NUREG/IA-0252 

 International 

Agreement Report

 

The Development and Verification of 

TRACE Model for IIST Experiments 

Prepared by:

Jong-Rong Wang1

. Hao-Tzu Lin1, 

Chin-Jang Chang1

 

Wei-Xiang Zhuang2

, Chunkuan Shih2 

1

Institute of Nuclear Energy Research 

Atomic Energy Council, R.O.C.

1000, Wenhua Rd., Chiaan Village

Taoyuan, 325, TAIWAN

2

Institute of Nuclear Engineering and Science 

National Tsing Hua University

101 Section 2, Kuang Fu Rd.

HsinChu, TAIWAN

A. Calvo, NRC Project Manager 

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

February 2011 

 

Prepared as part of

The Agreement on Research Participation and Technical Exchange 

Under the International Code Assessment and Maintenance Program (CAMP) 

 

Published by

U.S. Nuclear Regulatory Commission
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iii

ABSTRACT

A RHRP (Reduced-Height and Reduced-Pressure) IIST (Institute of Nuclear Energy Research 

Integral System Test) facility has been established in 1992 for safety studies of the 

Westinghouse three-loop PWR (Pressurized Water Reactor) NPP (Nuclear Power Plant). The 

research purposes of the IIST facility are as follows: (a) to enhance the understanding of 

thermal hydraulics phenomena during the accidents, (b) to contribute to evaluate and develop 

the safety computer codes, and (c) to validate the emergency operating procedure (EOP) during 

the accidents of PWR. The scaling factors of the IIST facility for height and volume of the 

reactor coolant system (RCS) are approximately 1/4 and 1/400, respectively. The maximum 

operating pressure of the IIST facility is 2.1 MPa. The IIST facility has three loops as well as all 

the systems which are about studying Westinghouse PWR plant system transients. The 

experiment of the IIST facility was finished which simulated a 2% cold-leg-break loss-of-coolant 

accident (LOCA) with total high-pressure injection (HPI) failure. This break was located in loop 2 

of IIST facility, which is one of the two loops that do not have a pressurizer. Besides, three 

cooldown experiments of IIST facility were also performed. In this research, the IIST facility 

experiments data and RELAP5 analysis results of IIST facility experiments are used to verify 

and establish the TRACE (TRAC/RELAP Advanced Computational Engine) IIST facility models. 

Comparing steady state results, it can be concluded that the steady state results of TRACE 

calculations are in agreement with those of IIST facility experiments data and RELAP5 analysis 

results of IIST facility experiments. On the other hand, comparing the transient results, it also 

indicates that they are in reasonable consistency. The verified results of TRACE IIST facility 

models reveal that there is respectable accuracy in the analysis of the 2% cold-leg-break LOCA 

and cooldown experiments.
iv
v

FOREWORD

The US NRC (United States Nuclear Regulatory Commission) is developing an advanced 

thermal hydraulic code named TRACE for nuclear power plant safety analysis. The 

development of TRACE is based on TRAC, integrating RELAP5 and other programs. NRC has 

determined that in the future, TRACE will be the main code used in thermal hydraulic safety 

analysis, and no further development of other thermal hydraulic codes such as RELAP5 and 

TRAC will be continued. A graphic user interface program, SNAP (Symbolic Nuclear Analysis 

Program) which processes inputs and outputs for TRACE is also under development. One of 

the features of TRACE is its capacity to model the reactor vessel with 3-D geometry. It can 

support a more accurate and detailed safety analysis of nuclear power plants. TRACE has a 

greater simulation capability than the other old codes, especially for events like LOCA. 

Taiwan and the United States have signed an agreement on CAMP(Code Applications and 

Maintenance Program) which includes the development and maintenance of TRACE. INER 

(Institute of Nuclear Energy Research, Atomic Energy Council, R.O.C.) is the organization in 

Taiwan responsible for the application of TRACE in thermal hydraulic safety analysis, for 

recording users’ experiences of it, and providing suggestions for its development. To meet this 

responsibility, the TRACE models of IIST facility have been built. In this report, the 2% 

cold-leg-break LOCA experiment and cooldown experiments data of IIST facility were utilized 

and conducted to confirm the accuracy of the TRACE models. 
vi
vii

CONTENTS

Page

Abstract .......................................................................................................................................iii

Foreword...................................................................................................................................... v

Executive Summary................................................................................................................... xi 

Abbreviations ............................................................................................................................ xiii 

1. Introduction ........................................................................................................................ 1-1 

2. IIST facility and experiments............................................................................................. 2-1 

2.1 IIST SBLOCA experiment ........................................................................................... 2-6 

2.2 IIST cooldown experiments ....................................................................................... 2-8 

3. The RELAP5 and TRACE IIST model description ........................................................... 3-1 

4. Results and discussions................................................................................................... 4-1 

4.1 IIST SBLOCA experiment ........................................................................................... 4-1 

4.2 IIST cooldown experiments ..................................................................................... 4-11

4.2.1 Test C61128 ........................................................................................................ 4-13

4.2.2 Test C61210 ........................................................................................................ 4-18

4.2.3 Test C70122 ........................................................................................................ 4-23

5. Conclusions.................................................................................................................. 5-1 

6. References.................................................................................................................... 6-1 
viii

Figures

Page

Fig.2.1 The schema of the IIST facility ........................................................................... 2-2 

Fig.3.1 The TRACE IIST facility model (model A):(a) Overall region (b) Loop 1 region (c) 

Loop 2 region (d) Loop 3 region (e) Pressure vessel region ..............................3-2

Fig.3.2 The TRACE IIST facility model (model B)........................................................... 3-5 

Fig.3.3 The power component simulation of IIST facility TRACE model ........................ 3-6 

Fig.3.4 The SG heat exchange simulation of IIST facility TRACE model:(a) the SG U 

tube part I (pipe 145 cell 1~6) (b) the SG U tube part II (pipe 145 cell 7~12).....3-7

Fig.3.5 The pressure vessel heat exchange simulation of IIST facility TRACE model:(a) 

model A (b) model B...........................................................................................3-8

Fig.3.6 The feedwater simulation of IIST facility TRACE model ..................................... 3-9 

Fig.3.7 The break simulation of IIST facility TRACE model .......................................... 3-10 

Fig.3.8 The timestep data of IIST facility TRACE model .............................................. 3-11 

Fig.4.1 The comparison of primary system pressure among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-4 

Fig.4.2 The comparison of break flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment .......................................................................................... 4-4 

Fig.4.3 The comparison of loop 1 flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment .......................................................................................... 4-5 

Fig.4.4 The comparison of loop 3 flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment .......................................................................................... 4-5 

Fig.4.5 The comparison of SG2-inlet tube top differential pressure among IIST facility, 

RELAP5, TRACE in the SBLOCA experiment .................................................. 4-6 

Fig.4.6 The comparison of SG2-outlet tube top differential pressure among IIST facility, 

RELAP5, TRACE in the SBLOCA experiment .................................................... 4-6 

Fig.4.7 The comparison of SG1-inlet plenum liquid level among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-7 

Fig.4.8 The comparison of SG1-outlet plenum liquid level among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-7 

Fig.4.9 The comparison of SG2-inlet plenum liquid level among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-8 

Fig.4.10 The comparison of SG3-outlet plenum liquid level among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-8 

Fig.4.11 The comparison of loop 3 hot-leg temperature among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-9 

Fig.4.12 The comparison of loop 3 cold-leg temperature among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................... 4-9 

Fig.4.13 The comparison of core collapsed liquid level among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................. 4-10

Fig.4.14 The comparison of Core cladding temperature among IIST facility, RELAP5, 

TRACE in the SBLOCA experiment .................................................................. 4-10

Fig.4.15 The comparison of Primary system pressure among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-14 

Fig.4.16 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-14 
ix

Fig.4.17 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-15 

Fig.4.18 The comparison of pressurizer collapsed liquid level among IIST facility, 

RELAP5, TRACE in the C61128 experiment .................................................... 4-15 

Fig.4.19 The comparison of core collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-16 

Fig.4.20 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-16 

Fig.4.21 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, 

TRACE in the C61128 experiment ................................................................... 4-17 

Fig.4.22 The comparison of Primary system pressure among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-19 

Fig.4.23 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-19 

Fig.4.24 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-20

Fig.4.25 The comparison of pressurizer collapsed liquid level among IIST facility, 

RELAP5, TRACE in the C61210 experiment .................................................... 4-20

Fig.4.26 The comparison of core collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-21

Fig.4.27 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-21 

Fig.4.28 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, 

TRACE in the C61210 experiment ................................................................... 4-22 

Fig.4.29 The comparison of Primary system pressure among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-24 

Fig.4.30 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-24 

Fig.4.31 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-25 

Fig.4.32 The comparison of pressurizer collapsed liquid level among IIST facility, 

RELAP5, TRACE in the C70122 experiment .................................................... 4-25 

Fig.4.33 The comparison of core collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-26 

Fig.4.34 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-26 

Fig.4.35 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, 

TRACE in the C70122 experiment ................................................................... 4-27

Fig.4.36 The animation of IIST facility TRACE model .................................................... 4-27
x

Tables

Page

Table 2.1 The comparison of major parameters between IIST facility and the Maanshan 

NPP .................................................................................................................... 2-3 

Table 2.2 The instruments data of IIST facility ................................................................... 2-4 

Table 2.3 The initial condition of the IIST facility SBLOCA experiment ............................. 2-7 

Table 2.4 The initial condition of the IIST facility cooldown experiments ........................... 2-8 

Table 4.1 The comparison of SBLOCA experiment initial condition among IIST facility, 

RELAP5, TRACE .............................................................................................. 4-3 

Table 4.2 The comparison of C61128 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE .................................................................................. 4-11

Table 4.3 The comparison of C61210 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE .................................................................................. 4-11

Table 4.4 The comparison of C70122 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE .................................................................................. 4-12
xi

EXECUTIVE SUMMARY

An agreement in 2004 which includes the development and maintenance of TRACE has been 

signed between Taiwan and USA on CAMP. INER is the organization in Taiwan responsible for 

applying TRACE to thermal hydraulic safety analysis in order to provide users’ experiences 

and development suggestions. To fulfill this responsibility, the TRACE models of IIST facility

were developed by INER. 

A RHRP IIST facility has been established for safety studies of the Westinghouse three loops 

PWR. The research purposes of the IIST facility are as follows: (a) to enhance the 

understanding of thermal hydraulics phenomena during the accidents(1)-(3), (b) to contribute to 

evaluate and develop the safety computer codes(4)-(5), and (c) to validate the EOP during the

accidents of PWR(6). The scaling factors of the IIST facility for height and volume in the RCS are 

approximately 1/4 and 1/400, respectively. The maximum operating pressure of the IIST facility 

is 2.1 MPa. The IIST facility has three loops as well as all the systems which are about studying 

Westinghouse PWR plant system transients. An experiment of the IIST facility was finished 

which simulated a 2% cold-leg-break LOCA with total HPI failure(7). This break was located in 

loop 2 of IIST facility, which is one of the two loops that do not have a pressurizer. Besides, 

three cooldown experiments of IIST facility were also performed(8). 

The codes used in this research are SNAP v 1.1.8 and TRACE v 5.0p1. By referring to the 

RELAP5 IIST facility model and IIST facility experiments data(7)-(8), the TRACE IIST facility 

model (named model A) was developed. The TRACE IIST facility model has three loops. Each 

of the three loops includes the simulation of the hot-leg, SG (Steam Generator) inlet plenum, SG 

U-tubes, SG outlet plenum, crossover leg, reactor coolant pump, and cold-leg. The pressurizer 

located in loop 1, the break valve located in loop 2, and several pipe components were used to 

simulate the IIST pressure vessel. The models of the three SG secondaries were identical. The 

secondary models can be subdivided into the downcomer, boiling section, and steam dome. 

The feedwater line was simulated using a time-dependent junction. The steam line was 

simulated by a break component, which simulated the pressure of steam line during the IIST 

experiment. The break flow area was simulated using a specific valve with the critical flow 

option. The heat source of IIST facility was simulated by a power component of TRACE, which 

used the power table option to simulate the power varying during the experiments. Besides, 

another TRACE IIST facility model (named model B) was developed in order to use the TRACE 

3D component-vessel instead of pipe components. 

Effectiveness of the proposed models were verified with the IIST facility 2% cold-leg-break 

LOCA experiment data, IIST facility cooldown experiments data, and the RELAP5 analysis 

results data of these experiments. The analytical results of TRACE IIST facility models 

indicate that the TRACE IIST facility models predict not only the behaviors of important 

parameters in consistent trends with experiments data, but also their numerical values with 

respectable accuracy. 
xii
xiii

ABBREVIATIONS

 

CAMP Code Applications and Maintenance Program

EOP Emergency Operating Procedure

HPI High-Pressure Injection

IIST Institute of Nuclear Energy Research Integral System Test

INER Institute of Nuclear Energy Research Atomic Energy Council, R.O.C.

LOCA Loss Of Coolant Accident

NPP Nuclear Power Plant

NRC Nuclear Regulatory Commission

PWR Pressurized Water Reactor

RCS Reactor Coolant System

RHRP Reduced-Height and Reduced-Pressure

RV Relief Valve

SBLOCA Small Break LOCA

SG Steam Generator

SNAP Symbolic Nuclear Analysis Program

TRACE TRAC/RELAP Advanced Computational Engine

US United States

 

 

 

 

 

 

 

 

 

 

 
xiv

 

 
1-1 

1. INTRODUCTION

The US NRC is developing an advanced thermal hydraulic code named TRACE for safety 

analyses of NPPs. The development of TRACE is based on TRAC and integrating with RELAP5 

and other programs. NRC has ensured that TRACE will be the main code used in thermal 

hydraulic safety analysis, without further development of other thermal hydraulic codes such as 

RELAP5 and TRAC in the future. SNAP, a program with graphic user interface, which 

processes the inputs and outputs of TRACE is also underdeveloped. One of the features of 

TRACE is its capacity to model the reactor vessel with 3-D geometry. It can support a more 

accurate and detailed safety analysis of NPPs. TRACE has a greater simulation capability than 

the other old codes, especially for events like LOCA. 

A RHRP IIST facility has been established for safety studies of the Westinghouse three loops 

PWR since 1992. The research purposes of the IIST facility are as follows: (a) to enhance the 

understanding of thermal hydraulics phenomena during the accidents(1)-(3), (b) to contribute to 

evaluate and develop the safety computer codes(4)-(5), and (c) to validate the EOP during the

accidents of PWR(6). The scaling factors of the IIST facility for height and volume in the RCS are 

approximately 1/4 and 1/400, respectively. The maximum operating pressure of the IIST facility 

is 2.1 MPa. The IIST facility has three loops as well as all the systems which are about studying 

Westinghouse PWR plant system transients. An experiment of the IIST facility was finished 

which simulated a 2% cold-leg-break LOCA with total HPI failure(7). This break was located in 

loop 2 of IIST facility, which is one of the two loops that do not have a pressurizer. Besides, 

three cooldown experiments of IIST facility were also performed(8). 

In this research, according to the greater LOCA simulation capability of TRACE, the IIST facility 

TRACE models are established and are verified with the 2% cold-leg-break LOCA experiment 

data of IIST facility and the RELAP5 analysis results of this experiment(7). Besides, the 

cooldown experiments data of IIST facility and the RELAP5 analysis results of these 

experiments are also used to establish and verify the TRACE models(8). 
2-1 

2. IIST facility and experiments 

Fig. 2.1 shows the schema of the IIST facility. IIST facility is established in order to simulate the 

thermal hydraulics phenomena of Maanshan NPP which is a Westinghouse three loops PWR. 

Maanshan NPP is the only Westinghouse-PWR in Taiwan. The rated core thermal power is 

2775 MW. The reactor coolant system has three loops, each of which includes a reactor coolant 

pump and a SG. The pressurizer is connected to the hot-leg piping in loop 2. 

The IIST facility consists of a pressure vessel and three loops. Each loop has a SG and a 

coolant pump. Except that there is a pressurizer in the loop 1, the three loops are identical. The 

scaling factors of height and volume in the RCS are approximately 1/4 and 1/400, respectively. 

Scaled safety injection systems (include HPI and accumulators) inject cooling water into the 

cold-leg of each loop. During the SBLOCA (Small Break LOCA) experiment, a catch tank is 

simulated to collect and measure the effluent from the simulated break. The comparison of 

major parameters between IIST facility and the Maanshan NPP is shown in Table 2.1.

The data acquisition system of the IIST facility records data from more than 200 instruments 

which include K-type thermocouples, venturi flowmeters, pressure transducers, and differential 

pressure transducers in order to measure temperature, flow rate, pressure, and differential 

pressure, respectively. The accuracies of the instruments are as follows(7): (1) Thermocouple 

accuracies are 2.2 K or 0.75% of the full scale. (2) Venturi flowmeters located in the downflow 

section of the crossover leg (the loop seals) are used to measure the loop flow rate which the 

accuracy is 1.66% of the range. (3) Pressure and pressure difference transducers are used to 

measure the system pressure and the local pressure drop in the loops. The accuracies of 

pressure and pressure difference are 0.25 and 0.77% of the ranges, respectively. (4) The 

collapsed liquid levels are calculated based on the differential pressures and temperatures for 

regions of the system when the local velocities are low. The accuracy of the collapsed liquid 

level is 1.8% of the range. (5) The break flow is discharged to the catch tank during the 

simulation of the LOCA experiments. So, the break flow rate is calculated from the multiplication 

of the liquid level rising rate, flow area, and liquid density in the catch tank. The accuracy of the 

break flow rate is 1.8% of the range. The detail description of the above instruments are listed in 

the INER report(9) and Table 2.2 shows some data of instruments which include the calculation 

range, location, and function. 

Besides, there are 50 view ports in the IIST facility in order to see the thermal hydraulics 

phenomena and thus enhance understanding of two-phase phenomena in the pressure vessel, 

hot-legs, SG inlet and outlet plenums, SG secondary sides, crossover legs, cold-legs, and 

pressurizer. However, a total of 13 video cameras are located at selected view ports to record 

the key thermal hydraulics phenomena during the IIST facility experiments. 
2-2 

Fig. 2.1 The schema of the IIST facility(7)
2-3 

Table 2.1 The comparison of major parameters between IIST facility and the Maanshan 

NPP(7)
2-4 

Table 2.2 The instruments data of IIST facility(9)
2-5 
2-6 

2.1 IIST facility SBLOCA experiment(7)

The experiment of IIST facility was performed in order to simulate a 2% cold-leg break (the 

break area is 2% of the scaled cold-leg cross-section area) with total HPI failure. A horizontal 

break nozzle was installed in the cold-leg of loop 2. In this experiment, the core power decay 

and pump coastdown during the SBLOCA experiment were not simulated. The initial condition 

of the experiment is showed in Table 2.3. 

The SBLOCA experiment started from the break occurred at time zero, the primary pressure of 

IIST facility dropped until it became only a little higher than the secondary-side pressure of IIST 

facility. Besides, the primary pressure decreased slowly because the energy content of the 

liquid discharged through the break was a little larger than the core energy generation. The air 

flowed through the hot-leg into the SG-1 U-tubes after emptying of the pressurizer at 128 sec. 

After 164 sec of the break, the loop 1 flow rate suddenly dropped to near zero, which means the 

decrease of the heat removal capability of SG-1. The effects of noncondensable air caused 

obviously slowed the rising temperatures in both the primary and secondary sides of SG-1 and 

the suddenly decrease of the natural-circulation flow rate in loop 1. An asymmetric coolant 

inventory distribution was observed in the three SGs during the two-phase natural-circulation 

and reflux condensation. In SG-1, the liquid holdup in the inlet plenum was not observed 

because the steam flowed into SG-1 which caused no flooding phenomena occurred during the 

reflux condensation. However, in SG-2 and SG-3, liquid holdup was shown in the upflow-side 

U-tubes and the inlet plenum resulting from the occurrence of flooding phenomena at the inlet of 

the SG U-tubes and hot-legs. The collapsed liquid level of core decreased sharply after the 

break occurred because of the subcooled liquid discharge in the time period between 0 to 146 

sec. Then, the collapsed liquid level of core decreased slowly, when the break flow became a 

two-phase mixture from 146 to 400 sec. Finally, because of no coolant makeup, the core was 

uncovered with heatup at 1734 sec. 
2-7 

Table 2.3 The initial condition of the IIST facility SBLOCA experiment(7) 

Parameter IIST test data

Primary coolant system

Core power (kW) 126

Pressurizer pressure (MPa) 0.958

Pressurizer water level (mm) 1459

Loop flow rate (kg/s)

Loop1 0.210

Loop2 0.217

Loop3 0.217

Hot-leg temperature (K)

Loop1 450

Loop2 449

Loop3 451

Cold-leg temperature (K)

Loop1 409

Loop2 408

Loop3 409

Secondary coolant system

Secondary-side pressure (MPa)

SG-1 0.301

SG-2 0.295

SG-3 0.295

Secondary-side fluid temperature (K)

SG-1 407

SG-2 407

SG-3 407
2-8 

2.2 IIST facility cooldown experiments(8)

In 1996, a break of pressurizer venting tube occurred at Maanshan NPP, which result in the 

coolant release to the containment and the action of cooldown and depressurization process in 

RCS. In this accident, the leakage was estimated that could be greater than 50 gpm. However, 

the RCS collapsed liquid level shrinks and decreases due to cooldown and depressurization 

which may lead to overprediction the leakage rate and misjudgment of the proper actions in 

accident management. Therefore, a series of IIST facility cooldown experiments were 

performed in order to study the shrink effect in the RCS and the verification of theoretical 

approach of leakage evaluation model. Besides, the IIST facility cooldown experiments results 

were also used for the assessment of RELAP5 IIST facility model. 

There are three cooldown experiments of IIST facility (C61128, C61210, and C70122) and the 

initial conditions are listed in Table 2.4. The cooldown experiments were divided two steps. The 

first step (0~1000 sec) was the intital primary pressure maintaining by regulating the power of 

the pressurizer heater and the secondary side pressure controlling by adjusting the opening of a 

control valve (located at the header of steam lines). The second step (after 1000 sec) was the 

relief valve (RV) of the steam generator which opens at 1000 sec and the core power was 

adjusted in decreasing rate of 1.75 kW every 50 seconds which resulted in cooldown in the 

RCS and depressurization in the secondary side. These cooldown experiments were performed 

with the cooldown rates ranging from 0.9 to 1.2 K/min, which were within the limitation of 

Maanshan NPP. 

Table 2.4 The initial condition of the IIST facility cooldown experiments(8) 

C61128 C61210 C70122

Pressurizer pressure (MPa) 0.972 0.979 1.82

Pressurizer water level (mm) 1241 1269 1771

Core power (kW) 100.4 120 100.3

Hot-leg temperature (K) 442.1 448.8 468.5

Cold-leg temperature (K) 410.3 412.2 436.1

SG pressure (MPa) 0.286 0.283 0.62

SG water level (mm) 2230 2264 2293

SG fluid temperature (K) 405 0.979 435
2-9 
3-1

3. The RELAP5 and TRACE IIST model description 

The RELAP5 IIST facility model was including 172 volumes connected by 175 junctions and 141 

heat structures, had been developed to simulate the IIST facility. The detail description of 

RELAP5 IIST facility models were in INER’s previous study(7)-(8). 

By referring to the RELAP5 IIST facility models and IIST experiments data(7)-(8), the TRACE IIST 

facility model was developed. The SNAP v 1.1.8 and TRACE v 5.0p1 were employed in this 

research. The TRACE IIST facility model (named model A) is showed in Fig. 3.1. It shows that 

the TRACE IIST facility model has three loops: loop 1 (pipe components 110 to 197, shown in 

Fig.3.1 (b)), loop 2 (pipe components 210 to 297, shown in Fig.3.1 (c)), and loop 3 (pipe 

components 310 to 397, shown in Fig.3.1 (d)). Each of the three loops includes the simulation of 

the hot-leg, SG inlet plenum, SG U-tubes, SG outlet plenum, crossover leg, coolant pump, and 

cold-leg. The pressurizer (pipe component 720, shown in Fig.3.1 (b)) located in loop 1, the 

break valve (valve component 805, shown in Fig.3.1 (c)) located in loop 2, and pipe components 

3~19 were used to simulate the pressure vessel of IIST facility (shown in Fig.3.1 (e)). The 

models of the three SG secondaries (pipe components 410 through 430, 510 through 530, and 

610 through 630, respectively) were identical. The secondary models can be subdivided into the 

downcomer, boiling section, and steam dome. The steam line was simulated by a break 

component, which simulated the pressure of steam line during the IIST facility experiments. The 

break flow area was simulated using a specific valve with the critical flow option. Besides, 

another TRACE IIST facility model (named model B) was developed in order to use the TRACE 

3D component-vessel instead of pipe 3~19. The TRACE IIST facility model B is shown in Fig. 

3.2. 

The heat source of IIST facility was simulated by a power component of TRACE (power 

component 32000), which used the power table (option 6) to simulate the power varying during 

the experiments, as shown in Fig. 3.3. Besides, the main heat exchange simulation of IIST 

facility TRACE models were as follows: (1) the heat exchange in the primary-side and the 

secondary-side of the SGs, shown in Fig. 3.4, (2) the internal heat exchange of the pressure 

vessel, shown in Fig. 3.5. The feedwater line was simulated using a time-dependent junction, as 

shown in Fig. 3.6. In all break components of IIST facility TRACE models, the break type used 

option 4 in order to use the tables to simulate the boundary conditions of IIST facility 

experiments (shown in Fig. 3.7). Finally, the timestep range (0.01~1×10-8 sec) of IIST facility 

TRACE models were used in the calculation process (shown in Fig. 3.8). 
3-2

(a) overall region 

(b) Loop 1 region
3-3

(c) Loop 2 region

(d) Loop 3 region
3-4

(e) Pressure vessel region 

Fig. 3.1 The TRACE IIST facility model (model A)
3-5

Fig. 3.2 The TRACE IIST facility model (model B)
3-6

Fig. 3.3 The power component simulation of IIST facility TRACE model 
3-7

(a) the SG U tube part I (pipe 145 cell 1~6) 

(b) the SG U tube part II (pipe 145 cell 7~12)

Fig. 3.4 The SG heat exchange simulation of IIST facility TRACE model 
3-8

(a) model A 

 

(b) model B 

Fig. 3.5 The pressure vessel heat exchange simulation of IIST facility TRACE model 
3-9

Fig. 3.6 The feedwater simulation of IIST facility TRACE model 
3-10

Fig. 3.7 The break simulation of IIST facility TRACE model
3-11

Fig. 3.8 The timestep data of IIST facility TRACE model
4-1

4. Results and discussions 

4.1 IIST facility SBLOCA experiment 

 

Table 4.1 shows the comparison of initial condition among IIST facility, RELAP5, TRACE. The 

TRACE analysis results are in good agreement with the IIST facility and RELAP5 data. Fig. 4.1

shows the comparison of primary system pressure among IIST facility, RELAP5, TRACE. Fig. 

4.2 shows the comparison of break flow rate among IIST facility, RELAP5, TRACE. The primary 

system pressure and break flow rate trends of TRACE are similar with the IIST facility and 

RELAP5 data. Besides, it also shows that the TRACE model A overpredicted the primary 

system pressure during 100~600 sec. From the data of IIST facility SBLOCA experiment and 

RELAP5 analysis(7), it shows three periods: (1) subcooled liquid break flow from 0 to 320 sec, 

(2) low-quality two-phase break flow from 320 to 620 sec, and (3) high-quality two-phase break 

flow after 620 sec. The above data also described that RELAP5 underpredicted the primary 

system pressure during the subcooled break flow period, and it overpredicted pressure during 

the low-quality two-phase break flow period. The differences of the primary system pressure 

between IIST facility and RELAP5 were caused by overprediction of the subcooled break flow 

period, underprediction of the low-quality two-phase break flow period, compared with the IIST 

facility data, as shown in Fig. 4.2. Therefore, the TRACE model A overpredicted the primary 

system pressure during the subcooled break flow and the low-quality two-phase break flow 

periods. It was due to underprediction of break flow rate during the subcooled break flow and 

the low-quality two-phase break flow, compared with the IIST facility data, as shown in Fig. 4.2. 

Asymmetric natural-circulation flow rates were observed in the three loops during the IIST 

facility SBLOCA experiment, but TRACE was unable to simulate these phenomena, which was

shown in Fig. 4.3 and Fig. 4.4. According to the previous paper(7), the above trend is also 

observed in the results of RELAP5 (shown in Fig. 4.3 and Fig. 4.4) and this paper described the 

difference generated from the inadequate simulation of the effect of noncondensable air in 

RELAP5 after emptying of the pressurizer. Hence, in this parameter analyses, the above results 

shows that there is the same defect in TRACE. 

Fig. 4.5 and Fig. 4.6 show the differential pressures of IIST facility, RELAP5, and TRACE in the 

upflow and downflow sides of the U-tubes for SG-2. The TRACE model A and RELAP5 

predicted more liquid holdup in both sides of the U-tubes. However, the TRACE model B 

predicted the similar result with the IIST facility data. The main difference in TRACE model A 

and model B is the simulation of IIST facility pressure vessel. Therefore, it may be the reason 

which caused the difference between analyses result of TRACE model A and model B in this 

parameter. 

For loop 1, the IIST facility data show the inlet and outlet plenum of SG-1 to empty after 500 

sec, as shown in Fig. 4.7 and Fig. 4.8. However, the TRACE and RELAP5 overpredicted liquid 

holdup in the SG-1 inlet and outlet plenum. The difference among IIST facility, RELAP5, and 

TRACE were caused by the reason which happened in Fig. 4.3. 

Fig. 4.9 shows the comparison of the liquid holdup in the SG-2 inlet plenum among IIST facility, 

RELAP5, and TRACE. There are the similar trends in this parameter. However, the value of 

TRACE is lower than IIST facility and RELAP5 after 400 sec. Fig. 4.10 shows the comparison of 

outlet plenum liquid level of SG-3 among IIST facility, RELAP5, and TRACE. The trends of their 
4-2

curves are generally consistent in 0~1000 sec. For the TRACE model B, it underpredicted after 

1000sec. Besides, RELAP5 also underpredicted after 1300sec. 

Fig. 4.11 and Fig. 4.12 show the fluid temperatures of the hot-leg and cold-leg in loop 3. The 

TRACE and RELAP5 predicted the loop 3 fluid temperature to be in good agreement with the 

IIST facility experiment data. 

Fig. 4.13 shows the comparison of the core liquid level among IIST facility, RELAP5, and 

TRACE. The trends of their curves are the similar. The core liquid level of RELAP5 was slightly 

lower than IIST facility. However, the TRACE results data are better than RELAP5. Besides, the 

TRACE and RELAP5 can well predict the time to reach the core uncover which caused the 

cladding temperature increase, as shown in Fig. 4.14. 

Overall, the TRACE analyses results are roughly consistent with the IIST facility and RELAP5 

data. Besides, the TRACE model B has better prediction than model A in the primary system 

pressure, break flow, SG2-inlet tube top differential pressure, and SG2-outlet tube top 

differential pressure. 
4-3

Table 4.1 The comparison of SBLOCA experiment initial condition among IIST facility, 

RELAP5, TRACE

Parameter IIST facility RELAP5 TRACE(model A)

/error (%)

TRACE(model B)

/error (%)

Primary coolant system

Core power (kW) 126 126 126 126

Pressurizer pressure (MPa) 0.958 0.958 0.964 /0.6 0.964 /0.6

Pressurizer water level 

(mm)

1459 1413 1463 /0.3 1394 /4.5

Loop flow rate (kg/s)

Loop1 0.210 0.227 0.219 /4.3 0.204 /2.9

Loop2 0.217 0.227 0.219 /0.9 0.198 /8.8

Loop3 0.217 0.227 0.219 /0.9 0.198 /8.8

Hot-leg temperature (K)

Loop1 450 445 448.7 /0.3 446.1 /0.9

Loop2 449 445 448.7 /0.1 446.1 /0.6

Loop3 451 445 448.7 /0.5 446.1 /1.1

Cold-leg temperature (K)

Loop1 409 409 409.5 /0.1 409.5 /0.1

Loop2 408 409 409.5 /0.4 409.5 /0.4

Loop3 409 409 409.5/ 0.1 409.5 /0.1

Secondary coolant 

system

Secondary-side pressure 

(MPa)

SG-1 0.301 0.301 0.303 /0.7 0.303 /0.7

SG-2 0.295 0.301 0.299 /1.4 0.299 /1.4

SG-3 0.295 0.301 0.299 /1.4 0.299 /1.4

Secondary-side fluid 

temperature (K)

SG-1 407 407 406.1 /0.2 406.0 /0.2

SG-2 407 407 405.6 /0.3 405.6 /0.3

SG-3 407 407 405.6 /0.3 405.6 /0.3
4-4

0 400 800 1200 1600 2000

Time (sec)

0

0.5

1

1.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.1 The comparison of primary system pressure among IIST facility, RELAP5, TRACE

in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

0

0.4

0.8

1.2

1.6

2

Flow rate (kg/s)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.2 The comparison of break flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment
4-5

0 400 800 1200 1600 2000

Time (sec)

-0.5

0

0.5

1

1.5

Flow rate (kg/s)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.3 The comparison of loop 1 flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment 

0 400 800 1200 1600 2000

Time (sec)

-0.5

0

0.5

1

Flow rate (kg/s)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.4 The comparison of loop 3 flow rate among IIST facility, RELAP5, TRACE in the 

SBLOCA experiment
4-6

0 400 800 1200 1600 2000

Time (sec)

-5

0

5

10

15

20

25

Pressure (KPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.5 The comparison of SG2-inlet tube top differential pressure 

among IIST facility, RELAP5, TRACE in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

-5

0

5

10

15

20

25

Pressure (kPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.6 The comparison of SG2-outlet tube top differential pressure

among IIST facility, RELAP5, TRACE in the SBLOCA experiment
4-7

0 400 800 1200 1600 2000

Time (sec)

-1

0

1

2

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.7 The comparison of SG1-inlet plenum liquid level

among IIST facility, RELAP5, TRACE in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

-1

0

1

2

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.8 The comparison of SG1-outlet plenum liquid level

among IIST facility, RELAP5, TRACE in the SBLOCA experiment
4-8

0 400 800 1200 1600 2000

Time (sec)

-1

0

1

2

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.9 The comparison of SG2-inlet plenum liquid level

among IIST facility, RELAP5, TRACE in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

-1

0

1

2

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.10 The comparison of SG3-outlet plenum liquid level

among IIST facility, RELAP5, TRACE in the SBLOCA experiment
4-9

0 400 800 1200 1600 2000

Time (sec)

300

350

400

450

500

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.11 The comparison of loop 3 hot-leg temperature 

among IIST facility, RELAP5, TRACE in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

300

350

400

450

500

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.12 The comparison of loop 3 cold-leg temperature 

among IIST facility, RELAP5, TRACE in the SBLOCA experiment
4-10

0 400 800 1200 1600 2000

Time (sec)

-2

0

2

4

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.13 The comparison of core collapsed liquid level 

among IIST facility, RELAP5, TRACE in the SBLOCA experiment

0 400 800 1200 1600 2000

Time (sec)

0

200

400

600

800

1000

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.14 The comparison of Core cladding temperature 

among IIST facility, RELAP5, TRACE in the SBLOCA experiment
4-11

4.2 IIST cooldown experiments 

 

In this section, Table 4.2, Table 4.3, and Table 4.4 show the comparison of initial condition 

among IIST facility, RELAP5, TRACE for the cooldown experiments(8). The TRACE analysis 

results are in agreement with the IIST facility and RELAP5 data. 

Table 4.2 The comparison of C61128 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE(8)

IIST facility RELAP5 TRACE (model A)

/error(%)

TRACE (model 

B)

/error(%)

Pressurizer pressure (MPa) 0.972 0.953 0.981 /0.9 0.961 /1.1

Pressurizer water level 

(mm)

1241 1225 1237 /0.3 1277 /2.9

Core power (kW) 100.4 100.4 100.4 100.4

Hot leg temperature (K) 442.1 438.6 444.8 /0.6 440.3/ 0.4

Cold leg temperature (K) 410.3 410.4 411.4 /0.3 411.0 /0.2

SG pressure (MPa) 0.286 0.286 0.281 /1.7 0.286 /0.0

SG water level (mm) 2230 2198 2258 /1.3 2244 /0.6

Table 4.3 The comparison of C61210 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE(8)

IIST facility RELAP5 TRACE (model A)

/error(%)

TRACE (model 

B)

/error(%)

Pressurizer pressure (MPa) 0.979 0.979 0.953 /2.7 0.944 /3.6

Pressurizer water level (mm) 1269 1342 1335 /5.2 1316/3.7

Core power (kW) 120 120 120 120

Hot leg temperature (K) 448.8 444.6 448.7 /0.02 448.1 /0.2

Cold leg temperature (K) 412.2 412.2 411.3 /0.2 412.5 /0.1
4-12

SG pressure (MPa) 0.283 0.289 0.287 /1.4 0.286 /1.1

SG water level (mm) 2264 2282 2249 /0.7 2229/1.5

Table 4.4 The comparison of C70122 cooldown experiment initial condition among IIST 

facility, RELAP5, TRACE(8)

IIST 

facility

RELAP5 TRACE (model A)

/error(%)

TRACE (model 

B)

/error(%)

Pressurizer pressure (MPa) 1.82 1.82 1.81 /0.5 1.82 /0.0

Pressurizer water level (mm) 1771 1748 1742 /1.6 1800 /1.6

Core power (kW) 100.3 100.3 100.3 100.3

Hot leg temperature (K) 468.5 462.4 466.6 /0.4 468.4 /0.02

Cold leg temperature (K) 436.1 435.7 434.5 /0.4 436.6 /0.1

SG pressure (MPa) 0.62 0.63 0.61 /1.6 0.64 /3.2

SG water level (mm) 2293 2288 2298 /0.2 2388 /4.1
4-13

4.2.1 Test C61128

According to the C61128 experiment data(8), it is high inlet subcooling (9.6K) and the cooldown 

rate is approximately equal to 0.9 K/min within the limitation range (≦ 1.85 K/min) of Maanshan 

NPP. Fig. 4.15 shows the comparison of Primary system pressure among IIST facility, RELAP5, 

TRACE. The TRACE was overpredicted in this parameter during 0~1500 and 2500~3800 sec.

However, RELAP5 was also overpredicted in this parameter during 0~4000 sec. At 1000 sec, 

the core power was adjusted in decreasing rate of 1.75 kW every 50 seconds and the RVs of 

the SGs opened which resulted in cooldown effect in the RCS. Therefore, the trends of curves 

decreased after 1000 sec. Fig. 4.16 shows the comparison of SG1 secondary side pressure 

among IIST facility, RELAP5, TRACE. The trends of TRACE were roughly consistent with the 

IIST facility and RELAP5 data. The SG secondary pressure keeps constant during 0 to 1000 sec. 

The RVs of SGs opens at 1000 sec and the pressure decreases; finally it remains at 

atmospheric pressure.

Fig. 4.17, Fig. 4.18, and Fig. 4.19 show that the SG secondary side, pressurizer, and core 

collapsed liquid levels of TRACE are consistent with the IIST facility and RELAP5 data. As the 

RVs open at 1000 sec, the collapsed liquid levels of SG secondary side and pressurizer 

decrease. However, the core collapsed liquid level is nearly the same during the overall time 

interval. 

Fig. 4.20 and 4.21 show the comparison of loop 1 hot-leg and cold-leg temperatures among 

IIST facility, RELAP5, TRACE. The TRACE predict the hot-leg and cold-leg temperatures in 

good agreement with the IIST facility experiment and RELAP5 data. 

Overall, the TRACE analyses results are roughly consistent with the IIST facility and RELAP5 

data. In the comparison of analysis results of the TRACE model A and B, they are similar in all 

parameters. 
4-14

0 1000 2000 3000 4000

Time (sec)

0

0.5

1

1.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.15 The comparison of Primary system pressure among IIST facility, RELAP5, TRACE in 

the C61128 experiment

0 1000 2000 3000 4000

Time (sec)

0

0.1

0.2

0.3

0.4

0.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.16 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C61128 experiment 
4-15

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.17 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, TRACE in 

the C61128 experiment

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.18 The comparison of pressurizer collapsed liquid level 

 among IIST facility, RELAP5, TRACE in the C61128 experiment 
4-16

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

 

Fig. 4.19 The comparison of core collapsed liquid level among IIST facility, RELAP5, TRACE 

in the C61128 experiment

0 1000 2000 3000 4000

Time (sec)

0

100

200

300

400

500

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.20 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, TRACE 

in the C61128 experiment
4-17

0 1000 2000 3000 4000

Time (sec)

0

100

200

300

400

500

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.21 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, TRACE 

in the C61128 experiment
4-18

4.2.2 Test C61210

According to the C61210 experiment data(8), it is low inlet subcooling (3K) and the cooldown rate 

is approximately equal to 1 K/min within the limitation range (≦ 1.85 K/min) of Maanshan NPP. 

Fig. 4.22 shows the primary system pressures of the IIST facility, RELAP5, TRACE. In this 

parameter, the trends of TRACE were roughly similar with the IIST facility data. Besides, TRACE 

was overpredicted in this parameter after 1500 sec. However, RELAP5 was also overpredicted 

in this parameter during the overall time interval. Besides, the value of RELAP5 was higher than 

TRACE. At 1000 sec, the core power was adjusted in decreasing rate of 1.75 kW every 50 

seconds and the RVs of the SGs opened which resulted in cooldown effect in the RCS.

Therefore, the primary system pressures of the IIST facility, RELAP5, and TRACE decreased 

after 1000 sec. Fig. 4.23 shows the comparison of SG1 secondary side pressure among IIST 

facility, RELAP5, TRACE. The trends of TRACE were in agreement with the IIST facility and 

RELAP5 data. The SG secondary pressure keeps constant during 0 to 1000 sec. The RVs of 

SGs opens at 1000 sec and the pressure decreases; finally it remains at atmospheric pressure.

Fig. 4.24 shows the SG1 secondary side collapsed liquid levels of the IIST facility, RELAP5, 

TRACE. In this parameter, TRACE was underpredicted after 1000 sec but the trends of TRACE 

were roughly consistent with the IIST facility and RELAP5 data. Fig. 4.25 and Fig. 4.26 show 

that the pressurizer and core collapsed liquid levels of TRACE are consistent with the IIST 

facility and RELAP5 data. Besides, comparing Fig. 4.25 and Fig. 4.26, it can found as the 

pressurizer collapsed liquid levels of TRACE are lower than IIST facility and RELAP5; the core 

collapsed liquid levels of TRACE are higher than IIST facility and RELAP5. As the RVs open at 

1000 sec, the collapsed liquid levels of SG secondary side and pressurizer decrease. However, 

the core collapsed liquid level is nearly the same during the overall time interval. 

Fig. 4.27 and 4.28 show the loop 1 hot-leg and cold-leg temperatures of IIST facility, RELAP5, 

TRACE. The hot-leg and cold-leg temperatures prediction of TRACE were the similar with the 

IIST facility experiment and RELAP5 data. 

Overall, the TRACE analyses results are roughly consistent with the IIST facility and RELAP5 

data. In the comparison of analysis results of the TRACE model A and B, they are similar in all 

parameters. However, in primary system pressure, the result of the TRACE model B is better 

than model A. 
4-19

0 1000 2000 3000 4000

Time (sec)

0

0.5

1

1.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.22 The comparison of Primary system pressure among IIST facility, RELAP5, TRACE in 

the C61210 experiment

 

0 1000 2000 3000 4000

Time (sec)

0

0.1

0.2

0.3

0.4

0.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.23 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C61210 experiment
4-20

 

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.24 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, TRACE in 

the C61210 experiment

 

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.25 The comparison of pressurizer collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C61210 experiment
4-21

 

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.26 The comparison of core collapsed liquid level among IIST facility, RELAP5, TRACE 

in the C61210 experiment

 

0 1000 2000 3000 4000

Time (sec)

0

100

200

300

400

500

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.27 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, TRACE 

in the C61210 experiment
4-22

 

0 1000 2000 3000 4000

Time (sec)

0

100

200

300

400

500

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.28 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, TRACE 

in the C61210 experiment
4-23

4.2.3 Test C70122

According to the C70122 experiment data(8), it is high inlet subcooling (12.1K) and the cooldown 

rate is approximately equal to 1.2 K/min within the limitation range (≦ 1.85 K/min) of Maanshan 

NPP. Fig. 4.29 shows the comparison of primary system pressure among IIST facility, RELAP5, 

TRACE. The TRACE model A and RELAP5 were overpredicted in this parameter during the 

overall time interval. Besides, the value of TRACE model A was roughly the similar with 

RELAP5. However, the result of the TRACE model B is better than TRACE model A and 

RELAP5. At 1000 sec, the core power was adjusted in decreasing rate of 1.75 kW every 50 

seconds and the RVs of the SGs opened which resulted in cooldown effect in the RCS.

Therefore, the primary system pressures of the IIST facility, RELAP5, and TRACE decreased 

after 1000 sec. Fig. 4.30 shows the SG1 secondary side pressures of IIST facility, RELAP5, and 

TRACE. The trends of TRACE were nearly the same with the IIST facility and RELAP5 data.

The SG secondary pressure keeps constant during 0 to 1000 sec. The RVs of SGs opens at 

1000 sec and the pressure decreases; finally it remains at atmospheric pressure.

Fig. 4.31 shows the comparison of SG1 secondary side collapsed liquid levels among IIST 

facility, RELAP5, TRACE. In this parameter, the trends of TRACE were roughly consistent with 

the IIST facility and RELAP5 data, but the TRACE model B was underpredicted after 1000 sec. 

Fig. 4.32 shows the pressurizer collapsed liquid levels of the IIST facility, RELAP5, and TRACE. 

Their trends were roughly the silimar, but the TRACE and RELAP5 were underpredicted after 

1000 sec. Fig. 4.33 shows the comparison of the core collapsed liquid levels among IIST facility, 

RELAP5, TRACE. The TRACE results were in agreement the IIST facility and RELAP5 data. As 

the RVs open at 1000 sec, the collapsed liquid levels of SG secondary side and pressurizer 

decrease. However, the core collapsed liquid level is nearly the same during the overall time 

interval. 

Fig. 4.34 and 4.35 show the comparison of loop 1 hot-leg and cold-leg temperatures among 

IIST facility, RELAP5, and TRACE. The TRACE predict the hot-leg and cold-leg temperatures in 

good agreement with the IIST facility experiment and RELAP5 data. 

Overall, the TRACE analyses results are roughly similar with the IIST facility and RELAP5 data. 

In the comparison of analysis results of the TRACE model A and B, there are bigger difference 

in the primary system pressure and SG1 secondary side collapsed liquid level. 

Furthermore, the animation of the TRACE model is presented using the animation function of 

SNAP/TRACE interface with the TRACE analysis results. The animation model of IIST facility is

shown in Fig. 4.36. 
4-24

0 1000 2000 3000 4000

Time (sec)

0

0.5

1

1.5

2

2.5

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.29 The comparison of Primary system pressure among IIST facility, RELAP5, TRACE in 

the C70122 experiment

0 1000 2000 3000 4000

Time (sec)

0

0.2

0.4

0.6

0.8

1

Pressure (MPa)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.30 The comparison of SG1 secondary side pressure among IIST facility, RELAP5, 

TRACE in the C70122 experiment
4-25

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.31 The comparison of SG1 collapsed liquid level among IIST facility, RELAP5, TRACE in 

the C70122 experiment

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.32 The comparison of pressurizer collapsed liquid level among IIST facility, RELAP5, 

TRACE in the C70122 experiment
4-26

0 1000 2000 3000 4000

Time (sec)

0

1

2

3

4

5

Liquid level (m)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.33 The comparison of core collapsed liquid level among IIST facility, RELAP5, TRACE 

in the C70122 experiment

0 1000 2000 3000 4000

Time (sec)

0

100

200

300

400

500

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.34 The comparison of loop 1 hot-leg temperature among IIST facility, RELAP5, TRACE 

in the C70122 experiment
4-27

0 1000 2000 3000 4000

Time (sec)

0

200

400

600

Temperature (K)

IIST facility

RELAP5

TRACE model A

TRACE model B

Fig. 4.35 The comparison of loop 1 cold-leg temperature among IIST facility, RELAP5, TRACE 

in the C70122 experiment

Fig. 4.36 The animation of IIST facility TRACE model
5-1

5. CONCLUSIONS

By using SNAP/TRACE, this study developed the TRACE models of the IIST facility. 

Effectiveness of the proposed models were verified with the 2% cold-leg-break LOCA IIST 

facility experiment data, IIST facility cooldown experiments data, and the RELAP5 analyses 

results data. In this research, the following results can be obtained: 

1. By referring to the RELAP5 IIST facility models and IIST experiments data(7)-(8), two kinds of 

TRACE IIST facility models were developed success. The main difference in two kinds of 

TRACE IIST facility models is the simulation of the IIST facility pressure vessel. The 

TRACE IIST facility model A simulated the IIST facility pressure vessel by pipe 

components. However, the TRACE IIST facility model B simulated the IIST facility pressure 

vessel by TRACE 3D component-vessel. 

2. In the 2% cold-leg-break LOCA IIST facility experiment, overall, the TRACE analyses 

results are roughly in agreement with the IIST facility and RELAP5 data. Besides, the 

TRACE model B has better prediction than model A in the primary system pressure, break 

flow, SG2-inlet tube top differential pressure, and SG2-outlet tube top differential pressure. 

3. In the IIST facility cooldown experiments, the TRACE analyses results are roughly 

consistent with the IIST facility and RELAP5 data. In the comparison of analysis results of 

the TRACE model A and B, they are similar in all parameters. However, in primary system 

pressure, the analysis result of the TRACE model B is better than model A. 

4. Finally, the analytical results of TRACE IIST facility models indicate that the TRACE IIST 

facility models predict not only the behaviors of important parameters in consistent trends 

with experiment data, but also their numerical values with respectable accuracy. 
5-2
6-1 

6. REFERENCES

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power plant—Investigation of PWR Natural Circulation”, Nucl. Sci. J., Vol.31, 83, 1994.

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“Experimental investigation of PWR small break loss-of-coolant accidents in IIST facility”, 

Nucl. Sci. J., Vol. 33, 251, 1996.

3. Lee, C. H., Liu, T. J., Way., Y. S., and Hsia, D. Y., “Investigation of mid-loop operation with 

loss of RHR at INER Integral System Test (IIST) facility”, Nucl. Eng. Des., Vol. 163, 349, 

1996.

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