EA71e4 GvýP%

-NUREGAA-001 4

Interatonal

Agreement Report

Analysis of the THETIS

Boildown Experiments

Using RELAP5/MOD2

Prepared by

M.G. Croxford, P.C. Hall

Central Electricity Generating Board

Barnwood, Gloucester

GL4 7RS

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

July 1989

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/AA-O01 4

Internationall

Agreement Report

Analysis of the THETIS

Boildown Experiments

Using RELAP5/MOD2

Prepared by

M.G. Croxford. P.C. Hall

Central Electricity Generating Board

Barnwood, Gloucester

GL4 7RS

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

July 1989

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 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 test the ability of RELAI5iM-OD2 to model two phase mixture

level and fuel rod heat transfer when the core has become

partially uncovered, post test calculations have been carried

out of a series of boildown tests in the AEEW THETIS out-of-pile

test facility. This report describes the comparison between the

code calculations and the test data.

Excellent agreement is obtained with mixture level boildown

rates in tests at pressures of 40 bar and 20 bar. However at

pressures below 10 bars the boildown rate is considerably

overpredicted. A general tendency for RELAP5/IOD2 to

overpredict void fraction below the two-phase mixture level is

observed, which is traced to defects in the interphase drag

models within the code. The heat up of exposed rods above the

two-phase mixture level is satisfactorily calculated by the

code.

The results support the use of RELAP5/MOD2 for analysis of high

pressure core boildown events in PWRs.

i
Executive Summary:

In the analysis of small break LOCAs in PWRs it is sometimes

necessary to calculate the two-phase mixture level in the core,

and heat transfer from exposed fuel rods, for conditions where

the core has become partially uncovered. To test the ability of

RELAP5/MOD2 to model such conditions, post-test calculations

have been carried out of a series of boildown tests in the

THETIS out-of-pile test facility at UKAEA Winfrith. In these

experiments the two-phase mixture level boildown rate was

measured in a full length electrically heated rod bundle at

decay power levels, at pressures between 2 and 40 bars.

The present report describes comparison between RELAP5

calculations and measurements of the mixture level, void

fraction distribution and exposed-rod heat-up rates, in the

boildown transients. Comparisons are also described between the

present calculations and the analyses of the THETIS tests

reported previously with RELAP5/MOD! and TRAC-PFl/MODl.

The prime conclusion is that the report supports use of

RELAP5/MOD2 for analysis of high pressure core boildown events

in PFRs. Detailed conclusions are as follows:

(a) When a fine node (24 axial volumes) representation was

used to model the THETIS rod bundle, excellent agreement

was obtained with mixture level boildown rates in tests

at pressures of 40 bar and 20 bar. However at pressures below 10 bars the boildown rate was considerably

overpredicted.

(b) It was found that there was a tendency for RELAP5/MOD2 to

overpredict void fraction below the two-phase mixture

level, with errors increasing with decreasing pressure.

The errors have been traced to defects in the interphase

drag models within the code.

(c) Calculations with a coarse node representation (six axial

volumes) of the rod bundle, typical of that used in

reactor transient analysis, again showed good agreement

at pressures above 20 bars. However, oscillations were

encountered in the simulation of the steady state

condition prior to boildown. These oscillations were

found to be due to the periodic triggering of the

RELAP5/MOD2 vertical stratification model.

(d) RELA?5/MOD2 gave a satisfactory representation of the

heat-up of exposed rods above the two-phase mixture

level.

(e) RELAP5/,OD2 performed much better than RELA5/MODI in

previous simulations of the THETIS experiments. In

particular, accuracy, stability, running speed and mass

conservation errors were much improved in the RELAP5/%!OD2

simulation.

ii
CONTENTS

Page No.

Abstract i

Executive Summary

Contents

I. Introduction

2. Experiment

2.1 Facility description and instrumentation

2.2 Test procedure and initial conditions

3. RELAP5/MOD2/CYCLE 36.04 Calculation

3.1 Description of model

3.2 Steady state calculation

3.3 Transient calculation - comparison of experimental

results and calculation

3.4 Computing time

4. Calculations with coarse node representation of rod bundle

4.1 Steady state calculation

4.2 Transient calculation

4.3 Computing time

5. Discussion

6. Conclusions

7. Acknowledgement

8. References

Appendix I

Table I

List of Figures

Figures

ii

iii

i

1

2

2

2

3

3

5

5

5

6

6

7

9

.[ii

L • INTRODUCTION

Ia the analysis of small break LOCAs in ?;Rs it is sometimes necessary to.

calculate the two-phase mixture level in the core, and heat transfer from

exposed fuel rods, for conditions where the core has become partially

uncovered. To test the ability of RELA5/M002 to model such conditions,

post-test calculations have been carried out 0f a series of boildown tests

in the THETIS our-of-pile test facility at UMAEA Wiafrith (I]. In these

experiments the two phase mixture level boildown rate was measured in a

full length electrically heated rod bundle at decay power levels, at

pressures between 2 and 40 bars.

The present report describes comparison between RELAP5 calculations and

measurements of the mixture level, void fraction distribution and

exposed-rod heat-up rates, in the boildown transients. Comparisons are

also described between the present calculations and the analyses of the

THETIS tests reported previously with RELAR5/M0D1[3] and T.AC-PFl/MODl[4].

2. EXPERDlIENT

2.1 Facility descriotion and instrumentation

The THETIS test facility is described in ref. (2]. It consisted of a

vertical bundle of electrically heated rods enclosed in a 130.6mm

O.d. circular shroud cobe placed inside a vertical cylindrical

pressure vessel (see Fig. 1). The shroud tube was closed at the

bottom but open at the top. Systems were provided to supply a

constant measured flow rate of make-up water to the bottom of the

test section, and to maintain the rig pressure at a pre-selected

value.

The pin bundle, which is shown in Fig. 2, consisted of 61 pins of

12.2=m outside diameter. 57 of the pins were electrically heated

fuel pin simulators with a heated length of 3.6m.

The design of the fuel pin simulators is shown in Fig. 3. Each pin

consisted of a central helically wound nichrome heating element

surrounded by magnesium oxide insulation and enclosed inside two

concentric stainless steel sheaths. A "chopped cosine" axial power

distribution was achieved by varying the pitch of the helical heating

element. Twelve Imm diameter thermocouples were located between the

inner and outer sheaths in each heater rod, allowing temperature

measurements to be made at a large nuber of axial stations within

the cluster.

Four pins in the cluster were tubes containing water filled

instrumentation lines connected to pressure cappings at different

locations along the tube length. Measurement of the differential

pressure between the pressure tappings allowed average void fractions

to be estimated in different axial zones wichin the bundle. The

elevation of the pressure tappings on the instrument tubes are shown

in Fig. 4. Also shown are the axial locations of thermocouple

junction elevations and spacer grid locations within the cluster.

I.
2.2 Test orocedure and initial condi:ions

The test procedure was described by Jowitt [2] and is briefly

surmarised here.

In each experiment the test section power was set to lOOkV and an

equilibrium condition was established in which the system pressure

was constant and the pipework had reached a steady temperature. In

the equilibrium state, sufficient make-up flow was provided to

compensate for the liquid boil-off rate so that the entire heated

length of the rod bundle was wetted. The data logger was then

started and after a short delay period the transient was initiated by

cutting off the make-up flow, so that the liquid level in the bundle

boiled down. Tests were carried out at pressures of 40, 20, 10, 5

and 2 Bar. Table I si-arises the experimental conditions for the

particular tests analysed in this report.

3. RELAP5/MOD2 CALCULATION

3.1 Descrinrion of model

The version of the code used for the analysis described in this

report was the latest available released version (cycle 36.04) with

minor error corrections as implemented by W. Bryce at UKAEA,

Winfrith.

The test facility was represented using 26 hydrodynamic volumes

(nodes) as shown in Fig. 5; the noding arrangement is similar to that

used in the calculations.described in ref. [4]. The test section,

(ie. the pin bundle and enclosing shroud tube) was modelled as a

RELAP5/MCD2 "pipe" component. The heated part of the test section

was represented by the nodes numbered 2-25 each of height 0.15m.

Nodes numbered 1 and 26 represented the unheated part of the bundle.

Heat structures, representing the heater pins, were connected to

nodes 4-25 of the heated length. In ref. [4] it was deduced that a

layer of sub-cooled water, -30cm deep, had formed in the annular

space between the shroud tube and pressure vessel during the boildown

tests, causing high heat losses at the base of the cluster. To

simulate these heat losses, heat input into the lowest two volumes of

the heated length (corresponding to volumes 2 and 3 in the present

simulation) was neglected in the ref. (4] calculation; the same

procedure was used in the present calculations to compensate for the

heat losses.

The steady make-up flow supplied prior to the boildown phase of the

experiment was simulated using a TIAE DEPENDENT VOLLYME and JUNCTION

connected to the bottom of the cluster. The top of the test section

was connected to a TIME DEPENDENT VOLUME at the required fixed

pressure.

In order to model radial thermal conduction, the pins were

represented as cylindrical heat structures with nine radial mesh

points. The locations of the radial mesh poincs are denoted by the

crosses in Fig. 3.

A sample input data deck for the test at a pressure of 40 bar is

included in Appendix I.

2.
3.2 Stead, state calculation

Before commencing the boildown calculation it was first necessar7 Co

simulate the steady state condition that existed prior to the

transient. This was done by performing a calculacion in which the

initial make-up flow, temperature and system pressure were set to the

values in table 1, at an initial power of zero. Thhe power was then

ramped up to the experimental value over a 200s period. Typically a

problem time of 600-1Z00s was required before an acceptable steady

condition was achieved. FPi. 6 shows a typical result of a steady

state calculation, and demonstrates that thermodynamic parameters are

well converged.

3.3 Transient calculation - com~arison of exnerimental results and

calculation

Comparisons between predictions and test data derived from ref. (1]

are described below. Code predictions are compared with the

following measured quantities;

(1) Dry-out level trajectory. This is defined as the trajectory of

the lowest point in the bundle at which the rods were dry. (2]

(2) Void fraction axial distribution at different times during the

transient.

(3) Pin temperature axial distributCon at different times during the

transient. (Note that thermocouple data is available only for

the tests at 5 and 20 bars).

lote that in the plots of experimental and calcul4ted results, time

zero refers to the time at which the make-up flow was reduced to

zero.

(a) 40 bar case

The measured and calculated dry out level trajectory for the 40

bar case is shown in fig. 7. In the UELA.5/MOD2 calculation the

dry out level ac a particular time is taken as the elevation of

the bottom of :he lowest hydrodynamic volume in which dry out Is

calculated at :hac t4_ze. It is seen that the calculated and

measured trajectories are in excellent agreaement, the maximum

error in calculated mixture level being 0.2=.

Th,,e measured and calculated profiles of void fraction versus

elevation in the bundle at three different times are shown in

fig. 8. The measured void profile shows a gradual increase in

void fraction up to the two-phase mixture level* followed by a

sharp transition to sceam only conditions. The characteristic

shape of the curves is seen to be reproduced quite well in the

code simulation. However, there is a tendency to overestimate

Yoid fraction below the two phase mixture level at higher

The . location of the two-phase mixture level can be identified with the

elevation at which the void fraction suddenly increases to unity in Fig. 8.

3.
elevations in the bundle with macimum errors in the two phase

mixture densityw reaching -20%.

It is 'clear by comparing Figs. 7 and 8 that whereas the code

tends to under-predict the mixture level elevation by up to

30cm, the dry-out level is predicted accurately (to better than

3cm). Although the discrepancies between these two calculated

levels are not large, there is evidently some cancellation of

errors in the RELAP5 calculation of the dry-out level, due

perhaps to the choice of void fraction at which RELAP5

calculates dry-out to occur.

(b) 20 bar case

The measured and calculated mixture level trajectories for this

test are shown in Fig. 9. Again, agreement is excellent.

Axial void fraction distributions are shown in Fig. 10. Similar

trends are observed to those noted in the 40 bar case. However

errors in void fraction are now somewhat higher, with maximum

errors in the fluid density below the two phase mixture level

reaching -40%.

Measured and calculated rod temperatures during boildown are

compared at three elevations in Fig. 11. The experimental

curves are the median value of measurements from several

different thermocouples at a given elevation. Typical scatter

in the experimental pin temperatures was in the range +7K to

+20K. It is seen that RELAP5 predicts the rod temperatures to

within this uncertainty range, though there appears to be a

slight tendency to overpredict rod surface heat transfer.

(c) 10 bar case

Results for the 10 bar case are shown in Figs. 12 and 13. The

error in calculated boildown trajectory is larger than in the

tests at higher pressure, with error In the mixture level

elevation falling from over 0.5m at early times, to about 0.25m

at the end of the test. Unfortunately, the measured void

fraction data are Incomplete, in that data for the top half of

the bundle in this test are not available. However the general

trends observed in the 40 bar and 20 bar cases are still

evident.

The maximum two-phase mixture density error at 10 bars is -45%,

for those locations where the data are available.

(d) 5 bar and 2 bar cases

Results for these cases are shown in Figures 14 to 17.

Agreement between measured and calculated boildown trajectories

is significantly worse than observed at the higher pressures.

At 2 bars, for example, dry-out is calculated to occur first at

intermediate elevations rather than at the top of the bundle as

* This density error is defined as:

(calculated mixture density - measured mixture density)

measured mixture denstcy

4.
obser-ed in the tests. This implies the calculation of premature

ejection of large quantities of water from this elevation in the

bundle. Similarly, the predicctons of void fraction are

significantly worse, than those observed at higher pressures. In

particular, the void fractions in the upper parts of. the bundle

are increasingly overpredicted as pressure is reduced.

Measured and calculated rod temperatures during boildown are

compared at three elevations for the 5 bar case in Fig. 18. As

observed in the 20 bar case, the code gives reasonably accurate

predictions of the rod temperatures.

3.4 Compuuing time

The calculations were executed on a CR.AY-.01P computer. CPU time was

60s for the 40 bar case rising to 600s for the 2 bar case. The

average time step was O.3s at 40 bars but decreased to O.03s at

2 bars, and the CPU time used per hydrodynamic volume per time step

was in all cases in the range of 6. 4 6xlO-4s to 6.6 7 xl0-4s.

4. CALCULATIONS WITH COARSE NODE REPRESENTATION OF ROD BUNDLE

In reactor transient calculations using R•LA25/HODZ it ts common to use six

vertically stacked nodes to represent the core, in order to !imi=

computational costs [5,61. In order to assess the adequacy of this level

of noding the calculations described above were repeated using a six-node

representation of the test bundle shown in Fig. 19. In this case the

lowest hydrodynamic volume was left unheated to give an approximate

representation of the heat losses discussed above. Other features of the

model were left unchanged. Results of the transient calculation with the

coarse node model are described below.

4.1 Steadv state calculation

The procedure for calculating the steady state cundition with the

6 node model was similar to that employed in the 24 node calculations

described above. Results for the 40 and 5 bar cases are shown in

Figs. 20 and 21. A noticeable feature of these is the large

amplitude void• fraction oscillations evident in the 5 bar case.

After some investigation, the origin of the oscillations was traced

to the periodic triggering of the 1ELAP5/'XOD2 vertical stratiflcatlon

model, which has the effect of sharply reducing interphase drag in a

volume when the void fraction in the vertically adjacent volumes

differs by more than 0.5.

To test the hypothesis that the oscillations were due to triggering

of the vertical stratification model, the logic in subroutine PAINT

was modified to prevent the vertical stratification model from being

invoked. The steady state calculations were then re-run with this

modified version of the'code. The results for the 5 bar case is shown

In Fig. 22. The oscillations are seen to have disappeared, though

the new steady state condition does not correspond to the mean value

of the previous oscillatory state.

To investigate the impl4cations of the change to the steady state

obtained with the modified code, it was decided to carry out the

analysis of some of the boildown transients using the modified code

version. The calculations are described later in the report.

5.
!'.2 Transient calculation

The measured dry out level :rajector7 in the 40 bar case and that

calculated with the standard code are shown in Fig. 23. Agreement

is still good, despite the coarser nodiag, with a typical error in

mixture level elevation of 0.2m. The measured and calculated

profiles of void fraction versus elevation at three different times

are shown in Fig. 24. The general trends observed in the 24 volume

calculations are still observed; the characteristic shape of the

experimental curves ?s seen to be reproduced quice well by the code,

but with a tendency to overestimate void fraction below the two phase

mixture level.at higher elevations in the bundle.

The measured level trajectories for the cases at 20, 10, 5 and 2 bars

are compared with calculations of the standard code in Figs. 25, 27,

29 and 31. Accuracy decreases as pressure reduces, with typical

errors in mixture level elevation of 2m at the lowest pressures. The

measured and calculated void fraction profiles for the same cases are

shown in Figs. 26, 28, 30 and 32. The general trends described in

the 40 bar case are still observed, with the void fraction

over-prediction becoming more severe as the pressure falls.

As in the fine node calculation, RELAP5 predicts the rod temperatures

to within the experimental pin temperature uncertainty range, though

with a slight tendancy to overpredict rod surface heat transfer.

As noted above, some transient calculations were repeated with a

modified version of .ELAP5/MOD2, in which the vertical stratification

model had been disabled. Figures 33 and 34 show the dr7 out level

trajectories for the 40 bar and 5 bar cases obtained with the

modified code. These can be compared to the results obtained using

the standard code in Figures 23 and 29. It is seen that there is

little effect on boildown simulation, despite the major improvement

on steady state calculation at the lower pressure.

4.3 Computing time

The coarse node calculations were also executed on a CRAY-.V-P

computer. The CPU time was 12s for the 40 bar case increasing to 34 s

for the 2 bar case. The average timestep was 0. 5s at 40 bars falling

to 0.2s at 2 bars. CPU time per volume per timesitep was in the range

5.9xlO-ts to 6.lx!O-'s in all calculations, similar to the values

found in the fine node case.

5. DISCUSSION

5.1 Review of current calculation

With the fine node representation of the THETIS test section

RELAP5/MOD2I Cycle 36.04 gives an excellent simulation of the dry out

level trajectory measured in the tests at 40 bar and 20 bar and an

acceptable representation of the test at 10 bar. The code also

gives a good representation of.dry surface heat transfer above the

mixture level for these conditions. Inspection of the measured and

calculated void fraction profiles shows a tendency for the code to

over-predict void fraction below the two phase mixture level, with

errors increasing with decreasing pressure. At 40 bars the maximum

error in calculated two phase mixture density is - -33Z, rising to

- -46% at 10 bars; these errors occur at an experimental void

fraction of about 0.4 (see Figs. 8 and 13).

6.
Ardron and Care [71 have assessed the performance of :he interphase

drag models used in RZAU25/MOD2 in vertical flow in the bubbly and

slug flow regime (a 4 0.75). They concluded that for condizions

pertinent to boil-off in a pin bundle geometr-y (liquid superficial

velocities - 0, hydraulic diameter - .Ocm) the models tend to

over-predict void fraction, with errors increasing as pressure

decreases. .According to Fig. 3a in ref. (7], the error in two-phase

mixture density at a void fraction of 0.4 is - -30% at 40 bars

increasing to - -50% at 10 bars. These values are quantitatively

consistent with our present findings, and indicate chat the errors in

void fraction are traceable to defects in the interphase drag models

used in the code. Despite the errors, it appears chat the

performance of :he models is acceptable at pressures above 40 bars,

which is consistent with the conclusions in ref. (7].

At pressures below 10 bars void fraction errors become unacceptably

large, leading to a large over-prediction of the liquid level

boildown rate. It appears therefore that at present RELAP5/MOD2 is

unsuitable for calculating boildown behaviour at these low

pressures.

With the coarse node model some loss of accuracy was seen in

comparison with the fine node case. However the dry out level

trajectories and the axial void distributions in the 40 bar and 20

bar cases are calculated with acceptable accuracy. The coarse node

calculation dlsplayed oscillations in the steady state, which are

evidently due to cyclic triggering of the vertical stratification

model used in the code. When this model was disabled the

oscillations were found to disappear. However, simulation of the

boildown phase was unchanged.

it is worth noting that in the analysis of small break LOCAs and

pressurised transients in FWRs, uncovered core conditions are

normally encountered onl7 at pressures above -40 bars, since at lower

pressures the reactor vessel is normally refilling due to injection

of ECC water from the accumulator system. The present study

indicates that the use of RELA25/MOD2 with a conventional coarse node

core representation will probably provide acceptable accuracy for

describing core boildown under these conditions.

5.2 Comnarison with nrevious calculations

The T!ETIS boildown experiments were previously analysed using the

codes RELA5P/MODl[3] and TRAC-PF1/MODl[4]. In the R.ELA25iMODI

analysis (3] considerable difficulty was encountered in establishing

a satisfactory initial steady state; consequently an initial

condition was selected corresponding to the experimental condition at

about 4 0s into the experimental transient. Careful selection of the

time steps was also found necessary to produce acceptable mass

conservation errors. Even with these adjus ments the accuracy of the

transient predictions was very poor both in terms of the trajectory

of the dry out elevation and of the heater rod temperatures. In

contrast, the agreement with experimental data at high pressures

produced by UE!A25/MOD2 is very good. Mass conservation errors in

the present calculations were typically less than 1' of the final

mass inventory, though errors rose sharply below 5 bars, reaching

10% at 2 bars.

7.
In the TaAC-?Fl/MODl analsis of TI-TTS boildown tests E4 ] difflcul-7

was also found in matching initial conditions; again the time origin

for the transient calculation had to be artificially adjusted. After

adjustment to the released version of TM.C-PFl/MODl, reasonable

agreement with volume tricall7 averaged void fraction in the test

section was achieved. Typical void fraction errors were -10% at high

pressure, rising to -35% at low pressure, though maximum errors were

higher than this. The trend of increasing void fraction errors with

reducing system pressure is qualitively similar to that observed

using RELA25/IMOD2 and the errors also appear to be quantitively

similar.

6. CONCLUSIONS

1. To assess the ability of RELAP5/MCD2/Cycle 36.04 to model core

uncovery in a ?JR, post-test calculations have been carried out of

core boildown experiments in the UKAZA Winfrith THZTIS test facility.

2. When a fine node representation was used to model the THETIS rod

bundle, excellent agreement was obtained with mixture level boildown

rates in tests at pressures of 40 bar and 20 bar. However at.

pressures below 10 bars the boildown rate was considerably

over-predicted.

3. it was found that there was a tendency for RELAP5/MOD2 to

over-predict void fraction below the two-phase mixture level,, with

errors increasing with decreasing pressure. The errors have been

traced to defects in the interphase drag models within the code.

4. Calculations with a coarse node representation of the rod bundle,

typical of that used in reactor transient analysis, again showed good

agreement at pressures above 20 bars. However, oscillations were

encountered in the simulation of the steady state condition prior to

boildown. These oscillations were found to be due to the periodic

triggering of the R.ELAP5/MOD2 vertical stratification model.

5. REAP5b/MOD2 gave a satisfactory representation of the heat-up of

exposed rods above the two-phase mixture level.

6. RELAP5/MODZ performed much better than REIAP5/MODl in previous

simulations of the THETIS experiments. In particular, accuracy,

stability, running speed and mass conservation errors were much

improved in the RELAP5/MOD2 simulation.

7. The calculations support the use of RELA21P/MOD2 for analysis of high

pressure core boildown events in PW'Rs.

7. ACXN.VOLEDGLENT

The authors wish to acknowledge the assistance of W.M. Bryce of UTIAEA,

Winfrith, in creating the modified experimental version of ELSA25 referred

to in section 4.1 of this report.

a.
8. REFERENCE S

1. PEARSON, K.

"Full Length Cluster Level Swell Data at Pressures for 2-40 bar"

AEEW R2193 to be published.

2. JOWITT, D.

"A new Voidage Correlation for level Swell Conditions" AEEW R1488

A-EW R1488 (Issue 2) June 1982.

3. CLARE, A.J. and OVERTON, R.S.

"RELAP5/MOD1 Calculations of a Simulated Core Boildown Experiment"

Internal CEGB report 1984.

4. DAWSON, J.T.

"TRAC-PFI/MOD 1 Calculations of a Simulated Core Boildown

Experiment". Proceedings of Specialist Meeting on Small Break LOCA

Analyses in LUR's, Pisa. Vol. 2 p4 15 June 1985.

5. FLETCHER, C.D. and KULLBERG, C.U.

"Break Spectrum Analyses for Small Break Loss-of-Coolant Accidents in

a RESAR-3S Plant". NUREG/CR-4384 March 1986.

6. HARWOOD, C.

"RELAP5/MCD2 Input Data for Sizewell 'B'".

Internal CEGB report November 1986.

7. ARDRON, K.H. and CLARE, A.J.

"Assessment of Interphase Drag Correlations in the RELAP5/MOD2 and

TRAC-PFI/MOD1 Thermal Hydraulic Codes".

CEGB Report GD/PE-N/557 (Revised). March 1987.

9.

SAMP-Z !NPU" DATA DECK FOR 40 BAR, 2-4 VOLUý CALCLtATION

-rTI.TIS BOILDCWN:40 bar, 24 volume

0000100 NEW

0000101 RILT

0000102 SI

0000105 1.0 A*

7.- LN S NT

SI

2.0

*Time step control;

*End time Min dt

0000201 1700.0 1.OE-7

Max dt Optn

0.3 1003 .4 mj

100

Rst freq

1700

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

M INOR EDlIT VARIA~BLES

0000301

0000302

0000303

0000304

0000305

0000306

0000307

0000308

0000309

0000310

0000311

0000312

0000313

0000314

0000315

0000316

0000317

0000318

0000319

0000320

0000321

00003:=

0000323

0000324

00003Z5

0000326

0000327

0000328

0000329

0000330

0000331

0000332

TMASS

7 M-AS S

VOIDG

VOIrG VOIDG

VOIEG

VOIDG

VOIrG

VOIDG

VOIDG

VOIDG

VO IDG

VOIDG

VOIDG

VOIDG VO IDG

VO IDG

VO IDG

VOIDG

VOIDlG

VOIDG

VOIflG

V0IDG VOICG

VOIDG VOIUG

VO JOG

T!IMPG

TELMPG

TE!MPG

TZMPG

M"-DG

0

0

001020000

001030000

001040000

001050000

001060000

COlO170000

001080000

001090000

001100000

001110000

00111=00

001130000

001140000

001150000

001160000

001170000

001180000

001190000

001200000

001210000

001220000

001230000

0012-40000

001250000

001260000

001030000

000140000

001050000

001060000

001070000

* Total mass i4 system * Estimate of mass error

Vapour void fraction
0000333

0000324

0000333

0000336

0000337

0000338

0000339

00003-0

00003461

0000342

0000343

0000344

0000345

0000246

0000347

0000348

000034.9

0000350

0000351

0000352

0000353

0000354

00CO353

0000356

0000357

0000358

0000359

0000360

0000361

0000362

0000363

0000364

0000365

0000366

0000367

0000368

0000369

0000370

0000371

0000372

0000373

0000374

0000375

0000376

0000377

0000378

0000379

0000380

0000381

0000382

0000383

0000384-

0000385

0000386

Tr-MPG

TZMFPG

TEE!PG

TZ•MPG

TM-MPG

TEMPG

TEMPG

TZ.MP=G

J-=..;..PG'

TMIPG TZ!PG

TEŽ!PG

VOIDGJ I.LOWJ

H-TEMP

M-EIMP

H= -MP

=-L MP

r.iT.MP

h= MP

TE•MP

=.16~!P T=MP

T=MPF

-"PF

J. • F

=MTF

=EMPF

TZ-MPF

.TZMPF

00o100000

001090000

001100000

001110000

001120000

001130000

001140000

001150000

001160000

001170000

001130000

001190000

001200000

00i2.10000

001220000

001230000

00 1240000

001250000

001260000

002000000

002000000

001100109

001100209

001100309

001100409

001100509

001100609

001100709

001100809

001100909

001101009

001101109

001101209

001101309

001101409

001101509

001101609

001101709

001101309

001101909

001102009

001102109

001102209

001030000

001040000

001050000

001060000

001070000

001080000

001090000

001100000

001110000

001120000

001120000

,-*

Single Juncticn void fraction

Single Junction mass flow

Mesh poLit temp. eratures

* Volume liquid temperatures
0000387

0000388

0000389

0000390

0000391

0000392

0000393

0000394

0000395

0000396

0000397

0000398

0000399

TE?!PF

,.E:!PF

TZL!PF

T-EMPF

TZ%!PF

TEM!PF

72EMPF

001140000

001130000

001160000

001170000

00118C000

0011900C0

00100c000

0012ICCOO

001220000

00i230000

001240000

001250000

001260000

0000501 TIME 0 GT NTULL 0 iC00.0 L Make up flow Crip

*COLMP0NEY1 I ; PIE -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

00010000 'CLUSTIR' PIPE

0010001 26

0010101 6.265E-3 26

0010301 0.1 1

0010302 0.15 :5

0010303 0.3 26

0010601 90.0 26

* Number of volumes

* Vclume flow area, volume number

* Volume leng-h

* Vertical angle

* Pipe volume fria:icn data;

* Rough Hyd-dia Vol no.

0010801 2.37-7 0.0122 26

* Pipe volume control flag;

0011001 00 26 ' Wall fric:icn component, ionequilibrium

* Pipe junc:ion control flag;

001ii01 0!.000 -5 * No choking, no area change,

* =centally located, non homogeneous.

11Pipe volume IC

1F lags

0011201 003

001iZ02 C03

00!1203 003

'inc:ion , _e 

* :LiqVel

0011301 0.0

?ressure Temp

4.026E6 310.0

4.0_6E6 440.0

41. 026E6 47. 0

IC's;

IVapVel intVel

0.0 0.0

Dummy

0.0

0.0

0.0

Ja -o

0.0

0.0

0.0

0.0

0.0

0.0

NV

I

25
* COIPCNENT 2 ; SNGLt.YU

0020000 'OUTLET' SNGLjLN

* Single junction geometry;

From To Area Loss-F Loss-B Flags

0020101 0010!0000 003000000 4.7E-3 1.0 0.3 0000

Single junction !C's;

Control ILiqVel IVapVel IntVel

0020201 0 0.0 0.0 0.0

*COIP0N7ENT 3 ; Tn!fPVOL

0030000 'S.LrRIr' TM1PVOL

TIMPVOL geometry;

* Area VolLen VolVol A-ang I-ang E.Change

0030101 I.OE6 100.0 0.0 0.0 90.0 100.0

* Rough Hyd-dia Fg

0030102 2.5E-7 9.1ZE-3 00

T=,PV0L data;

* Flag

0030200 002

Time Pressure Quality

0030201 0.0 4.026E6 1.0

*-------------------------------------------------------------------------------------------

* COMXPONENT 4 ; 7!DlPJU•N

0040000 'INLET' ThDPjLN

* T-•PJTJ gecmetr7;

From To Area

0040101 005000000 001000000 4.7E-3

0040200 1 501 * Control word

* T.DPJ'LY data;

* Time LiqFlow VapFlow IntFlow

0040201 -1.0 36.OE-3 0.0 0.0

0040202 0.0 0.0 0.0 0.0

*-------------------------------------------------------------------------------------------

* COMPONENT 5 ; TIDPVOL

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

0050000 'FEE-fl' TM•PVOL * T'PVOL geometry;

Area VolLen VolVol A-ang !-ang E1-Change

0050101 1.0E6 100.0 0.0 0.0 90.0 100.0

Rough Hyd-dia Flags

0050102 Z.1Z-7 9.12E-3 00

* T•-•PV0L data;

* Flag

0050200 003 * Time ?ressure Temera:ure

0050201 0.0 4.026E6 310.0
HE AT SLAB DATA

* General heat st•racture data; * qNH Mesh2Ps Gecmer-y Flag L-bound

10011000 22 9 2 0 0.0

* Heat s:trc:ure mesh flags;

• cn Format

10011100 0 1

* Meshi L-terval

10011101 3

10011102 2

10011103 1

10011104 6

data;

4.013:E-3

4.39-Z-3

.66*,2E-3

S. 38ZOE-3

* Heat structure

10011201 002

10011202 002

10011203 002

10011204 001

composition data;

3

3

6

8

* Heat source

i0011201 0.0

10011202 1.0

10011203 0.0

Imitial temp

* Tein

10011401 330.0

10011402 340.0

10011403 520.0

10011404 470.0

10011.03 &60.0

100114.06 430.0

distribution;

3

8

data;

Meshpt

4.

5

6

7

8

9

Boundary. conditions;

BVol IaC

10011501 0 0

10011601 001040000 10000

* Source

0011701

i0011702

10011703

10011704

10011705

10011706

10011707

10011708

10011709

10011710

data;

VD e

001

001

001

001

001

001

001

001

001

001

Mu1:p tyr

0.03463

0.03730

0.04011

0.04243

0. 041A6

0.04615

0 .04753

0.04858

0 . 0492S

0.04963

3CType

0

1

DH- left

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

SurArCd

1

OH- rght

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Heignt

9.13

9.15

NIH

22

2 2

* Left

* Right

HSno

1

3

.4

5

6

7

3

9

I0
10011711 Co0 0.04963 0.0 0.0

1001171Z 001 0.04928 0.0 0.0 12

10011713 001 0.04853 0.0 0.0 13 10011714 001 0.04733 0.0 0.0 14

10011713 001 0.04613 0.0 0.0 i5

10011716 001 0.0"446 0.0 0.0 16

10011717 001 0.04242 0.0 0.0 17 00171 001 . 0.0 0.0 1 3

10011719 001 0.03750 0.0 0.0 19

00117"-0 001 0.0246. 0.0 0.0 20

i 011 2 ..001 0.03132 0.0 0.0 -"

10011722 001 0.0213: 0.0 0.0 22

* Addi--ional righit ounda--i card;

* 71ag Hyd-dia H:Eq-dia ChanLen HS

10011901 0 0.0 0.0 3.66 22

TAEIRMAL PROPERTY DATA

* ThCond VolHtCap

20100100 T3L/FCTN 1 1 Stainless steel

20100200 TLiFCT 1 1 * Magnesium oxide

20100300 TBL,'ICT 1 1 * Nichrcme

* Stainless steel

* Temp ThCond

20100101 300.0 12.61

20100102 366.3 13.85

Z0100103 477.6 13.9Z

20100104 588.7 18.17

20100105 700.0 20.41

20100106 810.9 Z2.30

20100107 922.0 24.92

20100108 1033.2 26.33

20100109 1144.3 29.42

20100110 1477.6 36.06

* Temv Vc1Ht•Cap

20100131 300.0 3.801E6

20100132 366.5 3.908E6

20100153 477.6 4.084E6

20100134 588.7 4.260E6

20100133 700.0 4.436E6

20100136 810.9 4.663E6

20100137 922.0 4.919E6

20100138 1033.2 5.105E6

20100159 !477.6 5.727E6
.Magnesurm oxide;

* Temp ThCond

20100201 300.0 0.2520

201002.0 3-73.1 0.2451

010020•--3 22.04 0.2405

20100204 477.59 0.2352

20100205 333.15 0.2300

20100206 588.71 0.2249

20100207 64,4.26 0.2196

20100208 699.32 0.2143

20100209 733.37 0.2091

20100210 810.93 0.2029

20100211 366.-8 0.1987

20100212 922.04 0.1934

20100213 977.59 0.1882

20100214 1033.15 0.1830

20100215 1088.71 0.1777

20100216 14!.46.26 0.1725

20100217 1199.82 0.1673

20100218 1255.37 0.1621

20100219 1310.93 0.1568

20100220 1366.48 0.1316

20100221 1422.04 0.164 .

20100222 1477.59 0.'l'12

20100221 1533.15 0.1359

20100224. 1588.71 0.1307

20100225 164".26 0.1255

20100226 1699.82 0.4203

20100227 1755.37 0.1150

20100228 1810.93 0.1098

20100229 1866.48 0.1046

20100220 1922.04 0.0993

20100231 3000.00 0.0993

20100251

20100251

20100252

201002.54

20100255

2010025 6

201002-57

20100258

20100250

Z0100261

20100262

Z0100263

20100264.

20100265

20100266

20100267

20100258

Temp

300.0

373. 15

122.04

477.59

533.15

-88.71

6". 26

699.82

7,53.37

810.93

866.48

922.04

977.59

1033. 15

1088.71

1144 .26

1199.82

1253 .37

Vo iH:Cap

2076.81

2033.52

2004.39

1971.74

1938.87

1906.01

1873. 15

1840.29

1307.43

1774.56

1741.70

1708.84

1675 .96

1643. 11

16 10.25 1577.39

1.544.3

1311.67
20100279

20100270

20100271

20100272

20100273

2010027

20100275

201002176

20100277

20100273

20100279

20100230

20 0C_231

1213.93

1366.4"8

14.77.39

1333.13

1338.71 S6 '",. 2.

1699.32

11753.37

1310.93

1866.418

192_ .04

5000.00

l:73 .30

1"35 . 946

1412 .05

1380. 22

1347.33

1314.49

1231.63

128.77

1213 .90

1133.04

1130. 13

1!1- 12

111>.22

ThCond

I. 1163

1. 1163

1. 1:63

Vo lHtCp 2130 .30

2130.30

2130.30

2130 . 30

* Nichrzme;

Temp

20100301 300.0

20100302 373.13

20100303 1922.04

20:00304 o000.00

20100331

201002352

20100251

20 1002354

T.emu

300.0

373. 13

i922.04

5000.20

* General data table for power;

20200100 ?OEER

' %me Power

202,00101 0:0 0.0

20200102 20.0 0 1.0E3

* EN.D OF DATA DECX
TA2LE 1

T %.ST

LUMBER

561-2

551-2

553-4

555-6

557-8

PRESSURE

/Bars

2 .00

5.25

1O .21

2C.15

40.26

MAKE-UP FLOW

RATE/KgSec-I

120.0 x 10-

97.4 x 10-

47.4 x 10-

53.0 x 10-

36.0 x 10-

,MAKE-UP FLOW

TEM!PERATT3RE/ K

TEST SECTION

POE'R/KW

352

342

310

356

310

100

100

100

100

l00
LIST OF FIGURES

I. The Thermal Hydraulic Emergency Cooling Test Installation (THETIS).

2. 61 pin cluster cross section and pin numbering system.

3. Cross section of model fuel pin.

4. Thermocouple, pressure tap and spacer grid positions.

5. :.oding diagram for 24 volume calculations.

Steady state caiculation for 21 volume =ode-.

6. Calculated void fraction histories during steady state for 40 bar case.

21 volume transient calculation.

7. Heat structure dry out histories from start of transient for 40 bar case.

8. Void fraction profiles for 40 bar case.

9. Heat structure dry out histories for 20 bar case.

10. Void fraction profiles for 20 bar case.

11. Comparison of experimental and RELAP heater rod surface temperatures for

20 bar case.

12. Heat structure dry out histories for 10 bar case.

13. Void fraction profiles for 10 bar case.

14. Heat structure dry out histories for 5 bar case.

15. Void fraction profiles for 5 bar case.

16. Heat structure dry out histories for 2 bar case.

17. Void frac:ir.n profiles ±or 2 bar case.

18. Comparison of experimental and REL.AP heater rod surface temperatures for

5 bar case.

19. Noding diagram for 6 volume calculations.

Steady state calculation for 6 volume model.

20. Calculated void fraction histories for 40 bar case with standard code.

21. Calculated void fraction histories for 5 bar case with standard code.

2L. Calculated void fraction histories for 5 bar case with modified code.
Transient calculation with standard code

23. Heat structure dry out histories for AC

24.

25.

26.

27.

29.

30.

31.

32.

Void

Heat

Void

Heat

Void

Heat

Void

Heat

Void

fraction profiles

structure dry out

fraction profiles

structure dry out

fraction profiles

structure dry out

fraction profiles

structure dry out

fraction profiles

for 40 bar

histories

for 20 bar

histories

for 10 bar

histories

for 5 bar

histories

for 2 bar

case.

for 2C

case.

for I0

case.

for 5

case.

for 2

case.

bar case.

bar case.

bar case.

bar case.

bar case.

Transient calculation with modified code.

33. Heat structure dry out histories for 40 bar case.

34. Heat structure dry out histories for 5 bar case.
II

ZN ":;CL -E

22S VOLT

.6SC0 AMP

:;c SuPOLI

130.6mm

57-HIETED ROOS

4-uNI4EATIE0 ROOS

ROD OIA = ~2.mm

UP

PUMP

EA P RA1LJRE

EN SC A,

--8Y PASS

Filure 1: THE THERMAL HYORAULC EMERGENCY COCLING

TEST INSTALLAITION (THETISi
8 mm

PITCH 9--i~y

ICiACLE

Zs 5mm

(D UNHEAT72D P!'NS

PIN DIAMETER 12 2

I - SHROUO INNER DIAMIETER z130.6mrfl

F .iure 2: 61 PIN CLUSTER CROSS SECTION ANO PIN NUMBERING SYSTEM
7HER mQcoup,_ 16

/ CABLE

HEArER,7/ TAPE

MAGNESIA ;.NSULArOR-/ HE HE

iLgure 3: THERMOCOUPL5 IN UPPER HALF ARRANGED FOR

610mm -XIAL SPACING, lN LOWER HALF FOR

1a5mm AXIAL SPAC!NG

A. rER SHEATH

!CROSS -SEC IT ION OF MODEL FUEL PIN
PI S _ I___ OS ! r ' -% TYp I 3 1 3 6 4os 5 

PCSITlCNl' ý a 9 0 1 14.15 4,, [ 718 16,17 12, 13 P .ESS• S P-CEa

2, 22 123,24.,25 29,30,31 9,35,35 33.34 27, 2s TAPS GSIOS

.373859160 55,56.. 4..

E T 'i ES I E2I LN .7-H- -

E 3.220o

3"-0 ý m

m

3-048-

2704-

2 446-

2-8775

2-5- 2532- lID

2"0 1-

m

mll

m

m

2-102

1 758-4-

1 24-H .0-i

156-

0.984.- .O

5 _

0 _ HEATE 7 EQ NGTH

0-468-

LBOTTOM 0-075 o -.-.

F{G.4 THERMOCOUPLE, PRESSURE TAP AND

I

SPI ACER GRID POSITIONS
t'STMORM'S

FIG. 5. NOOING DIAGRAM FOR 24. VOLUME CALCULATION
1.4

C

9

TJE1TrS 30ILDOIJl rET,7 PRESSURE 4@ '83 4.VUI c

I-a

4117

1. 4

4 .8

,4.3

4.18

f.4

4.4

"4.11

a

Figure 6: CALCULATED WtD F';ZCTICfl HISTORIES DURING STEPOY STATE
IMETTS 3OILOOLfI 7-EST, PqESSURE *48 3AR, E4 VAJLUM" CASE

3 .5 ;.5.

.22 _ a .

i.9

Fig-ure 7: HEA~T STRUC7TURE ORY OUT HItSTORIES FqC!? START OF -RMtSTICIT

5..1 -. 1 s 3'

Figure 8: ýUJID P-PCT10" PPaF-:uS AT 3,5,3S is.SE C".IOS ~NIo 7R~ftSIENT
d

~RETS 3OILDOtJl TES1. ~ES~URE * 2g 3~R, ~4 ~~3Lu~ ~SE

J

N _________ _________

2.1 _________________________________________________________ ________ _________-.---.-,

~c ~, omawur

N

_________________ * -*----------------~.- - .

I-.

~ I.-.

U

HEAT STRUCTUREC ORY

2w 34

OUT HISrMRrES FROMl START OFMAnS lENT

T-i s

~i~ure 9:

.811

..2.~.-

1~~

I.']-

WEUD FRACTION1 PROFILES AT

2:5

Figure 1-0: SECOMOS INTO I~R1MS ENT
iHETIS 30!Loaum TEST, PQESSURE - 298ASR, 24 '.LUrt CA.SE

!

r,

TV%.Iu -im MW W~ TFigure 11: COMARISOM OF DPRMNA M REA HEATER RCOE SURAFCE T-EMWEATURES
TIHETIS 30ILDOOU "E-1 PqESSURE *83AQ, 24 !4LUM CASEE

a, --- . - - - .

"igure 12: 4NEAT STRUCTUJRE ORY~ OUT HISTGRIES FROM START OF TR~tfSIENIT

Fiue 3

£ -

LOED FRAC710m PQCOtLE3 AT S Z,18 ECCIOS 1INTo r~rms!E?IT 41a,.
,.e

%

0.5

fl4ETIS 3OILOOUI ~tSr, PQESSURE * S 3~R. ~' '.~LU~t C~S~

ili~K

___ ___________ ___ ___ I * N

* *9I~ 4 -

'J N~33E~ _______

N N

N S.1

________________________ _______________________________________________________________ _______________________________________ ________________________ ________________________ I

4.b

U

Figure 14:

I .1

S -

.~* 4 -

.1

IN ?W 30 N TA 4

HEAT STRUCTURE CRY OUT '41STORIES 7;.ZOM START OF 7MI3

40

row , i

.ýi,,ure 0 13:

'A.i 3.a 2.'s

Figure '.OD ;;ACTION9 13: P90FtLES- 4T 8. 158.3Sa SZC,-MOS VrITO M-MSIENT 1*
V

3.

3.

1.

IHETIS 30ILCOIJI 7ST, PRESSURE *2 BAR, 24 .VOLLU CaSE

[ _ * Lj 7_._

* *e.9

____ _ ____ *___ ___ ___ ___ ____ cI3.__ __ ___ ___ _ 

rug , I

Figure 16:

..

'.5.

A

~

HEAT STRUCTU'RE CIRY OUT HItSTORtES FROM¶ START OF IVAflSIEIIT

2.9 3'. 2.

Fic.ure .JIED --qgCT:ort PQOvrLES AT 3, :sa. 25 SEC"rIOS ',.TO ~RAM1SMNT '
7JET IS 3rL~OUW -EST, NqESSURE 5 s R. 24 IJOLUr CASE

r'r

7U*- ~w ~n -n 

310 

-_ *--*w

Fi~~~~~~gure~~~~~ ~ 1.:,MM-tO AEI MLAOR AP4AE O UFC IPEAU
'STMCRM'

FIG. 19. NODING DIAGRAM FOR 6 VOLUME CALCULATION
fl4CTIS Boa~nauw TEST, ~QESSU~E * 46 ~RR, ~ ~E~tur~ ~SE tJVfl4 S~flOARD CCDE

'.8 '..

a.vanm~.

I. I ____________________________________ _______________________

I.

Z7

I - -

I -~ ~.I _______

CALCULA~TED WI.D FRACTICH HISTORIES DURING STEADY STATE

tIm

Figure 20:
NhETTS 30ILDOUI EST. PESSURE - S 3AR, 6 'OLUM CA•S 4I7Th STAtMlORO CODE

Ij

. - .. ,~ ... . , .I,, i . ,_,

a.9$

' 0 •., too ., ini ! 'AG J• ,• l '

4.igure 2]1: CALCULATED 4010D PPAC7:N ~4!STCRlES DURING STEADVY STATE u-w

TMETtS SOILDOUI TrEST. PRESSURE - S BAR, 6 k40L6tM CASE urr14 I'OIFtED CODE

I.

Figure 22: CALC•'LATED VOID F;'CTIM HISTCRrES oURImG sTEQOY STATE
P4CTIS 30OtOU1M TEST, PRESSURE - 49 3AR, S .l2LUrf CASE UiET;4 STAMDOARD CODE

C

w

to 'so ~ .1 -,

-~q S

Figure 23: HEA~T STMUCTURE CRY 3Ur HrS',LRrES P;GM S7ART OF 7RAMMSET

S

J

|

Q

g

______ ______ __________ . --. ~ L~............ __________

I - 1* ," /. ' II \ S., - * * ~ - * -.-- * - -

/

1'

_____ ______ _____

- - .. .9.

* a

I ,; -

- -~-------.- I, ______

* ., - -_-

____ K! / ;.zi/ ____ _____

-. . ~

4 A, /7

I.. ~ -~. ~ '4.,

.2

a

.1

f. .5 I's 1.5

WOtD FPRCTIOH Pq0FILES AT

2A6 a.s

:igure 24: 2, 1a.sa '-'!5t3 I;. GMD ThMAS lENT
i~4(TI3 3OtL~CU1 ~TST. P~~3SL'~ * G ~Lur~ C45C ~.iflN STAftUARD CEDE

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Figure 25: HEAT STRUC7JVRE CRY OUT HISTORIES Paml START GF TRPISIEltT

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Figure 27: HEAT STRuCMURE CRY OUr 4ESCRIErS FROM START Or TRAN1SIEN¶T

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Figure 29%

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Figure 114: ~.ue3:HE;T STMUCTIJRE jyY OUT H4tSTlCtES F;an START O IZASFI

CENTRAL ELECTRICITY GENERATING BOARD

Dr.Norman Lauben.

Manager. ICAP Program.

Reactor and Plant Systems Branch,

Mail Stop 1130-SS

Office of Nuclear Regulatory Research.

U.S. Nuclear Regulatory Commission

Washington D.C. 20555

U.S.A.

Generation Development

and Construction Division

Plant Engineering

Department

Barnett Way,

Bamwood

Gloucester

GL47RS

Telephone: Gloucester 65-2222

Telex: 43501

Our ref Your ref Date

29 May 1987

Dear Dr. Lauben,

UKAEA/USNRC Administrative Aqreement WH36047

As you are aware, one of the features of the above Agreement was that the UKAEA obtained

access to the RELAP5/MOD2 code on behalf of the Central Electricity Generating Board. In

partial fulfillment of UK commitments under the above Agreement, and following discussions

with Mr J. Fell of UKAEA, I enclose copies of three reports produced recently by CEGB.

* GD/PE-4/544. RELAP5/MOD2 Analysis of OECD LOFT Test LP-SB-01. Please note that the

LP-SB-02 dat.u is proprietary to LOFT consortium members, and distribution of this report

should be limited accordingly.

" GD/PE-N/557. Assessment of Interphase Drag Correlations in the RELAP5/Mod2 and

TRAC-PFI/Modl Thermal Hydraulic Codes

This report describes comparisons of the void fraction calculated by the code with values

derived using recognised correlations for void fraction in fully developed vertical

two-phase flows. The study is restricted to void fractions below about 0.75.

* GD/PE-N/576 Analysis of the THETIS Boildown Experiments using RELAPS/Mod2

This report examines the performance of the code in predicting void fraction in a vertical

heated rod bundle. Results are consistent with the findings of GD/PE-N/557, indicating

acceptable performance above 2 MPa, but increasing errors at lower pressures.

I believe that these reports broadly conform to the guidelines for ICAP reports, and I have no

objection to your issuing them as NUREG reports. If you elect to do so please ensure that

proper reference is made to CEGB.

I note that we have not prepared data packages since I consider that they are unlikely to be

necessary for these reports. However if there is any additional information which you or your

contractors require I shall be happy to provide it.
For the record, I also enclose a copy of CEGB Report GD/PE-N/535, describing RELAPS/MOD2

analysis of LOFT test LP-SB-03. This report was handed out at the Meeting in Erlangen,

Germany in June 1986, and subsequently copied to Mr G.W.Johnsen and Dr. F. Odar (letter,

9th September 1986). I was somewhat surprised to find no record of this report in Tables 4

or 7 of Ref(1). Please let me know if you have any difficulty with this report.

Finally, I should like to give you an update on our current work with RELAPS/MOD2. As you

are aware, we have also been analysing LOFT tests LP-SB-02 and LP-FW-01 with RELAPS. To

obtain good agreement in these cases, we have found it necessary to develop (in

collaboration with Wallace Bryce at Winfrith) an alternative formulation for the flow quality

delivered to the breakline Tee (horizontal stratification entrainment model). We are also

making good progress on our analysis of Semiscale tests S-LH-1 and 2 with RELAPS/Mod2.

We hope to send you the reports on these analyses within a few months.

Yours sincerely

Peter Hall

Safety Technology Section

Reference (1). ICAP Annual Report. NUREG-1270

Ting, P., Hanson, R. and Jenks, R.

March 1987.

cc:

Mr G E Wilson EG&G(Idaho) (with atts)

Dr L Shotkin USNRC

Mr J Fell Winfrith

Dr W M Bryce Winfrith

Mr M E Durham .PMT

Mr P 0 Jenkins

Mr K H Ardron

Mr P C Hall

2
Mac FO'RM 3:115 U.I. NUCLEAR REGULATORY COMMISSION I REPORT NUMBER IA-9.deOv 1`1OC. *W Vol No. It 4y-

(241, NUREG/IA-0014 3201,,202 BIBLIOGRAPHIC DATA SHEET . D/PE-N/576

SEE INSTRUCTIONS ON rtE RIVERSE

Taj O U.•tJOTL' I LEAVE OLANK 2naT ysis of the THETIS Boildown Experiments Using

RELAP5/MOD2 4 DATE REPORT COMPLETED

MONTH . YEAR

S AUThOR(ES

M. G. Croxford, P. C. Hall P DATE REPORT ISSUED

MONTH I

S1989

7 PERFORMING ORGANIZATION NA"F -nV " 'NGAOORESS(,'I ZMCaftJ 8, PROJECTITASK/WORK UNIT NUMBER

Central Electricity Generating Board 9,,4OR GRNT NUME

Barnwood, Gloucester

GL4 7RS

United Kingdom 10 SPONSORING ORGANIZATION NAME AND MAILING ADORESS IIcMIW4eZoC*) I I.. TYPE OP REPORT

Office of Nuclear Regulatory Research Technical Report

U.S. Nuclear Regulatory Commission a. PERIOD COVREfDu,, m -

Washington, DC 20555

12 SUPPLEMENTARY NOTES

13. ABSTRACT ItZW.owOr~d 0

To test the abiltiy of RELAP5/MOD2 to model two phase mixture level and fuel

rod heat transfer when the core has become partially uncovered, post test

calculations have been carried out of a series of boildown tests in the AEEW

THETIS out-of-pile test facility. This report describes the comparison

between the code calculations and the test data.

Excellent agreement is obtained with mixture level boildown rates in tests

at pressures of 40 bar and 20 bar. However at pressures below 10 bars the

boildown rate is considerably overpredicted. A general tendency for

RELAP5/MOD2 to overpredict void fraction below the two-phase mixture level is

observed, which is traced to defects in the interphase drag models within the

code. The heat up of exposed rods above the two-phase mixture level is

satisfactorily calculated by the code.

The results support the use of RELAP5/MOD2 for analysis of high pressure

core boildown events in PWRs.

Ia DOCUMENT ANALYSIS o E•EORDS'OESCRIPTOMS

RELAP5/MOD2, boil-down, ICAP Program, THETIS

E IDIENTIFIERSIO$EN.ENDED TERMS




UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

SPECIAL FOURTH-CLASS RATE POSTAGE & FEES PAID USNRC

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