ML17266A446
| ML17266A446 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 04/20/1981 |
| From: | Jurgensen R WESTINGHOUSE OPERATING PLANTS OWNERS GROUP |
| To: | Check P Office of Nuclear Reactor Regulation |
| References | |
| IEC-80-15, OG-57, NUDOCS 8104280433 | |
| Download: ML17266A446 (105) | |
Text
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- EGUL'AT INFORMATION DISTR IBUTIO
.YSTEM (BIDS)
ACCESSION NOR: 8100280033 DOC ~ DATE: 81/04/20 NOTARIZED:
NO FACII::So-33S St. Lucie Plantr Unit ir Florida Power tt, Light Co ~
"AUTH~ NAME AUTHOR AFFII IATION JURGENSENrR,WE Westinghouse Operating Plants Owners Group REC lP 0 i'IAMB~
RECIPIENT AFFILIATION CHECKrP AS, Assistant Director for Plant Systems
SUBJECT:
For wards descr iptionrassumptions 8 results of study to ascertain potential for void formation
'in Westinghouse designed NSSS s during natUral circulations cooldown/depressur 1 za t i oner a si ants, DISTRIBUTION CODE:
A001S WOPIES RECEIVED:LTR J ENCL J SIZE: tr e TITLE: General Distribution for after Issuance of Operating License'OTES:
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&AERICANELKC7RJC POVIER Service Corporation 2 BroadToay, iVew York,iV. F. 10004 (212) 440-9000 Apri1 20, 1981 OG-57 Mr. Paul S.
Check Assistant Director for Plant Systems Division of Systems Integration U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue
- Bethesda, Maryland 20014 E,:T
'0+ cP ~ -9
Dear Mr. Check:
ST.
LUCIE COOLOOI'lR EVEIIT REPORT
(~'(X
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'I On June ll, 1980, a total loss of component cooling water flow to the reactor coolant pumps occurred at the St. Lucie Unit 1 plant.
When the cooling flow could not be restored in the time limit specified by the plants Technical Specifications, the reactor was manually tripped.
Within two minutes after the reactor trip, the reactor coolant pumps were also manually tripped.
Approximately 27 minutes later natural circulation cooldown was initiated.
It is evident that void formation occurred in the upper head region of the reactor vessel during the natural circulation cooldown at St. Lucie.
Apparently, the fluid in the upper head was much hotter than the rest of the primary system.
It is postulated that the steam bubble in the upper head area was produced when the system pressure dropped. below the saturation pressure corresponding to the temperature of the fluid in the upper head.
After the St. Lucie incident, the NRC recommended various action items for power reactor licensee consideration.
These items are listed in IE Circular 80-15 and include establishing a natural circulation cooldown/depressurization rate envelope to preclude void formation.
Subsequent to this, the Westinghouse Owners Group undertook a study with Westinghouse to ascertain the potential for void formation in Westinghouse designed NSSS's during natural circulation cooldown/depressurization transients and to develop appropriate modifications to Westinghouse Owners Group Reference Operating Instructions.
A description of the study, including major assumptions and results, is attached.
The Westinghouse Owners Group Reference Abnormal Operating Instructions are being modified to take the results of the study into account so as to preclude void formation in the upper head-region during natural circulation cooldown/
depressurization transients, and to specify those conditions under which 9" c upper head voiding may occur.
8104880'I $5 Very truly yours,
/pab Attachment Robert W. Jurge n,
airman Westinghouse 0
ers oup
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I.
INTRODUCTION On June ll, 1980, a total loss of component cooling water flow to the reactor coolant pumas occurred at the St. Lucie Unit 1 plant.
An elec-trical short across a solenoid valve terminal board caused one of the two series containment isolation valves in the component cooling water return from all reactor coolant pumps to fail shut.
When the cooling flow could not be restored in the time limit specified by the plants Technical Specifications, the reactor was manually tripped.
Within two minutes after the reactor trip, the reactor coolant pumps were also manual ly tripped.
Approximately 27 minutes later natural circulation cooldown was initiated.
Based on pressurizer level and primary system pressure response it is evident that void formation occurred in the upper head region during the natural circulation cooldown.
At St. Lucie, the measured hot and cold leg temperatures at the time of voiding were highly subcooled.
It appears that the fluid in the upper head was much hotter, relatively stagnant and in poor communication with the rest of the primary system.
It is postulated that the steam bubble in the upper head area was pro-duced when the system pressure dropped below the saturation pressure corresponding to the temperature of the fluid in the upper head.
The objectives of this study are twofold. First, the potential for void foriTiation in Westinghouse designed NSSS's during natural circulation cooldown/depressurization transients and the conditions under which such voiding (if any) can occur is to be established.
- Second, potential modifications to Westinghouse Owners'roup Reference Operating Instruc-tions are to be developed; if appropriate.
The results of the analysis are applicable to all 2, 3 and 4 loop Westinghouse plants.
Previous analyses performed for preparation of reference emergency operating guidelines and safety analyses reported in plant licensing documentation explicitly account for void formation in the upper head region if it is calculated to occur.
The results of the previous analyses indicate no safety concerns are associated with this ol23A AVVh Controls gr~ y48od83
possibility since voids generated in the upper head would be collapsed when they are brought in contact with the subcooled region of the system.
Furthermore, actual events which necessitated cooldown on natural circulation have shown no real safety issues attributable to any upper head flashing phenomenon.
II.
METHOD OF ANALYSIS A.
Parameter s Governing Void Formation There are several parameters which can have a significant effect on the formation of voids in the upper head region during natural cir-culation cooldown/depressurization transients.
One such parameter is the magnitude of the flow comunication between the upper down-comer and the upper head.
This flow is at a temperature equivalent to that of the cold leg fluid.
Hence, this flow directly affects the steady state upper head fluid temperature, which is a second factor which has an effect on the formation of voids in the upper head region.
Most currently operating Westinghouse plants have an amount of flow into the upper head region which results in an upper head fluid temperature between the cold leg temperature (TCOLD) and the core outlet temperature (THOT)
In the analysis described in this study the initial upper head tenperature for these plants is conservatively chosen as THOT.
Other Westinghouse plants operate with sufficient flow from the upper downcomer to the upper head region to make the upper head fluid temperature equal to the cold leg fluid temperature (TCOLD) 8oth types of plants are analyzed in this study.
Another parameter affecting void formation in the upper head which is analyzed in the study is the cooldown/depressurization rate of the primary system.
A final parameter important in the formation of voids in the upper head is the heat removal rate from the upper head.
The two primary means of heat loss are ambient heat losses and heat removal by the control rod drive mechanism (CRDM) fans.
8123A
The CROM cooling system consists of fans which maintain a suitable atmosphere within the CROM shroud to protect and prolong the life of the CROM motors.
The system induces cooler containment air into the CROM shroud and exhausts through the fans.
The effect of ambient heat losses through the reactor vessel on upper head temperature is small compared to the effect of the CROM fans and is neglected in this study.
The cooloff rate of the upper head due to ambient heat losses is less than 1 F/hr.
Metal heat addition to the upper head area from the reactor vessel and upper internals is taken into account.
S.
Major Assumptions The WFI ASH code (references 1
and 2) is used in the analysis.
WFLASH permits a detailed spagial representation of the primary system with the system nodalized into volumes interconnected by flow paths.
The transient behavior of the system is determined from conservation equations of mass, energy and momentum applied through-out the system.
The WFLASH code has two phase capability and can track void propagation if it occurs.
A 4-loop plant with a core thermal power of 3411 MW is used.
Since the analysis is not a design basis analysis, the transient response of the primary system is based upon the conditions more likely to occur during the event; i.e.,
a best estimate model is employed.
For the best estimate
- model, several changes were made in order to approach more realistic assumptions and more likely conditions dur-ing the cooldown transient than are presently found in the Appendix K model.
The principal differences between the best estimate and Appendix K models are listed in Table 1.
An inverted top hat upper support plate design is assumed since it results in a larger upper head volume and hence more total heat in 3123A
the upper. head area initially.
This design would offer the maximum thermal inertia for cooling of the upper head region.
The reactor and the reactor coolant pumps are assumed to be tripped at the initiation of the transient (at 2.0 seconds in WFLASH).
The pumps are tripped at the start of the transient to conservatively keep the upper head temperature higher by minimizing the flow com-munication between the upper head and the rest of the system.
The primary system pressure is maintained at approximately 2250 psia prior to initiation of natural circulation cooldown.
Natural circu-lation cooldown rates of 25 F/hr and 50 F/hr are analyzed.
These rates are in the range of typical plant cooldown rates.
While the analysis is based on a 4-loop plant, the results and con-clusions of the anlysis are applicable to 2 and 3-loop plants.
The power level to core/upper plenum volume ratio is essentially the same for 2, 3 and 4-loop plants
( 1.97, 1.75 and 1.8 for typical 2, 3
and 4-loop plants with inverted top hat upper support plates).
Thus the downcomer density to core/upper plenum density ratio remains essentially the same for 2, 3 and 4-loop plants.
As discussed in Section III.B, the driving force for the guide tube/spray nozzle flow is the downcomer density being greater than the core density.
A comparison of the guide tube/spray nozzle flow path resistance between 2,
3 and 4-loop plants can be gained from the percent of total plant flow passing through the spray nozzles.
The minimum percentage of total flow going through the spray nozzles for 2 and 3-loop plants (0.27% for a 2-loop plant and 0.175 for a 3 loop plant) is greater than that used in this analysis for 4-loop plants (0.15/ for THOT upper head).
The ratio of upper head heat removal by the CROM fans to upper head total energy is essentially the same for 2 and 3 loop plants
( 1.05 and 1.02 for typical 2 and 3-loop) as for 4-loop kw kw ft3
't3 plants (0.92 ft3
) ~
Thus the cooldown rates given above for the CROM 3123A
fans are applicable to 2 and 3 loop plants as well as 4 loop plants.
Since (1) the driving force for the guide tube/spray nozzle flow is essentially the same for 2, 3 and 4-loop plants, (2) the resistance to guide tube/spray nozzle flow is less for 2 and 3-loop plants than 4-loop plants and (3) the cooldown rate of the upper head by the CROM fans is effectively the same for 2, 3 and 4-loop plants, the results and con-clusions reached in this analysis are valid for 2, 3 and 4-loop plants.
8123A
III.
RESULTS A.
Establishing Natural Circulation With the input as described in the previous section; WFLASH is run until steady state natural circulation is established in the plant.
This occurred prior.to 720 seconds into the transient.
In this
- analysis, natural circulation cooldown is assumed to be initiated at 720 seconds into the transient.
The primary plant conditions at
,:, this time are listed in Table 2.
At 720 seconds the difference between the hot and cold leg temperatures is approximately 30 F, the primary system loop flow is approximately 500 lb/sec, and the reactor power (due to decay heat) is 2.3X of full power (nominal).
The loop flow rate of 500 lb/sec is approximately 5X of full power loop flow.
Natural circulation flow is observed to be 4.5Ã to 5.0Ã of full power flow at 2.3X of nominal power (see Figure
- 1) for a Westinghouse 4-loop plant based on 4-loop calculations and tests.
With forced flow (i.e., with the reactor coolant pumps running) the flow goes from the upper downcomer through the upper head spray nozzles into the upper head region.
From the upper head region the flow goes down through the guide tubes into the upper plenum/core region.
With the reactor coolant pumps running the vessel pressure distribution is such that flow is forced up the upper head spray nozzles.
Within 2 to 4 minutes after the reactor coolant pumps are tripped this flow reverses and goes up the guide tubes into the upper head region and down through the upper head spray nozzles into the uppe~
downcomer.
This flow reversal occurs due to the downcomer density being greater than the upper plenum/core density, and the upper plenum/core density being greater than the upper head den-sity.
This density variation forces flow up the guide tubes.
With the exception of the pressurizer, the primary system is sub-cooled when the natural circulation cooldown is initiated.
8123A
B.
TCOL0 Some Westinghouse PMR's (referred to as TCOLO plants) have suffi-cient bypass flow from the upper downcomer through the spray nozzles into the upper head area to keep the upper head fluid temperature equal to the cold leg fluid temperature during normal power opera-tion, of the plant.
Table 3 gives the initial upper head spray nozzle flow r ate, 609 lb/sec, and other pertinent data regarding the initial upper head flow for a TCOLp plant.
Mestinghouse plants with the upper head injection (UHI) system are TCOLO pl ants
~
- Thus, the resu 1 ts and conc 1 us ions reached in thi s study for T pl ants are valid for these units.
Two natural circulation cooldown rates are analyzed:
25 F/hr and 50 F/hr.
An update was made to WFLASH which permits the secondary 0
side temperature as a function of time to be input specified.
If a cooldown rate of 25 F/hr is prescribed for the secondary
- system, 0
the primary system in natural circulation will follow this cooldown rate.
For both cooldown rates natural circulation cooldown is initiated at 720 seconds.
The core inlet, hot leg and cold leg temperature transients are shown in Figures 2 through 7.
For both cooldown rates, the transi-ent is carried out until the hot leg temperature reaches 350 F, which is the temperature at which the Residual Heat Removal System (RHRS) could be employed for further cooldown.
Consistent with normal plant operations, charging flow is added to the primary system at a rate sufficient to keep the pressurizer mixture level relatively constant during the cooldown transient (Figures 8 and 9).
The primary system pressure response is shown in Figures 10 and ll.
Some depressurization occurs initially due to'ystem shrinkage caused by the cooldown.
Further depressurization results from the cooling of the pressurizer due to the addition of colder water from the hot leg to the pressuri zer in the latter part 8123A
of the transient.
Pressurizer heaters were not modelled for the analysis.
The upper head pressure transient is given in Figures 12 and 13.
A sensitivity study, discussed in Section III.C, verifies that the primary system depressurization rate effect on the upper head tem-perature is insignificant.
The hot leg 'and cold leg mass flow rate:
tr ansients are given in Figures 14 through 17.
The upper head spray nozzle flow is initially from the upper down-comer through the upper head spray nozzles into the upper head
- area, and from the upper head area down through the guide tubes into the upper plenum/core area.
In the first 2 to 4 minutes of the transient, this flow reverses (see Figures 18 and 19) due to the density in the downcomer being greater than the core density, and the reactor coolant pumps being tripped at the start of the transient.
Because of this flow reversal, upper head temperature rises early in the transient (see Figures 20 and 21).
The upper head temperature is initially equivalent to the cold leg temperature.
When the spray nozzle/guide tube flow reversal (discussed in the previous para-graph) occurs, hotter water from the core is introduced into the upper head area and causes the upper head temperature rise.
After this early increase, the upper head temperature steadily decreases.
From the upper head temperature transients, the upper head satura-tion pressure transients (see Figures 22 and 23) are determined.
As
- shown, the upper head saturation pressure is well below the primary system pressure (Figures ll and
- 12) at any given time during the calculated transient.
When the primary system temperature reaches S00 F during the cool-0 down transient the upper head temperature and corresponding satu-ration pressure are as given in Table 4 for both cooldown rates.
S123A
The same information is listed in Table 4 for a primary system temperature of 350 F.
If, for example, during the cooldown of the plant, the operator wanted the primary system pressure to be less than 1500 psia when the primary system temperature is 500 F, then the upper head saturation pressure for either'cooldown rate is well below 1500 psi a and there would be no void formation in the upper head area.
If a second condition for the plants cooldown is that the primary system pressure be less than 400 psia when the primary system temperature is 350 F (conditions under which the RHRS could be used),
then the upper head saturation pressure for either cool-down rate is well below 400 psi a and no voids would be formed in the upper head.
In effect, the analysis shows that formation of a steam bubble in the upper head area is avoided when cooling down at 25 F/hr because the primary system pressure can easily be maintained above the upper head saturation pressure shown in Figure 22 at any speci-fic time by maintaining 50 F subcooling in the hot leg.
For the 50 F/hr cooldown rate the primary system pressure is shown to 0
remain above the upper head saturation curve on Figure 23 if the hot leg is maintained 100 F subcooled.
It should be noted that no credit is taken for the effect on the upper head temperature of ambient heat losses for the reactor vessel or heat=removal from the upper head area by the control rod drive mechanism (CROM) fans in the analysis of TCOLO plants.
As des-cribed in section III.O, the CROM fans could considerably increase the upper head cooldown rate for a given RCS cooldown rate.
C ~
THOT P 1 ants Some Westinghouse PWR's have a bypass flow path characteristic from the upper downcomer through the spray nozzles into the upper head area which results in an upper head fluid temperature between the RCS cold leg temperature and the core outlet temperature.
In this study the initial upper head temperature for these plants (referred 8123A
0
to as T 0T plants) is conservatively assumed to be equal to the core outlet temperature.
Table 5 gives the initial upper head spray nozzle flow rate, 59.2 lb/sec, and other pertinent data regarding the initial upper head flow for a THDT plant.
Natural circulation cooldown rates of 25 F/hr and 50 F/hr are analyzed for T plants with the cooldown initiated at 720 seconds following plant trip for both cooldown rates.
The core inlet, hot leg and cold leg temperature transients are shown in Figures 24 through 29.
For both cooldown rates, the pri-mary system is cooled down via natural circulation until the hot leg temperature reaches 350 F, which is the temperature at which the 0
RHRS could be employed for further cooldown.
Charging flow is added to the primary system at a rate sufficient to keep the pressurizer mixture level relatively constant during the cooldown transient (Figures 30 and 31).
The primary system pressure response is shown in Figures 32 and 33.
Depressurization of the primary system occurs for the same reasons as stated for the T
plants (see Section III.B).
A sensitivity study was made to verify that the primary system depressurization rate has an insignificant effect on the upper head temperature.
Table 6 shows that for two significantly different primary system depressurization
- rates, the upper head temperature is essentially equal at any given time.
The upper head pressure transient is given in Figures 34 and 35 for each cooldown rate.
The hot leg and cold leg mass flow rate transi-ents are given in Figures 36 through 39.
As for the T
plants the spray nozzle flow is initially from the upper downcomer through the spray nozzles into the upper head
- area, and from the upper head area down through the guide tubes into the upper plenum/core area.
Approximately 2 minutes into the transient, this flow reverses (Figures 40 and 41) due to the density in the downcomer being greater than the core density and the reactor 3123A
coolant pumps being tripped at the start of the transient.
The resulting upper head temperature transients are given in Figures 42 and 43.
From the upper head temperature transients, the upper head saturation pressure transients (Figures 44 and 45) are determined.
When the primary system reaches 500 F during the cooldown
.I o~
transient the upper head temperature and corresponding saturation pressure are as shown in Table 7 for both cooldown rates.
The same information is listed in Table 7 for a primary system temperature of 350 F.
If,~'.for example, during the cooldown of the plant, it was desired to have the primary system pressure less than 1500 psia when the primary system temperature is 500 F, then the upper head 0
saturation pressure for the 25 F/hr cooldown rate is below 1500 psia and there would be no void formation in the upper head area.
- However, for. the 50 F/hr cooldown rate, some upper head void formation may occur at these conditions since the upper head saturation pressure is slightly above 1500 psia when the hot leg temperature reaches 500 F.
A second condition for the plant cooldown might be that the primary system pressure be 400 psia or less when the primary system tempera-ture is 350 F (conditions which would permit use of the RHRS).
From Table 7 it is seen that the upper head saturation pressure is well above 400 psia for either cooldown r ate when the hot leg tem-perature reaches 350 F.
To prevent void formation in the upper head area the natural circulation cooldown and depressurization should be terminated when the hot leg temper ature reaches approxi-mately 350 F to allow the upper head to cool off.
In determining the upper head cool off due to conduction through the 1.0 foot thick stainless steel upper support plate, the primary system is assumed to stay at 350 F since the heat added from the 0
upper head during the cool off period is small compared to the total heat in the primary system.
A window mode hand calculation of the conduction was performed which utilized the initial upper head temperature at the time the primary system reached 350 F.
From 0
8123A
)
the time the hot leg temperature reaches 350 F, it would require approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> to'reach an upper head saturation pressure of 400 psia for the 25 F/hr cooldown transient.
The corresponding upper head cool off period to reach a saturation pressure of 400 psia for the 50 F/hr cooldown transient is approximately 27 0
hours.
At this point the rest of the primary system could be depressurized to 400 psia and the RHRS employed for any further cooldown.
In the analysis of THDT plants described above no credit is taken for ambient, heat losses through the reactor vessel or heat removal from the upper head area by the CROM fans.
As described in Section III.D, the effect of the CROM fans could significantly increase the upper head cooldown rate for a given primary system cooldown r ate.
D.
Effect of CROM Fans For the 4 loop plant evaluated
- here, the CROM fans remove 780 KW at full power.
This translates.to a cooldown rate of 32 F/hr for the upper head fluid when the upper head fluid temperature is 600 F.
If it is ass@@ed that the heat removal capacity of the fans is pro-portional to the hT between the upper head metal'temperature and the contairment temperature (assumed to be 100 F), then the CRDM fans cooldown the upper head fluid at a rate of 17 F/hr with the upper head fluid at 350 F.
For TCDLD plants the upper head cooldown rate due to the CRDM fans varies from 30 F/hr (when the upper head temperature is at its highest temperature
- 572 F) to 17 F/hr when the upper head temperature is 350 F.
8123A
IV.
CONCLUSIONS A
TCOLD The average cooldown rate of the upper head fluid due to a 50 F/hr natural circulation cooldown r ate is about 34 F/hr for a TCOLO plant.
The total upper head cooldown rate due to both natural cir-culation cooldown and the CROM fans varies from a maximum of 64 F/hr to around 51 F/hr when the upper head temperature is 0
0 cooled to 350 F.
Thus, with the CROM fans operating during the
- cooldown, a TCOLO plant could be cooled at a natural circulation cooldown rate of 50 F/hr to the point where the RHRS could be employed for further cooldown without void formation occurring in the upper head area.
The operator should maintain 50 F subcooling during the depressurization.
Adding the cooldown rate due to the CROM fans to that from the natural circulation cooldown is conservative since the additional cooling due to the fans will enhance the density effect (discussed in Section III.A) which in turn increases the guide tube/spray nozzle flow rate.
Mith the CROM fans not available, a TCOLO plant can be cooled down to RHRS conditions at a natural circulation cooldown rate of 50 F/hr with no,void formation in the upper head area if the operator maintains 100 F subcooling during the depressurization (see Figure 46).
B.
THOT Plants The average cooldown rate of the upper head fluid due to the 25 F/hr natural circulation cooldown rate is about 10 F/hr for a THOT pl ant.
The total upper head cool down rate due to both the natural circulation cooldown and the CROM fans varies from 42 F/hr initially to around 27 F/hr when the upper head temperature is 0
cooled to 350 F.
Thus, with the CROM fans operating during the 8123A
- cooldown, a TH0T plant could be cooled at a natural circulation cooldown ra.e of 25 F/hr to the point where the RHRS could be used for further cooldown with no void formation occurring in the upper head area.
The operator should maintain 50 F subcooling during the depressuri zati on.
Without the CRDM fans a THDT. plant can be cooled down to RHRS conditions at a natural circulation cooldown rate of 25 F/hr with no void formation occurring in the upper head with appropriate pre-cautions being taken by the operators.
The operator should maintain 50 F subcooling until the primary system pressure reaches 1900 psia.
After the automatic safety injection signals are blocked, the opet ator should establish 200 F subcooling (approximately 430 F
in the hot leg) and maintain 200 F subcooling (or the Technical Specification limit if it is more restrictive) to a primary system pressure of 1200 psi a (see Figure 47).
The depressurization should be stopped at 1200 psia and the cooldown continued until the primary system temperature is less than 350 F.
At this point the operator must wait for approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> to allow the upper head to cool off to a temperature corresponding to a saturation pressure of 400 psia.
For plants with upper head thermocouples, they can provide further verification of the upper head temperature for guidance.
Finally the primary system should be depressurized to 400 psia and the RHRS used for any further cooldown.
C.
Suamary of Conclusions Table 8 swanarizes the recomnended maximum natural circulation cool-down rates and primary system subcooling requirements for TH T and TCDLD pl ants with and without fans .
The 1 imits noted provi de appropriate and conservative margin to the calculated limits.
8123A
REFERENCES 1.
Porsching, T. A., Murphy, J. H., Redfield, J. A., and Oavis, V. C.,
"FLASH-4:
A Fully Implicit FORTRAN-IV Program for the Oigital Simu-lation of Transients in a Reactor Plant,"
WAPO-TM-840; Bettis Atomic Power Laboratory.
2.
- Esposito, V. J.,
- Kesavan, K.
and Haul, B. A., "WFLASH-A FORTRAN-IV Computer Progr am for Simulation of Transients in a t<ulti-Loop PMR,"
WCAP-8200, Revision 2, July, 1974 (Proprietary) and WCAP-8261, Revision 1, July<
1974 (Non-Proprietary).
8123A
I 1
TABLE 1 BEST ESTIMATE WFLASH INPUT HOT Plant COLD Plant
~Aendix I A.
PLANT PARAMETERS 1.
Primary Hot Leg Nodes Modeled 2.
Continuous flow paths for crossover and hot legs Yes Yes Yes Yes Ho Ho 3.
Power Level 4.
Pressure drops 5.
Flow r ates B.
REACTOR l.
Decay heat-AiRS infinite 2.
Axial power shape 1005 Best Estimate Best Estimate Hominal BOL, First Core B.E.
100'(1) 102'hermal Design Thermal Design Thermal Design Thermal Design Nominal 120K BOL, First Worst Case Core B.E.
Envelope 3.
Reactor trip, sec.
4.
Reactor coolant pump trip, sec.
C.
PRESSURIZER 1.
Non-equilibrium pressurizer model 2.0 2.0 Yes 2.0 2.0 Yes Low RCS Pressure Signal Reactor Trip Signal No Pressure drops enthalpies flow rates and steam generator heat loads based on 102K power.
8123A
TABLE 2 PLANT CONDITIONS AT TIME NATURAL CIRCULATION COOLDONN IS INITIATED (720 SECONDS)
Primary system
- pressure, psia 2245 Secondary system pressure, psi a 1106 Hot -leg temperature, F
586 Cold leg temperature, F
557 RCS loop flow, lb/sec 506(1)
Reactor
- power, X of nominal 2.3 (1)
Loop. flow is 490 lb/sec for TCOLD plants at 720 seconds.
8123A
TABLE 3 UPPER HEAD FLOW - TCOLD PLANT Spray nozzle flow area, ft 0.192 Primary system loop flow, lb/sec 9757 Percent of total flow passing through spray nozzles
- 1. 56 Initial spray nozzle flow, lb/sec 609 8123A
0
TABLE 4 UPPER HEAO PSAT FOR TCOLO PLANT Temperature (oF)
Cooldown Rate (oF/hr) 50 Primary System 500 Upper Head 529 PSAT for Upper Head Temperature (psia) 878 25 1
500 516 785 50 350 426 329 25 350 372 178 8123A
TABLE 5 UPPER HEA0 FLOW THOT P LANT Spray nozzle flow area, ft
- 0. 0167 Primary system loop flow, lb/sec'868 Percent of flow passing through spray nozzles Init'ial spray nozzle flow, lb/sec
- 59. 2 8123A
TABLE 6 OEPRESSURIZATION RATE EFFECT ON UPPER HEAD TEPPERATURE Time (sec)
Oepressurization Rate 1
Primary System Upper Head Pressure (psi)
Temp.
(oF)
Oepressuri zati on Rate 2
Primary System Upper Head Pressure (psi
)
Temp. (oF) 1810 2060 612.0 2063 612. 0 5085 1912 605. 4 2014 605. 9 7560 1819 602.3 1975 602.5 10440 1708 597.1 1909 597. 5 8123A
TABLE 7 UPPER HEAD PSAT FOR THOT PLANT Temperature (oF)
Cooldown Rate (oF)/Hr) 50 Primary System 500 Upper Head 599 PSAT for Upper Head Temperature (psia) 1531 25 500 585 1382 50 350 549 1035 25 350 513 761 8123A
TABLE 8 MAXIMUM RECOMMENDED NATURAL CIRCULATION COOLDOWN RATES Upper Head CRDM Fans Maximum Cooldown Rate
( F/Hr)
Required Hot Leg Subcoo 1 i ng*
( F)
COLO Yes 50 50 COLD No 100 HOT Yes 25 50 HOT No 25 200~
Required hot leg subcooling to avoid reaching saturation pressure in the upper head.
Use Tech Spec limit if it is more restrictive.
Also, 200 F
0 subcooling required only between hot leg temperature of 350 F to 0
430 F.
8123A
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rtHE (SEC) w Ifl CV woIfl L&oo CCI FIGURE 21 I
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1
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Figure 2$
Core Inlet Temperature 50 F/Hr Cooldown Hot
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a<<
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4J CI.X I,OO.OO F00.00 200.00 tlHl tSLCl Figure 27 Hot Leg Fluid Temperature TH t - 50oF/HR Cooldown Hot
0
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{5 E C I CD CD I/I Figure 28 Cold Leg Fluid Temperature That 25F/HRCOOl dOLvn
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4J 100.00 300.00 200.00 Ch C7 iIIIE (SECI Figure 2'9 Cold Leg Fluid Temperature TH t - 50 F/HR Cooldo~>n
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~v 20.000 M
CL I0.000 0.0 C)
I
~
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Figure 30 Pressurizer Mixture Level T>i t - 25 F/Hr Cooldown
)lot
0
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TIIIE (SECI Figure 31 Pressurizer Mixture l.evel T< - 50 F/Hr Cooldown loot
25nn.n 2000.0 1500.0 1000.0 500.00 0.0 TIHE (SEC)
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2500.0 2000.0 1500.0 a
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CL CL CL
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1.60Ki0%
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=
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F000.0 2000.0 0.0 glut tstc>
Figure 37 Hot Leg t'1ass Flowrate Hot - 5o F/Hr Cooldotvn
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~
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