ML20070H759
| ML20070H759 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/1982 |
| From: | Anderson N, Han J Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-0918, NUREG-918, NUDOCS 8212270181 | |
| Download: ML20070H759 (39) | |
Text
- - - - ---
Prevention and Mitigation of Steam Generator Water Hammer Events in PWR Plants U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation J. T. Han, N. Anderson
,p* "%,,
g 2 g gi 821130 0918 R PDR
NOTICE Availability of Reference Materials Cited in NRC Publications Most documents cited in NRC publications will be available from one of the following sources:
- 1. The NRC Public Document Room,1717 H Street, N.W.
Washington, DC 20555
- 2. The NRC/GPO Sales Program, U.S. Nuclear Regulatory Commission, Washington, DC 20555
- 3. The National Technical Information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publications, i
it is not intended to be exhaustive.
Referenced documents available for inspection and copying for a fee from the NRC Public Docu-ment Room include NRC correspondence and internal NRC memoranda; NRC Office of Inspection and Enforcement bulletins, circulars, information notices, inspection and investigation notices; Licensee Event Reports; vendor reports and correspondence; Commission papers; and applicant and licensee documents and correspondence.
The following documents in the NUREG series are available for purchase from the NRC/GPO Sales Program: formal NRC staff and contractor reports, NRC-sponsored conference proceedings, and NRC booklets and brochures. Also available are Regulatory Guides, NRC regulations in the Code of Federal Regulations, and Nuclear Regulatory Commission Issuances.
Documents available from the National Technical Information Service include NUREG series reports and technical reports prepared by other federal agencies and reports prepared by the Atomic Energy Commission, forerunner agency to the Nuclear Regulatory Commission.
Documents available from puSlic and special technical libraries include all open literature items, such as books, journal and periodical articles, and transactions. Federal Register notices, federal and state legislation, and congressional reports can usually be obtained from these libraries.
Documents such as theses, dissertations, foreign reports and translations, and non-NRC conference proceedings are available for purchase from the organization sponsoring the publication cited.
Single copies of NRC draft reports are available free upon written request to the Division of Tech nical Information and Document Control, U.S. Nuclear Regulatory Commission, Washington, DC 20555.
Copies of industry codes and standards used in a substantive manner in the NRC regulatory process are maintained at the NRC Library, 7920 Norfolk Avenue, Bethesda, Maryland, and are available there for reference use by the public. Codes and standards are usually copyrighted and may be purchased from the originating organization or, if they are American National Standards, from the American National Standards Institute,1430 Broadway, New York, NY 10018.
NUREG-0918 Prevention and Mitigation of Steam Generator Water Hammer
' Events in PWR Plants Manuscript Completed: March 1982 Data Published: November 1982 l
J. T. Han, N. Anderson Division of Safety Technology Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission W:shington, D.C. 20566 f....,,
I
/
i l
l ABSTRACT Water hammer in nuclear power plants is an unresolved safet'y issue under study at the NRC (OSI A-1) (Reference 1). One of the identified safety concerns is steam generator water hammer (SGWH) in pressurized-water reactor (PWR) plants (References 2-4).
This report presents a summary of:
(1) the c1uses of SGWH, (2) various fixes employed to prevent or mitigate SGWH, and (3) the nature and status of modifications that have been made at each operating PWR plant. The NRC staff considers that the issue of SGWH in top feedring designs has been technically resolved.
This report does not address technical findings relevant to water hammer in preheat type steam generators.
iii
CONTENTS ABSTRACT.............................................................
iii LIST OF FIGURES......................................................
V I
ACKNOWLEDGMENTS......................................................
Vii 1.
INTRODUCTION....................................................
I i
2.
TECHNICAL DISCUSSION............................................
I 2.1 Definition and Possible Causes of Steam Generator Water Hammer..............................................
2 l
2.2 Modifications to Prevent ar.d Mitigate SGWH................
7 i
2.3 Summary...................................................
10 4
3.
DESCRIPTION OF MODIFICATIONS MADE AT OPERATING PWR'S............
12 j
4.
CONCLUSIONS.....................................................
26 5.
REFERENCES......................................................
28 FIGURES h
1.
A steam generator (SG and Main Feedwater Line) for a typical Westinghouse plant......................................
3 l
2.
A Westinghouse steam generator with the " unmodified" l
feedring using bottom holes to discharge water..................
4 3.
A Combustion Engineering steam generstor with the
" unmodified" feedring using bottom openings to discharge water.................
5 4.
Possible sequential events leading to steam generator water hammer.......................................
6 i
5.
Westinghouse and Combustion Engineering steam generator i
feearings using J-tubes to discharge from the top of the feedring........................................................
8 6.
Westinghouse-recommended designs to achieve the "short" horizontal feedwater pipe at steam generator inlet..............
9 v
1 7.
Babccck & Wilcox steam generator with external feedring (header)........................................................
11 8.
Steam generator feedring and feedwater system at Kewaunee, Prai rie Island 1 and 2, and Point Beach 1 and 2.................
33 9.
Preheat steam generator at McGuire 1............................
21 10.
Schematic of the McGuire 1 preheat steam generator with associated feedwater system.....................................
22 TABLES 1.
A summary of water hammer modifications for feedring SGs........
12 2.
Summary of SGWH modifications implemented at all W and CE operating plants.............................................
13
(
vi
ACKNOWLEDGEMENTS The authors are grateful to a number of people for providing valuable information and discussion during preparation of this report.
Special thanks are due to S. D. MacKay of NRC, who was responsible for the completion of most safety evaluation reports cited in the report.
Assistance from other NRC colleagues is also acknowledged; these include
- 0. D. Parr and the staff of the Auxiliary Systems Branch; C. C. Graves; R. Colmar; and project managers and resident inspectors of the operating PWR plants.
Steam generator information was received from F. C. Wellhofer and J. Schulties at Westinghouse, and R. E. Daleas and his staff at Combustion Engineering. The authors are grateful to them.
i v ii
1.
INTRODUCTION Water hammer in nuclear power plants is an unresolved safety issue under study at the NRC (VSI A-1) (Reference 1). One of the identified safety concerns is steam generator water hammer (SGWH) in pressurized-water reactor (PWR) plants (References 2-4).
This report presents a summary of:
(1) the causes of SGWH, (2) various, fixes employed to prevent or mitigate SGWH, and (3) the nature and status of modifications that have been made at each operating PWR plant. The NRC staff considers that the issue of SGWH in top feedring designs has been technically resolved.
SGWHs occurred in certan PWR plants before modifications discussed in this report were performed. Effects varied from plant to plant, usually ranging from noise to observed damage to feedwater piping.
The most severe recorded SGWH incident (Reference 5) occured on November 13, 1973 at the Indian Point Unit 2 Plant; the feedwater piping cracked and resulted in steam release into the containment building.
However, the plant was shut down safely and no damage to the reactor or primary system resulted.
Since then, Westinghouse has conducted several studies to identify causes of SGWH and develop modifications to prevent or mitigate SGWH (References 6-8).
Because of the the continuing occurrence of SGWHs in some Westinghouse (W) and Combustion Engineering (CE) plants, the NRC in September 1977 requested all W and CE PWR licensees to submit proposed hardware and procedural modifications necessary to prevent or mitigate SGWH (Reference 9).
Licensee responses were subsequently evaluated by the NRC staff, and conclusions were presented in safety evaluation reports and letters to licensees. As a result of these evaluations, the NRC staff prepared a Branch Technical Position ASB 10-2, " Design Guidelines for Water Hammers in Steam Generators with Top Feedring Designs" and incorporated this position into Section 10.4.7 of NRC's Standard Review Plan (NUREG-0800).
Since Babcock and Wilcox (B&W) plants had not reported damaging SGWH's, these plants were not required to make changes. However, recently (5/82) some B&W SG's have baen found to have damaged internal auxiliary feedring and support strv. ee.
These findings are discussed briefly in Section 2.0 and 4.0; m ft oa hations are underway.
Chapte if s report addresses the possible causes of water hammer in W and CE stean perator and feedwater systems, various modifications to help prevent SGWH, and an explanation of why water hammer is unlikely to occur in B&W steam generators.
Chapter 3 presents specific plant modifications approved by the NRC staff that have been implemented at each of the 38 operating W and CE plants. Chapter 4 presents staff conclusions.
Finally it should be noted that this report does not address the water hammer issue with respect to preheat steam generator designs, such as: W Models D2/D3 and D4/DS. Water hammer considerations for preheat SG's will be included in the staffs concluding water hammer technical evaluations for USI A-1.
2.
TECHNICAL DISCUSSION 1
2.1 Definition and Possible Causes of Steam Generator Water Hammer Steam generator water hammer (SGWH) is defined as steam condensation-induced water hammer occurring in the secondary side of a PWR steam generator (SG) at the connection to tne feedwater line (Reference 2).
Prior to the introduction of preheat SG's,* all PWR steam generators employed a feedring (i.e., ring-type sparger) through which the feedwater is injected into the downcomer between the baffle and the outer shell.
Figure 1 shows the SG and main feedwater line of a typical Westinghouse plant.
Figure 2 shows the internals of a Westinghouse SG with the
" unmodified" feedring with bottom holes to discharge water.
It should be noted that when the severe SGWH occurred in 1973 the SG feedring at Indian Point 2 was similar to the one shown in Figure 2(b) except that the main feedwater pipe was 18-in. Schedule 80 pipe.
Figure 3 shows a Combustion Engineering SG with the " unmodified" feedring using bottom openings to discharge water.
During certain plant transients, which result in a rapid reduction of feedwater flow, the SG water level may drop below the bottom of the feedring sparger. A bottom discharge feedring can be drained of water and filled with steam within 1 or 2 minutes after the feedring is uncovered if feedwater flow has been terminated (Figures 2 and 3). When the feedwater flow is resumed following such a transient (which is usually highly subcooled auxiliary feedwater) it enters the horizontal pipe run into the feedring, and flows under the steam blanket as depicted in Figure 4(a).
Rapid steam condensation can occur at the interface between the steam and the subcooled feedwater causing a countercurrent of steam to flow over the top of the feedwater.
Interaction forces between the steam and water can create enough turbelence to seal off a pocket of steam, as depicted in Figure 4(b).
Continued rapid condensation of steam in the pocket accelerates a slug of water into the void as depicted in Figure 4(c).
Acceleration forces on the water slug can be very large because the pressure on one side is at steam generator pressure, initially in excess of 1000 psi, while the pressure on the trapped vapor side can be greatly reduced depending on condensation rate. As a result the water slug can have a high velocity when it impacts against the incoming water column, and a pressure pulse is produced [ Figure 4(d)].
This constitutes one possible explanation of a steam generator water hammer.
The magnitude of the pressure pulse and its propagation through the feedwater line depend on many factors.
These include the steam void condensation rate, the initial volumes of the void and water slug, steam pressure in the SC, sonic velocity in the feedwater line, and piping geometry and layout (References 10, 11).
In a severe SGWH the pressure pulse may be as high as thousands of psi (References 2,4).
As the pressure wave travels upstream in the feedwater line [ Figure 4(d)],
dynamic forces are produced on the pipir.. system which can cause damage to The McGuire Unit Plant which uses feedwater injection nozzles at the bottom of the SG instead of a feedring is discussed in Chapter 3.
2
(
)
I generator r
swirl N
separators cogro ipYru"n ses (R) lp,*fg,i",9 e r
~
\\
- Heat pipe -
exchanger U tubes Containment wall I
J
\\ Primary coolant flow i
mEl. 21085 Figure 1.
A steam generator (SG and main feedwater line) for a typical Westinghouse Plant 3
w-,,w..
,,,--,a-
-m,
-w
,--,,,-a
~g
,,--~,------,-y,
F:
Steam outlet to turbine generator h
,g-3 Demisters secondary l M-~
moisture separator
(' --
Onfice rings
/
( }I *
- Secondary manway w
t WiEW_s>
w-4 Swiri vane primary W
Feedwater inlet ha "U'
" "E *#
g(
Main feedwater pipe
'4 O
(16 in., sch 80 pipe)
=
Upper shell Thermal sleeve p
(16 in., sch 80 pipe)
)'
' < N', ' ',
StG wall (to 6n., sch 40 pipe)
Feed ring Feedwater ring
,7 / / ~ 7((
d Antivibration bars Tube bundle Internal clearance
_=
Tube support plates cap = 0.020 2 0.015 6n.
16 in x 10 in reducing s
a Lower shell M
tee w,
s-- -x -
?
(C!D (2M) = 3/4 in. diameter flow holes
\\
(roughty eventy distnbuted about penphery)
C IhEL 21083 Tube sheet
?
Secondary handhole Primary manway Blowdown line i ')-
o
(
Pnmary coolant outlet Primary coolant intet 2a.
Typical Westinghouse feedring steam generator 2b.
Sketch of " unmodified" Westinghouse feedring Figure 2.
A Westinghouse steam generator with the " unmodified" feedring using bottom holes to discharge water
\\
2 r
~
i!
/ ~ ""'
,L";,:f.",,", **"
F dwat.r
- y i
M wall (12 In-. 8Ch ini.t Tn rm.i.
"\\ [N/
N
.si _. <
g$teutw N
f 22e in.
l
'N
)
g,1a in;,= $3
=.
i~s'
=
+
=,
)
^
t.
t 0
INEL 2 N89 3a. Typical CE steam generator 3b.
Sketch of CE " unmodified" feedring assembly Figure 3.
A Combustion Engineering steam generator with the " unmodified" feedring using bottom openings to discharge water
Tr nsi:nt
[Crnd:nsati::n hydriulic of steam Feedpipe waves FMW
/~
/ / / ~-
~4 Steam +
_ ~. _
_. c/_~ _
- ... arm Water flowf NpSteam Steam flow
~~F generator mixing nozzle Subcooled water (a) Possible Steam-Water Mixing Phenomena in the Feed system pSteam generator Feedpipe nozzle Feedring
[ Trapped steam vold,
q (7 % -Subcooled water'.~c - ~ ::r.
E_
]
F Water Steam
-r slug formation (b) Possible Trapping of a Steam Void Steam from vents in some systems Water slug Steam moves rapidly generator nozzle into void Feedpipe Feedring
(
M'
=-
~ _ ~ -
Slug M
Steam N
builds up
~
and Region near steam generator scoops up water at lead edge pressure (c) Possible Slug Acceleration into Void t
N impact Feedpipe Feedring s
[~ _- 8__.--
Steam f ---- - \\ ~ - ~-
~
r eam c - Pressure NSteam generator waves travel through system nozzle (d) Possible Water Slug impact INEL 21076 Figure 4.
Possible sequential events leading to steam generator water hammer 6
piping supports.and restraints (e.g., snubbers, and clamps) and to the piping. Both types of damage were evident in the severe SGWH incident in 1973 at Indian Point 2, where radial deformation or bulging of some feedwater piping was found (Reference 5). A half-circle steam-leaking
' fracture occurred in the main feedwater piping at the containment wall anchor point, which was probably caused by the excess bending stress due to pressure-wave-induced dynamic forces (Reference 12).
2.2 Modifications to Prevent and Mitigate SGWH The most effective method for preventing SGWH is to keep th. SG feedring and the feedwater line full of water so that steam will not enter the feedwater system. This is the case normally during plant operation.
However, during certain plant transients the SG water level may fall below the feedring.
In a feedring designed with bottom discharge holes (as shown in Figures 2 and 3), it will be drained in a few minutes.
To prevent rapid draining, multiple J-tubes are installed on top of.the feedring and the bottom-discharge holes are plugged by welding, as shown in Figure 5.
With this modification, the rate of water discharge from an uncovered feedring is greatly reduced
- and it will take about 20 minutes or more to drain a SG feedring with top-discharge J-tubes as compared to roughly one to two minutes for a SG feedring with bottom-discharge holes.
The installation of J-tubes and closure of the bottom holes on the feedring is the first modification most frequently made to prevent and mitigate SGWH.
It should be emphasized that the installation of J-tubes will significantly slow down but generally not stop the feedring from losing water when uncovered. This modification is effective only if feedwater flow can be j
reestablished before a significant amount of steam enters the feedring.
i The second modification is therefore to provide early feedwater (usually auxiliary feedwater) flow into the SG and thus to supply water to the feedring as soon as practical.
For W and CE plants, the highest elevation of the feedwater line is generally at the SG feedring and the connecting horizontal feedwater pipe at the SG inlet (Figure 1).
Draining of this part of the feedwater line g
can occur during those plant transients in which SG water. level falls below the feedring.
By shortening the length of the horizontal pipe at the SG l
feedwater inlet, the volume that can be drained in the feedwater line is reduced; consequently, the magnitude of the pressure pulse of a condensation-induced SGWH will also be reduced. The third modification is to shorten the horizontal feedwater pipe leading to the SG inlet nozzle by installing an elbow or U-bend as shown in Figure 6 (References 2,3,7).
A i
There is a thermal sleeve between the SG inlet nozzle and the feedring piping.
For many operating SGs, water from the feedring piping can leak through the sleeve into the SG. The important point is that the combined leakage through the thermal sleeve, the closed feedwater valve and evaporation loss is much less than that going through the bottom-discharge holes of the unmodified SG feedring.
The leak rate through the thermal sleeve has been estimated to be on the order of 10 gpm.
7
a J tube p
J-tubes on tee have f
lower outlet than feedring j
J-tubes Feedring S
m U
3.50-in. R j
J-tube positions 3.50-in. R $
evenly spaced around 2 Il2-in.
'#"8 g
1.12 in.
l j
i 6.69-in.
g s
{
s.36-in.[" % 'i'"-
, y 10-in.
Sb.
Cross-section of CE top discharge feedring with pipe 18-in.
J tubes E
On ring f,1 tee Sa. Westinghouse J tube feedring configuration at Indian Point 2 Figure 5.
Westinghouse and Combustion Engineering steam generator feedrings using J tubes to discharge from the top of the feedring
Steam generator shell FW inlet nozzle d
g L-S N
k_/
h D
l A
C Y
k U
U
)
U
~
o g
i f
=
B
=
(a) Preferred Layout (b) Second Best Layout "A"
to be not less "C"
to be not less than 36 inches than 24 inches "B" & "D" no requirement established L
7_
s
/
/
p
]
i
/
Njl w
}
x'
\\/
(
j E
(c) Acceptable alternative Layout (d) Acceptable alterative Layout "E" + "F" not to exceed Horizontal run L to be 8 feet minimum dimension not to exceed 8 feet INEL 21078 Figure 6.
Westinghouse recomended designs to achieve the "short" horizontal feedwater pipe at a steam generator inlet 9
90 -downward elbow at the SG inlet [ Figure 6(a)] minimizes the length of the horizontal pipe and is therefore the preferred design of those shown in Figure 6.
A U-bend at the SG inlet [ Figure 6(b)] serves the same purpose as an elbow except that the flow resistance is higher in the U-bend than the elbow. An inverted U-bend [ Figure 6(c)] has a longer-drained length than the elbow or U-bend because both the top and the left leg of the inverted U-bend can be drained. The maximum length specified for drainable feedwater line is 8 ft for designs shown in Figure 6.
This criterion was recommended by Westinghouse (Reference 7).
In an effort to reduce SGWH frequency, some licensees impose a maximum limit on feedwater flowrate when feedwater flow is initiated.
The maximum has been spec;fied at around 150 gpm per SG.
[This value is 50 gpm less than the 200 gpm upper limit experimentally determined in the SGWH tests at the Indian Point Unit 2 Plant (Reference 2).]
At a low feedwater flowrate the water velocity and at a water level in the pipe being low enough to preclude trapping a steam void (Figure 4) condensation-induced SGWH is unlikely to occur. However, it may be undesirable in some plant transients to limit the feedwater flowrate to 150 gpm per SG, and therefore this modification is not commonly used.
In addition, other measures and proceedures are possible.
For example, near-s.turated water (instead of highly subcooled water) can be used to refill a drained SG feedring minimizing the rate of condensation.
Furthermore, some nuclear plants (e.g., Kewaunee and Palisades) have unique features or modifications to prevent damaging SGWHs. These are discussed in Chapter 3, where a discussion of each plant is presented.
The Babcock & Wilcox steam generator design is a single pass heat exchanger, termed a Once Through Steam Generator (OTSG), which employs a vertical tube bundle that passes through a pool of secondary coolant as shown in Figure 7.
The B&W OTSG is designed to minimize, or eliminate water hammer since:
(a) separate feedwater and auxiliary feedwater headers (located external to the steam generator shell) are employed; these risers from the external feedwater header which function like J-tubes with respect to keeping the header full of water, (b) auxiliary feedwater injection directly on SG tubes rather than into feedwater headers, (c) modulated feedwater control using cascaded flow control valves. These design features appear to be effective since damaging SGWH's have not been reported by B&W plants.
However, some B&W OTSG's employ an internally located auxiliary feedwater ring (eg. Davis-Besse, Rancho Seco and Oconee No. 3); this design differs from that shown in Figure 7.
Recent (5/82) plant inservice inspections (Reference 13) have discovered damaged internal auxiliary feedring and support structures. The damage appears relatable to steam pocket collapse and is under evaluation by B&W and the NRR staff.
2.3 Summary Table 1 summarizes the modifications that help prevent and mitigate SGWHs.
For most operating PWR plants, a combination (i.e., simultaneous 10
n.
i n.
A{ g 0 4
9 t
f tf 6
3 6
80 1
2 L
E N
I sgn ir dee f
f f) /
~
c
[
x hc te k
S N
(
r b
/ d n.
ta e
7 fi w
dee r
F e
e y
p r
p ip '
ix tar a
ip l
r
)
n t
l e
te3 iae r
2 le u
lnf mtar n.
Awe i
.we
.d d
.o indd n e a mp
- e a i e e S (y 4 e e S
6f h t
1f h y
y s
r y
t le a
a ta ta2) a e
e n
w w
w w3 n
i n
n lp
(
t a
a a
n dt a
M M
ee M
1 tro el lo ep FI e
n o
bp 0
c 1
uu r
Ts 2
o L
tc E
a N
e 8
R ro lxD.
t
_[,
. f.. f s a
s l
i ~
r g
f n.
ne "L
b If i
i ge 8
f l
q:
/
I 4
iy L' f
7 1
i', '
l
]'
7 m
f' a
3 g
yi
~l e
{
i
>i'(
y
+
+
2 t
', =
S
~
(
(;,
~
.a re 7
ta tn w
a tro d
lo p
e le fle e
o n
f f
fa
)
c o
y fa 2(
b
)
r 2 r
b re tce i
it a
o(
mt t
n c
l r
e i
e al e p
ix*
p s
u p
tet w
alt a
r u
o eu i
A" U
So L
Ro D
n g s. " Q x m O h gg, b *'o' g
+r oe*3c mE c. 3 a
N, 3hn87 g c
- o D
x
(
t
[
Table 1 A Summary of Water Hammer Modifications for Feedring SGs No.
Modification Type Function 1
Top discharge J-tubes on feedring Hardware Significant delay in feedring draining 2.
Early feedwater flow into the SG Procedure Help keep feedring full of water 3
Short horizontal feedwater pipe Hardware Reduce magnitude of (less than 8 feet) at SG inlet SGWH 4
Limited flow to recover feedring Procedure Prevent forming of (150 gpm per SG)
& hardware water slug to trap steam void 5
Others (plant specific)
Hardware Or procedure employment) of the first three modifications has proved to be effective in preventing SGWHs. Other modifications have been made in some plants as discussed in Chapter 3.
In 1975 guidance for the review of designs fur prevention and mitigation of SGWd in application for construction permits and operating licenses was incorporated into Section 10.4.7 of the Standard Review Plan, Condensate and Feedwater Systems which includes as an attachment Branch Technical Position 10-2, Design Guidelines for Water Hammers in Steam Generators with Top Feedring Designs.
For plants with preheater-type steam generators, license reviews are conducted using NUREG/CR-1606, An Evaluation of Condensation Induced Water Hammer in Pre-Heat Steam Generators, as guidance.
3.
DESCRIPTION OF MODIFICATIONS MADE AT OPERATING PWR's In September 1977, the NRC requested all W and CE PWR licensees to submit proposed hardware and procedural modifications necessary to prevent or mitigate SGWH (Reference 9).
The modifications proposed by each licensee were evaluated on an individual plant basis. The effectiveness of these modifications had to be demonstrateo either by tests run at the plant or by tests conducted in a similar plant.
For some of the plants which have never had SGWHs, additional modification or backfitting was not required.
The modifications made on each W and CE operating plant are discussed below (plants are listed in alphabetical order). Table 2 presents a summary of the SGWH modifications implemented at 38 operating plants. Most of the plants have employed a combination of J-tubes on the feedring for top discharge, early feedwater flow into SG, and short horizontal feedwater pipe (less than 8 ft) at the SG inlet.
12
I s
Table 2 Simmisry of $331 modificattens taplausated et all u and C2 eperettel plants'
$nert Isrly nortrental Lietted
& Tubes fecemeter Feeemeter Flam to en Flew Pipe et Recover Other Test
' herettne Plants feedrina into 56
$$ inlet feedetas ($ee Romerts) Caneucted teferences teerts 1.
Artansas 2 a
a a
a 13.14 2.
Seaver falley 1 a
a a
16
' 3.
Calvert Citffs 1 a
a a
a 17.18 Separate austilary feedring 4 Calvert Citffs 2 a
a s
- a 17.18 Same 'as Unit 1
- 5. Coot 1 a
a s
a 20.22 I
6.
Cook 2 m
a a
e a
20.22
+
7.
Farley 1 a
a a
a 23 i
8.
Farley 2 a
a a
23 9.
Ft. Clahaue a
a a
24 Separate auslitary feedseter injectlee assale
- 10. Glaae a
a s
a 25
- 11. nedsas neck s
a 26
$1ow change of feedmater fleurete
- 12. ladian Point 2 s
a a
a a
27
- 13. Indian Potet 3 a
s a
28
- 14. towaunee e
a 29 Prostatte of auntliary feedseter tajectlen potat free M
- 15. ustne tankee a
30
- 14. ncGetre 1 a
a a
31.32.33 u preheat $$ estng lejeCtlen neffles E
- 17. altistone Point 2 a
a a
a 33,34
- 18. North Anna 1 a
a a
a 35,37
- 19. sorth Anna 2 a
a a
a 35.37
- 20. Paltsades*
a a
38.39
$aearate avstltary feeduster Itne. tests yet to es conducted
- 21. Potet Seach I a
a a
a 40 See Rewaunee
- 22. Point Seecg 2 s
a a
40 See tewaunee
- 23. Pratete Island I a
a a
a 41 See Newaunee
- 24. Pratrie Island 2 e
a a
41 See towaunee
- 25. Robinson 2 a
a 42 400 gym per $G for stese itae bream
- 26. St. Lucie 1 a
a e
43,44 FF. $ ales 1 a
s a
a 45.46
- 28. $ alee 2 e
a a
a 46.47
- 29. $an Onefre I s
es nata feedester is used whenever possible M. SeguDrah I a
a a
a 49-51 y
I
- 37. Sorry 1 a
a e
52 t
- 32. $erry 2 s
a e
52 l
l
- 33. frojan a
a a
a 53.54 I
- 34. Turney Potat 3 s
55
- 35. Turkey Potat 4 s
$5
- 36. Tantee-Roue a
a 56 male feedveter is preheated even at toe i
power operations
- 37. Iten 1*
a a
a a
s 57 One $6 feedelag is yet to have atubes lastalled
- 38. Iton 2 s
a a
a 57
- !aelearetation is yet to be casoleted (per Renarts).
l 1
i
[
13 t
i y.---
m,
,-.p,,-,-~..---
,-r-m,
-,--.,..--..p..,
w w,,-----.
--.en--.
,,,,,n,.,,-n_,---,-w.,.c.,.
g-
.,,7ng--,.,
,, +,
v,c,..
i I
For simplicity, " Arkansas 2" stands for the Arkansas Unit No. 2 Plant.
This notation is used for the rest of this chapter.
(1) Arkansas 2 (CE plant w/2 SGs)
Implementation Arkansas 2 has implemented (a) J-tubes on SG feedrings, (b) early initiation (within one minute) of auxiliary feedwater flow into the SG, and (c) short horizontal feedwater pipe at SG inlet (References 14,15). A test was performed (as part of the plant startup test program) to demonstrate that damaging SGWH did not occur and that auxiliary feedwater flow did start automatically within the time specified.
Status The staff has approved the present implementation at Arkansas 2 (Reference 14).
(2) Beaver Valley 1 (W plant w/3 SGs)
Implementation Beaver Valley 1 has implemented all of the first three modifications as listed in Table 1: (a) J-tubes on SG feedrings, (b) early initiation (within one minute) of auxiliary feedwater flow into the SG, and (c) short feedwater pipe at SG inlet (Reference 16).
[A flow limitation of about 150 gpm to recover a SG feedring was first imposed (Reference 16) but later it was removed (Reference 16).] No SGWH test was required because the tests performed at the Trojan plant (W plant with the same type of SGs) were deemed to be applicable to the Beaver Valley Unit 1 plant; SGWH did not occur in Trojan tests, which is discussed below.
Status The staff has approved the present lmplementation at Beaver Valley 1 (References 16).
(3) Calvert Cliffs 1 (CE w/2SGs)
(4) Calvert Cliffs 2 (same as Unit 1)
Implementation Calvert Cliffs Unit 1 and Unit 2 are identical CE plants.
Both plants have g
installed J-tubes on SG main feedwater feedring, but they do not have a short horizontal pipe (the horizontal length of the main feedwater line upstream of the main feedring is about 12 ft) (References 17,18). However, a unique feature is employed in their SGs-there is a separate auxiliary feedring to inject cold auxiliary feedwater into the SG.
There is no connecting path between the auxiliary and main feedwater lines, and the auxiliary feedwater is supplied into the SGs through the separate auxiliary feedring.
As a result, cold auxiliary feedwater cannot enter the main feedring.
Each SG is supplied with main feedwater through the main feedring until the main feedwater flow is decreased (for any reasons) to less than 750 gpm per SG (5% of full feedwater flow) and concurrently the SG water level falls below the main feedring; under this condition the main feedwater flow is stopped and auxiliary feedwater is supplied to the SG through the auxiliary feedring.
During the uncovery period, the main feedring drainage rate due 14
-to the leakage through its thermal sleeve (see Figure 2) is estimated in the order of 10 to 20 gpm; (References 17,18) a supply of main feedwater at 750 gpm or more will keep the main feedring full of water. Therefore, SGWHs during main feedring uncovery will not occur as long as main feedwater flow is supplied at 750 pgm per SG or higher.
The auxiliary feedring does not heve J-tubes but holes for bottom discharge.
Since November 1976 auxiliary feedwater flow has been supplied to the auxiliary feedring several times a year but no water hammer has resulted (References 17,18,19). The reasons are:
(1) The horizontal portion of the auxiliary feedwater line upstream of the auxiliary feedring is very short (less than a foot).
(2) Auxiliary feedwater is normally supplied at 9 ft/sec which is high enough to keep the 4-in. diameter auxiliary feedwater line and feedring filled with water so that entrapment of a steam void is unlikely in the pipe.
(3) The auxiliary feedring is located about 43 in, below the main feedring and is less likely to be uncovered.
Status The staff has approved the present implementation at Calvert Cliffs 1 and 2 (References 17,18).
(5) Cook 1 (W plant w/4 SGs)
(6) Cook 2 (same as Cook 1)
Implementation Both Cook 1 and Cook 2 have implemented the first four modifications listed in Table 1:
(a) J-tubes on SG feedring, (b) Early auxiliary feedwater flow into the SG (within about one minute after isolation of main feedwater supply),
(c) Short horizontal feedwater pipe upstream of the feedring, and (d) Feedwater flow limited by administrative control to 150 gpm per SG during feedring recovery (References 20,21).
Tests were performed in Cook 2 to demonstrate that no SGWH will occur (Reference 22).
Status The staff has approved the implementation at Cook 1 and 2 (References 20,22).
(7) Farley 1 (W plant w/3 SGs) 15
(8) Farley 2 (same as Farley 1)
Implementation Both Farley 1 and Farley 2 have implemented (a) J-tubes on SG feedrings, i
(b) early auxiliary feedwater flow into the SG, and (c) short hurizontal feedwater pipe leading to the feedring (Reference 23). Tests were performed in Farley 1 to demonstrate that no SGWH occurred.
Because Farley 2 has a similar plant design to Farley 1, no tests were required for Farley 2.
Status The staff has approved the present implementation at Farley 1 and 2 (Reference 23).
(9) Fort Calhoun (CE plant w/2 SGs)
Implementation Fort Calhoun has implemented (a) short horizontal feedwater pipe leading to SG feedring and, (b) early auxiliary feedwater flow into SG (within one minute) after a loss of main feedwater supply (Reference 24).
However, the SG feedring still has bottom-discharge holes instead of J-tubes. A separate injection nozzle (4-in. diameter and located above the feedring) is used to inject cold auxiliary feedwater into the SG when the main feedwater line is isolated; therefore, the cold auxiliary water will not enter a steam-voided feedring during SG refilling.
No SGWHs have occurred at Fort Calhoun, which has been in operation since 1974.
Status The staff has approved the present implementation at Fort Calhoun (Reference 24).
(10) Ginna (W plant w/2 SGs)
Implementation Ginna has implemented the first four modifications as listed in Table 1:
(a) J-tubes on the SG feedring, (b) early auxiliary feedwater flow into the SG (within a few minutes), (c) short horizontal feedwater pipe at SG inlet nozzle, and (d) a maximum feedwater rate of 150 gpm per SG during periods of SG feedring recovery (Reference 25).
Because Ginna has implemented all the four modifications, no SGWH tests were required.
Status The staff has approved the present implementation at Ginna (Reference 25).
(11) Haddam Neck (W plant w/4 SGs)
Implementation Haddam Neck has very short horizontal feedwater pipe (using an elbow) at the SG inlet (Reference 26). However, SGs do not have J-tubes for top discharge. Auxiliary feedwater initiation and control are performed manually (no automatic initiation of auxiliary feedwater flow), and the plant operator s administrative 1y required to change " slowly" the feedwater flow rate.
For example, during plant startup the main feedwater pump is started prior to shutdown of the auxiliary feed pump; and during the plant shutdown the auxiliary feed pump is started prior to shutdown of the main feed pump. Administrative procedures also require starting up a 16 i
i feed pump with the downstream discharge valve closed and that the valve be opened slowly. Nc SGWHs have occurred in Haddam Neck since 1975 (References 19,26).
Status The staff has accepted the present implementation at Haddam Neck; however, staff acceptance specified that the issue be reexamined if SGWHs occur in the future (Reference 26).
(12) Indian Point 2 (W plant w/4 SGs)
Introduction When the severe SGWH occurred in the No. 2 SG at Indian Point 2 on November 13, 1973 (Reference 5), the SG did not have any of the modifications listed in Table 1. [All SGs had an " unmodified" feedring using bottom holes for discharge (Figure 2.); the length of the horizontal feedwater pipe on the No. 2 SG was about 17 ft.]
Implementation Indian Point 2 has implemented the first three modifications and partially implemented the fourth (Table 1): (a) J-tubes on SG feedrings, (b) early feedwater flow into the SG (auxiliary feedwater flow will start automatically in less than a minute during plant transients), (c) short horizontal fedwater pipe immediately outside the SG, and (d) auxiliary feedwater flow is limited to 150 gpm per SG after any five-minute period during which feedwater flow has not been supplied to a SG (Reference 27).
Tests were performed to show that the fixes are effective in preventing SGWHs at the plant (Reference 27).
Status The staff has approved the present implementation at Indian Point 2 (Reference 27).
(13) Indian Point 3 (W plant w/4 SGs)
Implementation Indian Point 3 nas implemented:
(a) J-tubes on the SG feedrings, (b) early injection of feedwater flow into the SG (within a few minutes), and (c) short horizontal feedwr.ter pipe upstream of the feedring (Reference 28). Because the plant design of the SG and feedwater system at Indian Point 3 is similar to that at Indian Point 2, SGWH tests were not required.
Status The staff has approved the present implementation at Indian Point 3 (Reference 28).
(14) Kewaunee (W plant w/2 SGs)
Introduction Kewaunee in one of five Westinghouse 2-loop plants which have similar designs for the SG and feedwater system. The statements made here for Kewaunee are also applicable for the other four plants namely Point Beach Units 1 and 2, and Prairie Island Units 1 and 2.
17
Implementation Kewaunee, Point Beach 1 and 2, and Prairie Island I and 2 were among those for which no backfitting or modifications were required to prevent SGWH (Reference 29). These five plants have not had a single SGWH since tneir operation started in the early 1970's. However, all these plants will have the " unmodified" SG feedrings using bottom holes to discharge water (see Figure 2); the horizontal feedwater pipe at the SG inlet at Kawaunee and at Prairie Island 2 exceeds the 8-ft limit for a SG. Although the auxiliary feedwater flow starts automatically shortly after a reactor trip in which the feedring is uncovered, this rate of flow cannot maintain the feedring full of water at the maximum flow rate of the auxiliary feedwater, which is about 360 gpm per SG.
These plants have a unique piping layout which may be effective in preventing SGWHs (Reference 29).
In these five plants, the 3-in. diameter auxiliary feedwater pipe injects into the 16-in. main feedwater pipe at a location "very close" to the SG inlet nozzle (Figure 8).
The distance between the junction of the auxiliary and main feedwater pipes and the SG inlet is approximately 4 ft at Kewaunee and Prairie Island 1, 3 ft at Point Beach 1 and 2, and 7 ft at Prairie Island 2.
The value given is for the SG with the maximum distance. At the junction the auxiliary feedwater is injected at the horizontal centerline of the main feedwater pipe and normal to the main feedwater pipe. As the 3-in. jet from the auxiliary feedwater pipe splashes into the much larger 16-in. main feedwater pipe, condensation can occur if the pipe is voided. But because the travel distance into the SG feedring is so short, the sequential events that lead to SGWH (shown in Figure 4) are not likely to occur.
SGWHs have not occurred in over 60 SG years of operation (ten SGs operated at an average of six years).
Point Beach 1 and 2 have administrative controls which require the operator to limit feedwater flow to 100 gpm per SG during feedring recovery, and Prairie Island 1 and 2 have set the limit to less than 150 gpm per SG during feedring recovery. However, Kewaunee has no flow limit to recover the SG feedring.
Status The staff has accepted the present implementation at Kewaunee.
- However, the staff has stipulated that the matter will be reexamined if SGWHs occur l
in the future (Reference 29).
1 (15) Maine Yankee (CE w/3 SGs)
Implementation Maine Yankee has not had any SGWHs since its operation started in 1972, I
therefore, plant modifications to prevent IGWHs were not required (Refe ence 30).
The plant has very short norizontal feedwater pipe (about 3 ft long) upstream of the SG inlet; however, it still uses the unmodified SG feedring with bottom discharge (Reference 30).
Status The staff has accepted the present implementation at Maine Yankee.
However, the staff has stipulated that the matter will be reexamined if SGWHs occur in the future (Reference 30).
l 18 I
jf[ W]UlRR.Qg$j:AXTlQ W lfQ;?,jh'?.
M
.f f' $
i (16) McGuire 1 (W plant w/4 preheat SGs)
Background Information McGuire 1 is the first operating plant which uses Westinghouse preheat type steam generators. These SGs do not use a feedring but have two injection nonles for feedwater injection (References 3,4).
For this type of SG (including future CE economizer SGs), a NRC contractor report was published that evaluates the potential for SGWHs (Reference 31).
Figure 9 shows a preheat SG at McGuire 1 (Reference 31). Main feedwater is injected into the SG through the lower main feedwater nozzle which is 16-in. in diameter, and the auxiliary feedwater is injected into the SG through the upper auxiliary feedwater nozzle, which is 6-in. in diameter.
During plant startup, when power is below about 25% of full power, feedwater is fed into the SG through the upper nozzle; as power is increased beyond 25% of full power, the MAIN / AUX valve between the main and auxiliary feedwater lines (shown in Figure 10) is then closed and the main feedwater valve is opened so that the SG injection is through the main feedwater nozzle. During plant shutdown, as power is reduced below 25% of full power, the main feedwater valve is closed and the MAIN / AUX valve opened so that SG injection is switched from the main feedwater nozzle to the auxiliary feedwater nozzle.
SGWH Fixes Both the main and auxiliary feedwater lines have an elbow immediately outside the SG (Figure 10) to minimize the length of the horizontal pipe as recommended in Table 1.
Furthermore, the cold auxiliary feedwater is injected into the SG downcomer (i.e., the annular space next to the SG shell) so that only the main feedwater at elevated temperature is allowed to contact the tubes and flow baffles inside the SG.
A test was performed at McGuire 1 to show that damaging SGWHs did not occur.
[However, the test report has not been published as of publication date of this report (Reference 32).]
St tus The staff has approved the present implementation at McGuire 1 (Reference 33).
(17) Millstone 2 (CE plant w/2 SGs)
Implementation Millstone 2 has implemented:
(a) J-tubes on the SG feedring, (b) early injection of feedwater flow into the SG (within five minutes), and (c) short horizontal feedwater pipe at SG inlet (Reference 34).
Plant tests were performed to show that no SGWH occurred.
Status The staff has approved the present implementation at Millstone 2 (Reference 34).
(18) North Anna 1 (W plant w/3 SGs)
(19) North Anna 2 (same as Unit 1)
Implementation North Anna 1 and 2 have implemented (a) J-tubes on the SG feedring for top discharge, (b) early feedwater flow into the SG, and (c) short horizontal feedwater pipe at SG inlet (References 35-37).
19
3-in. dia auxiliary feedwater line Thermal sleeve Steam generator wall Check valve J
Tee connection
\\
- n. dia Feed ring 16-i
[
i l
feedwater line
/
LE&s=:K L
3/4-in. flow holes INEL 21084 Figure 8.
Steam generator feedring and feedwater system at Kewaunee, Prairie Island 1 and 2, and Point Beach 1 and 2 20
fi
- \\ :
nozzle
/
\\
. 7 f,
n e
e n g Steam separators W
h C [
[5 3
Tube bundle B
4 b
N Tube supports 4 4
':s n
d a
Preheater outlet Lower shell j 1 Feedwater nozzle 15-in. Schedule 80 s
C, (main feedwater) h t-
[
{
~
l Preheater section Y b Tube sheet cs Preheater outlet Primary coolant inlet Coolant channel INEL 21079 Figure 9.
Preheat steam generator at McGuire 1 21
Steam Topfeed generator nozzle
/
Auxiliary c
feedwater Main / auxiliary valve Check valve Purge
"' X 7
r Main Main FW valve feedwater V
Main feed INEL 21077 nozzle Figure 10.
Schematic of the McGuire 1 preheat steam generator with associated feedwater system 22
+.&
m sp-n
.c t
Tests were performed :t both Units 1 and 2 to show that SGWHs did not occur while the auxiliary feedwater was fed into the SG following the plant operating procedures to recover the feedring (References 35-37).
(Results for Unit 2 tests were not published.)
Status The staff has approved the present implementation at North Anna Units 1 and 2 (References 35-37).
(20) Palisades (CE plant w/2 SGs)
Implementation Palisades uses the bottom-discharge feedring (with no J-tubes) to inject main feedwater into the SG; the horizontal pipe of the main feedwater line leading to the SG is 28 ft long (Reference 38).
However, the plant has imposed a limited flowrate of 150 gpm per SG during feedring recovery.
The auxiliary feedwater line has been modified so that it does not inject into the main feedwater line (Reference 39). The auxiliary feedwater line has a short horitontal pipe leading to the SG inlet and uses an auxiliary feedring with top-discharge J-tubes for auxiliary feedwater injection (Reference 39).
Tests are scheduled to show that SGWH does not occur.
Normal plant operating procedures will be used during the test.
Status (as of November 1981)
Modification of the auxiliary feedwater line at Palisades has been completed. The staff's approval of the implementation at Palisades was contingent on successful SGWH tests (Reference 39). These tests were successfully conducted in December 1981.
(21) Point Beach 1 (W plant w/2 SGs)
(22) Point Beach 2 (same as Unit 1)
Implementation Point Beach 1 and 2 are similar to Kewaunee (Reference 40).
See Item 14 above for implementation.
Status The staff has accepted the present implementation at Point Beach 1 and 2.
However, this matter will be reexamined if any SGWHs occur at these plants in the future (Reference 40).
(23) Prairie Island 1 (W plant w/2 SGs)
(24) Prairie Island 2 (same as Unit 1)
Implementation Prairie Island 1 and 2 are similar in design to Kewaunee (Reference 41).
Please see Item 14 above for implementation.
_ Status The staff has accepted the present implementation at Prairie Island 1 and 2.
However, this matter will be reexamined if any SGWHs occur at these plants in the future (Reference 41).
=
23 5
m.
m
(25) Robinson 2 (W plant w/3 SGs)
Implementation Robinson 2 has short horizontal feedwater pipe (less than 3.5 ft) leading to the SG inlet (Reference 42).
The SGs still have an unmodified feedring with bottom holes (Figure 12); further, there is no flow limitation for recovering a SG feedring except in the case of a steam line break for which a limit of 400 gpm per SG is imposed.
Robinson 2 has not had any SGWHs in its ten years of plant operation.
Status The staff has accepted the present implementation at Robinson 2.
- However, this matter will be reexamined if any SGWHs occur at the plant in the future (Reference 42).
(26) Saint Lucie.1 (CE plant w/2 SGs)
Implementation St. Lucie 1 has implemented (a) J-tubes on the SG feedring for top discharge, (b) early feedwater injection into the SG, ano (c).short horizontal feedwater pipe leading to SG inlet (Reference 43).
Two plant tests were conducted to show that SGWHs do not occur as auxiliary feedwater is supplied to a drained SG feedring at 300 gpm and also at 600 gpm with a SG pressure of about 900 psig (Reference 44).
Status The staff has approved the implementation at St. Lucie 1 (References 43,44).
(27) Salem 1 (W plant w/4 SGs)
(28) Salem 2 (similar to Unit 1)
Implementation Salem 1 and 2 have implemented:
(a) J-tubes on SG feedring for top discharge, (b) early feedwater flow into the SG (in about one minute),
(c) short horizontal feedwater pipe leading to SG inlet (References 45,46).
In addition, Salem I has an administrative control on feedwater flowrate of about 150 gpm per SG to recover the feedring.
No tests were required at Salem 1 because it ha; incorporated the first four modifications recommended in Table 1.
A test was conducted at Salem 2 according to plant operating procedures to show that SGWH did not occur (Reference 47).
Status The staff has approved the existing implementation at Salem 1 and 2 (References 45-47).
(29) San Onofre 1 (W plant w/3 SGs)
Implementation San Onofre I has short horizontal feedwater pipe (less than 3 ft) leading to the SG inlet (Reference 48).
SGs still use the " unmodified" feedring
~
with bottom-discharge holes.
The auxiliary feedwater flow at the plant can only be started manually, this allows the plant operator to feed the SGs with heated main feedwater whenever possible.
(
24
Status The staff has accepted the present implementation at San Onofre 1.
However, this matter will be reexamined if any SGWHs occur at the plant in the future (Reference 48).
(30) Sequoyah 1 (W plcnt w/4 SGs)
Implementation Sequoyah I has implemented: (a) J-tubes on SG feedring for top discharge, (b) early feedwater flow into the SG, and (c) short horizontal feedwater pipe leading to the SG inlet (References 49-51).
Plant tests were performed to show that no SGWHs occurred (Reference 50).
Status The staff has approved the present implementation at Set uoyah 1 (References 49-51).
(31) Surry 1 (W plant w/3 SGs)
(32) Surry 2 (same as Unit 1)
Implementation Surry 1 and 2 have implemented:
(a) J-tubes on SG feedring, (b) early feedwater flow into the SG (in about one minute), and (c) short feedwater pipe leading to the inlet (Reference 52).
Surry 1 had a damaging SGWH before the modifications discussed above were implemented; (Reference 52) the 14-in feedwater line for SG A was displaced about 7 to 10 in., and all seven shock suppressors on the line failed. No SGWHs have occurred since modifications were made.
Status The staff has approved the implementation of SGWH modifications at both Surry 1 and 2 (Reference 52).
(33) Trojan (W plant w/4 SGs)
Implementation Trojan has implemented:
(a) J-tubes in SG feedring, (b) early feedwater flow into the SG (in about 1 to 2 minutes), and (c) short horizontal feedwater pipe leading to SG inlet (Reference 53).
Plant tests were performed with auxiliary feedwater supplied at flowrates ranging from 120 gpm to 440 gpm (maximum auxiliary feedwater flowrate) into a drained or partially drained SG feedring (with J-tubes and short horizontal feedwater pipe upstream).
No SGWHs were ovserved in the tests in which the SG's steam pressure was varied from 400 to 1100 psig and the feedring draining time varied from 1 to 120 minutes (References 53,54).
Status The staff has approved implementation of SGWH modifications at Trojan (References 53,54).
25
(34) Turkey Point 3 (W plant w/3 SGs)
(35) Turkey Point 4 (same.as Unit 1)
Implementation Turkey Point Units 3 and'4 have short horizontal feedwater pipe (less than 8 ft) leading to SG inlet (Reference 55).
SGs still have unmodified feedrings with bottom-discharge holes. No SGWHs have occurred since 1974 when the horizontal feedwater pipe leading to the SG inlet was shortened to less than 8 ft for all SGs.
(Prior to the pipe modifications, three water hammer events had occurred which caused deformation of some feedwater line supports and one elbow.)
Status The staff has accepted the present implementation at Turkey Point 3 and 4.
However, this matter will be reexamined if any SGWHs occur in the future (Reference 55).
(36) Yankee-Rowe (W plant w/4 SGs)
Implementation Yankee-Rowe has implemented short horizontal feedwater pipe at each SG inlet (Reference 56).
In addition, a steam line was installed so that steam from plant auxiliary boilers can be used to preheat main feedwater during startup, shutdown, and other low power operations when the normal steam supply from SGs is insuf ficient or unavailable to preheat feedwater.
The purpose is to reduce the magnitude and likelihood of any SGWHs.
Since the implementation of these modifications in 1966, Yankee-Rowe has not had any SWGHs.
SGs still use unmodified feedring with bottom-discharge holes.
Status The staff has accepted the implementation at Yankee-Rowe.
However, this matter will be reexamined if any SGWHs occur in the future (Reference 56).
(37) Zion 1 (W plant w/4 SGs)
(38) Zion 2 (same as Unit 1)
Implementation Zion 1 and 2 have implemented:
(a) J-tubes on the feedring of seven out of eight SGs (as of November 1981, one SG in Unit 1 does not have J-tubes),
(b) early feedwater flow into the SG, (c) short horizontal feedwater pipe leading to each SG, and (d) a flow limit at 150 gpm per SG at reinitiation of feedwater flow (Reference 57).
Status Zion 1 is committed to have J-tubes installed on the last SG feedring which still has bottom-discharge holes; the work was completed in February 1982.
The staff has approved the implementation at Zion 1 and 2 (Reference 57).
4.
CONCLUSIONS The NRC staff has evaluated and approved the SGWH modifications incorporated in all operating PWR plants.
Primary emphasis has been on W and CE SG designs.
The recommended design features set forth in NRC's Standard Review Plant (SRP), Section 10.4.7, Branch Technical Position 26 t
(BTP) ASB 10-2 appear to be effective in preventing (or minimizing) damaging SGWH's.
These features (for W and CE SG's having top feed-ring) are a combination of J-tubes on the feedring, short runs of horizontal feedwater piping (less than 8 feet), and limits on auxiliary feedwater injection rates. ASB 10-2 also calls for a preoperational SG test to verify that unacceptable feedwater hammer will not occur using the plant operating procedures for normal and emergency restoration of SG water level following loss of normal feedwater and possible draining of the feed-ring.
Damaging steam generator or feedwater system water hammers have not occurred at any operating PWR which has implemented the corrective measures discussed in this report.
A damaging water hammer event did occur at the San Onofre 2 PWR plant during pre-operational testing prior to power operation.
This event was due to overly stringent test conditions and does not change staff conclusions on the effectiveness of design provisions to eliminate steam generator water hammers. At San Onofre 2, the steam generator feedring was allowed to completely drain and fill with saturated steam.
The test was then initiated by ramping the feedwater from 0 to 1200 gpm in about 30 sec.
The resultant rapid steam condensation resulted in collapsing the feedring. The damage was not detected until later when a routine inspection of the steam generator was made. Although the feedring collapsed, function of the feedring was not impaired.
Until just recently (as noted in Section 2.0), the staff was not aware of any damaging SGWH phenomenon in B&W OTSG's. The damage to auxiliary feedwater rings at the Davis Besse, Oconee No. 3 and Rancho Seco plants is currently being evaluated by B&W, the B&W owners group and NRC staff.
It should be noted that the damage incurred did not impair plant normal operation and that repairs are underway.
Initial discussions (Refe-ence 58) resulted in recommendtions to return to the externally mounted auxiliary feedwater header design which has not experienced water hammer. More recently, Davis-Besse (Reference 59) has committed to returning to the external auxiliary feed ring design.
The NRC staff will continue to revewi and evaluate B&W OTSG modifications.
Based on studies, safety evaluations, and plant tests for steam generators employing top feedrings, we have concluded that the measures presented herein to prevent or mitigate the consequences of SGWH constitutes an acceptable resolution to the safety issues pertinant to SGWH.
With respect to preheat (or bottom feed) SG's (such as W D2/D3 and D4/05 models), the water hammer potential for such designs is being evaluated separately and will be included in the staff's technical finds regarding USI A-1, Water Hammer.
The basic preheat SG design concept lends itself to less chance for water hammer occurance.
27
REFERENCES 1.
U.S. Nuclear Regulatory Commission, " Water Hammer in Nuclear Power Plants," USNRC Report NUREG-0582, July 1979.
2.
Block, J. A., et al., Creare, Inc., "An Evaluation of PWR Steam
-Generator Water Hammer," USNRC Report NUREG-0291, June 1977.
3.
Saha, P., et al., Brookhaven National Laboratory, "An Evaluation of Condensation-Induced Water Hammer in Preheat Steam Generators," USNRC Report NUREG/CR-1606, September 1980.
4.
Green, S.
J., and Welty, C. S. Jr., " Workshop Proceedings: Steam Generator Water Hammer," EPRI WS-78-132, (June,1979).
5.
Cahill, W.
J., Feedwater Line Incident Report-Indian Point Unit No. 2, Consolidated Edison Co., AEC Docket No. 50-247, January 14, 1974.
6.
Roidt, R.
M., " Steam-Water Slugging in Steam Generator Feedwater Lines," Westinghouse Research Memo 74-7E9-F12NE-MI (January 2, 1975).
7.
Bennett, W. E., " Water Hammer in Steam Generator Feedwater Lines,"
Westinghouse Technical Bulletin, NSD-TB-75-7, Rev. 1 (March 9, 1977).
8.
Lissenden, C. J., Jr., " Water Hammer in Steam Generator Feedwater lines," Westinghouse Technical Bulletin, NSD-TB-79-8 (November 26, 1979).
9.
Letter from A. Schwencer, NRC, to D. C. Switzer, Connecticut Yankee Atomic Power Company, Docket No. 50-213, dated September 2, 1977.
(Similar letters were also sent to other PWR licensees.)
- 10. Wylie, E. B.,
and Streeter, V.
L., Fluid Transients, McGraw-Hill (1978).
11.
Chaudhry, M. H., Applied Hydraulic Transients, Van Nostrand Reinhold Co., New York (1979).
12.
U.S. Nuclear Commision, " Investigation and Evaluation of Cracking Incidents in Piping in Pressurized-Water Reactors, USNRC Report NUREG-0691, September 1980.
13.
T. M. Novak ;NRC) to R. D. Crouse (Todedo Edison Company) letter dated 6/23/82, " Auxiliary Feedwater Header Repair - Request for Additional Information."
14.
U.S. Nuclear Regulatory Commission, " Safety Evaluation Report related to operation of Arkansas Nuclear One, Unit 2,"
USNRC Report NUREG-0308, Supplement No. 2, September 1978.
28
15.
Letter from D. C. Trimble, Arkansas Power & Light Company, to K. V. Seyfrit, NRC, subject: Arkansas Nuclear One--Unit 2, Docket No. 50-368, License No. NPF-6, Startup Report (File:
2-0520.2), dated September 13, 1979.
16.
Letter from A. Schwencer, NRC, to C. N. Dunn, Duquesne Light Company,
Subject:
Amendment No. 24 to Facility Operating License No. OPR-66 for the Beaver Valley Power Station, Unit No. 1, dated January 25, 1980.
17.
Letter from A. Schwencer, NRC, to C. N. Dunn, Duquesne Light Company,
Subject:
Safety Evaluation of Steam Generator Water Hammer at Calvert Cliffs Nuclear Power Plant, Units 1 and 2, dated March 10, 1980.
18.
Letter from R. Reid, NRC, to A. E. Lundvall, Jr., Baltimore Gas &
Electric Company,
Subject:
Safety Evaluation of Steam Generator Water Hammer at Calvert Cliffs Nuclear Power Plant, Units 1 and 2, dated March 10, 1980.
19.
Licensee Event Reports, Available at the Nuclear Safety Information Center (NSIC), Oak Ridge National Laboratory.
20.
Letter from A. Schwencer, NRC, to J. Tillinghast, Indiana and Michigan Electric Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Donald C. Cook Nuclear Plant Unit No. 1, dated March 14, 1979.
21.
U.S. Nuclear Regulatory Commission, " Safety Evaluation Report related to operation of Cook Unit 2, Supplement No. 7, December 1977.
22.
Letter from G. P. Maloney, Indiana & Michigan Power Company, to E. G. Case, NRC, Docket No. 50-315, dated June 7, 1978.
23.
U.S. Nuclear Regulatory Commission, " Safety Evaluation Report for J. M. Farley Nuclear Plant Units 1 and 2, Docket Nos. 50-348 and 50-364, NUREG 75/034, Supplements 1-3.
May 1975.
24.
Letter from R. W. Reid, NRC, to W. C. Jones, Omaha Public Power District,
Subject:
Safety Evaluation Report Regarding the Potential for Water Hammer in Feedwater Piping at Fort Calhoun Station Unit No. 1, Docket No. 50-285, dated December 20, 1979.
25.
Letter from D. L. Ziemann, NRC, to L. D. White, Rochester Gas and Electric Corporation,
Subject:
Safety Evaluation Report for Steam Generator Water-Hammer at Ginna, Docket No. 50-244, dated December 20, 1979.
26.
Letter from D. L. Ziemann, NRC, to W. G. Counsil, Connecticut Yankee Atomic Power Company,
Subject:
Steam Generator Water Hammer Generic Istue, Docket No. 50-213, dated February 26, 1980.
29
I 27.
Letter from A. Schwencer, NRC, to W. J. Cahill, Jr., Consolidated Edison Company of New York, Inc.,
Subject:
Safety Evaluation Report Regarding Water Hammer in Feedwater Piping at Indian Point Nuclear Generating Unit No. 2, Docket No. 50-247, dated July 6, 1979.
- 28. Consolidated Edison Company of New York, " Final Safety Analysis Report for Indian Point Nuclear Generating Unit No. 3, Docket No. 50-286,"
l P.Q 10.24, Supplement 27, July 1974.
29.
Letter from A. Schwencer, NRC, to E. R. Mathews, Wisconsin Public Service Corporation,
Subject:
Safety Fialuation Report for Steam Generator Water Hammer at Kewaunee, dated September 13, 1979.
30.
Letter from R. W. Reid, NRC, to R. H. Groce, Maine Yankee Atomic Power Company,
Subject:
Safety Evaluation of Steam Generator Water Hammer at Maine Yankee Atomic Power Station, dated March 12, 1980.
31.
Duke Power Company, " Final Safety Analysis Report for McGuire Nuclear Station, Units 1 and 2," Vol. 4, May 30, 1974.
32.
Duke Power Company, McGuire Nuclear Station Unit 1 Docket 50-369, License NPF-9, Startup Report, dated February 1982.
33.
U.S. Nuclear Regulatory Commission, " Safety Evaluation Report related to operation of McGuire Nuclear Station, Units 1 and 2,"
USNRC Report NUREG-0422, Supplement No. 2, March 1979.
34.
Letter from N. W. Reid, NRC, to W. G. Counsil, Northeast Nuclear Energy Company,
Subject:
Safety Evalution of the Steam Generator Water Hammer Review for Millstone Nuclear Power Station, Unit No. 2, dated May 7, 1980.
35.
Letter from B. J. Youngblood, NRC, to J. H. Ferguson, Virginia Electric & Power Company,
Subject:
Issuance of Amendment No. 2 to License NPF-7, North Anna Power Station Unit No. 2, dated August 18, 1980.
36.
Letter from 0. D. Parr, NRC, to W. L. Proffitt, Virginia Electric &
Po ar Company,
Subject:
Issuance of Amendment No. 4 to Facility Overating License NPF-4, North Anna Power Station Unit No. 1, dated May 8, 1978.
37.
U.S. Nuclear Regulatory Commission, " Supplement No. 10 to the North Anna Power Station Unit 2. Safety Evaluation Rep" USNRC Report NUREG-0053, Supplement No.10, April 10,1980.
38.
Letter from D. L. Ziemann, NRC, to D. P. Hoffman, Consumer Power Company,
Subject:
Amendment No. 56 to Provisional Operating License No. DPR-20 for the Palisades Plant, dated April 30, 1980.
39.
Letter from D. P. Hoffman, Consumer Power Company, to D. M. Crutchfield, NRC,
Subject:
Docket 50-255, License DPR-20, Palisades Plant-Auxiliary Feedwater Modifications, dated December 1, 1980.
30
40.
Letter from A. Schwencer, NRC, to S. Burtstein, Wisconsin Electric Power Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Kewaunee, Point Beach Units 1 and 2, and Prairie Island Units 1 and 2, dated September 13, 1979.
41.
Letter from A. Schwencer, NRC, to L.0. Mayer, Northern States Power Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Prairie Island Units 1 and 2, dated September 13, 1979.
42.
Letter from S. A. 'Varga, NRC, to J. A. Jones, Carolina Power & Light Company, Docket No. 50-261, dated June 2, 1980.
43.
Letter from R. W. Reid, NRC, to R. E. Uhri'g, Florida Power & Light Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at St. Lucie Plant Unit 1, dated February 7, 1980.
44.
Letter from R. E. Uhring, Florida Power & Light Company, to D. L. Ziemann, NRC,
Subject:
St. Lucie Unit No. 1, Docket No. 50-335, License Condition C, dated March 2,1977 (ID L-77-70).
45.
Letter from A. Schwencer, NRC, to F. P. Librizzi,
Subject:
Safety Evaluation Regarding Water Hammer in Feedwater Piping at Salem huclear Generating Station, Unit No. 1, dated November 3, 1979.
46.
U.S. Nuclear Regulatory Commission, " Supplement No. 3 to the Safety Evaluation Report for Salem Nuclear Generating Station, Unit 2, Docket No. 50-311, USNRC Report NUREG-0517, December 29, 1978.
47.
U.S. Nuclear Regulatory C'mmission, Region I Inspection Report No. 50-311/81-22, Docket No 50-311, Facility Name:
Salem Nuclear Generating Station, Unit 2, C:tober 5, 1981.
48.
Letter from D. L. Ziemann, NRC, to R. Dietch, Southern California Edison Company,
Subject:
Steam Generator Water Hammer Issue, dated April 22, 1980.
49.
Letter from L. M. Mills, Tennessee Valley Authority, to L. S. Rubenstein, NRC,
Subject:
Water Hammer Test on Addition of Auxiliary Feedwater to Unit 1 Steam Generator at Sequoyah Nuclear Plant, Docket No. 50 327, dated April 15, 1980.
50.
Letter from A. Schwencer, NRC, to H. G. Parris, TVA,
Subject:
Sequoyah Water Hammer Tests, dated May 13, 1980.
51.
U.S. Nucler Regulatory Commission, " Safety Evaluation Report for Sequoyah Nuclear Plant, Units 1 and 2, Docket Nos. 50-237 and 50-238,"
USNRC Report NUREG-0011, March 1979.
52.
Letter from A. Schwencer, NRC, to W. L. Proffit, Virginia Electric &
Power Company, Docket Nos. 50-280 and 50-281, dated June 7, 1978.
(
53.
Letter from A. Schwencer, NRC, to C. Goodwin, Jr., Portland General Electric Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Trojan Nuclear Plan, Docket No. 50-344, dated October 18, 1979.
31 l
l
- 54. Letter from J. L. Williams, Portland General Electric Company, to l
W. R. Butler, NRC,
Subject:
Report on Testing of Auxiliary Feedwater Addition, Following J-tube Modifications to the Steam Generators of the Trojan Nuclear Plant, Docket No. 50-344, dated October 21, 1975.
55.
Letter from A. Schwencer, NRC, to R. E. Uhrig, Florida Power & Light Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Turkey Point Plant Unit Nos. 3 and 4, dated February 4, 1980.
56.
Letter from D. L. Ziemann, NRC, to J. A. Kay, Yankee Atomic Electric Company,
Subject:
Steam Generator Water Hammer Generic Issue, dated February 5, 1980.
57.
Letter from A. Schwencer, NRC, to D. L. Peoples, Commonwealth Edison Company,
Subject:
Safety Evaluation Report for Steam Generator Water Hammer at Zion Generating Station, Units 1 and 2, dated December
.2, 1979.
- 58. 6/24/82 Meeting at NRC in Bethesda, MD, B&W Owners Group discussion of generic repairs and design modifications related to damaged auxiliary feedwater header inside of steam generators.
%r l
l 32
U.S. NUCLEAR REGULATORY COMMISSION g,
BIBLIOGRAPHIC DATA SHEET NUREG-0918 h TITLE AN D SUBTITLE (Add Voeume No., d opreneel
- 2. (Leave b/mAJ Prsvention and Mitigation of Steam Generator Water Hammer Ever.ts in PWR Plants
- 3. RECIPIENT'S ACCESS!ON No.
- 5. DATE REPORT COMPLETED
- 7. AUTHOR (S)
Newton R. Anderson, James T. Han Nov her Q?
- 9. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (include I,p com/
DATE REPORT ISSUED U. S. Nuclear Regulatory Commission Nov ber
'5982 Office of Nuclear Reactor Regulation y 7t,,,,,,,,
Division of Safety Technology t!ashington, D. C.
20555
- a. It, u, ;
- 12. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS (/nclude I<a Codri
- 10. PROJECT /T ASK/ WORK UNIT NO.
Same as 9.
- 11. CONTRACT NO.
- 13. TYPE OF REPORT PE RIOD COVE RE D (loctusive damsJ Technical Report
- 14. (teeve alm 41
- 15. SUPPLEMENTARY NOTES
- 16. ABSTR ACT G00 words or lessJ Water hamer in nuclear power plants is an unresolved safety issue under study at the NRC (USI A-1).
One of the identified safety concerns is steam generator water hamer (SGWH) in pressurized-water reactor (PWR) plants. This report presents a summary of:
(1) the causes of SGWH, (2) various fixes employed to prevent or mitigate SGWH, and (3) the nature and status of modifications that have been made at each operating PWR plant. The NRC staff considers that the issue of SGWH in top feedring designs has been technically resolved. This report does not address technical findings relevant to water hammer in preheat type steam generators.
1 F. KEY WORDS AND DOCUMENT ANALYSIS 17a DESCR:PTORS l
Unresolved Safety Issue A-1 Steam Generator Water Hammer a
17tt IDEN TiflE RS OPE N E NDE D TE RVS l
l 19 SECURITY CLASS (TOs reports 21 NO OF P AGE S 18 AV AILABILITY ST ATEVE NT Unclassified Unlimited 2o SECuaiTY Ct4Ss <Tms o,,,
22 ea cE Unc1assified s
i N 8*C F ome 339 5 7 7 7 5
UNITED ETATES rosfa'tNs ffas 5'io
^
NUCLEA] REZULATORY COMMISSION WASHINGTON, D.C. 20565 j5*"j g
_ Pt awit 4 111 OFFICIAL BUSINESS Pf fe ALTY FOR PAIVATE USE, $300 O
O O
O e
i 120555078877 1 ANA!9X121314 US NRC ADM DIV CF TIDC POLICY & PilBL IC AT IONS MGT BR o
PDR NUREG COPY LA 212 WASHINriTON OC 20555 l
1 9
1 l
l A
I
- - - - - - -