fILLs NUREG/IA-0021 Intemational Agreement Report · 2012. 11. 21. · P.O. Box 37082 Washington, D.C. 20013-7082 and ... A dummy time-dependent volume was attached to the top of

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* -. NUREG/IA-0021

IntemationalAgreement Report

RELAP5/MOD2 Calculations ofOECD LOFT Test LP-SB-2

Prepared byP. C. Hall

Central Electricity Generating BoardGeneration Development & Construction DivisionBarnwood, Gloucester GL4 7RSUnited Kingdom

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 Application 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-0021

InternationalAgreement Report

RELAP5/MOD2 Calculations ofOECD LOFT Test LP-SB-2

Prepared byP. C. Hall


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 Application Program (ICAP)

Published byU.S. Nuclear Regulatory Commission

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 th'e 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 USNRCI 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.

GD/Pt-N/606

Abstract: To help in assessing the capabilities of RELAP5/MOD2 for PWRFault Analysis, the code is being used by CECB to simulateseveral small LOCA'and pressurised transient experimentsin the LOFT experimental reactor. The present report describesan analysis of small LOCA test LP-SB-02, which simulated a 1%hot leg break LOCA in a PWR; with delayed tripping of theprimary coolant pumps. This test was carried out under theOECD LOFT Programme.

An important deficiency identified in the code is inadequatemodelling of the quality of the fluid discharged from the hotleg into the break pipework. This gives rise to large errorsin the calculated system mass inventory. The effect of usingan improved model for vapour pull-through into the break isdescribed.-

A second significant code deficiency identified is the failureto predict the occurrence of stratified flow in the hot leg atthe correct time in the test. It is believed that this errorcontributed to gross errors in the loop flow conditions afterabout 1300s.

Additional separate effects data necessary to resolve the codedeficiencies encountered are identified.

i.

Executive Summarv:

The RELkP5/MOD2 transient thermal-hydraulics computer code isbeing used by CEGB for calculation of small break loss ofcoolant accident (LOCA) sequences for Sizewell 'B'. To asistCEGB in assessing the capabilities and status of this code, ithas been used to simulate SBLOCA test LP-SB-02 carried out inthe LOFT experimental reactor under the OECD LOFT programme.This test simulated a 1.0% hot leg break in a PWR, with delayedtripping of the primary coolant circulating pumps. This reportcompares the results of the RELAP5/MOD2 analysis withexperimental measurements, and with published analyses usingearlier versions of RELAP5.

Overall agreement between calculated results and experimentaldata was reasonably good for the first 1200s of the transient,but was unsatisfactory at later times. The principledeficiencies identified in the code were as follows:

(a) In common with previous analyses of Test LP-SB-02 usingRELAP5/MODI, RELAP5/MOD2 failed to predict the onset ofstratified flow in the hot leg at the correctconditions.

(b) The test data show that fluid quality in the offtake pipeleading to the break orifice was significantly highert•han that in the hot leg. The RELAP5/MOD2 horizontalstratification entrainment (HSE) model, designed to modelthis effect, failed to predict the correct behaviour inthis test. A modified code version incorporatiigimproved correlations for the quality in the offtake pipewas found to produce markedly more accurate results.

(c) Large errors in calculation of the loop flow wereencountered in the later part of the experiment. Themost likely cause of these errors is thought to be thefailure to calculate the correct flow regime in the hotleg, noted in (a) above.

To assist in developing code models which will give improvedagreement with similar experiments, further separate effectsexperimental data are desirable on the following:

(a) Transition to stratified flow in geometries resembling aPWR hot-leg.

(b) Flow quality in a offtake pipe connected to a largerhorizontal pipe in which there is a two-phase flow with amass velocity of more than 1000 kg m-2s 1 .

Experiments designed to provide this information are currentlyin preparation at AERE, Harwell.

ii.

TABLE OF CONTENTS

Abstract

Executive Summary ii

Contents iii

1. Introduction 1

2. Description of Test 1

3. Code Version and Input Model 1

4. Initial and Boundary Conditions 2

5. Base Case Calculation 3

6. Calculations Using Modified Code Version 4

6.1 Description of the Modified Horizontal Stratification 4Entrainment Model.

6.2 Comparison of results of the modified code with 5

experimental data.

7. Discussion and Comparison with Previous Analyses 7

8. General Code Performance and cpu Time. 8

9. Conclusions 8

10. References 9

Table 1 - Initial Conditions for LP-SB-2 11Table 2 - Sequence of Events for LP-SB-2 Calculation 12

Appendix 13

iii.

1. INTRODUCTION

The RELAP5/MOD2 code [E] is in use by CEGB for calculating Small-BreakLoss-of-Coolant-Accident (SBLOCA) and pressurised transient sequencesfor the Sizewell 'B' PWR. RELAP5/MOD2 uses a six-equation two-fluidmodel to describe two-phase flow in the reactor primary and secondarysystems. It supersedes the RELAP5/MODI code, which employed afive-equation model (one-phase constrained to be at thermal equilibrium)and used less sophisticated models for flow regime transitions andinterphase interaction terms.

To assist in assessing the capabilities and status of RELAP5/MOD2, thecode is being used by GDCD to simulate several small LOCA and pressurizedtransient experiments carried out, in the LOFT experimental reactor underthe OECD LOFT programme (2, 3, 4]. The present report describes ananalysis of small LOCA test LP-SB-02, which was part of this test series.Test LP-SB-02 simulated a 1% hot leg LOCA in a PWR with a delay ofapproximately fifty minutes in tripping the primary coolant pumps. Thetest is described in Refs. (5), [6] and [7].

Comparisons are given with earlier calculations of the same experimentcarried out with RELAP5/MODI, and described in Refs. (6], (8] and [9].The effect of modelling changes introduced into the MOD2 code version arehighlighted.

2. DESCRIPTION OF TEST

The sequence of key events is given in Table 2. The transient is brieflydescribed as follows. The test was initiated by opening the break (timezero) and isolation of the steam generator was initiated at SCRAM, l.8slater. High Pressure Injection (HPI) flow and auxiliary feed to thesteam generator were initiated at 42s and 64s respectively. At about600s the pump head degraded sharply and there was evidence of flowstratification in the hot leg. However, the pumps maintained a flowcirculation round the loop up to 1290s. Because of the complex effectsof the stratified flow, the density of fluid entering the break line wassystematically lower than the density of the fluid in the hot leg formost of this period. At about 1200s the entrance to the break linebecame completely uncovered, leading to an increase in thedepressurization rate. HPI flow matched break flow at about 2300s andpressure fell steadily to the set point of 3.16MPa when the pumps weretripped (approximately 2900s). Pump trip caused minor changes indifferential pressure and water distribution, but had no significanteffect on break line density or break flow. The test was terminated at6810s.

3. CODE VERSION AND INPUT MODEL

The basic code version used for this calculation was RELAP5/MOD2 cycle36.04, with several error corrections (primarily Cray conversion errors)implemented by UKAEA, Winfrith. The semi-implicit numerical scheme wasused throughout because code failure was found to result when use of thenearly-implicit scheme was attempted.

The input data was based on that used in Ref [2] for the analysis ofLOFT cold leg break test LP-SB-01. Standard values of the single andtwo-phase break flow multipliers, CDl and CD2 (0.93 and 0.81,respectively) were used (e.g Ref. [10]).

1.

The noding diagram is shown in Figure 1. The model consisted of 120volumes, 126 junctions and 125 heat structures. Junctions between thehot leg and break line, and between the hot land cold legs and the vesselwere modelled as cross-flow junctions. This meant that relatively shorthydrodynamic-volumes were required in the hot leg and in the vessel upperplenum and downcomer.

A microfiche listing of the code input and output has been filed underSafety Technology Section in the Microfiche Archive at GDCD, Barnwood.

4. INITIAL A.ND BOUNDARY CONDITIONS

To establish the required steady state, a pseudo-transient calculationwas run until the problem time reached lO0s, when the code indicated thata satisfactory steady state had been achieved. Parameters controlled toachieve the desired steady state were steam and feed flow, and the pumpspeed. A dummy time-dependent volume was attached to the top of thepressurizer to maintain the desired steady primary pressure. After.l00sthese steady state controllers were all removed, the dummy volumedeleted, and the calculation allowed to proceed for 20s before initiatingthe transient. Figures 2, 3 and 4 show the hot leg pressure, andpressurizer level, the flows into and out of the SG separator, and thesteam generator pressure and level during the steady state run. The slowfall in primary pressure after 100s shown in Fig. 2 is the result of heatlosses calculated from the pressurizer. These figures illustrate that asatisfactory steady state was achieved.

The RELAP5 calculated steady state initial conditions are compared withexperimental values from Ref. [6] in Table 1. These can all be seen tobe in agreement, except for the steam generator (SG) secondary sidelevel, which had to be set artificially high in order to eliminateperiodic emptying and filling of the separator volume. This modificationwas considered acceptable since in test LP-SB-02 the SG secondary playsonly a minor role in the overall primary system energy removal.

Boundary conditions used in the test were obtained from the EG&G datapackage, Ref. [7).

The main primary circuit system (PCS) boundary condition was the HighPressure Injection (HPI) flow. This was modelled as a table of flowversus PCS pressure, rather than flow versus time. For the steamgenerator secondary side, auxiliary feed-water flow rate was modelledusing a table of flow versus time, with flow being terminated 1800s aftertrip. Also modelled was the brief opening of the steam bypass valve toan area of 1.28.10-4m2 when SG pressure first exceeded 6.5 MPa.

As in previous analyses of SBLOCA in LOFT (e.g, [3]), it was foundnecessary to model steam generator leakage in order to obtain reasonablyaccurate calculations of secondary pressure. The existence of leakagein test LP-SB-02 is confirmed by the observation of a falling liquidlevel after auxiliary feed was terminated. Acceptable results wereobtained when the leakage was modelled by setting a minimum flow area forthe Main Steam Control Valve of 2.0.10"3m2 .

2.

5. BASE CASE CALCULATION

This section briefly describes comparison of the test results withpredictions obtained using the standard version of RtELAP5/MOD2, cycle36.04. Key results are illustrated in figures 5 - 8; solid linesrepresent the experimental data and broken lines represent the RELAP5calculations.

(a) Primary pressure.

Figure 5 shows that agreement between measured and calculatedprimary pressure is reasonably good until about 1200s. Also,beyond 1900s, the depressurization rate is accurately calculated.However, in the period 1200-1900s, there are significant errors inthe calculated depressurization rate, leading to a systematicoverprediction of pressure in the long term transient. Because ofthis pressure offset, the time of pump trip is overpredicted(approximately 4150s, rather than 2853s).

(b) Break flow rate.

Figure 6 shows the measured and calculated mass flow rate in thebreak nozzle. Before about 800s, the break flow rate isunderestimated by about 15%. Subsequently it is overestimated byup to 50%, leading to large cumulative errors in system massinventory. The overestimate in break flow is believed to arisefrom errors in the calculated conditions in the break line, asdescribed in (c) below. In spite of the underestimation of systeminventory, the calculation correctly predicted that no dryoutoccurred in the core.

In the early part: of the calculation, prior to 250s unrealisticallysharp steps in the break flow rate are evident. Similar behaviourwas observed in previous RELAP5 calculations of subcooled and lowquality discharge, e.g. Refs. (2, 3 and 9].

(c) Hot leg and break line density.

The hot leg density (Figure 7) is seen to be reasonably accuratelycalculated until about 1400s: thereafter large errors occur.

Figure 8 shows the measured and calculated fluid density in thebreak line. A large systematic overestimate is seen despite thefact that the hot leg density is well predicted until about.1400s.This discrepancy is believed to be responsible for the prolongedoverestimate of discharge flow rate noted in (b) above.

The results summarised above indicate reasonably accurate calculation ofthe transient up to about 1200s, with increasing errors thereafter. Theprimary source of the errors is evidently the failure to calculate thecorrect relationship between the density in the hot leg and break line.Similar discrepancies in the break line density were found inRELAP5/MODl analysis of LOFT test LP-SB-02 reported in Refs. (6] and[9]. The authors of Ref. (6] attributed the error to the effect of flowstratification in the hot leg, which caused a preferential discharge ofvapour into the break line T-junction.

3.

Unlike RELAP5/MODI, RELAP5/HOD2 contains a special purpose model (thehorizontal stratification entrainment model) designed to correct the voidfraction donored to an off-take pipe for the effects of flow

stratification in an upstream horizontal volume. However, this model isinvoked only when the horizontal stratified flow regime is calculated tooccur in the upstream volume. For the forced circulation conditionscalculated to exist in test LP-SB-02, REI.AP5/MOD2 predicted the slug orannular mist flow regimes to persist in the hot leg until about 2250s.However, in the test, stratification in the hot leg began to occur atabout 600s when the pump head degraded [6]. Therefore, the RELAP5/MOD2horizontal stratification model was not applied during the appropriatephase of the test. In consequence results were similar to those ofRef. [6] obtained using RELAP5/MOD1.

To investigate this effect further the test was recalculated with amodified version of RELAP5/MOD2 containing an improved horizontalstratification entrainment model, which is applied at high massvelocities. Calculations with the modified code version are described inthe next section.

6. CALCULATIONS USING MODIFIED CODE VERSION

As noted in the prev ious section, a revised horizontal stratificationentrainment model has been developed and included in a modified versionof REIAP5/MOD2. This section briefly describes the model and goes on tocompare calculations performed using the modified code with the data fromtest LP-SB-02.

6.1 Descrintion of the Modified HorizontalStratification Entrainment Model

In the standard version of REIAP5/MOD2 the void fraction at ajunction connected to a horizontal pipe containing stratified flowis calculated from an algebraic expression involving the void*fraction" in the donor volume, the phase velocities in the junctionand*thermodynamic and 'geometric properties.' The equation isintended to model the effects of flow stratification andvapour/liquid pull-through on the flow in the side branch. Themodel is applied only when stratified flow is calculated in the

_donor volume: in other flow regimes the junction void fraction istaken as the donor volume void fraction.

In the modified code version [11] the junction void fraction iscalculated from the expression:

S(1-Xj)pg "g,j/(xj Pf q Uf'j) )

where the subscript j refers to Junction properties. The junctionquality Xj is calculated from the empirical correlation given bySmoglie [12] based on air-water test data.

This method of calculating aj is used at mass velocities in themain pipe below 2500kg mzs-1. For mass velocities above 3000kg m"2sl the Junction void fraction is taken simply as the donor voidfraction.+ In between'these limits linear interpolation is used.

+ The mass velocity 3000 kg m12 s"1 corresponds typically to the transitionto the dispersed flow regime, in which effects of gravitationalseparation may be expected to be small.

4.

The modified code version has been found to give much improvedagreement with separate effects test data on two-phase flows inhorizontal T-junctions in which there is stratified flow in themain pipe, [11]. However, it should be noted that no test data areavailable to confirm the modelling approach when there is high massvelocity (exceeding 1000kg m" 2 s-1 in the main pipeý Furtherexperiments are desirable to support the use of the.model for theseconditions.

6.2 Comparison of results of the modified code with exDerimental data

The results of the calculation with the modified code version arepresented in figures 9 - 17. Experimental data are shown as solidlines and modified code calculations as chain-dotted lines. Thetiming of key events is given in Table 2. Results are describedbelow:

(a) Primary pressure.

Figure 9 shows that the code modifications described abovehave little influence on primary pressure until about 1000sbecause the mass velocity does not fall below the 3000kgm. 2 s"1 limit until about 800s. Thereafter the modifiedhorizontal stratification entrainment model has the effect ofincreasing the discharge enthalpy which increases thedepressurization rate. The relatively rapid drop in pressurewhich occurred in the test between 1250s and 1750s is not,however, correctly predicted. Failure to predict this featureleads to a delay of about 700s in the calculation of the timeof pump trip. This remaining error is discussed furtherbelow.

(b) Break flow rate and primary system mass inventory.

It can be seen from figure 10 that modified code produces amuch improved calculation of break flow rate from 800sonwards..

Figure 11 shows primary coolant system mass inventory. Asexpected, the improvement in accuracy of the calculated breakflow leads to more accurate calculation of the system massinventory, particularly later in the transient.

(c) Hot leg and break line density.

The prediction of the density in the hot leg after 1500s isconsiderably improved in the calculation with the modifiedcode (Figure. 12). This is a consequence of more accuratecalculation of the discharge flow rate. The fluctuations incalculated density arising at about 3600s are caused by thepump trip.

Figure 13 shows measured and calculated break line density.As expected the modified code version gives a majorimprovement beyond about 800s. Agreement with experimentaldata is reasonably. good thereafter, except for the period1250-2000s, Calculated errors in thisiperiod evidentlyarise primarily from errors in the calculated liquidinventory of the hot leg (see Figure 12).

5.

(d) Secondary pressure.

Figure 14 shows a comparison of measured and calculatedpressure in the SG secondary. Reasonable agreement isdemonstrated, but this is to a large extent due to the tuningof the calculated leakage through the main steam controlvalve, described in Section 4.

(e) Loop behaviour.

Measured and calculated coolant velocities in the-hot leg areshown in Figure 15. Measured data are from two turbine flowmeters situated towards the top and bottom of the hot leg.The upper meter can be seen to uncover and show increased(steam) velocity at about 1lOOs (see ref [5]). The lower(liquid) velocity continues to fall, indicating complete flowstagnation at about 2000s.

The calculated results are significantly different,indicating continuing loop flow at velocities of 4-6ms" 1

until pump trip.

A second important error is in the calculated flow regime inthe hot leg. The 3-beam gamma-densitometers in the hot legindicate a sharp increase in the vertical void gradientabout 600s (Ref. [6]). The existence of fully stratifiedflow in the hot leg at 1l00s is confirmed by the suddenincrease in the velocity measured by the upper turbine flowmeter, see figure 5. In the calculation using the modifiedcode version'stratification in the hot leg was not predicteduntil pump trip.

Surprisingly the observed occurrence of fully stratified flowin the hot leg at about il00s took place at a mass velocityof approximately 1800 kg m-2 s"1 , almost an order of magnitudeabove the normally expected upper limit for the existence ofstratified flow, e.g [1].

Additional evidence indicating errors in the calculated loopflow conditions is shown in Figure 16. This figure showsmeasured "and calculated coolant densities in the loop seal,just below the SG discharge. Virtually no water leaves theSG beyond 1500s. In contrast, the calculated results showvery similar densities in the loop seal (Figure 16,) cold leg(Figure 17) and the hot leg (Figure 12).

In summary, the experimental data indicate that forward flow ofliquid around the loop fell sharply after about 1300s, when most ofthe-water drained from the hot and cold legs. RELAP5/MOD2predicted a continuation of forced circulation of liquid around theloop until the time of pump trip (3580s). Therefore, throughoutthe primary coolant system, detailed flow conditions calculated bythe code were in error after about 1300s.

6.

Sensitivity calculations were carried out in an attempt to identifythe source of the error in the calculated loop flow-rate afterabout 1300s. These are described in Appendix 1. The sensitivitycalculations included changes to the noding of the steam generatorsand hoc legs and changes to the assumed pump characteristics. Noneof the revised calculations satisfactorily reproduced theexperimental behaviour.

7. DISCUSSION AND COMPARISON UqTH PREVIOUS ANALYSES

Test LP-SB-02 has been analysed previously with the code RELAP5/MODI[6, 8, 9]. In these calculations a significant overprediction of thebreak line density was also observed. This was attributed to failure tomodel the effect on the break flow of stratification in the hot leg,since RELAP5/MODl.did not contain a Horizontal Stratification Entrainment(HSE) model describing this effect.

The released version of RELAP5/MOD2 gives similar results to thoseobtained-previously with RELAP5/MOD1, indicating that the HSE model inRELAP5/MOD2 is ineffective in describing the flow separation observed inthis test. Considerably improved agreement is however obtained with thecode version containing the modified horizontal stratificationentrainment model. Contrasting the two models, it is concluded that themain defects of the HSE model in the released version of the code are asfollows:-

(1) failure to model effects of flow stratification at high mass.velocities;

(2) inaccurate calculation of fluid quality in the side branch forstratified flow conditions.

The second major error observed in the RELAP5/MOD2 calculations was thefailure to calculate rapid reduction-in the forced circulation of liquidafter about 1300s. Similar difficulties were encountered in the earlierRELAP5/MODl analyses, e.g [9]. Several sensitivity calculations wereperformed as part of the present analysis to try to trace the source ofthis error (see Appendix 1 for details). These included changes tonoding of the steam generators and hot legs, and reductions in theassumed fully degraded pump heat characteristic. None of the additionalcalculations satisfactorily reproduced the measured liquid flowcharacteristics.

It is concluded that- the error is probably connected with the failure ofthe code to correctly describe the flow regime in the hot legs. Asdiscussed in the previous section, data from the turbine flow meters andgamma-densitometers indicates that the flow regime in the hot leg becamefully stratified at t - ll00s, whereas stratified flow was not calculatedto occur until much later (Table 2). It is likely that the error inidentifying the flow'regime leads to an overestimate of the interphasedrag forces in the hot legs; this probably causes an erroneous predictionof continued forced circulation of liquid in the loop.

Further experiments on flow-regime transitions in representativegeometries would assist in confirming this hypothesis.

7.

8. GNEtrAL CODE PERFORMA. CE -AND CPU TIME

In the present calculations the code was found to be robust, stable andsubject .o negligible mass conservation errors. For the released codeversion,.,cpu:°real time ratio was 2.76:1 on a Cray XMP computer. Thecalculation with the.modified code version -ranslightly more quickly.The cpu time per mesh cell was 6.58ms.

The cpu:real timb ratio was about three times slower than that'?experienced in the Ref. [2] analysis of test LP-SB-01. This was: becausethe higher fluid velocities in the loop, which arose as a result .ofdelayed pump trip, led to the computational time steps being limited bythe Material Couran: Limit (MCL). The MCL restriction occurred in theshortest volumes, 104 and 184, which are used for the modelling of Tees'with the cross-flow Junction option and have a length to diameter ratioof unity in accordance with EG&G guidelines [12]. To investigate theneed for restricting the length of these volumes, a sensitivity study wascarried out in which the length of volumes 104 and 184 was increased by afactor of about 2.5. This change 'resulted in an increase in executionspeed-of x 1.8, yet the results were effectively identical. Thisobservation indicates that the guideline for modelling Tees whichrequires the use of very short volumes may be unnecessarily restrictivewhen using the semi-implicit numericalintegration scheme inRELAP5/MOD2.•

1. This report has describe'd.the results of a .EAP5/MOD2 calculationof OECD LOFT Test LP-SB-02; which simulated a 1% equivalent areahot leg loss of coolant accident with delayed trippingof.theprimary coolant pumps.

2. Overallagreement between calculated results and experimental datawas reasonably good for the first 1200s of the transient, but wasunsatisfactory at later times. .The principle deficienciesidentified in the code we're as follows:."

(a) In common withprevious 'analyses of Test LP-SB-02 usingREIAP5/MODI, RELAP5/MOD2 failed-tdpredict the onset of

,.stratified flow in the hot leg at the correct conditions.

(b) The test data show that fluid quality in the offtake pipe,...leading to the break orifice was iignificantly higher thanthat in the hot leg. The RELAP5/MOD2 horizontalstratification entrainment (HSE) model, designed to modelthis effect, failed to predict the correct behaviour in thistest. A modified code version incorporating 'improved .correlations for the quality in the offtake pipe was foundto produce markedly more accurate results.

(c) Large errors in calculation of the loop flow were encounteredin the later part of the experiment. The most'likely causeof these errors'is'thought to be the failure to calculate thecorrect flow regimein the'hot leg, noted in (a) above.

3. To assist'in developing code models which will give improvedagreement with similar experiments, further separate effectsexperimental data are desirable on the following:

8.

(a) Transition to stratified flow in geometries resembling a PWRhot-leg.

(b) Flow quality in an offtake pipe connected to a largerhorizontal pipe in which there is a two-phase flow with amass velocity of more than 1000 kg m- 2 s".

Experiments designed to provide this information are currently inpreparation at AERE, Harwell.

10. R

1. NUREG/CR-4312

2. GD/PE-N/544

3. GD/PE-N/535

4. GD/PE-N/597 DraftPWR/HTWG/P(87)497

5. OECD LOFT-T-3304

RELAP5/MOD2 Code ManualVolumes I and 2V.H. Ransom et al.

RELAP5/MOD2 Calculations ofthe OECD LOFT Test LP-SB-01.P.C. Hall and G. Brown.

RELAPS/MOD2 Calculationof OECD LOFT Test*LP-SB-3.C. Harwood, G.Brown

RELAP5/MOD2 Calculation ofOECD LOFT Test LP-FW-0O.M.G. Croxford and C. Harwood.

Dec. 1985

November 1986

April 1986

May 1987.

Quick-Look report onOECD LOFT experimehtLP-SB-2.S.M. Modro. August 1983

6. OECD LOFT-T-3205

7. OECD-LOFTExperiment LP-SB-2

8. PWR/LCSG/P(83)58

Experimental analysisand Summary report onOECD LOFT nuclearexperiments LP-SB-1 andLP-SB-2.S.M. Modro etal.

Tape Descriptions andSupplementary Information:EG&G (Idaho) Inc.

Blind Calculations ofLP-SB-l and LP-SB-2 UsingRELAP5/MOD1/C19/WIN 001'.C.G. Richards.

RELAP5/MOD1 Calculationsof the OECD LOFT LP-SB-1 & 2Small Hot-Leg BreakExperiments.A.J. Clare.

May 1984

1983

1983

9. *TPRD/B/0679/NS5

July 1985

9.

10. OECD LOFT-T-3303

11.

Best Estimate Predictionfor OECD LOFT ExperimentLP-SB-2.T.H. Chen, S.M. Modro.

Assessment of HorizontalStatification EntrainmentModel in RELAP5/MOD2.Unpublished CEGB Report.K.H. Ardron and W.M. Bryce.

Notes of RELAP5/MOD2Workshop, Wurenlingen,Switzerland.EG&G (Idaho) Inc.

June 1983

Unpublished CEGBreport.

August 1987

1985.12.

10.

Initial Conditions for LP.SB-02

Experiment REIAP5*

Cold Leg Temp. (K)

Mass Flow Rate (kg/s)

Core Temp Rise (K)

S.C. Secondary

Liquid Level (m)

Pressure (MPa)

Mass Flow (kg/s)

Pressuriser

Pressure (MPa)

Liq. Level (m)

Core Power (<M)

HPI Temp. (K)

557.2±1.5

480.0±3.2

18.6±1.7

3.13±0.1

5.60±. 05

26.70±0.8

15.08±0.16

1.109±.003

49.1±1.2

306±7

559.2

480.1

18.9

3.70

5.61

25.66

15.06

1.135

49.1

306

* End of Null Transient.

11.

Secuence of Events for LP-SB-02 Calculation

Time After Break Open (s)EventIII II

I Experiment I RELAP5/MOD2 I ModifiedS I I• Code

________________________________1_______ I_ 1 ________ _ _ _ _ _ _

Small-Break Valve Opened

Reactor Scrammed

Main Feed-water Shut Offý

Main Steam Control.Valve Started toclose

Main Steam Control Valve Fully Close,

Pressurizer Liquid Level Below Botto:

HPIS Flow Initiated

Subcooled Blowdown Ended (break linefluid reached saturation)

Auxiliary Feed-water Initiated

Onset of Stratification in Hot Leg

Stagnation of Liquid Flow in Loop

Primary System Pressure Became Lessthan Secondary System Pressure

Auxiliary Feed-water Shut Off

HPIS Flow Rate Exceeded Break Flow

Rate

Primary Coolant Pumps Tripped

Calculation Termination

d

m

*1

.1

LI

II

I.

I.

0

1.8±.05

1.8±.02

2.8±0 .2

14.8±0.2

36.4±0.2

42.4±0.2

50.2±1.0

63.8+0.2

600

1290

1290±45

1864.0±0.2

2284±200

2852.8±0.2

0

4.27

4.27

5.28

20

38

43.7

53

66.3

-2250

pump trip

2650

1866

>4000 +

4152*

4000

0

4.27

4.27

5.28

I 20s

I38

43.7

53

66.3

pump trip

pump trip

2320

1866

1-2500 +

3580

4000

* Approx. value, based on preliminary calculation.+ Time of minimum primary system inventory.

12.

APENDIX

.DescriDtion of Sensitivity Studies

The objective 6f-this'Appendix is to summarise the results of a number of.'sensitivity calculations performed in an attempt to establish the cause.of, the.failure of RELAP5 to predict the rapid riduction"in water flow in

the loop after about-1300.

The first possibility to be considered was that water was beingerroneously entrained into the Steam Generator (SG) either as a result ofoverestimates in interfacial friction or because of failure to accountfor separation in the hot leg/SG inlet elbow.

In calculating the interfacial drag at a jun tion, RELAP5/MOD2 averagesthe values of drag derived in the adjacent volumes. It is thereforepossible for the averaging process to suppress the effect of a volume in

;which low interphase drag is calculated, if high interphase drag iscalculated in.both upstream and downstream adjacent volumes. Because theSG' inlet plenum has :a large cross-sectional area relative to the two

adjoining volumes, it was considered possible that interphase drag withinthe plenum was effectively-overestimated. To eliminate this possibility,a sensitivity calculation was performed in which the SG inlet plenum inthe RELAP5 input model was split into two vertically stacked volumes. Asexpected, the interfacial'drag at the newly created internal Junction waslower than in the other junctions., and a noticeable amount of water was.calculated to accumulate in the SG inlet plenum. However, this•accumulation had only a transitory effect on.water flow into. the SG...:.

- :t tubes, and led to no long term improvement in the accuracy of thecalculation of liquid flow rate.

A second more speculative attempt to eliminate water. flow into the SGtubes was made by invoking, the modified horizontal.stratification off-take model developed for the hot leg/break line at the junction betweenthe horizontal and inclined sections of the. hot, leg .This.again-caused,sli-ght accumulation of water in the hot leg,'but produced no long termimprovement in calculated loop flow.

Finally, the pump"'degraded head data wai modified to reflect datauncertainties. Figure Al shows the measured pump.differential. pressure,compared with the value calculated using the modified version of the code(chain-dotted line). This indicates that the calculation overestimatestheldata somewhat; To assess the sensitivity of the system to errors in

S... calculated pump differential pressure, a calculation as'perfoilmed in"which'the fully .degraded pump head was reduced by about 30%. Thecalculation began at 600s, continuing until '2500s. Results are alsoshown on Fig. Al (broken line). Agreement with 'measurements is very goodin the critical period around 1300 - 1500s when loop water flow actuallyceased.

13.

The effect on calculated loop flow rates. is illustrated in Figure A2,which shows measured velocities at the top and bottom of the hot legalongside liquid and vapour velocities arising from the two calculationsmentioned above. The effect of reducing the fully degraded pumpperformance is to bring the calculated steam velocity into reasonableagreement with measured values (top of hot leg) for long periods. Inspite of this, the water velocity does not fall to zero as measured, andthe erroneous calculation of circulation of a near homogeneous two-phasemixture experienced in the previous calculations was maintained.

In this sensitivity analysis there were periods during which the hot legsteam velocity (Fig. A2) and hot leg mixture density (Fig. A3) werecalculated correctly (750-1 4 00s, 2000-2500s). Nevertheless, the codecontinued to calculate water flow along the hot leg and up the SG tubes.This implies that the failure to predict cessation of loop flow wasprobably due more to weaknesses in interphase drag calculation in the hotleg/SG inlet than to errors in the assumed pump characteristics.

14.

"11P

IT-

u

t"U,

z00

X

Z

P

r-0'10

0

r'-

,--

I-'"O

0

I

COI-

(-4

r-

o

KEY.12S COMPONENT

6 2 COMPONENT

PUMP

. BRANCH WITH JUNCTIONS222 JUNCTION OR VALVE

HEAT STRUCTURE-* CROSS flOW iIINIflTMN

STEAM GENERATOR

PRESSURIZER

.IS ...... . .... ..... TIO...

SiS

BREAKREACTOR

VESSEL

17S

350

6_0

0o~U'

LP-SB-02 STEAOY STATEC" (2]

-I

3-1

£

U

2W10,U

B.

.1-------.................. .... ......

................. ................. ... . . .

.~~~ ~ ~ .. ..... ..... .... .............. .................. .............. ..............

146 La Nru

i .l it ............... ............ ..... ....... .......

:3 1.............................V 0 1 1 1 ...... .............. .................... ........

1.16

1.14

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3

.89

.06

1.04

5.m

111E IS)

6 20 4G s oS

P16661 Ell CIIT1LU.12 (21 -

Fictu•c) 2 HOT LEG PRESSURE AtMl PRESSURIZER LEUEL

int t20T

LP-SB-82 STEADY STATE

................. ................ ............................ .......-.j6

fo

0

J

i.IL,

Se .... .. ........... .. ........ .... . I58

flIGeim eEmu~tu FL&.j2

..... ..................................................... ........... ... .................

L ......S-rcnnu rLou.

4 ., .4 . 4 1~

.0 20 40 Ge to *iINe 120

rTi (s,

111"OWU 0I861 t flLOIJ -"1.0tJ5688 -

fiGUIC3 STEAM GENERATOR SEPARATOR M1iSS FLOU RATES

LP-SB-02 STERDY STATE

hi

*1hi

U.

6r

ru1t1 s

P-52 (11 - .. cntLualR l21 -

FIC&UCe + STEAM GEIERATOR PRESSURE AMI1 LEUIL

(L0.

I.,

w9L

RELnPS'rlOD2 CnLCULATION OF LOFT TE5'~ LP -SB-02

14 .1 ............ ............ ......................... ..................

....... ................

.....1......... .4.* 1

... .. . .. .. ... ... . .. .... . .... .. .. . ... ... .... .. . .----------

0 Goo 10es 1500o 2•tl•B 0

iTs r "t"WXoDATn C.DEPE-PC-0I3 pl-oslP I

FIGURE ME : AESURED AND CALCULATED PREI'RY PRESSURES

me8 40011

UiflE (5)

RELflF'S/MOD2 CIILC[JLfI[IJM OF LOFT IESI LP-913-1-2I ......................... . . . . . . ........ ........................................................................... ... . .. . . . . ........ . .. . .. . . .. .. . . . . . ... I

.l . ..................... ....................... .......................... '...................... ................................................ ................................................. II9

6 . ....................... ....................... ...................... ......................... I ....................... ....................... ....................... 4........................ .g

lx

42- ... .. .

....-....... ............. ... .. 7... ................... . :

(Ia Or .. ... ... ... ... .. .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. ........... ................ i . . . . . . .......... ................................................

TEST . T S (.)

I.........I* ' a -IN

DAT C• D,. * S *

8-. . 16 1 ! ! F

* -- _ . , _ S

I . . . .

ZJ ,, ! " " I , I r, r , 'w ' "

hi I-u . IiI

TEST STAIOARo TilE (5)

VR-PC-S93 - tFLffOUJiOIB ....

FIGURE..6 : MqEASURED riD CAiLCULAITED BREAK FLOU RAITE

RELf1PS'f02- CflLCIJLAlrIONrl LOF turf -ir 1 P -SB --O.. .. .... .. .... . -------

.. . . . . . . .. . . . . . . .. . . . . ... .. . . . . .. . . . . ... ..... ....

............................................ .........

.. ... . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .

.. . . . . .. . .. . . ... . . . . . . . .. .. . .

T - 1 1 -................

. .............. . ..... ........

.. . .. . . .. .. ... . . .. .. .. . .. . . .. . . .. . . ... . . . .. .. . . .. . . . .. . . . .... .. . . . . . . ..

.. .. . ... . . .. .... . ... .. . . . . .. . .. . . . . . . .. . . .. .. . . . . . . . .. . .. . . . . .. . .. . . ... . . . . .. . .

. . . . .. . . . . .. . . ... . .. . . .. . . .. . . .. . . .. . . .. . . . . . .. . . .. . . .. . . .. . . ........ ...... ....... ...

.. . . . . .. . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .

(n 4 0.... .................... . .. . . . ..........4 0. . .... .....0....... .... ... .................... Itit

------------

............. .. .............. . .. ......... .. ......... ..... ... .. ... ..... ....... .. .. ... ........ ..................

SooJ 18 1098 2880 Mg8 3088 X008 40IO

DE-K'-265 -Pmt"i600t

FIGURE 7 : MEflSURED ArID CALCULnTED 1-JOT LEG DENISITIES

Z:

ltt

No9-

1e8-

109.

RELor'S'rOD2 (:O)L(:IJLflr[Orl OF LOFT iE51' IP-St3-F)

.... . .. . .. . .. . .. . ... . .. . . . ... . . .. . . . . .

..... .. .. . . .. . .. .. . . . . . ... ..... . . .. ..

.. . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .

... .*.. . . . . . . . . . . . .. .. . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . ... . . . . .. . . . . . . . . . . . . . .

...............................

............ .......................... ...........

...._ _.........I... .. .. ..... ............

.......................... ........... ....... .......................... .... .................

off"

..711,3

GMIt

(S')

0O see ~ 1000 Isue 2W MR,•uuu

TEST STItIOARO CDEODTADE-PC-S048 - RIIo1021 -----

FIGURE 8 : MEASURED OND CALCULATED BREAK LINE DENSITIES

3580OTlf1

RELAPS/MOD2 CALCULAT[ON OF LOFT TEST LP-SB-02

141 ..................

.......................

.......................

.......................12- ......................

.....................

....................... ?;........ t........•...... ....................... ........................

..........o........ .. ...........o°. .oooo~o ..o . o... ............. ............

. . .

... " ........ •............ S................ ..I............

........................

........................

........................ 1-42

-16

-14

........ . ....... ..........J - 1 8

a. 8-1

62

Ia_

.................... ....

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-................. . . .... - ........................ e

.......... ... .. ........

........................

.. .. ........

........................

.......................------------

.......................

--.... .. .. . .. .. .. .. . .. .. .. .. .. . .. .. .. .. . .. .. .. .. .. . .. .. .. .. . .. .. ... ... . .. .. .. .. . .. .. .. .. .. . .. .. .. ..1I I I I I I I0 Goo too@ .1909 2900 Kilo9 3800

ttvirrr SnMnRD TwoQcm COBE DnATPIMOI ..... 1,16941 PE-PC-W9~l

F IGURE 9 : MfASIJ'RED ANID CAlLCULA TED PR[MnRY PRESSURES

3i89 4000

TUC (5)

RELIHIS'rOD2. ;r(ILCU~nrT[N Or LOFT IEST LP 758-@02

a

JI.

cr'..1ý-4-

.. ..... ......... .. W. ,

.. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .T .. . . . . . . . . . . . . . . . . . . . . .

.... ... ... .. ... . . .. . .. . .... . .. . .. . .. ... . .. . .. . .. . .. . .... . .. . .. . .. .. . .. ... . .. .. .. . .. . .. . .. .4 . .. . .. . .. . .. .

16

........................

.....................

a

...................

........................

............................................... .......................

....................... ....................... . ......................

............. .................... .......................

........ . ...........

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.6

-4

Il-I -I ti

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: n 1888

SCODER

1508 I20Mg i2soo 3889 1~90TESTonm

410M

MEr (s)

1FlOWUJ1t33 ... _. tfLOUJA8398 . FR-PC-!93

FIGURE "0 : MEASURED AND :CALCULATED BREAK FLOU RATES

RELnPS/MOD2 CALCULATIOMI OF LOFT TEST LP-SB-02

low-

.. ........... ...........

.......... .:...........

. ... ..-- .... .... ..

...................... T................................

.......... .. .......... .. ........ ...I..........

.................... ......................................

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i

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-4906

lee,

|

I_ - i I I *e eeIBMe Isee 98 258 3m8 3566 40M8

mrcam MEruw - ros

CMER1C R? CMTPVW7 mss

FIGURE 11 : HZASIJRED AVio cniLC1JIA1TED PRIMARY COOtANT. SYSTEM MOSS INVJENTORY.

r VI (s)

REt-l)P5'rlOtX CALCIJLATPIO OF LO]FT l(1[:rL'K30.

*. . .........

...-.......... ...... ..... ............

....................... ........................ .o

.. . . . . . . . .. . . ... . . . . . . .. . . . .

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.. . . . . . . . . .. . . . . . . . . . . . .4 . . . . . . . . . .

... .. .... .......... .0

hi

.. ........ . .................... . .......................... ............ ............ . ......... .. ...... ....... .........

-------

- - - - - - -

MODIFIED STAflWA4O Ttsr IE SCODE CtODED~R14OIeeet ...... RnHaIeeI ---- OE-PC-M8

FIGURE 12 : MIEASUJRED AND CALCULATED HOT LEG DENSITIES

RELAPS'r-OD2 CflLCJLATIO1 O1F I-OFT TEST LP-!38-02

8110

-me

Go"

see-

Joe

200.

v ........................... ........ ......... ...................... .......................................... ............. .......................

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", a

............... ":.. .............. . . .

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. . .. . . . . . . .'-.. . . . ..... . ............

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: -a-

........... ... ....... ........ I ......... _ _ _ _ _ _ _ _ _ _ _ _ _ _

-I i i i

siloi

-711"

-5$',

E CS)

U

a see 1809

H0Ioi ED, STAflOA00COOE COD~ER111elt2t .. R1108281 ---

FIGURE-/3

10S 288 258 80

TESTDAMDE-PC-,84o

MEASURED AMID CALCULATED BREnK L[I'IE DENSITIES

4r

TI1

RELAPS'MOD2 CALCIJLATIOti OF LOFT. TE-sr LP-SB4J02

bea.

. 2: , |-'

., ................... ....................... .... ....... ............. ............ ..... . ....-....... ._... .........

I2

4 . .. . ... ... .. . ..2 ". "

n I

3. ...................... ..... -................. . • ..... ........ ....................... ...... .................

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............. °°°°°o °o°............-°.......... ........................ °°°° .. . .. .. °.........•.............

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I ........ .. ................ -'.......................I

-4

2080 ~ If841

mrroSrnwlFwe TEST T ItyLcow COD DAMP5281 ...... P538W PE-SGS-881 -

FIGURE J1/ : MEASURED ANID CALCULATED SECONIDARY PRESSURES.

IJ

(S)

. RELArPS/MOD2 CALCULfATION OF LOFT TEST LP-SB-02 USING MODI[FIED CODE

Ar

12-

18-

S

.. .. ... ..

i""..."....... "........

... o..... ........

°... ...........

1 o

......................

T...... .... .... ......... • o

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...................... 18

CnuLctA TElD 3cEI.

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........................

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..................

I.•i•...................

..........

I'

-6

-4

A I-............... .. ....... ................ .. . ....... .. .. - 1

-~.............. ................... ..

- -...................... I. .................. ;-4 ..... ;--............ ....................... I. .......... ....... -;... ................ ....... -- .............. .. .;

:.. +. . .+ .+: .i. -

S 2988

2s

FIGURE 15 : t1E9SURED iND CAlLCULATED COOLANT IEL(ICITIES I" 110T LEG

RELIIIPS/'l10D2 ClOJLfLA[Oll OF LOFT lEST LP-SB -02

I .

CA" .-.. ....... -... .......................... ............................................... -- -. .s . .. I • . . ,

74M . -...... .......... . .4 . ......... .................. ............... ...... .............. .-- ... ................... ............................................ .... .... ....... . 1

I . ... . . . . . . . . . . . . .....,......

I ~lL ,. i I ! i

..... 8.- .,. V.. _,t' ',... ... ... .. ... ... . .. . . . i . . . . . . . . . . . . . . . . . . . . I . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .t . . . . . . . . .• ~ •

"rli.-"i "3 -di -... I

I.,N

E

rhi0

~88

188

a

.... . .... ........ .o ..°.**°o °, ...... .. ° 0.. •.. ..... .. ...... ;. . ......

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........ .......

............. .......................................................*1228

.I ! wId ....................................... ... ;~*ool*e ....................... I....................... ....................... I

I iI I p

I6S1)WOI1CODERnIKIII2

W01FCED •TESTewe DAlTA..... I 180 ..... !IE-pc-Ms31

FIGURE lb : VEASURED ANID CALCULATED LOOP SEAL DENSITIES

Iq88

rTM: (S I

RELA1PS/MOD2 (:ALCJLAYTtIO OF Loi-r IEST LP-S[3-02

.. .........

... ... ...... ..........................

se ..... ........ .. .. .... . ............. ........... .... .. ............. .... ........ . ............. . so"~

..........w ........... ......... ............. ... ........ ..." .. ... ...... ...... "

kl0 -- - -

...... .... ... ....... ... .

.. ........... ........ ............. .. ..

see8 1000 IsUB 2088 2so8 360880 4000

tWOIF IEO STnnOWD TEST TIM (S)CODE CODE DAM~f

R1117Q .... RHO 1502 - O -- E41-1C0B5 _

FIGURE 17 : MEASURED AIND CALCULATED COLD LEG DEINS[TIES

4134

0.

w

in

Ile(L

A

Id

IL

REL(IPS/MOD2 (CflLCIJLAT([I]PI OF LOFT rEST LP-SB-0,? USING MJD[F[ED CODI)E

. ...................... ....................... .......... .............. ...................... ....................... ........................... : ............. : ......... •...................... ,,olJ

......................... ............... ........ :-.......... ...................................... ........................................ -...... ....................... -0

... ......... ..... . ................ :....................... ... .... ; .. •.. ...................... I......................... ...................... ........................ .. .................................................... ...................... ,0

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.. . . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . .. . . . . .. . . . . .. . . . . .. . . ... . . . . . .. . . . . . . . .•. . ... . . . . . . . . . . . . . . . . . . . . m

....................... :........... .. • .................... "•............ 1 ...................... : ....................... ....................... : ...................... .dl.44............

....................... ............................... ......... :7 ..........

....................... i....................... "...................... •-...................... ................ ... .............i..................... - " ' ' ..I Ix I

see ION I1soo 2e0M 2S90 3N041 3580 41041

ws r TIME (S)

tL4)0

13

11241r(110 PUtIP IATA STIWI4WD PI'I DATA DATAl

FIGURE 01 : MEAlSURED AN1D CAL.CULATED PUMP DIFFERENITEIAL PR[ESSUJRES

RELflI'S/HOo2 CflLCULflTIOri OFr LOFT TEST LP-SB3-0 USflING "I(DW lED COD)E

12-

......................

d

I..'4

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~1~~~~~

aI

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FIGURE A2 : MEAISURED ANID CALCULATED COOLnMT UEI.OCITIES IH HOT LEG

RELAn5'lol)D2 CflLIJulr[Ilrl OF LOFT TEST LP-SB-02 'lJSTlll MIODIFfE() CI)DE

l~ ~l ....................... ....................... ...................... i ..................... • ....................... ....................... ............................................... l Ol

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FIGURE..._ ....... .. MEASURE _____D H L I D SI

1..68 •l IW20 2S8 306 3!64

sra ienntW~EOWMr TI E (S.. .... ..... i ............ l ............. ............. ............. I............. C............. ............

FIUE01- EAUE Ot ALUAE HtLE DIISTE

NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER(2.89) (Ast( 0gnd by NRC. Add Vol.. Supp.. Rev..NRCM 102, and Addendum Numbers. It onvy.3201.3702 BIBLIOGRAPHIC DATA SHEET NUREG/^A-0021

(See instructions on the reGD/e] (rs• ;s,•c;o,• , ,h •o;GD/PE- N/606 ( Rev )2. TITLE AND SUBTITLE

RELAP5/MOD2 Calculations of OECD LOFT Test LP-SB-2 3. DATE REPORTPUBLISHED

MONTH YEAR

April 19904. FIN OR GRANT NUMBER

A68275. AUTHOR(S) 6. TYPE OF REPORT

TechnicalP. C. Hall 7. PERIOD COVERED inclusje aDres)

B. PERFORMING ORGANIZATION - NAME AND ADDRESS (fi NRC. provide b',siono Office or Region, U. S Nuclear Regulatory Commission, and mailing address; if contractor, providenwsne and mailing address.)


9. SPONSO RING ORGAN IZATION - NAM E AND ADD RESS Ifi NRC, type -Smeý as above" * If contractor, pro•/de NRC Division, Office or Reqlon, U.1 Nuclear Regulatory Commission,and mailing addres)

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

10. SUPPLEMENTARY NOTES

11. ABSTRACT 1200 words or kls

To help. in assessing the capabilities of RELAP5/tI0D2 for-PWR Fault Analysis, thecode is being used. by CEGB to simulate several small LOCA and pressurized transientexperiments in the LOFT experimental reactor. The present report describes ananalysis of small LOCA test LP-SB-02, which simulated a 1% hot leg break LOCA in aPIR, with delayed tripping of'the primary coolant pumps. This test was carriedout under the OECD LOFT Program.

12. KEY WORDSIDESCR!PTORS (List words or phrass that wilt assist researchers in locating the report.) 13. AVAILABILITY STAT EMENT

I lnIimi tpdOECD LOFT 14. SE CURITY CLASIFICATION

RELAP5/MOD2 (rtis Page)

LOCA IIncl assii fipd(This Reportl

Unclassified15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (269|

UNITED STATESNUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555

OFFICIAL BUSINESSPENALTY FOR PRIVATE USE, $300

SPECIAL FOURTH-CLASS RATEPOSTAGE & FEES PAIDU USNRC j

PERMIT No. G-67