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NUREG/A-0022

Inteonaional• Agreement Report

TRAC-PF1/MOD1 Post-TestCalculations of the OECDLOFT Experiment LP-SB-3Prepared byE. J. Allen, A. P. Neill

United Kingdom Atomic Energy AuthorityWinfrith, DorchesterDorset, England

Office of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionWashington, DC 20555

April 1990

Prepared as part ofThe Agreement on Research Participation and Technical Exchangeunder the International Thermal-Hydrauflc Code Assessmentand Applcation Program (ICAP)

Published byU.S. Nuclear Regulatory Commission

NOTICE

This report was prepared under an international cooperativeagreement for the exchange of technical information. Neitherthe United States Government nor any agency thereof, or any oftheir employees, makes any warranty, expressed or implied, orassumes any legal liability or responsibility for any third party'suse, or the results of such use, of any information, apparatus pro-duct or process disclosed in this report, or represents that its useby such third party Would not infringe privately owned rights.

Available from

Superintendent of DocumentsU.S. Government Printing Office

P.O. Box 37082Washington, D.C. 20013-7082

and

National Technical Information ServiceSpringfield, VA 22161

NUREG/IA-0022

• InternationalAgreement Report

TRAC'PF1/MOD1 Post-TestCalculations of the OECDLOFT Experiment LP-SB-3Prepared byE. J. Allen, A. P. Neill

United Kingdom Atomic Energy AuthorityWinfrith, DorchesterDorset, England

Office of Nuclear Regulatory ResearchU.S. Nuclear Regulatory CommissionWashington, DC 20555

April 1990

Prepared as part ofThe Agreement on Research Participation and Technical Exchangeunder the International Thermal-Hydraulic Code Assessmentand Applicatlon Program (ICAP)

Published byU.S. Nuclear Regulatory Commission

J!

NOTICE

This report is based on work performed under the sponsorship of the

United Kingdom Atomic Energy Authority. The information in this

report has been provided to the USNRC under the terms of the

International Code Assessment and Application Program (ICAP)

between the United States and the United Kingdom (Administrative

Agreement - WH 36047 between the United States Nuclear Regulatory

Commission and the United Kingdom Atomic Energy Authority Relating

to Collaboration in the Field of Modelling of Loss of Coolant

Accidents, February 1985). The United Kingdom has consented to the

publication of this report as a USNRC document in order to allow

the widest possible circulation among the reactor safety community.

Neither the United States Government nor the United Kingdom or any

agency thereof, or any of their employees, makes any warranty,

expressed or implied, or assumes any legal liability of

responsibility for any third party's use, or the results of such

use, or any information, apparatus, product or process disclosed

in this report, or represents that its use by such third party

would not infringe privately owned rights.

SUMMARY

Analysis of the small, cold leg break, OECD LOFT ExperimentLP-SB-3 using the best-estimate computer code TRAC-PF1/MODl ispresented.

Descriptions of the LOFT facility and the LP-SB-3 experiment aregiven and development of the TRAC-PFl/MODl input model isdetailed. The calculations performed in achieving the steadystate conditions, from which the experiment was initiated, andthe specification of experimental boundary conditions areoutlined.

Results of the TRAC-PFl/MODl calculation are found to begenerally consistent with those reported, by members of the OECDLOFT Program Review Group, in the LP-SB-3 "Comparison Report".Overall trends with respect to pressure histories, minimumprimary system mass inventory and accumulator behaviour arereasonably well reproduced by TRAC-PFl/MOD1. Prior to breakuncovery, the break mass flow rate is slightly over-predicted bythe TRAC critical flow model. (Subcooled and two-phase chokedflow multipliers of 1.0 were used throughout the calculation).The most significant discrepancy is in the rate with which thefuel rod cladding temperature rises during the core uncoveryphase of the transient. TRAC-PF1/MOD1, in common with othercodes, significantly over-predicts the rate with which the coreheats up. Contrary to experimental observations, conditions forreflux condensation are not predicted by TRAC-PFl/MODl duringthis-part of the transient. This, together with the under-prediction of core density by TRAC's interphase drag model, isconsidered a potential contributor to the poorly predicted rateof core heat-up.

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CONTENTS

SECTION 1 INTRODUCTION

2 THE LOSS OF FLUID (LOFT) TEST FACILITY

3 EXPERIMENT LP-SB-3

4 TRAC-PFI/MOD1

5 TRAC-PFI/MODI INPUT MODEL FOR LP-SB-3

6 STEADY STATE CALCULATION

7 BOUNDARY CONDITIONS FOR TRANSIENTCALCULATION

7.1 Decay Heat Data7.2 Primary Pump Injection7.3 Operational Setpoints

8 TRANSIENT CALCULATION

8.1 Introduction8.2 CPU Usage and Time Step Behaviour8.3 Chronology of Events8.4 Mass Depletion Phase

8.4.1 Primary and Secondary SystemPressures

8.4.2 Break Mass Flow Rate, BreakLine Density and PrimarySystem Mass Inventory

8.4.3 Primary System Densities8.4.4 Pumps Degradation

8.5 Core Boil Off Phase


8.5.2 Break Mass Flow Rate andPrimary System Mass Inventory

8.5.3 Primary System Densities8.5.4 Fuel Cladding Temperatures

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CONTENTS (Continued)

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8.6 Core Cool-Down and Recovery Phase


8.6.2 Fuel Cladding Temperatures8.6.3 Accumulator Injection Flow

9 CONCLUSIONS

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ACKNOWLEDGEMENTS

REFERENCES

APPENDIX I - MICROFICHE LISTING OF THETRAC-PFl/MODI INPUT DECK FORLP-SB-3

APPENDIX II - SERIES OF PICTURES SHOWINGPREDICTED SYSTEM CONDITIONSTHROUGHOUT THE LP-SB-3 TRANSIENT

APPENDIX III - COMPARISON OF BREAK MASS FLOW RATEPREDICTED BY TRAC-PFl/MODI WITHTHAT IMPLIED BY THE HOMOGENEOUSEQUILIBRIUM MODEL

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LIST OF TABLES

1 INITIAL CONDITIONS FOR EXPERIMENT LP-SB-3

2 OPERATIONAL SETPOINTS FOR EXPERIMENT LP-SB-3

3 CHRONOLOGY OF EVENTS FOR EXPERIMENT LP-SB-3

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LIST OF FIGURES

1 LOFT SYSTEM CONFIGURATION FOR EXPERIMENT LP-SB-3

2 TRAC-PFI/MOD1 PRIMARY SYSTEM NODALISATION DIAGRAM FORLP-SB-3

3 TRAC-PF1/MOD1 REACTOR VESSEL NODALISATION DIAGRAM FORLP-SB-3

4 TRAC-PF1/MOD1 STEAMDIAGRAM FOR LP-SB-3

5 LP-SB-3 CALCULATION



8 LP-SB-3 CALCULATION(0-300 SECONDS)

9 LP-SB-3 CALCULATION(0-6400 SECONDS)




13 LP-SB-3 CALCULATIONONSET

14 LP-SB-3 CALCULATIONONSET

GENERATOR SECONDARY SIDE NODALISATION

- CPU USAGE

- TIME STEP SIZE

- PRIMARY SYSTEM PRESSURE

- SECONDARY SYSTEM PRESSURE

- SECONDARY SYSTEM PRESSURE

- BREAK MASS FLOW RATE

- BREAK LINE DENSITY

- PRIMARY SYSTEM MASS INVENTORY

- ILHL DENSITY AND STRATIFICATION

- ILCL DENSITY AND STRATIFICATION

15 LP-SB-3 CALCULATION - PRIMARY COOLANT PUMPS DIFFERENTIAL

16

17

18

19

PRESSURE

LP-SB-3 CALCULATION - PRIMARY SYSTEM - SECONDARY SYSTEMPRESSURE

LP-SB-3 CALCULATION - PRIMARY AND SECONDARY SYSTEMPRESSURES

LP-SB-3.CALCULATION - PEAK CLADDING TEMPERATURE (0.05 m)

LP-SB-3 CALCULATION - PEAK CLADDING TEMPERATURE (0.28 m)

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LIST OF FIGURES (Continued)

20 LP-SB-3 CALCULATION - PEAK CLADDING TEMPERATURE (0.53 m)




24 LP-SB-3 CALCULATION - ACCUMULATOR MASS FLOW RATE

25 LP-SB-3 CALCULATION - ACCUMULATOR MASS FLOW RATE ANDSECONDARY SYSTEM PRESSURE

26 LP-SB-3 CALCULATION - ACCUMULATOR MASS FLOW RATE ANDSECONDARY SYSTEM PRESSURE (STEAM BYPASS VALVE FLOW AREAINCREASED)

AEEW - R 2275 (vii)

COMMERCIAL IN CONFIDENCE

1 INTRODUCTION

This paper describes a post-test calculation of the OECD LOFTsmall, cold leg break experiment LP-SB-3 using the"best-estimate" computer code TRAC-PFl/MOD1. Sections 2, 3 and 4describe the LOFT facility, the LP-SB-3 experiment and theversion of TRAC-PFl/MODI used, respectively. Development of theinput model is detailed in Section 5 and the calculationsperformed in achieving the steady state conditions, from whichthe experiment was initiated, are outlined in Section 6. Theexperimental boundary conditions, and the way in which they arespecified to the code, are defined in Section 7. Section 8describes the transient calculation. The main conclusions fromthe analysis are summarised in Section 9.

2 THE'LOSS OF FLUID TEST (LOFT) FACILITY

The Loss of Fluid Test (LOFT) facility, at the Idaho NationalEngineering Laboratory (INEL), is a 50 MW(t) Pressurised WaterReactor (PWR) system designed to simulate the major componentsand system responses of a commercial PWR during Loss-of-CoolantAccidents (LOCAs) or operational transient accidents. Theexperimental assembly is instrumented in order that systemvariables can be measured and recorded during transients. Thefacility is comprised of five major subsystems - the reactorvessel, the operating (intact) loop, the "broken" loop, theblowdown suppression system and the Emergency Core Cooling System(ECCS). The configuration of the major LOFT components, forexperiment LP-SB-3, is shown in Figure 1.

The operating (intact) loop simulates three loops of a commercialfour-loop PWR and contains a steam generator (of vertical, U-tubedesign), two primary coolant pumps (in parallel), a pressurizer,a venturi flowmeter and connecting piping. The break locationfor experiment LP-SB-3 was in the cold leg of the intact loopbetween the primary coolant pumps and the reactor vessel.

The broken loop consists of a hot leg and a cold leg connected tothe reactor vessel and the blowdown suppression tank header.Each leg contains a Quick-Opening Blowdown Valve (QOBV), arecirculation line, an isolation valve and connecting piping.The recirculation lines provide a small flow from the broken loopto the intact loop and are used to maintain the broken loop fluidtemperature at approximately the core inlet temperature prior toexperiment initiation. During experiment LP-SB-3, the QOBVs andthe isolation valves remained closed (because the break was inthe operating loop). Broken loop spool pieces, with orifices tosimulate the steam generator and pump hydraulic resistances, wereinstalled for experiment LP-SB-3.

The LOFT reactor vessel has an annular downcomer, a lower plenum,lower core support plates, a nuclear core (containing 1300 fuelrods) and an upper plenum. The downcomer is connected to thecold legs of the operating and broken loops, and the upper plenumis connected to the hot legs of the operating and broken loops.

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The LOFT ECCS consists of two accumulators, a High PressureInjection System (HPIS) and a Low Pressure Injection System(LPIS). Each system is designed to inject scaled flows ofemergency core coolant directly into the primary coolant system.The HPIS was not used during experiment LP-SB-3.

3 EXPERIMENT .LP-SB-3

Experiment LP-SB-3 was conducted on 5 March 1984 in the LOFTfacility at the Idaho National Engineering Laboratory. LP-SB-3was the sixth in a series of experiments, sponsored by aconsortium of countries under the auspices of the Organisationfor Economic Cooperation and Development (OECD).

The LP-SB-3 experiment simulated a 4.66 cm (1.84 inch) equivalentdiameter break in a cold leg pipe of a commercial PWR. The breakline piping and details of the break nozzle (0.88 cm diameter)are shown in Figure 1. The transient was specifically designedto achieve conditions which would allow an assessment of:

(i) The mechanism for core heat transfer under slow coolantboil off conditions.

(ii) The effectiveness of operator initiated steam generatorfeed and bleed recovery.

(iii) The effectiveness of accumulator injection when a smallpressure differential exists between the accumulator andthe primary system.

The experiment was initiated, from conditions representative ofthose in a commercial PWR, by opening a valve in the Intact LoopCold Leg (ILCL) break piping. The primary system depressurisedrapidly until fluid saturation conditions were reached in the hotleg at - 100 seconds. This resulted in a decrease in the primarysystem depressurisation rate and, with void formation in thefluid, a reduction in the break mass flow rate. The continuedoperation of the primary coolant pumps homogenised the fluid andthe primary system void fraction steadily increased as fluid wasdischarged out the break. The pumps were tripped after1600 seconds when approximately 2800 kg of coolant inventoryremained in the primary system. After pump trip, the fluidexpelled from the break was predominantly steam. The HPIS wasnot used during the experiment and the mass inventory was allowedto decrease, uncovering the core.

As the core became increasingly void of fluid, the fuel claddingstarted to heat up. The break was isolated, to prevent furtherdepressurisation of the primary system, when the claddingtemperature reached 835K. When the maximum cladding temperaturereached 988K, a steam generator feed and bleed procedure wasinitiated. The energy removal through the secondary systemdepressurised the primary system and the fuel cladding started tocool. Accumulator flow commenced when the primary system haddepressurised to 2.79 MPa and the fuel cladding was graduallyquenched, from the bottom, upwards. The LPIS, initiated at a

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primary system pressure of 1.03 MPa, quickly refilled the coreregion, thus terminating the experiment.

4 TRAC-PFI/MOD1

TRAC (Transient Reactor Analysis Code) is an advanced "best-estimate" computer code, developed at the Los Alamos NationalLaboratory, for analysing transients in thermal-hydraulicsystems. Specifically, TRAC-PFI/MODI was developed for analysingpostulated accidents in PWRs. The version of .the code used forthe calculations described in this paper was AEEW Version B02Awhich contains the LANL updates to TRAC-PFl/MODl Version 12.7.

5 TRAC-PFlI/MOD1 INPUT MODEL FOR LP-SB-3

The development of a TRAC-PFl/MODI input model for analysis ofLOFT small break experiments was based on a TRAC-PFI/MODl largebreak deck for the experiment LP-FP-I. The LP-FP-1 deck,developed at AEEW, originated from the LANL input deck forexperiment L2-3. Additional published data on the LOFT facility(1, 2, 3) were employed, where necessary, in producing the smallbreak deck.

The modifications, to the large break deck are described inReferences 4, 5, 6 and 7 and included:

(i) Replacement of the three-dimensional vessel with a one-dimensional representation.

(ii) Inclusion of the ILCL break.

(iii) Inclusion of the primary pump injection.

(iv) Renodalisation of the broken loop to provide a coarserrepresentation.

(v) Renodalisation of the ECCS to provide a coarserrepresentation.

(vi) Accurate repositioning of the ECCS injection point in theILCL.

With the exception of those modifications specifically requiredto model the LP-SB-3 experiment, the input deck was identical tothat used for the TRAC-PF1/MODl analyses of LP-SB-1 (7) andLP-SB-2 (8).

Figures 2, 3 and 4 show the nodalisation diagrams for the primarysystem, the reactor vessel and the steam generator secondaryside, respectively.

A total of 41 components, 47 junctions and 182 cells were used inthe model.

A microfiche listing of the TRAC-PFl/MODl input deck for LP-SB-3is contained in Appendix I.

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6 STEADY STATE CALCULATION

AEEW Version B02A of the TRAC-PFI/MODI code - which incorporatesthe updates contained in LANL Version 12.7 - was used for thesteady state calculations. Steady state mode calculations wererun for 410 seconds and, in order to determine system conditionsduring transient mode code operation, a short period (50 seconds)of transient mode "steady state" (ie with no break flow) was alsorun. In running the steady-state calculation, a total of773 seconds of CPU time were used with an average time step sizeof 0.096 seconds.

The calculations were performed with control systems governingthe behaviour of the steam generator secondary side steam andfeedwater mass flow rates and the speeds of the primary coolantpumps.

The initial conditions predicted by TRAC-PF1/MODI for experimentLP-SB-3 are compared with the measured data in Table 1. Thecalculations produced stable initial conditions, within, or veryclose to, the quoted experimental uncertainties, for allsignificant parameters.

The magnitudes of the steady state pressure drops around theprimary circuit, the environmental heat losses from the systemand the core bypass flow rates, obtained from the TRAC-PFl/MODlcalculations associated with analysis of the LOFT LP-SB-lexperiment, are reported (7) to be in reasonable agreement withthe available data.

7 BOUNDARY CONDITIONS FOR TRANSIENT CALCULATION

7.1 Decay Heat Data

Following reactor scram, decay heat data were specified to theTRAC-PF1/MOD1 transient calculation by means of a "power versustime" table. Data contained in Reference 9 were used throughoutthe transient.

7.2 Primary Pump Injection

During experiment LP-SB-3, the primary coolant pump injectionsystem was set up to deliver a total flow of 0.12 is- 1 to theprimary coolant pumps (10). This was simulated, in theTRAC-PF1/MOD1 model, by using "FILL" components to supply theprimary pump injection system with liquid at a constant rate of1.63875 x 10-3 ms- 1 . The flow areas of the pump injection pipeswere 3.66131 x 10-2 m2 which implied an injection rate of6.0 x 10-5 m3 s- 1 , or 0.06 ls-1, to each pump. The primarycoolant pump injection was inserted downstream of each pump.

7.3 Operational Setpoints

The operational setpoints (for reactor scram, main feedwatershut off, MSCV closure and opening, primary coolant pump trip,break valve closure, steam bypass valve opening, main feedwater

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initiation, accumulator injection initiation and LPIS initiation)measured during the experiment, and the way in which thesetpoints were specified in the TRAC-PFI/MODl calculation, aregiven in Table 2.

8 TRANSIENT CALCULATION

8.1 Introduction

The transient calculation was restarted from the end of thetransient mode steady state calculation by opening the VALVEcomponent in the ILCL break piping. As for the steady statecalculations, AEEW Version B02A of TRAC-PFI/MOD1 - whichincorporates the code updates contained in LANL Version 12.7 -was used for the transient calculation.

In this Section, the TRAC-PFl/MODl predictions are compared withthe experimental data and with the results presented - by membersof the OECD LOFT Program Review Group - in the LP-SB-3"Comparison Report" (11). For discussion purposes, results areconsidered separately for each of the three distinct phases ofthe transient ie mass depletion phase, core boil-off phase andcore cool-down and recovery phase.

8.2 CPU Usage and Time Step Behaviour

6400 seconds of elapsed transient were calculated, requiring4702 seconds of CRAY-XMP CPU time (see Figure 5). Thiscorresponds to a CPU/real time ratio of 0.73. The user-specified minimum allowable time step throughout the calculationwas limited to 1 x 10-5 seconds. At - 300 seconds, the codestarted to take very small time steps and it was found necessaryto reduce the user-specified maximum allowable time step sizefrom 0.5 seconds to 0.2 seconds for a short period, during whichthe calculation "recovered" (see Figure 6). The average timestep for the calculation (problem time/total number of timesteps) was 0.32 seconds.

8.3 Chronology of Events

A comparison of the measured and predicted timings of significantevents is given in Table 3.

Experiment LP-SB-3 was initiated by opening the break valve inthe ILCL break line. After 9.2 seconds, the primary system haddepressurised to the reactor scram set point of 14.19 MPa. Thesteam generator control system responded to the reactor scram byisolating the feedwater flow to the steam generator andpreventing the steam flow out of. the steam generator. The mainfeedwater pump was shut off at 9.4 seconds and the feedwater wasisolated by 10.8 seconds. The Main Steam Control Valve (MSCV)started to close at 9.5 seconds and took - 11 seconds to becomefully closed. The timings of these initial events werepredicted, by the TRAC-PFI/MODI calculation, to within -

2 seconds.

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Following reactor scram, the secondary system pressure increasedsharply due to the isolation of the feedwater and the MSCVclosure. In order to keep the secondary system pressure between6.35 MPa and 7.09 MPa, the MSCV cycled four times, during theexperiment, between 87.5 seconds and 1030 seconds. TRAC-PFl/MODlpredicted the MSCV to cycle only twice, at 27 seconds and at124 seconds.

TRAC-PFl/MODl correctly predicted the time at which fluidsaturation occurred in the primary system ie at - 100 seconds.

An abrupt degradation in the differential pressure across theprimary coolant pumps was observed at 875 seconds, in theexperiment. Pump degradation was predicted-to occur between700 seconds and 1100 seconds. In both the experiment and thecalculation, the primary coolant pumps were tripped at 1600seconds. This resulted in the break uncovering at 1612 secondsin the experiment and at - 1625 seconds in the calculation.

The start of core heat up (in the upper part of the core) causedby the slow boiling off of liquid was detected, in theexperiment, at - 3800 seconds. This was predicted, by theTRAC-PFl/MODl calculation, to commence - 260 seconds later. Whenthe highest indicated cladding temperature reached 835.2K, thebreak was isolated. This occurred, some 50 seconds later thanpredicted, at 4742 seconds.

The cladding temperature continued to rise until the highestindicated value reached 988K, at which time the secondary sidefeed and bleed operation was initiated by fully opening the mainsteam control bypass valve. This action, which .occurred at5415 seconds in the experiment and was predicted, by theTRAC-PFl/MODI calculation, to occur at 4964 seconds, caused avery rapid cooldown and depressurisation of the secondary system.The maximum fuel clad temperature was measured at 5422 secondsand predicted to occur at 4980 seconds.

In the experiment, the primary system pressure reached theaccumulator setpoint (2.79 MPa) at 5588 seconds. In theTRAC-PF1/MODI calculation, accumulator injection was predicted tocommence at 5308 seconds. The LPIS was initiated (at a primarysystem pressure of 1.03 MPa) at 6785 seconds in the experiment;the core quickly refilled and the experiment was terminated at6845 seconds. The calculation was terminated at 6400 secondswhen accumulator nitrogen was predicted to have entered thesystem.

A series of pictures showing the predicted void fractiondistribution, the liquid and vapour velocities and theoccurrences of stratified flow conditions, throughout the system,is presented in Appendix II.

8.4 Mass Depletion Phase

The mass depletion phase is defined as that part of the transientbetween break initiation (0 seconds) and pump trip(1600 seconds).

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8.4.1 Primary and Secondary System Pressures

A comparison of the measured and predicted primary systempressure histories is shown in Figure 7. The initial, rapidsubcooled depressurisation is well represented and the time atwhich fluid saturation conditions occur (' 100 seconds) is alsowell-predicted. Following the end of subcooled depressurisation,and prior to pump trip, (100-1600 seconds) the overall primarysystem pressure history is well reproduced; detailedcharacteristics of the primary system pressure behaviour,resulting from the cycling of the secondary side MSCV, are notrepresented exactly, however.

Following isolation of the main feedwater and closure of theMSCV, the rate at which the secondary system pressurises isslightly over-predicted, as shown in Figure 8, and the cycling ofthe MSCV is not accurately reproduced. During the experiment,the MSCV cycled four times, between 87.5 seconds and1030 seconds; it was predicted, by the TRAC-PFl/MODI calculation,to cycle only twice - at 27 seconds and at 124 seconds. It canbe seen in Figure 8 that the setpoints at which the MSCV wasopened and closed were not consistent throughout the experiment.Values of 7.09 MPa and 6.35 MPa (10), respectively, werespecified to the TRAC-PFl/MODl calculation. A further factor,complicating simulation of this part of the transient, is theleakage rate through the "closed" MSCV which is not specifiedprecisely in the experiment documentation. In the calculation,to account for steam leakage, the minimum MSCV flow area wasrestricted to 1.0% of its fully opened value. This correspondedto a leakage rate of - 0.12 kgs- 1 at 7 MPa and is of the orderimplied by Reference 10. As shown in Figure 9, the overall trendin secondary system pressure history is reasonably wellreproduced and, at the time at which the primary coolant pumpstrip (1600 seconds), the predicted secondary side pressure is- 0.1 MPa greater than the measured value.

Calculations presented by members of the OECD LOFT Program ReviewGroup also failed to reproduce precisely the experimental MSCVcycling behaviour and, in line with the TRAC-PFl/MODlcalculation, slightly over-predicted the secondary systempressure just prior to pump trip (1600 seconds).

8.4.2 Break Mass Flow Rate, Break Line Density and Primary SystemMass Inventory

A comparison of the measured and predicted break mass flow ratesis shown in Figure 10. Although well-predicted for the first- 500 seconds of the transient, TRAC-PFI/MODl slightlyover-predicts the break mass flow rate after this time, until theprimary coolant pumps are tripped at 1600 seconds. Figure 11indicates that the break line density is well reproduced duringthe mass depletion phase, suggesting that the slightly over-predicted break mass flow rate between - 500 seconds and1600 seconds is a consequence of the TRAC critical flow model.Subcooled and two-phase choked flow multipliers of 1.0 were usedthroughout the calculation. (It appears that a multiplier of

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- 0.8 would have given the best agreement over the 500 seconds to1600 seconds period.) The break mass flow rate predicted byTRAC-PFl/MODl (between - 500 seconds and 1600 seconds) is - 10%higher than that implied by the Homogeneous Equilibrium Model(12). Details are given in Appendix III. Since no ILCLstratification, prior to pump trip, is observed in theexperiment, serious deficiencies in the TRAC-PFl/MODI branchofftake model (highlighted during analysis of the LP-SB-I (7) andLP-SB-2 (8) experiments) are not manifested in this calculation.

Consistent with the over-predicted break mass flow rate, the rateat which the primary system mass inventory is predicted todecline is more rapid than that measured (see Figure 12). It isthought that the discrepancy between the measured and predictedinitial primary system mass inventories, as shown in Figure 12,is caused by a difference in interpretation, between theexperiment and the calculation, of what constitutes the "primarysystem". The predicted initial primary system mass inventoryincludes all system components except the secondary side of thesteam generator component (component numbers 20, 21, 22 and 27),the steam line valve (component number 23) and the ECCS upstreamof the valve in the accumulator line. A similar approach wasadopted for the TRAC-PFl/MODI calculations of LP-SB-1 (7) andLP-SB-2 (8), in which the initial primary system mass inventorieswere over-predicted slightly (by - 150 kg). The differencebetween the initial mass inventory predicted for LP-SB-3 andthose predicted for LP-SB-1 and LP-SB-2 results mainly from theinclusion, for LP-SB-3, of the broken loop steam generator andpump simulators and a larger part of the ECC line. The initialexperimental mass inventory on the LP-SB-3 experiment data tapeis only slightly (- 100 kg) greater than that for LP-SB-l andLP-SB-2 (13), despite the inclusion, in the LP-SB-3 experiment ofthe broken loop simulator section.

The break mass flow rates predicted by members of the OECD LOFTProgram Review Group are, generally, in good agreement with theexperimental data. These calculations used subcooled choked flowmultipliers of 0.93 to 1.0 and two-phase choked flow multipliersof 0.7 to 0.81.

8.4.3 Primary System Densities

A comparison of the measured and predicted ILHL and ILCLdensities are shown in Figures 13 and 14. The times at whichTRAC-PFl/MODl predicts stratification to occur are alsoindicated. The ILHL density is very well-predicted by theTRAC-PFl/MODl calculation; the density in the ILCL is slightlyover-predicted. Stratification is predicted in both legs whenthe primary coolant pumps are tripped at 1600 seconds.

The calculations performed by members of the OECD LOFT ProgramReview Group (11) consistently over-predicted the ILCL densityand, to a lesser extent, the ILHL density.

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8.4.4 Pumps Degradation

The measured and predicted differential pressures across theprimary coolant pumps are shown in Figure 15. The differentialpressure decreases steadily after fluid saturation conditions arereached due to void formation in the primary system. During theexperiment, oscillations in the pump differential pressure -associated with a change from symmetric flow through both pumpsto asymmetric flow through only one pump - were observed between- 700 and - 875 seconds (10). TRAC-PFl/MODl, in common withother codes (11), was not able to reproduce this situation. Thepump characteristics employed in the LP-SB-3 input deck werethose reported for the TRAC-PFl/MODI calculation of LP-SB-2(8 (calculation "A")). In the experiment, pump degradation wasconsidered to have occurred at 875 seconds; TRAC-PFl/MODlpredicted this to occur between 700 seconds and - 1100 seconds.The calculations performed by members of the OECD LOFT ProgramReview Group (11) tended to over-predict the time at which thepumps degraded (by up to - 700 seconds).

8.5 Core Boil-Off Phase

The core boil-off phase is defined as that part of the transientbetween pump trip (1600 seconds) and steam generator feed andbleed initiation (5415 seconds - experiment, 4964 seconds -calculation).


As shown in Figure 7, following primary coolant pump trip, theprimary system pressure history is well-predicted prior to thetime at which the break is isolated (4742 seconds - experiment,4688 seconds - calculation). Figure 16 shows the measured andpredicted differences between primary and secondary systempressures. Figure 17 shows the primary and secondary systempressure histories as predicted and as measured. Although thetrends in primary and secondary system pressure histories arereasonably well reproduced by the TRAC-PFl/MODl calculation, themeasured and predicted results (most noticeably for the secondarysystem) appear to diverge slightly after - 3500 seconds. Thepredicted difference between the primary and secondary systempressures, immediately prior to break isolation, is significantlylarger than that measured. Following break isolation, theprimary side pressure rises but is predicted to remain below thatof the secondary system until the secondary side feed and bleedis initiated. This represents an important departure from theexperiment in which, following break isolation and prior to feedand bleed initiation, there was a - 500 second period when theprimary system pressure was above that of the secondary systemduring which reflux condensation could occur. This differencebetween the measured and predicted relative primary and secondarysystem pressures has important consequences for the rate at whichthe core heats up, as discussed in Section 8.5.4.

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8.5.2 Break Mass Flow Rate and Primary System Mass Inventory

Following pump trip (at 1600 seconds) the break uncovers and, asshown in Figure 10, the break mass flow rate is well-predicted upuntil the time at which the break is isolated (4742 seconds -experiment, 4688 seconds - calculation).

As shown in Figure 12, the residual primary system massinventory, predicted by TRAC-PFl/MODl, at the time of pump trip(1600 seconds) is in good agreement with the experimental valueof - 2800 kg. It should be recognised, however, that theagreement is, to some extent, fortuitous because the over-predicted break mass flow rate prior to this time and the over-predicted initial inventory act as compensating errors. Theresidual mass (- 1500 kg) at the time at which the break isisolated is well-predicted and reflects the accurate reproductionof the break mass flow rate following pump trip. In line withthe experimental procedure, primary pump injection was turned offin the calculation following pump trip; the primary system massinventory therefore remained constant following break isolationuntil the accumulator flow was initiated.

8.5.3 Primary System Densities

Following pump trip, the liquid in the system falls to the lowestparts of the circuit, ie the reactor pressure vessel and the loopseals. As shown in Figure 13, the hot leg density risesimmediately after the pumps are tripped due to liquid drainingback from the "up-side" of the steam generator tubes. In theexperiment, the instrument measuring the loop seal density(positioned in the piping leading from the steam generatoroutlet) becomes immersed in liquid following pump trip andremains so until the end of the transient. In the calculation,the presence of liquid is not predicted in this part of thecircuit until - 3200 seconds (although liquid is present in the"pump side" of the loop seal prior to this time)- *seeAppendix II. Reasons for this discrepancy have-not been fullyinvestigated. However, factors which might adversely influencethe predicted behaviour have been identified, ie incorrectpressure imbalance across the loop seal and insufficientlydetailed nodalisation of the vertical sections of the loop seal.In general, the calculations submitted by members of the OECDLOFT Program Review Group (11) correctly predicted the loop sealdensity following pump trip (but over-predicted the density priorto pump trip).

8.5.4 Fuel Cladding Temperatures

The predicted peak fuel rod cladding temperatures (at each of thesix levels implied by the TRAC-PFl/MODl core noding scheme) arecompared with the experimental data (at the nearest correspondingelevation) in Figures 18-23. A fuel rod power peaking factor of1.6 (as implied in an AEEW input deck for LOFT test L2-6) wasassigned to the peak rated rod in the TRAC-PFl/MODl calculation.The following observations are made:

AEEW - R 2275 10

(i) The time at which the core starts to heat up is over-predicted by '- 260 seconds (see Figure 23). The times atwhich the break is isolated (peak clad temperature of 835.2K) and the steam generator feed and bleed is initiated(peak clad temperature of 988 K) are under-predicted by- 50 seconds and - 450 seconds, respectively.

(ii) The predicted rate at which the core heats up is greaterthan that measured. Agreement is considerably better atthe top of the core (see Figure 23) than at lowerelevations and agreement worsens following break isolation(see, for example, Figure 20).

(iii) As measured experimentally, no heat-up is predicted at thebottom of the core (see Figure 18). The heat-up at the0.28 m elevation, observed in the experiment, was notpredicted by the TRAC-PFl/MODl calculation in the cellrepresenting elevations from 0.15 m to 0.42 m (seeFigure 19).

The above observations are consistent with those presented, bymembers of the LOFT Program Review Group, in the LP-SB-3"Comparison Report" (11). It is widely reported (11, 14, 15)that an important factor, contributing to the over-predicted

.- rates of care heat-up, is the inability of the codes, using a,,:l-dimensional vessel representation, to correctly predict thedistribution, throughout the core, of reflux condensationreturning to the vessel. However, in the TRAC-PFl/MODI analysis,an important discrepancy exists between the measured andpredicted differences in primary and secondary pressure. Duringthe core heat-up phase in the calculation, the primary sidepressure is below that of the secondary and it is unlikely,therefore, for the presence of reflux condensation to bepredicted. It is suggested, therefore, that in the TRAC-PFI/MOD1calculation, it is the lack of reflux condensation, rather thanits poorly predicted distribution throughout the core, that mightlead to the heat-up rate being over-predicted. This certainlyappears to be the case following break isolation when, in theexperiment, the primary side pressure becomes greater than thatof the secondary and there is a significant reduction in the rateat which the core continues to heat up. In the calculation, theprimary side pressure does not exceed that of the secondary untilthe steam generator feed and bleed is initiated and no reduction

..in the rate of heat up is predicted following break isolation.

Although not fully investigated, it is thought that the tendencyof TRAC-PFl/MOD1 to under-predict the core density, duringcertain conditions, due to deficiencies in its interphase dragmodel (16) could result in the core drying out at a greater ratethan that measured and might contribute to the rate of core

.heat-up being over-predicted.

8.6. Core Cool-Down and Recovery Phase

The core cool-down and recovery phase is defined as that part ofthe transient between steam generator feed and bleed initiation

AEEW - R 2275 1i

(5415 seconds - experiment, 4964 seconds - calculation) andexperiment termination (6845 seconds).


As shown in Figure 9, steam generator feed and bleed initiationresults in a rapid decrease in secondary system pressure. Thecorresponding decrease in primary system pressure is shown inFigure 7. The rates at which the primary and secondary systempressures are predicted to decline are slightly under-predicted.Sensitivity of the pressure histories to the size assumed for thesecondary side steam bypass valve, used during feed and bleedoperation, and the consequent effect on the accumulator flowrate, is discussed in Section 8.6.3.

8.6.2 Fuel Cladding Temperatures

Following steam generator feed and bleed initiation, the coretakes slightly longer to quench in the calculation then in theexperiment. As shown in Figures 20, 21 and 22, the enhanced ratewith which the core is predicted to cool, following thecommencement of accumulator flow (- 5300 seconds) is very wellreproduced. However, in the calculation, as a result of theslightly under-predicted primary side depressurisation rate,there is a relatively longer period (approximately twice as long)between feed and bleed initiation and accumulator flowcommencement (during which the rate of cooling is less rapid).

8.6.3 Accumulator Injection Flow

Accumulator flow is predicted to commence - 280 seconds earlierthan in the experiment. As shown in Figure 24, its behaviour isreasonably well reproduced. The oscillatory accumulator flow,reported in other calculations (11),- is not observed in theTRAC-PFl/MODI analysis. Previously reported peaks in theaccumulator flow rate predicted by TRAC-PFl/MODl were found to bethe result of incorrect mass flow rates being attributed, byTRAC, to "signal variables" used for plotting. (The problemarises when the void fraction in the bottom cell of theaccumulator is % 0.0).

At - 6400 seconds, accumulator nitrogen was predicted to haveentered the system and the calculation was terminated. Finernodalisation of the bottom of the accumulator (to ensure a = 0.0in the bottom cell) could have prevented this situation.

The size of the steam bypass valve used during the feed and bleedoperation was not specified in the available documentation. Theeffect, on the secondary side depressurisation rate and theaccumulator flow rate, of increasing the valve area by - 70%(from 2.46 x 10-4 m2 to 4.093 x 10- m2 ) is shown in Figures 25and 26. The larger flow area produced a more rapid secondaryside depressurisation and, consequently, a greater accumulatorflow rate, in better agreement with the experimental data.

AEEW - R 2275 12

9 CONCLUSIONS

The main findings of the TRAC-PFl/MODl analysis of the OECD LOFTexperiment LP-SB-3 were as follows:

Mi) The calculation ran with a CPU to real time ratio of 0.73and an average time step of 0.32 seconds.

(ii) Despite the break line density being well-predicted,TRAC-PFl/MODI slightly over-predicted the break mass flowrate prior to pump trip. This is thought to be aconsequence of deficiencies in the TRAC critical flow model- the predicted break mass flow rate during this period was

10% greater than that implied by the HomogeneousEquilibrium Model. In general, the calculations reported(by members of the OECD LOFT Program Review Group) in theLP-SB-3 "Comparison Report" correctly reproduced theexperimental break mass flow rates by applying appropriatebreak flow multipliers (of < 1.0). (Subcooled and two-phase choked flow multipliers of 1.0 were used throughoutthe TRAC-PFl/MOD1 calculation).

(iii) Overall trends with respect to primary and secondary systempressure histories were reasonably well-predicted.Differences between the experiment and the calculation inthe relative magnitudes of the primary and secondary systempressures, however, resulted in conditions for refluxcondensation not being predicted during the core heat-upphase of the transient. This was contrary to theexperimental behaviour and was thought to contribute -particularly following break isolation - to the predictedrate of core heat-up being significantly greater than thatobserved experimentally. Although not fully investigated,under-prediction of the core density, due to deficienciesin the TRAC-PFl/MODl interphase drag model, has beenidentified as a potential contributor to the poorlypredicted rate with which the core temperature rises. Thecalculations presented in the LP-SB-3 "Comparison Report"also significantly over-predicted the rate of coreheat-up.

(iv) Minimum primary system mass inventory was reasonably wellreproduced. As observed in the experiment, no uncovery ofthe bottom of the core was predicted by the TRAC-PFl/MODIcalculation.

(v) The predicted time between steam generator feed and bleedinitiation and the core being quenched was slightly longerthan that observed experimentally. The main reason forthis was thought to be a delay, relative to the experiment,in the time at which the accumulator flow was predicted tocommence. This was caused by the predicted rate ofdepressurisation during feed and bleed operation beingslower than that measured and was shown to be rectifiedwhen the flow area of the steam bypass valve used duringthe feed and bleed operation (not specified in theavailable documentation) was increased.

AEEW - R 2275 13

(vi) During the core recovery phase, the mass flow rate from theaccumulator was reasonably well reproduced. Severeoscillations in the accumulator flow, reported in thecalculations performed by members of the OECD LOFT ProgramReview Group, were not observed in the TRAC-PFl/MODlcalculation.

(vii) Accumulator nitrogen was predicted to have entered thecircuit at - 6400 seconds and the calculation wasterminated at this time, ie before initiation of the LowPressure Injection System. The bottom cell of theaccumulator was partially full at this time and finernodalisation of the bottom of the accumulator could haveprevented the premature ingress of nitrogen.

The calculation reported should be considered a "Base Case", theresults of which have not been exhaustively analysed. With theexception of the rate at which the rod cladding temperatures roseduring the core uncovery phase of the transient, agreement withthe experimental data was considered reasonable. A fullerinvestigation of factors influencing the rate with which the coreheats up (including the effect of deficiencies in theTRAC-PFl/MODl interphase drag model) would be desirable.

10 ACKNOWLEDGEMENTS

The guidance of Dr C G Richards during the course of this work isgratefully acknowledged.

11 REFERENCES

1 REEDER D L, LOFT System and Test Description, July 1978,(TREE-1208, NUREG/CR-0247).

2 KEE K J, SCHALLY P J, WINTERS L, Base Input for LOFT RELAP5Calculations, July 1980 (EGG-LOFT-5199).

3 GRUSH W H, TANAKA M, MARSILI P, Best-Estimate Predictionfor the OECD LOFT Project Small Cold Leg Break ExperimentLP-SB-3, November 1983 (OECD LOFT-T-3005).

4 ALLEN E J, Internal Document.

5 ALLEN E J, Internal Document.

6 NEILL A P, Internal Document.

7 ALLEN E J, TRAC-PFl/MODI Post-Test Calculations of the OECDLOFT Experiment LP-SB-l (AEEW*- R 2254).

8 PELAYO F, TRAC-PFl/MODI Post-Test Calculations of the OECDLOFT Experiment LP-SB-2, March 1987 (AEEW - R 2202).

9 McPHERSON G D, Decay Heat Data for OECD LOFT Experiments,October 1985 (Letter to OECD LOFT Programme Review GroupMembers).

AEEW - R 2275 14

10 ALEMBERTI A, PROTO G, Experiment Analysis and SummaryReport on OECD LOFT Nuclear Experiment LP-SB-3 (DRAFT),December 1985 (T-20000-XX-140-020).

11 ALEMBERTI A, Comparison Report on OECD LOFT ExperimentLP-SB-3, August 1986 (T-20000-XX-140-021).

12 HALL, CZAPARY, Tables of Homogeneous Equilibrium FlowParameters for Water in SI Units, September 1980(EGG-2056).

13 MODRO S M, FELDMAN E M, NEWMAN N and PETERS M D, ExperimentAnalysis and Summary Report on OECD LOFT NuclearExperiments LP-SB-I and LP-SB-2, May 1984 (OECDLOFT-T-3205).

14 HARWOOD C, BROWN G, RELAP5/MOD2 Calculation of OECD LOFTTest LP-SB-03, April 1986 (GD/PE-N/535)..

15 GUNTAY S, RELAP5/MOD2 Assessment: OECD-LOFT Small BreakExperiment LP-SB-3, Gemeinschaftsberict Nr 13, April 1986.

16 ARDRON K H, CLARE A J, Assessment of Interphase DragCalculations in the RELAP5/MOD2 and TRAC-PFl/MOD1 Thermal-Hydraulic Codes, November 1986 (GD/PE-N/557 (Revised)).

17 Safety Code Development Group, Energy Division, LANL,TRAC-PFl/MODl: An Advanced Best-Estimate Computer Programfor Pressurised Water Reactor Thermal-Hydraulic Analysis,July 1986, (NUREG/CR-3858, LA-10157-MS).

AEEW - R 2275 15

TABLE 1

INITIAL CONDITIONS FOR EXPERIMENT LP-SB-3

PRIMARY COOLANT SYSTEM

Measured (10)

50.3 ± 1.2482.6 ± 2.6

Power Level (MW)Primary Coolant Mass Flow

Rate (kgs- 1 )Pressurizer Pressure (MPa)Pressurizer Liquid Level (m)ILCL Temperature (K)ILHL Temperature (K)

STEAMIGENERATOR SECONDARYSIDE

Liquid Level (m)Pressure (MPa)Liquid Temperature (K)Mass Flow Rate (kgs- 1 )

ECCS - ACCUMULATOR A

15.261.115

556.6576.6

0.215.58

535.626.67

2.84303.7

2.04

±±±±

0.110.0611

Predicted

50.3482.2

15.201.15

558.1577.6

0.215.57

536.026.40

2.84303.7

2.04

+ 0.005± 0.06± 3.6± 0.77

± 0.1±6± 0.01

Pressure (MPa)Temperature (K)Liquid Level (m)

AEEW - R 2275

TA1BLE 2

OPERATIONAL SETPOINTS TOR UMENT LP-SB-3

Measured During Experiment Specified to TRAC-PFI/MODl(10) Calculation

ActionReference

Reference Setpoint (component/ Setpointcell no)

Small BreakValve Opened

Reactor Scrammed

Main FeedwaterShut Off

MSCV Begins toClose

MSCV Begins toOpen

Primary CoolantPumps Tripped

Break ValveClosed

Steam BypassValve Opened

Main FeedwaterInitiated

AccumulatorInjectionInitiated

LPIS Initiated

Time

ILHL Pressure

ILHL Pressure

Secondary SystemPressure

Secondary SystemPressure

Primary CoolantSystem MassInventoryRemaining

Maximum CladdingTemperature



IUH Pressure

IL=L Pressure

0 secs

14.19 MPa

14.19 MPa

6.35 MPa

7.09 MPa

2800* kg

835.2K

988K

988K

2.79 MPa

1.03 MPa

Time

ILHL Pressure(1/4)

ILHL Pressure(1/4)

Initially:- ILHLPressure (1/4)

During MSCVCycling:-SecondaryPressure (21/2)

SecondaryPressure (21/2)

Time

Maximum CladdingTemperature of'SupplementaryRod

Maximum CladdingTemperature ofSupplementary

Rod

Maximum CladdingTemperature ofSupplementary

Rod

ILHL Pressure(1/4)

ILHL Pressure(1/4)

0 secs

14.19 MPa

14.19 MPa+0.2 secs

14.19 MPa+0.29 secs

6.35 M4Pa

7.09 MPa

1600 secs

835.2K

988.OK

988.OK

2.79 MPa

1.03 MPa

A A J. J

* It had been intended to trip the primary coolant pumps when 2000 kg of primarymass inventory remained.

AEEW - R 2275

'IBLE 3

CIMRlEMMGY OF EVEI' FOR '1PERII2T LP-SB-3

Time After ExperimentEvent Initiation (seconds)

Measured (10) Predicted

Small break valve opened 0.0 0.0Reactor Scrammed 9.21 ± 0.01 11.22Main feedwater pump shut off on scram signal 9.41 ± 0.01 11.42

signalMSCV started to close 9.5 ± 0.2 11.52Main feedwater valve isolated 10.81 ± 0.01 12.22MSCV closed 21 ± 0.2 24.7Pressurizer level below indicating range 67 ± 3 84.41First time MSCV cycled opened 87.5 ± 0.2 26.7Subcooled blowdown ended 98.5 ± 0.5 100Pumps differential pressure degradation 875 ± 3 700 - 11002

observedlast time MSCV cycled open 1030 ± 0.2 124.4Primary coolant pumps tripped 1600 ± 2 1600Break uncovered 1612 ± 5 1624Primary coolant pumps decoupled from 1626 ± 1 1650

flywheelsStart of core heat up 3800 ± 50 40603Break isolated 4742 ± 2 4688Steam generator feed and bleed initiated 5415 ± 5 4964Maximum cladding temperature reached 5422 ± 1 4980Accumulator injection initiated 5588 ± 3 5308Cbre quenched 5800 ± 50 55604LPIS initiated 6785 ± 2 -Experiment terminated 6845 ± 2

1 Defined as the time at which the liquid level in the pressurizer 4 0.01 m.

2 As implied by Figure 15.

3 Defined as the time at which Tmax peak rod - Tsat > 2K.

4 Defined as the time at which Tmax peak rod - Tsat 4 2K.

AEE3 - R 2275

APPENDIX I

MICROFICHE LISTING OF THE TRAC-PFI/MOD1 INPUT DECK

FOR LP-SB-3

The microfiche can be found on the inside of the backcover of this report.

APPENDIX II

SERIES OF PICTURES SHOWING PREDICTED SYSTEM CONDITIONSTHROUGHOUT THE LP-SB-3 TRANSIENT

The following series of pictures shows, at selected intervals,the predicted void fraction distribution, the liquid and vapourvelocities and the occurrences of stratified flow conditionsthroughout the system. The nodalisation may be compared withthat of Figures 2, 3 and 4.

AEEW - R 2275

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 0.0

VLIQ --

(10.0)VVAP --

(10.0)

VOID FRACTION

Pi .8

II

I

I

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTS

TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 107.9VLIQ --

(10.0)WVA? -ý

(10.0)

VOID FRACTION

I

I

I


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 210.4VLIQ -- k(10.0)

WVA --

10.0)

VOID FRACTION

<= 0.88

FII

I


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 300.6VLIQ -4ý(10.0)

WoAP -o

(10.0)

VOID FRACTION

FI

I

I


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 500.4VLIQ -- 4(10.0)VVAP --(10.0)

VOID FRACTION

0.. 8i

II Fri-nI

I


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 1000.4VLIQ -ý

(10.0)VVAP--(10.0)

VOID FRACTION

[;;A.8

AL.

II FrIlI

I

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 1513.

VLIQ -ý

(10.0)WVA? -ý

(10.0)

VOID FRACTION

1IF-F1--l-

IU

I


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 2002.(VLIQ -+(10.0)VVAP -- +(10.0)

VOID FRACTION

<:; 0.881

F-F17

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 2514.E

VLIQ - .(10.0)VVAP-4ý(10.0)

VOID FRACTION

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTTW TITLE OF FRAME,:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 3024.

VLIQ --( 10.0)wVAP -- +( 10.0)

VOID FRACTION

3.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTS

rITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 3505.VLIQ --

(10.0)(.AP -

( 10.0)

VOID FRACTION

F 10.88


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 4000.1VLIQ -- +( 10.0)VVAP

10.0)

VOID FRACTION

0 88

to4

-jn)


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 4515.VLIQ --

(10.0)VVAP ---

V 10.0)

VOID FRACTION

tri

LI:


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 5013.VLIQ -- ý(10.0)wAP -- t

(10.0)

VOID FRACTION

FX-.....]

.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTS

ITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 5500.VLIQ --( 10.0)

VVAP -- +

(10.0)

VOID FRACTION

[. A0.88


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 6019.4VLIQ -- f( 10.0)VVAP --- +(10.0)

VOID FRACTIONFiT]o o

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTTmo TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATIONTi 0.0VLIQ ---( 10.0)

wAP ---1(0.0)

VOID FRACTION

<-•.0.88.


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 107.9VLIQ --- *( 10.0)

VVAP --- +( 10.0)

VOID FRACTION

...<=:.0.889



(10.0)vvAP--

( 10.0)

VOID FRACTION

I':= 0~"'. 88,!hi::•"'

E


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 300.6VLIQ -+( 10.0)VVAP --- +(10.0)

VOID FRACTION

F--.7-]


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 500.4

(10.0)VVAP-+(10.0)m

VOID FRACTION

.11


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 1000.'VLIQ --(10.0)

WAP ---(10.0)

VOID FRACTION

1


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION

4.

Ti 1513.4VLIQ -- +

( 10.0)VVAP -- +( 10.0)

f •

VOID FRACTION

I; 0.A



.-

Ti 2002.(VLIQ -- +( 10.0)VVAP --- *

( 10.0)

VOID FRACTION

rzz- / OP


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 2514.iVLIQ -

( 10.0)WAP ---( 10.0)

VOID FRACTIOH


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 3024.fVLIQ -ký(10.0)

WVAP -ý

10.0)

VOID FRACTION

<;i• 0.88•iii•;iliii:i!


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 3505.2VLIQ -4(10.0)

VVAP ---(10.0)7ZZZZZZZJ

1.4

VOID FRACTION

F--018

rU-



(10.0)VVAP -- +( 10.0)

W4

VOID FRACTION

I~1* * * ~

S.M.A.R.T. SYSTEM MIMIC FOR ANALYSIS OF REACTOR TRANSIENTSTITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 4515.

VLIQ -k(10.0)VVAP ----(10.0)

VOID FRACTION

I

A:.~'.:i:


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 5013.(VLIQ -- +(10.0)VVAP -4

(10.0)77-71

VOID FRACTION

IT

-4


TITLE OF FRAME:- LOFT TEST LP-SB-3 TRAC CALCULATION Ti 5500.EVLIQ --( 10.0)VVAP -- +( 10.0)

[1 177I

*~ *~.-

~m'

VOID FRACTION



F-

Ti 6019.5VLIQ --

(10.0)WAP -- +

( 10.0)

VOID FRACTION

APPENDIX III

COMPARISON OF BREAK MASS FLOW RATE PREDICTED BY TRAC-PFlI/MOD1WITH THAT IMPLIED BY THE HOMOGENEOUS EQUILIBRIUM MODEL

As described in Section 8.4.2, although well-predicted for thefirst - 500 seconds of the transient, TRAC-PF1/MOD1 slightlyover-predicted the break mass flow rate after this time, untilthe primary coolant pumps were tripped (and the break uncovered)at 1600 seconds. The fluid conditions in the last cell of thebreak line, at 1000, 1200 and 1400 seconds, are given in TableAIII.l. The predicted break mass flow rates at these times arecompared with those implied by the Homogeneous Equilibrium Model(HEM) (12) in Table AIII.2. The TRAC-PFl/MODI predicted valuesare found to be - 10% higher than the HEM figures. Figure AIII.l- taken from the TRAC Code'Manual (17) - confirms thatTRAC-PFl/MOD1 is expected to over-predict mass fluxes (underthese conditions) when compared with the Homogeneous EquilibriumModel.

un~om

120000.

E

800000.

GO=yI00

TRAC-PF1. .urne (RELAP4/MOD6)HEM(Tuq=560 K, Psat=7.1 MPa)

40000-

7 7 L4.107

2fvvýnWHO I 8.0.106 I.040 1.20

Stagnation Pressure (Pa)~.1I•,,,07

FIGURE AIII.I

AEEW - R 2275

TABLE AIII.1

FLUID CONDITIONS AT END OF BREAK LINE

Time Pressure Temper- Liquid Vapour Void Liquid Vapour Average- Quality

ature Density Density Fraction Velocity Velocity Density

(seconds) (MPa) (K) (kgm- 3 ) (kgm- 3 ) (ms- 1 ) (ms-I) (kgm- 3 )

I

1000 7.14616 560.4 738.5 37.37 0.3350 54.05 56.85 503.62 0.0261

1200 7.11658 560.1 739.0 37.20 0.4389 61.20 64.07 ' 530.98 0.0396

1400 7.07897 559.8 739.7 36.98" 0.4969 66.16 69.08 ' 390.52 0.0490

:P

TABLE AIII.2

Break Mass Break Mass % by whichTime Flow Rate Flow Rate TRAC-PFI/MODI

Predicted by Implied by over-predictsTRAC-PFl/MODI HEM break mass flowcompared with HEM

(seconds) (kgs- 1 ) (kgs- 1 )

1000 1.6578 1.4996 9.5

1200 1.6070 1.4386 10.5

1400 1.5748 1.4028 10.9

FIGURES

In Figures 7-26, the following line types are used:

TRAC-PFI/MODI Calculation

------------ Experimental Data

AEEW - R 2275

Inlicl loop Intact loop roken Wtoo

Mr

tL1

A

1

2.64 cm

0.88 cm

T (0 .3 5 in .)

Break nozzle insertTo DST

Figure 1 LOFT configuration for cold leg intact loop small

break Experiment LP-BB-03

Component No Component Name Component No

18234

615

Intact Loop Hot LegPressurizerSteam GeneratorPump SuctionPump No 2Pump No 2 Injection TeePump No 1

636

717

131415

Component Name

Pump No 1 Injection TeePump DischargeILCL, Break Line + NozzleILCL + ECC LineECC LineAccumulator Line ValveAccumulator

8PRESSURIZER 2 ACCUMULATOR

15STEAM. GENERATORi

zPUMP INJECTIONn 61

7

1 ILMLPUMP SUCTION

143 INJECTION

BREAK LINE

ECC LINE

FIGURE 2 ACCUMULATOLINE VALVEPRIMARY SYSTEM NODALISATION DIAGRAM FOR LP-SB-3

(a) INTACT LOOP

Component No Component Name

31 Broken Loop Hot Leg41 Broken Loop Cold Leg

~2ZZ~~RABV

41

S

BLCL

.: 2 : 3 I :5:6

FIGURE 2

PRIMARY SYSTEM NODALISATION DIAGRAM FOR LP-SB-3(h~ TU~flTCF.M T.OOP(b) BROKEN LOOP

Vessel Representation for "System Mimic"79(See Appendix 11)

Vessel Representation for "System Mimic"80

32

81I

80

lIIIL!

84

87

2

I

82-q--Component No

7980

8182

8384

8586878889

90

Component Name

Bypass Path 5Upper Plenum

.(D'comer)Upper Plenum (core)Plenum Component

(D'comer)Bypass Path 4Plenum Component

(core)Downcomer BypassDowncomerPipe Above CoreCoreLower Plenum and

Core BypassLower Plenum

1

35

2

1

86

2 I

5

5

6

H

4

5

6

7

0

1

86

2

3

4

5

6

7

8

1

85

2

3

3

4

5

62

I

It 2

904

FIGURE 3 -- - I

TRAC-PFL/MOD1 REACTOR VESSEL NODALISATION DIAGRAM FOR LP-SB-3

MAIN STEAM LINE

21MAIN FEEDOATER

27

22 .. AUX FEEDVATER

23

Cells Numbered Compone

14,19 2028,29,31 2121-24,26 22I-6 23

27

FIGURE 4

it No Component Name

BoilerSteam DomeDowncomerSteam Line ValveMain and Auxiliary

Feedwater Tee

TRAC-PF1/MODl STEAM GENERATOR SECONDARY SIDE NODALISATION DIAGRAM FOR LP-SB-3

THE FOLLOWING ARE PLOTTED AGAINST REACTOR TIME

rTOTAL CPU TIMEt.!1tTj

6000

5500[

1WInfrithi

C-)

wU)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

REACTOR TIME , SECONDSFIGURE 5

LP-SB-3 CALCULATIONCPU USAGE

TIHE FOLLOWING ARE PLOTTED AGAINST REACTOR TIME

TIME STEP SIZE1Winfrithl

14)-4

1.

0.8

0.6

z0u

0.4

0.2

0.00 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

REACTOR TIME , SECONDSFIGURE 6

LP-SB-3 CALCULATIONTIME STEP SIZE

THE FOLLOWING ARE PLOTTED AGAINST TIME

PE-PC-002 ,PRESSURElwinfrith

-4t'

0. 20E

0. 18E

0. 16E

0. 14E

I0. 12E

0. fOE*

0. 80E

0. 60E

0. 40E

0. 20E

0. OOE0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME , SECONDS

FIGURE 7

LP-SB-3 CALCULATIONPRIMARY SYSTEM PRESSURE


ulj

1WinfrithlPE-SGS-001 ,SIGNAL VAR. NO. 6

8000000

7500000

7000000

* 6500000

*-N

6500000

6000000

5500000

5000000300

TIM-CE , SECONDSFIGURE 8

LP-SB-3 CALCULATIONSECONDARY SYSTEM PRESSURES (0-300 SECONDS)

THE FOLLOWING ARE PLOTTED AGAINST TIME 1Wlnfr'ithit:'1

t~3-4U'

PE-SGS-001 ,SIGNAL VAR. NO. 6

8000000

7000000

6000000

I I I I I I I I I I I I I

50000001

N

z

4000000

I I I I I I I I I I I I I

8000000

7000000

6000000

5000000

4000000

3000000

2000000

1000000

0

3000000

2000000

1000000

A

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME , SECONDSFIGURE 9

LP-SB-3 CALCULATIONSECONDARY SYSTEM PRESSURES (0-6400 SECONDS)

THE FOLLOWING ARE PLOTTED AGAINST TIME JW In f r I7hFR-PC-BPK ,CONTROL BLK ID -72

1010 I I I I S 10

66

cif

(_3V 4 4

2

0

II

'A

~

I-..

*1I- [ 1 I I - I I I I .

2

0I JI I I

0 500 I 2000 I 2 "" 3 4 4

I I I I a a . . I _

O 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000.

TIME , SECONDS

FIGURE 10

LP-SB-3 CALCULATIONBREAK MASS FLOW RATE

THE FOLLOVING ARE PLOTTED AGAINST TIME

til DELPC-SO5B ,MIXTURE DENSITY

I1000

N)N)-4ul

800

600

**

Nc.:i

400

200

00 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME 5ECONDSFIGURE 11

LP-SB-3 CALCULATIONBREAK LINE DENSITY

THE FOLLOVING ARE PLOTTED AGAINST'TIME

PCS-MASS IFUNCTION1Winfrith

I

N)

U1%

********

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0


LP-SB-3 CALCULATIONPRIMARY SYSTEM MASS INVENTORY

N~


DE-PC-205 ,IIIXTURE DENSITY STRATIFIED VOL FLAG

I

lwinfrithl

1. 0 •,• .|.

0.8

0.6

0.4

0.2

0. 0 r.• t-.ir••Azt4Zdc

2

cr

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


LP-SB-3 CALCULATIONILHL DENSITY AND STRATIFICATION.ONSET

THE FOLLOIV]NG ARE PLOTTED AGAINST TItlE

DE-PC-1O5 .MIXTURE DENSITY .1Wtlnfrithl

STRATIFIED VOL FLAGW

t')'.3-4ul

I

I',)

(_0

1.0

0.8

0.6

0.4

0.2

0. 0 ,, r ak'--'L0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME E , SECONDSl-IGUll~u 14

LP-SB-3 CALCULATIONILCL DENSITY AND STRATIFICATION ONSET.

THE FOLLOVING ARE PLOTTED AGAINST TIME lWinfrithiPOE-PC-O01 PUMP DELTA-P

600000

t550000

ul500000

450000

400000

350000

300000-

250000-

200000- I

150000-

100000-

500000

0:

-500001 , , , , I , , ,

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


LP-SB-3 CALCULATIONPRIMARY COOLANT PUMPS DIFFERENTIAL PRESSURE


FUNCTION ,CONTROL BLK ID -881WInfrithl

N)

1 i •~~ffI&uIJiJuuIj .. -

I I I a I I ~ I I I I

8000001

600000

400000

I II IIi tII

I ~IL4vv ~

tvI; ,j

I - I I I ~~II

200000-

1~

1%

I' II I I

-200000

-400000

-600000

I I I 1 I I I I ~ I ~

'I

I I

-8000001

I I I I I I I I I I I I•utuuuti-

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME , SECONDS

FIGURE 16

LP-5B-3 CALCULATIONPRIMARY SYSTEM - SECONDARY SYSTEM PRESSURE

THE FOLLOWING ARE PLOTTED AGAINST TIME UWinfrithlPE-SGS-001 ,SIGNAL VAR. NO. 6,PE-PC-002PRESSURE

80000009 , , , , 8000000

7000000 "-' ' -7000000

6000000 6000000

5000000 5000000

4000000 • _•,..le- 4000000

Z'.

3000000. 3000000

2000000- 2000000

1000000 1000000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME , SECOND5FIGURE 17

LP-SB-3 CALCULATIONPRIMARY AND SECONDARY SYSTEM PRESSURES.

THEFOLLOWING ARE PLOTTED AGAINST TIME lWinfr'ithiTE-5HOS-002 ,CLADDING TEMP -FINE

tI,

t%)

U'

1000

950

II I I I I I | I I I

900 -

850

8001-

750

(w•0J

700 1-

650

6001-

550

500

450

400

- - ----

-S

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIME ., SECONDSFIGURE 18

LP-SB-3 CALCULATIONPEAK CLAD TEMPERATURES (0. 05M)

THE FOLLOWING ARE PLOTTED AGAINST TIME Wunfrithl9~ TE-5G06-01I ,CLADDING TEMP -FINE

1000 I I I I I I I I I I I I I

950 -

900 I

850 [

800

750

.6wC3

700 I

650

600

550

500

450

/. nn

A

'I

I I I I I I I I I I I

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIMtE , SECONDSFIGURE 19

LP-SB--3 CALCULATIONPEAK CLAD TEMPERATURES (0. 28M)

THE FOLLOWING ARE PLOTTED AGAINST TIMETip

1WinfrithlTE-5106-021 ,CLADOING TEMP -FINE

-L

wC3

TIME SECONDS

FIGURE 20

LP-SB--3 CALCULATIONPEAK CLAD TEMPERATURES (0. 53M1)

THE FOLLOWING ARE PLOTTED AGAINST TIME IWinfrlthqTE-5J08-032 ,CLADDING TEMP -FINE

It'.

1

w,v

0 500 1000 1500 2000 2500 3000 3500 4000 4500'5000 5500 6000

TIME S SECONDSFIGURE 21

LP-SB--3 CALCULATIONPEAK CLAD TEMPERATURES (0.81M1)

THE FOLLOWING ARE PLOTTED AGAINST TIME:Rt.

tn

Winfr'IthTE-5HO7-049 ,CLADDING TEMP -FINE

w.

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

TIM-CE , SECONDS

FIGURE 22

LP-SB-3 CALCULAT IONPEAK CLAD TEMPERATURES (1.25M1)

THE FOLLOWING ARE PLOTTED AGAINST TIME 1W InfrI thTE-5GO6-062 ,CLADDING TEMP -FINE

1000,

.'950-'U'/

900 /

I850 /

I

800 II

750 II I•

700 / *..

0 ' 650 I

600-

550-

500'

450-

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


LP-SB-3 CALCULATIONPEAK CLAD TEMPERATURES (1.57M)

.THE FOLLOWING ARE PLOTTED AGAINST TIME

FR-ECC-OIA ',MASS FLOW RATEWInfrithl

tll

1~)-4U'

4.

3.5

3. 0

2.5

2..0

LUu-

N13,

1.5

1.0

0.

0.

-0.

-1.015000 5200 5400 5600 5800 6000 6200 6400


LP-SB-3 CALCULATIONACCUMULATOR MASS FLOW

THE FOLLOING ARE PLOTTED AGAINST TIME lWinfrithlFR-ECC-O1ASIGNAL VAR. NO.

,PE-SGS-0016

,MASS FLOW RATE

U'

4.0

3.5

3.0

2. 5

2.0

1.5

8000000

7000000 -

6000000 -

5000000 -

4000000

N,z

3000000 -

2000000 -

1000000 -

8000000

7000000

6000000

5000000

4000000L)

(5-

1.0

0.5

0. 0

-0. 5

3000000

2000000

1000000

-1.01,5000

0 05200 5400 5600 5800 6000 6200 6400

TIME , SECONDS

FIGURE 25

LP-SB-3 CALCULATIONACCUMULATOR MASS FLOV RATE AND SECONDARY SYSTEM PRESSURE


I

t.j-4U'

FR-ECC-OIASIGNAL VAR. NO.

,PE-SGS-0016

,MASS FLOW RATE

4.0

3.5

3.0

2.5

2.0

8000000

7000000

6000000

5000000

4000000

IWlnfrithI

8000000

7000000

6000000

5000000

uIul

EU.v

1.5

1.0

c'j

0.5

0.0

3000000 -

2000000

1000000 -

0 -

4000000

3000000

2000000

1000000

0-1.015000 5200 5400 5600 5800 6000 6200 6400

TIME , SECONDS

FIGURE' 26

LP-SB-3 CALCULATIONACCUM MASS FLOW RATE AND SEC PRES (ST BYPASS VALVE AREA INCREASED)

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ADDITIONAL

AKE WINFRJIT, DORCHESTER, DORSET, DT2 8DH

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NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER(2-89) fAaslgned by NRC. Add Vol., Supp., Rev.,NRCM 1102, and Addendum Numbers, If any.)3201,.3202 BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse) . NUREG/IA-00222. TITLE AND SUBTITLE AEEW-R 2275

TRAC-PFl/MODl Post-Test Calculations of the OECD LOFTExperiment LP-SB-3 3. DATE REPORT PUBLISHED

MONTH j YEAR

Apri 1 19904. FIN OR GRANT NUMBER

5. AUTHOR(S) 6. TYPE OF REPORT

......... '' "TechnicalE. J., Allen, A. P. Neill. .. ...

7. PERIOD COVERED (Inclusive Dares)

B. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC. provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address,* if contractor, providename and mailing addres) I :" -" ' .. ..... "

United Kingdom Atomic Energy AuthorityAtomic Energy Establishment, WinfrithDorchester Dorset DT2 BDHUnited Kingdom

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, typ sam as aboe- if contractor, provide NRC Div•ison, Offie or Region, U.S Nuclear Regulatory Commisin,and mailing address. .

Office of Nuclear Regulatory ResearchU. S. Nuclear Regulatory CommissionWashington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT 1200 words or less)

Analysis of the small, cold leg break, OECD LOFT Experiment LP-SB-3 using thebest-estimate computer code TRAC-PFl/MODl is presented.

Descriptions of the LOFT.facility and the LP-SB-3 experiment are given and developmentof the TRAC-PFl/MODl input model is detailed. Thecaluclations performed in achievingthe steady state conditions', from which the experiment was initiated, and thespecification of experimental boundary Conditions are outlined.

12. KEY WORDS/DESCR IPTORS (List words or phrases that will assist researchers In locating the report.) 13. AVAILABILITY STATEMENT

Ilni imiltrl14. SECURITY CLASSIFICATION

TRAC-PFl, OECD LOFT, Small break (This Page)

15. NUMBER OF PAGES

16. -PRICEI .. . .

NRC FORM 335 (2-89)

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