ML19221A474
| ML19221A474 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/10/1979 |
| From: | Muench R, Solbrig C, Thiesing J INDUSTRY ADVISORY GROUP |
| To: | |
| Shared Package | |
| ML19221A475 | List: |
| References | |
| OSP-790410, TASK 4, TASK-4, NUDOCS 7905230059 | |
| Download: ML19221A474 (6) | |
Text
.
'?
?pS < f' 3 4 - 4'-l BEHAVIOR OF RCS WITH STEAM GENERATORS IN CONDENSING MODE INDUSTRY ADVISCRi GROUP THREE MILE ISLAND F2 4/10/79 l'
Agreed to and understood by:
d t-Chuck Solbrig Rick Muench TJim Thiesing Harry LawToski Joe Palladino Bob Campbell 163 102 79052300 f7, pm c, "M
_o e
Abstract:
This report recommends that the low pressure natural circulation method of core cooling be utilized for long term use (1 year).
Three possible primary system fluid configurations can result from this type of cooling.
It is reccmmended that analysis 'oe performed to deterr.ine the heat transfer in each of these configurations.
==
Introduction:==
In the long tern, it would be desirable to cool the core with a r.inimum arount cf equipment in operation.. Natural circulation is a core cooling
~
cethod which meets this objective. Many people are studying natural circulation with detailed cocputer analyses, etc.
It appears that these studies are being performed at elevated pressures.
In the very long ters, hcwever, it is also necessary to bring the RCS to strospheric pressure.
In this conditicn, the RCS is ameneable to another cethod of cooling.
Using this method, the RCS can be opened to the containment atmosphere by opening the pressuri er relief valve.
The core will be allowed to achiev, nucleate pool boiling.
Theoretically the generated steam will displace RCS water out of the pressurizer vent, and flow to the steam generator.
In the steam generator, the steam will ultimately be condensed by a cold, wa+.er-solid secondary. After an equilibrium water level is achieved in the hot leg riser and ste1m generator, only occasional =ake-up will be needed to replenish the RCS for the s=all anounts of steam flow vented through the pressuri er vent.
Many techniques are available to provide this make-up.
7
\\63
\\D3
This method can be used in place of natural circulation.
Its real value, however, is as a back-up to natural circul.ition which cay not be sufficient or may break down completely at low pressures. This method is complicated by the possible presence of non-condensibles.
Non-condensibles may limit the flow of steam to the steam generator and/or reduce the condensation coefficient significantly.
The following description will amplify the effect of non-condensibles.
e D
S e
At the initiation of the tube side cendensing mode in the steam generator, the following initial conditions are presumed:
Initial Conditions 1.
Secondary side solid -- cold water 2.
Pressurizer vented to containment atmosphere, either by relief valve open or through 3/8" sample line re-plumhed to cont iinmen:
Primary system solid 4
Core flood tanks floating -- cither unJer.;; head or on head tank Little or no non-condensibles in RCS b.
RC pumps off
.\\ssume little or no natural circulation The behavior of the RCS in this mode is estimatcJ to be as follows:
1.
No Non-CenJensible Gas in Syster 1.
licat generation in core will form steam 2.
Steam will form bubble in top of ves3el 3.
St eam bubble will displace water and raise pressuri:cr level 4
Khen bubble t.ncovers top of hot Icgs, steam will (eventually) lide out hot leg, forming bubble at top of candy canc quite rapidly (roughly 5000 - 10000 cfm).
5.
The increasing bubble solume continues to drive water into pre-suri:er 6.
The increasing bubble volume in candy cane uncovers cold tubes in steam generator until such time as the condensing rate in steam generator equals or exceeds the steaming rate in the core.
7.
- Then, u.
If the system is heavily damped, a steady state steaming in corc/
condensing in steam generator condition will result.
_O_R b.
If the system is undamped which is nore likely the bubble in the steam generator and candy cane will collapse rapidly, and t he process will begin at Step 3 above again and repeat itself, ad infinitum,as long as there is a non-condensible free flow path through the candy cane.
The perculation frequency in this mode is estimated to be 0.5 to 0.05 see
-1.
II.
Non-Condensibles Present Non-condensibles formed during this time will be swept to the top of the candy cane where they will form a bubble at the top of the bend.
a.
f.f t er an undefined period of time, the bubble of non-condensibles may reach a size wherein it " seals" the top of t he candy' cane (i.e. t here is nn lonrer. free st eam flow space below the bubble through the
~
ca r,J) canel.
r-163 103
Reugh calculations Indicate that diffustre action will na-he sufficient to transport steam through the non-cendensible hubble.
The core st eaming rate in this mode is about 70 ft.0/sec, at 20 psia and a valve shich will rapidly (say in 10 seconds) drive the bubb]c into the steam generator ar.d disperse it therein If the non-conJensible bubble is not too large, a condition will develop in which heavier steam reaches the top of the candy cane and begins to " fall" into the steam generator displacing non-condensibles to the top of the candy cane.
9.
The steam generator and hot leg riser will seek a level which provides adequa t e tube area for conJensation. lnis area will increase as ncn-condensibles enter the steam generator and reduce av.ilable ecndens:ng heat transfer coefficients, and'the sweepirg action of the st eam flow will t end to concent rate non-condensibles in the steam generatot 10.
.is the level in the steam generator drops to provide adequate tube condensing area, the pressuri:er surge line may beconc uncovered, the pressure will build and drive the water leg out of the surge line perculating steam and non-condensibles tnrcugh the pressuri:cr.
11.
Eventually, as the steam /non-condensihle ratio ir the generator approaches :ero, the pressuri:er surge line will become the primar:
st eam relief p th, with the end point being steady perculation cf st eam through the pressuri:cr at a rate sufficient to remove the e
decay heat load.
In this mode, RCS pressure will be elevated to 100 - 200 psig to provide adequate steam flow capacity through the pressuri:er relief valve.
It would be undesircable if the non-condensibles forced the system to this state since we are back to a high RCS pressure and venting considerable RCS fluid to centainment.
In evaluating the desirability of this mode of long-term cooling, and to determine the likelihood of its ultimate utili:ation as a matter cf necessity, a number of calculations need be performed.
a.
Natural circulation at strospheric pressure (or near atmospheric pressure) cold primary system -- maximum core head loss to achieve natural circulation.
b.
Calculation of RCS behavior in steaming / condensing mode, in the absence of non-condensibles.
c.
Analytic quantification of RCS behavior as non-condensibles build up in system.
(Steps 8 t hrough 11 above).
63 106 Recommendation:
The l AC recommends that the mode of core cooling discussed above be seriously considered as the long term cooling mode, Analyses (a) and (b) mentioncJ above are l og i c:.1 atensiuns of t he sa t ur 41 c i rcul:.- i nn c:s ! w ul a r i c.m e
3 bc3ng performed by r.any peopli for t he Technical Suppert c,roup.
Tne output of analysis (b) can be used t o const ruct a simple todal to evaluate the possibic ef fect s of non-c anJensibles analysis (el.
These analyses should be performed
.i s soon as practical so further evaluation can be performcJ by the IAG.
as e
e 163 107 e