ML19305A673
| ML19305A673 | |
| Person / Time | |
|---|---|
| Site: | Crane, Davis Besse  |
| Issue date: | 10/06/1978 |
| From: | Winks R BABCOCK & WILCOX CO. |
| To: | |
| References | |
| TASK-TF, TASK-TMR NUDOCS 8001160741 | |
| Download: ML19305A673 (23) | |
Text
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86-2449 00 t
THE EFFECT OF NET MAKEUP FLOW AFTER REACTOR TRIP ON PRESSURIZER LEVEL AT DAVIS-BESSE 1 BY:
Robert;W[LWin! '
Babcock & Wileo"x Lynchburg, Va,
{(Octoberl6,[19781-
/
8 0 01 i so 79,
g 86-2449 00 Introduction
,y n. ~ _
7,studylofjthe change;in pressurizer. level:following a. trip of the reactor; gA.
was, perforned recently_for Toledo, Edison Compangspecifically, for the. Davis-Besse 1,
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plant. Themathematicaltechnique[ assumed}thatthecontractionofthefluid inthereactorcoolantsystemwouldoccurvitsnoInstgainor[lossAdmas~j s
{duiingthij4=at*disty.._eedond$1nterea$untilaminimumpressurizerlevelwas
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achieved. The purpose of this study is to determine the net addition of coolant to the RC system within this nominal sixty second period and to calculate the effect it has on the change in pressurizer level described in the previous report.
S n=rra rv Analysis of recorded dsta on seal injection, makeup and letdown flowrates during four specific reactor trip transients indicates that approximately 325 gallons of cold leg temperature fluid was added to the RC system to try to maintain RC pressure and pressurizar level in the interval of ti=e between reactor trip l
and minimum pressurizar level. This is equivalent to 14 inches of pressurizer I
level even though it represents only a 0.4: addition to : he total volume of l
t the RC system (%84,000 gallons).
The source of data for seal injection, makeup and letdown flowrates during the. reactor trip trar.sients was the Post Trip Review log.
Sd.nce it records l
l actual values of the monitored parameters once every thirty seconds, the number of data points for a nominal sixty second period between reactor trip and minimum pressurizer level is very limited. Hence, accurate knowledge of rhese in flow and ort,flov values for the RC system is very approximate.
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86-2449 00 In most cases, the volume of fluid added to the RC system is most strongly inf,'
meed by the makeup flowrate when two makeup pumps are operating.
Since the maximum indication of makeup flev' tate is 160 gpm and is approximately one half the expected or calculated flowrate, no verification of the makeup flowrate when two pumps are running is available.
The contraction of the reactor coolant due to the temperature change in a nominal sixty second interval of time is corrected by 0.4% using a calculated net addition of 325 gallons to the total volume of the system.
It is reasonable to assume that six temperature measurements, each having a time constant of approximately four seconds, could lead to an uncertainty in the calculated contraction nearly equal to 0.4%.
Since the addition of net makeup flow into the RC system is only known approximately and reduces the total change in pressurizer level due to the temperature contraction of the system, it will be more conservative to continue to use the assumption of constant RC system mass in calculating minimum pressurizer level for reactor trip transients.
Discussion of Analvsis With the assistance of Messrs Sushil Jain and Fred Miller of the Toledo Edison Company, a complete set of Post Trip Review data logs for the following reactor trip transients at Davis-Besse 1 was made available:
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86-2449 00 Reactor Trin Date Reactor Trio Ti=e SPR No.
2/24/78 05:51:06 431 4/2/78 08:30:12 435 8/2/78 09:50:44 476 11/29/77 22:43:24 396 The plant parameters required for this study were the following:
RC Pumps Seal Injection Flowrate F-782 RC System Letdown Flowrate F-717 RC System Makeup Flowrate F-740 RC System Pressure Reactimeter Loop 1 or 2 Cold Leg Temperature Reactimeter Seal Injection and letdown flowrates appeared to remain on-scale or decreased to O gpm during the reactor trip transients; however, makeup flowrate was frequently greater than 160 gpm which is the full scale indication.
A separate but related effort was performed for determining the maximum flowrate of makeup into the RC system at various pressures for either one or two makeup pumps operating.
In the following figures, the net additional volume to the RC system is the integral of the net makeup flowrate from reactor trip time to the time that minimu= pressurizer level occurs.
The net makeup flowrate is defined as:
seal injection + Wmakeup letdown
-W W
=W net All of these flowrates are measured at approximately 100F and represent the net volu=e addition to the RC syste= at 100F prior to being heated to the 1
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86-2449 00 cold les temperature of approximately 550F.
The ratio of volume for the mass of coolant being added to the RC system is approximately 1.3 and varies for each specific reactor trip transient due to slightly different cold leg temperatures at time of minimum pressurizer level.
Figure 1 shows the profiles of seal injection makeup and letdown flowrates following the trip of the reactor on February 24, 1978.
The lower portion of the figure displays the net makeup flowrate into the RCS based on these flowrate profiles. The total volume of fluid added to the RC system and corrected to 550F is 199 gallons which is equivalent to 8.3 inches of pressurizer level.
Figure 2 exhibits the seal injection, makeup, and letdown flowrate profiles after the reactor trip on April 2, 1978. Also shown is the net =akeup flowrate profile deter =ined from the individual flowrate profiles. Adjusting to a final temperature of 550F, the calculated final volume added to the RC system was 197 gallons. This volume is equivalent to 8.2 inches of pressurizer level.
Figure 3 also shows the seal injection. cakeup, and letdown flowrate profiles as derived from the Post Trip Review log from the reactor trip c cnsient of August 2, 1978. The lower portion of Figure 3 displays the net makeup flow-rate profile in the time interval until =ini=um pressurizer level was reached.
l The total volume of fluid added to the RC system at 555F was 548 gallons and j
is considerably larger than the other calculated volumes for two reasons:
(1) The operator turned on the second makeup pump about 15 seconds earlier than in previous reactor trip transients.
(2) The time to reach minimum pressurizer level was at least thirty sseends longer than fer other reactor trip transients.
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Th1 volume added to ch's RC system is equivalent to 22.9 inches of pressurizer level.
Figure 4 presents the flowrate profiles of seal injection makeup and letdown that occurred on the unusual reactor trip and station blackout transient of November 29, 1977. With loss of power, no seal injection flowrate and very little makeup flowrate existed until it was possible to re-start a makeup pump Shortly after four minutes beyond the time the reactor was tripped, pressuriser level dropped below a zero indication, therefore, the net makeup flowrate profile was integrated from 0 to 4 minutes rather than to the time estimated for minirsm pressurizer level.
In this way, measured and calculated changes in pressurizer level could be compared and he correction due to the added volume could be applied to the calculated change in pressuriser level.
The volute of fluid added to the RC system at a temperature of $29F was 352 gallons which is equivalent to 14.7 inches of pressuriser level.
Conclusion Though the Post Trip Review log was available for each of the four reactor trips,theNafrequent[updatetime}ofevery30secondsleadstoafairlyinaccurate determination of flowrate profiles for seal injection, makeup and latdown.
An effort to define the net makeup flowrate profile was accomplished for the four reactor trips and the total volume of heated fluid added to the RC system was calculated.
Since the primary source of fluid added to the system is that due to the =akeup pumps, it was necessary to calculate (and verify with other previous calculations) the maxi =um =akeup flowrate with valve wide open whenever one or two makeup pu=ps were operating. Figure 6 is included
86-2449 00 to show the sensitivity of makeup system flowrate with RC system pressure and the valve wide open condition is represented by the lines labeled K = 0.0050.
I Since all these makeup system flowrates exceed the maximum indication of the makeup flovrace indicator, there is no verification of the actual system flowrate at Davis-Basse 1.
For these two reasons, B&W recommands that this method of correcting calculated pressurizer level change following a reactor trip not be treated as an accurate or reliable technique for determining true minimum pressurizer level during any future reactor trip transients.
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