ML20063F263
| ML20063F263 | |
| Person / Time | |
|---|---|
| Site: | 05200001 |
| Issue date: | 02/07/1994 |
| From: | Fox J GENERAL ELECTRIC CO. |
| To: | Poslusny C Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9402140212 | |
| Download: ML20063F263 (8) | |
Text
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GE Nuclear Energy
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% en:.aa.m 75 C:tse" 4/ fad hh 12 C4 M7.*i February 7,1994 Docket No.52-001 Chet Poslusny, Senior Project Manager Standardization Project Directorate Associate Directorate for Advanced Reactors and License Renewal Office of the Nuclear Reactor Regulation
Subject:
Submittal Supporting Accelerated ABWR Schedule -
Containment Emergency Procedure Guidelines Issues
Reference:
R. W. Borchardt Letter to J. F. Quirk, "GE ABWR Containment Systems and Severe Accident Review issues",
December 29,1993
Dear Chet:
This letter responds to the Low-Pressure Venting Item 2 of the subject issues transmitted by the above reference. The item is repeated below followed by the response:
2.
Address suppression pool bypass mechanism through interconnection in the atmospheretc control system (ACS) and show the effect on the existing bypass analysis. Ensure that no other bypass pathways exist that have not been accounted for.
Response
See revised Subsections 6.2.1.1.5.3 and 6.2.1.1.5.5 and new Appendix 6E.
Sincerely, Jack Fox Advanced Reactor Programs cc:
Joe Quirk (GE) d],Mp/f Alan Beard (GE)
Norman Fletcher (DOE)
' f Umesh Saxena (GE) b 100u13 i
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nf % C12 9402140212 940207 3'
(A PDR ADOCK 05200001 V
A PDR M
FEB 07 '%
04:30Pt1.:Ct3 93 137 P. 3 '8 23A6100 Rev, 3 ABWR Stand 2rd SafetyAnalysis Report M,
= spray flow rate N,
- spray efficiency T
= containment temperature c
T,
= spray ternperature at the spray nozzles fg = latent heat of vaponzation of water H
C
= constant pressure >pecific heat or water p
l-The spray water ternperature is calculated from:
T,
- T - KHX x [(T - Tr) /(M, x C )]
p p
p where Tp suppression pool temperature
=-
KHX-RHR heat exchanger effectiveness T,,
senice water temperature
=
Containment sprays have a significant effect on the allowable steam bypass capability.
Use of sprays increases the maximum allowable bypass leakage by an order of magnitude and represents angff ctive ba{ku means of condensing ass steam. See Apps ~ dix G E 4-c#.A.
see ps., e.w rh u.
6.2.1.1.5.5 Suppression Pool Bypass During Severe Accidents The only mode of suppression pool bypass that presents any significant nsk during a severe accidentis acuurn breaker leakage. Vacuum breakcrleakage results in the l
passage of gas from the drywellinto the wetwell airspace. Vapor suppression and fission product scnibbing by the suppression pool are not available to the gas and vapor which pass through the vacuum breakers. The consequences associated with vacuum breaker leakage can be mitigated by use of containment sprays.
Large amounts ofleakage can occur as a result of catistrophic failure of valve components or a valve suckingopen Lesser amounts ofleakage can result from normal wear and tear including degradation of the valve seating surfaces. For sufficiently large amounts ofleakage during a severe accident without containment heat removal, the time to COPS activation or contamment overpressunzation can be reduced and the amount of fission produco teleased can be increased The probability that the vacuum breakers wdileak on suck open will be minimized by usmg materials selected for wear resistance and using high quality seating surfaces.
6.2 20 Conta nment Systems ~ Amenement 33
FEB 07 '96 04:30Pil 408 925 425T P.4-8 23AS100 Rsv. 3
.ABWR staxssrs suety Anslysis R:p:rt a
4 l
Mdot *, [(AM Y(28c(APv)/v) }
where dnwell steam specific volume, and v=
b total loss coefficient of the flow path.
(7) Compute the maximum allowable leakage path area. A/d as follows:
A/E
[(Maoi)/E(28c (AP )/V3
=
V
[(M /6t)/V(2gc (APv)/v]
3 wher e at=
Accident duration Using the procedure outlined above and assuming an accident duranon of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, the maximum allowable leakage path area under these circumstances is determined to be an effective flow area (A/UK) of 5 cm Sce APPd u 6E h 4 h.
2 6 pri c_m eA h o e S.
6.2.1.1.5.4 Bypass Capability With Containment Spray and Heat Sinks An analysis has been performed which evaluates the bypass capability of the containment for a spectrum of break sizes considering containment sprays and containment structural heat sinks as means of mitigating the effects of steam bypass of the suppression pool.
The containment system design provides two RHR spray loops, and each loop consists of both wetwell and drywell sprays In operation of RHR in spray mode, the wetwell and dr)well sprays acuvate simultaneously. Per loop, the design flow rate of drywell spray is 3
8 about 800 m / hour, and that of wetwell spray is about 114 m / hour. In this analysis t.
is assumed that sprayis to be initiated no sooner than 30 minutes after the wetwell gas 2
space pressure is reached to 1.05 kg/cm g. This assumed value of sprayinination l
pressure set point, which is higher than the EPGs pressure set point of 0.73 kg/cm g,is 2
expected to produce slightly conservative results. The suppression pool water passes thiough the RHR heat exchanger and is then injected into the drywell and werwell sprae headers located respectively in the upper region of drywell and wetwell gas space. Th:
spray will rapidly condense the stratified steam, creating a homogeneous air-steam mixture in the containment. Structural heat sinks (drywell and wetwell boundary surfaces) were considered with variable convecove heat transfer coefficients based on Uchida correlation. The reactor vesselshutdown rate was assumed to be 55.6*C/hr, and the maximum design semcc water temperature was used. This shutdown rate corresponds to the maximurn rate which does not thermally cycle the reactor vessel.
6224 Contamment Systems - Amendment 23
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6E Additional Bypass Leakage Considerations 6E.1 Bypass Mechanism through ACS Interconnection in accordance with the ABWR design, the ACS is provided to establish and maintain an iner atmosphere within the primary containment during all plant operating mt des, except during shutdown for refueling or equipment maintenance or access for inspection at low reactor power.
The ACS also maintains a slightly positive inert gas pressure in the primary containment during normal, abnormal and accident conditions to prevent air (oxygen) ieakage into the inerted volumes from the secondary containment.
Isolation valves F040 and F041 (see Figure 6.2-39), which are normally open, make a direct flow path connection between the drywell and the wetwell air space. Therefore, in the event of a pipe break inside the drywell, this direct flow path will become an additional steam bypass leakage path. However, this additional bypass leakage path will close in few seconds, because of automatic closure of these valves upon receipt of a LOCA signal. These isolation valves are designed to close autornatically within 15 seconds after receiving a high drywell pressure (2 psig) signal.
Valves Fail to Close Failure of the above two isolation valves to close, which may result in a continuous bypass pathway, is highly unlikely. Division 11 is the power source for these two valves, and they are fail to-close safe. Four independent sensors (one in each electrical division) detect high pressure in the drywell. Isolation system uses reverse logic (i.e, valve in open position with a low drywell pressure signal), and the isolation signal uses two-out-of-four logic. A loss of signal will de-energize the solenoid resulting in valve closure.
6E.2 Othcr Bypass Pathways 1
4 FEB.07 * %. 04: 31Ptt.208 925 4257 P68 4
All containment systems which communicate with the drywell and/or wetwell air space were examined for any potential steam bypass pathways during LOCA events. A careful review of their P&lDs revealed no 1
additionall bypass pathways.
6E.3 Effect on Existing Bypass Analyses The ACS interconnection, as described above, will become a bypass pathway during LOCA. This pathway willintroduce steam bypass leakage area, in addition to the bypass leakage area considered and analyzed in the existing bypass analyses (SSAR Subsections 6.2.1.1.5.3, and 6.2.1.1.5.4). Simple engineering analyses were performed to assess effect of this additional bypass leakage area on the these two existing bypass analyses.
6E.3.1 Estimate of Effestive Bvoass Leakage Area (ANK)
The fic"> area, A, through the ACS interconnection is determined 2
by the 2-in piping of Sch 80, which is about 0.02 ft. In determining the total loss coefficient, only local flow losses were considered.
Pipe friction losses were ignored for conservatism. A total flow loss _
coefficient of 11.5 was determined, which comprises of the following:
- a. Standard entrance loss coefficient:
0.5
- b. Flow loss coefficient for two 8.0 standard globe valves in series:
- c. Flow loss coefficient for two 2.0 standard elbows in series:
- d. Standard exit loss coefficient:
1.0 The effecuve bypass leakage area, ANK, is approximately 0.006 2
ft 2
FEB-0~ "96 04: 31Ft1 JOS 95 457' p,7, g -
-l
~
6E.3.2 Duration oLBynastE.loy! -
Bypass flow through this additional bypass pathway will terminate upon closure of the isolation valves. As noted above, these valves will close within 15 seconds after receiving a high drywell pressure (2 psig) signal. It was determined th,it the drywell pressure for a 2
small (0.02 ft ) steam break LOCA will reach to 2 psig in about 20 seconds after LOCA. Allowing for the 15 seconds of valve closure time, this additional bypass pathway w,il be active for first 35 seconds only. For assessment purposes, a continuous effective 2
flow area of 0.006 ft during first 35 seconds was assumed.
Decrease in flow area during the valve closure period was ignored
{
for conservatism.
6E.3.3Elfact on Existing Bypass Analvses
- a. Bypass Capability Without Sprays and Heat Sinks (6.2.1.1.5.3)
This analysis, which assumes continuous steam bypass leakage over 6-br period, determined an acceptable effective flow area of 2
2 0.005 ft (or 5 cm ). In this analysis, a stratified atmosphere model, which assumed steam only flow through the leakage path, was assumed to ensure conservative results.
It was estimated that this additional bypass leakage area of 0.006 ft will result in a total flow of about 10 lb of steam over the 35-sec 2
period. This additional flow of 10 lb of steam is about 0.1% (which is almost negligible) of the total flow of steam over the 6-br period in the existing analysis.
Given inherent conservatism in the analysis assumption, it is concluded that this ACS interconnection bypass pathway will haven negligible effect on the existing analysis results.
- b. Bypass Capability with Sprays and lieat Sinks i
3
rcs 07 '96 04:327tl 408 93 457 P. 8 "8 This analysis, which takes credit for heat sinks as well as manual -
actuation of sprays 30 minutes after the wetwell airspace' pressure 2
reaches to 15 psig (or 1.05 cm g), determined an acceptable 2
effective bypass leakage area of 50 cm Given manual actuation of sprays as defined abo te, it is concluded that this ACS interconnection bypass pathway should have no impact on this bypass capability analysis.
6E.4 Conclusion i
in view of the above results, it is concluded that the suppression pool bypass rnechanism through interconnection in the atmospheric control system (ACS) will have no effect on the existing bypass leakage analyses in SSAR Subsections 6.2.1.1.5.3 and 6.2.1.1.5.4 i
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