.
1 feedwater system.
This evaluation was concerned with the effectiveness of the means to reduce the potential for water hammer in the feedwater system during normal and hypothesized operating conditions.
.Various means to reduce the potential for steam generator water hammer are utilized at Donald C.
Cook Unit Ho.
1.
Since the potential for feedwater water hammer is eliminated if the system is maintained full of water, this evaluation was based on the effectiveness of these means to maintain the feedwater system full cf water during normal and transient operating conditions.
The information for this evaluation was obtained from 1) discussions with the licensee,
- 2) licensee submittals of July 14, 1975~
~ and June 7,
1978 per HRC request,
- 3) the Donald C.
Cook Final Safety t:23 Analysis Report,
- 4) Nuclear Power Experience',
and 5) "An Evaluation
[33 of PWR Steam Generat'or Water Hammer",
HUREG-0291~
~.
A description of the feedwater sys em at Donald C.
Cook Unit Ho.
1, its genera1 operation, and an account of steam generator water hammer events at'his facility are presented in Section Il.
The means to reduce the potential for water hammer in the feedwater system are pre-sented in Section III including a discussion of their effectiveness during normal and transient operating condi tions conducive to water hammer.
Finally, conclusions and recommedations are presented in Section IY concerning the adequacy of the means to reduce the potential for water hammer at this facility.
II.
FEEDWATER SYSTEH 1.
DESCRIPTION The feedwater system for Donald C.
Cook Unit No.
1 was designed to provide an adequate supply of feedwater to the secondary side of the four steam generators during all operational conditions.,
Feedwater is supplied to the two main feedwater pumps by the high pressure heater drain pumps and the condensate pumps via the 1'ow pressure heaters.
The main feedwater pumps are vertically split, single stage, double suction pumps each rated at a flow rate of 16,750 gpm at 2150 feet total developed head (TDH).
Each pump is driven by a variable speed steam turbine supplied with steam from the r cheater moisture separators durino normal reactor operation and from the main steam headers during startup and low power conditions.
Feedwater from the main feedwater pumps is supplied to a main header via the high pressure heaters.
The main header splits into four 16 inch feedwater lines. to supply a feedring inside each stear. generator.
Feedwater is discharged downward through inverted "J" shaped tubes on top of the feedring.
The "J" shaped tubes were installed in 1978 after two water hammer events had occurred.
On each steam generator, there is no horizontal piping between the steam generator and the first downward turning elbow.
The auxiliary feedwater system provides feedwater to the steam generators for primary heat removal during reactor startup, low power operation, and reactor shutdown.
.Auxiliary feedwater can be supplied by two redundant systems employing two electric motor driven auxiliary feedwater pumps in one system and a single turbine driven pump in the other system.
Lines from the auxi liary feedwa el pumps cat y <<'ater 0
-;-.e main feedwa.e.. lines at a point in each
."..ain line 'us-ou:si"'e'f
=ne containment building.
Each motor driven pump, rated for 450 gpm at 1545 psi TDH,.supplies two steam generators in each unit.
The pumps operate with normal offsite power or with power supplied by the emergency diesel generators.
The turbine driven pump, rated for 900 gpm at 1435 psi TDH, supplies all four steam generators and is driven by steam from the steam header of two steam generators.
The main water supply source for both auxiliary systems is the two condensate storage tanks (500,000 gal. capacity each) with a backup supply of water provided by the Essential Service Water System.
2.
GENERAL OPERATION During normal power operation of the reactor, the main feedwater system supplies feedwater to the steam generators for heat removal from the p'rimary system.
The feedwater flow is regulated to each steam generator by individual regulating valves in the main feedwater lines.
The positions of the valves are automatically controlled based on. steam generator
- level, secondary steam flow, and feedwater flow.
At low power levels and during startup and hot standby conditions, feedwater is manually regulated to maintain adequate water levels in the steam gener
, ators.
A ter the loss of main feedwater flow to one or more steam generators, automatic initiation of auxiliary feedwater flow will result upon receipt, of one or more auxiliary feedwater pump startup signals.
The motor driven auxiliary feedwater pumps start on 1) coincidence of two out of three steam generator low"low water level signals 'in any one steam generator,
The turbine driven auxiliary feedwater pump starts on coincidence of 1) two out of three steam generator low-low
~ater level signa!s in any two s.earn generators or 2) two out of 'o r r
reac:or coolant pumo undervcltage s'."nels.
The mo-or driven and tu i"e dr.ven pumps can also be started manually (local or remote).
Plant design specifications allow for a.".axi.-.u.".. delay, of one "inu-.e from loss of main feedwater flow to delivery cf a xiliary ';eedwater tc the steam generators.
Administrative guidelires require canu=l ccntrc and regulation of the auxiliary feedwater flow shor.ly after ".s auto-matic initiation for subsequent refill of the steam generators.
Nanua:
flow con.rol is continued to bring the water levels above
.he feedrings and to maintain. adequate levels in the steam g nerators.
3.
MATER HAMMER EXPERIENCE Two steam generator water hamme~ events assumed to be he result cf steam-water slugging occurred at Donald C.
Cook Unit No..l prior to the installation of the "J" shaped discharge tubes.
The damace from he first event was found on January 2,
1976.
The event occurred subsequen-
'o the November 14, 1975 star tup but the exac. da e
and ti"e cf:he event is unknown.
Prior to the Novmeber 14, 1975 smrtup, an ex ensive containment inspection was made by the licensee and no darage to the feedwater system was reported..
The damage that resulted from the first water hammer was limited w
. hydraulic snubbers on the main feedwater line in which the steam"water slugging was assumed to have occurred.
The three damaged
- snubbers, al',
attached to the feedwater line supplying the No. 4 steam generator, were located inside the containment crane wall.
Prior to continued opera-icn of Unit No.
1, the damaged hardware was either repaired or replaced.
The second steam generator water hammer occurred on Narch 10, 1977.
0 During recovery from a reactor trip, auxiliary feedwater flow was in-creased to over 200 gpm per steam generator which is above the 1=0 gym a 'ministrative maximum allowed during periods cf feedring
.".c=ve.y.
This cperatcr error resul:ed
'n a water hammer wh-:c.". was s"ai;. ass
."..ed steep.. Ia er 5 1ugginc.
An inspection after the incident revealed wo snuCbers failec outside containment on the feedwater line su:plying the Ho.
1 ste=--..
generator and one snubber failed inside con ain."..ent on the same I:ne.
A small crack was found in the auxiliary feedw=ter line supplying t".e No.
The crack was locate" near a s.anchion sac"le where it was welded to the line.
Repairs were made to the feedwater system prior to continued operation.
III.
MEANS TO REDUCE THE POTENTIAL FOR MATER HAMER 1.
DESCRIPTION The following means are employed at Donald C.
Cook Unit No.
1 to reduce the potential for water hammer in the feedwater system:
1.
"J" shaped discharge tubes were installed on top of the steam generator feedrings and the bottnm discharge holes were plugged 2.
"Loop seals" were installed in the feedwater piping to.reduce the effective horizontal length adjacent to the steam generators.
3.
The auxiliary feedwater system is designed to supply auxiliary feedwater to the steam generators within one minute after the interruption'f the main feedwater supply.
4.
Administrative control limits the.feedwater flow to about 150 gpm per steam generator when the water level in any stem~
generator is below the feedring.
The "J" shaped discharge tubes were installed on top of the feedrings to provide for top discharge of water rather than bottom discharge.
During periods of feedring uncovery, this arrangement increases the tice for complete drainage of the feedring and associated horizontal feedwater piping from less than one minute to about 30 minutes.
Also, the maximu-auxiliary feedwater flow (about 450 gpm per steam generator) was not sufficient to maintain the feedrings and feedwater piping full of water when the feedrings had bottom discharge holes.
The feedrincs eauipped with "'" shaped discharge
- tubes, however, permit feedwater
- low
". a.es as 1ow as aoout 10 gpm per steam oenerator to keeo the feecr'.ncs.an"
-,,aec-wate.
- oi o fu1. of wa er un
- 1 eed.
ng re v~ry o
- u. s.
an
~
w
~
m
~ w
~
I M ~
I g
crainage o
-he feedring and piping does nc: oc"ur for abou= " minu es which aflows time for 1) automatic actuation of :he auxiliary fee= a=er
system after the loss of main feedwater flow during nor;al power ope".,a: cn or 2) the operator to reestablish steam genera or wa.er level d rin" star.up and low power operating conditions during which:he water leve.
drops below the fe drings.in one or more steam generators.
The potent a, for ~ater hammer is eliminated if the feedrings and feodwater piping are kept full until feedring recovery.
"Loop seals" were installed in the main feedwater piping adjacent to each of the steam generators.
Each seal consists of an elbo~ in the feedwater line which is connected to the steam generator nozzle.
This arr angement eliminates the effective horizontal piping adjacent to the steam generators that could drain and become steam-filled during periocs of feedring uncovery.
By eliminating the horizontal piping geomet~
the potential for water hammer in these piping sections is also elimina.ed.
The prompt automatic startup of one or more auxiliary feedwater pumps after the loss of main feedwater flow provides feedwater flow -o keep the feedrings and feedwater
~ piping full of water until feedring recovery.
In conjunction with the "J" shaped discharge ubes, auxiliary I
feedwater flow from either the motor driven pumps or the turbine criven pump is more than sufficient to keep the feedwater system full of wate..
Bas>d on tests conducted at Indian Point Unit Ho. 2, an adminis ra-tive eedwater flow limitation of about 150 gpm was adopted at Conald C.
Cook Unit Ho.
1.
This flow limitation is implemented by the operator anytime the steam generator water levels drop below :he feedrings.
2.
EFFECTIYENESS OURING TRANSIENTS ANO CONDri ONS CONOUCIVE TO WATER HAR1ER 2.1 iaac or Trio res 1 t in a tu> bine trip and
- o coliapse to a level below plaI ~ t in normal cause the wa er the feedrings.
~
e g~ ~
o
~
v ~
V H
resulting steam generator low-low water level signals, the "-.or driven and turbine driven auxiliary feedwater pumps would auto-..at'.cally sta.
and supply auxiliary feedwater to the steam generators.
i he initia=;ng event for the reac or trip did not close the main feedwa e.
regulatinc valves (as would, for example, a safety injection signal),
he valves would close upon receipt of low primary coolant average temperature signals or steam generator high-high level signals.
Auxilia~ feedwater flow is normally under manual control shortly after an event that causes feedring uncovery.
The flow is regulated to refill and aainmin the steam generator levels above the feedrings.
The potential for water hamme~ occurring in the feedring or feedwater piping after a reactor trip is very low because the main and auxiliary feedwater keeps the feedrings and feedwater pipinc full of water until feedring recovery occurs.
2.2 Loss of Main Feedwater Pumps Any event that results in malfunction or isolation of the main feedwater pumps wilT result in automatic startup of the turbine driven and'otor driven auxiliary feedwater pumps upon receipt of -Ne steam generator low-low water level signals.
Either auxiliary feedwater system can provide more than sufficient flow to the feedrings and as-sociated horizontal feedwater piping of the steam genera.ors since the "J" tubes reduce the drainage rate to about 10 gpm per steam generator during feedring uncovery periods.
The loss of main feedwater flow and the likely uncovery o. the feedrings would not result in substantial feedring and feedwater piping drainage since the auxiliary feedwater pumps would start.o promptly to supply feedwater to the steam generators.
Therefore, the potential for water hammer is significantly reduced.
2.3 Loss of Off"Site Power The interruption of the off-site po~er su"ply wou.d result in a reactor trip and automatic startup of the e"ergency diesel genera.ors.
Automatic initiation of the motor driven an" turbine criven auxiliary feedwater systems would occu~ to supply feecwa er to the steam generators until feedring recovery.
The redundant auxiliary fee ~ater systems are fully functional without off-site power since the diesel generators and DC batteries independently supply necessary electrical power to both systems..
As was the case for the loss of the main feedwater pumps, auxiliary feedwater maintains the feedrings and feedwa:er pipinc full of water until feedring recovery occurs and again the potential for water. hammer is very low.
- 2. 4 Ooerator Error The potential for water hammer in the feedwater system increases greatly if uncovered feedr ings are allowed w drain su"stantial ly after an event causes the steam generator water levels to drop below the feedrings.
Admission of feedwater into the "rained feedr'.ngs and feed-
~ater piping could then result in water slugging and subsequent water hammer.
The uncovery of one or more feedrings is mos likely when the plant is operating at low power or is shutdown since feedwater is being regulated manually, rather than automatically.
Should feedring. uncovery occur, the "J" shaped discharge tubes keep the feedrings from draining. substantially fcr about 5 ainutes.
This time delay would allow sufficient time for '.."e operator to become aware of 'feedring uncovery and to establish sufficient auxiliary feedwater flow to maintain the feedrings and feedwate.
piping
<u'.1 of water.
Should feedring uncovery occur and the feed".:ncs and;".=ri""ntal pipinc we. e
.o drain, feecwa er flow would oe 1 imi==-"
o the
=-",".",i stra
- im-;-of 1=Q can u,",til,eedrino recover<
- 'o -n<="re wV w
~
~<
CI ~ w<Q<
water slugging.
2.5 Steam Line Sreak The potential for wate, hammer events resulting from or concurren with the rupture of a steam line inside containment was cons'idered..
The sequence of events following such a fai lure was evalua.ed to determine if the break would result in the
- 1) blowdown of one or more additional steam generators and/or 2) inability to supply auxiliary feedwater to the unaffected 'steam generators.
The rupture of a steam line would automatically result in a safety injection signal (SIS) and subsequent isolation of all feedwater lines'.
The loss of main feedwater flow to the steam generators would result in the automatic startup of the moto~ driven and turbine driven auxiliary feedwater pumps.
Feedwater would then be supplied for subsequent refill of he steam generators and recovery o
the eedrings.
The potential for water hammer is low after a steam line break since prompt delivery of auxiliary feedwater in conjunction with the "J"-tubes maintain full feedrings and feedwater piping in the unaffected steam generators until feedring recovery.
The turbine driven auxiliary pump ~ould receive adequate steam for driving power even if one of the two interconnected s
earn lines for the pump turbine was supplied by the blowdown steam generator.
Check valves in each supply line would prevent "crossover" blowdown through the supply lines from one steam generator to the associated blowdown steam generator.
Thus the means for avoiding water hammer would be fully effective under the conditions of a steam line break.
2.6 Loss-of-Coolant Accident The potential for feedwater water hammer curing a postula ed loss-of-oolant accident (L"CA) was examined beca s=
1) a water hammer coulC crease the consequen es 0
a (LOCA anc 2) the p(an-. protective act ons curi c
": LOCA cou(c.esul i ~ ~
3
~ i
'Q('.s wh a
e
~ ve 3 wa er hammer if the feedwater system is not kep. f li of water.
A LOCA would result in a SIS, a reactor trip, and subsequent isola i"n of the feedwater system.
The startup o
the motor driven and turbine driven auxiliary feedwater pumps would result and fcedwater would be supplied to the steam generators within 60 seconds of the reactor tr',p.
Refill of the steam generators and recovery of the feedrings would occ' in a manner typical of a reactor trip or the loss of off-site power.
The conditions conducive to water hammer in the feedring and fead-water piping resulting from a LOCA would be very similar to those from a reactor tri'p.
Therefore, the means to reduce the potential for water hammer would be fully effective during a
LOCA.'
IV.
CONCLUSIONS AND RECON".EHDATIOHS The assessnent of the capability of exis ing means to reduce tt:e potential for water hanmer during various hypothesized transients anc conditions was discussed in Section III.
This assessment has sho~n that under conditions which are most conducive to water hammer in the feed-water system (specifically, uncovered and draining feedrings and feed" water piping subjected to adnission of cold auxiliary feedwater), the means to r educe the potential for water hammer at Oonald C.
Cook Unit No.
1 are adequate to maintain sufficiently full feedrings and feedwatpr piping until feedring r ecovery occurs.
Therefore, since keeping the feedrings and feedwater piping full of water eliminates the potential for slugging, 'we fihd that the means to reduce the potential for. steam generator water hammer at this facility are adequate and we recommend acceptance by the NRC staff.
12
V.
REFERENCES 1.
Letter from R.
S. Hunter to K. Kniel ~ Subject - "Stew~
Generator Mater Hammer July 14, 1975 2.
Letter from G.
P.
Haloney to E.
G.
- Case, Subject - "S eaa Generator Water Hammer",
June 7, 1978 3.
Final Safet Anal sis Report, Donald C.
Cook Unit Nos.
1 and 2 Indiana and Hichi gan Electric Company
~
DOE Oocket No.
50-315
~
4.
Nuclear. Power Experience, Nuclear Power Experience, Incr 9
PMR Vol. VI. E.
119 5.
J.
A. Block, et al, An Evaluation of PMR S
earn Genera-or
~'ater
- Reamer, Creare, Imc.,
RUREG-0291,
- Oecember, 1976.
'