•- __% -I-

-NUREGAA-0012

Intemational

Agreement Report

RELAP/MOD2 Calculations of

OECD-LOFT Test LP-SB-01

Prepared by

P.C. Hall, G. Brown

Central Electricity Generating Board

Barnwood, Gloucester

GL4 7RS

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

January 1990

Prepared as part of

The Agreement on Research Participation and Technical Exchange

under the International Thermal-Hydraulic Code Assessment

and Application Program (ICAP)

Published by

U.S. Nuclear Regulatory Commission
NOTICE

This report was prepared under an international cooperative

agreement for the exchange of technical information. Neither

the United States Government nor any agency thereof, or any of

their employees, makes any warranty, expressed or implied, or

assumes any legal liability or responsibility for any third party's

use, or the results of such use, of 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.

Available from

Superintendent of Documents

U.S. Government Printing Office

P.O. Box 37082

Washington, D.C. 20013-7082

and

National Technical Information Service

Springfield, VA 22161
NUREG/IA-O012

International

Agreement Report

RELAP/MOD2 Calculations of

OECD-LOFT Test LP-SB-01

Prepared by

P.C. Hall, G. Brown

Central Electricity Generating Board

Bamwood. Gloucester

GL4 7RS

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

January 1990

Prepared as pant of

The Agreement on Research Parficpation and Technical Exchange

under the Internatfora Thewmal-Hy•rauk Code Ausesinent

and Appacatlon Program (ICAP)

Published by

U.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 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.
Abstract: To assist CEGB in assessing the capabilities and status of

RELAP5/MOD2, the code has been used to simulate SBLOCA test

LP-SB-O1 carried out in the LOFT experimental reactor under the

OECD LOFT programme. This test simulated a 1.0% hot leg break

in a PWR, withi.early tripping of the primary coolant circulating

pumps. This report compares the results of the RELAP5/MOD2

analysis with experimental measurements.

Comparison of the present calculation with earlier RELAP5/MOD1

calculations shows that significant improvements have been made.

Most notably, the horizontal stratification model in MOD2 was

found to enable improved calculation of fluid density close to

the break in this test. In addition mass conservation errors,

numerical stability and the computer run time were all greatly

improved, compared with an earlier CEGB analysis using MODi.

The major difference between the RELAP5/MOD2 results and the

experimental data is in the critical discharge flow rate. It is

concluded that!-the error arises from thermal disequilibrium

effects in thei discharge nozzle which are not modelled in the

code. However, the discrepancies are not considered unduly

significant for safety analysis of small break loss of coolant

accidents in nuclear power plants, since in this application

such effects would normally be allowed for by performing

sensitivity studies to break size, orientation, etc.
Executive Summary:

The RELAP*5/%OD2 transient thermal-hydraulics computer code is

being used by CEGB for calculation of small break loss of

coolant accident (LOCA) sequences for Sizewell 'B'. To assist

CEGB in assessing the capabilities and status of this code, it

has been used to simulate 8BLOCA test LP-SB-0i carried out in

the LOFT experimental reactor under the OECD LOFT programme.

This test simulated a 1.0% hot leg break in a PWR, with early

tripping of the primary coolant circulating pumps. This report

compares the results-of the RELAP5/fOD2 analysis with

experimental measurements.

RELAP5/MOD2 was developed from RELAP5/MOD1 and contains more

sophisticated hydraulic models and constitutive relationships.

Comparison of the present calculation with earlier HOD1

calculations shows that significant improvements have been made.

Most notably, the horizontal stratification model in MOD2 was

found to enable improved calculation of the effects of flow

stratification in the hot leg on the fluid density close to the

break in-this test. In addition mass conservation errors,

numerical stability and the computer run time were all greatly

improved, compared with an earlier CEGB analysis using MOD1.

Overall agreement with the experimental data was found to be

reasonably good, though the following twodeficiencies were

encountered:

(a) Systematic underprediction of critical discharge flow rates by

about 30% at the low quality conditions which occurred in the

early part of this test. The errors have been attributed to

thermal disequilibrium effects in the discharge nozzle which

cannot be modelled by RELAP5. However, the discrepancies are

not considered unduly significant for reactor loss-of-coolant

accident analyses,:since in this application such effects would

normally be allowed for by performing sensitivity studies to

break size, orientation, etc.,

(b) activation of the RELAP5/MOD2 vertical stratification model

in the upper plenum has been found to lead to the erroneous

calculation of sudden draining of the hot legs. The current

basis for general application of this model appears

questionable.

ii.
CONTE•:TS

Page

Abstract j

Executive Summary ii

Contents jjj

1. Introduction 1

2. Code Version and Input Model 1

3. Initial and Boundary Conditions 2

4. Comparison of of RELAP5/MOD2 Results with Experimental Data 2

4.1 Description of Test 2

4.2 RELAP5 Results 3

5. Discussion and Comparison with Previous Analyses 6

6. Conclusions 7

7. References 8

Table 1 10

Table 2 11

List of Figures 12

iii.

1. INTRODUCTION

The RELAPS/MOD2 code [11] is in use by CEGB for calculating small-break

LOCA (SBLOCA) sequences for Sizewell 'B'. RELAP5/MOD2 uses a six-equation

two fluid model to describe two-phase flow in the reactor primary and

secondary systems. It supersedes the RELAP5/MODi code, which employed a

five-equation two-phas*e flow model (one phase constrained to thermal

equilibrium) and used less sophisticated models for flow regime transitions

and interphase interaction terms.

To assist in assessing the capabilities and status of RELAP5/MOD2, the code

has been used to simulate SBLOCA test LP-SB-OI carried out in the LOFT

experimental reactor under the OECD LOFT programme.

LOFT test LP-SB-O1 simulated a 1% hot leg break in a Pressurized Water

Reactor (PWR) with an early trip of the primary circulating pumps. The test

is described in detail in refs. (1], [2]and [3].

The present report describes this analysis. Comparisons are given with

earlier simulations carried out with RELAPS/MODI described in refs. [2],

(4] and [5]. The effect of modelling changes introduced into the MOD2 code

version are highlighted.

2. CODE VERSION AND INPUT MODEL

The code used for this calculation was RELAP5/MOD2 Cycle 36.02.

This code version included several error corrections implemented by

UKAEA, Winfrith, including a correction to enable the junction

horizontal stratification model to be utilized at cross flow junctions;

and correction of Cray conversion errors.

The input data was based on that used in ref. [6] for the analysis of

LOFT cold leg break test LP-SB-03. Changes were introduced to describe

the revised break location, to model the emergency cooling system and

improve the representation of the inactive loop. The noding diagram

is shown in Figure l. The model consisted of 120 Volumes, 126 junctions

and 125 heat structures.,, A significant difference between the

RELAP5/MOD2 model and the RELAPS/MODI model used for the analyses in

refs. [2], (4] and (51 is that in the present case junctions between the

hot leg and the break line, and between the hot and cold legs and the

vessel, were modelled using cross flow junctions. This meant that new

hydrodynamic volumes were required in the hot leg and in the vessel upper

plenum and upper downcomer.

A microfiche listing of the code input and output has been filed under

Safety Technology Section in Microfiche Archive at Barnwood.

1.
3. INITIAL AND BOUNDARY CONDITIONS

To establish the required steady state, a pseudo-transient calculation

was run until the problem time reached 91.2s, at which the code indicated

a satisfactory steady state. Parameters controlled to achieve the

desired steady state were steam and feed flow, and the pump speed. A

dummy time dependent volume was attached to the top of the pressurizer to

maintain the desired steady primary pressure. Figures 2, 3 and 4 show

the separator void fraction, the flows into and out of the SG separator,

the pressurizer pressure and surge line flow during the steady state run.

These variables are sensitive indicators, and demonstrate that a very

satisfactory steady state was achieved.

The RELAPS calculated steady state initial conditions are compared with

experimental values for ref. [2] in Table 1. These can all be seen to be

in agreement, except for the steam generator (SG) secondary side level,

which had to be set artificially high in order to eliminate periodic

emptying and filling of the separator volume. This modification was

considered acceptable since in test LP-SB-O1 the SG secondary plays only

a minor role in the overall primary system energy removal.

Boundary conditions used in the test were obtained from the EG&G data

package, ref [3]. This did not include auxiliary feed-water flow-rate.

Appropriate data were deduced from the observed rate of change of liquid

level in the SG. A fixed value of 0.28 L/s, for the period 64.5s to

1864.8s was used in the calculation.

Ref. (1] stated that the steam bypass valve was opened once, early in the

test. Based on examination of the experimental secondary pressure and

discussions with INEL staff the bypass valve was modelled as being opened

when secondary pressure exceeded 6.5MPa and latched closed when the

pressuri fell below 6.5MPa. The area of the valve was taken as

3.2 10 m , in line with the RELAP5 input dataset given in ref. (7]..

Combined fission and decay power was inserted in the code as a table

based on that used in ref. (5]. For times greater than 250s, values were

taken from ref. (131.

4. COMPARISON OF RELAP5/MOD2 RESULTS WITH EXPERIMENTAL DATA

4.1 DESCRIPTION OF TEST

The sequence of events in the test is given in Table 2.

The transient is briefly described as follows. The primary coolant pumps

were tripped at t - 24.6s, and pump run-down was complete at t - 43s.

Two-phase natural circulation flow was maintained up to approximately

500s, at which time the system entered a reflux condensation mode and

the SG U-tubes, cold leg and hot leg piping successively drained. The

break line attached to the hot leg uncovered at t - 715s, approximately

the same time as the cold leg became empty. Reflux condensation in the

SGs terminated at about t - 1l00s.

The system inventory continued to fall until about 2000s when the

pressure reached a level at which the high pressure injection (HPI) flow

balanced the break flow. Thereafter the system inventory rose slowly.

The test was terminated when the primary pressure reached 2.5MPa. No

core dry-out was observed at any time.

.
4.2 RELAP5 RESULTS

(i) Initial Calculation

In the first calculation attempted, the break nozzle was modelled using

liquid (CDI) and two-phase (CD2) discharge miltipliers of 0.93 and 0.81

respectively, as in previous LOFT test analyses (5], [6]. The calculated

break flow-rate is compared with the measured value in Fig. 5. It is

seen that there is a systematic underprediction of flow-rate of 30% in

the period before nozzle uncovering at 715s. During this period the

quality in the break line is in the region 0-0.4%.

Similar discrepancies in flow-rate were found in the RELAP5/MODI

calculations in refs. [2], [4] and [5]. Refs. [2] and [5] attributed the

errors to the inability of RELAP5/XODI to correctly calculate the quality

of fluid entering the break line from the hot leg, since no account was

taken for the effect on the discharge quality of flow stratification in

the hot leg. RELAP5/MOD2 has a special model designed to correct the

break flow quality for the effects of flow stratification in an upstream

volume and this model was utilized in the present calculation. Fig. 6

shows the predicted fluid density in the break line. Comparison with

Fig. 7 shows that the calculated break line density is correctly

predicted to be higher than that in the hot leg, as a result of flow

stratification in the hot leg. This shows that the RELAP5/MOD2 flow

stratification model is working correctly. The implication is,

therefore, that the error in the discharge flow-rate is not attributable

to an error in the calculated discharge quality, as was postulated in

refs. [2] and [5].

It is believed that the more probable explanation for the error in the

predicted break flow-rates is the occurrence of thermal-disequilibrium

in the discharge nozzle, as was postulated in ref. (1]. The RELAP5

critical flow model approximates to a thermal equilibrium expansion in

the nozzle. Fig. 8 compares RELAP5/.IOD2 predictions of critical

flow-rate with calculations of the simple isentropic homogeneous thermal

equilibrium critical flow model (HEM), taken from ref. [8]. Calculations

are for a 12.7mm diameter nozzle discharging from a reservoir at 68.9

bars. It is seen that the RELAP5 prediction is very close to the HEX.

In the quality range 0.2-5% results are about 10% below the HEM.

The Henry-Fauske [9] critical flow model is frequently applied in the

analysis of nozzles and short tubes, where thermal-disequilibrium effects

are important. Predictions of the Henry-Fauske model for the conditions

of test LP-SB-O are shown in fig. 5, taken from ref. (I]. It is seen

that this model does indeed give a good prediction of the break flow-rate

during the period of low-quality discharge in test LP-SB-01.

It remains to be established if disequilibrium effects were likely to

have occurred for the particular nozzle geometry and range of qualities

encountered in test LP-SB-Ol. To see if this was the case, we examine

the data of Sozzi and Sutherland U [10] who measured steam-water critical

flow-rates in nozzles with the same length and diameter characteristics

as the LOFT nozzle [see''fig. 91. Test results are shown as the curves in

the figure. It is seen that for the range of stagnation qualities of

present interest, Xo- 0.0 - 0.004, thermal disequilibrium effects are

likely to give rise to departures from the HEM of about +40% for a nozzle

of the length and diameter used in test LP-SB-0.

3.
The above observations suggest that the break flow-rate discrepancies in

LP-SB-O1 are probably due to the fact that the RELAP5 critical flow model

is inappropriate for the particular nozzle geometry and range of

discharge qualities encountered in the period from 50s to 715s of this

test.

For the present calculation it is accepted that the RELAP5/,XOD2 critical

flow model underpredicts the data as a result of disequilibrium effects,

possibly by as much as 50%. So as to establish a suitable boundary

condition against which to assess the performance of the balance of the

code against this test, a second calculation was performed in which the

two-phase discharge multiplier CD2 was set to 1.18 (to fit the low

quality discharge data for LP-SB-01). When the void fraction in the

break line reached a value of 40%, the value of the two-phase flow

discharge coefficient (CD2) was reset to the value of 0.81 as used in

previous calculations. At this stage, it was judged that disequilibrium

effects would be relatively insignificant, (extrapolating the data of

Sozzi & Sutherland). This second calculation (termed the reference

calculation) is discussed in the rest of this report.

(ii) Reference Calculation

The reference calculation was run from t-O to 2000s, after which time HPI

flow exceeded break flow and little of interest occurred in the

transient.

(a) Break Flow-Rate

The break flow and primary system inventory are shown in figures 10 and

II. The agreement is good although this is to a large extent due to the

choice of a value of the two-phase multiplier, CD2 - 1.18 for the low

quality discharge period of the test.

(b) Primary and Secondary Pressures

Figure 12 shows calculated and measured primary pressure. The good

agreement indicates that the discharge quality and mass flow rate are

accurately calculated by RELAP5/Y0D2.

Also shown in figure 12 are measured and calculated secondary pressure

transients. There is a systematic overestimate of secondary pressure of

0.25-0.5MPa corresponding to errors in saturation temperature of 2.5 to

6K. This may arise from a tendency to overestimate heat transfer,

leading to the need for a smaller primary to secondary temperature

difference to drive the heat fluxes necessary to satisfy the primary

energy balance. Other possible explanations are errors in modelling heat

losses, or steam leakage via the main steam control valve. In view of

the small part played by the SGs in this test, this error was not

investigated in detail.

(c) Loop Flow-Rates and Densities

Figures 13 and 14 show the density in the hot leg and break line. In the

period prior to break uncovery (t<715s), stratification effects cause

the density in the break line to be higher than that in the hot leg. The

horizontal stratification model in RELAP5/MOD2 captures this effect well.

After break uncovery, the experimental data shows that the density in the

break line falls below that in the hot leg. Again RELAP5/MOD2 calculates

the correct trend.

4.
Figures 13 and 15 show significant errors in the calculated values of the

density in the hot and cold legs. The discrepancies in the period before

700s appear to stem from differences in the calculated natural

circulation behaviour and subsequent draining of the SG tubes. In the

calculation, natural circulation was predicted to cease at- about 270s.

This is the point in figure 16, where the calculated cold leg vapour

velocity falls sharply.: At the same time, calculated velocity in the hot

leg (close to the vessel) fell rapidly (figure 17), as the SG heat

removal mechanism switched from natural circulation to reflux

condensation. Measured velocities shown in figures 16-17 indicate that

natural circulation actually ceased at about 500s. (Note that the

absolute values of the measured velocities are less than the measurement

uncertainty, and can therefore be regarded as indicative only). It is

clear that these discrepancies in calculated natural circulation

behaviour contributed to the errors in calculated density in the hot leg

and to the erroneous prediction that the cold leg drains suddenly

(see fig. 15).

Figure 18 illustrates that the code correctly predicted the pump suction

to remain full of water at all times.

Fig. 13 shows that the draining of the active loop hot leg which began at

700s was reasonably well calculated up to 10SOs, when the calculation

indicated sudden emptying. Sudden draining was also calculated in the

upper plenum volume (252) and the inactive loop hot leg. Simultaneously,

water was calculated to appear in the cold leg, (figure 15) and the

calculated void fraction fell in the core outlet volumes. This movement

of water from the hot legs to the cold legs is believed to result from

the triggering of the RELAP5/XOD2 vertical stratification model, which

is designed to sharpen the void fraction gradient in a stack of vertical

volumes. The vertical stratification model is initiated when the

difference in void fraction in volumes above and below a given volume

exceeds 0.5. Figure 19 shows that this condition was satisfied in volume

250 at 1080s. The primary effect of invoking this model was to reduce

suddenly the interphase drag forces in the junction between volumes 250

and 252, causing the draining of volume 252 and the consequential

draining of both hot legs, which are connected to volume 252.

It is clear from these results that the vertical stratification model can

produce unphysical draining of the loop pipework. Ref. 11 suggests that

the model was developed :o model pressurizers where the geometry is much

simpler than in the vessel inlet and ouclet plena. The current basis for

general application of the vertical stratification model therefore

appears questionable.

(d) CPU Time and General Code Performance I'

The calculations presented here were run on a Cray -1 computer at a

CPU/real timrI ratio of 1.16. The maximum and minimum time steps were

0.1s and 10- s, with the code selecting the maximum time step

continuously from t - 70s onwards. The code was found to be robust in

that no failures were encountered, other than those arising from Cray

conversion errors.

5.
5. DISCUSSION AND COMPARISON WITH PREVIOUS ANALYSES

It is useful to highlight the major differences between the present

calculation and the analyses of LP-SB-O1 reported previously in

refs. [2] and [5] using RELAPb/MOD1. The main points are as follows:-

(a) Effect of Stratification on the Break Flow-Rates

The RELAP5/MOD2 analyses in refs. [2] and [5] highlighted the difficulty

of correctly calculating the break line density in the period when

stratified flow existed in the active loop hot leg, to which the break

line is connected. As described above, the present calculation indicates

that this problem has been successfully resolved in RELAPS/MOD2.

(b) Critical Flow Model

Significant errors occurred in the calculated break flow-rate in the low

quality discharge phase prior to break line uncovering at 700s (see

figure 5). Similar errors were found in the RELAP5/MOD1 analysis in [2],

[4] and (5]. As discussed in section 4, these errors are almost

certainly due to the effects of thermal-disequilibrium of the critical

flow-rate in the nozzle. RELAP5/MOD2 includes a model, based on the work

of Alamgir and L nhard (14] designed to take account of the effect of

nucleation delay on the choked flow of subcooled liquid. This model is

extended into the low quality region in order to smooth the calculated

critical flow at the transition from subcooled to saturated upstream

conditions. However, it does not appear to have had any significant

effect in the analysis reported here. In any case, the implementation of

the model is in a very simplified and approximate form, and would not be

expected to provide accurate calcuations of the effects of detailed

changes in the geometry of discharge nozzles on critical discharge flow

rates. The magnitude of these thermal-disequilibrium effects depends

strongly on the geometry of the break nozzle and the thermodynamic

conditions.

For reactor analysis it is probably not worthwhile to try to develop a

model detailed enough to describe these trends, for incorporation into

RELAP5/,4OD2. This is because in reactor safety analysis it is

possible to allow for potential departures from thermal equilibrium

behaviour by performing sensitivity studies with respect to break size

and the magnitude of the break discharge coefficients.

(c) Flow Regime Calculation

In the RELAP5/MOD 1 analysis in ref. [5] it was noted that the transition

to the stratified flow regime in the hot leg occurred at about 550s;

experimental measurements indicated partial stratification at about 50s

representing a significant error. The new flow regime maps included

in RELAP5/MOD2 led to the prediction of stratified flow in the hot leg at

220s. The prediction of lower (i.e. closer to measured) steam and

water velocities in the present calculation may also have been a

contributory factor in this improvement.

6.
(d) Stability and Heass Conservation

In the RELAP5/4ODl calculation in ref. (5] mass conservation errors of

about 700kg were observed, mostly arising in the SG secondary side

during injection of auxiliary feed-water. The maximum mass conservation

error in the present calculation was 1kg, which is negligible.

In ref. [5] it was also reported that RELAP5/MOD1 produced non-physical

spikes of steam temperature in steam filled volumes. No evidence of

anomalies of this kind was seen in the present analysis.

(e) CPU Time

RELAP5/XIOD2 appears to run much faster than the MODi. The RELAP5/MODI

calculation in ref. (5] was executed on a Cyber 176 at a CPU/real time

ratio of 34.2. As noted above the present calculation was executed on a

Cray-1 at a CPU/real tim 7 ratio of 1.16. The same maximum and minimum

time steps CO.ls and 10- s) were used in both analyses. The different

machines used make exact comparisons difficult, but extensive studies by

Kmetyk et al. [12] using RELAP5/XOD1 suggest that the Cray-i is 1.5 to 2

times faster than the Cyber. This implies that in the simulation of test

LP-SB-01, RELAPS/MOD2 ran faster than RELAP5/OD1 by a factor of between

15 and 20.

6. CONCLUSIONS

This report has described the results of a RELAP5/XOD2 calculation of

LOFT test LP-SB-01 which simulated a 1% hot leg loss of coolant accident

in a PWR.

Overall agreement with experimental data was reasonable and the code

performed better than RELAP5/XOD1 which has been used previously to

simulate this experiment. In particular the difficulty of accounting for

the effect of flow stratification in the hot leg on the density in pipe

leading to the break orifice, encountered by previous workers, has been

overcome in RELAP5/XOD2. Furthermore, MOD2 was found to run between 15

and 20 times faster than MODl, and to be virtually free of numerical

instabilities.

The principal deficiencies encountered were as follows:

(a) errors were seen in the calculation of critical discharge flow

rates at the low quality conditions which occurred in the early

part of this test. The errors have been attributed to thermal

disequilibrium effects in the discharge nozzle which cannot be

modelled by RELAP5. However, the discrepancies are not considered

unduly significant for reactor loss-of-coolant accident analyses,

since in this application such effects would normally be allowed

for by performing sensitivity studies to break size, orientation,

etc.,

(b) activation of the RELAP5/MOD2 vertical stratification model in the

upper plenum has been found to lead to the erroneous calculation of

sudden draining of the hot legs. The current basis for general

application of this model appears questionable.

7.
7. References

1. OECD LOFT-T-3204 Quick-Look report on

OECD LOFT experiment

LP-SB-i.

M.D. Peters.

July 1983

2. OECD LOFT-T-3205

3. OECD-LOFT

Experiment LP-SB-1

4. UKAEA Internal

Draft Report

5. TPRD/B/O679/N85

6. GD/PE-N/535

Experimental analysis

and Summary report on

OECD LOFT nuclear

experiments LP-SB-1 and

LP-SB-2.

S.M. Modro et al.

Tape Descriptions and

Supplementary Information:

EG&G (Idaho) Inc.

Blind Calculations of

LP-SB-I and LP-SB-2 Using

RELAP5/MODL/C19/WIN 001.

C.G. Richards.

RELAP5/MODI Calculations

of the OECD LOFT LP-SB-1 & 2

Small Hot Leg Break

Experiments.

A.J. Clare.

RELAP5/MOD2 Calculation

of OECD LOFT Test LP-SB-3.

C. Harwood, G.Brown

Best Estimate Prediction

for OECD LOFT Experiment

LP-SB-1.

T.H. Chen, S.M. Modro

RELAP4/MOD5: A Computer

Programme for ThermalHydraulic Analysis of

Nuclear Reactors and Related

Systems. User's manual.

Vol. 1.

K.R. Katsma et al.

The Two-Phase Critical Flow

of One-Component Mixtures in

Nozzles,. Orifices and Short

Tubes.

Robert E. Henry,

Hans K. Fauske.

May 1984

1983

1983

July 1985

April 1986

7. OECD LOFT-T-3203

8. ANCR-NUREG-1335

9. Journal of Heat

Transfer,

page 179.

May 1983

1976

May 1971

8.
10. NEDO-13418

75 NED43

11. NUREG/CR-4312

EGG-2396

12. NLUREG/CR-3802

13. Letter to LOFT PRG

Critical Flow of Saturated

and Subcooled Water at

High Pressure.

G.L. Sozzi, W.A. Sutherland

RELAP5/HOD2 Code Manual

Volumes l.and 2

V.H. Ransom et al.

RELAP5 Assessment;

Quantitative Key Parameters

and Run Time Statistics.

L.N. Kmetyk, L.D. Buxton,

S.L. Thompson

Decay Heat Data for OECD

LOFT Experiments. Letter

from G.D. McPherson to OECD

LOFT Program Review Group.

Correlation of Pressure

Undershoot During Hot Water

Depressurization.

M.D. Alamgir and J.H. Leinhard.

July 1975

Dec. 1985

Oct. 1984

Oct. 22 1985

14. Journal of Heat

Transfer, Vol. 103

pp 52-73.

1981

9.
TABLE 1

INITIAL CONDITIONS FOR EXPERIMENT LP-SB-O1

Parameter Measured Calculated

Primary Coolant System

Core T (K)

Hot leg pressure (XPa)

Cold leg temperature (K)

Mass flow-rate (kg/s)

Reactor Vessel

Power level (MW)

Steam Generator Secondary Side

18.5+1.7

15.00+0.08

557.2+1.5

483.1+3.2

19.57

15.099

558.36

483.1

48.8+1.2 48.8

Pressure ("'!Pa)

Mass flow-rate (kg/s)

Liquid level (m)

5.53 +0.05

25.79+0.77 3 .12.i-0.01

5.546

25.5

3.699

Pressurizer

Liquid volume (m3 )

Water temperature (K)

Pressure (MPa)

0.625+0.001

615.8+8.2

15.06+0.11

0.5905

615.6

15.06

Emergency Core Cooling System

BWST temperature (K) 304+7 304

10.
TABLE 2

SEQUENCE OF EVENTS FOR EXPERIMENT LP-SB-1

Event Experiment Calculation

Small break valve opened 0.0 0.0

Reactor Scrammed 1.4 + 0.05 2.5

MSCV started to close 3.4 + 0.2 2.5

MSCV fully closed 15.4 + 0.2 19.0

Primary coolant pumps tripped 24.6 + 0.2 24.1

Steam bypass valve opened not known 26.0

HPIS flow initiated 41.4 + 0.2 45.4

Steam bypass valve closed not known 50.0

Subcooled blowdown ended 57.5 + 0.2 49.7

Auxiliary feed-water initiated 63.4 + 0.2 64.5

Break started to uncover 715 + 3 615

Primary system pressure becomes less

than secondary system pressure 1077 A 10 833

Auxiliary feed-water shut off 1864.8 + 0.8 1864.8

11.
LIST OF FIGURES

1. RELAP5 noding diagram

2. Separator void fraction

3. SG separator mass flows

4. Pressurizer pressure and surge line flow

5. Break flow - preliminary calculation

6. Break upstream density - preliminary calculation

7. Hot leg density - preliminary calculation

8. Comparison of critical flow-rate calculated using HEM

and RELAP5/MOD2

9. Selected data of Sozzi and Sutherland

10. Break flow

11. Primary system inventory

12. Primary and secondary pressure

13. Hot leg density

14. Break upstream density

15. Cold leg density

16. Cold leg fluid velocities and void fractions

17. Hot leg fluid velocities and void fractions

18. Loop seal density

19. Upper plenum void fractions

12.
'n

;o

En

z

0

Q

0

1>

~3'r

0

n

n

c:

KEY,

121 COMPONENT

6 COMPONENT

(51 PUMP

DRANCH WITH JUNCTIONS

111• JUNCTION OR VALVE

= HEAT STRUCTURE

W-t- CROSS FLOW JUNCTION

STEAM GENERATOR

PRESSURIZER

416

I1$

REACTOR

BREAK VESSEL

176

0SO

0

0s

m'
IJISION REF[REHCE FILE LP-SI-tiLOT1a4

.3;* I I I i

_____ I I ___________ I ___________ i ________ I I 1I 1.,

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UOIDGSOOOI -

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60 60 8O 90)

Tin* (a)

FIGURE a SaparaLor void fraction. (SteadU at tL)
UISIOtt REFERENCE rILE lP-SS-1ILOM~4

300.

208-

I-O

too

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1

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t21 10 410 510 (50S 70

RELAP RELAP RCLAP

I¶FLOUJSOOOI - HFLOUJU000a ..... flFLd,UJF00IV

FIGURE 3 SG 3aparator mass flous. (StaadU state)

soI 90I

Time is
'JISION REFERN~tCE FILE LP-51-11LOFT14

Clll [a]

a

II

~IT

PW ...... ..-. ............ . ! ..... ... 

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P4160? (13 - tIFLOUJ4@OSI [23 ....

FIGURE 4 Pressurtser pressaure and surge ltine flow* (StvvidU sat~e)
LOFT TEST LP-SB-I*COMPARISOII OF RELAPS/flODa/CY36.0a UITH EXPERIIMEHT.

l .......................... i ....................... .................................. ................................................... ........ .......... .... .l

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10-........ ................ . . ....................... S.I*I

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* S t ISII£II~iOH[U 5iiPllllllfI IOILIIII IO£

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FIGURiE S Drobk I lou - prolLminmrU c~llulailon,
LOFT TEST LP-SB-lCOMPARISOH OF RELAPS/MOD2/CV36.B2 UITH EXPERIMENT.

seee400G

................ ................ ..................................................~eoo

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°.°H•.*°soo-IoIA

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w

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FIGURE B reak up:Lroam doa~ltU - protintintirU catcutation.

-10

Time Is)
LOFT TEST LP-SD-1,COMPARISOH OF RELAPS/HOD2/CV36.02 UITII EXPERIMENT

1886.

i

400

0

....... ......!.i .i .i ..ii .l i i ..iii... .

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RIIO18OBI

1~o -O0 :JdO IOU0 bull bUIU I'Wuev,

p a, P3E a 4 bl

DE-PC-266 -

FIGURE 7 lloL log dcnstLU - pralLmlnaru calcuaLtion.

Tima is)
FIGURE 8 COMPARISON OF CRITICAL FLOWRATE CALCULATED USING

THE HOMOGENEOUS ECUILISRIUM MOC.EL AND RELAPs/MOD2
'1

in

to

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LOFT TEST LP-SB-1,COlIPARISOHI OF RELAP'HOD-/CV36.0a UITHl EXPERIMElT.

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FIUEi ra ow; • 
UISION RIFIRCIICt FILE LP-sa-IILOFTsi

LOFT TEST LP-SB-Oi CALCULATION USING RELAPS/MODB/CV36.,Ga.

................ .... "..... " ".......... ........... "..... "........ !...... . ' .................. " ...... • ' "..... "..................... .•................ I................

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CNTALU...........................T.....TA.a

FIUE * P 9mr * aLmlno~oU
LOFT TEST LP-SD-I 1 COMPARISON OF RELAPS/1OD2-/CY36.02 UITIt EXPERIMENT.

16 . ................ .......... .................................................... ................ ................................... ................ • ........... . - 16

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

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12 ........ I........ .......... .................. .... ...... ... ...... .. . . .. . . . .. . .. . .. . .19

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P I " 9 T (

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PRilSAy SECOn'DARY Ti.. (*8

SICLAP EXP11IIc(hT AILAP [NPERIDIi IT

PtIOI........ eC-e-0aa- e0aaal ... PE-sOs-sl.

FIGURE 12. PrlmarU and secondsrU prssurea.
LOFT TEST LP-SB-ICOMPARISOH OF RELAPS/4OD2/CV36.oa UITH EXPERIMENT.

.16-

406-

200.

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

* I * A

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,............... |.. °..... ....... .• .6 ............. ....... .... .... .

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1696 Ii60 2008

Time Wa

RELAP EXPEI3In(iT

R1I010081 ........ DE-PC-266

FIGURE I' Hot' logj donsItU.
LOFT TEST LP-SB-ICOMPARISOH OF RELAPS/MOD-2/CY36.02 UITH EXPERIMENT.

ll i ........... ......... ; ........................ ........................ ' . ...... ............................................ ee

.1.............. too&e

S. .:

88 ............. ........ 

I a i j a. . .

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

i* ........ .... ... ..............

ElLA i........ :........................0

s ................ ................ ............... •............... !............................ ................ I ................ ..... ................... e

...i~i#P~I/iIi~W.i..........a~ ... I............

•Tm Is)

FIGURE .................... 14....................... .... ............ 680 680•- I: :"' ....................

................. .. i

a .'

1 400 ........... •................ I......................... I.-.. ......... I..........I .......................................... 0

* i a . a a

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...................... ................. . .-I....-. ......... ........................................... .... ..... *i•• I a a

:a• * a o •• I o I • * . a 

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FIGURE 1 Bra up •r~ dsstU
LOFT TEST LP-SB-ICOMPARISOH OF RELAPS/MOD2/CV36.,2 UITH EXPERIIEHT.

11

'I

'I

. .......... .......... ..... ... ...... ......... * a *

...... .............. ! ......... .................

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

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

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

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seel

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I'

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RELAP £XENI4¶ENI

28400

Time. (a)

FIGURE IS Cold log. dansit•.
LOFT TEST LP-SB-ICO1PARISOH OF RELAPS/IOD2/CY36.02 UITII EXPERIIIENT.

II

_....

I'

I.

-2

II 1!

UAPOIR UELOCITV BOTTOM TOP

AELAP EXPEFIM11T EXPERIKE•.T

UELCJA88Bl ........ FE-PC-O6lA ... FE-PC-BOIC -

FIGURE 16 Cold tlg fluid vatociLlo3.

Time Is|
LOFT TEST LP-00-1,COMPARISON OF RELAP9/tMODB/C036.0a UWTI UhPERMfEtT.

.............. †††††††††††††††††††††

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

.I..~~~........... . . . . .I .

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-3 J-3 .I I. ........

I a a I

I @ Ie .O

UAqPOUR VELOCITY IIOTTOt TOP Tina (3)

AR'LAP EXE£RM T Er~l XPER iM[iT VELGJIGGBi ....... FE-PC-882A .... FE-PC- 2C

FIGURE 17 Ilot, lag fluid velocitLas.
LOFT TEST LP-SD-1,COMPARISON OF RELAPS/MODB/CY36.Oa UITH EXPERIMENT.

.OO ................ ................................... . . . . ...... . ............. ................ :................ :.................................• ................ .l l

se e .. ....... I .. .... ... .. .... ... .. ... ... .e. .. . W . ..

a . ........ ......................... ................ ................ ... ..... ... ..... .........

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9 S e

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FIGURE S8Lo 5,s do 5l
UISIOH REFERE[CE FILE LP-SI-ILOFTsi

LOFT TEST LP-SB-i CALCULATION USING RELAPS/MOD2/CV36.02

" * * 1 , . ...... . ......... ........... .......... .. .... ....

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

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U~ll)•lliiU~llit~........... lltii_....a....

FIUElIUp. inmvid(u~os

NRC FORM ]31 U.& NUCEIA1AR REGUULATORY COW I EPORT NUMBER ,AO..by TIO , v V . j, j 12441

3201.3202 BIBUOGRAPHIC DATA SHEET NUREG/IA-0012

US, INSTRUCTION4S O THE REVERSE GD/PE-N/544

2. TITLE ANO "IATITLE 3 LEAVE ILANK

RELAP5/MOD2 Calculations of OECD-LOFT Test

LP-SB-01 4. DATE REPORT COMPLETED

MONTH 1 8AR

S AUTHORtS• May 1987

P. C. Hall, G. Brown 4. DATE REPORT ISEO

MONTH I YEAR

January ' 1990 7. fERFORMING o440ANIZATION NAME ANO MAILING AODRESS IItlM* 10i. Co. 8. PROJECTr'TASN•fORK UNIT NUMBER

Central Electricity Generating Board ___FINORGRANT____________

Barnett Way, Barnwood .PI, ORANT NMER

Gloucester GL4 7RS

UNITED KINGDOM 10. SP4ONSORING ORGANIZATION NAME ANO MAILING ADOORESS (lIA* Z,0 COW 114. TYPE OF REPORT

Office of Nuclear Regulatory Research Technical Report

U.S. Nuclear Regulatory Commission 1. ""too COVERED 141--0.,.

Washington, DC 20555

12 SUPPLEMENTARY NOTES

13J, ABSTRACT 1XV -%4 PO

To assist CEGB in assessing the capabilities and status of RELAP5/MOD2,

the code has been used to simulate SBLOCA test LP-SB-01 carried out in

the LOFT experimental reactor under the OECD LOFT programe. This test

simulated a 1.0% hot leg break in a PWR, with early tripping of the

primary coolant circulating pumps. This report compares the results of the

RELAP5/MOD2 analysis with experimental measurements

14 DOCUMtNT ANALYSIS o KE'WOROS'CESCRIPTONS IS AVAILABILITY

STATEMENT

RELAP5/MOD2, ICAP Program, Small Break, LOFT Unlimited

16 SECURITY CLASSIFICATION

6. ,OENTIFIERS.OPENENOEO TERMS 'rnUMi assifie,

Unclassifiei

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