ML20064N274
| ML20064N274 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/08/1983 |
| From: | Boman B, Tally C BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML20064N269 | List: |
| References | |
| 86-1140819, 86-1140819-00, NUDOCS 8302160171 | |
| Download: ML20064N274 (18) | |
Text
W ag Wty n
g%$fM;sm@g$g,.$e.g$ep@
w.w.&pw.%.m%.;mq/gw s 4
. :... e.
o @x pe d.
%g$.s1 f
9 s
g amps ;Wi,. ; b
- egf;.gc.;4
- .44. g,gN.3,.
t 3,.,,.
. e.
%~u~f%@g.e.p %%wy,,.:;7n,p,
,,,s < ;.
.e 9
Q O
f',I 9
i i
1 ex.,.y., p:.y w'v4 Cl@ M@$pyY;j,n16
/m $
g
- 1..y s.
r n.
,,;' f(p y
(,
m I;a1Emm u :,5 s
's j-
., ::u.7lg d
~
e
),
hp q.35'bk '- T I
p(
.n s
p s.
n h
.c:wS w$w $ : pA:
eM) a
.~
8 a
l} x4 m-
+,
i:
.gp.
E I
u m#e,:m s
sv a q we s A4 gS
.e ;i A
q.h
~
3
. /$ $
?k U~
N1 k 'Ikhf!
b['$R Y
, :i 5 Q$V4$,
W
@nfq.% ;' %
gh W
1c wa h,t
,%gp,. N,y t
r
,a w,.,
rf, f,,4)
,5;l.
I:,,'M e-k 4.kdyhd;,fp.!gl.[p f
x w
pu
.. n.
/ehh 3IbhfkD
$0_
jf$$fh'bI / $
.~.,k N
fh 3
- 3]
M ME!!${b'$hkh$kilhbkdhMiffdfilN I ? k[
/
yh hghg$!l9#EnlkgfY sk gin rin 4S:ervic se ^
J.
bh h h h-m
,$b!
k lk Yi. apg g L 4 E Lg
..u,me =en waame nowa&ps y
e
- r i
w s:at m w n u w 4,w w m m.
. u m z iu,
..w
.~ m.,.
>.a.,
.+... u ;..,
a g?
I L~?Sii*I. xua...?.<::M:h*WkML'lll@$N>p9$y 9 f6' iqs)f
'; R s$k
~
R882in8aP 4888sla d# d W Bab60ck ilcos.
Og !
n,': /.. A?.5 J=%%).'G;mR$:g( y;jy[r O,kjg l6 yggs' ngsNi-if/n F
PDR w.
G
- W:h0d.%6:nL~%CuMW;ehhGr<b?MMMW GK :
.=.
[-
t i
.i i.
. f A
l s
-l.
1 i
r.
4 REACTOR VESSEL HEAD C00LDOWN DURING NATURAL CIRCULATION C00LDOWN TRANSIENTS l
I.
I Prepared for-
}
ANO-1
-1 I
Prepared by: d j.T< Wem
- 8. L. Boman 1
Reviewed by:
kid b
.;L/8l83
-C.Wyally
\\J i
BABC0CK & WILC0X UTILITY POWER GENERATION DIVISION P.O. B0X 1260 LYNCHBURG, VA 24505 86-1140819-00
T A
l F
i i
i
'i 2
r i
CONTENTS 4
-f PAGE-l
'I
'l.
INTRODUCTION.
i
~ 1
- 1.1 Scope of Work 1.2 Background...........
1 1
1.3 Summary I
r j.
1 l:
2.
ANALYSIS...........
1 2.1 Analytical Methods 1
i l
2.2 Analytical Results-
.5
[ -l i
3.
CONCLUSIONS 8
4.
REFERENCES..............
8
~
l L
- +e7--e a
s.-Wi-wek'weda?+w+ws-
- w
--u*-e--
'rbwe er,-et-en-re-w+ wm4-4=>wws - +, ee k er eetow.#+.. - = -ee n.ee g -w -re+ pe e gw - r wre,m rw-et---T"+wttr'=me r 7= r a'=
my~
'-**-emf-M e T 'r'W' F*'
a
+*
t I
1.0 INTRODUCTION
1.1 Scoce of Work This document provides the minimum time required to reach the' decay heat removal system cut-in point during a natural circulation cool--
down without flashing in the reactor vessel head. The decay heat removal system (DHR) cut-in point was assumed to be 291 osig and 280 F (Ref. 1).
i
1.2 Background
During natural circulation, the fluid in the upper reactor vessel j
head (above the plenum cover) is essentially stagnant and does not i
thermally communicate with the rest of the reactor coolant system.
j The cooldown rate of the head metal and fluid is very slow and'is controlled by heat transfer to the reactor building and to the small amount of coolant that flows over the plenum cover.
- Hence, if the RCS is depressurized and cooled rapidly, flashing of the head fluid and uneven thennal stresses may result.
Therefore, I
the head cooldown controls the amount of time required to reach the DHR cut-in point.
1.3 Summarv l
Figure 5 shows the maximum RV head fluid temoerature as a function of time,and Figure 6 plots the corresponding saturation pressure.
l In order to start the decay heat removal system at 291 psig, the head fluid temperature must be below 419.1 F (Tsat at 291 psig).
This also assumes the rest of the RCS is at or below 280 F.
- Thus, I
it takes about 135 hours0.00156 days <br />0.0375 hours <br />2.232143e-4 weeks <br />5.13675e-5 months <br /> to cocl the head to this temperature.
i 2.0 ANALYSIS 2.1 Analvtical fiethods The cooldown rate of the RV upper head under natural circulation conditions was detennined using a finite difference heat transfer 86-1140819-00,..
'1m+
model.
The model consisted of nodes' representing the co'olant, plenum cover, vessel wall, insulation, and the air trapped between the insulation and metal (see Figure 1).
Heat transfer mechanisms considered were conduction, convection, and radiation.
Figure.2 shows the heat transfer paths and mechanisms.
The flow through the upper head region was derived from nrevious j
hydraulics calculations, and Figure 3 shows these flow paths.
The RV head temperature was assumed to be 604 F.
This is approximately the hot leg-temperature for 100 percent power. The head fluid i
temperature was initially set to 585 F (assuming the pumps continue to run for a short period after the reactor trips). However, as I
shown in the results, the fluid temperature quickly increases to
- tne metal temperature.
The RCS loops, including the hot leg, were 1
i 1
assumed to cool down at 100 F/hr from 585 F to 310 F.
Other important assumptions used in this analysis are listed below:
1.
Convective heat losses from the control rod drive (CRD) were effectively modeled as conductive heat losses.
Instead of a Q = hA AT equation, a Q = -kA dT/dx equation was used with the CRD temperature set at 120 F three -fest~
t above the RV head.
l 2.
The flow rate for natural circulation was 3 percent of full flow.
I 3.
Where conductive heat transfer exists between adjacent 1
nodes of different materials with different thermal f
conductivities, the smaller or limiting value was used.
4.
Radiative heat transfer was used for the reflective insulation heat losses to the containment atmosohere.
An emissivity value of 1.0 was used.
5.
The ambient (reacter building) temperature was assumed constant at 120 F.
86-1140819-00 -..
1 Typical RV head mirror insulation transference values were used at insulation / air interfaces.. The upper portien of the RV and internals was divided into a multinode representation -
as shown in Figure 1.
A mass transfer model was superimposed on this multinode mocel as indicated by the solid and dotted flow paths.
A solid line from one node -to another signifies mixing. A dotted line signifies no mixing,'such as the case for coolant rising inside the column weldments from the upper plenum to the RV upper head.
Figure 1 shows that mixing is assumed only in the first layer of nodes in the RV upper head.
This assumption is critical to the results of the analyses-j and, as discussed above, is conservative, t
j As shown on Figure 1, each node represents a three-dimensional ring in the analysis.
Finite difference ecuations were then written for each node volume. This set of finite difference equations was then solved simultaneously for each discrete time step.
A 20-second time step was chosen based on conven-i tional stability criteria.
Future node temperatures were calculated based on the current temperature plus the heat anc
)
mass transfer over the time step.
The general form of the finite difference equations is:
future present * ^ (Ok*Oh m
r T
O+O) pxC xV p
where:
i at = time step, Q = conduction heat transfer = -kA x aT/aX, k
Q = convection heat transfer = hA ST, h
Q = heat transferred with mass = o x V x C x (T
- present)/Al' m
p new Q = radiation heat transfer = B x A x (Tpresent)
- (Tadj) '
r a = density of node material, C = specific heat of node material, p
V = volume of node, l
86-1140819-00 I
k = thermal conductivity of node material AT = temperature difference across interface, AT/aX = temperature gradient across node, h = convection coefficient, B = Stefan-Boltzman constant, Tadj = temperature of adjacent node (both T and T I" O equation are absolute),
present adj r
T
= new temperature of' node due to mass transfer, new in)exp((-M/pxv1)at)+T
=(T
-T present in'
,f m = mass ficw rate into node, T
= weignted mass average incoming temperature, in i
T resent = present node temperature I
Conductive heat transfer was considered at the boundaries of similar media (air-air, steel-steel, water-water, insulation-insulation).
Convective heat losses were considered at other boundaries, (air-steel, air-insulation, steel-water).
Finally,
- radiative heat transfer was considered for insulation-ambient air conditions.
l The CRD convective heat losses (to the service structure region) i
- I were modeled as conductive heat losses. Ambient conditions of 120 F were assumed:
l Q.= -kA(dT/dx) k l
l where:
l Q = heat transferred by conduction, k
k.= thermal conductivity of carbon steel, A = horizontal-cross sectional area, l
dT/dx = linear temperature gradient along CRD length 86-1140319-00
[
.The additional Q term above was added to the finite difference l
equat! ions for nodes in the RV head (dome) that contain CRD nozzles.
j The leadscrews and column weldments were modeled similarly. The i
masses and volumes 'of these components were distributed among the applicable node rings to take into account the cooling by these comoonents.
All sources of heat--both into and out of each nede--were summed and then divided by the mass and C of the node. This term was p
added to the present temperature to obtain the new node temperature.
The process was carried out for all nodes before continuing on to the next time step.
2.1 Analytical Results The results of the reactor vessel head co31down analysis are shown in Figure 4.
The temperatures of the hottest RV head coolant node and the hot leg coolant are shown as a function of time.
The maxi-mum coolant cooldown rate in the RV head is 1.70 F/hr while the f
primary coolant cooldown rate is 100 F/hr (Ref. 2). The analysis assumed the following:
0 Initial coolant temperature of 585 F 8 Initial sheli temperature of 604 F 0 Ambient temperature of 120 F 0 Natural circulation flow of about 3 percent _ normal flow -
i.
'4 l
The analysis assumed that flow up through the plenum cover affected t
only the first layer of nodes above the cover.
These nodes cooldown j
at the same rate as the circulating coolant (100 F/hr).
Hence, if flow were to extend farther above the plenum cover, the cooldown rate would increase.
However, there is no data or evidence to suggest that additional j
penetration would occur during natural circulation.
Flow velocities a
1 l
86-1140819-00 ;
2
t into-the upper head region from below-the plenum cover. ar4 expected, _
9' to be less than two' feet per second and could not cause'aopreclable.
penetration up -into the dome region.
It should.be pointed out'that.~
the dome region is a large volume, approximately 500 ft.3, with a plenum cover to dome top distar.ce of about Si feet.
Even if twice the penetration had been assumed, the'results would not'-
change dramatically.
}'
The model's results were compared with simple independent hand.
calculations which determined the initial cooldown. rate with the.
head at 585 F. ' The agreement was good, confirming the model's general accuracy.
4
[
These results cannot be directly supported nor, refuted by field O
data.
No B&W plant has ever performed a natural circulation cooldown.
In addition, the necessary instrumentation to measure the RV head-cooldown rate is not presently install.ed at any site.
As shown in Figure 4, the model only simulated about eight hours
~
of cooldown.
Since the head fluid temperature is about 586'F at eight hours, the results need to.be~ extrapolated.to reach the-decay heat-removal system cut-in point.
Since the cooldown rate is dependent upon the head fluid / ambient temperature differential',
the cooldown rate will decrease as this differential decreases.
The long-term cooldown is expected.to be_ governed by the following~
equation:
TRVH (t) - TA
-t/r (Equation 1)
TRVH (t=0 - TA where:
Tgyg (t) = temperature of the RV head fluid TRVH (t=0) = approximately 600 F Tg = ambient temperature, 120 F
-1
- = time constant, hr 86-1140319-00 4
The time constant was evaluated using data from the eight hours of simulation.
t From Ref. 2, the peak RV head fluid temperature is 599.2 F at
.17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />, and the fluid temperature is 586.2 F, 7.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> after the peak.
(
Therefore:
-t
-7.7 s 280 hr-1
{
TRVH(t) - TA (586.2 - 120)
TRVH(t=0)-T A
.l Figure 5 has been constructed to extend the head fluid. temperature vs. time plot using Equation 1.
Note that it requires about 135 hours0.00156 days <br />0.0375 hours <br />2.232143e-4 weeks <br />5.13675e-5 months <br /> to cool down to 419.1 F (T at 291 psi 9).
sat Figure 6 plots the saturation pressure corresponding to the head temperature as a function of time.
This gives the minimum RCS pressure vs. time to avoid flashing durina a natural circulation f
cooldown.
Figure 7 shows head fluid temperature vs. saturation pressure superimposed with the NDT limits (Ref. 3). A subcooling margin line for the head saturation line has been developed by adding 25 psi and 10 F for instrument errors.
Information has also been added to Figure 7 regarding the cooldown of the rest of the RCS. Assus..ng the hot leg conditions at full power are approximately 604*F and 2170 psia, the RCS could be depressurized i
I and cooled to 350 F and 1500 psia in less than three hours (100 F/hr) without flashing in the head or violating NDT limits.
Then as the I,
system is slowly depressurized and the head fluid slowly cools over the next 130 plus hours, the RCS should be cooled to at least 280 F.
In summary, to prevent flashing in the head, the head fluid conditions
- rust lie above and to the left of the head subcooling line.
86-1140819-00 '
m.,.
3 l
- As previously mentioned, it is possible to cool the rest o'f the a
RCS down at 100 F/hr from 604*F to 350 F if the head subcooling line'and NDT limits are not violated.
However, the resulting thermal stresses.from having the-head at 600*F and the rest of the RCS at'350 F may be significant and have not been. evaluated.
l I
3.0 CONCLUSION
S Important conclusions of this document.are:
0 In order to prevent flashing in the head during a natural circulation, at least 135 hours0.00156 days <br />0.0375 hours <br />2.232143e-4 weeks <br />5.13675e-5 months <br /> are required to reach the decay heat removal system 1
cut-in point.
This may also require large amounts of AFM to remove decay heat for such an extended time period.
8 Once the decay heat removal system cuts in, the RCS depressurization must still be slow since the RV head fluid will still be stagnant and cooldown very slowly.
4 '. 0 REFERENCES i
1.
" Plant Limits and Precautions for AN0-1,'i B&W Doc. No. DP 1101, Rev. 1.
l 2.
"177 FA Natural Circulation Cooldown Rate,'? B&W Doc. No. 32-1132883-00, August 16, 1982, 3.
" Arkansas Nuclear One Unit 1 Technical Specifications," B&W Doc. No.
05-0003-06.
1
. l 1
86-1140819-00 8-1
,ig,,
-s,
, ---,,--m,-.
,-,.-m
,,-e
-f,<y-,
,--y-,e-
- + + -, - -,
e
,-.,y
l Figure 1 N00 LNG GIAGRA:1 (NO ELEED CASE)
AXIS OF 90 TAT 10N I__ ___
f l
3 6
I f
f f
a i
,-- AN81 ENT 4
-- - - +- - T- -l -l - t-
/
l f
I I
l L
l, L
/
l__ _ 8 i
4
_ _L. L L 'r.___
4 -
L ' '-
' - - - -M [ lNSutATton l- - i i_ _
i 1
'I I
l a
i 1
1 j
l ll l
7 STAGNANT l_
d -",
AIR SPACE i
i i
i I 'i I
l I
I I
I l!
'l
' __ _,1l '
L
_L __
i_ _ L _
'i _ _ _ L.,
,l _
i I
v HE40 RG0 l 00NE)
,4 l
l l
ji<
l t
F'
- - -+ -
,l l[
l 1
l q
PLENUM l
A
'A lA i A l A i80 i
i l
COVER hl l
ll 1'
1 i!!
' }A !)
\\
l I
II l
l t
m RV A80VE I
I Ll l ___ _ l Ai1
_j. _i_ ___ ! 'L_4 l d a '
]
HOT LEG i
ll I'.t fl 'l l lJ e J
- J RV UPPER s l;
4 3;3 g,., A M e s '
M P' ElluM PLENUM t
))--lt
[ li )l; j
6.~
]
CYLINDER
'~
REGION I
l yA Il l
l i
i t _ J p
.1 di7 I i
i GUTER
=-
m i
i n
annulus l
l ll l1 l
I l
3 ll l
l l1 Ii l
l I
I 11 _
_ '--y 1
I i
3
)
I,1 1 _,,
- L
/
,1 COOLANT FLO'#
HOT LEG NOTE:
THIS N0 DING DI AGRAM IS ONLY A ONE-HALF CROSS SECTION AND INTERNALS.
IN THE ANALYSIS, THIS N00 LNG OI AGRAM IS ROTATED ABOUT THE LE
'IERTICAL AXIS SO THAT THE RV AND INTERNALS ARE 'iODELED EACI N00E THUS SECOMES A RING.
36-1140819-00
_q_
F
--1--
a-
FIGURE 2:
HEAT 77ANSFER MODEL
@s a
1
@p g 1
& w' G. 9 ll c=
e
/
c 4
/
9 9 7
e p
3 m
y g_. %
y, gi @
~ N, ( 'E {/'>1 b, 2E ',
u ;y(
1
$}
j l I
NM i
r t r /,'
s 'a g
8
-4 Q l
l a
i pn s.,
yn \\
(-
4hg 4
k ww/
24 f
N#
h
/
4
/
i
/
/-
~
G,
...,t._
-...t...-
~
(a)
Diesman Caver te W90er fleshe 3
14)
Cahame =elemoset to coeer Ptems a
'3*
'Ja C20 me 21e 1
' al tv mese te Air taaec (*.elettee i
- t
..testattan ta Centstement 31 8v noes ts 7'ema cavec 1
13 sm aettee *3 *Jeler Caelent tooes 3
as 14 *ess ts Castaat 19 'Joeer *eae s
...,... co s..t t...mm c....
1 (4) age 'faaer Insulation es !assistion
't
'bl 8m wetoe ta Caoles *oses of stase eelemat u
- =,.w. t. C,.t.,
s,t 4#
- sta a e t194 t3 Cantalwt
.s
- 1.,
>> e a i. o,e.P.i~ co...t 43 048vettien l
$4 IJReutt104
- u
..e,. t,e.
i
- =
w.
....- t a 1::r.: 3,,et.
e.
36-1140819-00
- ura s; afi
- i ?'iWM M si U?i3 all'O
'AASS TRMISFER '40 DEL GD gD v gW
'\\
\\
N
/N
\\.
A N
N @,f Y Of&'q; f
D h'/
f i
o'%
v
\\
\\
,.- a o
c f/
[
\\
l [
I 9
/
/l
%l 0)sL-7 i
W
/
k y
/ /s s
\\
~a n l
<l/..j P5 I
[ 5,*
f,
'1* "
\\
f\\
j w
e hj-)
d gI i
ch 4
/
s k
W Ab
/
/.
c3 e
b s
/*9
/i f a '
b
\\. '
f 3
/
/
/
/
1 rg eees
's enee set.9 PeteNet*ea 2
4 Sm Fuel assensly wooer one fittiaq flKF) tate Calimus meisumet (Cd8 3
Sm Fuel Assamely stF *ata slenia osan eroe 4
5 FN tastae td to elema eeen ecos t3m tsmee estt aorts a
4
- e *all caswee weewet 5
Aatal flow ta essaim evea eroe
- 5
- 'im J iace ioses 's sieme csl. ta outlet waste I
satel fime to stoma eoen aree 1
%m 22. ene 24.saca pe6es in sieme cyl. :s steaus cy). auter samneus I
l1
%rv Waaca wies to stoma cyl. s sieme evt.
- star annee.s I
- 1
'm Weace Poles to saame cyt, ta outlet netzte i
- 3 See CW too caos te voeur mees
- 3 il Bru pianum cover ammulus to plasm cvt. auter
- 3 3ru sleese cover emnet e to eatlet nesale 1
- 5 n ema cy.. =te,e -. is orie.,e w e 36-11d0819-00
s Figure 4:
REACTOR VESSEL llEAD COOLDOWN j
o ES 600
'?
f 9
- ' I I UN
-T RV HEAD MAX dt 550 177 FA N.C. COOLDOWN 500 C
INITIAL SHELL TEMPERAIDRE = 604 F 450 i
as IN111AL WATER TEMPERATilRE = 585 F
[TRCS AMBIENT TEMPERATURE = 120 F NATURAL CIRCULATION FLOWRATE = 1141 #/HR 400
~ dT = 100 f.'HR dt 350 l
300 1
8 I
I l
i I
2 3
4 5
6 7
0 i
t(lit S. )
l 1
~
^
0 6'
N 1
.~
~
4, '
. 0 L
3 4
1 l
g a
is p
)
1 n
9 i
0 E
2
- 2 t
8 l
1 I
t u
T a c tR 5
V i
ai sD
~
E T
(
R s
0 N
i 0
R 1
E
~1 P
N 1
t E
T D
)
r, s g r
h p
0
(
8 3
e a m
7 i d T
j
~
it r
M UM 0
6 T
A.
M 5
~
E.
R J
0 G'
4 I
F 0
2 0
0 0
0 0
0 0
0 0
0 0
0 7
6 5
4 3
2
.mem g $ 2w a a.u a5x >x 5r xnx uso 7
On ~~bom~o OO (cI se
' ~w i 4
,l
o i
e i'
~t.
.s I
f1
/
iC y
c-
'I.
l c.=
nm
.- M c.
a=-
UON j
l M fl C1 I
'O c-N w
I E
-+
.i.
.I m
I W
3 3e
-5, c
m tJ
/
i
=*~
l n
=
i e
c
.=
n
-.c e
ca a
=
s l--
m i
=
c
/
W
=
{
.8 e
wa:=e u.
- ce l
l e
~N
/.
i e
e e
e o
O C
C O
O m
o e
a m
N N
c*
VISd '3EOSS3Bd 86-1140819-00
i l
1 - Minimum Pressure for 100 F/hr cooldown of RCS to 350 F (t s 2.5 hrs) 2 - Maximum RCS Temperature (280 F) for DHR cut-in.
(t s 135) 2500 i
2000 100'F/hr Cooldown k
G
\\
c.
ur NDT Limits for CooldownX yO g
1500
/
~
g Head Subcooled,
f Line G
1000 f
I 500 7
" Head 2
Saturation l
Line l
i 1
1 f
f 200 300 400 500 600 TEMPERATURE l
FIGURE 7:
PRESSURE - TEllPERATURE DIAGRAM FOR NATURAL l
CIRCULATION C00LDOWN 85-1140819-00 I
~
-