ML19308B818
| ML19308B818 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear, Crane  |
| Issue date: | 04/03/1975 |
| From: | Govers R, Phinney J BABCOCK & WILCOX CO. |
| To: | Cavanaugh W ARKANSAS POWER & LIGHT CO. |
| References | |
| TASK-TF, TASK-TMR NSS-8, NUDOCS 8001170357 | |
| Download: ML19308B818 (2) | |
Text
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Babcock & WilCOX
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P.O. Box 1260. Lynchburg. Va. 24505 4
Telephone: (804) 384 5111 7
April 3, 1975 t
i-Mr. W. Cavanaugh, til Manager, Nuclear Services 7
Arkansas Power & Light Company P.O. Box 551 Little Rock, Arkansas 72203
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Subject:
Arkansas Nuclear One - Unit One Pressurizer Level Setpoint O
B&W Reference NSS-8 90 @ $
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Reference:
NDC 2360, 3/3/75
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Dear Mr. Cavanaugh:
l HDC 2360 expressed concern over the momentary loss of pressurizer level indication following a reacter trip and requested additional information to clarify that l
h maintaining' RC ' pressure above 1500 psig -(HPSI automatic actuation setpoint) would
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Fd' ensure that the reactor core remains covered with water.
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This protection can be demonstrated by using a very. simple principle:
reactor coolant system pressure is. determined by the saturation pressure for the hottest water in the' reactor coolant system.
In all operating situations except extreme i..
l accident conditions, this water is, of course, pressurizer water at about 650oF, l.. i corresponding to a saturation pressure of 2155 psig while the average water T6 temperature in the reactor core of 579 F has a saturation pre.ssure of~about 1300 L"
psig.
Within about 20-30 seconds after a reactor trip, all water in the reactor h
coolant system (except pressurizer water) will be below 579 F as the reactor power-sustained differential temperature across the core collapses and as the reactor coolant system is cooled to about 550oF (due to turbine bypass valves
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being set to control OTSG pressure at 10'10 psig).
Even though the pressurizer water out-surge during system cooldown will allow system pressure to fall below 2155 psig,, data from reactor trips at B&W's operating plants shows that RC pressure e.g remains well above 1000 psig.
With the RC cooldown established by means of the
. turbine bypass valves' pressure setpoint, RC pressure will not drop to 1500 psig
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~ ' unle'ss the pressurizer;is completely drained. ' l' the pressu'rizer were to drain a
, completely, RC pressure would drop rapidly to the saturation pressure;for the hottest water remaining in the RC system.
The temperature of. this water would be
' between 550 F and 579 F with a resulting RC pressure of(1010.psig to 1300 psig.
This resulting RC pressure band if the pressurizer were to empty following a 2.h1 reactor trip is we:ll; bel,ow the 1500 psig'HPSI aut'omatic initiation 'setpoint.
Thus 1500 psig is an adequate low pressure setpoint for ensuring that the reactor core remains covered with water.
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Y The Babcock & Wilcox Company / Established 1867
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nney/ Covers to Cavanaugh April 3, 1975
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you have any further questions in this matter, please advise.
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.Very truly yours, 1...
3 J
D. Phinney', Manager Operating Plant Services & Maint.
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