ML20083F728
| ML20083F728 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 12/13/1983 |
| From: | Koenig J, Rich Smith, Spriggs G LOS ALAMOS NATIONAL LABORATORY |
| To: | NRC |
| Shared Package | |
| ML20083F721 | List: |
| References | |
| REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR NUDOCS 8401030323 | |
| Download: ML20083F728 (69) | |
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7 p ;Ti TRAC ANALYSES OF POTEhTIAL OVERC00 LING TRANSIENTS AT CALVERT CLIFFS-1 FOR PTS RISK ASSESSMENT
- Preliminary Summary by J. E. Koenig G. D. Spriggs
. R. C. Smith l
December 13, 1983 Update 1 ee t Work performed under the suspices of the U. S. Nuclear Regulatory Commission. 8401030323 831223 l PDR ADOCK 05000 , P l
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{ Table of Contents i i - i 1. Introduction t j 2. Model and Steady-state Calculations t
)
J
- 3. Transients 5
- 4. Transient 1 i
- 5. Ttansient 2 3
- 6. Transient 3
- 7. a. Transient 4
- b. Transient 4a
- 8. Ttansient 5
- 9. Transient 6
- 10. a. Transient 7
- b. Itansient 7a
- 11. Transient 8 .
- 12. Transient 9 l
- 13. Transient 10 -
- 14. Transient 11 e
t 4 i
}
ABBREVIATIONS ADV Atmospheric Duup Valve AFAS Auxiliary Feedvater Actuation Signal a ATW Auxiliary Feedwater Flow BC&E Baltimore Cas & Electric Co. CC Calvert Cliffs CE Combustion Engineering Inc. RFP Hot. Full Power steady-state conditions HPI High-Pressure Injection'
; HIP Hot. Zero Power steady-state conditions LOTW Loss of Feedwater MFIV Main Feedwater Isolation Valve MTRV Main Feedwater Regulating Valve
, MSIV Main Steam Isolation Valve
; NRC Nuclear Regulatory Commission ORNL Oak Ridge National Laboratory PORV Power-Operated Relief Valve PTS Pressurized thermal shock RCP Reactor Coolant Pump SC Steam Generator SCIS Steam Generator Isolation Signal SIAS Safety-injection Actuation Signal T3V Turbine-bypass Valve TSV Turbine-stop Valve 9
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_ ____-_______ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ . _________________________n
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[ 1. Introduction I i Reactor vessels in older plants have a risk of cracking if subjected to a l thermal shock with a subsequent system repressurization (referred to as
]
- pressurized thermal shock). After years of radiation exposure from the reactor j core, the vessel wall and welds become embrittled and their reference temperature for nil-ductility transition (RTET) increases. This means that as the fluence to the vessel wall and welds increases, the temperature at which it
+
i will crack increases. Overcooling transients that may bring the vessel wall temperature rapidly below its RTET followed by a primary reprersurization have been postulated to lead to FIS. For this reason, the NRC has identified this problem as Unresolved Safety Issue A-49 (USI A-49). A major effort among several organizations (BG&E, CE, NRC, ORNL, and Los Alamos) has been established to resolve the PTS issue. Intense cooperation of 30&E, CE, WRC, ORNL, and Los Alamos has been required to adequately address USI A-49. BG&E and CE have put extensive effort into supplying infor=ation about the plant and its operation. Los Alamos has taken this infor=ation and prepared a TRAC-PF1 model to calculate the thermal-hydraulic events of several postulated overcooling transients. TRAC-PF1 is a three-dimensional transient computer code for ther=al-hydraulic predictions. ORNL's job is both to specify the overcooling transients to be calculated by Los Alamos and to extend these calculations by predicting other postulated accidents. Also, ORNL will receive these data from Los Alamos so that fracture-mechanics analysis may be performed for transients that may be a FIS risk. The NRC oversees the entire project. Calvert Cliffs is a CE-vendored pressurized water reactor located on the Chesapeake Bay in Maryland. It is owned by the Baltimore Cas & Electric Co. Unit 1 of the Calvert Cliffs Nuclear Power Plant began operation in January 1975. Unit I has a 2x4 loop arfangement: two hot legs and two steam generators with four cold legs and four reactor coolant pumps. It presently operates at 2700 }Gth* The following pages briefly describe the TRAC-PF1 model, the steady-state conditions, and the transients calculated by Los Alamos. I 1 l i l i
!I 11 !I '
- 2. TRAC-PF1 Model and Steady-state Calculations
- 1 l
ji Figures 2.1-2.3 depict the basic TRAC noding of the Calvert Cliffs-1 power jj plant. Extensive technical information about the plant and its operation was j; received from both BC&E and CE. Using measured plant data for both steady-state and transient operations, the TRAC model was normalized to match these data. i il! l Slight variations in the basic noding are required to simulate each specific l transient. A brief summary of the basic TRAC model of Calvert Cliffs follows.
. (A more detailed description of the TRAC noding and applicable references are documented in an audit report to be issued at a later date.)
On the primary side, the three-dimensforal vessel is divided into 12 axial j levels, 2 radial rings, and 6 theta segments. The first level represents the ! a lower plenum. The inner ring of the second level is the lower core support ! assembly with levels 3-7 modeling the core region. The upper plenum is modeled with three 2evels. Two levels are used for the upper head to more accurately predict liquid draining from this region. The core barrel is the basis for the
, radial division in the vessel. The six theta segments allow for the six piping j penetrations in the vessel. Bypass flow paths including keyway, control-element-assembly shrouds and hot-leg connections, are modeled. Fictitious pipe components have been placed in the lower plenum to produce the correct net effect for loop-to-loop fluid mixing.
- /11 four cold legs are modeled separately. Because of some calculational j
difficulties, the steam generator is noded more finely for some of the calculations. (Figure 2.1 represents the more finely noded SG model.) Single-phase head and torque curves for the RCPs are provided by CE. The pressurizer model includes a lower " heating" section to simulate the region in which the backup and proportional heaters are located. The control of these heaters is modeled with the control system of the plant model. The TRAC model also contains the pertinent parts of the Calvert Cliffs control system. The three-mode and single-mode control on the feedwater
- regulating valves is modeled. Also, the main-feedwater pump speed controller j based on the pressure difference across the feedwater regulating valves is
- modeled. Valve control for the ADVs. TSVs. TBVs, SRVs, and PORVs is also 1
c:od eled.
- Two separate steady-state models are necessary to allow for the variations in plant conditions between hot, zero power and hot, full power. Tables 2.1 and 2.2 give the steady-state calculational results for the initial seven transients presented at the September 20-21, 1983 meeting in Baltimore. These numbers
- - reflect the information updates received f rom BC&E and CE following the TRAC ll model review meeting held at Los Alamos on June 27-28, 1983. The steam generator was renoded somewhat for the final six transients so that the steady-state calculations had to be rerun; the results did not vary significantly.
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i TABLE 2.1 Comparison Between TRAC and Design / Plant at Hot, Zero Power Conditions. j { cr Design / Plant TRAC Data Predictions PRIMARY SIDE Power 100 hours after shutdown Decay heat - 9.38 MW Pump power - 17.38 MW Pressure 15.52 MPs 15.52 MPa (2250 psia) (2250 psia) Mass Flow 19300 kg/s 19700 kg/s (42,549 lb/s) (43,431 lb/s) Average Temperature 550.9 K 551.8 K (5320F) 533.6 0 F) Pressurizer Level 3.68 m 3.68 m (144.0 inches) (144.0 inches) SECONDARY SIDE Teedwater flow per SC 10.1 kg/s 11.8 kg/s (22.3 lb/s) (26.0 lb/s) SC Dome Pressure SC 11 (TRAC 6.20 MPa 6.17 MPa
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component 22) (900 psis) (895.5 psia) SC 12 6.20 MPa 6.17 MPa (900 psia) (895.5 psia) Feedwater 299.8 0F 299.8 0F l Temperature (80.0 0F) (80.0 0F) l TBV % open - 5.0 SC Liquid Mass 102058 kg 102058 kg l (225,000 lb) (225,000 lb) l l l t '
t TABLE 2.2
,' Comparison Between TRAC and Design / Plant at . Full Power Conditions.
n. Design / Plant TRAC Data Predictions PRIMARY SIDE Core power 2694 MW 2700 MW Vessel flow -25.27 m3 /s 25.28 m3 /s (401.121 gpm) (401,324 spm) APy ,,,,y - 0.28 MPs (40.65 psid) 0.19 MPa 0.24 MPa AP'I (28.15 psid) (34.60 psid) LP loop 0.54 MPa 0.538 MPs (78.73 psid) (76.28 psid) T hot 585.7 K 585.6 K 0 (594.6 0F) . (595.1 F)
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T eoid 559.3 K 559.6 K (547.0 0F) (547.6 0F) AIvessel 26.4 K 26.4 K (47.6 0F) (47.5 0F) SECONDARY SIDE Feedvater flow
~
per SG 749 kg/s 737 kg/s (5.95 M1b/hr) (5.85 M1b/hr) SG Dome Pressure SG 11 5.90 MPs 5.90 MPa (856 psia) (852.9 psia) l SG 12 5.86 MPa 5.89 MPa (850 psia) (853.7 psia) l < . MFW Pump Discharge Pressure MFW 11 7.8 MPa 7.67 MPs (1130.7 psia) (1112.6 psia) ) MFW 12 7.63 MPs 7.57 MPa l (1106.7 psia) (1097.4 psia) s I t I
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I l 1 Feedwater 494.8 K 496.2 K - Temperature (431.0 F) (433.5 'F) MFRV I open ~90 88.9 0, SC liquid mass 62,350 kg 64,600 kg (137,458 lb) (142,419 lb) i 5 2 e 9 i 1 l l ! > i I l f
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- 3. Transients Table 3.1 summarizes the thirteen transients specified by ORNL. Four of ' the transients are steamline , breaks from hot, zero power conditions. The remaining nine transients are from hot full power and include three steamline break / valve failures, two primary breaks, one PORV/ADV failure, and two j runaway-feedwater cases.
Co= mon to all of these tran[ients (except in Transient 10) is the assumption that following SIAS the operator will manually trip all the RCPs. In addition, it is further assumed that no other operator intervention is allowed (except in Transient 11). Hence, once the HPI and charging flow are initiated, they are allowed to run unthrottled. During transients 'in which mass is not being Icst from the primary system, the pressurizer will completely refill and repressurize to the PORV setpoint. If ATW is initiated, it is assumed that the operator will not turn off the ATW system when the steam generators regain level. Therefore, it is possible during some of these transients to fill the SGs and start to fill the stes= lines with cold liquid. The following sections su==arize the results of these thirteen transients. Table 3.2 indicates the minimum downcomer liquid temperature and pressure and if the system repressurizes and if the flow stagnates in either one of the cold legs.
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e 4 TABLE 3.1 CALVERT CL*FFS-1 INITI AL PTS TRANSIEffr SPECIFICATIONS (AS SUPPLIED BY ORNL) Initial Equipment Plant Initiating Faltures on Operation No. Descriptive Title _ State _ Event Demand Actions 1 1-ft2 steam line break at Hot 0% 1.0-ft2 hole None None standby Power in steam line A 2 Full double ended guillotine Hot 0% Full steam- Auxiliary feed- None steam line break Power line break water ( AFW) is , not isolated
,-3 1-ft2 steam line break at 100% 1.0-ft2 hole None None bp full power , Power in steam line
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'4 Turbine-trip with turbine- 100% Turbine trip TBV sticks wide None I,b g,F 4
bypass valve (TBV) stuck open Power open 4a Turbine trip with one TBV TSV & MSIV and one MSIV stuck open stick open 5 Primary power-operated and 100% PORV transfers 1 ADV opens on None atmospheric-dump valve ( ADV) Power to wide open demand and stuck open sticks open 6 AFW overfeed after AFW 100% MFW system AFW delay AFW valves response failure Power trips off for 8 ntnutes opened fully at 8, minutes 7 Small break loss of coolant 100% An 0.02-ft2 None. None accident with blocked Power hole appears natural circulation in the hot leg Ses11 break LOCA wtth no 100% None None 7a artificial flow blockage Power 8 Main feedwater overfeed g,0$ Turbine trip Q RVs stick None
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, c Initial Equipment Plant Initiating Failures on Operation Descriptive Title State Event Demand Actions No.
9 Main feedwater overfeed to 100% Turbine trip 1 MFRV sticks None one'SG Power open 10 1ft2 steamline break Hot 1.0 ft2 hole None None i with 2 RCPs left operating 07, Power in steam line 11 Full double ended Hot Full steam line MSIVS fati to AFW turned guillotine steam line 0% Power break close off at 8 min. 4 4
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. TABLE 3.2
'I Summary of Minisua 'teeperatures and Pressures 'l , j Minimum Minimum Repressuri- Flov Transient T (K) P (MPa) urization Stagnation l 1 2 1 1.0 ft MSLB from BZP 395 4.8 yes yes { . 2 Double-ended MSLB from H2P ' 377 3.7 yes yes 3 1.0 ft2 MSLB from HFP 450 6.0 yes yes 3a Transient 3 rarun 468 6.6 yes yes 4 Stuck-open TBV from HFP 530 10.8 yes no 4a Transient 4 with one MSIV 500 11.4 yes no stuck open 5 Stuck-open PORV & ADV from HFP 407 6.0 no yes 6 Runaway AFW Following LOFW 375 6.5 yes yes from HFP 7 Hot-leg break from HFP 342 2.6 no specified-with forced flow blockage yes 7a Transient 7 with no blockage 440 3.8 no yes 8 Runaway-feedwater with 480 7.0 yes no 2 MTRVS stuck open 9 Transient 8 with 1 MFRV 490 6.4 yes yes stuck open 10 Transient 1 with 2 RCP 446 3.9 yes specified-running no 11 Transient 2 with 2 MSIV 376 4.5 yes no stuck open and no AFW after 8 min. 9 o
m---__-- __ - - - 1
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I j 3j 4. Transient 1 1.0 f t2 Main Steaaline Break Froe EZP , I
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2; This transient is initiated by a 0.0929 m2 2 (1.0 ft ) break in steamline A while the plant is at hot, sero power condicions. The break is q downstream of the flow restricter ,and upstream of the MSIV. Timing for the
; major events is summarized in Table 4.1. In this transient, the ADVs never
; open and the TBVs close immediately. Until SGIS is reached on low SG pressure of 4.6 MPa at 18.4 s, both SGs blow down. Af ter SGIS, SG B is isolated from the break by the closure of the MSIV. On the primary side, overcooling because of the blowdown of both SGs depressurizes the system
; below the SIAS setpoint of 12.1 MPs at 54.1 s. Thirty seconds later, the RCPs trip, an operator action specified by ORNL. No voiding occurs on the primary during the 7200 s transient.
SG A continues to depressurize af ter SGIS and reaches 1.0 MPa at about 1 200 s. AW flow to SG A has been valved out based on a SG pressure differential greater than 0. 8 MPa . The SG-A secondary drives a natural circulation flow of 500 kg/s in loop-A primary af ter the RCPs coast down around 200 s. This circulation continues until SG A dries out at 1325 s. ' Af ter this, a circulation flow of 250 kg/s continues, driven by the gravity head between the downeomer and upper plenum that is induced by the decay heat and the charging flow. This flow continues until 4100 m when natural circulation begins in loop B. SG B isolates at 18.4 s with a pressure of 4.6 MPa. A large mass inventory still remains and additionally, an AW flow of 20 kg/s begins at i 90.1 s. AW is injected at 277.4 K (40 0F). SG B secondary-side liquid becomes hotter than the primary side of loop B because of the cooling from SG A; reverse heat transfer opposes any natural circulation on loop B for the first 4100 s of the transient. At 3250 s, the SG-B secondary side fills co=pletely with liquid and a natural circulation flow of 300 kg/s begins on the secondary side of the SG. This mixes the colder liquid in the SG downcomer with the liquid in the tube region. This flow on the secondary
~
removes energy from the stagnant fluid on the primary side. By 4100 s, the energy removal from loop-B primary is enough to drive a natural circulation flow of about 350 kg/s in loop B. This flow reduces the circulation in loop i A from 250 kg/s to 50 kg/s. I t Figures 4.1-4.4 give the primary pressure, downeomer liquid temperature, heat-transfer coefficient at the vessel wall, and the downcomer liquid velocity. The HPI flow begins at about 50 s and ends at 1000 s. After this, flow from the charging pumps repressurizes the system, reaching the PORV ' setpoint at 3120 s. After this, the PORVs cycle to maintain a system l pressure of about 16.1 MPe. The downcener liquid temperature decreases to 395 K as a result of SG-A and SG-B secondary blowdown and from the HPI injection ana' charging flow. As the system pressure increases, the HP1 flow i terminates and the primary temperature levels off. Af ter SG A dries out at I
; 1325 s, primary temperature increases slightly. At 4100 s when natural l 1 circulation begins in loop B primary, the primary temperature decreases to
{ 420 K. The calculation is terminated at 7200 s, as specified by ORNL. l .' 4 fI) L. O c ..,v.- , .
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1 d li i TAB 1.E 4.1 li Transient 1 1.0 ft2 Main Steamline Break Fos BZP , Sequence of Events l q ' Time (s) Event Setpoint 0.0 0.0929 m 2 (1,o gg2 ) ysty g ,go,p A TBVs close i< 9.1 Pressurizer heaters trip off following 2.56 m low pressurizer level (101 inches) / 18.4 SGIS on low secondary pressure 4.61 MPa
- _ (653 psig) h 28.4 Asymmetric SG pressure 0.80 MPa
- (115 psia) i 54.1 SIAS on low primary pressure 12.1 MPa (1740 psig)
{* 70.0 HPI flow begins 8.87 MPa (1270 psig) l-l l 84.1 RCPs trip; high natural circulation in loop A begins l 90.9 AF. to SC 3 begins -4.3 m (-170 in) l 632.4 Pressurizer proportional heaters tripped 2.56 i-Sack on because of level recovery (101 inches) i.' 700.0 Minimum pressure of 4.8 MPa is reached I 1000.0 HPI flow ends (charging flow continues) 8.87 MPa (1270 psig) l. l 1?25.0 SG A dries out (natural circulation in loop A drops from 500 to 250 kg/s) j; 2800.0 Pressurizer heaters trip because of 15.7 MPa high system pressure (2275 psia) h 3120.0 System repressurizes to PORV setpoint 16.5 MPa (2400 psia) i, 3250.0 SG B fills with liquid and natural circulation j on secondary side begins - il "
- ) 4100.0 Natural circulation of 350 kg/s on loop B begins .
- I 7200.0 Calculation terminated (i
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, 5. Transient 2 l ,
l! Double-ended Main Steamline Break From HZP l 1 i This transient results from a double-ended guillotine break in steamline A j between the flow restictor and MSIV. Before the transient, the reactor is
! assumed to be off-line in an HZP condition and steam is being bled through the ' TBV to maintain secondary pressure at 6.20 MPa. Further, it is assumed that the operator f ails to isolate AFU to SG A when the asy==etric SG pressure signal is received.
The transient event sequence is su==arized in Table 5.1 and the system pressure, downcomer liquid temperature, heat-transfer coefficient, and liquid velocity are given in Figures 5.1-5.4. Basically, this transient generates severe conditions because continuous charging flow causes repressurization and AFW flow to a ruptured SG results in a very cold heat sink. Initially, depressurization of the secondary side following the break results in flashing and rapid cooling of the primary. The resulting pri=ary contraction causes SIAS on low pressure and the RCPs are tripped shortly af ter. Thereafter, natural circulation to the ruptured SG centinues to cool the primary towards the atmospheric boiling point, while H?I and charging flow reverse the primary voiding that occurred in the upper head and eventually refill the pressurizer and repressurize the system. The calculation was terminated at 3275 s because of time step limitations that resulted from liquid discharge through the pressurizer PORVs and safety valves. Hosever, at this point the pressure is =aintained between 15.7 and 16.5 - MPa by PORV cycling . and the downco=er te=perature is steady at 380 K with the SG-A heat sink at 373 K (boiling in SG A at at=ospheric pressure). These conditions are expected to re=ain stable until at least 7200 s because the charging flow will continue to maintain 'the pressure at the PORV setpoint, and decay power is sufficient to heat the AFW to the atmospheric boiling temperature. s 1 I s
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TABLE 5 1 1 Transient 2 ) 'a DOUBLE-ENDED STEAMLINE BREAK FROM HOT, ZERO POWER
.} ] Sequence of Events -s
'-! Time (s) Event Setpoint
.4 i 0.0 Double-ended break in loop A i
1.8 AFAS on low wide-range level in SG A -4.3 m a) MFIVs close (due to model error; (-170 inches) effect negligible) b) ATW delivered to both SGs 2.4 Pressurizer heaters trip off following 2.56 m low pressurizer level (101 inches) 9.1 SCIS isolates SG B 4.61 MPa (653 psig) 18.7 Asy etric SG pressure fails to isolate 0.8 MPa AW to SG A (115 psid) 41.2 SIAS 12.1 MPa (1740 psig) 65.0 HPI flow begins 8.8 MPa (1270 psig) 71.2 Operator trips all RCPs ., 90.0 Uppcr head begins voiding 350.0 Upper head refilled; repressurization begins 2980.0 PORVs open; pressure levels off 16.5 MPa (2400 psia) 3270.0 Calculation terminated; HPI flow continues; Conditions stable d i e
\
' ii - y .s i i
+ -
3
~ -
1 I i l , , too j 300 , , , Sto-
! . -too .
Sao-
~
- E
- s -
-4co 4 mo-i
- g. a ,,
T 1
-3oo de-1 Sto- "S
-200 aso-
=
32o- . soo 293 sono 2000 Sooo 4o00 Scom 6com 700o o toco twt (i) Fig. 5.1. Downcomer liquid temperature during Transient 2. (s io'
- 2450 te to'- ((f .
-2'a i..,,,.
- f750 u.io'-
Z T toio'- , a n s.oio. -!
- W g eso s s.Sio*-
7o0 a.mio'-
-~ 3**
2.oio'- o.o . .
-o rooo sooo .noo soon sooo 7000 sooo o sooo Twt (s)
Fig. 5.2. Downconer pressure during Transient 2. ( l i-)
l.
'l t
l 4 . . . . . . I
' l 1
~
j 3 . .w - 2- .
'S I
- s. -
o- - o
~^[
)
-s
-2 o woo roco sooo 4:co soc: scoo toco a:oo M (s)
Fig. 5.3. Downcomer liquid velocity in z-direction during Transient 2. 10000 sooo- . E 2000" moo-a000-S000-4000-E 3000-h3000-A 2000-e adoc sooo adoo edoo 8000 edoo 1o'00 a000 TIME W Fig. 5.4". Downcomer heat transfer coefficient during Transient 2. I i . I , 1
- - -. . . - - ~
! l
- i i 1 2
- 6. Transient 3*
2 1.0 ft Main Steamlina Break from Full Power This transient is initiated by a 0.0929 m2 (1.0 f t 2) break in steamline A while the plant is operating at full power. Table 6.1 tabulates the sequence of events that occurred during this transient and Figs. 6.1 - 6.4 give the parameters of interest. As seen in Figure 6.1, the primary fluid temperature reaches a minimum at the point in timecin which the broken steam generator dries out. All heat losses from the primary to the broken steam generator cease at this point. The primary fluid temperature begins to increase at this point because of the decay heat from the reactor core, and the energy transferred from the system structural material back into the fluid as the system seeks a new thermal equilibrium.
. A s=all amount of energy is continually being transferred with the intact-steam generator throughout the transient. Before 600 seconds, the primary temperature drops below the temperature of the secondary side of the intact SG resulting in heat being transferred from the secondary side to the primary.
This creates a gravity head in the steam generator tubes that opposes the gravity head created in the vessel, causing the intact steam generator loop to stagnate for the time period between 100 seconds and 600 seconds. As cold AFW continues to be supplied to the intact steam generator, the average temperature in the secondary side of the intact steam generator drops below the primary temperature, and heat transfer from the primary to the secondary side is reestablished. This now creates an additional gravity head in the intact-steam-generator tubes that acts in parallel to the gravity head created in the vessel between the downcomer and the core region. A natural circulation flow in the intact loop is. established that is approximately twice the natural circulation flow in the broken loop. The natural circulation in the broken loop is driven only by the gravity head in the vessel. At 1400 seconds, the primary system repressurizes because of the continued injection of charging flow. s
*This calculation was rerun in order to access the impact of an error in the initial liquid temperature in the pressurizer which lead to a primary depressurization that was much too rapid. (This error was present in the
! steady-state full power deck used during transients #3, #4, #5, and #8.) The initial 2500 s were recalculated. A revised sequence of events is shown Table 6.2. The original run section is retained to provide a means of extrapolating the Transient-3-rerun to 7200 s. l . . l i
- _ , _ . _ , , - , - - - y-,4 -- ,p---_,,_.2a , , . , _ , -%,_ g__ s_-g.,,.-,_ _ _.-.pq & . 7-w ~ ,i. -9., , ..,
. + . . . . . . . . . - . . . . . ~ . . . .. _. m . - - . .. ... -~ . . . . . s-i l
4 l ..' TABLE 6.1 1 Transient 3 l 1.0 ft2 MAIN STEAMLINE BREAK FROM FULL POWER Sequence of Events
! Time (s) Event Setpoint . 0.0 0.0929 m2 (1.0 ft )2 steamline break on loop A -
a) Turbine / reactor assumed to be tripped b) ADVs and TBVa open on " quick-open" logic 2.6 Pressurizer backup heater trip on 15.16 MPa because of low primary pressure (2200 psia) 15.5 SIAS on low primary pressure 12.1 MPa (1740 psig) 20.6 Pressurizer heaters tripped off following 2.56 m low pressurizer level (101 inches) 29.0 TSVs and ADVs close on low primary 552 K temperature (534 0F) 41.2 SGIS 4.6 MPa s) Feedwater pumps tripped off (668 psia) b) MFIVs and MSIVs begin to close 45.5 Reactor coolant pumps assumed to be manually tripped 49.2 Asy==etric SG pressure ob't'ained 0.8 MPs (115 psi) 64.0 HPI begins 197.9 AFAS initiated to intact SG because of -4.3 m low SG 1evel (-170 inches) 400.0 SG A dries out 545.5 Pressurizer proportional heaters tripped 2.56 m back on because of recovery of pressurizer level (101 inches) 610.0 HPI ends - charging flow continues 139*/.0 PORVs open because of high primary pressure 16.55 MPs l
. (2400 psia) 5000.0 3G B completely full (because of SG model error which underestimated SC volume by 37 m3 )
4 6300.0 Secondary SRVs on loop-B open on high 6.9 MPa
- steamline pressure (1000 psia) 7200.0 Calc'ulation terminated 4
,- .,.w... . . . , . - + . , . - . , . - .,n . ,,.. , , ,. ,
'o !. i 4
4 48 . . . . . . . 1 . g W * ' 'l i 3 k at it ' t i gtI' 98 'll Nfs i els e'e
-=
.d.- / .
, ud- = 1190 I 48-[ ..
-,g }
{ m L l s d_ .
- -700 dbd- -
gg.- e .- 363 l O CA . . . . . . O 200 2000 3000 4000 5000 6000 7000 8000 Tiut (s) , j rig. 6.1. Downcomer liquid temperature during Transient 3. 590 600 MO - e
--500 l 33o. .
i
) , - _ -
~
SCO-k, ~
-400 W 470 - y
\ 4 b 440 l
-SCO y l $ 410 -
1 ' 8 - 380-
. -200
- m. .
320- , go l _ 290 . . . . . . 7000 s000 l' O 1000 2000 3000 4000 S000 6000 ! Tiut (s) i Fig. 6.2. Downcomer pressure during Transient 3. >.ty l t 4 se
- I , . .
}
I i 4 . , , . .
- 88 3 ~
. s. ~ $
.4 s
=
1 5 5 I g gig.k.r-: .-;,:e- l 4 c..=.=.=.=.=.=.=. =.
..s
-2 o eco zoco scoo coo scoo s:co toco a:oo MM Fig. 6.3. Downcomer liquid velocity in z-direction during Transient 3.
icoe: oooo. seco- - F - Toco-l, oooo. sooo. neo- \ IE i
~
l Scoo-g l l _y ..-----=
. . . . . ~ , _ _ ..
~
2000- \ n q\ < j' .,. g A . W^- . . isoo. 9 ,,,, 7 .- . . k g ,kg-+ - - - e o moo zoco aooo moo sooo 2000 7000 8000 l MW j Tig. 6.4. Downcomer heat transfer coefficient during Transient 3. 1 i l I
< - - - - =- -
- I 1
.4
;I -: (
TABLE 6.2 Transient 3 - Rerun ' 2 $ 1.0 f t MAIN STEAMLINI BREAK FROM FULL POWER Sequence of Events -- Event Setpoint Time (s) O.0 0.0929 m2 (1.0 ft2) steamline break on loop A - - a) Turbine / reactor assumed to be tripped b) ADVs and TBVs open on " quick-open" logic 4.3 Pressurizer backup heater trip on 15.16 MPa (2200 psia) because of low primary pressure l 20.1 Pressurizer hesters tripped off following 2.56 m
- j. low pressurizer level (101 inches) j 29.0 TBVs aad ADVs close on low primary 552 K
! t emperature (534 0F) 32.2 SIAS on low primary pressure 12.1 MPa l (1740 psig) T 44.3 SGIS 4.6 MPa a) Feedwater pumps tripped off (668 psia) b) MFIVs and MSIVs begin to close 62.2 Reactor coolant pu=ps assumed to be
- manually tripped 52.5 Asymmetric SG pressure obtained '
0.8 MPa (115 psi) I 70.0 HPI begins j 58.4 AFAS initiated to intact SG because of -4.3 m low SG 1evel (-170 inches) i 30'0.0 SG A dries out 595.4 Pressurizer proportional heaters tripped 2.56 m back on because of recovery of pressurizer level (101 inches)
! 495.0 HPI ends - charging flow continues ,
1975.7 PORVs open because of high primary pressure 16.55 MPa (2400 psia) l ) 2500.0 Calculation terminated
-- - .m,, , . .
e
" e m+ m n
i: l l' . . 1 1
..I 7.a. Transient 4*
i Stuck-open TBV from BFP t !
-t 1 ' This transient is a simple loss-of-load from full power with the complication thst one TBV f ails to .. reseat. A summary of the major events is given in Table 7.1. The first 50 s are no different from a standard loss-of-load. With the TBV-failure, both SGs depressurize until SGIS based on low SG pressure of 4.6 MPa is reached at 509.1 s. For this transient the thermal-hydraulic behavior, both primary and secondary, is symmetric. On SCIS, the stuck-open TBV la isolated from the SG secondary and no longer plays a part in the transient.
Initially on the primary side, the turbine trip causes a reactor trip. Low primary pressure produces an SIAS at 28.4 s. The RCPs trip 30 s later at 58.4 s. The pressure is never low enough for HPI flow; only charging flow is injected. No voiding occurs on the primary side in this transient. Af ter SCIS, both SGs begin repressurizing from 4.6 MPa until the ADVs open on high primary temperature (greater than 552 K) at 1050 s. SG secondary side prescure is maintained at about 6.3 MPa until AFW begins at 4200 s. AFV is initiated based on low-low level in the SGs. The AFW injection gradually lovers the SG secondary side pressure. Figures 7.1-7.4 show the primary pressure, downcomer liquid temperature, downcomer heat-transfer coefficient, and downcomer liquid velocities for the transient. The primary pressure decreases initially because of the turbine-trip. The depressurization and cooling between 50 s and 509 s is a result of the TBV f ailure. After this, the primary side heats and pressurizes because of the SG secondary side isolation and charging flow. The PORV setpoint is reached at 1269.9 s. The primary initially cools because of the stuck-open TBV. After SCIS, the primary temperature becomes so high that the operation of the ADVs is necessary to prevent further primary heating. Because main feedwater has been valved out, the SG mass inventory eventually is low enough (because of flow out the ADVs) for AFW actuation at 4200 s. This injection cools the primary to 530 K by 5800 s. The calculation ended at 5800 s because of a code /model problem and will be continued if necessary. However, the downcomer temperature and pressure for the next 1400 s are predictable; it is expected that the downcomer temperature would reach a minimum of 510 K.
*The initial portion of this transient was rerun to determine the timing for the major events because of an error in the liquid temperature in the pressurizer.
(The same error addressed for Transient 3 in Section 6.) The initial portion corresponds to .0-570 s in Transient 4a.
~
( i I i l
- , t, ~e
2 TABLE 7.1 Transient 4 STUCK-OPEN TBV FROH HFP Sequence of Events
'l Setpoint Time (s) Event Reactor / Turbine trip O.0 ADVs and TBVs receive qu,1ck-open signal 28.4 SIAS on low primary pressure 12.1 MPa (1740 psig) 38.2 Pressurizer heaters tripped off 2.57 m due to low pressuriser level (101 inches) 50.0 All four TBVs should have resented but one failed; 552.4 K ADVs close (534.6 0F)
(900 psig) 58.4 RCPs trip 509.1 SGIS; Minimum pressure of 10.8 MPs 4.61 MPa l is reached (653 psig) j 1050.0 ADVs open on high primary temperature 552.4 K
, (534.60F) 835.5 Pressurizer proportional heaters tripped back on 2.56 m following level recovery (101 inches).
1100.0 Pressurizer proportional heaters tripped off 15.6 MPa
~
because of high system pressure (2275 psia) 1269.9 PORV setpoint is reached 16.5 MPa (2400 psia) 4200.0 AFAS -4.3 m (-170 inches) 4300.0 ADVs close on low primary 552.4 K temperature (534.6 *F) 5800.0 Minimum temperature of 530 K is reached (calculation ended-cooldown very slow) i H
p . l 300 . , . . . . . 800 980- - ~. S30- . -300
~. g ~
{
' 4#
l gyg . . l M- -
-3o0 410 - -
300- . 3 300 35o- - 320- - 10 0 233 . 1000 2000 5000 4000 5000 6000 7000 8000 Tiut (s) Fig. 7.1. Downcomer liquid te=perature during Transient 4. toiO' , L& to'- / fy'eY'5A M)Nykk-f,'gf[,f,jd',8g - tego?_ -2.o 4 10'- , .-1750 Z T 1410'-- .- n400 S 8Dio'- . Lo
..,. g 8A 60'- .
700 dbto'- .
. 2Dio'
~
t
., o.o .
, o 1 o 1000 200o 3000 400o 500o scoo 700o sooo
, IlWC (s)
Fig. 7.2. Downcomer pressure 'during Transient 4. i e
,,j g
3 . I, 4 . l 4 . . . , ,1,
- s. ,
. m
-1 l.
- 4 2- -
w
- 5 -
. 5 . t- - ' f -4 5
o- _ .
- -o $
8 [ 7 _ ___ .- .
.i
.s
-2 0 1000 2000 3000 4000 5000 6000 70C0 8000 Twt (s)
Fig. 7.3. Downcomer liquid velocity in z-direction during Transient 4. 100C0 , , s000- - a000- - E A 7000- - s000- - s000- - t:' 4000- - E q 3000- t I M " _N ' 2000- -~ - - . i e00 - 3
.-~ w s .,, ,r i o .
O 1000 2000 3000 4000 5000 6000 7000 8000
- Twt (s) i
- l Fig. 7.4. Downcomer heat transfer coefficient during Transient 4.
.i l
- l 1, .
..,y.- ., ,-.,,,.g._, .~ ,,
, , ._d,t.-
,,g _ y ,, t r ;;* ,, ,
.-{
. ;. p v :,' _
, - . , . . - ., -_n,, , . - . . _ . . , , . , , _ . . - .
i i
?
7.b. Transient 4A 1
' One TBV and MSIV Stuck Open from BFF j, .:-
Transient 4A is initiated by a turbine trip from full power conditions. A l sequence of events is given in Table 7.2 and Figs. 4.5-4.8 give a few key system i parameters. he first 85 s of the transient are no different from a normal
- loss-of-load transient. he TBVs and ADVs open because the primary temperature is above 552 K (5390F ). By 85 s , the TBVs begin closing but one fails to rescat, initiating a small stesaline
- break". he ADVs close normally.
he small " break" slowly begins cooling and depressurizing the primary. The conditions on each loop are identical before SGIS. Removal of the energy from the core and system metal depletes the liquid inventory on the secondary side of both SGs; AFAS is reached at 422 s. AW is then delivered to both SGs. By 470 s, the system pressure is low enough for SIAS, with the RCPs tripping 30 s later. The system presure is never low enough for the initiation of HPI flow, however. He at removal by the steam generators slows with the loss of i forced convection from the RCPs. SGIS occurs at 570 s with MSIV-A failing to close (the variation from Transient 4). The small main feedwater flow through the MFBVs ends at this time. The failed-valve induces asy=metries on the primary side with loop A having a higher natural circulation flow than loop B. At 639 s, AW is valved out to SG A based on an asymmetric pressure signal. Most of the energy is removed through SG A until it dries out at about 1750 s. Loop B flows then increases as SG B becomes the heat sink. The system repressurizes to the PORV setpoint by about 2500 s. ne calculation was terminated at this point because the request by ORh1 had been satisfied. his transient helps to address the effect of the error in Transient 4. Because some of the liquid in the pressurizer was erroneously subcooled initially, the primary side depressurized much too rapidly. A more accurata l~ timing for the events during 0-570 s is given in Table 4.2. The time for AFAS cannot be compared because in Transient 4 both SGs were bottled up after SGIS and mass was lost only af ter the ADVs opened on high primary temperature. The effect of SGIS occurring before or af ter AFAS would have some significance on the outcome of Transient 4. However, because of uncertainties in the behavior of instru=entation under transient conditions, the sequence of SGIS and AFAS may l be absolutely determined. 4 6
;1 I
i 1
\
l l
" " . 4 ie t ,} 's '
TABLE 7.2 TRANSIENT 4A . ONE TBV AND MSIV STUCK OPEN (FROM BPP) f 3 Sequence of Events i . Time (s) Event Setpoint 0 Turbine trip / reactor trip; T3Vs/ADVs " quick-open" 39 Pressurizer heaters trip 2.56 3 on low-low level (101 inches) 85 One TBV sticks while closing 522 K on low primary temperature (5340F) 135 ADVs c1cse on low primary 552 K temperature (5340 7) 422 AFAS on low SG liquid level 45,000 kg (AFW to both SG) (99,200 lbm) 470 SIAS on low primary pressure 12.1 MPa (1740 psig) 500 RCPs trip SIAS + 30 s
~
570 SGIS on low secondary 4.6 MPa pressure; MS1V-A sticks open (653 psig) 639 Asy= metric SG pressure (AFW to 0.8 MPa SG-B only) (115 psid) 1750 SG-A dries out
. 2092 Pressurizer proportional heaters 2.56 m trip back on because of (101 in) level recovery 2400 Pressurizer proportional heaters 15.7 MPa trip off because of high (2275 psia) system pressure 2500 PORV setpoint reached 16.5 Mrs (2400 psia) 2500 Calculation terminated
\
' * ' ~
.-:qt z ); ,
c
hl . . -
,t t
380 . . . 800
-{ . . . 1 esO- ,
33g.
. . -s00 sco- \* -
2 -
-400 E
*O .
- m. .
-300 4to - -
3e0 .
-200 3n0 .
- m. .
-PO 290 .
O 900 2000 3000 4 Coo SOC 3 Ecco 7000 1000 ht (s) Fig. 7.5. Downcomer liquid te=perature during Transient 4A. L810'
- 2450 t610'- - -
1410'- - t210'- -- f750
^
e A. 7 t* 'O,-_ - S _ woo
$ =
; . . ,0 - 3 -
).
-1050 f
s aiO*- - _y00 ab10'- -
,, ,0 .
=0 0.0 . . , . 0 0 1000 20u0 3000 4000 00C3 CD03 7C 3 SC00 mt (s) l Fig. 7.6. Downcomer pressure during Transient 4A. l I
, "l .,h* , s Gy
* ' y'
- ) ,
I 4 . . . . . . .
. 10 3-
. .} f 2-f
- g. .
4 , 0- . 0 u F' )
-1
--S
-2. .
0 200 2000 3000 4000 5000 GOOD 7000 8000 THE (s) Fig. 7.7 Downcomer liquid velocity during Transient 4A.
- 10000 9000-s000- -
7 - 7000- , C~ _ s000-a 5000-g 4000-IE t tg 3000- _ e%, - y . 2000-1000-o . . , , O. 1000 2000 3000 4000 5000 6000 7000 8000 Twt (s) Fig. 7.8 Downcomer heat-transfer ccefficient during Transient 4A.
- )
i
)
O'
l
- 8. Transient .5* l Stuck-open FORV and ADV From HFP
~
The transient was initiated from the steady-state run by opening one of the two PORVS completely. A summary of the transient events is given in Table 8.1.
? Figures 8.1-8.4 show the primary pressure, downcomer liquid temperatures, l ' downcomer heat-transfer coefficient and downcomer liquid velocities for the :
transient. From the beginning of the transie'nt, the system rapidly depressurizes to about 6 MPa. The reactor power trips on low pressure at 14.6 seconds and follows the decay-heat curvv. The HPI is initiated as the pressure falls below 12.1 MPa. The RCPs trip at 61.2 seconds and then follow the coast-down curve. The upper head begins to void at about 210 seconds and is completely vapor by 328 seconds; this is because of the residual heat stored in the vessel heat slabs. For the first 61 seconds, the mass flow rate through the core is essentially constant until the pumps trip. After the pump trip, the core mass flow rate drops with the pump speed. Following reactor trip at 15 seconds, the MW pumps for loops A and B begin to run back, the ADVs open, the TBVs open, and TSVs close. SCIS occurs at 836 s resulting in the closure of both the MFIVs and MSIVs. The AW activates at 3279 seconds into the transient when the level in SG A drops too low. However, due to asymmetric SG pressure exceeding 0.8 MPa, the AW flow is directed only to SG B which has the higher pressure. The pressure curve for the balance of the 7200 s transient is fairly smooth except for the dip at 2600 s that results from a rapid condensation of all of the vapor in the upper head. At about 7000 seconds, a pressure dip also occurs when the vapor condenses in the pressurizer dome. These pressure dips are probably physically unrealistic. The calculation was ter=inated at 7200 s.
*The authors wish to acknowledge Clay Booker of 1.os Alamos National Laboratory for performing this calculation.
i l l M
- - y .
j TABLE 8.1 Transient 5 STDCK-OPEN PORV AND ADV TROM HFP Sequence of Events 1 Event Setpoint Time (s) 0.0 PORV fails full open ., 14.6 Reactor / turbine trip 14.5 MPa TBVs/ADVs " quick open" (2100 psia) 31.2 SIAS 12.1 MPa (1740 psig) 61.2 RCPs are manually tripped 62.1 Pressurizer heater are tripped 2.56 m off based on low level (101 inches' 165.0 HPI flow begins 8.8 MPa (1270 psig) 210.0 Upper head in vessel voids 227.0 Loop-B ADV tloses while loop-A ADV sticks full open; TBVs close
- 846.0 SGIS 4.61.MPa a) Feedwater pumps tripped (653 psig) b) MFIVs and MS1Vs begin to close 1032.4 Asy==etric SG pressure signal 0.8 MPa is received . (115 psid) 2637.0 Upper head refills 32i9.0 AFAS (AFW to'SG B) -4.3 m
(-170 inches) 7200.0 Calculation terminated 114.7 Pessurizer proportional heaters 2.56 m trip on because of level recovery (101 inches) t I
I
)
i l 'I No . . . . . . . soo See-
- 888 , sac s
soo. - 2 .
+
-4ao E
,o .
44o. .
~
. son
}
a 4m- - no.
-2co me. .
saa. .
. .no 2s0 . .
o 10 o 0 2000 300o 4000 5000 6000 7000 800o NE (s) Fig. 8.1. Downcomer liquid temperature during Transient 5. 5000000 .
- 3aSO 16000000- -
W000000- - nDooooo- - -- uso l 00000o- -,,,, i ;
. js00cooo. -
3
-eso {
' ~ ' ' ~ * '
scooooo- -
-no ;
4000000- - 2000000-' - l o . , , , , . , o 9 1000 2 coo 300o 4000 S000 6000 700o 800o l MC(s) l ! Fig. 8.2. Downcomer pressure during Transient 5. , l l l I l W
l J 4 5 4 I 8 4 4 4 s- -
. -n s
3 E I
} '~
k
...s2%fM!&%%c==?~~' , _
--s
~2 . . .
o 1000 2000 3000 4000 500o 6000 7000 8o00 M (0 Fig. 8.3. Downce=er liquid velocity in z-direction during Transient 5. 10000 , , Soco- . soco- . SP 7000- . E sooo- . i o sooo- . sooo- . 2: sooo. .
$ r M i ip 3,, ,)
2000-
. b .
L ,,. IL D ti[' ay1 F..^ , . , -qi, . o . , o 5 00 2000 woo 4000 seco sooo 7eco acuo
- r. M (s)
( Fig. 8.4. Downcomer heat transfer coefficient during Transient 5.
)
1.
^
1 ? l l _ i
ii
- 9. Transient 6 i
! Runaway ATW Following 1,0FW from HFP
~l i This transient is assumed to result from a 1,0FW initiated by a MFW pump
.9 trip and followed by a 20-minute delay in AFW delivery. Furthermore, it la
} assumed that the operator deliberately, maximizes AFW flow to the SCs by fully
~
opening all of the AFW valves. A sequence-of-events summary is given in Table 9.1. Figures 9.1-9.4 give the system pressure, downconer temperature, heat-transfer coefficients, and downconer velocities for the transient. f The LOW causes rapid depletion of the SG inventories and by 36 s the reactor and turbine trip on a low-level signal from the SGs. The ADVs and TBVs
" quick open" as a result, and the transient proceeds as a total LOTW for the next 1200 s. SGIS occurs at 837 s which isolates the SGs. Dryout occurs at 898 s, at which time the PORVs open on high pressure. Although the primary begins to heat folicwing SG dryout, it does not saturate before AFW flow begins.
When the operator finally succeeds in activating the ATW system at 1200 s, the AW preferentially flows to SG B. This occurs because initial AW flow into each SC causes more condensation in SG B, and the resulting vacuum provides suction to divert essentially all of the AFW to SG B causing even more condensation to sustain the vacuum. However, by ~2300 s SG B and its steamline are water-solid, and the subsequent pressurization diverts AW to SG A. By
~2500 s, however, SG A and its secondary are also water-solid, and the secondary SRVs begin to lift to relieve the pressure. Because the steamlines,are slightly asy= metric and a slight pressure difference is sufficient to open an SRV enough to relieve the AFW flow, the relief occurs primarily through the SRV on the SG A steamline. ,
Between ~1900 s and ~2300 s when the AW is filling and cooling SG B, the flow in loop A of the primary stagnates. When this stagnation occurs SG B cools the primary enough to establish reverse heat transfer in SG A which opposes natural ciculation. Similarly, af ter ~3000 s the: flow in loop B stagnates because SG A receives almost all of the AFW and cools the primary below the SG-B temperature. If AFW flow was delivered equally to both SGs (with AFW valve control), this stagnation would not occur. By ~3200 s the HPI and charging flow refill the primary enough to , l repessurize the system to the HPI dead-head pressure, and thereaf ter charging ' flow alone continues to pressurize the system. By 5836 s the PORVs lift and j' begin cycling to relieve charging flow to the water-solid system. The calculation was terminated at 6152 s with the primary pressure cycling between the PORV setpoints, 15.7-16.5 MPa (2280-2400 psia). The downcomer liquid
- temperature is gradually decreasing from 370 K (2000 F) and AFW is flowing to SG A with stagnate, conditions in both SG B and loop B.
1 1 l L
- m.--g -
$ u-, .%,.---.m -- -
-e------e '
3 W, j' TABLE 9.1
- ' Transient 6 RUNAWAY AFW FOLLOWING LOFW FROM HFP Sequence of Events Event Setpoint Time (s) 0.0 Loss-of-feedvater to both.SGs because of MFW pump trip 36.0 Reactor and turbine trip on low -1.27 m ,
narrou-range SG 1evel; (-50 inches) ADVs and TBVs " quick open* 42.6 Pressurizer back-up heaters activate 15.2 MPa on low pressure (2200 psia) 2.56 m i 76.9 Pressurizer heaters trip off on low level in pressurizer (101 inche.) 537 Pressurizer proportional heater activate 2.56 m j when low-level trip clears (101 inches) I Pressurizer proportior.a1 heaters turn 15.5 MPa
- ~815 off at the setpoint (2250 psia) l SGIS on low SG pressure; 4.61 MPa 837 TBVs are isolated (653 psig) ,
j PORVs open on high pressure because 16.5 MPa 898 both SGs dry out (2400 psia) 5 1200 Operator activates all ATW pumps and fully opens all valves to both SGs j- PORVs close as secondary cooling 15.7 MPa
~1200 (2280 psia) is quickly recovered i Pressurizer proportional heaters 15.5 MPa activate as pressure falls (2240 psia)
SIAS occurs on low pressure 12.1 MPa 1229 l (1740 psig) ADVs close on low reactor temperature 552 K 1258 (535 F) 1259 Operator trips all RCPs Pressurizer proportional heaters trip 2.56 m 1279 off on low level in pressurizer (101 inches)
~1800 HPI flow resumes
- , ,,-a -
1 1 'i
~1900 Loop A stagnates
~2300 Loop A flow resumes
-c 2824 Pressurizer proportional heaters activate 2.56 m when low-level tri'p clears (101 inches) 2912 Pressurizer proportional heaters trip 2.56 m off on low level in pressurizer (101 inches)
~3000 Loop 3 stagnates 3070 Pressurizer proportional hesters activate 2.56 m when low-level trip clears (101 inches)
~3200 BPI pumps dead-head 8.89 MPa (1275 psia) 5836 PORVs open because primary is 16.5 MPa water-solid from charging flow (2400 psia) 6152 Calculation ter=inated with future conditions predictable 4
-% .-e ._. ._. ,
- w .. ._ ._ .. -- .__ ._.
s i f i 980 , , , 800 ,.
- se0- . .
t i sie. . see l F
- 2 .
o *M 9 g, _ g
" $ -soo y so- .
_ . 1
-200 3:0- -
330-se m 0 man : Coo sooo 4co0 300o .0oo ma sooO w 4) Fig. 9.1.'Downcocer liquid tenperature during Transient 6. 3 sac 5- \, ,
-rec w-j .
n-- .-1F30 T
} m- .
.. S O e .
e- - m 4-2 0 . 3 0 1000 3 00 3000 4000 4000 0000 70o0 80o0
- M h) 1 Fig. 9.2. Downcomer pressure during Transient 6. j
,.,a-5 -e. .,,
e
=_-- ,~ -.m I' '
. e
't
~l, i
\
1 1 i
.se s, ,,,, ,
il Ilgi .
'j-esoo
.$ 7 .
u .t. 2 00-
- 4 eens-u SoCo
$ m-
- h .
3 ""' :. 4[ i - hi f . k.. . meco- ; I
.k~. ..Dr t%
,/ . . N .
o lo0G EQ 4000 *GC0 3'000 M M 8# Tled (s) Fig. 9.3. Downcomer liquid velocity in z-direction during Transient 6. l }fI ll 4 1 "l
, ..e 3-]
I i c 2- '
' I
-t i
- 5
. i-g a
8- T , Sh
, e, , s'
. ., -l il!
, e Pk -
\. ! :a ...
- u. ,
l , ( -2 g--' 1 ,,,, 3 un ecco moo aos I m 11 *** i :, Fig. 9.4. Downcomer heat transfer coefficient during Transient 6. l-. , . -.g i> 0A
*j .
e'f LsM. i 7,. -, .,, mj.,e,- ; . , , ; _ - . . - _ y. .. . . _ . , ,
- .c ,
)
'i l
10.a. Transient 7 Hot-leg 3reak with Blocked Natural Circulation from HFP . LI . j l This transient is assumed to result from a .00186 m 2 (0.02 ft 2) break in ' j hot-leg A during RFP and is aggravated by an assumed loss of all natural
, circulation when the primary pressure falls below 7.93 MPs (1150 psig). A sequence-of-events sumanary is given in Table 10.1. Figures 10.1-10.4 give the system pressure, downcomer liquid temperatures, heat-transfer coefficient, and downcomer velocity for the transient.
The hot-leg break causes the primary to depressurire, and the reactor trips on low pressure in about 16 s. SIAS occurs at 34 s as the pressure continues to fall, and the RCPs are tripped 30 s later. By 110 s the primary pressure reaches 7.93 MPa (1150 psig), and natural circulation is terminated by co:pletely blocking the pri=ary inlets and outlets of both SGs. The sudden loss of heat sink and flow stagnation result in rapid core heatup, and bulk boiling co=mences within 60 s. The primary te=perature and pressure rise abruptly and peak at ~615 K (640 0F) and ~14.7 MPa (2130 psia), respectively, at ~600 s. Thereafter, both te=perature and pressure decrease as cold charging flow and HPI slowly refill the system and displace the relatively hot fluid being discharged at the hot-leg break. Nevertheless, bulk boiling persists until roughly 4500-5000 s when subcooling is finally regained. By 7200 s the primary pressure has fallen to ~2.8 MPa (400 psia), the downcocer temperature is ~340 K (15007) but the upper head is still voided. em M f 4 b
, ,, g ..,.
~l TABLE 10.1 Transient 7 2
'I ! 0.02 f t BOT-LEG BREAK FROM HTP Sequence of Events
'I Time (s) Event Setpoint ; 0.0 0.02 ft2 break appears in hot leg A 4.8 Pressurizer back-up heaters activate 15.2 MPa on low pressure (2200 psia) 15.7 Reactor trips on low pressure (thermal 14.5 MPa margin / low pressure); turbine trips simultaneously (2100 psia) 15.8 ADVs and TBVs " quick-open" on turbine trip 34.0 SIAS on low pressure 12.1 MPa (1740 psig) 34.5 Pressurizer heaters trip eff on low level 2.56 m (101 in.)
64.0 Operator trips all RCPs
~110 Bulk boiling in the core begins
-200 Upper head begins voiding
~4500 Subcooling in core returns 7200 Calculation ended e
9 0 0 m s "
- 6* , & %- ?6
l 300 , . . . . . 800 300- ~, 300
- m. .
i M-gyg. ) m- -
- 300 de- % -
380-
-200 360-320-
- - 10 0 290 0 1000 2000 3000 4000 5000 6000 7000 8000 Tiut (s)
Fig.10.1. Downcomer liquid temperature during Transient 7. L810' 2450 t>d- . 2mo 3 4.g. .
--fr50 t2 m'-
T g *** '
~6400
{ s.Se'- - iO50 "f som'- -
- 700 8 -
d.44 -
-- 350 2 o m'-
0.0 . 0 0 1000 2000 3000 4000 5000 6000 7000 8000
. rut (s)
Fig. 10.2. Downcomer pressure during Transient 7. I F *' .M *, * % , e s ,
, s- ,
^
)'d' . .~. . ~ l ~ ~---- - - = . - ~ . -- - - - - - - ~ - **-* '~~*
'! , .d e lI
'I 1
l 4 , , , , , , , t i', !
'I g. .
. -n 4
1 2- - r I' . 3
> g. .
1- tit.)${ '3gggar__. --- l
.g. -
.5
-2 O 10C0 2000 3000 4000 5000 C000 7000 8000 Tiut (s)
Fig. 10.3. Downcocer liquid velocity in z-direction during Transient 7. 4000c = 9000-g 3000-3 1000-
- t. . coo.
\
5000 - 4000-l 4 - o . , , , . .
. o anco anco sooo 4oo0 anco acoo sono acon TIME W Fig.10.4. Downcomer heat transfer coefficient during Transient 7.
s l
.i,'-
)-. _ _
9 i l i 10.b. Transient 7A Hot-leg Break (0.02 f t2) Without Flow Blockage from RFF .. l This transient is assumed to result from a .00186 a2 (0.02 ft2) break in hot-leg A during HTP. This transient differs from Transient 7 in that natural I circulation is not artificially blocked. A sequence of events summary is given i in Table 10.2. Figures 10.5 - 10.8 give the system pressure, downcesar liquid temperatures, heat transfer coefficient, and downcomer velocity for the
, transient.
The hot-leg break causes the primary to depressurize, and the reactor trips on low pressure in about 16 s. SIAS occurs at 24 s as the pressure continues to f all, and the RCPs are tripped 30 s later. As the RCPs coastdown the pressure f alls below the HPI pump dead-head and HPI flow rapidly begins to surpass the limited flow available from the positive-displacement charging pumps. By 502 s, the hot fluid discherred through the hot-leg break pressurizes the contain=ent to 4 psig, causing SGIS. SGIS isolates the TBVs but the effect l 1s minimal because the primary and secondary are essentially in thermal equilibrium. In fact, by 529 s the ADVs close as the primary temperature falls below 552 K (535 F). However, without the additional cooling from the open i ADVs, the cooling provided by the HP1 and hot-leg break is insufficient to I prevent the primary from gradually reheating to the ADVs' setpoint. The ADVs j reopen slightly,at 664 s but close permanently at 968 s. Af ter the ADVs close the seco'ndary sides of both SGs are bottled-up, and - the HPI flow causes the primary temperature to fall belo'w the secondarr. The resulting reverse heat transfer tends to retard natural circulation in the loops. By ~6500 s the reverse heat transfer in conjunction with flow ascaping through the break in hot leg A causes the flow to stagnate in loop A downstream of the break. The calculation was terminated at 6636 s with the primary pressure and downcomer temperatures gradually decreasing from ~3.5 MPa (500 psia) and ~440 K (330 T-), espectively. The. stagnate condition in loop A causes the cold-leg temperatures to fall below 350 K (1700 7), ) 9 4 r + = . . . - , . g s f
.m
t
. . e TABLE 10.2 Transient 7A 2 ;-
0.02 ft ROT-LEG BREAK WITHOUT FLOW BLOCKAGE FROM HTP Sequence of Events Event Setpoint Time (s) ) 0.0 0.02 ft 2 breakappearsilnhotlesA 4.8 Pressurizer back-up heaters activate 15.2 MPa on low pressure (2200 psia) 15.7 Reactor trips on low pressure (thermal 14.5 MPs margin / low pressure); turbine trips simultaneously (2100 psia) l 15.8 ADVs and TBVs " quick-open' on turbine trip 34.0 SIAS on low pressure; maximum charging 12.1 MPa i flow begina (1740 psig) 34.5 Pressurizer heaters trip off on low level 2.56 m (101 in.) 64.0 Operator trips all RCPs; HPI flow begins 8.8 MPa (1270 psig) 502 SCIS on high contain=ent pressure; 0.129 MPa TBVs are isolated ' (4 psig) 529 ADVs close on low reactor temperature 552 K (535 F) 664 ADVs open on high reactor temperature 552 K (535 F) 968 ADVs close on low reactor temperature 552 K (535 F)
~4500 Flow stagnates in loop A 6636 Calculation terminated 4
e e c g 4
i son . . o. sm -
. see g "" -
m E
,o c NS .
h hi . mo 410 . mo- . .
-ano no- .
ms
-90 m '
- o n.oo noo aooo sooo uroa sooo noa sooo M (s)
Fig. 10.5 Downcomer liquid te=perature during Transient 7A. mac s- .
,p ,-roo C- - -1750 1 1 6
g e - ... 1 n
" s- l -
E -( ess {
- e. .
7eo 4-I 2- -380 o o i o lovC- Joao 4001 acco novo 4000 7D00 scoo w (.) l l 1 l Fig. 10.6 Downconer pressure during Transient 7A. , l l
- 1 5'[ ,' * *
- e ,
.w
/-
e e a9* d , , 3- -
. s 3- .' .
l 1
.. : l 5
4
-__... 4 l
~ --- p- figjy,7,W,u E "*
p;..,_.
-S
-2 0 8000 2 00 3300 4000 toc 3 800o Neo sees wW l
Fig. 10.7 Downcomer liquid velocity in z-direction during Transient 7A. aco 9^00- - . w n- . 7 xco- . A sm- -
- N u socs -
800o- I - a i m e- r . 3 itt-- - di a am s(
=m%
_ L.. s ., . 34-
. e moo anos mo . coo tooo esos moo esse wW Fig. 10.8 Downcomer heat transfer coefficient during Transient 7A.
I { i l-f
! l
- 11. Transient 8 Two Stuck-Open MTRVs from HFP ,,
l This transient is initiated by a failure of both main feedwatcr regulating , i valves to close following a turbine trip. Table 11.1 tabulates the sequence of I events that occurred during this transient, and Figures 11.1-11.4 show the time history of the requested parameters. ,., As seen in Figure 11.1, the primary fluid temperature reaches a minimum and the MFW pumps trip on low suction pressure following loss of liquid inventory in tha condenser /hotwells. The steam lines are partially filled at this time; however, the void fraction downstream of the MSIVs remained so large during this interim that adequate high quality steam was continuously delivered to the MFW pu:np turbines prior to the low suction prassure trip. Following the MFW pump trip, decay heat and energy transferred from the system structural material back into the primary fluid exceeds the heat being transferred into the relatively colder SGs, resulting in primary fluid heating. The pri=ary system repressurizes to the PORV setpoint because of the heatup and the charging flow refilling the primary system. e 9
+
4
a . . i
; TABLE 11.1 Transient 8 ; Two Stuck-Open MTRVs from HFP _
Sequence of Events Time (s) Event Setpoint 0.0 Turbine / Reactor trip; main feedwater regulating valves fail to close; ADVs and TBV open on -
" quick-open" logic 3.4 Pressurizer backup heaters trip on 15.2 MPa following low primary pressure (2200 psia) 26.4 SIAS 12.1 MPa (1740 psig) 33.5 Pressurizer heaters trip off following low 2.56 m level in pressurizer (101 inches) 51.7 High level in SGs 1.27 m (53 inches) 56.4 Reactor coolant pumps assumed to be -
manually tripped off 30 s after SIAS 60.0 ADVs close
- 120.0 SGs completely liquid full .18x106 g
(.397x10 lb) 156.0 HPI begins 217.9 MFW pumps trip off following loss of liquid .291x106 kg inventory in condenser /hotwells 6 4 (.642x10 lb) 490.0 HPI ends 629.9 Pressurizer proportional heaters trip on fol- 2.56 m lowing level recovery in Pressurizer (101 inches) 2131.2 Pressurizer proportional hanters trip off 15.34 MPa following high primary pressure (2275 psia) 2310.1 PORVs open following high primary pressure 16.55 MPa (2400 psia) 7200.0 Calculation terminated - I d e w n
, ..,,n,. - - - - --
e. i
- Mo . . i i i . Soo i eso- .-
', 330 4soo M-l a. :~ -
M-
- -3co g i 45-38o-l
- -2co 350-32o-too 29o o too 2cCo 3 moo sooo Soon 6oDo 7ooo Sooo TNI(s)
Fig. 11.1. Downcomer liquid temperature during Transient 8. to to'
- 245m wo' ('lTa#17.'.",.t#'lllM"l1#02$24 i
i
-25*
u.io,. ._ -
-- oso u.to'-[
Z ) T gt >to - .
. ,,,, a 5 Y d
{ saio*. - s o to*-
-ioso f
- -roo Abio'- -
2 bio'-~ . o.o o o icoo 2ooo 3 coo 4o0a sooo sooo voco sooo indt (s) Fig.11.2. Downcomer pressure during Transient 8. i
- ~ .
9
j . . 1 l 1 1 4
.I 4 . . . . . .
J
~ ,4
.=
.-9
- g.-
4 d 2-
-5
> g.
N N i -
- r. ,-=_..- - - _ -
l F 1
.5
-2 8000 0 200 20C0 3000 4000 5000 6000 7000 T'ut (s)
Fig. 11.3. Downec=er liquid velocity in z-di:.ection during Transient 8. se000 9000-S000-p . 7000-B S000-S000-4000-E \ - Q 3000-M . . _p " - 2000- ) k_ - y %- ~ , m -- 1 l -
=00 - _
0 0 1000 2000 3000 4000 5000 6000 7000 8000 Tiut (s) Fig. 11.4. Downcomer heat transfer coefficient during Transient 8. l l 1 l l
, ---< - - - - ,- . . . - . . , . ~ .
- 12. Transient 9 One Stuck-Open MTRV from HFP -
Transient 9 is initiated when the turbine trips from hot, full power conditions. Normally, both MTRVs would closa in 20 s and both MFBVs would open to allow 5% steady-state MFW flow. However, in this transient, the MTRV in loop A f ails to close allowing full feedwater flow until the MFW pumps trip. This trip could occur on low condenser /hotwell inven:ory or a low void fraction in the steamlines that drive the turbines of the MFW pumps. This transient was performed to determine if flow stagnation occurs in the intact pri=ary loop, a situation in which PTS to the reactor vessel can be of concern. The pri=ary pressure, liquid te=perature, velocity, and heat-transfer coefficient in the vessel flows are given in Figs. 12.1 - 12.4. The turbine trip causes the reactor to trip and a quick-open signal to be sent to the ADVs and TBVs. MTRV-B closes in 20 s as required but MTRV-A re=ains open delivering the full feedwater flow of 740 kg/s (5.85 Mlb/hr) or = ore to SG A. Because the turbine has tripped and no steam is available to heat the feedwater the feedwater temperature continually decreases. The " runaway" feedwater overcools the primary until the MFW pu=ps trip at 303 s on low condenser /hotwell inventory. On the pri=ary in loop A, high heat transfer drives a natural circulation flow of about 400 kg/s after the RCPs trip at 153 s. On loop B, the SG secondary liquid is hotter than the primary liquid and flou stagnation does occur between 500 and 1000 s. The system pressure is low enough for HPI injection flow between 250 and 600 s so that the peried of flow stagnation overlaps so=ewhat with HPI flow. These conditions can be of interest in the PTS analysis. - The primary fluid cooling ends when the MFW flow ends and heating begins as-the HPI flow stops. Charging flow repessurizes the system to the PORV setpoint at 1850 s. The fluid heating (from core decay heat ed the system metal) creates a driving force in SG B which causes a naturr.1 circulation flow in loop B also. Both loops have natural circulation flows of about 400 kg/s. AFAS occurs on low liquid inventory in SC B at 4800 s; this provides a small amount of additional cooling. The calculation was ter=inated at 5800 s; the primary pressure and temperature can be extrapolated to be 16.1 MPa and 520 K by 7200 s. 9
- ( '
e TABLE 12.1 , Transient 9 One Stuck-Open MFRV from BFP Sequence of Events Time (s) Event ', Setpoint
' O Turbine trip / reactor trip TBVs/ADVs receive quick-open signal 34 Pressurizer heaters trip off based 2.56 m on low-low level (101 in) 75 ADVs close on low primary 552 K te=perature (534 F) 123 SIAS on low primary pressure 12.1 H?a (1740 psig) 126 Feedwater-heater-drain tank flow trips off on low level 153 RCPs trip 30 s after SIAS 250 HPI flow begins 8.87 MPa (1270 psig) 303 MFW pumps trip on low condenser /hotwell .291x106 Kg inventory (.642x10 6 lb) 303 TBV closes on low secondary 6.17 MPa pressure (895.5 psia) 600 HPI flow ends as system pressure 8.87 MPa recovera (1270 psig) 665 Pressurizar proportional heaters 2.57 m tripped back on because of level recovery (101 in) 1700 Pressurizer proportional heaters 15.7 MPs tripped off because of high system (2275 psia) pressure 1850 PORV setpoint reached 16.5 MPs 2400 psia)
. 2650 ADV/TBV reopen on high primary 552 K temperature (534 F)
~
3' 45,000 kg 4800 AFAS on low liquid inventory 7j (99,200 lba) j 5800 Calculation terminated h . .; g , . g.. ~ ~ _ , , -
neo . . . . -eas
~
ene- . . j gie.4 . 888 4 see-2 . .se E es. s
- m. .
. .aos ee- -
ase. - ass ane- - a -
- m. -
nc , . . o soo seco sooo acco sooo sooo moo sooe M (4 Fig. 12.1. Downcomer liquid te=perature during Transient 9. woooooc , wooooon / k% Y W M Y,$ W l[ - ame woooooo. .. . goooooo - 05o Z T
-- a L
- eoooooo -
I,
. mea j eoococe -
Me m . l ano e . . .
. . -e e soo sooo soon eoso sooe cose noo sooo
. MM -
) Fig. 12.2. Downcomer pressure during Transient 9.
h e k
' ~
~ * ._ , .= s
1 l.
-i i s , , , , -
- s q
1 .
~ % . _ _._
1 - _ 1
-s :
*E- l a.
-4 1
..s *
. l .
< 1 l
-s- .
.as
-as l
- ..se
-4 , , . . .
0 900 2000 3000 4CC3 3000 4000 Poes teos M (s) 1 1 Fig. 12.3. Downcomer liquid velocity in z-direction during Transient 9. 3t006 . > > p, . m. i r- ,
. moos .
N 33.e. t E -
.3 .
, mee-ses- _-
Mg-x^ ^ W i , l e 8 5 5 S m m m H H t wW i .h Fig. 12.~4. Downcomer heat transfer coefficient during Transient 9. l* 'i ? l. l (. I s
+,';.
e * *n*;
c- - _ _ _ _ _ _ _ _ _ _ - ____- __ ______ _____ __
- 13. Transient 10 1.0 ft2 MSLB with 2 RCP from HZP
~
This transient is the same as Transient 1 except that only two of the four l RCPs are tripped 30 e efter SIAS. This, of course, changes the nature of the entire transient. Flow stegnation is not of PTS concern in this transient; only a low bulk fluid temperature would be .of PTS interest. Table 13.1 lists the sequence of events for the transient and Figs. 13.1-13.4 give a few system para =eters. Transient 1 and Transient 10 should be identical until the RCPs trip at 112 s. However, because of model changes to the steam generator and pressurizer, the timing of the two transients are not the same. The discrepancies in timing give an indication of the sensitivities involved in the calculations. Following the break in steamline A, both SG rapidly blow down. SGIS occurs at 34 s, isolating SG B. By 45 s, the pressure differential between the SGs causes the AFW-valves to SG A to close (although AW has not initiated). The SIAS setpoint is reached at 82 s with 2 diagonally-opposite RCPs tripping 30 s later. The forced-convection flow drops to about 50% steady-state flow in the hot legs. In the cold legs, the two operating RCPs pump about 70% steady-state flow with 20% reverse flow in the cold legs with tripped RCPs.
. With two pu=ps in operation, much higher heat-transfer rates occur in both SGs.
*4hile SG A removes energy more rapidly than in Transient 1, SG B adds considerably more energy to the primary during 80-500 s. The net result is that the minimum pri=ary te=perature is 50 K Mgher in Transient 10 than in Transient 1. ,
HPI flow initiates at 115 s. AFAS is based on a collapsed-liquid level in Transient 10 as opposed to a Ap-=easurement in Transient 1. AFW is delivered to SG B only at 222 s based on a low liquid inventory in SG A. SG A dries ou*. by 500 s, at which time the primary te=perature begins increasing slightly. HPI and charging flow repressurize the system until the shutoff head of the HPI pu=ps is reached at 930 s;. charging flow then brings the system pressure to the PORV setpoint at 2406 s. Because 2 RCPs are operating and velocities are relatively high, the Courant limit keeps the time step fairly low. This limit resulted in a slow-running problem and so the calculation was ter=inated at 5300 s. The system pressure is at the PORV setpoint and the primary te=perature will probably re=ain around 450 K for the rest of the transient. d
TABLE 13.1
;} Transient 10 j 1.0 ft2 MSLB WITH 2 BCP FROM BZP -.
i
) Sequence of Events
'i
.) Time (s) Event Setpoint
,] O 0.0929 3 2 (1,o ft )'~g3L3 2 in loop A, TBVs close 22 Pressurizer heaters trip off 2.56 m on low-low level (101 inches) 34 SGIS 4.6 MPs (653 psig) 45 Asy: metric SG pressure 0.8 MPa (115 psid) 82 SIAS 12.1 MPa (1740 psig) 112 Two of the four RCPs are tripped SIAS+30 s 115 HPI flow begins 8.8 MPa (1270 psig) 222 AFAS - -4.3 m
- (-170 inches) 500 SG A driec out
, 579 Pressurizer proportional heaters 2.56 m tripped back oa because of level recovery (101 inches)
- 930 Pressurizer heaters tripped of on high 15.6 MPa I pressure; HPI flow ends (2275 psia) 2406 PORV setpoint reached 16.5 MPa (2400 psia) 5300 Calculation terminated; conditions stable 9
i 4
l
]
1 1, 300 , , . . . -e00
*e
- m. .
s
.-300 ej 53o.
1
.t s00-E . aCo 8
,,o . . .
. 440-
. 3ao se0-
- 200
- m. -
,uo . .
- 10 0 ree-O moa 2000 3000 4000 $c00 6000 7000 8.900 Twt (s)
Fig. 13.1. Downcomer liquid temperature during Transient 10. 1810'
- -240 ts ic'- 4'.[p //rbdf M l -
t4.to'-( , 6 t;.go'.-I --1750 Z T toio'- -. ,, 3 i*' - iE B.0 $0'.
* -1050 [
... 0 -
a.s10'. V f -
-700 i - 35'
(. 2.>,c .
, c.o . .
.0 0 1000 7000 3000 4000 5000 Gooi 7000 8000 t
Twt (s) l Fig. 13.2. Downcomer pressure during Transient 10. I'i l I 1 g gg .
1 i
+ - .i 1
t l
' \
-d . . .
-a l
.s_ . .
--as i
f 5 .p. - I I
..as *
-s- -
-* -..so
-te o imo mo soon sooo sono c. con reno sooo ME (5)
Fig.13.3. Downcomer liquid velocity in z-direction during Transient 10. 31ooo 279o0 - assoo-
? ~ .
. 2non.
960o- - N u esco- -
= s____
unco- %. -
, s 93co -
stoo - 3Co-o . o ano soon . woo sono soon rooo icos sooo mt (s) Fig. 13.4. Downcomer heat transfer coefficient during Transient 10. e 1 l E e
-w - . - ,
e- e- - , - --g-
i
- 14. Transient 11 Double ended Steam Line Break from RZF with '
Stuck Open MSlVs This transient is initiated by a double-ended guillotine break in stesaline A between the flow rerrtrictor and the MSlV. It is asssssed that when SG15 is obtained due to low SG pressure that the MSIVs fail to close. Hence, both SGs continue to blowdown. It was farther specified that the operator would turn off tra cuxiliary feedwater system eight minutes into the transient. Table 14.1 tabulates the sequence of events that occurred during this transient, and Figures 14.1-14.4 show the time history of requested parameters. As seen in Figure 14.1, the primary fluid tetsperature reaches a sinfaum temperature of 376 K and levels off at that value. This temperature corrasponds to a few degrees above the temperature of the water remaining in the bc :toin of each SG following the bicwdown to .1 MPA (1 ata.) of the secondar- side. Because of the decay heat from the core and the energy transferred f rom the structural material to the primary fluid, each SG is operating at approximately 9 Mw. This power continues to slowly boil off the water remaining in each SG at a rate of approxi=ately 4 kg/s per SG. The power produced by the decay of the heat slabs is expected to decay to zero as the slab temperatures come into thermal equilibritan with the primary fluid. The power to each SG from the core decay heat will eventually approach 4.65 Mw and the boiling rate will decrease to approximately 2 kg/s per SG. Based upon an extrapolation procedure, it is estimated that each SG will dry out at approximately 6350 seconds. The primary system repressurizes to the PORV setpoint because of the charging flow refilling the primarf system liquid solid. O A e 8
, e -
1 l l l TABLE 14-1 Transient 11 Double-Inded Steam Line Break with Stuck Open MSrfs e Sequence of, Events Time Event Se t point r 0.0 Double-Ended steam line break on loop A - 6.0 Pressurizer backup heaters trip on due to low primary preesure 2200 psia 11.2 SCIS 4.6 MPs (668 psia) 12.8 Pressurizer heater tripped off following 2.56 m low pressurizer level (101 inches) 32.2 SIAS 12.1 MPa (1740 psig) 37.5 HPI begins 8.65 MPa (1250 psis) 62.2 RCFs assumed to be manually tripped - - 91.9 AFAS (based upon collapsed liquid level) -4.3 m (-170 inches) 480.0 Operator assumed to turn of f aux feed - to both SGs 654.8 Pressurizer proportional heaters tripped on - following pressurizer level recovery 1250.0 HPI ends 8.65 MPa (1240 peig) 2444.3 PORVs open due to high primary pressure 16.55 MPa 3300.0 calculation terminsted 6350.0 SGs dry out (based upon extrapolation) l l i i , - - - - , l
-- ....___...m_--._ ._. \
t T wo . . . . soo soo-sm-
. set I soo.
g no-ue - -
-soo ato -
soo- m. --
.aoo m-aro- - too 29o o tooo 700o Sooo 40oo Sooo 6ooo 7ooo Acco TWC (s)
Fig.14.1. Downcomer liquid temperature during Transient 11. 181o'
- 2A50 t&to'- ,
LA io'-
' ' .- 175 o 12.lo'-
Z .
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S toio'- . ,, U . g a.ote'-
.eSo
' s.oio'-'
-7Do 4.0 10'-
~
'N pg .8
. o o.o . 7ooo sooo o moo 70o0 sooo 400o soon sooo TWC (i)
Fig. '14.2. Downcomer pressure during Transient 11. I A r
4 l ' o* i
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d . . . . 3- ee 2- - 3
" t- - y b< d R
1 0- (C 43 pr - 0 $ g P
..s
-2 0 1000 7000 3030 4000 S000 f00G 7000 A*40 T1wE (s)
Fig.14.3. Dowscoser liquid velocity in z-direction during Transient 11. , ex: i 9000-8000-7 - 7o00-3 5000-5000-
, 40C0-E q 3000-T I 2000-I 1000-g=. -
4 0 . . 0 1000 2000 3000 4000 5000 6000 7000 8000
. M (s)
Fig. 14.4. Downconer heat transfer coefficient during Transient 11. l' l-e l l l 1
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