ML19224D248
| ML19224D248 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/07/1979 |
| From: | Hanauer S Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUDOCS 7907110174 | |
| Download: ML19224D248 (3) | |
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~ 5ehavior of the Level Instrumentation at TMI-2 Durine the ~nitial Transient 1.
Conclusion The question has artsen, whether the leval instrumenta-icn at TMI-2 was ind.cating 7
falsely high during the initial transient (say, 30.inutes).
e have concluded that the error caused by flashing in the reference leg was small - less than 12 incnes - and that the pressurizer was essentially full after
=6 minutes as incicated
- 6 ne.nstrumants.
The : asis for 1is c;r.:iusi r.s :is:assi-bair.
2.
Descriction The generai layout of a typical one of the three pressuri:er level instrumentati~
systems is given in Fig. 1.
Two impulse lines connect to the pressurizer.W a m one near the top and one near the bottom., The lines are routed to the difterencial-
,w.h n ~ i,. : -,.
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,v pressur transmitter, located in the annular region be ween the shield v.all and the i
a.
{'containmentwall. The transmitter is located about feet belcw the top of :..e p ress uri zer,,Cicn 1 s ----.
ree: Oe6on t!Te cott m.'... m sser!::e.
The instrument reacs, in principle, a pressure difference tnat ecuals tne pressure head of the liquid in the pressurizer, which is the product of the liquid density times its height. Thisis,ineffect,theweight(3erunitarea)oftheliquid
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' bove the elevation ei-the lower impulse lineh, connects to the pressurizer.
4 If the licuid den:,;ty changes, due to a temperature change, the " weight" measurement is unaffected ::ut its calibration in neight (level) anits will vary; in TMI-2, this is corrected automatically and continuously by a tomoerature instrument applying a correction in the level readout it.strument.
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'If the linuid _i_n the cressurizer flashes, the level instrument will read the collapsed 3
level, as though the bubbles were not there. Thus under these conditions the 7
actual (mixture) level would be higher than the level indicated by :ne instrt: ment.
The use of inculse lines to a remotely located differential - pressure transmitter introduces an additional potential source of errors. The lines must be constant in pressure crop or rise due to the difference in ele).'a:icn.
In practice, they are Operated full of wat r.
For -he line connected :o :ne ua:er sp;ce in:ne pressurizer n
~
(10..er ccnnection), thie., no problem after the iritial h EM : and venting.
Fcr the line ecnnec ec in the s: gam space (upper cnnnect{an;, nere is a :::ential for flashing of the water in the line during pressure decreases.
This, if it occurred, would make the instrument read falsely high; that is, a level nigner than the actual level.
( The fluid in the impulse line will flash unenever '.ts pressure is belcw the satura-tion pressure for the fluid tem 0erature.
Thus it is the temoerature, distribution G
of :ne imouise-line fluid that is im;ortant.
For ne TMI-2 ;ressurizer levei it.strumentation impulse lines, the configuration is as shown in Fig.
The upper end of the lines is initially at 650*F, and thy thermal inertia of the pressurizer wall holds it at that temperature for all transients except the slowest.
The temperature of the first foot or two of the line depends in a complicated
.a.%
aay on conductioni '.' the hot pressurizer wall (650*F) and connecticjn CO0 ling by the containment atmosphere (":lCO*F).
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