ML20042E090
| ML20042E090 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 03/31/1990 |
| From: | BECHTEL GROUP, INC. |
| To: | |
| Shared Package | |
| ML20042E089 | List: |
| References | |
| M-005, M-005-R-00, M-5, M-5-R, NUDOCS 9004200073 | |
| Download: ML20042E090 (17) | |
Text
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ATTAG.H M ENT !12
- 1 ,,
REPT M 005 Revision 0 I
.j Description of the Limerick Inadvertent Spray Actuation-Analysis' Bechtel' Corporation-March'1990-l i
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' l-Description _of:the LGS ISA Analysis; i
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gggg; ;l 1,0 , Description ~ of Inadvertent Spray' Actuation' Analysis - 2' '
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1,1 Vacuum Breaker [(VB): Simulation l2 ,
. 1.'2-. Containment: Spray: Simulation? .
(l4:. j
- 1.3. Initial Conditions and . Major: Operating' Parameters. 5: 7
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, 2.0, Discussion of Two"and Three Vacuum' Breaker. Flow-Paths': Study'.
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3,0=. Comparison of This'ISA, Analysis and.That in Revision 58: 9 l- of.the FSAR ;
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4,0 References- . -10 : . '-~ f
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. Figures 1;
, Ll.1- Drywell Pressure 1, 2, & 3'VB; Flow Paths 4
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'1,2 " Drywell Pressure - 4 & 5 -~VB: Flow . Paths -
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. 2,1.lWetwh11toDrywell; Differential; Pressure'-:1,2,4&3'VB:FlowPaths 13 2.2: Wetwell to Drywell Differential. Pressure-- 4 & 5 VB' Flow. Paths
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L j 3,1. Drywell Temperature -;1, 2, &.3 VB Flow: Paths.
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.3.2 'Drywell. Temperature .4-&,5,VB Flow Paths l '16 L .l
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REPT M 005, Revision 0 Description of the LCS ISA Analysis,
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l-l '1. 0 DESCRIPTION OF THE-INADVERTENT SPRAY ACTUATION-ANALYSIS The Limerick inadvertent spray ' actuation (ISA)- drywell depressuri?.ation analysis-
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was performed by a transient computer program developed specifienlly for. the ISA I
analysis.'- In this computer analysis, the ISA event scenario was postulated as- ,
follows: ,
(1) A small break LOCA has occurred. The d'rywell is saturated with steam '
and all* drywell noncondensibles have been swept to the wetwell. -The t wetwell is pressurized by the noncondensibles swept from the drywell.
All " carry over" steam is quenched., The drywell pressure is equal to the wetwell pressure plus the hydrostatic head'at the-bottom of the downcomers due to suppression pool submergence, conservatively assuming-that the downcomers are fully' filled'with steam, q (2) .The inadvertent actuation of a-single loop of the.RHR system drywell spray occurs. The spray condenses the steam thereby depressurizing' ;
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the drywell.
l (3) When the differential pressure between the.wetwell and drywell reaches l 2.81 psid, the wetwell-to-drywell: vacuum breaker assembly starts ' to open. When the differential pressure reaches; 4.48 -psid,1the vacuum l
-breaker assembly is fully open..
L In the transient computer analysis of the. ISA, ~ the drywel. .nd wetwall mass and L energy balance of the homogeneous steam and noncondensible mixture -in each volume:
was - calculated. For a detailed description- of the . analysis , - including the -
conservatisms inherent in the computer model, see FSAR Section 6.2.1.1.4. . Key ,
L parts of the analysis are described below.
l-1.1 Vacuum Breaker Simulation l.
In _the ISA computer analysis, the vacuum relief mass flow rate was. derived based on the steady state' theoretical compressible flow equations of critical and non. - i
. critical flows. To compare conservatively with test data' specifically performed
- for Limerick Generating Station (LGS) and Susquehanna Steam Electric Station
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- For purposes of evaluating the; performance of two operable vacuum breaker assemblies an additional conservatism was included. A small quantity of noncondensibles was assumed to be discharged.from the primary containment prior
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'i to purge valve closure, to minimize the amount of noncondensibles available'to-return to the drywell.
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REPT M 005, Revision.0; l r
Description of the-LSS ISA Analysis i
(SSES)', the parameters in the theoretical'~ flow equation are then modified by imposing valve opening' pressures and assuming a linear: opening' characteristic. _.
'No valve disk . inertia was cons ide re d'. The modeling of the vacuum breakers j produces a relatively slow opening time, about six seconds. Test data shows that as the valve' disk opens beyond 20 degrees the flow area increases rapidly with. t a small increase in differential pressure.. Since the ISA transient is not a fast:
transient and since conservative valve opening' pressure and flow characteristics - t were assumed,' neglecting disk inertia is reasonable.
The following are _the significant test results and _ parameters used.in the of ISA vacuum breaker (VB)- assembly mass flow calculation. Each vacuum breaker assembly
- consists of two' valves in series.
Actual Test Results:
VB assembly starts to open: AP .1.0 psid (across two valves).
. Valve disk open at 20 degrees: AP - 1.80 psid.(across two valves)-
VB assembly is fully open: AP --2.89'psid (across two valves). ;
(In all test cases the front disk opening is slightly different from the.
rear valve disk by less than either:2.5 deg or 10%.)
ISA Computer Analysis-Vacuum Relief Valve Assembly, Mass Flow-Calculation:
VB assemblytstarts to open: AP - 2.81 psid (across two valves)'
VB assembly is fully open: AP - 4.48 paid '(from wetwell to drywell)
Note: Until the vacuum breaker assembly starts to open the differential !
. pressure across the two valvesois-equal to tho' differential pressure between the wetwell and the drywell.
All comparisons with test data are based on the - same " specification air" as , l presented in the test report. Flow losses representative of the as-built ;
condition of the vacuum breaker flow path, including entrance, branch and exit losses were accounted for in the ISA calculation. ;
The ISA vacuum. breaker assembly mass flow calculation includes the e following conservatisms:
4 o The valve opening is delayed by using a very conservative valve opening <-
differential pressure of.2.81 psid across the two valves vs. test data -
of 1.0 psid. This opening pressure conservatively neglects'the small
. actual mass flow during the initial stage of valve opening (to 20 ;
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p o -1 REPT M 005 Revision'0' Description oflthe LGS ISA-Analysis ;
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'I degree disk open position as shown in the test), and includes another '
1 psi margin to compensate.for any other effects, .such as inertia.
o' . The valve is assumed to be fully opened when the wetwell to drywell- O differential pressure reaches 4.48 psid. . The valve flow ' area is ;
linearly ramped between the opening differential pressure of'2.81 psid and the fully,open differential pressure of 4.48.psid. In comparison with test data, this flow characteristic results-in a less=cass flow-vs. differential pressure than the - test' results demonstrate will actually occur.
- 1,2 containment Spray Simulation 1'
The severity of drywell depressurization is determined..byi the rate of energy.
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removed by the spray. The rate of energy removed .by, the espray is in turn determined by the mass flow rate, the temperature and the efficiency of the spray. ,
The spray mass flow is based on the licensing basis assumption of the: inadvertent +
actuation of one RHR spray loop. The other parameters, such as spray temperature ar.d. spray ' efficiency, are : conservatively established to maximize the~ drywell
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depressurization.
- The spray efficiency, which determines the final temperatureiofithe spray water- :
after absorbing heat from the- drywell steam and noncondensible mixture.. is ' a :
function of droplet size and the mass ratio of steam to noncondensibles in the drywell. A mean droplet size of 1000 microns in diameter (0.0305 inches); is 1 assumed and the spray efficiency is determined based'on test: data asidescribed i in Bechtel topical report BN-TOP 3.2 The spray efficiency, c,-is. defined as T, T a
- "T y T -
where T is the spray-water final temperature, T,, is the spray water temperature .
at the spray nozzle exit, and T, is the drywell temperature.
Spray efficiency as a function of steam / air mass ratio is illustrated. in FSAR i Figure 6.2-18. In the ISA' analysis the'drywell initially contains only steam.
Therefore,'the. spray efficiency conservatively remains at a-value of 1.0 until' i
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REPT M-005, Revision 0- '
Description.of the ISS ISA Analysis well'into the transient. The= spray efficiency' at the moment the drywell pressure ,
approaches its_ peak value.is 0.73.
~ The spray temperature is determined by the . suppression pool temperature, the RHR-service water temperature and the effectivenessLof the RRR heat exchanger-. The '
spray temperature was' conservatively calculated as'follows:
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-(1) Very conservative suppression pool' and iRHR-. service water initial, temperatures of 50 F and 40LF,' respectively,.were assumed.
(2) The value for RHR heat exchanger: effectiveness was derived based on design values for higher differential. temperatures, . which tend - to exaggerate the cooling of the RHR spray water'by'the RHR service _ water for the low differential temperatures associated with the ISA event.
Thus, a conservatively low RHR spray water temperature :results.
Initial' Conditions and: Major Operating Parameters-l.3 Initial conditions prior.to small break LOCAi drywell: P - 14.8 psia
- f T - 150 F*- . _
Relative Humidity'- 100%* ;
wetwell: P - 14.8 psia
- LT - 50 F Relative Humidity - 100%
atmosphere: 14.7 psia Initial conditions prior to ISA:
drywell: P - 34.436 psia
- T - 258.33 F*'
Saturated Steam
.t wetwell: P - 29.131 psia
- T - 50 F .i Relative Humidity - 100%
- See' note on next page
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r REPT M 005, Revision 01 Description of the 14S ISA Analysis downcomer submergence: 12.25 feet below high suppression pool water level
- N (steam assumed to fill the inside of the downcomers); !
atmosphere: 14.7. psia ISA Operating Parameters: 4 drywell volume: 248,950 cu ft*
wetwell volume: 146,283 cu ft* -
suppression-pool surface area: 4983 sq ft*
spray-flow: 9500_gpm (one loop) spray temperature: 47.6 F'(initially) 49.7 F (at 300 seconds) spray efficiency: 1.0.(initially)
RHR RX effectiveness: 0.249 ;
i RHR service water flow: 9000 gpm.
- RHR service water temperature: 40 F
. Vacuum breaker full open area: 2.053 f t' each VB flow path dP at which VB assembly starts to open: across two valves - 2.81 psid dP at which VB assembly is fully open: from wetwell'to -drywell - 4 48;psid i
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- NOTE: These initial conditions and parameters differ slightly from those shown i in - FSAR Table 6.2-9. The use of these conditions and associated -j assumptions, such as the ~1oss of noncondensibles through the purge lines, i produces a more severe transient for purposes of comparing the performance
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of two vs. three operating vacuum breaker assemblies. j 6-1
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,;,. 7 REPT M 005 Revision 0
- Description of the: LGS ISA Analysis 2.0 DISCUSSION OF TWO AND THREE VACUUM' BREAKER FLOW PATHS STUDY- d The following was observed in the computer analysis' which analyzed two.and three.
operating vacuum breaker assemblies:
(1) The simulation of the vacuum breaker assemblies did not- allow the valves to start to open until the wetwell-to-drywell differential' pressure reached 2'.81 psid. This occurred at approximately 15 seconds into: the L ISA event . regardless of- the - number of . Vacuum breaker -
assemblies used.
-(2) The-drywell' pressure at:the instant.when:thervacuum breakerLyalves-started to open was +11.7 psig.
(3) - Drywell pressure approaches a peak negative value at about 120 seconds into the transient. (Note: This result remair.s true for four Land
- five operating vacuum breaker flow-; paths--as shown in another -
preliminary evaluation.)' .
The peak drywell negative pressures. reached in.the.' case of two,and, three vacuum breaker assemblies'are: ,
I Two VB assemblies: -4.845'psig Three VB assemblies: -4'821 psig-The analysis results indicated that the minimum number of operating vacuum breaker assemblies' required to keep the negative =drywell pressure less than-5.0 psig is' two. Additional ' operating vacuum breaker assemblies will not e reduce the peak drywell negative pressure significantly. Further - review of the calculation f results found the following explanation as to why additional operating vacuum' j breaker assemblies; will not- significantly reduce the idrywell. peak. negative ;
pressure below that which can be achieved with two vacuum breaket assemblies. ,
(1) With fewer vacuum breaker assemblies opercting (but not less than-two), the differential pressure from' wetwell-to-drywell will; be higher, and each vacuum breaker will remain in the fully open position. l
' for a significant period of time. In the case of two operating vacuum 1 breaker assembly analysis, each vacuum breaker reached-the; fully open f position at approximately 21 seconds, and remained at the' fully open (
position until approximately 73 seconds into the ' transient. The i unavailability of additional operating vacuum breaker assemblies ~is i partially compensated for by the longer operating. time at this higher.
. relief flow position, y i
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. REPT M 005, Revisipn 0 Description of the LCS ISA Analysis i
(2) In the analysis with three operating vacuum' breaker assemblies,.the' [
vacuum breakers never reached the fully' open position. Thus..the peak vacuum relief flow rate of three vacuum breaker assemblies was only about 18% greater than that of two vacuum breaker assemblies.
-(3)J With.an' adequate amount of noncondensibles returned to the drywelll ;
andi the drywell condensation rate rapidly reduced due; to a lower drywell - temperature. and - a lower mass ratio -~ of drywell'. steam to.
noncondensibles, the' effectiveness .of additional operating vacuum: [
breaker assemblies diminishes.
In' June 1989, a preliminary parametric ~ study was performed using LGS. data to evaluate the effects of one, four, and: five. vacuum breaker flow' paths on the ISA drywell depressurization transient. The results for drywell pressure, wetwell-to drywell differential pressure and drywe11' temperature are shown in the attached figures. The results further confirmed the conclusion that availability of more than two vacuum breaker flow paths will not significantly- affect' the: drywell:
negative peak pressure.
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REPT M 005, Revision 0 Description of the LGS ISA Analysis-3.0 COMPARISON OF THIS ISA ANALYSIS AND THAT IN REVISION 58 0F THE FSAR The initial conditions used for the ISA analysis detailed in Revision 58 of the
~ Limerick Generating l Station FSAR are _ specified in FSAR Table 6.2-9 and are based on-an earlier revision _ of the computer analysis (Revision 7 of Reference 4)l than -
was used for the current study; The results documented in:this report.are based
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on analysis using slightly different values for initial conditions such as'drywell and suppression- chamber gas volumes, temperatures, pressures, and downcomer
' submergence.
'In1 addition, review- .of case studies documented in earlier revisions . of the computer analysis indicate that the largest negative drywell pressure occurs when-the large containment purge valves are assumed to be'open at the time:of the LOCA which allows some of the noncondensibles to be blown _ out of the containment before the containment isolation valves-close. Although this is not a design basis assumption,-it was included in ' the current analysis in' order = to maximize the negative- drywell_ pressure for purposes of comparing the performance of two varsus !
three~ operable' vacuum bre'aker assemblies, j l
The effects that the . differences in initial conditions and / assumptions: have on l the results of the computer analysis can be noted by comparing the peak negative j
drywell pressure for three operable vacuum breaker assemblies. _-In-the design basis analysis, the peak negative drywell, pressure is -4.286 psig__(FSAR Section- J 6.2.1.1.4),' whereas in this analysis the ' peak negative drywell pressure for three operable vacuum breaker; assemblies is'-4;821 psig. ^ Since the; results of the- y cnalyses for three operable vacuum breaker assemblies showi that ' the larger ;
negative drywell pressure. occurs for the parameters used in the current analysis, !
these parameters would-also produce a larger negative drywell pressure for two ;
operable vacuum breaker assemblies. Using the design basis. parameters specified- !
in the FSAR the magnitude of the peak negative drywell pressure for_ two operating i vacuum breaker assemblies would be smaller than -4.845 psig. }
l In conclusion, the differences in the assumptions and initial conditions used for ~'
j this' analysis produce a result that is more conservative than-for. design basis conditions but do not affect the conclusion.that two-vacuum breaker assemblies are adequate to ensure containment integrity.- ,
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.REPT M 005, Revision-0 Description of the LGS ISA Analysis-I t
4.0 REFERENCES
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'1. .Bechtel Mechanical' Staff Calculation.VER-13
Subject:
- ; Inadvertent Spray "
Actuation 'ISA,-NE441, Rev. O, December ~1982.
r
- 2. Flow Test Results for AGCO's 24; CVil Vacuum Breaker Valve' Assembly, N05- '
9005-130~,. September 21,-1983,- Anderson,' Greenwood & Co.,. Houston, Texas.
~
- 3. - Performance and - Sizirg of Dry Pressure Containments , . BN-TOP.3 Rev. 4, Bechtel Power Corporation, March.1983,' Figure'2, 4 Bechtel Mechanical Staff Generic . Calculation, 1401,-'Rev 8 and Rev.:9,.
Project: Limerick Generating Station Unit 1,-
Subject:
. Inadvertent-Spray Mtuation' . Drywell Depressurization, ' April' 6, - 1984 and June - 20,~1989, respectively. t x
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Fig. 1.1 Drywell Pressure - 1, 2 & 3 VB Flow Paths LGS DRYWELL PRESSURE TRANSIENT 4
20 18 2
16 14 12 g 10 ,
S 8 -
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, -4 %- Ww k' W
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) TIME (SEC) :
3 VALVES --+- 2 VALVES -*-- 1 -VALVES
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O Fig.1.2 ' Drywell Pressure - 4 & S V8 Flow Paths LGS DRYWELL PRESSURE TRANSIENT '
20 ,
- y 18 { 5 1
16 --- '
14 -
l 12 - --- - - - -
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w 10 ,
!, . In ( -
a 8 ---- \ -- . '
v -
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in
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i en 4 - -- - - -
w i.
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a . 2 - ----- ' -
o-
-2 -
xx
-4 x . k. . .
-6 %i ES o%-
-8' 4 O' 40 80 120' 160 ' 200- -240 280 TIME (SEC) .
4 VALVES /_. 5 WEvE3 P
& s- -
--p3- --
3 % f5 y <eg 4 g 4c. o, v ,-s.aa .. , .-3.'. ,,,um -
m ..___-m,___1. .__-E,_wm,w ..
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Fig. 2.1 Wetwell to Drywell Differential Pressure - 1, 2, & 3 VB Flow Paths LGS WETWELL-DRYWELL PRESS DIFF. VS TIME 12 11 - N - -
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10 N ---
= - -
8 / \
7 *
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x \
& 4 "
k k :.
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'U' a 3 ___ k __
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.s 2 --
hl n 1 0
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-2
-3 "x
,m
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Y
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--6 0- -40 -80 120 160 200 240 280' TIME (SEC)
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- 3 VALVES 2 VALVES -* 1 VALVES'
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Fig. 2.2 Wetwell to Drywell Differential Pressure - 4 & 5 V8 Flow Paths
LGS -WETWELL-DRYWELL PRESS DIFF. VS TIME 12 11 - - - - -- -
, 10 --- --- --
9 --
8 -
7 -- --
6 t
G 5 - - -
- n. 4 -
h v w
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! -3 -- --
-4 .N l
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-S 86
, g _ ,1
-6 O 40 80' 120 160 200. -240' 280-i TIME (SEC) .
u 4 VALVES --*-- 5 WILVES
. L,- .. . ~. .,. , - , :: . . ,-.. , ,, ;,,.-..,- -~, . . . _ - , . _ - _ , _ _ _ _ _ _ _ . _.- __
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Fig. 3.1 Drywell Temperature - 1, 2 & 3 VB Flow Paths LGS DRYWELL TEMPERATURE TRANSIENT 260 250 \ ----
y 240 \, -
230 220 -
3 210 -
200 C 190-o 180 '
W o 170 k. -
160 y
y
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$ 150 '
Q 140 o'
w 130 k
$ 120.
3
$ 110--
100 \\
90 \\ -
-80 -\T 70 % FA
=
<y 60 - --
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-3 w- -
g g g '.
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0 40 80 120 160 200 240 280 TIME' (SEC) 3 VALVES -+-- 2 VALVES - -*- - 1 VALVES _
_ _ _ _ . _ _ _ . . _ . _ . ~ _ . . . . _ _ _ _ _ . _ - _ . _ _
. m, e. . _ . . . _ . . .
1-Fig. 3.2 Drywell Temperature - 4 & 5 VB Flow Paths LGS DRYWELL TEMPERATURE TRANSIENT 260 240 , - - - - -
f 220 T -- -
200 k 8
.n
- u j
o 180- - - - -
w O
v g 160 -- - - ---- -
- 1. x o,
' a k
e 140 i- - - -- - -
w (L
y 120 - -
w l-
-i 100
^
t
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so __ _ . --
ww (D rn - '
<T.
so - - - - -
1
's ~
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=a 40 o <n O-1 0 40 80 120 160- 200- 240 280 TIME (SEC).
o 4_ VALVES. -*- 5 WHEB
.-_ _- ,m , ._, : ... .1- ,,.:,-,, . . - - . _ - - . , , - . . , , , , . ',-c.-~~..4.,. ,.c . . . - , . . - ._.____-_-.s ._-_____m_m_ m.__,_.. __