ML19257C039
| ML19257C039 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 05/15/1979 |
| From: | EG&G, INC. |
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| Shared Package | |
| ML19257C036 | List: |
| References | |
| NUDOCS 8001240014 | |
| Download: ML19257C039 (22) | |
Text
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STEAM GENERATOR WATER HA M ER TECHNICAL EVALUATION ZION UNITS NO. 1 AND NO. 2 March 1979 EG&G Idaho, Inc.
REVISED MAY 15, 1979 '
<L W 8001240 0 %
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CONTENTS I.
INTRODUCTION................._.......
1 II.
FEEDWATER SYSTEM......................
2 1.
DESCRIPTION......................
2 2.
GENERAL OPERATION...................
3 3.
WATER HAMMER EXPERIENCE................
5 III. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMMER.......
9 1.
DESCRIPTION.........................
9 2.
EFFECTIVENESS DURING TRANSIENTS AND CONDITIONS CONOUCIVE TO WATER HAMMER.......... 11 2.1 Reactor Trip................... 12 2.2 Loss of Main Feedwater Flow............ 13 2.3 Loss of Offsite Power 14 2.4 Operator Error.................. 14 2.5 Stemn Line Break................. 16 2.6 Loss-of-Coolant Accident.............
17 IV.
CONCLUSIONS AND RECOMMENDATIONS..............18 V.
R EF ER ENC ES.........................
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TABLES I.
Zion Steam Generator Water Hamer Experience.........
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\\
I.
INTRODUCTION An evaluation was performed for the Zion Power Station (ZPS) feedwater systems. The purpose of this evaluation was to assess the effectiveness of the means utilized at the ZPS to adequately reduce the potential for steam generator water hammer. The potential for water hamer due to steam-water slugging in the feedwater systems (specifically, the feedrings and associated horizontal feedwater piping) was considered in this review.
The potential for steam generator water hamer is eliminated if the feedwater systems are maintained full of water. Hence, this evaluation was based on the effectiventss of the means to maintain the feedwater systems full of water during normal and hypothetical transient operating conditions.
The information for this evaluation was obtained from:
- 1) discussions with the licensee, 2) licensee submittals of July 17, 1
2 1975 and January 20, 1978, 3) the " Zion Power Station Final Safety Analysis Report"3 4) " Nuclear Power Experience" 4, and
- 5) "An Evaluation of PWR Steam Generator Water Hamer", NUREG-0291 5, A description of the feedwater systems at the ZPS (Unit Nos. 1 and 2), their general operation, and an account of steam generator water hamer events at this facility are presented in Section II. The means to reduce the potential for water hamer in the faedwater systems are presented in Section III including a discussion of their effectiveness during operating conditions conducive to water hamer.
Finally, conclusions and recomendations are presented in Section IV concerning the adequacy of the means to reduce the potential for water hammer at this facility.
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II. FEEDWATER SYSTEM 1.
DESCRIPTION Each feedwater system for Zion Unit Nos. 1 and 2 was designed to provide an adequate supply of feedwater to the secondary side of the four steam generators in each unit during all aperating conditions.
Feedwater is supplied to the main feedwater pumps by.the heater drain pumps and by the ' condensate booster pumps via the low pressure heaters.
Feedwater from the main feedwater pumps is supplied to a main he'ider via the high pressure heaters.
The main header of either unit splits into foer 16 inch feedwater lines to supply a feedring inside each steam generator.
The three main feedwater pumps in each unit share common suction and discharge headers.
Two of the pumps are each driven by a 9350 hp variable speed turbine and the third pump is driven by an 11,000 hp electric motor.
The pumps are all rated for a flow rate of 17,400 gpm at a discharge pressure of 1027 psig. Steam to power the turbine driven pumps is supplied from the reheater moisture separators during normal reactor operation and from the main steam headers during low power operation.
The motor driven pump is used during startup and as a backup to the turbine driven pumps. Power for the motor driven pump is nonnally supplied by offsite power with a reserve supply available from station power.
Feedwater is discharged downward through holes uniformally distributed on the bottom of the feedrings in all steam generators except steam generator C in Unit No. 2.
In this steam generator, feedwater is discharged downward through inverted "J" shaped tubes on top of the feedring. Top discharge was implemented in the 2C steam generator in February 1978 following a series of water hammer events that occurred in this steam generator.
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The auxiliary feedwater system provides feedwater to the steam generators for heat removal during reactor startup, low power operation, and reactor shutdown. In each unit, 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 auxiliary feedwater pumps carry water to the main-feedwater lines at a point in each main line located inside of the containment building.
Each motor driven pump, rated for a flow rate of 450 gpm at a discharge head of 3138 feet, is driven by a 60 hp electric motor and
~
can supply all four steam generators. The turbine driven pump, rated for 900 gpm at 7. discharge head of 3138 feet is driven by a variable speed turbine rated at 990 hp.
This pump can also supply all four steam generators. The motor driven pumps operate with offsite power with a backup supply avail'ible from the diesel generators. The turbine driven pump operates with steam which can be taken from either of two.
The main water supply source for both auxiliary feedwater systems is the condensate stcrage tank (containing a minimum of 170,000 gallons) with a backup supply available from the service water system.
2.
GENERAL OPERATION During normal power operation of either unit at the ZPS. the main feedwater system supplies feedwater to the steam generators for heat removal from the reactor coolant system. The feedwater flow is regulated by individual regulating valves in the main feedwater lines to each steam generator. The positions of the valves are automatically controlled based on steam generator level, steam flow, and feedwater flow.
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During reactor startup and during operation at less than 5% power, feedwater is suoplied by the motor driven auxiliary feedwater pumps.
Feedwater is manually regulated to maintain adequate water levels in the steam generators.
Above power levels of 5% and until adequate steam is available to operate the turbine driven main feedwater pumps, feedwater is supplied to the steam generators by the motor driven main feedwater pump.
Feedwater is supplied via low flow bypass lines which bypass the main feedwater regulating valve in each main feedwater line. Feedwater flow is automatically regulated by low flow bypass regulating valves in each bypass line. The positions of the bypass valves are automatically controlled based on steam generator level, steam flow, and feedwater flow. The bypass valves allow more accurate and respcnsive feedwater flow control than would be possible with the larger main regulating valves during low power (and low feedwater flow) operation.
After the loss of main feedwater flow to one or more stu 1 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 any one of the following conditions: 1) two out of three steam generator low-law water level signals in any one steam generator, 2) the loss of off-site power, or 3) a safety injection signal (SIS). The turhine driven auxiliary feedwater pump starts on any one of the following conditions:
- 1) two out of three steam generator low-law water level signals in any two steam generators or 2) two out of four reactor coolant pump under-voltage signals. The motor drhan and turbine driven pumps can also be started manually (local or remote).
Plant design specifications allow for,a maximum delay of one minute from receipt of any auxiliary feedwater pump startup signals to delivery of auxiliary feedwater to the steam generators.
Administrative guidelines require manual control and regulation of the 4
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auxiliary feedwater flow after its automatic initiation for subsequent refill of the steam generators. Manual flow control is :antinued to bring the water levels above the feedrings and to maintain adequate levels in the steam generators.
3.
WATER HAMER EXPERIENCE The IPS has reported 12 steam generator water hamer events with all but two assumed to be the result of steam-water slugging in the feedwater systems. A description of the events is presented in Table I.
Independent of the precursor event, each water hamer event usually caused a SIS that resulted from false high steam line differential pressure (high delta p) signals. Water hamers that were undetected by other means were identified in this manner. The high delta p signals were spurious spikes mechanically induced by pipe vibrations caused by the water hamers. The mechanical vibration of
- he feedwater piping due to water hamer is transmitted to the steam sine pressure transmitters via pipe supports and connecting structures. The signals originate from pressure tranducers located in the main steam line from each steam generator. The spikes are induced by disturbing the pressure transmitters which are located by the check valves in the main feedwater piping of each loop.
High delta p signals are generated in a given loop when pressures are sensed that are 100 psi or more below the comparable pressure measurements in any two of the remaining three loops. For example, a water hamer in the feedwater piping of loop A would induce vibrations in the pressure transmitters of loop A and loop C.
(The pressure transmitters for loop A and loop C are located in close proximity of each other as are the transmitters for loop B and loop 0). The resultant false pressure spikes would then cause high delta p signals e
to be generated in either loop B or loop D.
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4
! I i
l TA8tf I l
ZION STEAM EENERATOR WATER IW9tER EXPERIENCE Reactor Timi laterval Water Date of Power Previous Unit Status from Reactor Trip tlammer Water Unit to Reactor Trip at 16me of Precursor Event Feedring(s) to Water Hammer feedring(s)
Event No.
Hasper A (5 of Full Power) of Water Hammer to Water liasumer Uncovered (Minutes)
Recovered 1
8-29-74 2
30 HSDC 28 reactor coolant pump yes 10 i
tripped 2
12-30-74 2
82 HSD 2C main feedwater regu-yes 27 in process lating valve closed 3
3-18-75 2
85 itSD High 20 steam generator no NA9 KA level 4
5-25-76 2
85 HSD 28 feedwater pump tripped yes 36 la process 5
6-20-76 2
100 HSD Planned manual turbine trip yes 62 in process 6
6-20 76 1
20 HSD liigh delta pe loops no KA KA C
I A and 2C + SIS 7
9-26-76 1
NA C50d unit in process of being no NA KA brought to CSD 8
7 8-77 1
90 HSD Reactor trip during re-yes 5
no ar. tor protective logic
~%j testing b
9 7-10 77 2
l HSD 2A feedwater pump had trip-yes 27 no C:P' ped and was being restarted O
10 9-14-18 1
i HSD i
yes 12 no N
11,128 12-5-78 1
RA HSD Cooling IC main feedwater yes Several hours no
-~~~
regulating valve with con-densate flow a
Consecutive identical events b
Unknown or unsure c
Blot shutdown d
Cold sbatduwn liigh steam line dif ferential pressure signals e
f Safety injection signal g
Not applicable
- e.
9
TABLE I (Cont.)
ZION STEAM GINERATOR WATER HAMMER EXPERIENCE Auxillary Water Loop (s) in Feedwater Flow Rate Hammer nelch Water Per Steam Generator at Evidence of Type of Event No.
Hammer Occurred Time of Water Hamner(qpe)
Water Itammer Damage Water Hammer 1
2C 7
High delta p on loop D + SIS 2 Broken snubbers S-WI 2
28 or 2D 1
High delta p on locp D+ SIS lione S-W 3
28 None Observed movement of 28 feedwater 1 Broken snubber Not S-W3 line 4
2C 100 High delta p on loops 8 and 0+ S15 None S-W S
2C 7
High delta p on loops 8 and D +S15 None SW N
6 207 None High delt6 p on loops A and C +Sl5 None Not S-W 7
ID f
High della p on loops A and C+ SIS
& Broken hangers S-W 8
IAT
>300 High delta p on loop 8+ S15 None S-W 9
All loopsi
>100h High delta p on loops 8 and C + 5IS, Cracked motor S-W audible indication of water hammer housing on 2A, 28, 4
and 20 feedwater isolation valves 10 18 or ID
<l50 High delta p on loops A and C+ SIS None S-W g
N 11.12 IC None High delta p on loop 8 + S15 None S-W N
h Auxillary feedwater flow was 100 gpa per steam generator but an unmeasured main feedwater flow was leaking past main regulating valves i
Water hammer the to steam-water slugging j
Water hamaer probably not due to steam-water slugging, cause unknown
Following event No. 5, administrative control was implemented to reduce fedwater f. low to 50 gpm per steam generator when recovering feedrings in Unit No. 2.
This flow limit supplemented the existing 105 gpm limitation imposed anytime the steam generator water levels drop below the feedrings. Continued occurrence of water hamers in this unit, however, prompted installation of "J" shaped discharge tubes on the 2C feedring in February 1978. The majority of water hamers had occurred in loop 2C but none have been reported in this loop since the modificatons were made to the feedring.
The difficulties involved in properly regulating feedwater flow at all times during feedring uncovery and subsequent recovery was demonstrated during event No. 9.
The motor driven main feedwater pump in Unit No. 2 was being restarted after it had tripped out and caused a reactor trip. While the pump was being restarted, feedwiter was leaking past the closed main feedwater regulating and bypass valves.
Thus, in addition to the auxiliary feedwater flow of 100 gpm per steam generator, an unmeasured amount of main feedwater was being introduced into the steam generators. The approximate time of the water hamers coincided with the startup of the motor driven main feedwater pump.
The events that occurred in Unit No. 1 did not occur preferentially in any one loop as they did in loop 2C of Unit No. 2.
The majority of events in Unit No.1 did occur in loops with uncovered
.feedrings.
In Unit No. 2, most of the events occurred in the loops with feedrings in the process of being recovered.
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III. MEANS TO REDUCE THE POTENTIAL FOR WATER HAMiER 1.
DESCRIPTION The following means are employed at the ZPS to reduce the potential for water hamer in the feedwater systems:
1.
"J" shaped discharge tubes were installed on top of the feedring of the 2C steam generator and the bottom discharge holes were plugged.
2.
The auxiliary feedwater systems are designed to supply auxiliary feedwater to the steam generators within one minute after the interruption of the main feedwater supply.
3.
The horizontal length of feedwater piping adjacent to any steam generator is less than 8 feet..
4.
Administrative control requires the operator to limit the feedwater flow to about 105 gpm when the water level in any steam generator is below the feedring.
The "J" shaped discharge tubes were installed on top of the 2C steam generator feedring to provide for top discharge of water rather than bottom discharge. During periods of feedring uncovery, this arrangement increases the time for complete drainage of the feedring and associated horizontal feedwater piping from less than one minute to about 30 minutes. Also, the maximum auxiliary feedwater flow (about 450 gpm per steam generator) was not sufficient to maintain the 2C feedring and feedwater piping full of water when the feedring had bottom discharge holes. The feedring equipped with "J" shaped discharge tubes, however, pemits feedwater flow rates as low as about 10 gpm to keep the feedring and feedwater piping full of water until 9
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N feedring recovery occurs. Substantial drainage of the 2C feedring and piping does not occur for about 5 minutes which allows time for:
- 1) automatic actuation of the auxiliary feedwater system after the loss of main feedwater flow or any event resulting in 2C feedring uncovery during normal power operation or 2) the operator to reestablish steam gererator water level during startup and low power operating conditions during which the water level drops below the feedring in the 2C steam generator.
The potential for water hamer is eliminated if the feedrings and feedwater piping are kept full until feedring re::overy. This requirement can be satisfied during conditions conducive to water hamer by employing "J" shaped discharge tubes in conjunction with prompt automatic initiation of auxiliary feedwater flow.
The present main feedwater piping geometry adjacent to each steam generator consist.s of a horizontal run (7 feet 9 inches maximum) from the steam generator to the first downward turning elbow in each line.
This arrangement allows the horizontal run of piping in each line to drain into its associated steam generator and become steam filled during periods of feedring uncovery.
Tests conducted at Indian Point Unit No. 2 have indicated that reduced feedwater flow to steam generators with uncovered and draining feedrings reduces the potential for water hamer. Evidence of water hamer was observed in two loops with steam generators having uncovered and drained feedrings when feedwater was delivered at greater than 200 gpm per steam generator under hot standby test conditions. No water hammer was observed in tests when the auxiliary feedwater flow rates were below 200 gpm. The events occurred in the two loops with the shortest horizontal piping runs which are about 4 feet and 7 feet.
The horizontal piping runs in the other two loops are 10 feet and 12 feet.
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The water hammer was hypothesized to be the result of turbulent, wavy flow patterns in the horizontal feedwater piping creating a water slug that " sealed" the piping and isolated a pocket of steam.
Subsequent collapse of the condensing steam pocket caused the slug to accelerate, resulting in the water hanner.
The results of tests conducted at Doel Unit No.1 in Belgium are contrary to the Indian Point No. 2 tests. A water hammer event occurred in a steam generator (or possibly, its associatea horizontal piping) while auxiliary feedwater was being supplied at a rate of only 40 gpm. The steam generator was " hot" but at only'45 psia at the time of the event. The event occurred in a very long (about 18 feet) horizontal section of piping adjacant to the steam generator. The tests at Doel indicate that feedwater water hammer is possible at even very low feedwater flow rates with reduced steam generator pressures.
Administrative control limits the feedwater flow to 'ny steam a
generator at the ZPS to 105 gpm anytime the water level in that steam generator is below the feedring. The valves in the auxiliary feedwater lines are normally in throttled positions such that auxiliary feedwater flow is limited to 105 gpm in the event of automatic initiation of auxiliary feedwater flow. The flow is further reduced manually'to 50 gpm per any steam generator subsequent to the water level in that steam generator reaching the " narrow" instrumentation range. The 50 gpm flow is maintained until the feedring is recovered.
2.
EFFECTIVENESS DURING TRANSIENTS AND CONDITIONS CONDUCIVE TO WATER HAMMER The normal and hypothetical transients and conditions conducive to steam generator water hammer are discussed in this section. With the exception of subsection 2.4 entitled " Operator Error", each subsection 11 1796 076
describes a transient resulting from a single initiating event or failure with the unit (either No. 1 or No. 2) in normal power operation. Potential compo tent or system failures as a direct result of a hypothetical steam generator water hamer are accounted for in the analysis.
A single criterion was the basis for evaluating the effectiveness of the means to adequately reduce the potential for steam generator water hamer. This criterion is to maintain the feedwater system full of water during the time from the intiating event resulting in feedring uncovery to subsequent feedring recovery and stabilized steam generator water inventory.
2.1 Reactor Trio A reactor trip with the plant in normal power operation would result in a turbine trip and cause the water level in all steam generators to collapse to a level below the feedrings. Within 60 seconds of the resulting steam generator low-low water level signals, the motor driven and turbine driven auxiliary feedwater pumps would automatically startup and supply auxiliary feedwater to the steam generators. If the initiating event for the reactor trip did not close the main feedwater regulating valves (as would, for example, a safety injection signal), the valves would close upon receipt of: 1) low primary coolant average temperature signals, 2) steam generator high-high water level signals, or 3) the main generator trip relay signal 50 seconds after the turbine trip.
A reactor trip that did not result in feedwater isolation would cause the regulating valves in the main feedwater lines to open fully to help restore steam generator water level for residual primary heat removal. After a reactor trip from full power, main feedwater supplied to the steam generators after a turbine trip (50 seconds of full flow) 12 1796 077
is not sufficient to recover the feedrings. Refill of the steam generators and feedring recovery would be accomplished by auxiliary feedwater flow throttled to the administrative limits and under operator control.
The maximum auxiliary feedwater flow is not sufficient to maintain the feedrings and associated horizontal feedwater piping full (except in loop 2C) during steam generator refill subsequent to a reactor trip.
Thus, the potential exists for water hamer.in all feedwater loops except for loop 2C since the "J" shaped discharge tubes allow the 2C feedring and feedwater piping to remain full of water until feedring recovery.
2.2 Loss of Main Feedwater Flow The main feedwater supply could be interruoted due to the
- 1) malfunction or tripping of the main feedwater pumps, 2) loss of suction to the main feedwater pumps, or 3) closure of the main feedwater regulating and/or isolation valves. 'A reactor trip would occur upon receipt of.the resulting steam /feedwater flow mismatch signals and low steam generator water level signals.
The reactor trip would cause the water levels in all steam generators to collapse to a level below the feedrings. The motor driven and turbine driven auxiliary feedwater pumps would startup upon receipt of the subsequent low-low steam generator water level signals.
Auxiliary feedwater would then be used to refill the steam generators and recover the feedrings Auxiliary feedwater flow is insufficient te keep the feedwater system full of water after the loss of main feedwater flow.
Thus, the potential for water hamer exists in the feedwater loops with bottom discharge feedrings.
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2.3 Loss of Offsite Power A complete interruption of offsite power would result in a reactor trip, turbine trip, and startup of the diesel generators. The motor driven and turbine driven auxiliary feedwater pumps would startup to supply feedwater to the steam generators upon receipt of the resulting steam generator low-low ~ water level signals. The redundant auxiliary feedwater systems are fully functional without offsite power since the diesel generators and DC batteries independently supply necessary electrical power to each of the systems.
The main feedwater pumps would trip off due to loss of suction following interruption of power to the condensate and condensate booster pumps. Auxiliary feodwater would be required to restore the water inventory in the steam generators.
As was the case for a reactor trip or the loss of main feedwater flow, the interruption of offsite power would result in similar conditions conducive to water ' amer. Auxiliary feedwater flow will n
not keep the feedrings and feedwater piping full (except in loop 2C) during steam generator refill. Thus, the potential exists for water hamer in the loops with bottom discharge feedrings.
2.4 Operator Error The potential for water hamer in the feedwater system increases greatly if uncovered feedrings are allowed to drain substantially after an event causes the steam generator water levels to drop below the feedrings. Admission of feedwater into the drained feedrings and horizontal feedwater piping could then result in water slugging and subsequent water hammer. The uncovery of one or more feedrings is.most likely when the plant is operating at low power or during startup since feedwater is being regulated manually, rather than automatically.
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A reactor trip with the reactor at low power levels may not result in feedring uncovery while a reactor trip at high (normal) power levels would cause the steam generator water levels to drop substantially below the feedrings. Between certain intermediate power levels, the steam generator water levels would drop below the feedrings resulting in low steam generator water level signals. However, the water levels may not drop far enough to result in low-low steam generator water level signals.
Automatic initiation of auxiliary feedwater flow could, therefore, not result after a reactor trip at certain power levels.
A reactor trip not resulting in automatic auxiliary feedwater pump startup would require manual startup of the pumps by the operator upon receipt of audible low steam generator water level signals.
The time delay associated with manual startup of the auxiliary feedwater pumps would be several minutes longer than would be required for automatic startup.
Should feedring uncovery occur in the 2C steam generator, the "J" shaped discharge tubes would keep the feedring from draining substantially for about 5 minutes. This time delay would allow sufficient time for the operator to become aware of feedring uncovery and to properly regulate auxiliary feedwater flow to recover the feedring and to maintain the feedring and feedwater piping full of water.
If uncovery of the bottom discharge feedrings occurred, substantial drainage of the feedrings and horizontal piping would result in less than one minute. Auxiliary feedwater flow would not be sufficient to keep the feedrings and piping full of water during any period that the feedring is uncovered. Thus, the potential for water hamer exists in the feedwater loops with bottom discharge feedrings.
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2.5 Steam Line Break The potential for water hammer events resulting from or concurrent with the rupture of a stema line inside containment was considered.
The sequence of events following such a failure was evaluated 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 SIS causing a reactor trip, a turbine trip, and isolation of all main feedwater lines. The loss of main feedwater flow to the steam generators would result in the automatic startup of the motor driven and turbine driven auxiliary feedwater pumps. Feedwater would 'len be supplied for subsequent refill of the steam generators and recovery of the feedrings.
The turbine driven auxiliary pump would be fully operable since it would receive adequate steam for driving power'even if one of the two interconnected steam lines for the pump turbine was supplied by the blowndown steam generator. Check valves in each supply line would prevent " crossover" blowdown through the supply lines from ore steam generator to the associated 510wndown steam generator.
Auxiliary feedwater flow is not sufficient to keep the bottom discharge feedrings and associated horizontal piping full of water in the feedwater loops with steam generators not affected by the steam line break. Since the potential exists for water hammer in these unaffected loops, the potential also exists for a rupture of the main feedwater piping adjacent to the steam generators. The rupture of a feedwater line due to a water nammer would result in the blowdown of the associated steam generator. Blowdown of another steam generator in conjune. tion with the first blowdown steam generator could result in containment building ovarpressurization.
16
The potential for water hamer exists in the feedwater loops with bottom discharge.feedrings following a steam line break. Although the potential for water hamer may be decreased by reduced auxiliary feedwater flow and horizontal piping lengths, the potential is still significant based on operating experience.
2.6 Loss-of-Coolant Accident The potential for feedwater water hamer during a postulated loss-of-coolant accident (LOCA) was examined because 1) a water hammer could increase the consequences of a LOCA and 2) the plant protective actions during a LOCA could result in conditions which are conducive to water hamer if the feedwater system is not kept full of water.
A LOCA would result in a SIS, a reactor trip, a turbine trip, and subsequent isolation of the feedwater system. The startup of the motor driven and turbine driven auxiliary feedwater pumps would result and feedwater would be supplied tc the steam generators within 60 seconds of the reactor trip. Refill of the steam generators and recovery of the feedrings would occur in a manner typical of a reactor trip or the loss of offsite power.
The potential for blowdown of a steam generator during a LOCA exists because of feedwater water hamer. Slowdown of a steam generator in conjunction with a LOCA could result in more severe containment building pressurization than would occur during a LOCA.
The conditions conducive to water hammer in the feedrings and feedwater piping resulting from a LOCA would be very similar to those from a reactor trip. Thus, the potential exists for feedwater water hamer in the loops with bottom discharge feedrings.
17 1796 082
IV. CONCLUSIONS AND RECOMMENDATIONS The assessment of the capability of existing means to reduce the potential for water hammer during various hypothesized transients and conditions was discussed in Section III. This assessment has shown that under conditions which are most conducive.to water hammer in the feedwater system (specifically, uncovered and draining feedrings and feedwater piping subjected to admission of cold auxiliary feedwater),
the means to reduce the potential for water hammer at the ZPS are inadequate to maintain sufficiently full feedrings and feedwater piping until feedring recovery occurs. Therefore, since keeping the feedrings and feedwater piping full of water is the criterion for this evaluation, we find that the means to reduce the potential for steam generator water hammer at this facility are inadequate. We therefore recommend plugging of all bottom discharge holes and installatio: of "J" shaped discharge tubes on all steam generator feedrings.
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~.
V.
REFERENCES 1.
G. J. Plimi lte to R. A. Purple, Subject
" Response to May 13, 1975 NRC letter on Stea.1 Generator. Water Hammer", July 17, 1975.
2.
D. E. O'Brien itr to A. Schwencer, Subject
" Response to September 2,1977 NRC letter on Steam Generator Water Hammer",
January 20, 1978.
3.
Firal Safety Analysis Report, Zion Station, Commonwealth Edison, DOE Docket Nos. 50-295 and 50-304.
4.
Nuclect Power Experience, Nuclear Power Experience, Inc., PWR vol. XVI.C. bib, 3/9.
5.
J. A. Block, et al, An Evaluation of PWR Steam Generator Water Kammer, Creare, Inc., NUREG-0291, Decemoer 1376.
19 1796 084