NUREG/IA-0 120

- -. EST-SIJAN-22

.International

Agreement Report

Assessment of the Turbine

Trip Transient in Cofrentes

NPP with TRAC-BFl

Prepared by

F. Castrillo/Hidroelectrica Espanola (H.E.)

A. Gomez/Union Iberoamericana De Tecnologia (UTTESA)

1. Gallego/Union Iberoamericana De Tecnologia (UTTESA)

Unidad Electrica, S.A.

c/Francisco Gervas, 3

28020-Madrid, Spain

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

June 1993

Prcparcd as part of

The Agreement on Research Participation and Technical Exchange

under the International Thermal-Hydraulic Code Assessment

and Application Program (ICAP)

Published by

U.S. Nuclear Regulatory Commission
NOTICE

This report was prepared under an international cooperative

agreement for the exchange of technical information. Neither

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

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

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

use, or the results of such use, of any information, apparatus product or process disclosed in this report, or represents that its use

by such third party would not infringe privately owned rights.

Available from

Superintendent of Documents

U.S. Government Printing Office

P.O. Box 37082

Washington, D.C. 20013-7082

and

National Technical Information Service

Springfield, VA 22161
NUREG/IA-O 120

International ETS~2

Agreement Report

Assessment of the Turbine

Trip Transient in Cofrentes

NPP with TRAC-BFl

Prepared by

F. Castrillo/Hidroelectrica Espanola (H.E.)

A. GornezfUnion lberoamnericana De Tecnologia (UITESA)

1. Gallego/Union lberoamnericana De Tecnologia (UITESA)

Unidad Electrica, S.A.

c/Francisco Gervas, 3

28020-Madrid, Spain

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

June 1993

Prepared as part of

The Agreement on Research Participation and Technical Exchange

under the International Thermal-Hlydraulic Code Assessment

and Application Program (ICAI')

Published by

U.S. Nuclear Regulatory Commission
NOTICE

This report documents work performed under the sponsorship of the Consejo De

Seguridad Nuclear of Spain. The information in this report has been provided

to the USNRC under the terms of an information exchange agreement between the

United States and Spain (Technical Exchange and Cooperation Agreement Between

the United States Nuclear Regulatory Commission and the Consejo De Seguridad

Nuclear of Spain in the field of reactor safety research and development,

November 1985). Spain has consented to the publication of this report as a

USNRC document in order that it may receive the widest possible circulation

among the reactor safety community. Neither the United States Government nor

Spain 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.
FO0R E WOR 0

This report has been prepared by Hi droel ~ctri ca Espafiol a

in the framework of the ICAP-UNESA Project.

The report represents one of the application calculations

submitted in fulfilment of the bilateral agreement for cooperation in thermal hydraulic activities between the Consejo

de Seguridad Nuclear of Spain *(CSN) and the United States

Nuclear Regulatory Commission (USNRC) in the form of Spanish

contribution to the International Code Assessment and Applications Program (ICAP) of the USNRC whose main purpose is

the validation of the TRAC and RELAP system codes.

The Consejo de Seguridad Nuclear has promoted a coordinated Spanish Nuclear Industry effort (ICAP-SPAIN) aiming to

satisfy the requirements of this agreement and to improve

the quality of the technical support groups at the Spanish

Utilities, Spanish Research Establishments, Regula'tory Staff

and Engineering Companies, for safety purposes.

This ICAP-SPAIN national program includes agreements

between CSN and each of the following organizations:

- Unidad E15ctrica (UNESA)

- Uni6n Iberoamericana de Tecnologia El~ctrica (UITESA)

- Empresa Nacional del Uranio (ENUSA)

- TECNATOM

- Empresarios Agrupados

- LOFT-ESPARA

The program is executed by 12 working groups and a generic code review group and is coordinated by the "Comit'6 de

Coordinaci6n'. This committee has approved the distribution

of this document for ICAP purposes.

D -1/90- MP N V iii

TABLE OF CONTENTS Page

1.- INTRODUCTION 1-1

2.- PLANT DESCRIPTION 2-1

3.- TEST DESCRIPTION 3-1

4.- CODE INPUT MODEL DESCRIPTION 4-1

4.1.- Vessel 4-1

4.2.- Recirculation system 4-2

4.3.- Main Steam Lines4-

4 .4.- Fuel elements 4-4

4.5.- Core power and Reactivity Feedback 4-4

4.6.- Control systems and trips 4-4

5.- STEADY STATE 5-1

6.- TRANSIENT RESULTS AND COMPARISON WITH PLANT MEASUREMENTS 6-1

7.- RUN STATISTICS 7-1

8.- CONCLUSIONS 8-1

V
F IGURES

Page

3.1.- Measured power (APRM) 3-2

3.2.- Measured dome pressure 3-3

3.3.- Measured pressure at steam collector 3-4

3.4.- Measured steam flow 3-5

3.5.- Measured vessel level 3-6

3.6.- Measured feed water flow 3-.7

3.7.- Measured core flow 3-8

3.8.- Measured Recirculation flow3-

3.9.- Measured Recirculation pump speed 3-10

3.10.- Measured bypass valve position 3-11

3.11.- Measured Recirculation FCV position 3-12

4.1.- C.N. Cofrentes model for TRAC-BF1 4-7

4.2.- Core channels distribution 4-8

4.3.'- Pressure control system4-

4.4.- Feedwater control system 4-10

4.5.- Recirculation control system 4-11

6.1.- Power (APRM) 6-6

6.2.- Dome pressure 6-7

6.3.- Pressure at steam collector 6-8

6.4.- Steam flow 6-9

6.5.- Vessel sensed level 6-10

6.6.- Feed water flow 6-11

6.7.- Core flow 6-12

6.8.- Recirculation flow 6-13

6.9.- Recirculation pump speed 6-14

6.10.- Level Setpoint 6-15

6.11.- Bypass valve position 6-16

6.12.- Recirculation FCV position 6-17

6.13.- Dome pressure 6-18

6.14.- Sensed level 6-19

6.15.- Dome pressure (sensitivity to Hgap) 6-20

6.16.- Dome pressure (sensitivity to DHMUL) 6-21

vi
Page

6.17.- Vessel level 6 void fractions 6-22

6.18.- Sensed level (sensitivity to vol. fraction) 6-23

6.19.- Level Setpoint (sensitivity to vol. fraction) 6-24

6.20.- Feedwater flow (sensitivity to vol. fraction) 6-25

7.1.- Ratio (CPU time/transien time) vs. transient time 7-2

TABLES

5.1.- Reference Steady State conditi on. 5-2

6.1.- Steady State conditions at transient initiation 6-4

6.2.- Sequence of events 6-5

vii

EXECUTIVE SUMMARY. -

This report presents the results of the assessment of TRAC-BF1 (G1-41) code with the model of C.N. Cofrentes for

simulation of the transient originated by the manual trip of the

main turbine.

C.N. Cofrentes is a General Electric designed BWR/6 plant, with a

nominal core thermal power of 2894 Mwt, in comertial operation since

1985, owned and operated by Hidroelectrica Espafiola S.A. The plant

incorporates all the characteristics of BWR/6 reactors, with two

turbine driven FW pumps

The objective of this assessment is to generate a Cofrentes model

for TRAC-BF1 and compare code results with plant recorded data

during the start-up test transient of "manual turbine trip" with the

plant at 70% thermal power.

The model has been developped from plant drawings and documentation,

and a documented and validated RETRAN model.

Principal characteristics of the model include a 4 rings-8 levels

vessel, two recirculation loops and one representative steam line;

control systems and trips were also modelled.

A reference/nominal steady state situation was then adjusted by

connecting submodels of portions of the system (vessel,

recirculation loops, steam lines) previously tunned to the desired

conditions. In the same way separated models for each of the

control systems (feedwater/level, recirculation, pressure) were

devel opped.

The point kinetic option was selected for core neutronic feedback,

as considered adequate enough for this kind of mild operational

transients. Reactivity coefficients were obtained from

perturbations on the 3D simulator, around the initial steady state

situation.

i x
The transient selected to be reproduced with TRAC-BF1 was the "MA-.

NUAL TURBINE TRIP" start-up test.

Simulation of this operational transient with TRAC-BF1 will

contribute to the assessment of the performance of the code/model

features related to dynamic level tracking, recirculation and jet

pumps performance in normal operating conditions, and check models

generated for the control systems

A 45 seconds transient was run, this time including all the

important phenomena occurring in the system. The transient was

initiated by the closure of the turbine stop valves, which

originates the reactor trip and a rapid increase of the system

pressure, further relieved by steam discharge to the main condenser

through the bypass valves.

Some adjustment was made on the residual heat to be able to

reproduce reactor pressure, taking into account that this test was

performed in the early portion of first cycle.

Sinsed level was the most critical plant variable to reproduce.

Based on sensitivity analysis, volume and area fractions in the

vessel model corresponding to the separator region, were tunned, as

well as the pressure loss coefficient for the dryer, to get a better

simulation of level behaviour

The rest of variables measured were accurately reproduced by the

code.

As a result of this assessment a model of C.N. Cofrentes has been

developped for TRAC-BF1 that fairly reproduces operational transient

behaviour of the plant. A special purpose code was generated to

obtain reactivity coefficients, as required by TRAC-BF1, from the 3D

simulator.

x
1.- INTRODUCTION

Hidroelectrica Espafiola (HE) joined ICAP as a member of the UNESA

group in order to simulate two transients of C.N.Cofrentes with

TRAC-BF1 code and compare simulation results with data recorded at

the plant.

The code information package, including tape with source program of

GiJi version, was received and implemented on a SIEMENS 7590-F

computer. Some adaptation was needed on the source received (CDC

version) to make it compilable; test cases were run, with results

slightly different to those provided as reference in some of them.

Later, on August 1989, the IBM version, as converted by Pennsylvania

State University, was released to HE representatives by INEL.

Implementation of this version is currently in progress.

Due to the above mentioned problems, the model and cases described

in this report were developed using the TRAC-BF1 GiJi version

implemented in a CONVEX computer owned by VITESA. This version has

been vectorized using the proper option during the code compilation,

achieving a reduction in the CPU time consumption of about 70%. The

graphics option has been implemented for this computer and an

interactive graphic system has been developped as a user friendly

tool to plot output data

1-1

2.- PLANT DESCRIPTION

Cofrentes Nuclear Power Plant, ownwed and operated by Hidroel~ctrica

Espafiola S.A., has a BWR/6 reactor (Mark III containment), designed

by General Electric, with a rated thermal power of 2894 Mwt.

Located 50 Km from Valencia (Spain), Cofrentes comertial operation

started in 1985 and is presently running its sixth cycle.

Design features of the Nuclear Steam Supply System (NSSS) include

two loop recirculation system, driven by two centrifugal pumps,

feeding a total of 20 jet pumps, with a flow control valve in each

loop. Feed-water is supplied by two turbine-driven pumps. Four

main steam lines supply the main turbine with the steam generated in

the reactor, each line equipped with isolation valves (MSIV),

safety/relief valves (SRV) and turbine stop and control valves (TSV

and TCV). Six bypass valves blowdown steam to the condenser from a

common header connected to the four steam lines, with a nominal

capacity of 35% rated steam flow.

The core consists of 624 fuel elements (8x8)*with an active length

of 150 in. and 145 control rods. Core power is monitored by 33

vertical strings, each holding 4 Local Power Range Monitors (LPRM),

arranged in a uniform pattern throughout the core, these sensors are

ion chambers wich measure local neutron flux. Four Average Power

Range Monitors (APRM) measure bulk power, each one averaging 24 LPRM

signals. APRM are calibrated based on a reactor thermal balance.

NSSS instrumentation of interest for the transients analized in this

report and related to the Control systems and Reactor Protection

System (RPS) are briefly described: Dp transducers are used to

measure flow in the recirculation, steam and feedwater lines; water

level in the vessel downcomer is also measured by a Dp transducer,

pressure signals are avaliable from sensors located in the steam

dome and in the averaging manifold in steam lines at the entrance of

TSV' s

21-1
During start-up tests a special program for collecting plant signals

was carried out. Prior to each significant transient test, a set of

signals considered relevant for later analysis and simulation of the

transient was defined. The Emergency Response and Information

System (ERIS) was used as Data Adquisition System for sampling and

recording selected signals.

2-2
3.- TEST DESCRIPTION.-

This transient, identified as Start-up test PPN-27/2B, was carried

out on December 1984 with the plant operating at 71% thermal power

and 94.5% core flow

The transient was initiated by manual trip of the main turbine,

i.e.: closure of stop valves; signal from position switches on this

valves produces reactor scram and recirculation pumps transfer to

low speed (25% of nominal).

Pressure increase, due to the fast turbine valves closure, is sensed

by the pressure control system and bypass valves are opened

discharging steam to the condenser. None of the relief valves did

open as their setpoints were not reached

When steam flow though the main lines reduces below 35% a low steam

flow signal is generated wich trips one of the two feedwater pumps.

Core void content is reduced, due to initial presurization, and

level drops reaching low level alarm (L4), then the Recirculation

runback logic is activated and flow control valve closes to 26% open

position. Feedwater control system speed-up the remaining pump

which is later lost due to the shutoff of steam to the pump turbine.

Figures 3.1 to 3.12 present plots of measured variables for the 40

seconds of interest, including 2 seconds previous to the initiation

of the transient.

3-1
MEASURED POWER (APRM)

900.. .. .. . . . . ....... ... ..... J...L.... . . . .

g0 . . .. . . . .. . . . .

70

3,o 0 ... .... ....... ........... ....... .......... . .* .*

40 .. . . . . . . .. . . .. .. .. . .. . . . .

20 ......... 1-........ * * * * ....... 

0

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 4

10 ~ S ~ ~ S ~ S S ~ S ~ S ~ - * S ~ * ~ S TM s. S S S S S

TIMUE 3.1
MEASURED DOME PRESURE

t~j

tAJ

7200000 -

7100000 -

7000000 -

6900000 -

6800000 -

Pa. 6700000 -

6600000

6500000 -

6400000 -

6300000 -

6200000

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

. . . . .. . . . .. 

* C C C C C C C . C.. .C.C.. . .C.. .C.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIME s.

FIGURE 3.2
MEASURED PRESSURE AT STEAM COLECTOR

7200000 -

7100000 -

7000000 -

6900000

6800000 -

Pa 6700000 -

6600000 -

6500000 -

6400000 -

6300000 -

ngnnnnn -

* * * * * * * * * * * * , * * * * .

* * * * * * * * * * * * * * * * * * * * *

* * S S * * S * S S S S S S S S S S S S S S S

S....S...........5.....5.....5.........5

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S * S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

* ~S....S S *S....S S S S S S ~S..............

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

S S S S S S S S S S S S S S S S S S S S S S S

S S S S S S S S S S S S S S S S S S S S S S S

I I -- ~ ______ I I ~ I I ______ I I I _______I ______________ I ______ ~ ~ I I I I

I I I I I I I I I S S I S S S S I S S

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 410 42 44 '16

TIME s.

FIGURE 3.3
MEASU1RED STEAM FLOW

L.i

U'

1100

1000

900

600 -

700 -~

600 -

Kg/s

500 -

400 -

300 -

200 -

100 -

An

* ~ ~~ . . . . . . . . . . . .

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

*~~~~. . . . . . p . .

p . .

p.

* p p p p p p p p p.p.p p.p.p..p.p.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 38 38 40 42 44 46

TIME s.

FIGURE 3.4
MEASUEDWAERLVEL

M

0.9 . .. .. . . .

0.8 .. . . . . . . ......

0.7 . . ........-

0. 2 . . 6. 10 12 14 16 18 20 22 . 24. 26 .. 28 . 30 32 34 36 38 40 42 44 46 

0.5 ..... ..~~~~~~~~IM .. .. .... ......... ............

0.4 .. .. ...... .FIGUR . 3.5........ . .
MEASURED WATER FLOW

13

1200-

1100

1000

900-

800

700-

Kg/s 600-

500-

400-

300-

200-

100

A

. . . . . .............. U...... . . .............. . ........ .. . ...---------------. .

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

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

U

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIME s.

FIGURE 3.6
MEASURED CORE FLOW (1/2)

tco

5400-

4800-

4200

3600-

3000

Kg/s

2400

1800

1200

600

* , * * * * * * * * * * * * * * * , , * *

* * * * * * * * * * * , * * * , * , * *

* * * * * , * , * * * * * * * * * *

* * * , * * * , * * * , * * , * * * *

* * * * , * * , * , * * , * * * * , , *

* * * * * * * * * * * , * * * * * * * , *

* * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * , * * * * S S

* S S * S S S S S * S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

-. -A...,. - ~S......S....S....S....a.......................

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

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

* S 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S..................................S S

* S S S S S S S S S S S S S S S S S S 5 5 5 5

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

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S 5 5 5

* 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

~ I ~ ____ I ~ ____ I I ~ I ~ ~ I - I I I I I I I

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIME s.

FIGURE 3.7
MEASURED RECIRCULATION FLOW (I LOOP)

1500 -

1200 -

900 -

Kgfs

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

* * * * * * * * * * * * * * * * * * * * * * *

* * * S S S S S S S S S S S S S S S S S S S S

S S S S * S S S S S S S S S S S S S S S S S

* S I S S S S S I S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S * S S S S

* S S S S S S S S S S S S S S S S S * S

* S S S S * S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S * S S

* S S S S S S S S S S S S * S S I S S S

* S S * S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S * S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S

* S S S S S S S * S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S * S S S S S S S S S S S S S S

* S S S S S S S * S S S S S S S * S S * S

* S S S * S S S S S S S * S S S S S S

* S S S S S S S S S * S S S S S S S

I I I I I I I I I I I I I I I I I I I I I I I

600 -

300 -

0 * I I I I I I I I I i I I I I I I I I I I I I I

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 416

TIME s.

FIGURE 3.8
MEASURED RECIOCULATION PUMP SPEED

160

140-

120

100-

0 radls 80 -

60 -

40-

20

0~

S

. . . ft ft . . ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

I.............I - ft ft

* ft ft ft ft ft ft ft f * ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft * ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft . ft....................................ft

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

* ft ft ft ft ft ft ft ft ft ft ft ft ft f

ft ft ft ft ft ft ft ft ft ft ft ft ft ft f

______ I - ___ I I I ~ I I I I I I r z r r r r r 1 r r r ft ft ft ft ft ft ft ft ft I ft ft ft

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIME s.

FIGURE 3.9
MEASURED BYPASS VALVE POSITION

100 . .. . . .. . . .. . . . . . . . .. . . . .

90-....... .................... .*....... ...... .... .. : .. :. . . . . . . . .

7 0 . . . . . . . . . . .

50 . .. a a

2 . .... . . ..........

1 0 a a . .a . . . . a . . a . . . a a .a a a a 

* 0

1a a a aa0a a

0 6 a a a a0 a2 a4 20 a6 a8 a2 28 a4 a6 34 a0 a2 38 40 a6 42 44 4

a ~ ~ ~ ~ ~ ~ ~ ~ a ~ TM a as. a a a a a

20-....................................... 3 .10 .. :.............
MEAWHIED RECIRCULATION FCV POSITION

60 -

50

(fi 40 -

30 -

20

.................. . t. . S.....................

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

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

* . * . * * * * * S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S ~S S S S S S S S S S S 5 5 5 5 5 5 5 5

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S* S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S * S S S S S S S S S S S S S S S

* S S S S S S S S S S 5 5 5 5 5 5 5 5 5 5 5 5

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S

I

* S S S S S S S S S S S * S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S i _______i ______ t a ______ a a A ______ I I 1 1 .1 1 I_______ I u -- ~a a - * a * * S S S S S

0 *2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 '10 42 44 '16

TIME s.

FIGURE 3.11
4.- MODEL DESCRIPTION.-

Figure 4.1 shows the Cofrentes model which includes reactor vessel

and core, recirculation loops, steam lines from vessel to turbine

valves, and control systems. Input data were mainly obtained from a

documented RETRAN model.

The main components of the model are discussed in the following

sections.

4.1.- VESSEL.-

Using the VESSEL component of TRAC-BF1, 4 rings and 8 axial levels

were considered to model the reactor vessel. The three inner rings

represent the volume inside the core shroud, with the core in levels

3 and 4, and the outer ring models the downcomer. As illustrated in

Figure 4.1, levels 1 and 2 represent the core inlet plenum, with jet

pumps discharge located in bottom of level 2 (ring 4); core exit

plenum is represented by level 5 (rings 1,2,3).

For the type of transient being analized, it would be enough one

single ring to model the core region, with one average bundle (CHAN

component) to represent the fuel elements. However, three rings

were considered to allow for future accident analysis (LOCA, ATWS),

in which upper plenum 2D/30 effects, when spray is activated, are

important to simulate the distribution of coolant over the fuel

bundles.

The 624 fuel elements have been divided into three groups:

high power

average power

low power (including peripheral elements)

connected to the lower and upper plenum in each core ring, as

illustrated in Figure 4.2.

4-1
No metal structures were modeled as the time of interest in the

transients to be analized is relatively small (150 sec. maximum),

and temperature change in the vessel is not relevant

Separators and dryer are modelled in the axial level 6 using the

perfect Separator option, after some failed attempts to use the

mechanistic model; stand pipes are also included in this level.

Vessel connections to other components include feedwater inlet,

modelled as a fill, governed by the level control system,

discharging in the downcomer via a leak path (level 5, ring 4).

Steam outlet is located in level 7, ring 4. Outlets to

Recirculation loops from lower downcomer *are located in level 2

(ring 4). Recirculation flow mixes in the jet pump (component

external to vessel) with driven flow from downcomer level 4, to

discharge into lower plenum.

Channel components representing fuel bundles are connected to lower

and upper plena, with leakage flow discharging to the bypass flow

region (levels 3-4, rings 1-2-3)

ECCS injections have been also modelled, using the leak path

feature, although they are not used in the transient.

4.2.- RECIRCULATION SYSTEM.-

Both Recirculation loops have been

modelled, each being divided into three components:

- PUMP 11-21, representing the suction pipe, from vessel

downcomer, and centrifugal pump

- VALVE 12-22, representing the flow control valve and

discharge pipe up to jet pump inlet

- JETP 15-25, modelling the 10 jet pumps connected to each

loop.

4-2
Pump transfer to low speed has been modelled with control blocks and

trips, that switch from normal to low speed motor pump torque curves

based on pump speed response.

Flow control valve area is defined by the Recirculation control

system.

Recirculation discharge piping consists of one main raiser that

divides into ten branches to feed the corresponding jet pumps; these

branches have been lumped into one single line, on the basis of

maintaining steady state pressure drop.

The JETP component of TRAC-EFi has been used to model the 10 jet

pumps connected to each loop.

4.3.- MAIN STEAM LINES.-

One single equivalent line has been used to

model the four parallel steam pipes, with 5 main components:

- TEE 80, models pipes from vessel exit to MSIVs, relief valves

are connected to this component aithoug not actuated during

the transient

- VALVE 81, represents MSIVs and associated pipe

- TEE 82 represents pipes from MSIVs to turbine control/stop

valves, and branching to bypass valves that discharge to main

condenser.

- Turbine control and stop valves, modelled by VALVE 83, with

position governed by pressure control system; they discharge

to BREAK 92, which represents pressure boundary condition at

turbine inlet.

- Bypass valves are modelled by VALVE 70 with boundary

condition represented by BREAK 73

4-3
4.4.- FUEL ELEMENTS.-

The 624 fuel elements of the core have been divided into three

groups (Figure 4.2), corresponding to the three inner rings of the

vessel model:

80 central high power

436 central average power

108 peripheral low power

The CHAN component of TRAC-BF1 has been used to model the

characteristics of the fuel bundles. 11 axial nodes have been

selected, with active length between nodes 3 to 10, and one group to

represent the 8x8 fuel rods

Leakage flow to the bypass region surrounding fuel channels has been

considered by means of a leak path from the second axial node of the

channels to vessel level 3.

4.5.- CORE POWER AND REACTIVITY FEEDBACK.-

Reactivity feedback has been modelled using the point kinetic

option, with void and Doppler coefficients and scram curve obtained

from perturbations on the 3D simulator (SIMULATE-2), performed

around the steady state situation of the core

A common axial power distribution is defined for the three types of

fuel channel/bundles modelled.

4.6.- CONTROL SYSTEMS AND TRIPS.-

The three control systems typical of boiling water reactors are

included in the model, as well as trips associated to Reactor

Protection System and other automatic actions.

4,.4
4.6.1.- Pressure control system.-

This system governs turbine and

bypass steam flow, as a function of pressure upstream turbine

control valve.

Figure 4.3 illustrates the scheme of the model developped. Special

attention was paid to the proper representation of turbine control

valve characteristic, to reproduce actual behaviour in terms of

steam flow versus position

Bypass system performance has been modelled including adjustment of

flow to the condenser, via flow restrictor characteristics, and

logic to simulate fast opening of the valves

4.6.2.- Feedwater control system.-

Based on a level error signal and

mismatch between steam and feedwater flows, this system controls the

amount of feedwater entering the vessel.

Downcomer water level, as computed by TRAC, is corrected based on

dryer pressure drop, to obtain downcomer water level as measured in

the plant. Sensors and controllers are modelled by available

control blocks following the actual system design (Figure 4.4). A

special logic was developped to reproduce coastdown of one pump and

to obtain a smooth transition on total feedwater flow when the

remaining available pump speeds-up in response to controller demand.

4.6.3.- Recirculation flow control system.-

As the plant is operated

in manual mode, only the portion of the system representing this

function has been considered.

The output of the system determines Recirculation control valve

position, which has been translated into valve area by a separate

calculation, using a specific model of the valve to reproduce the Cv

4-5
versus position curve as given by the manufacturer.

One of the objectives of the test analyzed in this report was to

verify the behaviour of the recirculation runback. A logic has been

incorporated to the model that switches the manual valve position

demand to a fixed position (26% open) corresponding to a core flow

demand of 53.15% when low level alarm is detected, provided one

feedwater pump is tripped (Figure 4.5).

4-6
FIGURE 4.1.- C.N. COFRENTES MODEL FOR TRAC-BFI

I I I

IIOR / SPARAFORS

I I I I I

I- -i .- - - -- - -

10

F7

I PPPER1 PLENVM

12 I.J.JJw tu~ta I

K' I

so EllI

LOWE1 PLNU

a--

r-- - <a FEED WATER

oe - r -- <RKLPCI

-- <ELPCS

fit

@ FCV

RECIRCULATICN

LOWf

4-7
FIGURE 4.2.- CORE CHANNELS DISTRIBUTION

RING

RING

RING

RING

HIGH POWER

*AVERAGE POWER

13 LOW POWER (PERIPHERALS)

4-8
FIGURE 4.3. PRESSURE CONTROL SYSTEM

TUIRDINE CONTROL VALVES

PISs. Surawi.

IYrASS CON4TROL VALVC

-~1{~44

-ft "W"

I.Wij -1,1 I
FIGURE 4.4. LEVEI./FW. CONTROL SYSTEM

WIV 'n4 l 3 INSW

-

1 'CO F4ICEF S- I70H 6 -47riNjT -. M18FNGt

I ~IE 3f 4 4 j '. L ....J T hF" "

~ 56 ~.............C. .... AD.

-7-61SENSED LEVEL

SENSE SI . LOSIRA S

Ic 3

BA.13s 

Iv 5fP 

I

6 0

1N01 DO IfT 

T a

I LAGL 60MI.OG1 58 1 TR 6

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

... ......

MASTLR LEVEL LUNIRUL

_1 ýo (Týl P ý31G -14FNG TAILA 4ý4

.';Iwsu 161NSW Nu

-IN T-M

7RI 15

-'PW'U 

'61

R1

IfTN G DFH MAN/Atan

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

FNG1

.FN G I --- A 6 IL6 (I PUUP TRP)

DISP I THA

(q::A AIJ

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

:Tfflýjjj 

I ... "I'll, ---- *------"*",--*** .....

[!6!6U!t)Lg 5pmu 33ý-Rý-jyH--G. ýj

.- FWýNGIL FFSOTFý -. FYIAG . ..... [I ý _._I

I I TAKA 5

64mci PRESION 

RCSZIIL

Lt&A 

Jml, mi

J2 ....... P . .. ...................

crpq (per %) PRES WHO 54rNrt fTo-ri-TTL

(I PtJUP IFIC)

DISP I IRRA
FIGURE 4.5. RECIRCULATION CONTROL SYSTEM

VALVULA A

VALVULA B

5.- STEADY STATE.-

A nominal steady state of the system (Table 5.1) was defined as a

reference or base line condition

Flow split to the three modelled channels and bypass were calculated

by a steady state analysis of the core with FIBWR code.

To adjust a steady state situation, with TRAC-BF1, for a model as

that described for Cofrentes, is a hard task to perform if one has

to deal with the whole system and too many variables and parameters

to control. The approach followed was to adjust separately pieces

or submodels with the proper boundary conditions, and assemble them

one by one to build up the entire model.

Partial models were adjusted for channel, jet pumps, steam lines,

recirculation loop, vessel and each of the control system

Tole final steady state reached is presented in Table 5.1 for the

most significant variables, wher~e comparison with target values is

also included.

A null-transient, from the steady-state reached, was run, with the

reactivity feedback mechanism activated, to verify stability of

steady state conditions.

5-1
Table 5.1.- Reference Steady State condition

Variable Reference TRAC

Core flow (Kg/s) 10646 10642

Recirculation flow, 1 loop (Kg/s) 1550 1550

Steam flow (Kg/s) 1569 1565

Feedwater flow (Kg/s) 1569 1565

Dome pressure (Pa) 7.17E6 7.17E6

Steam collector pressure (Pa) 6.765E6 6.764E6

Water level, from downc. bottom (in) 10.71 10.71

Core support plate pres. drop (Pa) 0.17E6 0.169E6

Core bypass flow (Kg/s) 1127.5 1129

5-2
6.- TRANSIENT RESULTS AND COMPARISON WITH PLANT MEASUREMENTS.-

The initial conditions prior to initiation of the transient, as

measured in the plant on December the 18th, 1984, are presented in

Table 6.1

From the reference steady state, the model was conducted to a new

one corresponding to the above conditions, by adjusting the

necessary control systems setpoints, and letting it run as a null

transient to verify stability. Using the EXTRACT feature of TRAC,

the model input file was updated to the test initial condition.

Table 6.1 shows initial conditions of the model prior' to initiation

of the transient

Figures 6.1 to 6.12 show plots comparison of calculated and measured

values for the most relevant variables; all plots include 2 secs. of

steady state previous to the initiation of the transient.

The computed results presented were obtained after several adjustments based on the conclusions drawn from sentitivity studies

described below.

The sequence and timing of relevant events is presented in Fig 6.2

In the first run of this transient there were two of the variables

that didn't agree with measurements.

The evolution of pressure in reactor dome and steamlines was very

close to measured values during 10 seconds after initiation of the

transient (Figure 6.13) but, later on, the decrease rates were

different (slower for calculations) and consequently some delay on

bypass valves closure was obtained.

6-1
On the other hand, downcomer water level behaviour showed an

increasing divergence from measurement, with no recovering after

initial decrease, as shown in Figure 6.14.

Two sensitivity analysis were made to correct pressure response;

first two calculations, with two different values for the fuel gap

conductivity (Hgap), were performed, resulting in an advance of 1

sec. in the bypass valve closing time, for the low Hgap value, but

in the first portion of the transient a greater divergence from

measurements was obtained (Fig 6.15 a,b). The second sensitivity

a Inalysis to correct pressure response was based in the fact that

this test was performed in the begining of the initial core, and

decay heat, after reactor scram, was low. Several runs were made

with different values for the input variable OHMUL (multiplier for

decay heat), getting the best adjustment for DHMIJL=O.2 as shown in

Figures 6.16 a,b.

To improve water level response, the distribution of liquid in the

upper part of the vessel, for TRAC results, was investigated. It

was detected some accumulation of liquid in the level 6, (rings

1,2,3),. which represents the steam separator, as shown in Figure

6.18 where the void fraction in the four rings of level 6 is

plotted. This plot indicates that liquid is retained inside the

separator (rings 1, 2 and 3) instead of going to downcomer. To

correct this situation, the volume fraction for rings 1,2 and 3 was

changed, leading to a clear improvement in level response,as can be

seen in Figure 6.19 where the results for one of the sensitivity

cases (vol. fract. = 0.39) are shown and a better level behaviour

is observed as compared with initial results in Fig 6.14.

Divergence from measured level, after 30 sec., is also due to the

different timing calculated for the level setpoint modification,

activated when low level (L3) is reached, compared in Fig 6.20; as a

result of this anticipation, feedwater flow is reduced earlier than

in the plant as shown in Fig 6.21. Some improvement in the level

response, for the 0-18 sec. range, was obtained when decay heat was

decreased and

6-2
time of steam discharge to the condenser was reduced to

the actual measured value. Final adjustment of level response was

made by tunning also the dryer loss coefficient and flow area

fraction in the upper downcomer outside of the separator region.

The rest of the compared variables shows a good agreement with

measured values

6-3
s

Table 6.1.- Steady State conditions at transient initiation

Variable Plant TRAC

Core power (Mwt) 2054.74 2055

Core flow (Kg/s) 1070.3 9912

Recirculation flow, 1 loop (Kg/s) 1377.4 1412

Steam flow (Kg/s) 1046 1040

Feedwater flow (Kg/s) 1046 1040

Dome pressure (Pa) 6.873E6 6.878E6

Water level (in) (ref. to 0 instr.) 0.88 0.877

Core support plate pres. drop (Pa) 0.109E6 0.1009E6

6-4
Table 6.2.- Sequence of events

TRAC Plant Event

0 -2 s. 0 - 2s. steady state

2 s. 2 s. turbine trip (stop valves closure)

2.06 s 2.06 s. reactor trip

2.1 s. 2.1 s. bypas valves open

2.14 s. 2.14 s. recirculation pumps transfer to low speed

2.33 s. 2.59 s. one FW pump trip (on low steam flow)

2.8 s. 3.12 s. low level alarm (L4)

2.8 s. 3.12 s. recirc. runback (L4+1FW pump tripped)

18.1 s. 17.05 s. bypass valves close

17.8 s. 17.36 s. recirc. pumps at low speed

19 S. 20.87 s. low level signal (LU)

19 S. 20.87 s. level setpoint modification

6-5
POWER (APRM)

100

90................. ................................................

80

70 2 4.6..1 1 .. 4.16 .. 18 .20 22 .24 26 .28 .0 .32.4.36.3. 40. 4. 44. 4

2 5 TIME5 s. 5 

2 r Lftn a I is it C

FIGURE 6.1
DOME PRESSURE

0~

-J

7200000

7100000

7000000

6900000

6800000

Pa. 6700000

6600000

6500000

6400000

6300000

6200000

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

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

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

. . . . . . . . . .

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

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

. . . ... . . 4L

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

.......*

0 2 4 6 8 10 12 14 16 18 20 22 24

TIEMPO s.

26 28 30 32 34 36 38 40 42 44 46

2 I t

FIGURE 6.2
PRESSURE AT STEAM COLLECTOR

7200000

7000000

0~~ 6800000

co Pa

6600000

6400000

6200000

. . . . . . . . . . . . . . . . I . . I . . I. . . . . . . . . . . . . . . .*

2

.. . .. . .. .. . . . . . . . .. .. S .. * .. .. .. S . .. S . S ....... 

* S S S S S S . . . . . . ... . . ... . . S SL

S ~ ~~~~ 2

S S S ~ ~ i I f f i , -- ~ .2

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 30 40 42 44 416

TIEMPO s.

1 2

aN I' P - TRAC

FIGURIE 6.3
Ch

Kgls

1100

1000

900

800 -

700

600 -

500

400

300

200

100 -

0n

STEAM FLOW

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

*~~~. ..... ... 5. . . S . . . . .. ....... 

.. . . . .. . . . . .. . .. . ......................... ......... S 2 5 25 5 5 S 5 S 5 5 5

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

. . . J. . . . . . . .. . . . . .. . . . . . S . . . . . J

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

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

PAT ? TRAC

FIGURE 6.4
VESSEL SENSED LEVEL.

0.9 - .... . . . *. a:...........-.......

0.7 .

0.6.......... a . . . .. .. I a . . *. . . . a a a a a a a a

00.

M.

m02+ i i j -. i-ia ~

0. 2 4 6 8 . 10 12. 14 16 18 .0 20 .4 .8 22. 24 26 28 ....... 32 ..... 36 40 42 . 44 46 

T2P s2

0.2~~~~~~ II..].I .N ..T ... ... ...

FI UR 6.5 ... . ........ . .
FEED WATER FLOW

1300

1200

1100

1000

900

800

700

Kg/s 600

500

400

300

200

100

0

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

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

* ~~ . .. . . . . . . . . . . . . .

..... .. ..a ......... .... ... . . ... .. .a.. . .. L. .. . ... . . . . .. ... ... . ... . .

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

a a a a a a a a a a a a a a a a a a a a

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

-PLANT -ý TAAC

FIGURE 6.6
CORE FLOW/ (1/2)

0y)

I Kg/s

5400

4800

4200

3600_

3000

2400_

1800

1200

600 -

0

S

* * * S * S S S 5 4 5 5 . S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

S S S S S S S S S S S S S S S S S S S S S S

S

* S S S S S S S *S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S - S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

.5

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

* S S S S S S S S S S S S S S S S S S S S S S

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

S

S S S S S S S S S S S S S S S S S S S S S S S

S S S S S S S S S S S S S S S S S S S S S S S

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

9PuLitA.T TRAC

FIUURE 6.7
RECIRCULATION FLOW (1 LOOP)

1500

30 ** . . . . * . . C . . . . . . . . .. C C C C

* C C C C C C C C C C2

* C C C C C C C C C C C C C C2

0 C----CC C C C C C C C ----

0 2 4 8 C 12 C0 14 18 C6 22 C0 24 26 28 30 32 34 C6 40 C8 42 44 4

* ~ ~ ~ ~ ~ ~ ~ ~ C ~ C TEP C C s. C C C C

I- PLANT -? TRAC I

FIGURE 6.8
a'

RECIRC. PUMP SPEED

140 ............................. ................ ........... .....

120 5........................ ........ .........

* S S S S S S S S S S S S S S S S2

2 - -0 -- - - - - - - S S S S S S S

0

0 2 4 6 8 10 12 14 16 1 20 22 24 26 28 30 32 34 36 3 40 42 44 4

100--- .~~~~~~....~~ - .:....... ~ TE .. s~.. ..........-. . ..-

S PL SS N ? S S

FIGURE 6.9
LEVEL SETPQINT

1.4..................'****................... ........ s : ...........

0.2 .... * ... ........ a . . . . a .. . .. . . ......... a

0. . . a.. .. . . . . . .a.a.a.a.a. a.a.. . .. . .a. . . .a.. . . .a.

0.4 a a a a a a aa

0 a 6 a 10 a 12 16a a4 18 20 2* 4 2 8 3 2 3 6 3 0 4 4 4

"A A I a a

FIGURE 6.10
BYPASS VALVE POSITION

2

100 ~

90 S * ....... S S

80 . . .. . . . .......... .. . .... . .... * * **

80......... .. . . . . . . . . . . . . .

70 ....... ....................................... ................................. S S

60.............................................. ........ ....... .................

01~ 2 4 6 0 2 1 16 18 20 22 24 26 28 3 2 3 6 3 0 4 4 4

0'1 * * * * . * * * * , . O s. * * * * * . .*

* ~ ~ ~ ~ ~ S ~ S ~ ~ S L Sý N S S S S S S S

FIGURE 6.11
RECIRC FCV POSITION

60 . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . .

2 1

50 . . .. . .. . . . . . . . . . . .. . . .. . . ....... ....... I . .

% 40 . . . .. . . . . . . .. . . . . . . . . . . S

30 . . . . . . .

*2 2

50s

2o S S S S S S S S

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 4

* ~ ~ S ~ S ~ S ~ S ~ S ~ ~ S S ~ S TE S P s. S S S S S S

* ~ ~ ~ ~ S ~ S ~ S L S N S m? S S S S

* ~ ~ ~ ~ ~ S ~ S ~ S ~ S F G S R 6.12 S S 5 5 5
DOME PRESSURE

7000000 .

6800000 ... ......

SPa.

6600000 .. -------

6400000 ....

0 2 4 6 8 10 12 14 16 18 ?0 22 24 26 28 30 32 34 36 38 '10 42 44 46

TIEMPO s.

PWAn I TflAC

FIGURE 6.13
SENSED LEVEL

-0.......... Pa..................... ................... ....... ............ . ..... .. .. ...................................

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

*~ ~ ~~ ~~~~ . . . .V . .(6'A123=~ . . .

1 2

-PLANT ?TRAC

FiGURE 6.14
a) DOME PRESSURE (HGAP = 5600)

7200000 ..........1...............................................

7000000 *.... I..I................ ............ ............ ............... ............ a

Pa.

6600000 . .. . . . . . . . . . . .

040000 .~. .......... .. '....~... ............

62000001

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

-PLAN ETRACI

b) DOME PRESSURE (HGAP =6600)

7200000 . . . . . ..

7000000 ..a...~................ ....... a. ....................................... ...... a

Pa.

6400000 ..... ................... .. ......... a............. ............ ............. a

6200000

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

PAT TRAC

FIGURE 6.15

6-20
a) DOME PRESSUiiz (DH-MUL =1)

7200000 .. . . . .1 -. . . .. . . . . . .

7000000 ............

6800000............... .......... .......... . . . . . . . .

6600000 ....................... ...............................................

6600000 ..... .... ... ..... .. ..................

6200000

0 2 4 8 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 A6

TIEMPO s.

IPLANT E TRAC

B) DOME PRESSURE (DHMUL = .2)

72000........'........................................... ...... ... ...

Pa7200000 71'. . ... .. .. . .. . .. . .........

6400000 ....... ................... ...........

6300000 . .. ... . .

6200000 .... ... . . .

0 2 4 6 8 10 12 14 16 15 20 22 24 26 28 30 32 34 36 38 40 42 44 46

TIEMPO s.

FIGURE 6.16

6-21
VESSEL LEVEL 6 VOID FRACTIONS

a'

t')

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

p ~ ~ R I G 1 ,2 ,3 1_______________________________

0 5 10 15 20 25 30 ~35

TIME (a)

FIGURE 6.17
a%

ti m

SENSEL LEVEL (SENSITIVITY TO VOL FRACT.)

0.85..........

0.375 ...... .. ... ............ ...............................

0.125....................... .. .. a..a..a..a..a

-0.375 . 4..] j j j I j I j...... j.4 f j .... .. ...... .. . 4. ...

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52

TIEMPO s.

PLANT2 TA

FIGURE 6.18
LEVEL SETPOINT

1.9 . . . .. . . . . . . . . . . .. .

0. S S . S S * . .,...... S S S

1.5........ .. ........... . ......... . .** S. . . . . . .5

1.1.......................1 .......

-0.9............. ...-.... .............- . . ... -. . .......... ...

0/0 0.7................ . . . ........

-0.3.............. ...................... . . . . . .. . * . , .

-0 .5 S S S S S S 5 5 5 5 5 5

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52

TIEMPO s.

PLANT TRAC

FIGURE 6. 19
FEEEDWATER FLOW

L'

1400

1300

1200

1100

1000

900

800

Kg/s 700

600 -

500 -

400 -

300 -

200 -

100 -

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

* ~~~~ ~ ~ ~~ . . . . . . . . a 

. a . .. . a . . .a . . a a a a a a. a2

*~~ a a a a a a a a a a .. a . . .. .. . .

.~~ ~ ~ ........ a .

. . . . . . . . . .

U

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52

TIEMPO s.

PLANT 2TRAC

FIGURfE 6.20

7.- RUN STATISTICS.-

All TRAC runs were made on a CONVEX-C120 vectorial computer owned by UITESA.

Figure 7.1 is a plot of the relation: "CPU time/transient time", as

a function of transient time

Required calculation of "grind time" for this transient, with a to-,

tal number of 128 cells, for the 23 components of the model, is as

follows:

CPU (total execution time) = 7240 s.

C (total number of volumes) = 128

OT (total number of time steps) = 147

RT (transient time) = 45

(CPU x 103)/(C x DT) = 38.47

7-1
CPU TIME/ TRANSIENT TIME

700

600

500

30

t'.) 400 C-)

1 00-

0

0 5 10 15 20 25 30 35 40 45 50

Transient Time (s.)

FIGURE 7.1
8.- CONCLUSIONS.

A model of C.N. Cofrentes for TRAC-BF1 has been

developped and proved to be adequate for operational transient

analysis.

The start-up test of "Turbine Trip" has been reproduced with this

model and results have been compared with plant measured data.

A good agreement between calculated results and measured test data

has been achieved.

Control systems models closely simulates the response of plant

controllers.

Sensed level simulation is a difficult task in presurization

transients with drastic core flow reduction, due to the unknown

transient distribution of the fluid into the complex flow paths in

the separator region. Tunning of geometric vessel parameters for

the region (level and rings) representing the separator/dryer leads

to acceptable reproduction of sensed level.

Separator and dryer have been modelled considering perfect

separation as the mechanistic model included in TRAC-BF1 didn't work

properly.

Recirculation and core flow are the variables which have the

greatest differences between measurements and calculations.

Improvenment of recirculation loop model,and jet pump dynamic

performance, are the areas identified for further work in this

model.

8-1

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

(2-89) IAssignd by NRC. Add Vol.. Su Rev..

30,22BIBLIOGRAPHIC DATA SHEET NtJREG/IA-Ol 20-

ISe* instruc. ions on the reverse] EST-S IAN-22

2. TITLE AND SUBTITLE

Assessment of the Turbine Trip Transient in Cofrentes 3. DATE REPORTPUBLISHEO

NPP with TRAC-BFl MONTH I YEAR

OU ne 11993

4. FIN OR GRANT NUMBER

___ ___ ___ ___ __ __ ___ ___ ___ ___ ___ __ ___ ___ ___ __ ___ ___ ___ __ L2245

5. AUTHOR (S) 6. TYPE OF REPORT"

F. Castrillo/flidroelectrica Espanola (H.E.) Technical

A. Gomez/Union Iberoamericana De Tecnologia (UITESA) 7. PERIOD COVERED finclusive Dorme

I. Gallego/Union Iberoamericana De Tecnologia (UITESA)

8. PER FORMING ORGANIZATION - NAME AND ADDRESS (It NRC. po~vide vulon. Office orfiaplen. V.1. Nuclear Roguiawuv Cornmiuon. and mailing address.,iIt contracto,.pmvidv

one,, and magirwn addj'm)~

Unidad Electrica, S.A.

c/Francisco Gervas, 3

28020-Madrid, Spain

9. SPONSORING ORGANIZATION -NAME AND ADDRESS (If NRC. type Sameawsabovr."-/f contractor. Provide NRC Division. Office or Rotion. U.1. MuciaperRguateryCemmntion.

&Wd mailing address.1

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

10. SUPPLEMENTARY NOTES

11. ABSTRACT 1200 *were or iesm)

This report presents the results of the assessment of TRAC-BFl (G I-J I) code with the model of C. N. Cofrentes for

simulation of the transient originated by the manual trip of the main turbine.

C. N. Cofrentes is a General Electric designed BWR/6 plant, with a nominal core thermal power of 2894 Mwt, in

commercial operation since 1985, owned and operated by Hidroelectrica Espaflola, S. A. The plant incorporates all

the characteristics of BWRI6 reactors, with two turbine driven FW pumps.

As a result of this assessment a model of C. N. Cofrentes has been developed for TRAC-BFl that fairly reproduces

operational transient behavior of the plant. A special purpose code was generated to obtain reactivity coefficients, as

required by TRAC-BFI, from the 3D simulator.

12. K EY WORDS/DESCR IPTORS (List vwdrt "Prasesm thsat will wist ,wseatcwser In locating the report.) 13. AVAiLABILITY STATEMENT

Cofrentes 14.SEURITY 4SIFICATION

TRAC IT/sit Page)

Turbine Trip Unclassified

Irish Aepeni

Unclassified

15. NUMBER OF PAGES

16. PRICE

NAC FORM 335 12491
Federal Recycling Program

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NUCLEAR REGULATORY COMMISSION

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