NUREG/IA-0090

International

Agreement Report

Assessment of RELAP5/MOD2

Using the Test Data of

REWET-JI Reflooding

Experiment SGI/R

Prepared by

A. tiimiil~iinen

Technical Research Centre of Finland

Nuclear Engineering Laboratory

P.O. Box 169

SF-00181 Helsinki, Finland

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

May 1993

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-0090

International

Agreement Report

Assessment of RELAP5/MOD2

Using the Test Data of

REWET-I1 Reflooding

Experiment SGI/R

Prepared by A. H~imirniiiinen

Technical Research Centre of Finland

Nuclear Engineering Laboratory

P.O. Box 169

SF-00181 Helsinki, Finland

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

May 1993

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 documents work performed under the sponsorship of the Imatran Voima

Oy of Finland. The information in this report has been provided to the USNRC

under the terms of an information exchange agreement between the United States

and Finland (Technical Exchange and Cooperation Arrangement Between the United

States Nuclear Regulatory Commission and the Imatran Voima Oy of Finland in the

field of reactor safety research and development, February 1985). Finland has

consented to the publication of this report as a USNRC document in order that

it may receive the widest possible circulation among the reactor safety

community. Neither the United States Government nor Finland 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

An analyses of a reflooding experiment with RELAP5/MOD2 cycle 36.04 is

presented. The experiment had been carried out in the REWET-II facility simulating the reactor core with a bundle of 19 electrically heated

rods. On the basis of the results of two calculations recommendations

for the core nodalization are presented, and a modification to the

code is proposed.

iii

Table of contents Page

1. Introduction ............................................ 1

2. Facility description .................................... 1

3. Test description ........................................ 3

4. Code input model description ........................... 3

4.1 Loop and vessel model ............................... 3

4.2 Core model .......................................... 5

4.3 Steady state ........................................ 5

5. Results ................................................. 5

6. Run statistics .......................................... 7

7. Conclusions ............................................. 8

8. References .............................................. 9

List of Tables:

1. REWET-II facility characteristics

2. Geometric data of the volumes

List of Figures:

1. Simulation of the VVER-440 reactor vessel with the REWET-II

facility.

2. REWET-II test facility

3. Test rod arrangement in the core of the REWET-IH facility

4. Axial power distribution and the spacer grid elevations in the

core.

5. Nodalization scheme of the REWET-II facility

Plots of case 1:

6. Liquid temperature in the lower plenum and in the middle and upper

part of the core

7. Steam temperature in the middle and upper part of the core

8. Cladding temperature in the lower and middle part of the core

9. Cladding temperature in the upper part of the core

10. Cladding temperature below and above the spacer grid elevation

11. Quench front elevation/position of the CHIF point, collected from

V
the printouts

12. Shroud temperature

13. Heat transfer coefficient in the core

14. Void in the core

15. Void in the upper plenum

16. Pressures in the lower plenum, downcomer head and upper

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

Plo

37.

38.

39.

40.

plenum head

Differential

Differential

Differential

Differential

Differential

Differential

Differential

Differential

pressure 1,

pressure 2,

pressure 3,

pressure 4,

pressure 5,

pressure 6,

pressure 7,

pressure 8,

between

between

between

between

between

between

between

between

vols

vols

vols

vols

vols

vols

vols

vols

100060000-100130000

100170000-100200000

100030000-100060000

220020000-220010000

105010000-115010000

100030000-100200000

220030000-220020000

230010000-205010000

Collapsed liquid level in the downcomer

Collapsed liquid level in the upper plenum

Collapsed liquid level in the core

Liquid velocity in the downcomer and core inlet

Steam velocity in the core inlet

Liquid mass flow to the core

Liquid mass flow in the downdomer

Liquid mass flow in the broken loop

Liquid mass flow in the intact loop

Steam mass flow in the intact loop

Steam mass flow in the broken loop

Consumed CPU time versus real time

ts of case 2:

Cladding temperatures in the lower and middle part of the core

Shroud temperature

Liquid mass in the entrainment water tank

Consumed CPU time versus real time

vi
ASSESSMENT OF RELAP5/MOD2 USING THE TEST DATA

OF REWET-II REFLOODING EXPERIMENT SGI/R

Anitta Hamalainen

Technical Research Centre of Finland,

Nuclear Engineering Laboratory

P.O. Box 169

SF-00181 Helsinki

Finland

Executive Summary

An experiment carried out in the framework of the REWET-project in

1983 has been used as an experimental database in the RELAP5/MOD2 assessment as a part of the International Code Assessment and Application Program (ICAP).

The REWET-II facility is a scaled-down model of the Loviisa 1 and 2,

VVER-440 type reactors. The core in the facility consists of 19 electrically heated fuel rod simulators. The facility has been used in reflooding experiments with downcomer and/or upper plenum ECC injection.

Two calculations have been done. The number of the subdivisions of the

reactor core heat structures describing the rod simulators has been

the varied parameter. In both calculations the nodes in the core were

quite short. The maximum possible number of subdivisions was used in

the first calculation, and 1/8 of it in the second.

The code's ability to represent the phenomena during this reflooding

test was good. The small differences in cladding temperatures and

quenching times between the analysis and the measurements show the

vii
code to be slightly conservative. The oscillating nature of many parameters, seen in the experiments, is also present in the calculations,

and even more strongly.

The calculations have mainly been performed using a maximum time step

of 0.01 second. The total number of time steps was 97767. The total

CPU-time consumption per volume (node) and per time step was 0.013

seconds.

viii
1. Introduction

The REWET-project, started in 1976, is carried out in cooperation

between the Technical Research Centre of Finland and the Lappeenranta

University of Technology. The project has contributed to the experimental database of reflooding and natural circulation phenomena for

code assessment. Reflooding has been studied in two test series, first

to study the reflooding in general, reported in reference /1/, and

secondly to study the effect of the spacer grids on the reflooding

process (SGI), reported in reference /2/. The analyses of the tests

have been performed with several codes but the main tool has been the

NORCOOL-I code, developed in Nordic cooperation. The knowledge from

the earlier analyses has given the basis of the modeling of the facility for the RELAP5/MOD2 code. In comparison of the capabilities of

different codes to describe reflooding phenomena, the SGI/R test has

been used as the reference test.

Special features of the VVER-reactor as well as, a) the use of atmospheric pressure, b) the short heated length of the core, c) the stepwise varying linear power in the REWET-Il facility with rather cold

rod ends and d) the smnall injection flow rates in the SGI/R test, have

been the reasons why the modeling of the core has not followed all the

recommendations given in the RELAP5/ MOD2 manuals. The modeling of the

core has been the main point of interest in the two assessment calculations performed.

2. Facility description

The REWET-II test facility was originally designed to investigate the

phenomena during the reflood 'phase of a LWR LOCA. The scaling factor

between the facility and the reference reactor, the VVER-440 type

reactor is 1:2333. The main design principle is accurate simulation of

the specific features of the rod bundle geometry and the primary system elevations (Fig.l). The steam generators and the primary pumps are

simulated as flow resistances. Fig.2 shows schematically the REWET-II

test facility, and the facility characteristics are given in Table 1.

A more detailed description of the facility, is in the reference /4/.

I
The test section of the facility consists of 19 electrically heated

full length fuel rod simulators in a triangular grid (Fig.3), an upper

plenum, a lower plenum and a downcomer. One intact primary loop and a

broken loop in the test facility simulate the five intact loops and

*the broken loop of the reference PWR, respectively. The heating coil

of a fuel rod simulator is packed in magnesium oxide inside a stainless steel cladding. The test section is thermally isolated. The spacer grid elevations and the rod simulator power distribution are shown

in Fig.4.

The primary measurements in the experiment are rod surface temperatures, pressures, pressure differences, coolant flow rates and the

heating power.

The data acquisition system consists of a measurement and control processor and a desk-top computer. During an experiment 96 data channels

are scanned once in a second.

Fuel rod simulators:

Heated length

Outer diameter

Power distribution

Axial peaking factor

Number of rods in bundle

Vall thickness of housing

Bundle arrangement

Lattice pitch

ECC injection location

Fuel rod simulator bundle power

Average fuel rod simulator power

Average linear heat rating

Flooding rate

System pressure

Maximum cladding temperature

Coolant temperature

242 cm

0. 91 cm

chopped cosine

1.5

19

2 mm

triangular

1.22 cm

upper plenum and/or

downcomer

0-90 kW

0-4.7 kW

0-20 U/cm

0-15 cm/s

0.1-1.0 MPa

1000 0C

15-120 OC

Table 1. REWET-Il facility characteristics

2
3. Test description

In preparation for a test, the system is heated up by steam. The lower

plenum is filled up with water to the bottom level of the core heated

section. The fuel rod simulators are heated up until the initial cladding temperature is reached in the middle of the core. The pressure

difference measurements are set to show zero in the beginning of the

test.'In the reference test SGI/R the test parameters were:

Initial rod temperature 600 0C + 3 'C (<400 'C),

± 0.75 % (>400 'C)

Average power/bundle 30 kW

Coolant temperature 30 - 34 CC + 3 0C (<400 'C),

+ 0.75 % (>400 0C)

Flooding rate 0.069 kg/s + 1.0 %

ECC injection location downcomer

Pressure 0.1 MPa + 1.0 %

4. Code input model description

4.1 Loop and vessel model

The REWET-II facility was modeled with 60 volumes and 60 junctions.

The nodalization scheme is shown in Fig.5 and the main geometrical

data of the volumes are listed in Table 2. The lengths of the nodes

were chosen taking into account the measurement locations. The injection pipe lines are not considered, nor is the downcomer overflow

tank. The containment simulator tank is modeled with two time dependent volumes. Part of the containment tank volume was included in the

entrainment over flow tank.

The pipe walls were modeled as cylindrical heat slabs, one in each

node, except none in the upper head volume. The thickness of the pipe

walls is 1.0-2.0 mm described with three radial mesh points.

In the first short calculation it was noticed that the cold water injection into the. downcomer, full of steam in the beginning, resulted

in very short time steps and water property errors. From the measured

3
data it could be seen that no water was flowing to the downcomer overflow tank until the downcomer was full of water up to the loop connection point. Hence, in the further calculations the injection point was

moved to a lower part of the downcomer.

Node

PIPE 10001

10002

10003

10004

10005

10006

10007

10008

10009

10010

10011

10012

10013

10014

10015

10016

10017

10018

10019

10020

10021

PIPE 10501

10502

10503

10504

BRANCH 11000

PIPE 11501

11502

PIPE 32001

32002

32003

32004

PIPE 12001

12002

12003

12004

BRANCH 12500

SNGLVOL 13000

PIPE 14001

14002

THDPVOL 15001

TMDPVOL 19001

PIPE 19501

19502

SNGLVOL 20501

BRANCH 21001

TMDPVOL 21101

PIPE 22001

22002

22003

22004

22005

22006

SNGLVOL 23001

PIPE 24001

24002

24003

24004

24005

24006

Area

(m2)

.0019813

.0019813

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.0013182

.00312

.00312

.00312

.00312

.00312

.00312

.0553

.000412

.000412

.000412

.000412

.000412

.000412

.000412

.000412

.005891

.04983

.000412

.000412

.500

.500

.000412

.000412

.00080425

.00080425

100.00

.00080425

.00080425

.00080425

.00080425

.001237

.001237

.00183225

.00183225

.00183225

.00183225

.00183225

.0040838

.0026609

Length

(m)

0.205

0.205

0.15

0.15

0.127

0.127

0.1255

0.1255

0.131

0.131

0.131

0.131

0.1295

0.1295

0.129

0.129

0.1305

0.1305

0.1375

0.1375

0.168

0.60

0.60

0.60

0.60

0.432

0.56

0.10

0.40

0.70

0.70

0.67

0.40

0.70

0.70

1.40

0.15

0.602

0.525

0.525

1.768

1.768

0.60

0.60

0.61

0.935

10.0

1.27

1.27

1.090

0.775

1.3465

1.3465

0.675

0.608

0.608

0.608

0.608

0.620

0.592

Elevation

change

(m)

0.205

0.205

0.15

0.15

0.127

0.127

0.1255

0.1255

0.131

0.131

0.131

0.131

0.1295

0.1295

0.129

0.129

0.1305

0.1305

0.1375

0.1375

0.168

0.60

0.60

0.60

0.60

0.432

0.56

0.10

0.0

0.70

0.70

0.0

0.0

0.70

0.70

0.0

0.0

0.602

0.0

0.0

1.768

1.768

0.0

0.0

0.61

0.935

0.0

1.27

1.27

1.090

0.775

1.3465

1.3465

0.0

0.608

0.608

0.608

0.608

0.620

0.592

Hydraulic

diameter

(m)

0.01165

0.01165

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.00715

0.063

0.063

0.063

0.063

0.063

0.063

0.265

0.0229

0.0229

0.0229

0.0229

0.0229

0.0229

0.0229

0.0229

0.0866

0.252

0.0229

0.0229

0.7979

0.7979

0.0229

0.0229

0.032

0.032

11.28

0.032

0.032

0.032

0.032

0.0395

0.0395

0.0483

0.0483

0.0483

0.0483

0.0483

0.0721

0.0582

Table 2. Geometric data of the volumes

4
4.2 Core model

The number of the heat slabs and nodes in the core was chosen with the

help of a hand calculation of the axial heat transfer in the quench

front. In this calculation an average quenching temperature of 400 'C

and a minimum quench front velocity of 2.4 mm/s were used. The calculation gave mesh division lengths of about 1.5 - 1.6 mm. Based on this

the core was modeled-with 21 nodes and heat slabs, two per each axial

power step. The number of subdivisions (number of mesh points) in each

heat slab was 128 in the first calculation. In the second calculation

the number of subdivisions was only 16.

In the core two heat slabs per volume were used, one for the fuel rod

simulators and one for the housing. Fine mesh reflood calculation was

performed only in the heat slabs describing the rod simulators.

The radial description of the rod simulator consists of three materials: cladding, magnesium oxide and combined magnesium oxide and heating coil. The total number of radial mesh points in the rod was

seven.

4.3 Steady state

In the beginning of the calculation the radial temperature profile in

the core was determined during the heating period with a model consisting of only the core and one time dependent volume. The temperature

profile was included in the final steady-state calculation, which took

only a few seconds. In the first calculation this calculation of the

heating period resulted in too low shroud temperatures. In the second

calculation the shroud temperatures were raised to the measured

values.

5. Results

The plots from the first calculation are shown in Figs 6-36 and from

the second calculation in Figs 3.7-40. Because of the oscillating nature of many parameters both in the experiment and in the calcula5
tions, comparisons with the experimental data have been done by drawing the average values from the experiments on the plots from the

calculations. The measured cladding temperatures in the plots are

collected from different levels in different rods. The original plots

of the experiment are from reference /3/.

The water temperatures in Fig.6 show that the U-tube oscillations are

not large enough to mix the cold water in the lower plenum. In spite

of this, the cladding temperatures in the lower part of the core are

well predicted but the calculated quenching times are somewhat longer

than in the experiment (Fig.8). The maximum temperatures and the turn

over times are well predicted.

In the calculations the upper part of the core quenches more slowly

(Fig.9) than in the experiment, the reasons of which are discussed

later. In Fig.l1 the calculated quench front elevations are actually

the CHF-points in the core (taken from the listings because the code

did not accept the parameters of the plot variables descriped in the

code manual). In Fig.1O the temperatures measured below and above a

spacer grid are compared with the calculated ones.

The shroud temperatures in case 1 (Fig.12) and case 2 (Fig.38) show

how important it is for the exact prediction to have quenching models

for all of the heat slabs. This is not possible in the RELAP5 model,

so dividing the core flow channel into two channels describing the

inner and outer regions, may have given better results.

The measured pressure differences give information of the actual water

inventory in each part of the facility. The pressure differences DP1,

DP2, DP3 and DP6 (Fig.17,18,19 and 22) give an indication of having

the correct water inventory In the lower part of the core, but too

much water in the upper part. In spite of having more water in the

calculation than in the experiment the cladding temperatures are

higher and the quenching times longer. In the experiments the water

forms liquid films on surfaces and quenches the rods from top down.

The upper plenum is more voided (DP5, Fig.21) in the calculation.

In the calculation the injection to the bottom end of pipe 220 instead

of the upper part of the downcomer as in the experiment caused a faste

6
rising water level in the downcomer and larger pressure differences

DP7 (Fig.22) and DP8 (Fig.23). From the pressure difference DP4 (Fig.

19) it can be seen that the actual water inventory in the downcomer

was well predicted.

The calculation of the liquid mass collected in the entrainment water

tank descriping the entrainment water going from the core through the

upper plenum to the loops was not succesfull in the first calculation.

This water inventory in the second calculation is shown in Fig 39. A

small amount of water is collected into the tank before the level

gauge gives any signal. So the start of water collection in the tank

may actually happen at the same time, but the water mass flow to the

tank is too small in the calculations, even if the steam flow in the

broken loop is overestimated (Fig.35). The steam mass flow in the

intact loop is well predicted as shown in Fig.34. When the water

starts to flow into the loops the measurements are no longer reliable

as can be clearly seen in Figs 34 and 35.

In the second calculation with 16 subdivisions in the heat slabs of

the core, the main difference compared to first calculation is a delayed quenching esspecially in the middle of the core (Fig.37). The

pressure differences, flow rates and fluid temperatures are nearly

equal in both calculations.

6. Run statistics

The first calculation was made by using the maximum time step of 0.01

second, which was slightly below the listed Courant-limit. In some

restarts smaller time step limits were needed (0.004 sec) in order to

overcome errors that stopped the calculation. The total number of time

steps was 97767. The consumed CPU time versus real time is shown in

Fig.36. The average CPU-time consumption per volume and per time step

was 0.013 seconds.

In the second calculation the same maximum time step of 0.01 s was

used, but the CPU-time consumption was reduced over 40 % (Fig.40) due

to the smaller number of the subdivisions in the quench front calculation.

7
7. Conclusions

The capability of RELAP5/MOD2 to calculate this REWET-II test with the

downcomer injection seems to be good. The maximum cladding temperatures, temperature turn over times, quenching temperatures and quenching

times in the middle of the rod bundle are well predicted. U-tube oscillations are stronger. than in the experiments. Water inventories are

quite well predicted, only the separation of water and steam phases in

the upper part of the core with the phenomena of the falling films was

less well predicted.

One of the main practical problems in the calculations was the need of

using short nodes in the core and a large number of subdivisions in

the heat structures as well. CPU time saving could be obtained by

changing the number of subdivisions at different levels of the core or

by making the number of subdivisions dependent of the linear power

variations. CPU time saving could also be obtained by a user defined

subdivision number in each heat slab and a larger maximum number of

subdivisions. The heat slabs and nodes could then be longer.

8
8. References

1. Kervinen T., Hgmdldinen A., Miettinen J., Reflood Experiments in

the REWET-II Rod Bundle Facility Including Comparisons with Computer

Calculations, Proc. Second International Topical Meeting on Nuclear

Reactor Thermal-hydraulics at Santa Barbara, California, January

11-14, 1983.

2. Kervinen T., Purhonen H., Kalli H., REWET-II Experiments to

Determine the Effects of Spacer Grids on the Reflooding Process. Fifth

International Meeting on Thermal Nuclear Reactor Safety, Karlsruhe,

FRG, September 9-13, 1984.

3. Kervinen T., Purhonen H., Kouvo J., Experimental Data Report for

REWET-II Reflooding Test SGI/R, Technical Research Center of

Finland/Nuclear Engineering Laboratory, Technical Report, 1983.

4. Kervinen T., Purhonen If., Description of Rewet-II an Rewet-III

facilities, to be published.

9
REWET 11

UPPER PLENUM

ECC-INJECTION

PRIMARY

CIRCUIT

NOZZLES

REACTOR CORE

CORE SIMULATOR

DOWNCOMER

LOWER PLENUM

Fig.l Simulation of the VVER-440 reactor vessel with the REWET-Il facility

10
Fig.2 REWET-II test facility 11
Fig.3 Test rod arrangement in the core of the REWET--II facility

SoACA CAM

03

Sooo 1300 1600 23000 3.33

THCAMOCOUtPZ LOCATION ".

Fig.4 The axial power distribution and the spacer grid elevations in the

core

12
115

195 140

19:

1100

4

240

225 235

Fig.5 Nodalization scheme of the REWET-I1 facility

13
REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

LIOUID TEMPERATURE

0

LEGEND 0 = VOL 23001

& = VOL 10012

+ = VOL 10020

00 600 Q0 0 180.0 240.0 300.0 360 0 420.0 480.0 540.0 600.0

TIME (SEC)

Fig.6 Liquid temperature in the lower plenum and in the middle and upper

part of the core

F.ig.7 Steam temperature in the middle and upper part of the core

14
RENET-1I EXP SGI/R, RELAP5/MOD2, VTT

CLADDING TEMPERATURE

LEGEND

0 - HS 1001003

- HS 1001006 + - HS 1001008 x-HS 1001012

- - EXP

60.0 0.0 I20.0 13'0.0 21,0.0 300.0 3,0.0 48..0 1 J.O i0.L 600.0

TIME ISECI

Fig.8 Cladding temperature in the lower and middle part of the core

Fig.9 Cladding temperature in the upper part of the-core

15
Fig.1O Cladding temperature below and above the spacer grid elevation

-0gQ-n

REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

QUENCH FRONT ELEVATION

h

0 0

a 00

S

• II 0

0

0 0 0* 0

0 0*

0O 0

0

0 0 LEGEND o = RELAP5

a = EXP 0

0

0

0

T I I I - I

00 60 0 120 0 180.0 24'0.0 300.0

TIME (SEC) 360.0 420.0 40 0 540.0 600 0

Fig.11 Quench front elevation/position of the CHF point, collected from

the printouts

16
5

V

REWET-11 EXP SGI/RI, RELAP5/MOD2,

SHROUD TEMPERATURE

VTT

LEGEND o- HS 1002008 - HS 1002016 + - 15 1002012

--- EXP

0.0 60.0 220.0 180.0 360.0

_________TIME 15ECI

Fig.12 Shroud temperature

REWET-II EXP 5GI/R, RELL[PS/NO[12. VTT

HEAT TRANSFER COEFFICIENT

00

II.I..III.II III - i - i "I 

0.0 60.0 . "220.0 10.0 2410.0 300.0 360.0 412.0 16O.O

* TIMF lFrfi

Fig.13 [feat transfer coefficient in the core

17
REWET-1I EXP SGI/R, RELRP5/MOD2, VTT

VOID IN CORE

0;

0

Fig.14 Void in the core

9

REWET- II EXP SGI/R. RELAP5/MOD2,

VOID IN UPPER PLENUM

VTT

0

.4

60

0O

6N

LEGEND

0 - VOL 10501

I I

0.0 60.0 120.0 180.0 240.0 300.0

TIME (SECI

360.0 420.0 480.0 54,0.0 6,00.0

Fig.15 Void in the upper plenum

18
REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

PRESSURE

300.0 360 0

TIME (SEC)

600.0

Fig.16 Pressures in the lower plenum, downcomer head and upper plenum head

REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

DIFFERENTIAL PRESSURE 1. VOL 100060000-100130000

.I'0.0 •180.0 2-10.0 300.0 340.0 0.0 .

11cII[ 3EI,

Fig.17 Differential pressure 1, between vols 100060000-100130000

19
RENET-I1 EXP SGI/R, RELFIP5/lOD2, VTT

DIFFERENTIAL PRESSURE 2, VOL 100170000-100200000

LEGEND

o0 -OP 2 oil .- - EXP

I• ., 6.o 12'0.0 1610.) 210.0 300.0 360.-, 40.v 480.0 si5rj.,, 600.0

TIME "3ECI,

Fig.18 Differential pressure 2, between vols 100170000-100200000

RENET-I1 EXP SGI/R, RELAP5/NOD2, VTT

.DIFFERENTIAL PRESSURE 3, VOL 100030000-100060000

C0

LEGEND - OF'

- EX E.P

(.0 6,;.o0 ~ 18,0.0 3-)* .o~ 3677o .730.0 510 .0

___ ___ _ ___ _ ___ ___ ___ T11nE ______

Fig.19 Differential pressure 3, between vols 100030000100060000

20
RENET-II EXP SGI/R, RELAP5/MOD2, VTT

DIFFERENTIAL PRESSURE 4, VOL 220020000-220010000

C!!

LEGEND"

C,- LOp A

- E'P

1Z 0.0 60.0 12)0.0 210. '..02ooo 360.0 420.0 1,1.0

___T ITIE"ECI

Fig.20 Differential pressure 4, between vols 220020000-220010000

0

0~

p5

.1 ~ a S

5

2:

o'1o

0

RENET-1I EXP SGI/R, RELAP5/MOD2, VTT

DIFFERENTIAL PRESSURE 5, VOL 105010000-115010000

LEGEND

'- OP 5 - EXP

12). 0 41.0 SJ0.0 61&.0

TH 1;,-13ECI

Fig.21 Differential pressure 5, between vols 105010000-115010000

21
3

REWET-1I EXP SGI/R, RELAP5/MO02,

DIFFERENTIAL PRESSURE 6, VOL 100030000-100200000

VTT

LEGENO

A)- OFP 6

-- Exp

t•.0 66.0 , .M 18'o0.0 24'0.0 300.0 __________TI ;I':D] s5i0.0) 00.0

Fig.22 Differential pressure 6, between vois 100030000-100200000

RENET-II EXP SGI/R, RELAP5/MO02,

DIFFERENTIAL PRESSURE 7, VOL 220030000-220020000

VTT

21

a

a

LEGEND

:- DP 7

- - EXP

's10.0 600.Oj

I..- ....... I .... ...... r - -I 3.0 6.0 120.0 . 40.0 2V0.0 300.0 ;r-00 t010.0

'_I TIME__'3EG '

Fig.23 Differential pressure 7, between vols 220030000-220020000

22
9

C:,

RENET-1I EXP SGI/R, RELAP5/MOD2, VTT

DIFFERENTIAL PRESSURE 8, VOL 230010000-20S010000

LEGEND

0 - OP 8 - - EXP

0.0 600.0

Fig.24 Differential pressure 8, between vols 230010000-205010000

REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

COLLAPSED LIOUID LEVEL IN DOWNCOMER

r

LEGEND

,:- LDC --- C/P

90.0 2~.;).0 30)0.0 360.0 420.0 480.0 510.0 '0)00

TII:r 13E10____ __

Fig.25 Collapsed liquid level in the downcomer

23
RENET- I1 EXP SGI/R, RELRP5S/M0D2, VTT

COLLAPSED LIOUID LEVEL INUPPER PLENUM

9

C--

LEGEND

0- LUP

o o

_ 0

{- o

0.0 60.0 120.0 1B0.0 210.0 300.0 360.0 420.0 480.0 s40.o 600.0

TIME ISECI

Fig.26 Collapsed liquid level in the upper plenum

REWET- I I EXP 5GI/R, RELAP5/HOD2, VTT

COLLAPSED LIOUID LEVEL IN CORE

VQ,%V1_J1W' r_

LEGEND

0 - LCORE

60.0 110.0 180.0 240.0 300.0

TIME ISECI

180.0 540.0 600.0

Fig.27 Collapsed liquid level in the core

24
o:

REWET-11 EXP SGI/R, RELAP5/MOD2, VTT

LIOUID VELOCITY

LEGEND 0 - JUN 22003

a - JUN 21500

510.0 600.0

TIME ISECI

Fig.28 Liquid velocity in the downcomer and core inlet

e~

RENET-II EXP SGI/R, RELAP5/MOD2,

STEAM VELOCITY

VTT

C. r

0:

°0

0

LEGEND

0 - JUN 24500

F J II

0.0 60.0 120.0 180.0 21.0 300.0

TIME ISEC)

360.0 420.0 480.0 510.0 600.0

Fig.29 Steam velocity in the core inlet

25
Fig.30 Liquid mass flow to the core

Q

r ;

C;

0.

RENET- II EXP SGI/R, RELAP5/NOD2,

LIOUID MASS FLOW IN DOWNCOMER

VTT

TIME [SEC)

Fig.31 Liquid mass flow in the downcomer

26
RENET-1I EXP SGI/R, RELAP5/MOD2, VTT

LIOUID MASS FLOW IN BROKEN LOOP

o

6-0

8- LEGEND 0- JUN 19501

-r- -r i ' r - - -

- 0.0 60.0 120.0 180.0 2C0.0 300.0 380.0 420.0 80.0 510.0 800.0

TTMI Iqrr)

Fig.32 Liquid mass flow in the broken loop

REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

LIOUID MASS FLOW IN INTACT LOOP

LEGEND

0= JUN 32003

- 0

If i

00 60 0 110 0 180.0 240.0 300.0 360.0 420.0 480.0 540.0 600.0

TIME (SEC)

Fig.33 Liquid mass flov in the intact loop

27
Q

CD

REWET-1I EXP SGL/R; RELAP5/MOD2, VTT

STEAM MASS FLOW IN INTACT LOOP

I -

1-3 : I b.0 60.0 120.0 180.0 240.0 300.0 360.0 420.0 t1.0J.O 540.0 600.0

_______ ~~~TInIE ,$EC' ____ ___

Fig.34 Steam mass flow in the intact loop

Fig.35 Steam mass flow in the broken loop

28
RENET-II EXP SGI/R, RELAP5/MOD2, VTT

USED CPU TIME

Li

C-)

LEGEND

I~ 0- CPUTIIIE

0.0 60.0 1:0.0 180.0 240.0 300.0 360.0 420.0 480.0

TTMF I(FT1

Fig.36 Consumed CPU time versus real time

29
Fig.37 Cladding temperatures in the lower and middle part of the core,

case 2

x

REWET-I1 EXP SGI/R, RELAP5/MOD2, VTT

SHROUD TEMPERATURE

0

0" LEGEND o - HS 1002007

a - HS.1002011 + - H5 1002015

"- EXP

0'

0

1.0 120.0 180.0 2t0.0 S40.0 600.0

TIME ISEC)

Fig.38 Shroud temperature, case 2

30
RENET-I1 EXP SGI/R, RELAP5/MOD2, VTT

LIOUID MASS IN ENTRAINMENT WATER TANK

o

LEGEND

0- VOL 13001

V-- EXP

.0 606.0 20.0 180.0 240.0 300.0 360.0 420.0 480.0 540.0 600.0

TIME ISECI

Fig.39 Liquid mass in the entrainment water tank, case 2

I

RENET-II EXP SGI/R, RELAP5/lOD2, VTT

USED CPU TIME

3 0

o C, ~Li

• LEGEND

0o CPUTIME

0.0 60.0 120.0 180.0 240.0 300.0 360.0 420.0 48.0

Timr rýzPr,

Fig.40 Consumed CPU time versus real time, case 2

31

NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER 1249t IAsItgnad by NRC. Add Vol.. Supp.. Rev.. NRCM 1102, and Addendum Numbe•r. If May.) 3201.3202 BIBLIOGRAPHIC DATA SHEET

/S$g instructions on the reverse)

2. TITLE AND SUBTITLE

Assessment of RELAP5/MOD2 Using the Test Data of 3. DATE REPORT PUBLISHED

REWET-Il Reflooding Experiment SGIR MONTH YEA

May 1993

4. FIN OR GRANT NUMBER

L2245

S. AUTHORIS) 6. TYPE OF REPORT

Anitta Hftmnil~inen Technical Report

7. PERIOD COVERED liclusie Calms

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC. provide Division. Olfice or Region. U.1. Nuclear Regulatory Commiuion, and mailing address: if contractor, provide name and m#0l4ng eddivis)

Technical Research Centre of Finland

Nuclear Engineering Laboratory

P.O. Box 169

SF-00181 Helsinki, Finland

9. SPONSORING ORGANIZATION - NAME AND ADDR ESS (If NRC. type "Sane as .above' if cotractor. provide'NRC Dvision. Office or Reg•on. U.S1 Nuclear Regulatrorv Commision. and marelitg addre ss

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or les)

An analyses of a reflooding experiment with RELAP5/MOD2 cycle 36.04 is presented. The experiment had been

carried out in the REWET-Il facility simulating the reactor core with a bundle of 19 electrically heated rods. On the

basis of the results of two calculations recommendations for the core nodalization are presented, and a modification

to the code is proposed.

12. KEY WORDSIDESCR;PTORS (List words orphreses that will asist mearhe#rs In locating the report.) 13. AVAILABILITY STATEMENT

ICAP Program Unlimited

RELAP5/MOD2 14. sECuR ITY CLASSIFICATION

REWEITI-II Reflooding SGI/R ,T1,, PARe)

Unclassified

I rnis Reportl

Unclassified

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (2481


Federal Recycling Program

NUREG/IA-0090 ASSESSMENT OF RELAPS/MOD2 USING THE TEST DATA OF

REWET-II REFLOODING EXPERIMENT SGI/R

MAY 1993

UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555-0001

FIRST CLASS MAIL

POSTAGE AND FEES PAID

USNRC

PERMIT NO. G-67

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300