NUREG/IA-0036

TPRD/L/3209/R87

PWR/HTWG/P(87)496

International

Agreement Report

Analysis of LOBI Test BLO2

(Three Percent Cold Leg Break)

With RELAP5 Code

Prepared by

A. H. Scriven

Central Electricity Generating Board

Technology Planning and Research Division

Central Electricity Research Laboratories

Kelvin Avenue

Leatherhead Surrey KT2275E

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

March 1992

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
-I

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.

I

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-0036

TPRD/L/3209/R87

PWR/HTWG/P(87)496

International

Agreement Report

Analysis of LOBI Test BLO2

(Three Percent Cold Leg Break)

With RELAP5 Code

Prepared by

A. H. Scriven

Central Electricity Generating Board

Technology Planning and Research Division

Central Electricity Research Laboratories

Kelvin Avenue

Leatherhead Surrey KT2275E

United Kingdom

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

March 1992

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 andthe 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.
TPRD/L/3209/R87

PWR/HTWG/P(87)496

ANALYSIS OF LOBI TEST BL02 (THREE PERCENT COLD LEG BREAK)

WITH THE RELAP5 CODE

by

A.H. Scriven

SUMMARY

The test BL02 was a UK specified test conducted on the electrically

heated 2 loop test system at Ispra, North Italy as part of the LOBI

series of tests sponsored by the Joint European Research Commission.

'B'

The pretest calculations for this test were performed with the RELAP5

MODM code, and the post-test analysis was carried out using RELAP5 MOD2.

Comparisons between the codes predictions and the test data are given,

and for the case of the post-test MOD2 calculation, detailed studies of

the codes performance in a number of areas are included.

Of particular note in this test is the stratified break offtake

condition for part of the test, the sensitivity to accurate bypass

modelling and the clearance of both loop seals early in the transient.

The correct modelling of these inter-related effects is a good test for

the code.

This test also benefits from a reliable and accurate break mass flow

measurement system, installed since the International Standard Problem

(ISP18) test, which enables better determination of the boundary

conditions of the test.

Job No. VQ 045

BOAT No. DA 01

Approved: . , "

Contents ........ M.W.E. . .Cone .....

Acting Section Head

Fluid Dynamics Section

ribution

D.H. Wilkinson, Branch Head

Engineering Sciences Branch

Date ?26..oi...ber 1987 Date...................

Classification and Dist

iii

-1 -

Table of Contents

1.0 TEST SPECIFICATION

1.1 General Aims and Objectives - Particular Physical Phenomena

1.2 System Configuration

1.2.1 Loop components

1.3 Controlled Trips and Events

1.4 Initial Conditions and Setpoints

1.4.1 Initial conditions

1.4.1.1 Primary side

1.4.1.2 Secondary side

1.4.2 Relief valve setpoints

1.5 Boundary Conditions

1.5.1 Heating power

1.5.2 Pump speeds - intact and broken loops

1.5.3 HPIS operation

1.5.4 Auxiliary feedwater operation

1.5.5 Pressurizer and surge line, spray/cooling system

1.5.6 Pressurizer relief valve

1.5.7 Accumulator injection system

1.5.8 Cooldown of secondary side

1.5.9 Upper head - upper plenum connections and bypass flow paths

1.5.10 Main coolant pump seal water injection

1.5.11 End of test

Page

3

3

4

A

6

7

7

7

7

8

8

8

8

9

10

10

10

10

10

10

1.1

11

2.0

2.1

2.2

RELAP5 MODELS

Model Used For RELAP5/MOD1 Pro-Test Prediction

Model Used For RELAP5/MOD2 Post-Test Prediction

12

12

12

3.0 TEST ANALYSIS

3.1 Boundary Conditions

3.1.1 Initial conditions

3.1.2 Transient conditions

3.2 Brief Synopsis of Experimental Phenomena

3.3 Overview of RELAP5 Predictions

3.4 Noding and Sensitivity Studies

3.5 Primary Side Pressure Response

3.6 Secondary Side Response

3.6.1 Relief valve modelling

3.6.2 Steam leak and auxiliary feed flow actuation

3.7 Break Flow

3.8 Loop Seal Clearance

3.8.1 Study of mechanism of both loops clearing

3.8.1.1 Draining of steam generators

3.8.1.2 Bypass effects

3.8.1.3 Counter-current flow limiting

3.9 Rod Heatup

3.9.1 Core mixture level

3.10 Loop Differential Pressure

3.10.1 Pertaining to bypass effects

13

13

13

13

14

14

14

16

16

17

17

17

19

19

19

21

22

22

22

24

24
-2-

Page

4.0 CONCLUSIONS 25

REFERENCES 26

Appendix A. RELAP5 MOD2 INPUT DECK. TEST SPECIFIC INPUT 27
-3-

1.0 TEST SPECIFICATION

This section gives details of the exact specification of the test and is in most part identical to

the pre-test specification report, (Scriven 1986), which was issued on limited circulation and

is therefore not available to many people wishing to understand the test.

Where the initial conditions in the test departed markedly from those specified, the actual

conditions are given alongside. However this Report is not concerned with reporting the exact

details of test execution which will be fully documented in the LOBI Experimental Data Report

when this is published.

Experiment BL02 was a 3% cold leg break Intended to extend and supplement the study of

break size effects which were begun with the previously performed tests ISP18 and BLO0.

There was only one execution phase for the test but conceptually the test can be thought of

as comprising three stages typical of small break transients.

1. Rapid depressurization of the primary side via mass loss though the break with reverse

heat transfer from the secondary side and extensive voiding in the core region.

2. A slow depressurization as the break flow subsides to a point at which it can be approximately balanced by the HPIS system. The length and nature of this balance are vital to

the understanding of small break core uncoveries.

3. A progressive refilling of the system as the accumulator setpoint is reached together with

an increasing HPIS flowrate.

The balance achieved in stage 2 is highly dependent on the interacting effects of break flow,

HPIS flow, core vapour generation rate and liquid Inventory in different parts of the loop. This

test is seen as being one of a series designed to examine the effects of varying these parameters in a systematic manner, and because of this the specification was intended to be

as similar as possible to the previously performed tests ISP18 and 1-00.

Those readers familiar with tests BLOO (0.4% CL break) and ISP18 (1.0% CL break) may be

satisfied with knowing that this test is identical to BLO0 except for:-

* Break size is 3%.

* HPIS flowrate is as specified for ISP18.

1.1 General Aims and Objectives - Particular Physical

Phenomena

1. Study of a range of break sizes. (comparison with ISP18 and BLO0)

2. Study of the depth and time of core uncovery.

3. Study of heat transfer from heater rods to high void fraction.

4. Study of fluid drainage from the steam generators and loop piping.
-4-

5. Characterization of break behaviour by study of pressure response in a test which is not

tied to secondary side cooldown rates.

6. Effect of reverse heat transfer from secondary side to primary.

7. Behaviour of loop seals and effect of bypass flows.

8. Effect of condensation and non-equilibrium during HPIS and Accumulator injection.

1.2 System Configuration

The following sections describe the detailed setup of the LOBI facility with respect to geometrical arrangement, instrumentation connections and data logging and recording systems.

The loop and its components have been described in great detail by the LOBI project in three

reports Addabbo, Piplies and Riebold, 1983; Ohlmer, Sanders and Eder, 1983 and Ohlmer,

Sanders, Doeringand Floegel, 1983. Reference will be made to these descriptions in the following sections, and the reports, together with detailed drawings released by the LOBI team

will be referred to as the 'LOBI base set'. A schematic diagram showing the main components

of the loop is given as fig. I

1.2.1 Loop components

The loop was configured according to Table I on page 3 which is the same as for BLOO except

for break size.
-5- IJ

Break position

Break assembly

Break size

Upper head

Pressurizer

HPIS

Accumulators

Containment

Pump seal water drainage

Locked rotor simulators

Auxiliary feedwater

Cold leg break between main coolant pump and pressure vessel.

Standard configuration for small breaks. (see LOBI

documents)

I * 0.03 the area of a main coolant pipe, 3% (break

orifice 5.2mm dia)

Connected In normal way to upper plenum and upper

downcomer. (see LOBI documents)

Connected In normal way to Intact loop hot leg.

Injection into Intact loop, characteristics given in Table

5 on page 8

Injection into Intact loop cold leg.

Connected to atmosphere.

Continuous drainage from upper plenum in steady state,

then from lower plenum draining during transient.

Intact loop fully open. Broken loop to be valved into

'resistance' position after pump reaches zero speed.

Operational in both loops. See relevant section for details.

Table. I System configuration for LOCA test BL02.
-6-

1.3 Controlled Trips and Events

Set point Trip or Event

Before -200 sec

-240 sec

-5 sec

0 sec

0 sec

131 Bar

131 Bar

131 Bar + delay 2 sec

131 Bar + delay 5 sec

Pressurizer cooling and additional heating off, loop now

in steady state condition

Start closure of shutoff valve in tube to top of upper

head. Valve has closure time of 8 seconds.

Start closure of drain valve In upper plenum. Valve has

closure time of 8 seconds.

Open valve In break assembly.

Turn off normal pressurizer heaters.

Shut off valve In steam line. Valve has closure time of

1.5 seconds.

Main coolant pumps begin coastdown.

Scram. Heating power begins to decay.

Shut off valves in feed water lines. Closure time 5 seconds.

Auxiliary feedwater on (3% of nominal feedwater.)

Main pumps at zero speed. 4 seconds later locked

rotor simulator operated in broken loop.

HPIS starts.

Activate cooldown control for secondary side.

Accumulators begin injection.

End of test. Isolate break. Measure liquid refill to restore

Initial levels.

131

131

Bar + delay 60 sec

Bar + delay 201 sec

117 Bar

117 Bar

41 Bar

10 Bar

+ delay 35 sec

" delay 600 sec

Table. 2 List of most Important trips and events
-7-

1.4 Initial Conditions and Setpoints

1.4.1 Initial conditions

1.4.1.1 Primary side

Specified Actual

(if different)

Mass flows

Intact loop

Broken loop

Pressure

Upper plenum

Fluid Temperatures

Intact loop vessel Inlet

Broken loop vessel Inlet

Pressurizer

21.0 Kg/sec

7.0 Kg/sec

15.8 MPa

294.0 C

294.0 C

346.0 C

15.6

290.5

290.5

Heater Power

Core

Water Level

Pressurizer

5.28 MW 5.09

(and failing)

4.8 m

1.4.1.2 Secondary side

Feedwater mass flows

Intact loop

Broken loop

Pressure

Steam dome Intact and broken loop

Main feedwater Temperatures

Intact loop

Broken loop

Recirculation ratio

Intact loop

Broken loop

Collapsed Water Level

Intact loop downcomer

Broken loop downcomer

2.0 Kg/sec

0.68 Kg/sec

6.45 MPa

210.0 C

210.0 C

6.5 (approx)

4.5 (approx)

8.33 m

8.23 m

6.25

(and falling)
-8-

1.4.2 Relief valve setpoints

The relief valves on both steam generator secondary sides were set to open at 79 bar and

close at 78 bar. These valves function during the time after the main steam valve is closed

and up to the time of activation of the secondary side cooldown.

1.5 Boundary Conditions

1.5.1 Heating power

Power remains at 100% until trip on low primary pressure (131 bar in upper plenum with delay

of 2 seconds.) Power then decays according to Table 3 on page 6 throughout the transient.

Time from power trip

(seconds)

Heating Power

(fraction of full power)

0.0

1.0

2.0

3.0

5.0

7.0

9.0

13.0

15.0

16.0

17.0

18.0

20.0

24.0

30.0

40.0

68.0

110.0

170.0

270.0

470.0

870.0

1000.0

2000.0

4000.0

6000.0

10000.0

1.00

0.90

0.73

0.65

0.51

0.40

0.32

0.20

0.161

0.15

0.14

0.13

0.12

0.10

0.08

0.065

0.048

0.04

0.035

0.028

0.023

0.02

0.019

0.016

0.013

0.011

0.010

Table. 3 Heating power as a function of time after trip

1.5.2 Pump speeds - intact and broken loops

After the break opens, pump speed is fixed at constant 100% value until tripped on low primary pressure of 131 bar in upper plenum. After this both pumps coast down according to

Table 4 on page 7 until they reach zero speed.
-9-

Two seconds after pump speed reaches zero speed, the mechanical brakes are applied, and

two seconds after this the locked rotor resistance simulator in the broken loop is valved into

position. This is the 'standard' multi-hole orifice plate used in both ISP18 and BL0O, whose

characteristics and dimensions are part or the LOBI base geometry set.

Time from pump trip Normalised Speed

(seconds) (%)

0 100

5 88

10 71

15 59

27 41

40 32

50 26

120 11.5

200 11.5

201 0

Table. 4 Pump speed coastdown curve after trip

1.5.3 HPIS operation

The HPIS was set up to be the standard LOBI simulation of two out of four pumps as used in

ISP18. The injection is into the cold leg only with Injection characteristics of pressure versus

flow as given in Table 5 on page 8 with the initiating trip being primary pressure reaching 117

bar with a delay of 35 seconds.

Pressure Mass flowrate

(Pascals) (Kg/sec)

1.0E5 0.201

11.0E5 0.192

21.OE5 0.183

31.0E5 0.172

41.0E5 0.160

50.0E5 0.147

61.0E5 0.132

71.0E5 0.1162

81.0E5 0.098

91.0E5 0.077

101.0E5 0.052

111.0E5 0.0218

117.0E5 0.0

Table. 5 Characteristics of HPIS pumps.
- 10 -

1.5.4 Auxiliary feedwater operation

The auxiliary feedwater system is used In this test.

* The temperature of the feed should be 150 C.

* The flowrate should be 3% of the nominal Initial flow.

* The feed water control is to maintain level in the downcomer of each steam generator at

that level which exists at the initiation of the auxiliary feedwater. (132 bar pressure +

delay of 60 seconds.)

1.5.5 Pressurizer and surge line, spraylcooling system

The pressurizer has the extra heating and/or cooling systems switched off before transient

commences, and rig should be in steady state without these.

At break opening the normal heating systems in the pressurizer are switched off.

1.5.6 Pressurizer relief valve

Not required for this test.

1.5.7 Accumulator injection system

The simulation is as for BLO0 modelling a plant with three out of eight accumulators functioning. The injection Is into the intact loop only.

The set point is 41 bar.

The volume of water in the accumulator was modelled on a plant system with water volume

of 28 cubic meters and accumulator volume of 47 cubic meters. In LOBI this translates to a

liquid volume of 140 I in an accumulator of 280 I.

1.5.8 Cooldown of secondary side

* The cooldown is activated by pressure in upper plenum falling below 117 bar + a delay

of 600 seconds.

* The rate of cooldown Is 56 K/h, determined from the pressure on the secondary side, and

achieved by venting steam from the Steam Generator discharge valves.

* The intact and broken loop steam generators remain connected throughout, and thus

cooldown together.

1.5.9 Upper head - upper plenum connections and bypass flow paths

The arrangement for the upper head and bypass connections is the same as in BLOO and

ISP18 and has been described in detail in the LOBI base geometry set. The resistances in the

bypass lines are not changed from normal operation.

The pump seal water drain line which is connected to the upper plenum was closed before the

transient began and the lower drainpoint from the vessel lower plenum was used throughout

the transient to compensate the measured seal water injection flows. Around -240 seconds

the line connected to the top of the upper head used for warmup was Isolated.
- 11 -

1.5.10 Main coolant pump seal water Injection

The seal water injection was continous thoughout the transient, and was measured. The

characteristics of this flow have been given as part of the LOBI base set.

Compensation for pump seal water via draining from the lower plenum was used in this test

commencing from time upper plenum takeoff was terminated.

1.5.11 End of test

Primary pressure falls below 10 bar.
- 12 -

2.0 RELAP5 MODELS

2.1 Model Used For RELAP5lMOD1 Pre-Test Prediction

The model used for the pre-test prediction was very similar to the LOBI base input deck as

described in LOBI report LPC 86-20. The author had spent some seven months working on the

production of this deck at ISPRA .some three years ago, so the similarities are not surprising.

Full details of this input deck have been provided by LOBI, and a copy could be provided on

request by the author should this be desired. Significant changes had been made in the detail

of the steam generator modelling, and in the control systems, but these have little impact on

this test.

One aspect of the deck which is important was that the bypass flow paths, discussed later and

shown diagramatically in fig. 3 were modelled rather crudely, being lumped into a single flow

path with an area which appears in the light of more recent data to have been somewhat

small.

2.2 Model Used For RELAP51MOD2 Post-Test Prediction

The model used for the post-test calculations was based on the same input deck, but with

modifications appropriate for the MOD2 version of RELAP5. In addition small volumes were

introduced at the downcomer entry and upper plenum exit elevations, connected to the loop

pipework by cross-flow junctions. The bypass paths were modelled as three distinct paths of

the correct sizes, and the heat losses from the pressurizer were increased to account for the

latest thermal coastdown experiments performed by LOBI. Furthermore, a very detailed

model of the secondary side control system was incorporated to account for the observed

behaviour. This system comprised large and small valves, each with rate of stem travel limits,

stem versus area characteristics, and precise modelling of the electronic control system for

these valves. A simplified schematic of the primary side noding is given as fig. 2 and Appendix A gives the test specific input data for this test. Previous Reports have listed the full

Input deck which is not reproduced here to reduce bulk.
- 13-

3.0 TEST ANALYSIS

The test was performed In March 86. At the time of writing no reports of this test have been

received, and the data reported here is derived from a preliminary datatape only.

3.1 Boundary Conditions

3.1.1 Initial conditions

Understanding the data from the datatape was not straightforward. Initial examination shows

some disturbing facts.

1. The loop was not at steady state at test Initiation. Core power was dropping rapidly and

was well below specified value, secondary side pressure was dropping and system was

out of balance.

2. The initial pressure on the primary side, specified as 158 bar, was also falling. If taken

from the pressure transducer In the pressurizer vapour space it was 152 bar at test start.

This value agrees with the value measured In Intact loop hot leg, but not with that measured in the vessel upper plenum, which should be almost exactly the same. The difference

Is some +5 bar (3% error). A note had been given with the datatape suggesting only the

pressurizer pressure measurement could be relied on due to Interference, however if the

temperatures in the pressurizer are examined, they clearly support a saturation pressure

of 157 bar as given by the upper plenum pressure.

3. Because of dropping core power, the secondary side pressure was falling up to the time

of test Initiation, and was some 2 bar low. As a result. wall temperatures will not be at

steady state.

In conclusion the specified conditions were significantly different from those specified ( 4 degrees on temperature, 4 bar on pressure and core power 4% low.) This makes direct comparison with the pre-test calculation difficult for the early part of the test, although does not

affect the overall system behaviour or the phenomena seen.

3.1.2 Transient conditions

Most of the specified transient boundary conditions were well met in the test. The exception

being the secondary side control.

In the test, as becomes evident from a study of the datatape, the auxiliary feedflows to the

steam generators were Incorrectly tripped. This occurred in conjunction with a small steam

leak, probably through the main steam valve not closing completely, which depressurized the

secondary side far too rapidly. These effects cannot be expected in the pre-test calculation,

and are in the post-test calculation on the basis of reasonable guesses for these effects.

With these points in mind we can assess the calculations.
- 14 -

3.2 Brief Synopsis of Experimental Phenomena

The loop depressurized to saturation conditions, holding around 80 bar until the break uncovered at around 400 seconds allowing steam to exit the break and producing a more rapid

pressure fall. At this time both loop seals cleared, which was the cause of the break uncovery

as steam flow round the steam generators then reached the break.

Depression of the core level was rather mild, amounting to around I m before the loop seals

cleared, recovering then dropping some 0.5 m later. As a result rod heatup was only seen in

the unheated length at or above the nozzle elevations.

HPIS flow quenched the rods at nozzle elevation and restored core inventory before accumulator injection around 800 seconds.

3.3 Overview of RELAP5 Predictions

The pre-test calculation ran well till accumulator injection, at which point it crashed. Several

short post-test calculations were performed as will be discussed latter, the finat calculation

which is presented here ran successfully, with a CPU to problem time ratio of around two.

The illustrations fig. 4 to fig. 14 show the major system parameters for this test. Looking

quickly through these we can see primary system depressurization well calculated in both

pre- and post- test calculations (rig. 4 ). Accumulator injection occurs at exactly the right time

in the post-test calculation, (fig. 7 ) due to the good prediction of system pressure. For the

pre-test calculation, the code failed at the time of Injection. Based on the predicted pressure

at this time, agreement would have been reasonable.

Integrated break mass loss (fig. 8 ) shows correct mass depletion, while (fig. 10 ) gives the

cladding temperature rise at the nozzle elevation and shows approximately correct behaviour

for both calculations However In the pre-test calculation the elevation below this level also

showed temperature rises not seen In LOBI, and the level depression In the vessel was too

great. This was primarily caused, as mentioned above, by an Incorrect bypass modelling,

coupled with a failure to predict the loop density distribution. The generated vapour had to

depress the core level rather than escape via the hot legs and core to downcomer bypasses.

This effect causes the pre-test calculation to be significantly in error in all the test details.

In the pre-test calculation the loop seal did not clear, in the post-test calculation the broken

loop seal cleared at the right time but in the test both loop seals cleared.

Finally fig. 11 to fig. 14 shows clearly that RELAP is failing to calculate the loop density distribution. The broken loop cold leg density is well predicted, but the failure to clear the intact

loop seal is evident in the high RELAP5 density in the intact loop cold leg after 400 seconds.

Both hot legs show incorrect draining around 400 seconds and these density plots, more than

most other system parameters, suggest that major details of the calculation are in error.

In the following the post-test calculation will be presented, together with an analysis of the

LOBI data, and code deficiencies identified.

3.4 Noding and Sensitivity Studies

Experience with modelling the International Standard Problem 18 (ISP18) LOBI test has shown

the importance of the bypassed steam flow In the vessel. Referring to fig. 3 when steam is

being produced in the vessel and a level is established several routes exist for steam escape.

Flow via the hot legs towards the steam generators, bypass via the upper head, bypass via

the two small holes at the top of the vessel and bypass at the nozzle elevation. This last bypass is rather large, and the total LOBI bypass amounts to some 5%, far greater than typical

plant values. It is the exact flow though these bypasses, governed by liquid level in the vessel,

which controls the pressure buildup in the vessel and hence the core level depression.
- 15 -

In many small cold leg break transients, the level in the downcomer Is fixed at about the cold

leg elevation for quite some time. Under these conditions quite stable stratification can exist

in the cold leg with steam from the core passing through the bypasses and flowing over the

liquid in the downcomer and along the cold leg.

This steam flow is not condensed by the liquid, despite the often high subcooling of the liquid

as much HPIS has reached the broken loop cold leg passing round the downcomer.

The quality at the break and hence the break flow are strongly affected by this process.

Furthermore the cold HPIS, penetrates the downcomer via bouyancy effects and reaches the

lower plenum, producing subcooling here.

The input deck used to calculated ISP18 did not manage to produce either of these phenomena

correctly. The volume at the juncture of downcomer and cold leg mixed the bypasses steam

with the subcooled HPIS, producing incorrect break enthalpy, and wrong lower plenum subcooling.

In an attempt to improve this modelling, the downcomer was split into two volumes connected

by a cross-flow junction. The idea was to allow HPIS to enter from the intact loop side and

steam from the volumes above into the broken loop side and suppress the condensation

caused by the mixing. This scheme is shown in fig. 15 where the volumes 301 and 302 represent the annular region at nozzle elevation. These volumes were tried both as normal vertical volumes, and as shown, as horizontal volumes in which the horizontal stratification model

could be applied. This latter was an attempt to allow the liquid and vapour to flow together

towards the broken loop cold leg (239), and to make use of the junction orientation model for

stratified volumes which accounts for entrainment and pullthrough, by applying this model at

entry and exit from these horizontal volumes. It was also thought this may circumvent the

problem with connecting a horizontal stratified volume, the cold leg, to a vertical volume, the

downcomer, were the vertical stratification model, switching on discontinuously in the vertical

volume can drain out the horizontal volume unphysically.

This approach showed some promise but could not be used because it repeatedly caused

code failure, often around the time of accumulator injection, but occasionally before. It also

resulted in a reduced running speed. The problem seemed to be the extremely small size of

these volumes, coupled with the X-flow junction option. Recent changes made at Winfrith on

behalf of the Board to the junction entrainment model may have helped this modelling approach, but the failure would probably still occur. It remains as a possible nodalization for

portions of a test, via a restart renodalization, especially if the mechanism of failure Is better

understood. A small separate effects test of the code could shed some light on this topic, and

is being considered as a future project.

The calculation was therefore performed with a single X-flow volume at the nozzle elevation,

and this volume was given a height equal to the diameter of the Intact loop pipework, as recommended by the code developers for tracking liquid levels.

A second area where modelling changes were tried was the exact location of the bypasses.

Clearly the upper plenum bypass position is fixed, and the bypass via the 5mm holes is defined, but at nozzle elevation the position of the bypass is unknown. This is in fact significant.

Steam generation depresses the core level which reaches first the elevation of the two holes.

Enhanced steam flow though these holes relieves the pressure somewhat and slows the level

fall.

The fall in level then reaches the top of the nozzle connection on the intact loop side, as this

is higher than the broken loop side. If significant steam bypass occurs at this elevation, the

level can remain here for a considerable time. Under these conditions the broken loop hot leg

would remain full.

Conversely if the major portion of the bypass occurs at the bottom of this connection, the level

will fall to this point before stabilizing. Here the broken loop hot leg would be fully uncovered

and could drain completely. Thus the position of this bypass can result in a vastly different

observed density behaviour in the hot legs.
- 16 -

To assess this effect calculations were performed with the bypass in both the extreme positions. Although different behaviour was seen, It was not possible to conclude which was

closest to the LOBI behavior due to other modelling problems which led to an incorrect mixture level in the vessel. This problem is explained in detail in a later section. For the calculation reported here the bypass position was set to be the centre of the nozzle elevation.

The last sensitivity is the size of the bypasses, especially the one at the nozzle elevation.

Measurements by LOBI under cold conditions have provided an estimate of the combined

bypass, from which this bypass can be inferred, but this gives rise to considerable error,

maybe around 2%. For completeness a short run was performed with a reduced bypass.

It would be expected that this could force more vapour round the loops, thus having an effect

on liquid holdup in the hot legs and steam generators, and indeed this was a prime reason for

trying this calculation, but the increased pressure buildup in the vessel caused the loop seal

to clear far too early, and gave very much worse agreement with the LOBI test than the 'best

estimate' bypass value.

These results were not conclusive so far as defining the actual bypass, as a known deficiency

in RELAP5 MOD2 is the tendency to overpredict the interphase drag in bubble/slug regimes.

This effect could prevent the vapour passing round the loop and thus force a loop seal clearance, even if the steam flow had been correctly calculated. However it was felt that for the final

calculation the larger bypass value must be used.

From the above we see three distinct areas where uncertainties exist in the best model of

LOBI. Some rather delicate balances exit In the BL-02 test which make it difficult to vary these

parameters so as to reach firm conclusions as to their overall effects, and as will be seen later

other effects come to dominate many of the features where these uncertainties would otherwise manifest themselves. There is definite scope for further investigation of the areas, although it is believed that for BL02 the current model is adequate.

3.5 Primary Side Pressure Response

The primary side response seen in fig. 6 reflects the system mass and energy depletion rates.

For a 3% break the dominant mechanism is the break flow. The pre-test calculation was untuned, and used a break multiplier of 1.0 for the subcooled discharge and 0.85 for the twophase region. The choice of 0.85 was based on prior experience with the MODI choked flow

model, but was not based on any data from 3% LOBI tests.

The post-test MOD2 calculation used a multiplier of 0.85 for both subcooled and twophase.

An initial short calculation with the default values of 1.0 showed significant overprediction of

break flow in both regimes. The break flow multiplier was therefore modified, and it is this

'tuned' value that gives rise to the rather good pressure history seen.

A discussion of this point is given in the section on break flow.

With this fit of the pressure drop, it is unsurprising but gratifying that the accumulator injection

and HPIS injection are well predicted, as both are tripped on a pressure signal.

3.6 Secondary Side Response

The calculated response from the post-test prediction can be seen in fig. 5. The pre-test value

is not shown as previously mentioned the test boundary conditions were too far from those

specified to admit comparison.

To achieve this response several factors had to be included in the post-test calculation which

were not in the pre-test.
- 17-

3.6.1 Relief valve modelling

The valves used on the secondary side as pressure relief valves have uncertain discharge

behaviour. The valve manufacturers provide data on the discharges they measure through

these valves, both in normal and choked conditions, together with the variations with stem

position. A short study was performed, using RELAP5, to see how best to model these valves.

A valve sizing input deck was set up which was designed to vary the area of a valve to achieve

a given flow rate. This was used to see what area RELAP5 required to match the manufacturers data.

In the event, the areas required for normal and choked flow were quite different. It was decided to use the area appropriate for choked flow in the BL02 input deck. This was rather

larger than the area derived from the manufactures discharge coefficients.

Later information suggests that the manufacturers data may have a large scatter, maybe

some + or - 30% for a given valve.

The matter is further complicated by the sharp knee in the relation between stem lift and area.

When the valve is initially opening, controlled by the electronic differential/integral controller

but limited by its maximum stem travel time (which was 45 seconds), then for a very significant

time at the start of a pressure transient the valve is only very sightly open. Very small errors

here can result in the effective valve area being in error by factors of Two or three, thus

making initially pressure responses completely incorrect. The exact nature of these curves

is unknown and can only be deduced from their observed response.

The input deck used for BL02 Included the deduced valve responses used in the ST02 transient

analysis (Scriven, 1987), which were found to best fit the rather tortuous secondary side response of that test.

3.6.2 Steam leak and auxiliary feed flow actuation

The cooldown of the secondary side in the time before the controlled cooldown becomes active is very much faster than would be expected even assuming a high limit for the heat losses

of around 25kW.

This is due to two effects. As was seen in the BLO0 test, and also indicated in the ST02 transient, there appears to be a small steam leak during the whole transient. The most likely site

for this leak is the large steam control valve, which is shut at the start of the transient. A 1mm

diameter hole would be appropriate to explain the observed pressure histories. This size of

leak was included in the BLO2 deck as being the valve area when the stem was at zero position.

The second effect is the faulty activation of the auxiliary feedwater. In the specification this

was tripped on by pressure reaching 131 bar with a delay of 60 seconds, and was set at 3%

of normal feed, controlled by liquid level in SG downcomer. In the test the auxiliary feed came

on at 65 seconds in the intact loop and at 90 seconds in the broken loop. These then remained

on till tripped off at 380 and 350 seconds respectively. These timed valves were used in the

post-test calculation instead of the specified behaviour. The effect of tripping off the auxiliary

feed can be seen in the kink in the secondary side pressure response at around 380 seconds

in fig. 5

With all the above included, the secondary side response in predicted reasonably well.

3.7 Break Flow

As mentioned above, the break flow was tuned for this calculation.

Referring to fig. 14 we see that RELAP5 is predicting the density near the break rather well.

This is probably the best density prediction for the loop. Despite this in an Initial short test run

the break flow was found to be too high.
- 18 -

The LOBI condensing weightank system provides a total measure of break mass loss. A small

program was written to process this measurement and to derive the instantaneous break

mass flow via numerical differentiation. While this process produces rather a lot of noise, It

still gives a quite accurate overall value for the break flow.

This derived data was compared with the Initial RELAP5 break mass flow, and It was seen that

RELAP5 overpredicted the flow both in the single phase and two-phase region. Based on this

comparison break flow multipliers of 0.85 were used for both the subcooled and two-phase

discharge coefficient and the result can be seen in fig. 16 where the agreement is now seen

to be good. The success of this approach is seen in fig. 8 where the overall integrated break

flow is given.

The question now arises as to the source of the overprediction In RELAP5. fig. 17 and fig. 18

show the LOBI measured densities on either side of the break offtake volume. The density in

the volume between break and vessel is most representive of the conditions in the break

volume itself.

Firstly we can see stable stratified conditions exiting from around 100 seconds up to the point

of loop seal clearance. This was the time of greatest break flow error as it covers the subcooled and two-phase discharge. Following 400 seconds the flow is mostly single phase

vapour.

As mentioned above RELAP5 predicts this density very well, and furthermore is also predicting stratified flow in the time region and using the horizontal stratified flow regime map. Thus

the upstream conditions are in good accord.

The break offlake in LOBI is directly in the side of the pipe on the centreline. This configuration

would require some allowance to be made for conditions at the break junction being different

from those in the donor upstream volume. Clearly with a liquid level above the break the

junction void fraction would be mostly liquid despite a volume voidage which could be close

to 50%. RELAP5 has a special model for this condition.

In the two-phase discharge region there is a possibility that the liquid entrainment / vapour

pullthrough model employed in RELAP5 is not giving the correct junction voldage at the break.

Recent literature studies by Ardron have highlighted likely problems with the model as currently coded, and Ardron in conjunction with Bryce has implemented an updated version of

the model in a test version of RELAP5 which has given improved results in LOFT test analysis.

(Ardron and Bryce private communication). This work is presently being assessed and will be

communicated to the RELAP5 developers in due course. It is presently uncertain if the model

as Implemented will cause stabilty problems and consequent code failures.

This could definitely contribute to the break mass flow error, but another effect predicted by

Bryce (Bryce, 1986) in a recent theoretical study of the RELAPS critical flow model is thought

to be a larger influence in this case.

Bryce's study suggests that if the upstream condition are equilibrium subcooled, that is if the

volume given time to reach equilibrium would contain no vapour, then RELAP5 will overpredict the break mass flow. The reason is that in calculating the break junction conditions,

the liquid and vapour components derived from the upstream volume will not be kept sufficiently in non-equilibrium, and the vapour will 'condense out'. Thus the break junction density

will be too high, and hence the mass flow will be too high.

In the present calculation the liquid in the cold leg pipe is around 20 degrees subcooled due

to cold ECCS reaching the broken loop cold leg via the downcomer. These are exactly the

conditions in which overprediction of break density can occur, and it is believed this is the

primary source of error in the break flow.

In the early subcooled flow region, neither of the above sources of error can be invoked. There

is no stratification, and no vapour present, yet a multiplier of 0.85 was still required. It is uncertain what the source of this error is. The vena- contracta calculated by the code for abrupt

area change may be inappropriate for the LOBI side offtake geometry, particularly when there

are high loop flows past the break, or the subcooled break discharge model itself may be

calculating the wrong sonic velocity limit.
- 19 -

The RELAP5 critical flow model appears still to require refinement, and while not being so

important for plant scoping studies, the need for accurate 'untuned' break predictions for experiment analysis is paramount.

3.8 Loop Seal Clearance

The experiment exhibited one phenomena totally unseen in the calculation, that of both loop

seals clearing at around 400 seconds. At first thought this appears an unlikely event. Consider

the mechanism to blow a loop seal.

Generation of steam in the core creates a pressure difference between the top of core and the

top of the downcomer. The magnitude of this pressure difference depends on the rate of

generation of steam and the rate of escape of steam via the bypasses and round the loops.

This pressure difference depresses the core liquid level and ultimately controls the degree

of rod heatup seen in the early stages of these small break tests.

The flow of steam round the loops, which would remove this pressure rise, is inhibited by the

liquid remaining in the 'U' tube at the pump Inlet. As the pressure rises so the level in the loop

seal is depressed on the steam generator side giving rise to a head of liquid on the pump side.

The maximum value for this head is the depth of the loop seal. Once the pressure difference

reaches this magnitude, then the liquid is expelled from the loop seal in a rapid surge. Any

vapour passing round the bottom bend will enter the up side reducing the density there and

hence the head. The reduced head will allow more vapour to follow amplifying the process

and clearing the loop seal.

With a loop seal cleared, steam can pass freely round the loop thus equalizing the pressure

difference and restoring the core level. It would therefore be expected that once one of the

loop seals blows, the resulting fall in pressure difference will prevent the other loop seal from

being cleared in the same way. It Is therefore immediately surprising that in BL-02 both seals

were blown.

Furthermore, the construction of LOBI is such that the intact loop seal is some 0.5m deeper

than the broken loop seal. This Implies that to clear this loop seal would need a pressure

difference of some 3500 Pa more than that needed to clear the broken loop, and this ignores

the fact that with the break being In the broken loop cold leg there will be an even greater

tendency for this loop to clear first.

In the test the intact loop seal blew before the broken loop seal.

RELAP5 in fact predicts a clearance of the broken loop, with consequent reduction in forcing

pressure, and no clearance of the Intact loop.

3.8.1 Study of mechanism of both loops clearing

To understand the behaviour of LOBI It is necessary to look In detail at the distribution of liquid

in the loop.

3.8.1.1 Draining of steam generators

There is another part of the loop which has the ability to prevent vapour flow from the core,

and that Is the up side of the steam generator 'U' tubes. Any liquid blocking these tubes will

exert a pressure head countering the driving pressure difference in the core, and this head

will be combined with the head produced In the loop seal.

The LOBI datatape contains differential pressure readings at different elevations within the 'U'

tubes. A small program was written to process these values to produce collapsed and mixture

levels, assuming negligible pressure difference due to flow. (This will be valid after about 50

seconds in the transient as the flows decay rapidly). The results can be seen in fig. 19 for both

the broken and Intact loops. The levels shown are referenced to the loop piping centrelines
- 20 -

as shown in the scaled picture which gives some idea of the position corresponding to the

marked level.

As can be seen the intact loop steam generator drains more rapidly than the broken loop

steam generator. At the time when the intact loop steam generator is empty the broken loop

still has almost im of head still In it. The loop pressure difference at this time Is great enough

to blow the intact loop seal being equivalent to around 2.5 m head, but the total head needed

to blow both the broken loop SG and the loop seal would be 3 m. So the intact loop blows first.

As seen in this figure, the level in the intact loop steam generator then recovers! It rises to

around 2 m. By this time the broken loop SG has finished draining, and because the head in

the intact loop SG has causes a revival of the loop pressure difference back up to 2 m, the

broken loop seal can then blow.

The timing and exact nature of these events are critical.

The recovery of the level in the intact loop can be understood by looking at the mixture level

in the core riser region. This parameter was calculated in a similar way to the derived collapsed steam generator levels, via a specially written program, except this time the mixture

level is the most important value. This value Is calculated by processing a chain of delta-P

signals to find the level at which a step change occurs. Between these two pressure tappings

will be the mixture level. By calculating the voldage between the pressure tappings directly

below this level and using this to calculate a mixture level with respect to the bottom tapping

of the two containing the step change an accurate value for this parameter can be derived.

fig. 20 plots this derived value together with the previously plotted steam generator collapsed

level with the zero line being the loop centreline as indicated. As soon as the intact loop seal

blows, the steam in the upper core region begins to flow round the intact loop, thus relieving

the pressure difference. This allows the core mixture level, which had until then been depressed to some Im below the nozzle elevation, to rise. Because of the greater diameter of

the intact loop pipework compared to the broken loop pipework, and because of the flow into

the intact loop hot leg, liquid is first carried from the riser back into the intact loop hot leg. This

happens at around 375 seconds as can clearly be seen as the rising core level results in a

rising level in the intact loop steam generator. This is the mechanism of the recovery of the

liquid level seen earlier, and which is responsible for the subsequent blowing of the broken

loop seal.

It can be seen that to calculate the loop seal behaviour requires a very accurate prediction

of the steam generator draining behaviour, together with an exact core mixture level calculation. We look first at the draining of the steam generators, bearing in mind that the density

plots already given as fig. 11 to fig. 14 have shown a problem in following the hot leg densities.

An indication of the conditions in the hot legs can be gained by looking at the temperatures

measured at the bottom of the hot leg tube, and the output from the flow direction indicators.

These latter devices, consisting of two thermocouples mounted either side of a small heating

coil, can be used to deduce both flow direction and some idea of flow magnitude. At low flows

the temperature rise above ambient measured will be quite large, reducing at larger flows.

However at very small flows the heated fluid will not be convected to the thermocouple, and

thus will produce a close to zero reading too. Fortunately it is normally clear which of the two

cases it is.

These values are shown in fig. 21 for the broken loop. The positive value for the flow direction

indicator represents flow from the vessel towards the steam generator, and the temperature

has been scaled to show clearly on the same plot.

As expected the flow is positive and decreasing as the pumps coast down, and by around 150

seconds the flow has become stagnant. This is seen both in the irregular output from the flow

indicator, and interestingly in the subcooling of the fluid temperature at the bottom of the tube.

In this case this is not due to cold liquid from the steam generators failing back into the hot

leg as may be thought, but rather is due to the rather high local heat losses from the instrumented spool piece which contains the thermocouple. This spool piece contains cooling

adaptors, mounted in the lower third of the tube, which can remove some few Kw of power in
- 21 -

a very local region. When the flow is truly stagnate this will cause local subcooling as seen

here. This is a prime example of a LOBI specific effect which can easily be misinterpreted.

At around 250 seconds there is a clear indication of flow reversal, and now we would expect

countercurrent flow with steam flowing towards the steam generator and liquid draining back.

Finally at loop seal clearance the flow again becomes positive.

Looking at the draining of the steam generator 'U' tubes themselves, in fig. 22 and fig. 23 the

differential pressures over the 'U' tubes are shown for both RELAP5 and LOBI. The overall

agreement Is not too bad, and the time at which the 'U' tubes empty are quite close, with the

RELAP calculation draining the intact loop steam generator some 20 seconds too early and

the broken loop a few seconds late. The exact nature of the draining is however wrong. In

LOBI there is a very rapid pressure fall at 100 seconds followed by a plateau region from 150

to 200 seconds. This is at the time of flow stagnation before flow reversal in the hot leg. RELAP

shows no trace of this effect.

However it can be concluded that the 'U' tube draining is predicted well enough to give the

correct conditions leading up to loop seal clearance. Any deficiencies are to be found elsewhere.

Referring back to fig. 19 it is seen that after the 'U' tubes empty there is still a head of some

3.5 m between the loop pipework centreline and the top of the steam generator inlet plena.

Differences in the draining behaviour between RELAP5 and LOBI must occur in this region.

It has already been seen from fig. 11 and fig. 14 that the hot legs drain completely in the

RELAP5 calculation, well before the loop seal clears. Therefore from about 300 seconds when

the 'U' tubes empty to around 350 seconds when the calculation drains the hot legs, RELAP5

must be incorrectly predicting the draining from steam generator inlet plena, down into the

vertical entry section and along the hot leg itself.

The boundary condition for this draining are the clearance of the steam generator 'U' tubes

already discussed, the exit condition from the hot legs into the vessel and the steam flow

passing along the hot legs. Taking the matter of the exit conditions into the vessel, consider

fig. 24 which shows the hot leg densities and riser mixture levels for both LOBI and RELAPf.

(They have been scaled, but only trends are important here). In LOBI the core mixture level

drops below the nozzle elevation at some 200 seconds, and remains below until loop seal

clearance. Thus the boundary condition in LOBI is discharge into a steam filled upper plenum.

In RELAP5 the mixture level does not fall below the nozzle elevations until 320 seconds, and

immediately it does so, the hot legs drain completely. There is no Indication in the RELAP5

calculation that the hot leg can remain nearly full when the upper plenum is voided, as happens in LOBI.

This immediately raises two questions.

1. Why is the RELAP5 calculated mixture level wrong?

2. Why does RELAP5 drain the hots legs so much faster than LOBI?

3.8.1.2 Bypass effects

Both of these questions could be resolved by supposing that the modelled bypass flows are

too large. This would have the effect of reducing the pressure difference available to depress

the core level, and reducing the steam flow round the loops which would otherwise limit the

drainback in the hot legs.

This possibility is considered unlikely for a number of reasons. The previous sensitivity of

bypass effects showed that the effect of increasing the loop steam flow by reducing the bypass

flows was to blow the loop seal far too early, and gave much worse agreement with the steam

generator draining behaviour discussed before. The error in core mixture level can be understood without recourse to a smaller bypass as will be shown later. The loop differential

pressure calculated by RELAP5 is not consistent with this theory, although it is possible that

the position of the bypass may be a contributory factor.
- 22 -

For these reasons bypass alone Is discarded as the source of these errors.

3.8.1.3 Counter-current flow limiting

An approach to this problem which gives a more satisfactory explanation is to examine the

counter-current flows occuring In the hot legs, and entry to the steam generators. Appraisal

of the velocities and areas shows that the critical points would be the vessel entry point and

the steam generator Inlet.

Although there is no data from LOBI on these flows, much can be deduced from the RELAP5

calculated results. Firstly in a specially written program the liquid and gas velocities at these

locations were combined with the predicted voidage and pipe areas to produce the superficial

velocities. These are shown in fig. 25 and fig. 26 with the positions diagramatically indicated.

The counter current flow is clearly visible from 130 seconds up to the draining of the hot leg.

There is a possibility that during this period excessive liquid drainback occurs, and to investigate this the Wallis flooding criteria was calculated, being SQRT(Jg *) + SQRT(Jf *). This is

shown plotted in fig. 27 and fig. 28 for both locations mentioned above, and in the steam

generator 'U' tubes for completeness. Also on this graph Is included the typical limit of .7

given for this parameter.

Two thing are clear. Firstly the SG 'U' tubes show a lower value and hence would not be expected to control the flooding. Secondly the flooding limit of .7 would not cause a change in

the RELAP5 calculated draining rate.

However the .7 limit is really applicable to vertical tubes, and does not account for end effects

or bends. Also the liquid holdup in LOBI keeps fluid In the horizontal hot leg section implying

that the limit is being imposed in the horizontal section, not the vertical section. Finally recent

preliminary experimental work at CERL with an air-water rig modelling exactly this geometry

has shown that very significant amount of water can be held in the hot leg with zero liquid flow

and a gas flow corresponding to a flooding limit of 0.4. This value is also suggested for horizontal pipework from some theoretical works.

Imposing such a limit on the graphs would completely change the calculated draining

behaviour for RELAP5, prevent the hot legs emptying and better predicting the liquid head in

the loop.

It is believed that the current version of RELAP has no explicit flooding model. The interphase

drag which Is calculated based on flow-regime and voldage considerations is the mechanism

for limiting liquid draining. Further study of the behaviour of this model under simple conditions may be required to understand its detailed behaviour.

It is felt that test BL02 is a clear Indication of the need to better model counter-current flow

flooding in the RELAP5 code. Further work is needed to assess exactly what flooding limit is

appropriate, and following this such a limit should be Included In RELAP5 in an appropriate

form.

3.9 Rod Heatup

The exact nature of the rod heatup seen in fig. 10 can now be explained. For clarity fig. 29

shows this excursion as a temperature difference from saturation plotted together with a

scaled version of the mixture level in the riser. Clearly to correctly predict rod temperatures

requires correct prediction of riser mixture level.

3.9.1 Core mixture level

As mentioned previously the RELAP5 calculation produces an incorrect riser mixture level.

This is shown in more detail in fig. 30 with a diagramatic representation of the part of the level

displayed. Although the magnitude of the maximum depression of around Im is the same, the

timing and detail of the level behaviour are quite different.
- 23 -

Now the mixture level depends critically on the voidage in the core region. The system has to

be balanced with the downcomer full of liquid to the nozzle elevation equaling the loop pressure difference plus the head of liquid in the core. For instance for zero loop pressure difference and.10% voidage, the core mixture level would be 10% higher than the downcomer level

(roughly).

This means that the greater the core voldage, the higher the core mixture level would have

to be to balance the downcomer head. For a given loop pressure difference a greater core

voidage would result in a higher mixture level In the core.

The loop pressure difference is shown In fig. 31 for both RELAP5 and LOBI. It can be seen that

for RELAP5 this value reaches its maximum of around 18kPa earlier than in LOBI. This would

imply an earlier depression of the mixture level when in fact the reverse is seen. These facts

point to an error In the calculated core voldage.

To examine this the LOBI vessel differential pressure data was processed to obtain the

voidage at various elevations. This Is shown In fig. 32 and fig. 33 for both LOBI and RELAPS.

The voidage just below the nozzles records the fall of the mixture level, while that in the upper

plenum is fairly representative of the value throughout the core. It is Immediately clear that

RELAP5 in overpredicting the voldage, calculating a mean value around 30 to 40% against the

LOBI derived value of 20%.

This fact alone explains the Incorrect mixture level behaviour to a large degree.

The reason for this overprediction Is to be found In the interphase drag calculated by RELAPS.

For low voidages in bubbly and slug type flow, and especially In rod bundle geometries, RELAP overpredicts the interphase drag. This Is partly due to the reduced drag on bubble

swarms, partly due to profile slip effects and may be influenced by the rod bundle geometry

itself.

This effect has been implicated before, particularly In respect to voidage profiles in the riser

of the steam generator secondary side. If the downcomer level Is set correctly to the measured value, the total mass Inventory Is often found to be low. If the downcomer level Is raised

to compensate, the riser level can enter the separators, and wreck the steady state conditions.

In a recent analysis of the ST02 transient test In which Initial mass Inventory on the secondary

side proves to be critical, this was a major problem, although due to the void profile being

present only during flowing conditions It was not possible to prove conclusively that it was

wrong.

Recent work by Ardron and Clare (1987) on an assessment of the interphase drag in RELAP5

has compared code values to correlations by Wilson for low flows and Rooney for high flow.

The conclusion of this work was that density errors of around -20% to -40% could exist for

small diameters, and these would reduce for large diameters and higher pressures. (The

density errors were calculated as

Rho(R5) - Rho(Wilson)

Rho(Wilson)

For the LOBI case the density error is around -25%. suggesting that this corresponds to a

'small' diameter, and reinforcing Ardrons calculations. However Ardron tended to suggest that

the models in RELAP5 were not In excessive error, and perhaps could be acceptable. As the

work was a study compared to other correlations this conclusion is reasonable, but test BL02

has provided definite evidence of the incorrect voidage distribution and has given firm values

to the errors.

The present work has shown the problems which errors of this kind can produce, and the

far-reaching effects they have on both the primary, the secondary side and on rod heatup.

These errors are therefore considered by this author to be unacceptable, and work should

continue to correct them.
- 24 -

3.10 Loop Differential Pressure

The above factors of incorrect core voidage and liquid holdup in the steam generators combine to expain the rather odd behaviour of the loop differential pressure. This parameter

highlights the degree of mismatch between experiment and calculation, and will be discussed

in detail.

Referring to fig. 34 and fig. 35 we see the totally different behaviour of the systems. In LOBI

the loop differential pressure increases as steam is produced. The riser level falls to the

nozzle elevation at which point it pauses as extra steam Is bypassed. Continued steam production overcomes this and the level falls to around -1m, corresponding to a pressure difference of 18Kpa or so. At this point the system is balanced until the emptying of the steam

generators reduces the loop pressure head to this value, and the intact loop seal blows. The

riser mixture level recovers as the loop pressure difference falls.

Expulsion of liquid into the hot legs and steam generator inlets recreates a pressure head in

the loop, and the loop pressure difference can again increase. Superimposed on this is the

gradual fall off in steam production.

This is the sequence in LOBI up to around 450 seconds. Now consider the RELAP prediction.

Here the pressure difference rises, but the mixture level cannot reach the nozzle elevation to

allow steam to bypass due to the excess core voidage requiring a greater pressure head to

depress the mixture level. Thus the mixture level tend to remain around the nozzle elevation

for too long. This is accentuated by the need for the upper plenum X-flow junction to be completely empty before pure vapour flow is allowed through the bypass at this elevation. Before

this the junction void fraction will be the volume mixed value. In reality as soon as part of the

bypass in uncovered, vapour will have free passage and so the pressure rise can be slowed.

Eventually the level does fall as the hot legs drain completely, and shortly after the broken

loop seal blows, relieving the pressure and allowing steam to reach the break. The events

following this in both RELAP and LOBI are a second depression of the core level despite a

lower pressure difference. In RELAP this depression proceeds too far and reaches, coincidentally, the level of the first depression in LOBI.

The reason for this is seen in fig. 36 and fig. 37 where the downcomer voidage is superimposed. At the time of break uncovery the sharp drop in pressure causes flashing of the liquid

in the downcomer. This is Increased by the considerable input of stored heat in the vessel

walls. In LOBI we see this beginning at 400 seconds, and rising to around 20%. It is this reduction in the density of the downcomer fluid which allows the core level to be depressed

again with a lower head needed to do so.

For RELAP the same factor allows the deep core depression, but this time the voidage rises

to some 30 to 40% thus explaining the overprediction of the level of depression. As mentioned

earlier, experience with ISP18 had shown that significant amounts of cold HPIS penetrate the

downcomer in LOBI, and the split downcomer noding, abandoned due to code running problems, had been tried to model this better. The RELAP calculation is predicting insufficient

downcomer subcooling because of this and hence is producing an excessive vapour generation and resulting voidage error.

3.10.1 Pertaining to bypass effects

It is seen from the above discussions that the effects of hot leg draining, ECCS penetration and

core void profile all inter-relate to control the transient. The other effects of bypass size and

position while of definite significance, cannot be extricated from the other effects in this test,

and therefore firm conclusions regarding the correctness of these factors cannot be drawn

from this calculation.

Possibly if the other errors could be corrected In the RELAP5 model then sensitivities on bypass could yield meaningful results.
- 25 -

4.0 CONCLUSIONS

The BL02 test was performed satifactorily so far as the major boundary conditions were concerned, despite problems with the secondary side control, which is of small effect in this

transient, and some problems with the initial drift of the 'steady state' conditions.

All of the main objectives were met, with the exception of a deep core uncovery and rod

heatup. Future tests especially BL21 and BL12 will cover this area. Many interesting phenomena were seen and analysis of these together with the differences between the experiment and the prediction have resulted in an understanding of most of the major effects and

have led directly to the discovery of modelling problem areas.

These areas can be split into two groups, those which results from poor definition of parts of

the LOBI loop and can be addressed by the LOBI team, and those which result from deficiencies in the RELAP5 MOD2 code.

There remain uncertainties over the correct modelling of parts of the LOBI facility. The bypass

sizes and positions have been seen to be significant and poorly defined. It is recommended

that these are reassessed, possibly in conjuction with code sensitivities in experiments which

allow better interpretation of their effects than did BL02.

The attempt to better model the bypass steam/ECCS mixing in the upper downcomer region

indicated possible benefits from this kind of split downcomer nodalization. An effort should

be made to determine the source of the code running problems encountered, and to pursue

this form of pseudo-3D noding. It is expected the effects of ECCS penetration of the downcomer

and steam/ECCS cocurrent flows will be encountered many times in small break analyses,

indeed the over prediction of the downcomer voidage and subsequent excessive core level fall

are direct consequences of this modelling problem In the BL02 test.

The calculation has highlighted some of the problems with the RELAP5 break flow model. Although not thought to be so significant for this test, the model implemented by Ardron in a test

version of RELAP5 to improve the offtake from stratified conditions should be further developed to assure stability, and could then be used to assess the magnitude of its effect on this

calculation.

The problems with the two-phase break model forseen by Bryce have been found to be real,

and encouragement should be given to the code developers to rectify these problems.

It Is felt the draining of the hot legs In test BL02 is a clear indication of the need to better model

counter-current flow flooding in the RELAP5 code. Further work is needed to assess exactly

what flooding limit is appropriate, and following this such a limit should be included in

RELAP5.

Test BL02 has provided definite evidence of the incorrect voidage distribution in bubbly and

slug flow In vertical bundle type geometries. The cause of this error, the overprediction of

interphase drag, gives rise to several problems In initializing secondary side models correctly,

and has now been seen to strongly influence vessel behaviour and rod heatup in small break

tests. It is considered important to correct this failing in the code.
- 26 -

REFERENCES

A. H. Scriven. 1986 Test Specification LOBI MOD2 Test BL-02 3% Cold Leg Break with

Secondary Side Cooldown at 56K/hr

W. Bryce 1986 Some comments on the critical flow model in RELAPS MOD2 HTWG paper

PWR/HTWG/P86444

K. Ardron and A. Clare 1987 Assessment of the Interphase Drag correlations in the

RELAP5/MOD2 and TRAC-PFI/MODI Thermohydraulic codes. TPRDIBIO8611R86

A. H. Scriven. 1987 Analysis of LOBI test ST02 with the RELAP5 MOD2 code.

C. Addabbo, L. Piplies and W. Riebold. 1983 LOBI-MOD2: Facility description and specification for OECD-CSNI International Standard Problem No 18. Volume I: Geometrical

Configuration of the Test Facility.

E. Ohlmer, J. Sanders and J. Eder. 1983 LOBI-MOD2: Facility description and specification

for OECD-CSNI International Standard Problem No 18. Volume I1: Measurement instrumentation and Data Aqcquisition System.

E. Ohlmer, J. Sanders R. Doering and K. Floegel. 1983 LOBI-MOD2: Facility description

and specification for OECD-CSNI International Standard Problem No 18. Volume II:

Pressure Drop and Heat Losses.

W. Piplies, H. Staedtke and W. Kolar. 1984 LOBI-MOD2: Facility description and specification for OECD-CSNI International Standard Problem No 18. Volume IV: Specifications.

Appendix A, Drg. No. RL3.5.2580-2598 attached-
- 27 -

Appendix A. RELAP5 MOD2 INPUT DECK. TEST

SPECIFIC INPUT

=BL-02 SMALL BREAK 3.0% TEST

* =FLAGS MAJOR INPUT SEGMENTS

$$$$ FLAGS SUBSECTIONS WITHIN MAJOR INPUT SEGMENTS *****************tto*Q*oe************ooo*o*Qt***eet******* ****

SYSTEM CONTROL BLOCK

*...*.....* *.** .. ** ***........**.....*** .. ... *e .......*..*.*

PROBLEM SPECIFICATION .. **** .... *...* ... .................. •... ........... * 

0000100 NEW TRANSNT

0000101 RUN

0000102 SI

*0000104 NONE

0000110 NITROGEN

* TIME STEP CONTROL CARDS

* START OFF BY FORCING SMALL TIME STEP AND LET CODE INCREASE IT * OTHERWISE MAX VALUE IS USED FOR FIRST STEP, AND PROBLEMS RESULT

0000201 0.001 1.OD-6 0.01 00003 1 10 1000

0000202 200.0 1.OD-3 0.5 00003 20 400 400

0000203 1400.0 i.OD-7 0.25 00003 8 800 800 *0000204 1000.0 1.OD-7 0.5 00003 4 400 400

* MINOR EDIT VARIABLES

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

P 350010000

MFLOWJ 584000000

MFLOWJ 510010000

CNTRLVAR 501

TEMPF 139010000

TEMPF 100010000

MFLOWJ 950000000

CNTRLVAR 43

P 560010000

CNTRLVAR 598

MFLOWJ 594000000

MFLOWJ 610010000

CNTRLVAR 601

TEMPF 239010000

TEMPF 200010000

MFLOWJ 950000000

MFLOWJ 390000000

P 660010000

CNTRLVAR 599

CNTRLVAR 81

* UPPER PLENUM * RELIEF VALVE FLOW

* DOWNCOMER

* ILSG LEV " TEMP IN COLD LEG

* TEMP IN HOT LEG

* BREAK MASS FLOW * PRESSURIZER LEVEL

* STEAM DOME PRESSURE " RELIEF VALVE CONT

* RELIEF VALVE FLOW * DOWNCOMER

* BLSG LEVEL

* TEMP IN COLD LEG * TEMP IN HOT LEG

* BREAK MASS FLOW

* SEAL DRAIN FLOW

* STEAM DOME PRESSURE

* STEAM CONTROL

* TOTAL CORE POWER
- 28 -

321 CNTRLVAR 911 * TOTAL PRIMARY MASS

322 CNTRLVAR 920 * NET FLOW OUT OF PRIMARY

323 CNTRLVAR 921 * TOTAL MASS LOSS

324 MFLOWJ 300020000

325 MFLOWJ 301030000

326 MFLOWJ 363020000

CONTROL SYSTEM

• THIS BLOCK CONTAINS ALL THE INFORMATION WHICH SETS UP THE

SYSTEM SETPOINTS, AND RESPONSES. BY CHANGING THIS ALL

• NON-HARDWARE CHANGES TO LOBI CAN BE MIMICED.

* VARIABLE TRIPS *

• 501 = START OF TRANSIENT (PRESSURIZER TMDPVOL VALVED OUT)

* (switch seal drain to lower plenum)

* 502 START + DELAY ON BREAK OPEN

• 503 CLOSURE OF UPPER PLENUM BYPASS VALVE

* 510 = PRESSURE SETPOINT ONE < 131 BAR IN UPPER PLENUM

• 511 POWER TRIPS OFF

• 512 START OF INTACT LOOP SECONDARY COOLDOWN

• 513 START OF BROKEN LOOP SECONDARY COOLDOWN

* 514 CLOSURE OF INT LOOP STEAM ISOLATION VALVE * 515 CLOSURE OF BRK LOOP STEAM ISOLATION VALVE

• 516 CLOSURE OF TERTIARY SIDE ISOLATION VALVE

• 517 CLOSURE OF MAIN FEED WATER LINES

• 518 INTACT LOOP AUX FEED COMES ON

• 519 BROKEN LOOP AUX FEED COMES ON

• 520 = PRESSURE SETPOINT TWO < 117 BAR IN UPPER PLENUM

* 521 = HPIS FLOW

• 530 = PRESSURE SETPOINT THREE < 110 BAR IN UPPER PLENUM

• 531 INTACT LOOP PUMP TRIP

• 532 PUMP REACHES ZERO SPEED

* 533 PUMP LOCKED ROTOR RESISTANCE VALVED INTO PLACE

• 536 BROKEN LOOP PUMP TRIP

• 537 PUMP SPEED REACHES ZERO

• 538 PUMP LOCKED ROTOR RESISTANCE VALVED INTO PLACE

• 549 = CLOSURE TIME FOR VALVES

* PRESSURIZER VALVE SETPOINTS

* 560 = PRESSURIZER PRV RE-SEAT PRESSURE

• 561 = PRESSURIZER PRV LIFT PRESSURE

• TRANSIENT TRIPS AND CONTROLS

501 CNTRLVAR 99 GE NULL 0 0.5 N *START

501 TIME 0 GE NULL 0 200.0 L START

502 TIME 0 GE TIMEOF 501 0.0 L * BREAK OPEN

503 TIME 0 LE NULL 0 20.0 N 0.0
- 29 -

510

511

512

513

514

515

516

517

518

519

520

521

P

TIME

TIME

TIME

TIME

TIME

TIME

TIME

TIME

TIME

350010000 LE NULL

0

0

0

0

0

0

0

0

0

GE

GE

GE

GE

GE

GE

GE

GE

GE

TIMEOF

TIMEOF

TIMEOF

TIMEOF

TIMEOF

TIMEOF

TIMEOF

TIMEOF

TIMEOF

0

510

520

520

510

510

510

510

501

501

131.0E5 L

2.0 L

600.0 L

1.0E6 L

1.0E6 L

1.0E6 L

0.0 L

1.5 L

65.0 L

90.0 L

* SET I

" POWER

* I.L. COOL

".B.L. COOL

" I.L. ISOL

* B.L. ISOL

* STEAM LINE

* MAIN FEED

* AF on il

" Af on bl

P 350010000 LE NULL 0 117.0E5 L *SET 2

TIME 0 GE TIMEOF 520 35.0 L * HPIS

530 P 350010000 LE NULL 0

531 TIME 0 GE TIMEOF 510

532 PMPVEL 125 LE NULL 0

533 TIME 0 GE TIMEOF 532

110.0E5 L * SET 3

0.0

0.0

i.OE6

L

L

L

" PUMP TRIP

* ZERO SPEED

* RESISTANCE

* PUMP TRIP

* ZERO SPEED

" RESISTANCE

536

537

538

TIME 0

PMPVEL 125

TIME 0

GE TIMEOF 510

LE NULL 0

GE TIMEOF 537

0.0 L

0.0 L

4.0 L

SYSTEM SET POINTS DURING STEADY STATE RUNNING

549 TIME

560 P

561 P

* special trips

578 TIME

579 TIME

0 GT NULL 0 1.0E6 L

410010000 GT NULL

410010000 GT NULL

experiment specific

0 GE TIMEOF

0 GE TIMEOF

0 170.0E5 N * PRESSURIZER

0 165.OE5 N •RELIEF VALVE

501 380.0 L

501 350.0 L'

" AF off i1

" Af off bl

t

$$$$ INTERACTIVE CONTROL BLOCK $$$$

CONTROL VARIABLE FUNCTION

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

99

100

SET TEMP FOR PRIMARY COLD LEGS

CORE POWER

SET SPEED FOR INTACT LOOP PUMP

SET SPEED FOR BROKEN LOOP PUMP

SGI DOWNCOMER THROTTLE VALVE

SG2 DOWNCOMER THROTTLE VALVE

SG2 DOWNCOMER SET LEVEL

SG2 DOWNCOMER SET LEVEL

PRESSURIZER SET LEVEL

PRESSURIZER SET PRESSURE

HPIS FLOW

CORE POWER MODIFICATION OPTION

HPIS FLOW MODIFICATION OPTION

PRESSURIZER HEATER CONTROL

SGI RELIEF VALVE SET POINT

SG2 RELIEF VALVE SET POINT

BREAK OPEN (0 CLOSED, 1 OPEN)

PROBLEM STOP (0 RUN, I STOP)

END PROBLEM TRIP VIA INTERACTIVE CONTROL

(OR VIA PRESSURE TRIP)

TRIP 597 IS END OF PROBLEM ON LOW PRESSURE (< 10 BAR)

SET UP TRIP 598 TO BE PERMANENTLY ON

TRIP 599 TO BE CONTROLED BY CONTROL VAR 100
- 30 -

597 P 350010000 LT NULL 0 10.0D5 L

598 TIME 0 GT NULL 0 -1.0 L 0.0

599 CNTRLVAR 100 GT NULL 0 0.5 N

699 597 OR 599 N

* SET END OF PROBLEM TRIP TO BE 699

600 699

* PRIMARY TEMP

20507000 PRIMTEMP TRIPUNIT 563.60 0.0 1

20507001 598

* CORE POWER

20507100 COREPOWR FUNCTION 5.090D6 0.0

20507101 TIME 0 100 ea**.* a...... *a*.aa a. a... *a***a*..*a* a....a.. .. a tea..a

* INTACT LOOP PUMP SPEED

20507200 SETFLOWI TRIPUNIT 21.0 0.0

20507201 598 .a***.*aaaaaee.....................................t a . .....

BROKEN LOOP PUMP SPEED

20507300 SETFLOW2 TRIPUNIT 7.0 0.0

20507301 598

SG1 THROTTLE VALVE FOR RECIRC RATIO

20507400 RECIRCI TRIPUNIT 0.35 0.0 1

20507401 598

" SG2 THROTTLE VALVE FOR RECIRC RATIO

20507500 RECIRC2 TRIPUNIT 0.22 0.0

20507501 598

" SGI DOWNCOMER SET LEVEL

20507600 SGILEVEL TRIPUNIT 8.33 0.0

20507601 598

* SG2 DOWNCOMER SET LEVEL

20507700 SG2LEVEL TRIPUNIT 8.23 0.0

20507701 598

.............. ......... aa ***.......a*** aa.......

" PRESSURIZER SET LEVEL

20507800 PRESLEVL TRIPUNIT 4.80 0.0

20507801 598

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

PRESSURIZER SET PRESSURE

20507900 PRIMPRES TRIPUNIT 155.0 0.0

20507901 598

" HPIS FLOW RATE

20508000 HPISFLOW . FUNCTION 1.0 0.0 1

20508001 P 139010000 10

* CORE POWER WITH HEATLOSS COMPENSATION SWITCH IF NEEDED

20508100 POWER SUM 1.0 0.0 1

20508101 0.0 1.0 CNTRLVAR 71 DECAY POWER FROM TABLE

°20508102 -?? CNTRLVAR ?? * MODIFICATION
- 31 -

* HPIS REDUCED IF WANTED

20508200 HPIS SUM 1.0 0.0 1

20508201 0.0 1.0 CNTRLVAR 80 HPIS FROM TABLE

*20508202 1.0 CNTRLVAR ?? MODIFICATION

................. . ......... *..*****t* b... *.* ........

" PRESSURIZER HEATER CONTROL

20508300 PRESHEAT TRIPUNIT 1.OE-12 0.0

20508301 598

.. ........... ** ***•..... . * . . f ***** *** a... *

" SGI RELIEF VALVE SETPOINT

20508400 SGIRVLV TRIPUNIT 79.OE+5 0.0

20508401 598

* SG2 RELIEF VALVE SETPOINT

" TURNED OFFI

20508500 SG2RVLV TRIPUNIT 80.OE-+-6 0.0

20508501 598

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

* SATURATION TEMPERATURE IN INTACT LOOP HOT LEG

20509000 SAT-T FUNCTION 1.0 0.0 1

20509001 P 100010000 3

* SET UP CONTROL VARIABLES 99 AND 100 FOR BREAK OPEN AND PROBLEM

" STOP VIA INTERACTIVE CONTROL

20509900 BREAKOPN TRIPUNIT 0.01 0.0 1

20509901 598

20510000 PROBEND TRIPUNIT 0.01 0.0 1

20510001 598

20510100 TIMESTEP SUM 1.0 0.001 0 1 1.OE-6

20510101 0.0 1.0 TIME 0

20510102 -1.0 CNTRLVAR 102

20510200 LASTTIME MULT 1.0 0.0 0

20510201 TIME 0

" LOGICAL TRIPS

* PRESSURIZER RELIEF VALVE HYSTERYSIS

605 606 AND 561 N

606 605 OR 560 N " PRESSURIZER RELIEF VALVE OPENS BY SOME SIGNAL (OPTION)

607 -598 AND -598' L * SWITCHED OFF

608 607 OR 606 N "

609 -608 AND -608 N *

610 518 . AND -578 N TRIPS AUX FEED ON/OFF

611 519 AND -579 N * TRIPS AUX FEED ON/OFF

• $$$$ INVERSE TRIPS $$$$$

620 TRUE THROUGH STEADY STATE UP TO START OF TRANSIENT
- 32 -

620 -501 AND -501 N 0.0 * STEADY STATE

621 TRUE THROUGH STEADY STATE AND UP TO MOMENT OF SCRAM

621 -510 AND -510 N 0.0 * UP TO SCRAM

622 TRUE THROUGH STEADY STATE AND UP TO IL COOLDOWN

622 -512 AND -512 N 0.0 * UP TO IL COOLDOWN

623 TRUE THROUGH STEADY STATE AND UP TO BL COOLDOWN

623 -513 AND -513 N 0.0 * UP TO BL COOLDOWN

624 TRUE THROUGH STEADY STATE AND UP TO MAIN FEED OFF

624 -517 AND -517 N 0.0 * MAIN FEED ON

• 625 TRUE THROUGH STEADY STATE AND UP TO AUX FEED ON

625 -518 AND -518 N 0.0 * AUX FEED OFF

626 TRUE THROUGH STEADY STATE AND UP TO AUX FEED ON

626 -519 AND -519 N 0.0 * AUX FEED OFF

628 521 AND 521 N * HPIS

UNIT TRIP CONTROL VARIABLES FOR STATE SWITCHING

* STATE 1 UP TO START (STEADY STATE)

20505000 STEADY TRIPUNIT 1.0 1.0 1

20505001 620 THIS IS JUST .NOT.501

• STATE 2 AFTER START

20505100 BREAKOPN TRIPUNIT 1.0 0.0 1

20505101 501

• STATE 3 UP TO MOMENT OF SCRAM

20505200 FULLPOWR TRIPUNIT 1.0 1.0 1

20505201 621 * THIS IS JUST .NOT.502

* STATE 4 AFTER SCRAM

20505300 SCRAM TRIPUNIT 1.0 0.0 1

20505301 510

• STATE 5 UP TO START OF IL COOLDOWN

20505400 STEAM TRIPUNIT 1.0 0.0 1

20505401 622

* STATE 6 AFTER START OF IL COOLDOWN

20505500 COOLDOWN TRIPUNIT 1.0 0.0 1

20505501 512

* STATE 7 UP TO START OF BL COOLDOWN

20505600 STEAM TRIPUNIT 1.0 0.0 1

20505601 623

** * ***..*.* . ******.e. .... ...

* STATE 8 AFTER START OF BL COOLDOWN

20505700 COOLDOWN TRIPUNIT 1.0 0.0 1

20505701 513

* STATE 9 UP TO START OF INTACT LOOP AUX FEED

20505800 AUXFEED TRIPUNIT 1.0 0.0 1
- 33 -

20505801 625

" STATE 10 AFTER START OF INTACT LOOP AUX FEED

20505900 AUXFEED TRIPUNIT 1.0 0.0 1

20505901 518

* STATE 11 UP TO START OF BROKEN LOOP AUX FEED

20506000 AUXFEED TRIPUNIT 1.0 0.0 1

20506001 626

* STATE 12 AFTER START OF BROKEN LOOP AUX FEED

20506100 AUXFEED TRIPUNIT 1.0 0.0 1

20506101 519

* $$$$$ CHANGABLE DATA FOR EXPERIMENT SELECTION $$$$$$

* $$$$$ TABLES, FLOW VALUES AND CURVES SET BY CONTROL LOGIC $$$$

* = PRESSURIZER SURGE LINE CONNECTION

4000303 2.800 3 " FOR INTACT LOOP CONNECTION

"4000303 5.33 3 FOR BROKEN LOOP CONNECTION

4050101 400010000 103000000 1.3685D-4 0.0 0.0 00100 * INTACT

"4050101 400010000 203000000 1.3685D-4 1.0 0.5 20001 *BROKEN

* -BREAK SIZE AND MULTIPLIER

THIS IS THE BREAK FLOW MULTIPIER FOR JUNCTION 950

9500102 0.85 0.85

ACCUMULATOR ENABLE/DISABLE SWITCH

685 598 AND 598 L * ACCU ON FOR THIS TEST

* THIS TABLE CONTROLS THE BREAK ISOLATION VALVE

* ARGUS BALL VALVE OPENING CHARACTERISTICS *

* NORMALISED STEM POSITION AGAINST NORMALISED FREE AREA *

* IN HERE WE PUT THE FRACTION OF THE 100% FLOW AREA WHICH THE BREAK

* REPRESENTS

3% BREAK

20215000 NORMAREA 0 1.0 0.03

20215001 0.0000 0.00

20215002 0.2556 0.00

20215003 0.3889 0.11

20215004 0.4444 0.19

20215005 0.5000 0.27

20215006 0.5556 0.35

20215007 0.6111 0.44

20215008 0.6667 0.52

20215009 0.7222 0.60

20215010 0.7778 0.69

20215011 0.8333 0.77

20215012 0.8889 0.85
- 34 -

20215013 0.9444 0.93

20215014 1.0000 1.00

* THIS TABLE contains the stem position versus area

• function for all the control valves on the * pressurizer and steam generators

20215100 NORMAREA 0 1.0 1.0

20215101 0.0000 0.00

20215102 0.04 0.00

20215103 0.05 0.045

20215104 0.10 0.050

20215105 0.2 0.076

20215106 0.3 0.105

20215107 0.4 0.145

20215108 0.5 0.200

20215109 0.55 0.235

20215110 0.6 0.276

20215111 0.65 0.324

20215112 0.7 0.381

20215113 0.75 0.447

20215114 0.8 0.525

20215115 0.85 0.617

20215116 0.9 0.725

20215117 0.95 0.851

20215118 1.0 1.00

.... .... o ..... . . * aat t.•a•t***a. a...*a.AA . ..a. a... * A t**. 

• THIS TABLE contains the stem position versus area "

for the relief valve of the pressurizer. Because the valve

• is much larger than the orifice junction area this

• compensates for the odd turn on/off behaviour. a*.ta•~ t*A a•**••A*•• *Ae t ..•*.*••Aata•a••.*A.•e..***.AA. *ot•a

20215200 NORMAREA 0 1.0 1.0

20215201 0.0000 0.00

20215202 0.026 1.0 * full orifice area when partially open

20215203 1.0 1.0

• THIS TABLE contains the stem position versus area

• for the steam closure valve to mimic small leak.

• The valve closes over 1.5 seconds.

• When stem is fully closed, small leak remains

• Valve area is 44.0d-4

20215300 NORMAREA 0 1.0 1.0

20215301 0.0000 2.OOD-4 * small leak area about 1mm dia hole

20215302 0.01 0.01

20215303 1.0 1.00

" THIS TABLE contains the stem position versus area

" function for the large relief valve on the Intact loop * SG WHICH MAY BE DIFFERENT FROM OTHERS

20215400 NORMAREA 0 1.0 1.0

20215401 0.0000 0.00
- 35 -

20215402 0.04 0.00

20215403 0.05 0.045

20215404 0.10 0.050

20215405 0.2 0.076

20215406 0.3 0.105

20215407 0.4 0.145

20215408 0.5 0.200

20215409 0.55 0.235

20215410 0.6 0.276

20215411 0.65 0.324

20215412 0.7 0.381

20215413 0.75 0.447

20215414 0.8 0.525

20215415 0.85 0.617

20215416 0.9 0.725

20215417 0.95 0.851

20215418 1.0 1.00

- POWER DECAY ----

..................... ................ ..b.a.b. ........

* ELECTRICAL POWER CONTROL CURVE - ANS 100% CORRECTED FOR LOBI (ISP18) ...... *bbb .. *.**...* ..... b..*b ... *bba ... ** ....... ***..a.a b

" THIS CURVE IS MULTIPLIED BY CNTRLVAR 71 TO GIVE POWER " THE CNTRLVAR CAN BE ALTERED DURING STEADY STATE RUNNING TO

* MIMIC RIG CONTROL, AND THEN GO INTO THE DECAY TRANSIENT

20210000 POWER 511 1.0 1.0

20210001 0.0 1.00

20210002 1.0 0.90

20210003 2.0 0.73

20210004 3.0 0.65

20210005 5.0 0.51

20210006 7.0 0.40

20210007 9.0 0.32

20210008 13.0 0.20

20210009 15.0 0.161

20210010 16.0 0.15

20210011 17.0 0.14

20210012 18.0 0.13

20210013 20.0 0.12

20210014 24.0 0.10

20210015 30.0 0.08

20210016 40.0 0.065

20210017 68.0 0.048

20210018 110.0 0.04

20210019 170.0 0.035

20210020 270.0 0.028

20210021 470.0 0.023

20210022 870.0 0.02

20210023 1000.0 0.019

20210024 2000.0 0.016

20210025 4000.0 0.013

20210026 6000.0 0.011

20210027 10000.0 0.010

HPIS

* TABLE OF HPIS FLOW AS A FUNCTION OF SYSTEM PRESSURE

* THESE VALUES ARE MULTIPLIED BY CNTRLVAR 80 TO GET

HPIS FLOWS, AND CAN BE ADJUSTED BY OPERATOR DURING TRANSIENT

* TO MIMIC CONTROL OF HPIS PUMPS.

* HPIS SYSTEM CURRENTLY MODELLING

2/4 PUMPS INJECTING INTO THE INTACT LOOP COLD LEG
- 36 -

(SAME AS ISP 18)

20201000 POWER 0 1.0 1.0

20201001 1.OE5 0.201

20201002 11.0E5 0.192

20201003 21.0E5 0.183

20201004 31.0E5 0.172

20201005 41.0E5 0.160

20201006 51.0E5 0.147

20201007 61.0E5 0.132

20201008 71.0E5 0.1162

20201009 81.0E5 0.098

20201010 91.0E5 0.077

20201011 101.0E5 0.052

20201012 111.OE5 0.0218

20201013 117.0E5 0.0

20201014 170.0E5 0.0

* PUMP SPEED-TIME CURVES - TEST BL-00

* INTACT LOOP PUMP SPEED-TIME CURVE FROM TRIP ON PRESSURE AT 131 BAR

* TRIP

20212500 POWER 531 1.0 1.0

* (TIME-TRIP TIME) NORMALIZED SPEED

20212501 0.0 1.000

20212502 5.0 0.88

20212503 10.0 0.71

20212504 15.0 0.59

20212505 27.0 0.41

20212506 40.0 0.32

20212507 50.0 0.26

20212508 120.0 0.115

20212509 200.0 0.115

20212510 201.0 0.00

* BROKEN LOOP PUMP SPEED-TIME CURVE FROM TRIP ON PRESSURE AT 131 BAR

* TRIP

20222500 POWER 536 1.0 1.0

* (TIME-TRIP TIME) NORMALIZED SPEED

20222501 0.0 1.000

20222502 5.0 0.88

20222503 10.0 0.71

20222504 15.0 0.59

20222505 27.0 0.41

20222506 40.0 0.32

20222507 50.0 0.26

20222508 120.0 0.115

20222509 200.0 0.115

20222510 201.0 0.00

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

* INTACT LOOP PROGRAMMED COOLDOWN CURVE

* INTACT LOOP COOLDOWN-TIME CURVE FROM TRIP 512

* TRIP CONVERT TO PA

20250500 POWER 512 1.0 1.0E5

* (TIME-TRIP TIME) PRESSURE DIFFERENCE (BAR)

20250501 0.00 - 0.0

20250502 360.0 6.16 * 56 DEGREES PER HOUR

20250503 720.0 11.95

20250504 1800.0 27.00
- 37 -

* BROKEN LOOP PROGRAMMED COOLDOWN CURVE

* BROKEN LOOP COOLDOWN-TIME CURVE FROM TRIP 513

* TRIP CONVERT TO PA

20260500 POWER 513 1.0 1.0E5

* (TIME-TRIP TIME) PRESSURE DIFFERENCE (BAR)

20260501 0.00 0.0

20260502 360.0 6.16 * 56 DEGREES PER HOUR

20260503 720.0 11.95

20260504 1800.0 27.00

* GENERAL DEADBAND FUNCTION... USED BY FEW DELTA T CONTRLVARS

20250600 REAC-T

20250601 -100.0 -100.0

20250602 -0.0001 -0.0001

20250603 -0.0001 0.0

20250604 0.0001 0.0

20250605 0.0001 0.0001

20250606 100.0 100.0

* PUMP SPEED CONTROLLER - INTACT LOOP

* THIS IS THE MASS FLOW CONTROLLED ERROR SEEKING PUMP SPEED

* WORK OUT MASS FLOW ERROR SIGNAL

20511400 FLOWER1 SUM 1.0 0.0 1

20511401 0.0 1.0 CNTRLVAR 72 * SET FLOW

20511402 -1.0 MFLOWJ 125010000 * MINUS REAL FLOW

20511500 INTERI INTEGRAL 1.0 0.0 1

20511501 CNTRLVAR 114

20511600 PSPEED1 SUM 1.0 505.00 0

20511601 0.0 1.0 PMPVEL 125

20511602 10.0 CNTRLVAR 114

20511603 0.8 CNTRLVAR 115 *..*.... ***.*.... . *****..-... **.................

* CONTROL VAR 116 IS NOW PUMP SPEED TO BE USED FOR STEADY STATE

• (SET FLOW CAN BE CHANGED FOR INTERACTIVE PUMP CONTROL)

* PUMP SPEED TABLE -"INTACT LOOP PUMP -SET FOR INTERPOLATION ONLY

1256100 598 CNTRLVAR 122 * TRIP IS SET PERM ON

1256101 0.0 0.0 * SO THIS I TO I MAPPING

1256102 1000.0 1000.0 * IS ALWAYS USED

SET UP CNTRLVAR 120 TO BE DESIRED COSTDOWN CURVE

20512000 SPEEDT1 FUNCTION 1.0 0.0 1

20512001 TIME 0 125

20511700 STORE MULT 1.0 0.0 0

20511701 CNTRLVAR 51 * 0 UP TO BREAK, I AFTER
- 38 -

20511702 CNTRLVAR 119 S.*........*.....*..**...*..*.. *......*.....

20511800 SPEED MULT 1.0 505.0 0

20511801 CNTRLVAR 50 1 UP TO BREAK, 0 AFTER

20511802 CNTRLVAR 116 * CONTROLLED SPEED * * ee~** ** *****4  ** ********* *4 44* * *4*4 ***eet~eae e*e*

20511900 OLDSPEED SUM 1.0 505.0 0

20511901 0.0 1.0 CNTRLVAR 117

20511902 1.0 CNTRLVAR 118

20512100 DECAY MULT 1.0 0.0 1

20512101 CNTRLVAR 117

20512102 CNTRLVAR 120

20512200 PUMPVEL SUM. 1.0 505.0 1

20512201 0.0 1.0 CNTRLVAR 118

20512202 1.0 CNTRLVAR 121

• PUMP SPEED CONTROLLER - BROKEN LOOP PUMP

20521400 FLOWER2 SUM 1.0 0.0 1

20521401 0.0 1.0 CNTRLVAR 73

20521402 -1.0 MFLOWJ 225010000

20521500 INTER2 INTEGRAL 1.0 0.0 1

20521501 CNTRLVAR 214

20521600 PSPEED2 SUM 1.0 396.00 0

20521601 0.0 1.0 PMPVEL 225

20521602 15.0 CNTRLVAR 214

20521603 1.5 CNTRLVAR 215

* PUMP SPEED TABLE - BROKEN LOOP PUMP

2256100 598 CNTRLVAR 222 * TRIP IS SET PERM ON

2256101 0.0 0.0

2256102 1000.0 1000.0

20522000 SPEEDT2 FUNCTION 1.0 0.0 1

20522001 TIME 0 225

20521700 STORE MULT 1.0 0.0 0

20521701 CNTRLVAR 51

20521702 CNTRLVAR 219

20521800 SPEED MULT 1.0 396.0 0

20521801 CNTRLVAR 50

20521802 CNTRLVAR 216

20521900 OLDSPEED SUM 1.0 396.0 0

20521901 0.0 1.0 CNTRLVAR 217

20521902 1.0 CNTRLVAR 218

20522100 DECAY MULT 1.O 0.O O

20522101 CNTRLVAR 217

20522102 CNTRLVAR 220

20522200 PUMPVEL SUM 1.0 396.0 0

20522201 0.0 1.0 CNTRLVAR 218

20522202 1.0 CNTRLVAR 221

4** ..... *.** ..... 4 . . .* 44 ... .***...... 4 *4 .... .4444 * .......
- 39 -

* PRESSURE RELIEF VALVE AND PROGRAMMED CONTROL FOR SECONDARY SIDE

* INTACT LOOP

* SET UP CNTRLVAR 561 TO BE PROGRAMMED RESPONSE

* PRESSURE DIFF STARTING FROM TRIP 512

20556100 PROGRAM FUNCTION 1.0 0.0 1

20556101 TIME 0 505

562 IS THE SETPOINT FOR THE INTEGRAL CONTROLLER, BEING

THE RELIEF VALVE UPPER LIMIT MINUS PROGRAMMED COOLDOWN

20556200 SETPOINT

20556201 0.0 1.0

20556202 -1.0

SUM 1.0 0.0

CNTRLVAR 84

CNTRLVAR 561

1

" RELIEF SET POINT

" MINUS COOLDOWN IF ACTIVE

* control system for relief valve based on LOBI data

" stem = Va( (X-XO)/DXO + 1/Ti( Int(X-XO)/DXO

• with Va = 0.25 DXO = 10.0 MPa Ti = 1.0

20556300 PROGDIFI

20556301 0.0 1.0

20556302 -1.0

SUM 1.OE-7 0.0 1 * scale factor

P 560010000 * CURRENT VALUE

CNTRLVAR 562 * MINUS SETPOINT

20556400 DEADBN1 FUNCTION 1.0 0.0 1

20556401 CNTRLVAR 563 506 * USE DEADBAND TO REDUCE CHATTER

• NOTE LIMIT TO +VE VALUES ONLY IN INTEGRAL

20556500 INTTSECl INTEGRAL 1.0 0.0 0 3 0.0 10.0

20556501 CNTRLVAR 564

20556600 CONTROLI

20556601 0.0 1.0

20556602 1.0

SUM 0.25 0.0

CNTRLVAR 564

CNTRLVAR 565

0 3 0.0 1.0

20556700 SWITCH MULT 1.0 0.0 1

20556701 CNTRLVAR 566 SWITCH OUT THIS TERM WHEN steady state

20556702 CNTRLVAR 51 • PROGRAM LIMITS

20556900 SWITCH MULT 1.0 0.0 1

20556901 CNTRLVAR 567 * SWITCH OUT THIS TERM WHEN SMALL VALVE IS OFF

20556902 CNTRLVAR 50 * OFF

• BASIC CONTROL FOR SMALL VALVE ON SG

" THE FOLLOWING SYSTEM ENSURES THE VALVE CAN ONLY MOVE AT SOME LIMITED " SPEED AS GIVEN BY THE LOBI TEAM DATA.

20557000 AREACHNG SUM 1.0 0.0 0 3 -1.0 1.0

20557001 0.0 1.0 CNTRLVAR 569 DESIRED VALVE POSITION

20557002 -1.0 CNTRLVAR 599 - CURRENT VALVE POSITION

• LIMITED TO < 2% IE 50SEC

20557100 DA/DT DIV 1.0 0.0 1 3 -0.02 0.02

20557101 CNTRLVAR 101 CNTRLVAR 570 * AREA RATE OF CHANGE

20557200 AREALLOW MULT

20557201 CNTRLVAR 101

1.0 0.0 1

CNTRLVAR 571 * AREA CHANGE FOR THIS DT

* LARGE VALVE CONTROL

20557900 SWITCH MULT 1.0 0.0 1

20557901 CNTRLVAR 567 * SWITCH OUT THIS TERM WHEN LARGE VALVE IS OFF

20557902 CNTRLVAR 51 *ON
- 40-

" BASIC CONTROL FOR LARGE VALVE ON SG

" THE FOLLOWING SYSTEM ENSURES THE VALVE CAN ONLY MOVE AT SOME LIMITED

* SPEED AS GIVEN BY THE LOBI TEAM DATA.

20558000 AREACHNG SUM 1.0 0.0 0 3 -1.0 1.0

20558001 0.0 1.0 CNTRLVAR 579 DESIRED VALVE POSITION

20558002 -1.0 CNTRLVAR 598 - CURRENT VALVE POSITION

* LIMITED TO 1.0 SEC

20558100 DA/DT DIV 1.0 0.0 1 3 -1.0 1.0

20558101 CNTRLVAR 101 CNTRLVAR 580 * AREA RATE OF CHANGE

20558200 AREALLOW MULT 1.0 0.0 1

20558201 CNTRLVAR 101 CNTRLVAR 581 * AREA CHANGE FOR THIS DT

• CNTRLVAR .598 CONTROLS THE LARGE VALVE ON THE STEAM GENERATOR

20559800 CONTROL SUM 1.0 0.0 0 3 0.0 1.0

20559801 0.0 1.0 CNTRLVAR 598 ITS OWN OLD VALUE

20559802 1.0 CNTRLVAR 582 + AREA CHANGE

CNTRLVAR 599 CONTROLS THE SMALL VALVE ON THE STEAM GENERATOR

20559900 CONTROL SUM 1.0 0.0 0 3 0.0 1.0

20559901 0.0 1.0 CNTRLVAR 599 ITS OWN OLD VALUE

20559902 1.0 CNTRLVAR 572 + AREA CHANGE

* BROKEN LOOP

SET UP CNTRLVAR 661 TO BE PROGRAMMED RESPONSE

20566100 PROGRAM FUNCTION 1.0 0.0 1

20566101 TIME 0 605

20566200 SETPOINT SUM 1.0 0.0 1

20566201 0.0 1.0 CNTRLVAR 85 * RELIEF SET POINT

20566202 -1.0 CNTRLVAR 661 * MINUS COOLDOWN

20566300 PROGDIF2 SUM 1.OE-7 0.0 1 * int control

20566301 0.0 1.0 P 660010000 * CURRENT VALUE

20566302 -1.0 CNTRLVAR 662 MINUS SETPOINT

20566400 DEADBN2 FUNCTION 1.0 0.0 1

20566401 CNTRLVAR 663 506 * USE DEADBAND TO REDUCE CHATTER

20566500 INTTSECI INTEGRAL 1.0 0.0 0 3 0.0 10.0

20566501 CNTRLVAR 664

20566600 CONTROL2 SUM 1.0 0.0 0 3 0.0 1.0

20566601 0.0 1.0 CNTRLVAR 664

20566602 0.1 CNTRLVAR 665

20566700 SWITCH MULT 1.0 0.0 1

20566701 CNTRLVAR 666 * SWITCH OUT WHEN OUTSIDE PROG LIMITS

20566702 CNTRLVAR 51

* THIS IS THE BASIC VALVE RATE LIMITING CONTROL SYSTEM (SMALL VALVE)

20567000 AREACHNG SUM 1.0 0.0 0 3 -1.0 1.0

20567001 0.0 1.0 CNTRLVAR 667 " DESIRED VALVE POSITION

20567002 -1.0 CNTRLVAR 699 - CURRENT VALVE POSITION

LIMITED TO < 2% IE 5OSEC
- 41.-

20567100 DA/DT DIV

20567101 CNTRLVAR 101

1.0 0.0 1 3 -0.02 0.02

CNTRLVAR 670 * AREA RATE OF CHANGE

20567200 AREALLOW MULT 1.0 0.0 1

20567201 CNTRLVAR 101 CNTRLVAR 671 * AREA CHANGE FOR THIS DT

• SG2 RELIEF VALVE OPERATION

20567900 SG1PRV2 TRIPUNIT 1.0 0.0 1

20567901 549 * OFF

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

* THIS IS THE BASIC VALVE RATE

20568000 AREACHNG SUM 1.0

20568001 0.0 1.0 CNTRLVAR

20568002 -1.0 CNTRLVAR

* LIIM

20568100 DA/DT DIV 1.0 0.

20568101 CNTRLVAR 101 CNTRL

LIMITING CONTROL SYSTEM (LARGE VALVE)

0.0 0 3 -1.0 1.0

679 * DESIRED VALVE POSITION

698 * - CURRENT VALVE POSITION

/IITED TO 2.5 SECONDS

.0 1 3 -0.4 0.4

.VAR 680 * AREA RATE OF CHANGE

20568200 AREALLOW MULT

20568201 CNTRLVAR 101

1.0 1 0.0 1

CNTRLVAR 681 * AREA CHANGE FOR THIS DT

* CONTRLVAR 698 IS LARGE VALVE STEM POSITION

20569800 CONTROL

20569801 0.0 1.0

20569802 1.0

SUM 1.0 0.0

CNTRLVAR 698

CNTRLVAR 682

0 3 0.0 1.0

* ITS OWN OLD VALUE

* + AREA CHANGE

* CONTRLVAR 699 IS SMALL VALVE STEM POSITION

20569900 CONTROL SUM 1.0 0.0 0 3 0.0 1.0

20569901 0.0 1.0 CNTRLVAR 699 * ITS OWN OLD VALUE

20569902 1.0 CNTRLVAR 672 + AREA CHANGE

* SGI MAIN FEED LEVEL CONTROLLER, INTACT LOOP

20550100 ILSGLVL SUM 1.0

20550101 0.0 1.105 VOIDF 5

20550102 1.402 VOIDF 5(

20550103 2.000 VOIDF 5

20550104 2.000 VOIDF 5

20550105 2.000 VOIDF 5

20550106 0.750 VOIDF 5!

20550200 SG1LVERR SUM 1.0

20550201 0.0 1.0 CNTRLVAR

20550202 -1.0 CNTRLVAR

20550300 FEEDFLOI SUM 1.0

20550301 0.0 1.0 MFLOWJ

20550302 2.0 CNTRLVAR

0.0

55010000

00010000

10010000

10020000

10030000

51010000

0.0

76

501

1

1

2.1 0

580000000

502

* SG2 MAIN FEED LEVEL CONTROLLER, BROKEN LOOP

20560100 BLSGLVL SUM 1.0 0.0 1

20560101 0.0 1.128 VOIDF 655010000

20560102 1.304 VOIDF 600010000

20560103 2.000 VOIDF 610010000

20560104 2.000 VOIDF 610020000

20560105 2.000 VOIDF 610030000

20560106 0.750 VOIDF 651010000

20560200 SG2LVERR SUM 1.0 0.0 1

20560201 0.0 1.0 CNTRLVAR 77
- 42 -

20560202 -1.0 CNTRLVAR 601

20560300 FEEDFLO2 SUM 1.0 0.7 0

20560301 0.0 1.0 MFLOWJ 680000000

20560302 0.667 CNTRLVAR 602

SG1 AUX FEED LEVEL CONTROL, SET TO MAINTAIN LEVEL IN DOWNCOMER

* WHICH EXISTS WHEN AUX FEED COMES ON

* FIRST ARRANGE TO STORE LAST LEVEL BEFORE AUX FEED TRIPS IN

20551000 STORE MULT 1.0 0.0 0

20551001 CNTRLVAR 59

20551002 CNTRLVAR 512 ..................... S** .* .* ......... * .... ......

20551100 LEVEL MULT 1.0 0.0 1

20551101 CNTRLVAR 58

20551102 CNTRLVAR 501

20551200 OLDLEVEL SUM 1.0 0.0 1

20551201 0.0 1.0 CNTRLVAR 510

20551202 1.0 CNTRLVAR 511

* CALCULATE LEVEL ERROR AND SET AUX FEED ACCORDINGLY

• (FULL AUX FEED FOR A LEVEL 5CMS LOW, OFF IF HIGH)

* MAX AUX FEED

20551300 AUXFEEDI SUM 2.0 0.0 0 3 0.0 0.06

20551301 0.0 1.0 CNTRLVAR 510 . note level diff not used, feed on fully when tripped

*20551302 -1.0 CNTRLVAR 501

* SG2 AUX FEED LEVEL CONTROL, SET TO MAINTAIN LEVEL IN DOWNCOMER

WHICH EXISTS WHEN AUX FEED COMES ON

* FIRST ARRANGE TO STORE LAST LEVEL BEFORE AUX FEED TRIPS IN

20561000 STORE MULT 1.0 0.0 0

20561001 CNTRLVAR 61

20561002 CNTRLVAR 612

20561100 LEVEL MULT 1.0 0.0 1

20561101 CNTRLVAR 60

20561102 CNTRLVAR 601

20561200 OLDLEVEL SUM 1.0 0.0 1

20561201 0.0 1.0 CNTRLVAR 610

20561202 1.0 CNTRLVAR 611

* CALCULATE LEVEL ERROR AND SET AUX FEED ACCORDINGLY

• (FULL AUX FEED FOR A LEVEL 5CMS LOW, OFF IF HIGH)

* MAX AUX FEED

20561300 AUXFEED1 SUM 1.0 0.0 0 3 0.0 0.021

20561301 0.0 1.0 CNTRLVAR 610 . note level diff not used, feed on fully when tripped

"20561302 -1.0 CNTRLVAR 601

PRESSURIZER LEVEL CONTROL VIA PUMP SEAL FLOW BLEED

20539000 PRELVERR SUM 1.0 0.0 1

20539001 0.0 1.0 CNTRLVAR 43 *REAL LEVEL

20539002 -1.0 CNTRLVAR 78 * - SET POINT

* SUM SEAL FLOWS FOR INTACT AND BROKEN LOOPS TO ALLOW COMPENSATION

* DURING TRANSIENT IF SPECIFIED
- 43 -

SET SCALE FACTOR TO ZERO TO TURN OFF THIS OPTION

* 1.

20539100 DRAINFLO SUM 1.0 0.0 1

20539101 0.0 1.0 MFLOWJ 124000000

20539102 1.0 MFLOWJ 224000000

PRESSURIZER CONTROL VALVE LOGIC

20549900 PORVOPEN SUM 1.0 0.0 0 3 0.0 1.0

20549901 0.0 1.0 CNTRLVAR 83
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 44 - TPRD/L/ 3209/1387

FIG. 1 LOBI-MOD2 FACILITY, PRIMARY CIRCUIT

(C)

AHS (4.11.871RL 3.52680
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 45 - TPRD/L/3209/R87

Pressurizer

S

Generator

213 F13-0 125

Break

Core

Broken Loop Intact Loop

320

FIG. 2 SIMPLIFIED NODING DIAGRAM FOR LOBI PRIMARY SIDE

Bypaos via upper head

FIG. 3 ILLUSTRATION OF BYPASS PATHS IN LOBI VESSEL

(C) AHS (4.11.87)RL 3.52581
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 46 - TPRD/L/ 3209/R87

Is. Experimental data

Relap5 Mad2 Past-test

14- Relap5 Modl Pre-test

12.

6 .

4-

2.

D 200 600 800 1000 1200 1400

Tims (sec)

FIG. 4 COMPARISON OF PRIMARY PRESSURES:

AND MOD2 WITH LOBI DATA

8.50-

RELAP5 MODI

•RELAP5

I !

1200 1400

Time (see)

FIG. 5 SECONDARY SIDE PRESSURES: POST TEST WITH DATA

(C)

AHS (4.11.87)RL3.5.2582
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 47 - ,TPRD/L/ 3209IR87

L..-.

16-n

14-

12-

I4]

2

1.a13

RELAP5

-RELAP5

Secondary

Primary

Secondary

Primary

Al

|J

-200

I I I I I -- -

0 200 400 600 800 1000 1200 1400

Time (sec)

FIG. 6 PRIMARY AND SECONDARY PRESSURES TOGETHER:

POST TEST WITH DATA

0.50

RELAP5 W002

1.0111 mensuremen t

I

0.30.

D.20-

D.,0o

-0.

0 200 400 600 B00

FIG. 7 ACCUMULATOR INJECTION COMPARISON

(C)

AHS, (4A1.S7IRL-36.26 3
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 48 - TPRD/L/3209/R87 '

LOBI data

RELAP5 MOD2 posttest

- RELAP5 MDI pretest

m

a

11

0 200 400 600 300 1000 1200 1400

Time (see)

FIG. 8 COMPARISON OF INTEGRATED BREAK FLOWS

.... RELAP5 OD2 post-test

LOBI thermocouple

-_LOBI thermocouple

•300-

280-

E

.~250-

1200 1400

Time (tic)

FIG. 9 CLAD TEMPERATURES AT TOP OF UNHEATED LENGTH

(C)

AHS (4.11.87)RL 3.5.2584
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 49 - TPRD/L/3209/R87

•- RELAP5 MOD2 post-test

MOD2 post-test .RELAP5 

--- RELAP5 MODI pretest

0 200 400 Goo 800 1000 1200 1400

Time (#at)

FIG. 10 CLAD TEMPERATURES NEAR NOZZLE ELEVATION

, 000

800,

ZIELI 1112

E

a.

400-

200-

0 200 400 600 BOO 1000 1200 1400

Time (set)

FIG. 11 DENSITIES ROUND LOOP: INTACT HOT LEG

(C)

AMS (4.11 .87) R L3.5 258 5
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 50 - TPRD/L/3209/R87

1,000-

BooLOB I

[- RELAP5 M002

.5-

ml

600-

400-

200-

0 200 400 600 ROD 1000 1200 1400

Time (sit)

FIG. 12 DENSITIES ROUND LOOP: BROKEN HOT LEG

I-,

2

5-

n.

61

0 200 400 600 g00 1000 1200 1400

Time (sic)

FIG. 13 DENSITIES ROUND LOOP: INTACT COLD LEG

(C)

AHS (4.11.87)RL 3.5.25 86
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 51 -

BOOD

E 400

- -

- 400 -l

_ A• •~g

TPRD/L/ 3209/R87

--- LOB I

1200 1400

Time (see)

FIG. 14 DENSITIES ROUND LOOP: BROKEN COLD LEG

Broken loop

Hot leg

Cold leg E3

Intact loop

Hot leg

Cold leg

FIG. 15 NODING WITH SPLIT DOWNCOMER

(C)

AHS (4.11.871RL 3.52587
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 52 - TPRD/L/ 3209/1187

S..... LOBI derived dota 1 Relap5 calculation

S.-

"1 .00*

a

L..

:0.50

a

-200 0 200 400 600 B00 1000 1200

Time (sec)

FIG. 16 BREAK FLOW COMPARISON

Strotified Conditions

0 200 40D 600 800 1000 1200 1400 1600

Tim# (3sc)

FIG. 17 DENSITIES DOWNSTREAM BL PUMP: LOBI DATA

(C)

AHS (4.11.71B L 3.52.588
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 53 - : TPRD/L/ 3209/R87

--- iameterai beam

Peripheral beamI

800-

700-

600-

Stratified Conditions

C

D 100 200 300 400 500 600 700 800

Time (sec)

FIG. 18 DENSITIES BETWEEN BREAK AND VESSEL: LOBI DATA

II

EP

48

- .v

.Broken loop

tbwIntect loop

to blow Ill sea[l

50 100 150 200 250 300

Time (sic)

350 400

FIG. 19 COLLAPSED LEVELS IN SG UP SIDES: LOBI DERIVED DATA

(C)

AHS (4.11.87)RL 3.5.2589
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 54 - TPRD/L/3209/R87

........ Collapsed level on up side of Intact Loop SC I 5.

I- Mixture level in Vessel Riser

E

7-

1000 1200 1400 1600 1800 2000 2200 2400

Time (ste)

FIG. 20 DISPOSITION OF LIQUID IN LOOP: LOBI DERIVED DATA

40-

= F

-20-

" 10-

0

S0.

-20-

aw +ve and decreasing

Flow direction indicator

- Temperature at tube bottom (Offset)

Flow stagnant

I It

I" J , -

FIlow reversal 'I

a'

'I

-- _1 lJ

I I I I I I I I

0 50 100 150 200 250 300 350 400

Time (sle)

FIG. 21 CONDITION IN BROKEN LOOP HOT LEG: LOBI DATA

(C)

AHS (4.11.87)RL 3.5.2590
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 55 - TPRD/L/3 209/RS7

-- RLAP5

0.070-

0.060-

0.

0 50 100 150 200 250 300 350 400 450 500

Time (ooc)

FIG. 22 DIFFERENTIAL PRESSURE UP SIDE IL SG

RELAP5

LOB I

0.

- 0. 040

CL

D.020-

0 50 100 150 200 250 300 350 400 450 500

Time (esc)

FIG. 23 DIFFERENTIAL PRESSURE UPSIDE BL SG

(c)

AHS (4.11 W7)RL 3.52691
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 56 -

.

2IO-

-2-

E -4

-- 4

*

TPRD/L/ 3209/R87

-- LORI Djensity

--- LOI Mixture level

- RELAP5 Mixture level

-1

100 150 200 250 300 350 400 450 500

Time (usc)

FIG. 24 RISER MIXTURE LEVEL AND HOT LEG DENSITY

E

-0.002

•- -0.20-

100 150 200 250 300 350 400 450 500

Time (sac)

FIG. 25 SUPERFICIAL VELOCITIES IN INTACT LOOP HOT LEG:

RELAP5 PROCESSED RESULTS

(C)

AHS (4.11.87)RL3.5.2592
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 57 -

0.40- ',,

Go

S0.20- I

•-~n in- b•neL•

TPRD/L/3209/R87

100 150 20D 250 300 350 400 450 500

Tim, [lot)

FIG. 26 SUPERFICIAL VELOCITIES IN BROKEN LOOP HOT LEG:

RELAPSPROCESSED RESULTS

In SC 'U' tubes

In vertical entry to SC

100 150 200 250 300 350 400

Time (wee)

FIG. 27 COUNTER CURRENT FLOODING LIMIT FOR INTACT LOOP:

RELAP5 PROCESSED RESULTS

(C)

AHS (4.11.87)R L 3.5.2593
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 58 - TPRD/L/ 3209/R87

Typical flooding limit

to SC

FIG. 28 COUNTER CURRENT FLOODING IN BROKEN LOOP HOT LEG:

RELAP5PROCESSED RESULTS

Mixture level In riser

Departure from caturatli

10D 

0- --- "C

= I gI

- Is

Time (seec)

FIG. 29 RELATION BETWEEN TEMPERATURE EXCURSION AND LEVEL:

LOBI DATA

(C)

AHS (4.11.87) R L3.5 2694
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 59 - TPRD/L/3209/R87

I --- RELAP5 MOD2 post-test

- LO09 derived data

Iv I I

II I II I I I I

10D 200 3D0 400 50D 600 70D 800 900 1000

Time (tee)

FIG.30 COMPARISON OF MIXTURE LEVELS IN VESSEL RISER

-- RELAP5 MOD2 post-teslt

1.0000-

1.011BI measurement

-0.0050-I

0 100 200 300 400 5;0 6;0 700 800 000 1000

Time (sec)

FIG. 31 DIFFERENTIAL PRESSURE OVER INTACT LOOP

(C)

AHS (4.11.87)RL 3.525 95
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 60 - TPRD/L/ 3209/R87

1.00-

[.ELAP5 U002

0.80-

0..

>'0.40-

'II *s* B 

'J-uu- - I

100 200 300 400 50D 600 70D 800 900 1000

Time (soe)

FIG. 32 VOIDAGE IN UPPER PLENUM REGION

I

0.80.

0. a.

a•

"a

0

0

FIG. 33 VOIDAGE IN RISER JUST BELOW NOZZLE ELEVATIONS

(c)

AHS (4.11 .87) R L3.5 2596
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 61 - TPRD/L/ 3209/1487

--- 0.40-

'-'-0 50-

100 200 300 400 5D0 600 700 800 " ODD 100D

Time (sec)

FIG. 34 RELATION BETWEEN MIXTURE LEVEL AND LOOP DP:

LOBI DATA

10D 200 300 400 50D 600 700 800 900 1000

Time (see)

FIG. 35 RELATION BETWEEN MIXTURE LEVEL AND LOOP DP:

RELARI RESULTS

(c)

AHS (4.11.87)R L 3.5.2597
CENTRAL ELECTRICITY RESEARCH LABORATORIES - 62 - TPRD/L/ 3209/R87

100 200 300 400 500 500 700 800 900 0DD0 1100 1200

Time (eIC)

FIG. 36 LOBI DOWNCOMER VOIDAGE, RISER LEVEL AND LOOP DP

....... Downcomer voidage

--- Riser mixture level

- Loop Delta-P

S,.

0 100 200 300 400 500 a00 700 ODD o00 1000 1100 1200

Time (see)

FIG. 37 DOWNCOMER VOIDAGE, RISER LEVEL AND LOOP DP:

RELAP5 RESULTS

(c)

AHS (4.11.87)RL 3.5.2598
- 63 -

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NRC FORM 335 U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

(2-89) (Avauned by NRC. Add Vol., Supp., Rev., NRCM 1102, and Addendum Numbers, If any.)

3201.3202 BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse) NUREG/IA-0036

2. TITLE AND SUBTITLE TPRD/L/3209/R87

Analysis of LOBI Test BL02 (Three Percent Cold Leg Break) PWR/HTWG/P(87)496

With RELAP5 Code 3. DATE REPORT PUBLISHED

MONTH YEAR

March 1992

4. FIN OR GRANT NUMBER

A4682

5. AUTHOR(S) 6. TYPE OF REPORT

A.H. Scriven

7. PERIOD COVERED (Inclusive Dares)

8. PERFORMING ORGANIZATION - NAME AND ADDRESS If NRC, provide Division, Office or Region, U.$. Nuclear Regulatory Commission, and mailing aNddress; Hf contractor, provide

name and mailing address)

Central Electricity Generating Board

Technology Planning and Research Division

Central Electricity Research Laboratories

Kelvin Avenue

.eaShOrIOead 'lT nj . I ingdmnSurrey KT2275E

9. SPONSORING ORGANIZATION - NAME AND ADDRESS If NRC, typ °Smi as above"; if contractro, prov~de NRC Divsin, Offie or Region, U.S Nuckar Regulatory Commisson,

and mailing addres&l

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or kl)

The test BL02 was a United Kingdom specified test conducted on the electrically

heated 2-loop test system at Ispra, North Italy, as part of the LOBI 'B' series

of tests sponsored by the Joint European Research Commission.

The pretest calculations for this test were performed with the RELAP5/MOD1 code and

the post-test analysis was carried out using RELAP5/MOD2. Comparisons between the

code predictions and the test data are given, and for the case of the post-test MOD2

calculation, detailed studies of the codes performance in a number of areas are

included.

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

ICAP Program Unlimited

RELAP5/MOD1 Code 14. SECURITY CLASSIF•I•CATION

RELAP5/MOD2 Ithis Page)

BL02 Experiment Unclassified

LOB I(This Repo-,

Uncl assi fied

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (2-89)


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