ML20070D933
| ML20070D933 | |
| Person / Time | |
|---|---|
| Site: | 05200001 |
| Issue date: | 05/26/1994 |
| From: | Fox J GENERAL ELECTRIC CO. |
| To: | Boyce T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9407130176 | |
| Download: ML20070D933 (11) | |
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d, l 1.) I, May 26,1994 Docket No.52-001 Tom Boyce, Senior Project Manager Standardization Project Directorate Associate Directorate for Advanced Reactors and License Renewal Office of the Nuclear Reactor Regulation
Subject:
SubmittalSupporting Accelerated ABWR Schedule-AmVR Containment Sprays
References:
Letter, R. W. Borchardt to Joseph Quirk, Remaining Actions on the Advanced Boiling Water Reactor (ABWR), May 13, 1994
Dear Tom:
In response to the Reference Letter, we have performed additional analyses to assess the impact of drywell spray actuation following a LOCA to ensure that the bounding scenario was evaluated. In addition, we have re-assessed the drywell spray initiation limit curve and have determined the impact of drywell spray actuation on the differential pressure capability of the containment. Results of these analyses show no adverse impact of the drywell spray actuation on the differential pressure ccpability of the containment.
Please provide a copy of this transmittal to John Monninger.
Sincerely, bei Jack Fox Advanced Reactor Programs GE)E) cc:
Alan Beard DO Norman Fletcher Joe Quirk GE Umesh Saxena GE CalTang (GE i
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Reference:
Letter, 5/13/94, Borchardt (NRC) to Quirk (GE);
REMAINING ACTIONS ON THE ADVANCED BOILING WATER REACTOR (ABWR) REVIEW INTRODUC1lON Two of the RHR loops in the ABWR design provide containment spray cooling subsystems. In the normal, or the preferred, mode of operation drywell (DW) and wetwell (WW) sprays actuate simultaneously. In addition, the system design allows for independent operation of wetwell or drywell sprays through a series of operator actions. Compared to simultaneous actuation of drywell and wetwell sprays, independent actuation of drywell spray only will result in somewhat higher drywell depressurization. In view that independent actuation of drywell spray (and no wetwell spray) will require series of operator actions, independent actuation of drywell spray is intended for surveillance testing of system equipment such as pumps and valves.
After reviewing SSAR Amendment 34 (Reference letter), Staff has requested GE to consider and assess the impact of drywell spray actuation on the SSAR containment depressurization analyses. It is perceived that actuation of drywell spray only may result in undesirable negative DW to WW and DW/WW to RB differential pressure results. The two analyses identified for further assessment in reference letter are:
- 2. Drywell Spray Initiation Limit (DSIL) curve (in SSAR Section 18A).
In response to staff request, additional analyses were performed to assess the impact of drywell spray actuation on these two analyses. Though a very low probability event, it is postulated that upon start of the preferred mode of containment spray operation wetwell spray injection valve failed to open resulting in actuation of drywell spray only and no wetwell spray.
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JuL 12 '94 10:09At1 GE tOCLEAR BLDG J P.4/12 ANALYSES
- 1. Sizing of the WW to DW vacuum Breakers A. SSAR Analysis The primary requirement for the ezing basis of the wetwell-to-drywell vacuum breaker system (WDVBS) is to limit the drywell-to-wetwell negative pressure differential below its allowable value during the drywell depressurization events.
The drywell depressurization is primarily caused by two major events:
1.
post-LOCA ECCS flow 2.
inadvertent actuation of DW/WW sprays.
Following the break of a FWL, the drywell air is purged into the wetwell air space leaving the drywell full of steam. Subsequent condensation of this steam by cold ECCS flow out of the break results in depressurization of the drywell. Likewise, actuation of DW/WW sprays will concense the steam in the drywell resulting in depressurization of the drywell. A higher and colder flow into the drywell will result in higher depressurization in the drywell.
The sizing of the WDVBS was determined and based on the post-LOCA ECCS flow event. As a conservative assumption, a maximum combination of ECCS 3
(HPCF/LPFL/RCIC) flow of 2,642 lb/sec (4,316 m /hr), at CST temperature of 60
- F, was assumed in the sizing analysis. This assumption of ECCS flow into the drywell at 60 F is excessively conservative since it neglects heating of the ECCS flow inside the vessel before it flows out of the break. In contrast, drywell/wetwell spray (maximum flow rate of 584 lb/sec or 950 m /hr) should be expected to result in substantially much lower drywell depressurization.
In calculating the drywell depressurization,100% of the ECCS break flow was mixed with the drywell atmosphere. This assumption of 100% mixing of the ECCS flow will result in conservative depressurization effect, considering that in reality a portion of the ECCS flow will fall directly on to the floor without mixing with the drywell steam. The gravity settling of the ECCS flow was mechanistically calculated. As reported in SSAR, the design-calculated sizing of r au w m
JuL 12 '94 10:10At1 GE fiuCLEAR BLDG J P.5/12 1
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the WDVBS (an effective flow area of 28.3 ft or 0.77 m ) limited the negative pressure differential values below the design value of 2.0 psid. The drywell-to-wetwell maximum negative pressure differential was calculated to be 1.4 psid, i
and the drywell/wetwell-to-reactor building negative differential was calculated to be 0.85 psid.
B. Additional Evaluation An additional study was performed to evaluate the impact of the drywell spray following a LOCA on drywell-to-wetwell negative pressure differential. For comparison purpose with the drywell spray case, the ECCS break flow was re analyzed and modeled as spray flow. The gravity settling of spray flow was mechanistically calculated. Assuming a spray efficiency of 100% (a conservative assumption) and a CST temperature of 60*F, the ECCS flow of 2,642 lb/sec produced drywell-to-wetwell maximum negative pressure differential of about 1.72 psid. For the purpose of sensitivity study only, a CST temperature of 40 *F resulted in a maximum negative pressure differential of about 1.84 psid.
For the purpose of this analysis, drywell spray flow rate of 612 lb/sec (1,000 m /hr) was assumed, instead of the maximum expected flow rate of 584 lb/sec, for an added conservatism. In addition, a constant spray temperature of 40 *F was assumed for additional conservatism. Analysis results showed a maximum negative pressure differential of about 0.52 psid, which is substantially lower than that produced by the ECCS break flow case. These results suggest no adverso impact of drywell spray actuation following a LOCA.
C. C.caelusion The drywell-to-wetwell negative pressu'e differential is limited by the conservative analysis based on the full ECCS flow out of the break. The drywell spray following a LOCA will have no adverse impact on the WDVBS sizing analysis.
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JUL 12 '94 10:10At1 GE fiuCLEAR BLDG J P.6/12 a
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- 2. DSIL Curve of the EPGs Additional analyses were performed to evaluate the impact of drywell spray actuation on the Drywell Spray Initiation Limit (DSIL) curve of the EPGs contained in SSAR Amendment 34, Append!x 18A. A range of drywell and wetwell initial conditions pertaining to the DSIL curve were analyzed. The allowable negative pressure differentialis 3.0 psid to preclude failure of the containment liner.
A. Analysis Descriotion it is postulated that upon start of the RHR subsystem in its preferred spray mode wetwell spray injection valve failed to open. This would lead to and result in actuation of drywell spray only. A summary description of initial conditions for this analysis and their basis are shown in Exhibit A. The key modeling assumptions are described as below;
- a. A constant spray flow rate of 612 lb/sec (1,000 m /hr) is as::umed.
Considering that the RHR pump maximum flow rate is 584 lb/sec (954 3
m /hr), this assumption of drywell spray flow rate of 612 lb/see provides additional margin in the analysis.
- b. Spray efficiency of 100%. This implies instantaneous heating of the spray flow to the drywell temperature condition.
- c. Assume a total of six (6) wetwell-to-drywell vacuum breakers are operable.
This allows for one single failure and one out M :orvice. This is a conservative assumption since failure of one vc0aum breaker will require a plant shutdown within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> by Tech. Specs.
- d. A constant spray temperature of 60 *F.
- e. Vacuum breakers are full open at a wetwell-to-drywell pressure differential of 0.5 psid.
f.
Structural heat sinks in the drywell and wetwell are ignored for conservatism.
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34
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JUL 12 '94 10:11At1 GE NUCLEAR BLDG J P.7/12 a
- g. Heat and mass interaction between suppression pool and the womell airspace are ignored.
B. Analysis Calculations The pressure / temperature state conditions which were evaluated are shown in Exhibit B. In order to cover a broader range of state conditions, some cases happened to have non-rnechanistically higher than the nominal mass of total noncondensibles. For the purpose of sensitivity study only, a few cases were analyzed assuming a constant spray temperature of 40 'F.
The wetwell-to-drywell maximum negative pressure differential was determined by taking the difference of the drywell and wetwell pressure values calculated by the code. The drywell/wetwell-to-reactor building negative pressure differential was determined through end-point calculation. In t'he long term the drywell and wetwell will come to common pressure and temperature equilibrium conditions. At equilibrium condition, the drywell and wetwell atmosphere will be saturated air at the spray temperature. The end-point equilibrium pressure, P.,
will be given by the sum of partial pressures of air and water vapor. That is, P. + Py P.
=
(M, x R x T.)/(Vi),
and P.
=
saturation vapor pressure at T..
Py
=
combined sum of drywell and wetwell noncondensibles M
=
i specific gas constant R
=
end-point equilibrium temperature, equal to spray temperature T.
=
combined volume of drywell and wetwell air space V
=
i Example:
32,600 lbm, Let M
=
i 500 'R (i.e.,40 F spray temperature)
T,
=
3 470,060 ft V
=
i 53.3 ft-lb,Ilbm *R Re
=
1
- :n m m
JuL 12 '94 10:11AM GE t#JCLEAR BLDG J P.8/12 For these given values, the final equilibrium pressure in both drywell and the wetwell air space is 12.96 psia.
= 12.84 + 0.1216
=
P.
Assuming the reactor building (RB) pressure of 14.7 psia, the DW/WW-to-RB negative pressure differential is given by 12.96 - 14.7 = -1.74 psid.
=
C. Analysis Results The analysis results for the cases evaluated are summarized and presented in Exhibit C. These results show that the negative pressure differentials due to the drywell spray actuation will remain below the allowable value of -3.0 psid for the state conditions in the spray region of the DSil curve (see Exhibit B).
D. Conclusion The results presented in Exhibit C show no adverse impact of drywell spray actu; tion on the differential pressure capability of the containment. Based on aur evaluation of these results, we conclude that there are no limitations for initiation'of containment sprays from conditions on the right region of the DSIL curve of the EPGs given in SSAR Amendment 34. Further, we believe that the pressure / temperature conditions analyzed in this evaluation study are representative of and bound the entire range of pressure / temperature conditions expected on the right region of the DSIL curve.
CONCLUSION Additional analyses were performed assessing the impact of drywell spray actuation on wetwell-to-drywell negative pressure differential and the DSIL curve of the EPGs as given in SSAR Amendment 34. Results from these analyses show no adverse impact of the drywell spray actuation on the differential pressure capability of the containment.
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Initial Conditions for ABWR-Specific Drywell Spray Analysis 3,
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4 Item EPG Assumption ABWR Assumption Basis g
Spray temperatwe 40*F 60*F Lowest reasonably achievable g.
Drywell humidity -
0%
approaching 0%
SHEX code will not perfonn r,;
calculations at 0% Rd in the B
drywell P
8 Drywell ternperature 545*F 340*F ADS qualification
' temperature; Sprays are initiated prior to reaching this temperature in Step DW/T-2 Drywell pressure range -
O to 20 psig 3 Points: 5,10, and 15 psig To address reasonable range of conditions-Drywell noncondensible mass Entire mass from both drywell Mass thatis predicted by Ideal Consistent with a mechanistic l
and wetwell Gas Law for the drywell calculatian volume, presswe, and i
temperature TH y
0 E'
de '
e
,1 *s F
M E'
~Wetwell hmnidity Not considered 100 %
Wetwell typically has a high M3' relativeImmidity; consistent with mechanistic calculation S
Wetwell temperature Not considered
[ 80*F and 280*F
! Low temperature minimizes.
5 the wetwell depressurization R-E rate, High temperature (taken from the low pressure.
{
. endpoint of the HCTL) m minimizes the mitigative effect of the wetwell-to-drywell vacumn breakers Wetwell pressure range -
Same as drywell pressure Same as drywell pressure Same Wetwell-drywell AP O psid 0 psid
- Same Vacuum breaker operability None until airspace saturated, One out ofservice
' Consistent with Tech Spec then sufficient aanber
. requirements and mechanistic (unspecified) to mitigate any '
analysis father pressure decrease 3
Spray ciliciency Instantaneous airspace 100% spray' efficiency Maximize the depressurization saturation rate for a mechanistic analysis
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JUL 12 '94 10:12f41 GE FUCLEAR BLDG J P.11/12 i
EXHIBIT B DRYWELL SPRAY INITIATION LIMIT aso _
319.E e.
W
(
W 260 l
m.
150 -
n d
100 k
ss O
O.0 0.5 1.0 1.5 2.0 2.5 3.0 0.21 0.75 DRYWELL PRESSURE (kofem2 9) 1 l
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ABWR-SPECIFIC DRYWELL SPRAY ANALYSIS
^
INITIAL CONDITIONS AND
SUMMARY
RESULTS 5
- b. DW spray flow rate of 1,000 m%h (No WW Spray)
Spray efficiency of 100%
w Key Modehng Assumptions;
- c. Spray temperature of 60 *F
- d. WN-DW V8s operab!c, with cne out of seonce S
a.
Containment Negative Differential Pressure Capability AP = - 3.0 psid Case DW DW Rel DW WW WW Ret WW DWMMI DW-WW Drywell Wetweil Total Air S
Temp.
Humidity Pressure Temp.
Humidity Pressure to RB AP Air Mass Air Mass Mass O~)
(psia)
M (psia) ap(2)
(psid)
(Ib)
(Ib)
('b) h n
(psid}
1W.
340.0 0.005W l's.O 80.0 1.0 15.0
-3.08
-2.00 12,490 15,380 27.870 E
2W.
340.0 0.005 20.0 80.0 1.0 20.0
+0.87
-2.15 18,820 20.690 37,510 8
3.
340.0 0.005 25.0 80.0 1.0 25.0
+4.78
-2.25 21,150 25.990 47,140 4.
340.0 0.005
~,0.0 80.0 1.0 30.0
+9.62
-2.25 25,490 31,300 59.000 SW.
340.0 0.005 15.0 200.0 1.0 15.0
-5.19
-1.75 12,490 3.020 15.510 6W.
340 0 0.005 20.0 200.0 1.0 20.0 4.58
-1.87 16.820 7,360 24,180 7.
340.0 0.005 30.0 200.0 1.0 30.0
+2.50
-1.99 25.490 1S,040 41.530 8.
340.0 0.005 50.0 280.0 1.0 50.0
+3.27
-1.48 42,820 620 43,440 T
9PM).
340.0 0.005 15.0 80.0 1.0 15.0
-3'11
-2.20 14.3B0 13.480 27.860 57 10.
550.0 0.005 30.0 80.0 1.0 30.0 l
+5 33
-2.57 17,000 31,300 48.300 11.
400.0 0.005 30.0 80.0 1.0 30.0
+7.87
-2.45 23,190 31.300 54,490 c) 12W.
340.0 0.205 30.0 130.0 0.92 30.0
-1.70
-1.75 5,550 27,170 32,720 13.
550.0 0.048 50.0 205.0 1.0 50.0
-1.27
-2.48 90 32,030 32,170 14W 550.0 0.048 50.0 205.0 1.0 50.0
-1.91
-2.68 90 32,060 32,170 15.
340 0 0.205 30.0 130.0 0.92 30.0
-1.56
-1.7 5.550 27.170 32,720 16W.
170.0 0.118 30.0 250.0 1.0 30.0
-1.83
-0.55 32.240 140 32,380 17W.
340.0 0.011 40.0 267.0 1.0 40.0
-1.37
-1.73 33,540 0
33,540 1BW 550.0 0.003 50.0 280.0 1.0 50.0
-1.67
-2.50 32,170 620 32,790 19W 340.0 0.101 50.0 200.0 1.0 50.0
+11.61
-1.86 33,110 33,400 66.150 20 340.0 0.001 20.0 80.0 1.0 20.0
+1.98
-2.20 17,230 20,680 1
37,910 y
21W 250.0 1.0 30.0 80.0 0.396 30.0
-2.06 0.50 170 31,620 31.790 22 170.0 0.118 30.0 250.0 1.0 30.0 l
-1.19
-0.50 32.240 140 32,380 l
(1) Code requires a minimum non-zero value (2) End-point equit. pressure at spray temperature.
(3) Spray tempesture of 40 "F y
(4) State conditionslie in NO-SPRAY region E
.