NUREG/IA-0466 

International 

 Agreement Report

Analysis of the OSU-MASLWR 001 and 

002 Tests by Using the TRACE Code

 

 

Prepared by: 

 Fulvio Mascari, Felice De Rosa, Brian G. Woods*, Kent Welter**, Giuseppe Vella***, Francesco D’Auria**** 

ENEA- Via Martiri di Monte Sole 4, Bologna, Italy 

*Department of Nuclear Engineering and Radiation Health Physics 

116 Radiation Center, Corvallis, OR 97331-5902, USA.

**NuScale Power Inc., 1100 NE Circle Blvd, Suite 200, Corvallis, OR 97330, USA.

***Dipartimento dell’Energia, Università degli Studi di Palermo,90128 Palermo, Italia

****San Piero a Grado, Nuclear Research Group (SPGNRG), University of Pisa 

K. Tien, NRC Project Manager 

 

Division of Systems Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Manuscript Completed: October 2015

Date Published: August 2016

Prepared as part of 

The Agreement on Research Participation and Technical Exchange

Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by

U.S. Nuclear Regulatory Commission

NUREG/IA-0466 

International 

 Agreement Report

Analysis of the OSU-MASLWR 001 and 

002 Tests by Using the TRACE Code

 

 

Prepared by: 

 Fulvio Mascari, Felice De Rosa, Brian G. Woods*, Kent Welter**, Giuseppe Vella***, Francesco D’Auria**** 

ENEA- Via Martiri di Monte Sole 4, Bologna, Italy 

*Department of Nuclear Engineering and Radiation Health Physics 

116 Radiation Center, Corvallis, OR 97331-5902, USA.

**NuScale Power Inc., 1100 NE Circle Blvd, Suite 200, Corvallis, OR 97330, USA.

***Dipartimento dell’Energia, Università degli Studi di Palermo,90128 Palermo, Italia

****San Piero a Grado, Nuclear Research Group (SPGNRG), University of Pisa 

K. Tien, NRC Project Manager 

 

Division of Systems Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Manuscript Completed: October 2015

Date Published: August 2016

Prepared as part of 

The Agreement on Research Participation and Technical Exchange

Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by

U.S. Nuclear Regulatory Commission

iii

ABSTRACT

The Oregon State University (OSU) has constructed, under a U.S. Department of Energy grant, a 

scaled integral test facility to examine natural circulation phenomena characterizing the MultiApplication Small Light Water Reactor (MASLWR) design. The MASLWR is a small modular PWR 

relying on natural circulation during both steady-state and transient operation, which includes an 

integrated helical coil steam generator within the reactor pressure vessel. Testing has been 

conducted in order to assess the operation of the prototypical MASLWR under normal full pressure 

and full temperature conditions and to assess the passive safety systems performance. The 

experimental data produced are useful also for the assessment of the computational tools 

necessary for the operation, design and safety analysis of nuclear reactors.

This report describes the assessment of TRACE code predictions, conducted under the NRC CAMP 

program, against the MASLWR tests OSU-MASLWR-001 and the OSU-MASLWR-002, respectively. 

This activity has been conducted in collaboration with the Italian National Agency for the New 

Technologies, Energy and Sustainable Economic Development (ENEA), the Department of Energy 

of the University of Palermo, the Gruppo di Ricerca Nucleare San Piero a Grado (GRNSPG) of 

University of Pisa, the Department of Nuclear Engineering and Radiation Health Physics at OSU

and NuScale Power Inc. In particular the OSU-MASLWR-001 test, an inadvertent actuation of one 

submerged ADS valve, investigates the primary system to containment coupling under design basis 

accident conditions; the OSU-MASLWR-002 test, a natural circulation test, investigates the primary 

system flow rates and secondary side steam superheat for a variety of core power levels and feed 

water flow rates. The assessment against experimental data shows that the TRACE code predicts 

the main phenomena of interest of the selected tests reasonably well for most conditions.

v

CONTENTS

Page

ABSTRACT.................................................................................................................................... iii

CONTENTS ....................................................................................................................................v

FIGURES................................................................................................................vii

TABLES..................................................................................................................xi

ABBREVIATIONS....................................................................................................xiii

1. INTRODUCTION..................................................................................................................... 1-1

2. OSU-MASLWR TEST FACILITY DESCRIPTION.................................................................. 2-1

2.1 OSU-MASLWR Overview.............................................................................................. 2-1

2.2 OSU-MASLWR RPV Description .................................................................................. 2-5

2.3 OSU-MASLWR Secondary Side ................................................................................... 2-7

2.4 OSU-MASLWR Containment Structures..................................................................... 2-10

2.5 OSU-MASLWR ADS Lines.......................................................................................... 2-11

2.6 OSU-MASLWR Data Acquisition and Control Subsystem Overview.......................... 2-13

2.7 OSU-MASLWR Testing Campaign ............................................................................. 2-14

2.7.1 OSU-MASLWR-001 Test Description ............................................................. 2-15

2.7.2 OSU-MASLWR-002 Test Description ............................................................. 2-18

3. CODE APPLICATION............................................................................................................. 3-1

3.1 TRACE Code Description.............................................................................................. 3-1

3.2 TRACE Model Description............................................................................................. 3-2

3.3 Analyses of the OSU-MASLWR-001 Calculated Data.................................................. 3-8

3.4 Analyses of the OSU-MASLWR-002 Calculated Data................................................ 3-25

4. CONCLUSIONS...................................................................................................................... 4-1

5. REFERENCES........................................................................................................................ 5-1

APPENDIX A EXPERIMENTAL DATA VERSUS CODE CALCULATION FOR THE 

 OSU-MASLWR-001 TEST.................................................................................A-1

APPENDIX B EXPERIMENTAL DATA VERSUS CODE CALCULATION FOR THE 

OSU-MASLWR-002 TEST.................................................................................B-1

vii

FIGURES

Page

Figure 1 MASLWR Conceptual Design Layout [1,3,18,19,20] ............................................... 1-1

Figure 2 OSU-MASLWR Experimental Facility Photo [3,18,19,20] ....................................... 2-1

Figure 3 OSU-MASLWR Test Facility Process and Instrumentation Diagram [19,35] .......... 2-2

Figure 4 RPV Internals Component [3,18,19,20] ................................................................... 2-5

Figure 5 Lower Core Flow Plate Layout [7,19,20] See Figure 6 for Flow 

Blockage Detail......................................................................................................... 2-6

Figure 6 Auxiliary Flow Hole Blockage by Core Shroud [7,19,20]. ........................................ 2-6

Figure 7 Core Shroud Photo [7,19,20].................................................................................... 2-7

Figure 8 Helical Coil SG Bundle Photo [18,19,34] ................................................................. 2-8

Figure 9 Helical Coil SG Bundle [19,35] ................................................................................. 2-8

Figure 10 Main Steam Line Photo [19] ..................................................................................... 2-9

Figure 11 OSU-MASLWR Containment Structures [3,17,19,20] ........................................... 2-10

Figure 12 High ADS Lines Photo [20]..................................................................................... 2-11

Figure 13 HPC and CPV Penetration Elevation [34].............................................................. 2-12

Figure 14 Data Acquisition and Control System [34] .............................................................. 2-13

Figure 15 Data Acquisition and Control System Main Control Screen [34]. .......................... 2-13

Figure 16 RPV and HPC pressure behavior during the OSU-MASLWR-001

test [1,3,19,20]................... . ................................................................................... 2-16

Figure 17 RPV Water Level Behavior during the OSU-MASLWR-001 

Test [1,3,19,20]....................................................................................................... 2-16

Figure 18 HPC Water Level Behavior during the OSU-MASLWR-001 Test [20] .................. 2-17

Figure 19 Inlet/Outlet Core Temperature Behavior during the OSU-MASLWR-001

Test [1,19,20].. .........................................................................................2-17

Figure 20 RPV Flow Rate during the OSU-MASLWR-001 Test [1,19,20]............................. 2-18

Figure 21 Inlet, Outlet Core and Top of the Hot Leg Temperature Behavior during 

the OSU-MASLWR-002 Test [1,18,19].................................................................. 2-20

Figure 22 Steam Superheat at the SG Outlet Behavior during the OSU-MASLWR-002 

Test [3,19]............................................................................................................... 2-20

Figure 23 Difference of Fluid Temperature at the Inlet of the Core and at the Exit of 

the SG Primary Side during the OSU-MASLWR-002 Test [18,19]........................ 2-21

Figure 24 TRACE/SNAP Environment Architecture [18,20,46] ............................................... 3-1

Figure 25 OSU-MASLWR Model [11-32,37-43] ....................................................................... 3-2

Figure 26 Heat Structures Modeled in the TRACE Nodalization [11-32,37-43] ....................... 3-3

Figure 27 Correspondence Between the TRACE Model and the Facility Lower Shell

Section [11-32,37-43] ............................................................................................... 3-4

Figure 28 Measurement Points in the TRACE Nodalization [37-43] ........................................ 3-7

Figure 29 SNAP Animation Model Showing the Fluid Condition of the TRACE Model

at 50s Before the SOT (REF Plot Reference - Cold HPC). ................................... 3-11

Figure 30 SNAP Animation Model Showing the Fluid Condition of the TRACE Model

at 50s Before the SOT (SEN1 Plot Reference - Hot HPC)................................... 3-11

Figure 31 Experimental Data versus Code Calculation for PRZ (PT-301) and 

HPC (PT-801) Pressure ......................................................................................... 3-12

Figure 32 Experimental Data versus Code Calculation for RPV Level 

(LDP-106) ............................................................................................................... 3-13

Figure 33 Experimental Data versus Code Calculation for HPC Level (LDP-801)................ 3-13

Figure 34 Experimental Data versus Code Calculation for Core Outlet Temperature

(TF-106)............................................................................................................................ 3-14
viii

Figure 35 Experimental Data versus Code Calculation for the Average Core Inlet

Temperature (Average Value of TF-121, TF-123, TF-124). .................................. 3-14

Figure 36 Experimental data Versus Code Calculation for RPV Volumetric Flow 

Rate (FDP-131) ...................................................................................................... 3-15

Figure 37 Long Term Cooling Flow Path Typical of the MASLWR Design. .......................... 3-15

Figure 38 Experimental Data versus Code Calculation for TF-811 ....................................... 3-16

Figure 39 Experimental Data versus Code Calculation for TF-815 ....................................... 3-17

Figure 40 Experimental Data versus Code Calculation for PRZ (PT-301) and HPC 

Pressure (PT-801) for REF and SEN1 Case ......................................................... 3-18

Figure 41 Experimental Data versus Code Calculation for Core Outlet T (TF-106) 

for REF and SEN1 Case ........................................................................................ 3-18

Figure 42 Experimental Data versus Code Calculation for TF-821 for REF and SEN1

Case.................................................................................................................................. 3-19

Figure 43 Experimental Data versus Code Calculation for RPV Level (LDP-106) for 

REF and SEN1 Case ............................................................................................. 3-19

Figure 44 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=0s (REF Plot Reference) .................................................................... 3-20

Figure 45 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=0s (SEN1 Plot Reference) .................................................................. 3-20

Figure 46 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=80s (REF Plot Reference) .................................................................. 3-21

Figure 47 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=80s (SEN1 Plot Reference)................................................................ 3-21

Figure 48 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=515s (REF Plot Reference) ................................................................ 3-22

Figure 49 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=515s (SEN1 Plot Reference) ............................................................. 3-22

Figure 50 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=1750s (REF Plot Reference) .............................................................. 3-23

Figure 51 Fluid Condition and Temperature Visualization of the HPC, by Using 

SNAP, at T=1750s (SEN1 Plot Reference) ........................................................... 3-23

Figure 52 SNAP Animation Model Showing the SOT Condition of the TRACE 

Model (REF Plot Reference). ................................................................................. 3-26

Figure 53 Experimental Data versus Code Calculations for Fluid Temperature at 

the Core Outlet (TF-106)........................................................................................ 3-27

Figure 54 Experimental Data versus Code Calculations for Fluid Temperature at 

the Core Inlet (Average Value of TF 121, 123, 124).............................................. 3-27

Figure 55 Experimental Data versus Code Calculations for Primary Volumetric 

Flow Rate (FDP-131).............................................................................................. 3-28

Figure 56 Experimental Data versus Code Calculations for Core Delta T ............................. 3-28

Figure 57 Experimental Data versus Code Calculations for PRZ Level ................................ 3-29

Figure 58 Experimental Data versus Code Calculations for PRZ Pressure. ......................... 3-29

Figure 59 Experimental Data versus Code Calculations for the Difference of Fluid 

Temperature at the Inlet of the Core and at the Exit of the SG Primary Side ....... 3-30

Figure 60 Experimental Data versus Code Calculations for the Average Fluid 

Temperature at the SG Coil Outlet. ........................................................................ 3-31

Figure 61 RPV Temperature Profile for the OSU-MASLWR-002 Test

(2555s after the SOT) ............................................................................3-32
ix

Figure 62 SG Primary Side and Equivalent Helical Coil Temperature Diagram for the 

OSU-MASLWR-002 Test (2555s after SOT)......................................................... 3-32

Figure 63 SNAP Animation Model Showing the Condition of the TRACE Model

1000s after the SOT ............................................................................................... 3-33

Figure 64 SNAP Animation Model Showing the Condition of the TRACE Model 

2700s after the SOT ............................................................................................... 3-34

xi

TABLES

Page

Table 1 OSU-MASLWR Main Scaling Parameters [1,34] ..................................................... 1-3

Table 2 Test Performed in the OSU-MASLWR Test Facility Available at the International 

Community [1,43]...................................................................................................... 1-3

Table 3 OSU-MASLWR Test Facility Instrumentation [34] ................................................... 2-3

Table 4 OSU-MASLWR Instrumentation Type [34] .............................................................. 2-4

Table 5 SG Geometrical Data [18] ........................................................................................ 2-9

Table 6 Summary of the Previous DOE Tests Conducted in the 

OSU-MASLWR [1,3,19] ........................................................................................ 2-14

Table 7 OSU-MASLWR-002 and OSU-MASLWR-003A Test Conditions [1,3,7,19].......... 2-19

Table 8 Facility Instrumentation vs TRACE Nodalization Measurement Points [37-43]....... 3-5

Table 9 Facility Configuration Before the SOT of the OSU-MASLWR-001 Test.................. 3-8

Table 10 SOT Thermal Hydraulic Conditions Comparison (TRACE Calculated Data vs 

Experimental Data) for the OSU-MASLWR-001 Test.............................................. 3-9

Table 11 Facility Configuration for the Simulation of the OSU-MASLWR-001 Test............. 3-10

Table 12 Event Transient Sequence of the OSU-MASLWR-001 ......................................... 3-10

Table 13 Test versus Phenomena, TRACE Prediction vs Phenomena [43, 49-52] ............. 3-24

Table 14 Facility Configuration Before the SOT of the OSU-MASLWR-002 Test................ 3-25

Table 15 SOT Condition Predicted by the TRACE Code vs Experimental Data for the 

OSU-MASLWR-002 Test ....................................................................................... 3-26

Table 16 Main Phenomena vs Facility and vs TRACE [43, 49-52] ....................................... 3-35

xiii

ABBREVIATIONS

ADS Automatic Depressurization System; 

BIC Boundary and Initial Condition

CL Cold Leg; 

CPV Cooling Pool Vessel;

FW Feed Water;

HL Hot Leg; 

HPC High Pressure Containment; 

IAEA International Atomic Energy Agency; 

ICSP International Collaborative Standard Problem; 

LOCA Loss of Coolant Accident; 

LP Lower Plenum; 

LWR Light- Water Reactor; 

MASLWR Multi-Application Small Light Water Reactor; 

OSU Oregon State University; 

PRZ Pressurizer; 

PWR Pressurized Water Reactor; 

RPV Reactor Pressure Vessel; 

SBLOCA Small Break Loss of Coolant Accident; 

SG Steam Generator; 

SOT Start of the Transient;

SNAP Symbolic Nuclear Analysis Package; 

TRAC Transient Reactor Analysis Code;

TRACE TRAC/RELAP Advanced Computational Engine; 

UP Upper Plenum; 

USNRC U.S. Nuclear Regulatory Commission.

1-1

1. INTRODUCTION

The Oregon State University (OSU) has constructed, under a U.S. Department of Energy grant, an

integral test facility called MASLWR. The purpose of this integral test facility is to examine the 

natural circulation phenomena characterizing the MASLWR design in steady and transient 

conditions.

The MASLWR [1]1 reactor concept is shown in Fig. 1 and was developed by Idaho National 

Engineering and Environmental Laboratory, OSU and NEXANT–Bechtel. It is a small modular

Pressurized Water Reactor (PWR) relying on natural circulation for steady-state and transient 

operation. The design includes an integrated Steam Generator (SG) consisting of banks of vertical 

helical tubes contained within the Reactor Pressure Vessel (RPV) and located in the upper region of 

the vessel outside of the Hot Leg (HL) chimney. During steady-state conditions the primary fluid, in 

single phase natural circulation, removes the core power and transfers it to the secondary fluid via 

shell-side of the SG. Then the Feed Water (FW) is fully vaporized in the tube-side of SG resulting in 

superheated steam at the SG outlet.

PRZ

HL

(Middle ADS Valves)

Depressurization

Valve

Steam Generator

Tube Bundle

Sump

Recirculation

valve

Feedwater

Steam Gen

Turbine Generator

Feedwater

Pump

(High ADS Valves) Vent Valve

Containmnet

Condenser

Reactor Pressure Vessel

Water

Steam

Water

Core

Figure 1 MASLWR Conceptual Design Layout [1,3,18,19,20]

The RPV is surrounded by a cylindrical containment partially filled with water that provides pressure 

suppression and liquid makeup capabilities during design basis events. The containment is 

submerged in a pool of water that acts as the ultimate heat sink. The RPV can be depressurized 

using the Automatic Depressurization System (ADS) which consists of six valves discharging into 

various locations within the containment. Specifically, the ADS design includes two independent 

vent valves (high ADS valves), two independent depressurization valves (middle ADS valves) and 

two independent sump recirculation valves (low ADS valves).
1-2

The integral arrangement of the MASLWR reactor allows avoiding pressurized primary components 

outside the RPV eliminating the possibility of large break Loss of Coolant Accident (LOCA) and 

reducing the potential for Small Break LOCA (SBLOCA) events. Of particular interest is the 

SBLOCA mitigation strategy based on a passive primary/containment coupling and natural 

circulation. For example, given an inadvertent opening of an ADS valve, the primary side blows 

down into the containment takes place. The RPV blowdown causes a primary pressure decrease 

and a consequent containment pressure increase causing a safety injection signal. When a safety 

signal is received, the high ADS valves automatically actuate, along with the middle ADS valves and 

the sump recirculation valves. As the primary and the containment pressures equalize, the 

blowdown is terminated, and a natural circulation flow path is established between the containment 

and primary system. When the sump recirculation valves are opened the vapor produced in the core 

travels to the upper RPV and exits through the high ADS valve. The vapor is then condensed on the 

inside surface of the containment with the condensate being captured in the lower part of the 

containment. The condensate in the lower part of the containment is then returned to the primary 

system via recirculation valves. The containment is also submerged in a pool and acts as the 

ultimate heat sink [2,4,19,20] for design basis events. 

A scaling analysis of the OSU-MASLWR experimental facility was performed in order to evaluate 

potential scaling distortions in the test facility compared to the prototype reactor. The scaling method 

used for the design of the facility was the Hierarchical Two-Tiered Scaling (H2TS) Methodology [2, 

4, 5, 6]. The detailed OSU-MASLWR scaling analyses is reported in [2,4]. Some of the main facility 

scaling parameters are reported in Table 1 [1,34]. 

A testing program has been conducted in order to assess the operation of the MASLWR design 

under full pressure and full temperature conditions and to assess the passive safety system 

performance. The experimental data produced are useful also for the assessment of the 

computational tools necessary for the operation, design and safety analysis of nuclear reactors [1-

4,19].

After the completion of the first test series, through a grant from the International Atomic Energy 

Agency (IAEA), the OSU-MASLWR test facility core was reconfigured to eliminate a recurring 

grounding problem and improve facility reliability in anticipation of conducting an IAEA International 

Collaborative Standard Problem (ICSP) on "Integral PWR Design Natural Circulation Flow Stability 

and Thermohydraulic Coupling of Primary System and Containment During Accidents". This ICSP 

was hosted at OSU with experimental data from the OSU-MASLWR facility. The data provides

insights into single/two-phase flow instability phenomena under natural circulation conditions and 

coupled containment/reactor vessel behavior in integral type light water reactors [33-43].

Table 2 shows the test performed in the OSU-MASLWR and available at the international 

community.

____

1

The MASLWR design is the basis for the NuScale Power integral reactor design [9,10].
1-3

Table 1 OSU-MASLWR Main Scaling Parameters [1,34]

Parameter MASLWR OSU-MASLWR Note

Time Scale 1:1 1:1 Time preserved facility

Volumetric Scale 1:1 1:254.7 Reduced volume facility

Height Scale 1:1 1:3 Reduced height facility

Design Primary 

Pressure (MPa)

8.6 11.4 Full pressure facility

Loop Number 1 1 Integral test facility

Hot Leg Riser D (mm) 914.4 102.3

Power (MW) 150 0.6 Full power facility

Core Rod Number 6336 56

Core Rod DIA (mm) 9.5222 15.9

Heated Length (m) 1.35 0.686

SG Type Vertical oncethrough helical 

tubes

Vertical oncethrough helical 

tubes

SG Bundle 2 3

SG Tubes Number For 

Bundle

506 5, 5, 4

SG OD Tube (mm) 15.9 15.9

Table 2 Test Performed in the OSU-MASLWR Test Facility Available at the 

International Community [1,43]

Test Test Type

DOE OSU-MASLWR-001 Inadvertent Actuation of 1 Submerged ADS Valve

OSU-MASLWR-002 Natural Circulation at Core Power up to 210 kW

OSU-MASLWR-003A Natural Circulation at Core Power of 210 kW

OSU-MASLWR-003B Inadvertent Actuation of 1 High Containment ADS Valve

IAEA ICSP test SP-2 Loss of Feedwater Transient

ICSP test SP-3 Power Maneuvering

2-1

2. OSU-MASLWR TEST FACILITY DESCRIPTION

2.1 OSU-MASLWR Overview

As a result of the scaling analyses the OSU-MASLWR [1- 7,19, 34,35] test facility, shown in Fig. 2, 

is scaled at 1:3 length scale, 1:254.7 volume scale and 1:1 time scale, is constructed entirely of 

stainless steel, and is designed for full pressure and full temperature prototype operation. It includes 

the primary circuit, consisting of the RPV and ADS lines, the secondary circuit and the containment 

structures. In addition to the physical structures that comprise the test facility, there are data 

acquisition, instrumentation and control systems. Auxiliary lines and systems are present in the 

facility. The OSU-MASLWR test facility process and instrumentation diagram are shown in Fig. 3. 

Table 3 shows the OSU-MASLWR test facility instrumentation; Table 4 shows the OU-MASLWR 

instrumentation type. 

Figure 2 OSU-MASLWR Experimental Facility Photo [3,18,19,20]
2-2

Figure 3 OSU-MASLWR Test Facility Process and Instrumentation Diagram [19,3

2-2
2-3

Table 3 OSU-MASLWR Test Facility Instrumentation [34]

Tag number Description

LDP-501 Feed water storage tank level

FMM-501 Feed water mass flow rate

TF-501 Feed water temperature

FCM-511 Feed water supply in the steam generator outer coil mass flow rate

PT-511 Feed water pressure in the steam generator outer coil supply pipe

FCM-521 Feed water supply in the steam generator middle coil mass flow rate

PT-521 Feed water pressure in the steam generator middle coil supply pipe

FCM-531 Feed water supply in the steam generator inner coil mass flow rate

PT-531 Feed water pressure in the steam generator inner coil supply pipe

LDP-601 Feed water supply collector level

PT-602 Main steam pressure

FVM-602-P Main steam pressure

FVM-602-T Main steam temperature

FVM-602-M Main steam mass flow rate

TF-603 Steam drain line temperature

TF-611, 612, 613, 614, 

615 

Thermocouples inside the outer coil pipe of the steam generator exit

TF-621, 622, 623, 624, 

625 

Thermocouples inside the middle coil pipe of the steam generator exit

TF-631, 632, 633, 634 Thermocouples inside the inner coil pipe of the steam generator exit

TF-101, 102, 103, 104, 

105, 106 

Center of core thermocouple rod, six thermocouples spaced 6 inches apart, 

measuring water temperatures

TH-141, 142, 143, 144, 

145, 146 

Core heater rod temperatures

TF-121, 122, 123, 124 Core inlet temperatures

TF-131, 133, 134 Primary containment water down flow temperatures after steam generator coils

TF-132 Primary containment water temperature inside chimney below steam generator 

coil

TF-111 Primary containment water temperature at top of chimney

TF-301 Steam temperature in pressurizer

PT-301 Steam pressure in pressurizer

LDP-301 Primary containment water level in the pressurizer

DP-101 Pressure loss in the core

DP-102 Pressure loss between core top and riser cone

DP-103 Pressure loss in the riser cone

DP-104 Pressure loss in the chimney

DP-105 Pressure loss across steam generator

DP-106 Pressure loss in the annulus below steam generator

LDP-106 Primary containment water level

TF-811, 821, 831, 841, 

851, 861 

Water temperatures located inside the HPC near the heat transfer plate

TF-815, 825, 835, 845, 

855, 865 

Water temperatures located inside the CPV near the heat transfer plate

TW-812, 822, 832, 842, 

852, 862 

Wall temperatures within the heat transfer plate between the CPV and the 

HPC, nearest to the HPC

TW-813, 823, 833, 843, 

853, 863 

Wall temperatures at the midpoint of the heat transfer plate between the CPV 

and the HPC

TW-814, 824, 834, 844, 

854, 864 

Wall temperatures within the heat transfer plate between the CPV and the 

HPC, nearest to the CPV

TH-891, 892, 893, 894 Temperatures of Heaters located on the walls of the HPC

TW-891, 892, 893, 894 Temperatures within the walls of the HPC, between the heaters and the water
2-4

TF-871A, 871B, 872A, 

872B, 873A, 873B 

Water temperatures inside the automatic depressurization system (ADS) lines 

outside of the HPC vessel

PT-801 HPC pressure

LDP-801 HPC level

LDP-901 CPV level

TF-882 CPV water temperature

FDP-131 Differential pressure from V-Cone flowmeter within hot leg chimney

KW-101, 102 Measures power to the core heater rod bundles

KW-301 Measures power to pressurizer heater

Table 4 OSU-MASLWR Instrumentation Type [34]

Instrumentation type Tag number

Vortex flow meter FVM-602

Coriolis flow meter FCM-511, -521, -531

Magnetic flow meter FMM-501

Thermocouple TW-xxx, TF-xxx, TH-xxx

Pressure meter PT-511, -521, -531

Pressure meter PT-301

Pressure meter PT-602

Pressure meter PT-801

Differential pressure meter DP-101, -103, -105

Differential pressure meter DP-102

Differential pressure meter DP-104

Differential pressure meter DP-106

Differential pressure meter DP-107

Differential pressure meter DP-108

Flow differential pressure meter FDP-131

Level differential pressure meter LDP-106

Level differential pressure meter LDP-301

Level differential pressure meter LDP-501, -801

Level differential pressure meter LDP-901

Level differential pressure meter LDP-601

Power meter KW-101, -102
2-5

2.2 OSU-MASLWR RPV Description

The internal components of the RPV, Fig. 4, are the core, the HL riser, the Upper Plenum (UP), the 

Pressurizer (PRZ), the SG primary side, the Cold Leg (CL) downcomer and the Lower Plenum (LP). 

PRZ

PRZ Heaters

Core Flange

RPV

SG Coils

SG Steam Drum

Cone

Core

Lower Plenum

HL Riser

Upper Plenum

Chimney

Cold Leg

Figure 4 RPV Internals Component [3,18,19,20]

The core is modelled with 56 cylindrical heater rods distributed in a 1.86 cm pitch square array with 

a 1.33 pitch to diameter ratio. The nominal power of each heater rod is 7.1 kW resulting in a 

maximum core power of 398 kW. The diameter of the core rod is 1.59 cm. A lower core flow plate, 

Fig. 5, contains 76 auxiliary flow holes of 0.635 cm of diameter, arranged at 1.86 cm pitch square 

array, and 57 core rod flow holes. In order to create a flow annulus between the flow plate and the 

core rod, the holes of the rodded lower core flow plate are oversized at 1.72 cm. The core is 

shrouded, Fig. 6, to ensure all flow enters the core via the bottom and travels the entire heated 

length. The shroud is shaped to partially block the primary coolant flow through the outermost 

auxiliary flow holes in order to ensure that each heated rod receives approximately equal axial 

coolant flow. The amount of blockage is dependent on the number and location of heated rods 
2-6

adjacent to each auxiliary flow hole. At mid elevation a core grid wires, Fig. 7, is considered in order 

to maintain the radial alignment of the core rods. Four thermocouples for measuring the core inlet 

temperatures are located at the bottom CL entering the core. The core heater rod temperatures are 

measured. Six thermocouples vertically spaced every 15.24 cm measuring water temperatures, are 

located in the center of core thermocouple rod. The pressure loss in the core is measured; the 

power to the core heater rod bundles is measured as well. 

Figure 5 Lower Core Flow Plate Layout [7,19,20] See Figure 6 for Flow Blockage 

Detail

Figure 6 Auxiliary Flow Hole Blockage by Core Shroud [7,19,20]
2-7

The HL riser, Fig. 4, consists of a lower region, an upper region and a transition region. The lower 

region consists of a pipe with an outside diameter of 20.32 cm, an inside diameter of 19.71 cm and 

a wall thickness of 0.305 cm. The upper region consists of a pipe with an outside diameter of 11.43 

cm, an inside diameter of 10.23 cm, and a wall thickness of 0.602 cm. The transition region consists 

of a cone with a 0.305 cm thickness and an half angle of 20.61°. The pressure loss between core 

top and riser cone, the pressure loss in the riser cone and the pressure loss in the chimney, from the 

exit of the transition cone to the UP, are measured. Along the riser a thermocouple measures the 

water temperature inside chimney below SG coil and another one measures the water temperature 

at top of chimney. The flow rate within the HL chimney is measured with a differential pressure cell 

used to measure flow. The primary containment water level is measured as well.

Figure 7 Core Shroud Photo [7,19,20]

The UP is separated from the heated upper PRZ section by a thick baffle plate having eight 2.54 cm 

holes, spaced uniformly around the baffle plate periphery, which allow free communication of the 

PRZ to the remainder of the RPV during normal operation and for volume surges into and/or out of 

the PRZ due to transients. 

The PRZ is integrated in the RPV and is located in its upper part. In the PRZ are located three 

heater elements, each 4 kW, that are modulated by the test facility control system to maintain 

nominal primary system pressure at the desired value. The PRZ steam temperature and pressure 

are measured. The PRZ level is measured as well.

The CL downcomer region, Fig. 4, is an annular region bounded by the RPV wall on the outside and 

the HL riser on the inside, and the flow area reduces at the HL riser cone. In the SG primary side 

section is inserted the SG helical coil bundle, Fig. 8 and 9. Thermocouples are located in the CL 

downcomer region to measure water down flow temperatures after SG coils. The primary side 

pressure loss across SG and the pressure loss in the annulus below SG are measured. The RPV 

shell is covered by Thermo-12 hydrous calcium silicate insulation.

2.3 OSU-MASLWR Secondary Side

The secondary circuit includes the FW treatment and storage system, the Main FW Pump (MFP), 

the Main FW (MFW) system supply lines, the SG secondary side internal to the vessel, the Main 

Steam (MS) system and associated FW and steam valves. 
2-8

Potable water, coming from the city water supply, passes through a mechanical filter and a resin bed 

to remove impurities and flows to the FW storage tank. The MFW system supplies deionized and 

demineralized water to the SG. The MFP is a positive displacement pump and can be isolated from 

the downstream main FW system supply lines by pneumatic motor operated globe valve MF-508 

(FW supply valve). The MFP controller is interlocked with the MFP discharge isolation valve MF-508 

position, to ensure that the MFP is not energized unless MF-508 is fully open. The single MFW line 

splits into three supply lines, one for each coil bank of SG tubes. 

Figure 8 Helical Coil SG Bundle Photo [18,19,34] 

Figure 9 Helical Coil SG Bundle [19,35]

The SG of the facility is a once through heat exchanger and is located within the RPV in the annular 

space between the HL riser and the inside surface of the RPV. The tube bundle, Fig. 8 and 9, is a 

helical coil consisting of fourteen tubes. There are three separate parallel coils of stainless steel 

tubes. The outer and middle coils consist of five tubes each while the inner coil consists of four 
2-9

tubes. Some SG geometrical data are reported in Table 5. 

Table 5 SG Geometrical Data [18]

Inner Mid Outer

Number of Tubes in Bank 4 5 5

Number of Rotations From Feed Inlet to Steam Outlet 13 9.5 7.5

Average Tube Length of The Bank (m) 6.05 6.15 6.21

Total Average Tube Length (m) 6.21 6.30 6.36

Total Tube Bank Surface Area (m2) 1.209 1.532 1.550

Individual Tube Outside Diameter (m) 0.0159 0.0159 0.0159

Individual Tube Wall Thickness (m) 0.00165 0.00165 0.00165

Each coil is joined at a common inlet header and each of them exhausts the superheated steam into 

a common steam drum from where it is subsequently exhausted to atmosphere via the MS system. 

The FW, enters at the bottom of the SG and boils off after travelling a certain length in the SG. This 

boil off length is a function of both core power and MFW flow rate. Nominally, the boil off length is 

approximately 40% shorter than the actual length of the SG tubes so the steam will leave the SG 

superheated. The value of the degree of the steam superheat is changed in order to control the 

facility.

The steam received in the SG steam drum goes to the MS line, Fig. 10, and that exhausts the SG 

superheated steam to atmosphere. A pneumatic motor operated globe valve MS-502 (MS header 

drain line isolation valve) is immediately downstream of the SG steam drum. Another motor operated 

globe valve, MS-503 (MS header isolation valve), isolates the MS header from the steam header 

drain line. In order to have always an open discharge for the SG, the MS-502 and MS-503 are 

interlocked to prevent them both from being simultaneously commanded shut. 

SteamDrum

SteamLine

Exhaust Steam Header

Figure 10 Main Steam Line Photo [19]
2-10

2.4 OSU-MASLWR Containment Structures 

The HPC, Fig. 11, consists of a lower cylindrical section, an eccentric cone section, an upper 

cylindrical section and an hemispherical upper end head. For scaling reasons, in order to have an 

adiabatic boundary condition in all the wall of the HPC except through the heat transfer plate wall 

where the condensation has to take place, four groups of containment heaters have been installed 

permitting the heat transfer takes place only between the CPV and HPC containment. These 

heaters are located in the exterior surface of the HPC, under the insulation, and above the 

containment water level. The temperatures of the heaters located on the walls of the HPC and the 

temperatures within the walls of the HPC, between the heaters and the water, are measured. The 

HPC level and pressure are measured. The entire HPC is covered by Thermo-12 hydrous calcium 

silicate insulation. 

RPV

CPV HPC

FW lines

Steamline

Heat Transfer Plate

Vent Valves

( High ADS Valves) 

ADS Blowdown Valves

( Middle ADS valves)

ADS Sump Recirculation Valves

Figure 11 OSU-MASLWR Containment Structures [3,17,19,20] 

The CPV consists of a tall right cylindrical tank. One disk rupture is connected between the HPC and

the CPV. The CPV level and water temperature are measured. The CPV is covered by Thermo-12 

hydrous calcium silicate insulation. 

The heat transfer plate, having the same height of the HPC without the hemispherical head, 

provides the heat conduction between the HPC and CPV. The heat transfer plate is scaled in order 

to model the heat transfer area between the MASLWR design high pressure containment vessel 

and the cooling pool in which it sits. 

Five thermocouples are located at six different elevations to measure the temperature distribution 

from the HPC to the CPV. In particular one group of thermocouples measures the water 

temperatures located inside the HPC near the heat transfer plate, one measures the water 

temperatures located inside the CPV near the heat transfer plate, one measures the wall 

temperatures at the midpoint of the heat transfer plate between the CPV and the HPC, one 

measures wall temperatures within the heat transfer plate between the CPV and the HPC nearest to 

the HPC and one measures wall temperatures within the heat transfer plate between the CPV and 

the HPC nearest to the CPV. 
2-11

2.5 OSU-MASLWR ADS Lines

The high ADS lines, Fig. 12, are horizontally oriented and connect the PRZ steam space with the 

HPC. A pneumatic motor operated globe valve is located in each line. Downstream from each 

isolation valve is a transition piece with an internal square-edge orifice. The two high ADS lines 

enter the HPC above the waterline, penetrate it and then terminate with a sparger. 

Figure 12 High ADS Lines Photo [20]

The middle ADS lines are horizontally oriented and connect the RPV CL to the HPC. A pneumatic 

motor operated globe valve is located in each line. Downstream from each isolation valve is a 

transition piece with an internal square-edge orifice. These two lines enter the HPC, penetrate it and

then turn downward before terminating below the HPC waterline. A sparger is considered at the end 

of these lines. 

The ADS sump recirculation lines are horizontally oriented and connect the RPV lower CL to the 

HPC. A pneumatic motor operated globe valve is located in each line. Downstream from each 

isolation valve is a transition piece with an internal square-edge orifice. These two lines enter the 

HPC, penetrate it and then turn downward before terminating below the HPC waterline. No sparger 

is considered for these lines.

The water temperatures inside the ADS lines outside of the HPC are measured. The penetration 

elevation of the HPC and CPV are shown in Fig. 13. 
2-12

Figure 13 HPC and CPV Penetration Elevation [34] 
2-13

2.6 OSU-MASLWR Data Acquisition and Control Subsystem Overview

The data acquisition and control system, Fig. 14 and 15, consists of various field input/output 

modules, a programmable logic controller module, and a desktop computer. The data acquisition 

and control subsystem processes input signals from system components, generates control signals 

as determined by the control logic, and applies those control signals to applicable system 

components. The operator can monitor parameters and alarms in the main control screen, via a 

graphical user interface. Individual system component operation algorithms are considered in the 

facility.

Figure 14 Data Acquisition and Control System [34] 

Figure 15 Data Acquisition and Control System Main Control Screen [34] 
2-14

2.7 OSU-MASLWR Testing Campaign

The first tests conducted on the OSU-MASLWR facility [1, 3, 19] were in support of the MASLWR

concept design verification and are shown in Table 6. 

Table 6 Summary of the Previous DOE Tests Conducted in the OSU-MASLWR 

[1,3,19]

Name of the test Type of test ADS line configuration

Middle 

ADS 1 

(%)

Middle

ADS 2 

(%)

High 

ADS 1 

(%)

High 

ADS 2 

(%)

Sump 

Recirc 1 

(%)

Sump 

Recirc 2 

(%)

OSU-MASLWR-001 Inadvertant actuation of 1 

submerged ADS valve.

Failed 

Shut

100 100 100 100 100

OSU-MASLWR-002 Natural circulation at core 

power up to 210 kW.

N/A N/A N/A N/A N/A N/A

OSU-MASLWR-003A Natural circulation at core 

power of 210 kW.

(Continuation of test 002,

establishing the initial 

conditions for the 003B test)

Failed 

Shut

N/A N/A N/A N/A N/A

OSU-MASLWR-003B Inadvertant actuation of 1 

high containment ADS 

valve

Failed 

Shut

100 Failed 

Shut

100 100 100

The purpose of the test OSU-MASLWR-001, a design basis accident for MASLWR concept design, 

was to determine the behavior of the RPV and containment pressure following an inadvertent 

actuation of one middle ADS valve. The test successfully demonstrated the behavior of the 

MASLWR during one of its design basis accident. The normal opening sequence used in the 

MASLWR for the ADS valves is the middle submerged lines first, after the high containment lines

and finally the sump recirculation lines. This sequence minimizes the rise in containment pressure 

since a large fraction of the energy transferred to the containment is direct into the subcooled 

containment coolant. However, if the high containment lines are actuated first, the rise in 

containment pressure will be larger than the previous. Also the chocked flow in the high containment

line will limit the rate at which the containment and vessel pressure equalize. Therefore the purpose 

of the OSU-MASLWR-003B test is to study the pressure transient in the containment and in the 

primary system during the inadvertent actuation of the high containment ADS vent line. This test 

represents a beyond design basis accident scenario for the MASLWR and demonstrates the vessel 

containment coupling and containment vessel condensation phenomena during the transient. 

The test OSU-MASLWR-002 and OSU-MASLWR-003A investigated the primary system flow rates 

and secondary side steam superheat for a variety of core power levels and FW flow rates. OSUMASLWR-002 test stepped power level incrementally up to 165 kW, varying FW flow rate at each 

power level, and OSU-MASLWR-003A test was an extended 210 kW steady-state test establishing 

initial conditions for the OSU-MASLWR-003B test. During these two tests seven different core 

powers as well as nine different FW flow rates were used. Since the slope of the MS superheat 

curve increases if the value of the core power increases and decreases if the value of the FW flow 

rate increases, the target of these tests was to acquire primary system flow rates and secondary 

side steam superheat for different core powers and FW flow rates. 
2-15

2.7.1 OSU-MASLWR-001 Test Description

The purpose of the OSU-MASLWR-001 test [1,3,4,7,19,20], a design basis accident for MASLWR 

concept design, was to determine the pressure behavior of the RPV and containment following an 

inadvertent actuation of one middle ADS valve. The test successfully demonstrated the blowdown 

behavior of the MASLWR test facility during one of its design basis accident. The main phenomena 

of interest in this kind of transient are [43,49-52]:

• RPV:

o Single phase natural circulation;

o Two-phase natural circulation;

o Heat transfer in covered core;

o Distribution of pressure drop through primary system;

o Primary containment coupling during blowdown and long term cooling typical of the

MASLWR design;

o Structural heat and heat losses;

• HPC:

o Thermal stratification;

o Steam condensation;

o Effect of non-condensable gases on condensation heat transfer;

o Primary containment coupling during blowdown and long term cooling typical of the

MASLWR design;

o Condensation on containment structures - HPC/CPV thermal coupling through the

heat transfer plate;

o Structural heat and heat losses.

• CPV:

o Thermal stratification;

o HPC/CPV thermal coupling through the heat transfer plate.

Following the inadvertent middle ADS actuation the blowdown of the primary system takes place. A 

subcooled blowdown, characterized by a fast RPV depressurization, takes place after the Start Of 

the Transient (SOT). A two-phase blowdown occurs when the differential pressure, at the break 

location, results in fluid flashing. A choked two-phase flow condition prevails and a decrease in 

depressurization rate of the primary system is experimentally observed. When the PRZ pressure 

reaches saturation, single phase blowdown occurs and the depressurization rate increases. The 

RPV and HPC pressure experimentally detected and the primary saturation temperature are shown 

in Fig. 16. The Psat, saturation pressure, is based on the temperature at the core outlet.

At 539s after the SOT the pressure difference between the RPV and the HPC reaches a value less 

than 0.517 MPa, one of the high ADS valve is opened and, with approximately 10s of delay, the 

other high ADS valve is opened equalizing the pressure of the primary and HPC system.

At 561s after the SOT the pressure difference between the RPV and the HPC reaches a value less 

than 0.034 MPa, one of the sump recirculation valves is opened and, with approximately 10s of 

delay, the other sump recirculation valve is opened terminating the blowdown period and starting the 

refill period. The refill period takes place for the higher relative coolant height in the HPC compared 

to the RPV. Fig. 17 shows the RPV level evolution experimentally detected during the test. The RPV 

water level never fell below the top of the core during the execution of the test 1. Fig. 18 shows the 

HPC level behavior experimentally detected.
2-16

During the saturated blowdown period, the inlet and the outlet temperature of the core are equal 

each other assuming the saturation temperature value. A core reverse flow and a core coolant 

boiling off at saturation is present in the facility during this period. When the refill takes place the 

core normal flow direction is restarted and a delta T core is observed depending on the refill rate 

and core power, Fig. 19.

Figure 16 RPV and HPC Pressure Behavior during the OSU-MASLWR-001 

Test [1,3,19,20]

Figure 17 RPV Water Level Behavior during the OSU-MASLWR-001 Test [1,3,19,20]
2-17

Figure 18 HPC Water Level Behavior during the OSU-MASLWR-001 Test [20]

Figure 19 Inlet/Outlet Core Temperature Behavior during the OSU-MASLWR-001 

Test [1,19,20]

When the refill of the reactor takes place the level of the coolant reaches the location of the flow rate 

HL measurement point, therefore a “large” increase of the RPV flow rate is detected for this 

phenomenon, Fig. 20. 
2-18

Figure 20 RPV Flow Rate during the OSU-MASLWR-001 Test [1,19,20]

2.7.2 OSU-MASLWR-002 Test Description

The test OSU-MASLWR-002 and OSU-MASLWR-003A [1,3,7,18,19] investigated the primary 

system flow rates and secondary side steam superheat for a variety of core power levels and FW 

flow rates. Table 7 shows the OSU-MASLWR-002 and OSU-MASLWR-003A test conditions. 

The main phenomena of interest in this kind of transient are [43, 49-52]: 

• RPV:

o Single phase natural circulation;

o Heat transfer in covered core;

o Distribution of pressure drop through primary system;

o Direct heat exchange between riser and downcomer (by pass heat transfer [18, 43]);

o Heat transfer in SG primary side;

o Structural heat and heat losses.

• RPV-SG:

o Heat transfer in SG secondary side;

o Steam superheated on secondary side.

The OSU-MASLWR-002 stepped power level incrementally up to 165 kW, varying FW flow rate at 

each power level. Since the 210 kW data in OSU-MASLWR-002 was not used, because of a liquid 

carry over in the SG, the OSU-MASLWR-003A was an extended 210 kW steady-state test 

establishing initial conditions for the OSU-MASLWR-003B. During these two tests seven different 

core powers were used as well as nine different FW flow rates. Fig. 21 shows the inlet/ outlet core 

and the top of the HL temperature during the OSU-MASLWR-002 test. 
2-19

In general the value of the degree of the steam superheat is changed in order to control the facility. 

Since the slope of the MS superheat curve increases if the value of the core power increases and 

decreases if the value of the FW flow rate increases, the target of these tests was to acquire primary 

system flow rate and secondary side steam superheat for different core powers and FW flow rates. 

The difference between the MS saturation temperature and the measured MS temperature is used 

to estimate the value of the MS superheat. Fig. 22 shows the steam superheat data for the test 

OSU-MASLWR-002. 

By analysing the experimental data, related to the flow temperature after the SG coils primary side 

section and the core inlet temperature, it is evident that the direct heat exchange, by pass heat 

transfer, through the internal shell, between the fluid ascending the HL and the fluid descending the 

CL, is a crucial parameter for the evaluation of the core inlet temperature and, therefore, the core 

outlet temperature. In fact, the experimental data show that, along the downcomer region, the fluid 

increases its temperature between the end of the SG primary side section and the core inlet . Fig. 23 

shows the difference of fluid temperature at the inlet of the core and at the exit of the SG primary 

side for the OSU-MASLWR-002 test. 

Table 7 OSU-MASLWR-002 and OSU-MASLWR-003A Test Conditions [1,3,7,19]

Test

Start

time

(s)

End 

Time

(s)

Primary Secondary

Core

Power 

(kW)

T_in

(K)

T_out

(K)

Flow 

(L/min)

Vel

(m/s)

T_in

(K)

T_Out

(K)

P

(MPa)

Feed

Water

(kg/min) 

002

0 127 80.0 489 506 65.6 0.13 292 482 1.41 1.13 

250 550 100.0 491 509 77.9 0.16 292 488 1.40 1.81 

750 1200 100.0 490 508 80.0 0.16 292 494 1.38 2.14 

1380 1570 100.0 486 505 81.9 0.17 292 494 1.37 2.50 

1670 1920 110.0 483 503 84.9 0.17 292 493 1.36 2.49 

2060 2250 125.0 482 503 88.5 0.18 292 493 1.35 2.50 

2450 2600 160.0 481 505 104.1 0.21 292 488 1.36 3.85 

2700 2930 165.0 478 503 105.0 0.21 293 482 1.35 3.83 

003A

0 450 210.0 501 528 118 0.24 293 507 1.581 4.14 

550 1000 210.0 499 526 120 0.24 293 509 1.567 4.56 
2-20

Figure 21 Inlet, Outlet Core and Top of the Hot Leg Temperature Behavior during 

the OSU-MASLWR-002 Test [1,18,19]

Figure 22 Steam Superheat at the SG Outlet Behavior during the OSU-MASLWR002 Test [3,19]
2-21

Figure 23 Difference of Fluid Temperature at the Inlet of the Core and at the Exit of the 

SG Primary Side during the OSU-MASLWR-002 Test [18,19]

3-1

3. CODE APPLICATION

3.1 TRACE Code Description

In the past, to support independent vendor review of reactor LWR designs, the USNRC has 

maintained four separate computer codes (RAMONA, the RELAP5, the TRAC-B and the TRAC-P) 

for analysing system thermal hydraulic response. 

Over the past ten years, the NRC has developed an advanced best estimate thermal hydraulic 

system code, by merging, among other things, the capability of the previous codes into a single 

code. This new code is called TRAC/RELAP Advanced Computational Engine or TRACE [44], and 

is a component-oriented code designed to perform best estimate analyses for LWR. In particular 

TRACE is developed to simulate operational transient, LOCA, other transient typical of the LWR and 

to model the thermal hydraulic phenomena taking place in the experimental facilities used to study 

the steady state and transient behavior of reactor systems. 

TRACE is a finite volume, two-fluid, code with 3D capability which gives user the ability to model 

heat structures and control systems that interact with component models. It can be run coupled with 

the 3D reactor kinetics code PARCS as well. TRACE can be used together with a user-friendly front 

end, Symbolic Nuclear Analysis Package (SNAP) [45], which allows direct visualization of selected 

calculated data using the animation model capability, visualization of models, and accepts existing 

RELAP5 and TRAC-P input. The computational complexity of a generic TRACE model is only 

limited by the availability of the computer memory. Fig. 24 shows the TRACE/SNAP environment 

architecture. 

SNAP System

ModelDatabase

RELAP5 ASCII

Input

TRAC-P ASCII

Input

TRAC-B ASCII

Input

SNAP

TRACE Input 

Processing

Computational

Engine

Other Support

Applications

3D Neutron

Kinetics

Platform Independent

Binary File 

Interprocess Message

Passing Service

Figure 24 TRACE/SNAP Environment Architecture [18,20,46] 
3-2

The code is based on two fluid, two-phase field equations. This set of equations consists of the 

conservation laws of mass, momentum and energy for liquid and gas fields. The resulting equation 

set is coupled to additional equations for non-condensable gas, dissolved boron, control systems 

and reactor power. Relations for wall drag, interfacial drag, wall heat transfer, interfacial heat 

transfer, equation of state and static flow regime maps are used for the closure of the field 

equations. The interaction between the steam-liquid phases and the heat flow from solid structures 

is also considered. These interactions are in general dependent on flow topology and for this 

purpose a special flow regime dependent constitutive-equation package has been incorporated into 

the code. TRACE uses a pre-CHF flow regime, a stratified flow regime and a post-CHF flow regime. 

In order to study the thermal history of the structures the heat conduction equation is applied to 

different geometry. A 2D(r and z) treatment of conduction heat transfer is taken into account as well. 

A finite volume numerical method is used to solve the partial differential equations governing the 

two-phase flow and heat transfer. By default, a multi-step time-differencing procedure that allows the 

material Courant-limit condition to be exceeded is used to solve the fluid-dynamics equations [8,11-

32,44]. 

3.2 TRACE Model Description

The OSU-MASLWR TRACE model [11-32,37-43] was developed using SNAP and is shown in Fig. 

25. This model has been revised and applied for the simulation of the IAEA-ICSP test SP-2 and SP3 [37-43]. In particular, a complete review of the facility geometry has been implemented (height VS 

volume plot, mass and surface of the heat structures, etc); a first estimation of the heat losses of the 

facility has been completed. The IAEA-ICSP SP-3 value of about 5 kW has been assumed for the 

heat losses calibration [37-43].

Figure 25 OSU-MASLWR Model [11-32,37-43] 

The nodalization models the primary and the secondary circuit, the HPC, the heat transfer plate and 

the CPV. The ADS blowdown lines, vent lines and sump recirculation lines are modelled as well. 

The “slice nodalization” technique is adopted in order to improve the capability of the code to 
3-3

reproduce natural circulation phenomena. This technique considers mesh cells of different

nodalization zones, at the same elevation, with the same cell length. In this way errors due to the 

position/elevation of the cell nodalization center that can influences the results of the calculated data 

when natural circulation regime is present are reduced. If the “slice nodalization” technique is not 

used, this error has to be taken into account and its effect increases if larger nodalization cells are 

used. In this case it can be reduced by using a “fine nodalization”. In general, its effect on the results 

is less important when forced circulation regimes are simulated. However the “slice nodalization” 

technique could require nodes of small length which would increase the numerical error and the 

computational time. The “code user” has to take into account these disadvantages during the 

nodalization development [20]. 

The primary circuit of the TRACE model comprises the core, the HL riser, the UP, the PRZ, the SG 

primary side, the CL downcomer and the LP. After leaving the top of the HL riser, the flow enters

the UP which is divided into two thermal hydraulic regions connected to the PRZ. After leaving the 

UP the flow continues downward through the SG primary section and into the CL downcomer 

region. The core is modelled with one thermal hydraulic region thermally coupled with one 

equivalent active heat structure simulating the 56 electric heaters. The PRZ is modelled with two 

hydraulic regions, connected by different single junctions, in order to allow for simulation of potential

natural circulation/convection phenomena. The three different PRZ heater elements are modelled 

with one equivalent active heat structure. The thick baffle plate is modelled as well. Fig. 26 shows 

the heat structures considered in the TRACE nodalization. The direct heat exchange by the internal 

shell between the hotter fluid in the hot leg riser and the colder fluid in the descending annular 

downcomer is modelled by heat structures thermally coupled with these two different hydraulic 

regions. Fig. 27 shows the correspondence between the TRACE model and the facility lower shell 

section.

RPV Shell +Insulation

PRZ Heaters

Thick Baffle Plate

Helical Coils

Hot Leg Lower Shellthermal coupling

between ascending and descending side

Hot Leg Upper Shell thermal coupling

between ascending and descending side

Flange

Core Active Length

CoreNon Active Length

Core Shroud

RPV Bottom

RPV Head + insulation

SteamDrum Externall Shell+Insulation

SteamDrum Shell

Figure 26 Heat Structures Modeled in the TRACE Nodalization [11-32,37-43] 
3-4

Figure 27 Correspondence Between the TRACE Model and the Facility Lower Shell 

Section [11-32,37-43] 

SG coils are modelled with only one “equivalent” vertical group of pipes thermally coupled by an

equivalent heat structure with the SG primary side section. A model with three different equivalent

oblique groups of pipes has been implemented as well. Previous analyses, based on the TRACE

simulation of the OSU-MASLWR-002 test [18], show that the instabilities of the superheat condition 

of the fluid at the outlet of the SG, observed in previous analysis [11] as well, are also related to the 

equivalent SG model. Since in these analyses a model with one equivalent vertical group of pipes 

shows a more stable fluid temperature at the SG outlet, this model is used as reference for the 

analysis of the OSU-MASLWR 001 and 002 test presented in this document. Since no specific 

helical coil heat transfer correlations have been implemented in the TRACE V5 patch 3, considering 

the results reported in [21, 22, 23, 43], in order to reach the initial conditions of the OSU-MASLWR001 and 002 tests, the heat transfer area of the equivalent helical coil SG heat structure is 

incremented. 

The RPV, HPC and CPV shell and the connected insulation are modelled. In particular the HPC is 

modelled with one hydraulic region connected by a heat structure, representing the heat transfer 

plate, to the CPV simulated with another hydraulic region. The ADS lines are modelled separately in 

order to simulate the OSU-MASLWR-001 test logic. The sparger (vent and blowdown ADS lines) is 

modelled in the ADS line along with the orifice (sump return, vent and blowdown lines) and the heat 

structure with related insulation [13, 20]. The heat losses of these lines are taken into account. The 

RPV, HPC and CPV shell and the connected insulation are modelled. 

The list of the facility instrumentation versus TRACE model measurement points is shown in the 

Table 8 and it is presented in the Fig. 28. 
3-5

Table 8 Facility Instrumentation vs TRACE Nodalization Measurement Points[37-43]

Facility 

Instrumentation

TRACE model 

measurement points

PT 301 1325 cell 2

TF 121, 122, 123, 124 51 cell 1 - sv 175

TF 106 21 cell 2 – sv 176

FDP 131 111 edge 1 - cb15

TF 111 141 cell 2 - sv 177

TF 131, 133, 134 91 cell 1 – sv 178

TF 132 21 cell 12 – sv 195

TF-301 1325 cell 2 – sv 196

DP 101 [RV 101 - 102] cb22 [1 cell 1 - 21 cell 2]

DP 102 [RV102 - 103] cb23 [21 cell 2- 21 cell 5]

DP 103 [RV 103 - 104] cb24 [21 cell 5 - 21 cell 8]

DP 104 [RV 104 - 108] cb25 [21 cell 8 - 141 cell 2]

DP 105 [RV 105 - 108] cb55 [141 cell 2 - 101 cell 1] 

DP 106 [RV 101 - 105] cb56 [101 cell 1 - 1 cell 1]

LDP 301 cb12

LDP 106 cb18

KW-101, 102 Heat structure 915 - Power 

915

FCM 511 1071 edge 5

FCM 521 1061 edge 3

FCM 531 1051 edge 2

PT 511 1071 cell 5 

PT 521 1061 cell 3

PT 531 1051 cell 2

PT-511-521-531 ave 903 cell 1

TF 611, 612, 613, 614, 

615 771 cell 1

TF 621, 622, 623, 624, 

625 621 cell 1

TF 631, 632, 633, 634 431 cell 1

Average SG Outlet T

(611-634)

431 cell 1 ( one equivalent 

SG) – sv 179

1196 cell 1 – sv 194
3-6

FVM 602 T 1021 cell 20 – sv 180

FVM 602 P 1021 cell 20

Secondary steam 

superheat cb30

FMM-501 1315 edge 1

TF 501 1315 cell 1 – sv 181

Heat Losses cb2

TF 811 1595 cell 9 – sv 182

TF 821 1595 cell 18 – sv 183

TF 831 1595 cell 24- sv 184

TF 841 1595 cell 30 – sv 185

TF 851 1595 cell 36 – sv 186

TF 861 1595 cell 38 – sv 187

TF 812, 822, 832, 842, 

852, 862 1615 A9, 18,24,30,36,38 R02

TF 813, 823, 833, 843, 

853, 863 1615 A9, 18,24,30,36,38 R03

TF 814, 824, 834, 844, 

854, 864 1615 A9, 18,24,30,36,38 R04

TF 815 1605 cell 14 – sv 188

TF 825 1605 cell 23 - sv 189

TF 835 1605 cell 29- sv 190

TF 845 1605 cell 35 – sv 191

TF 855 1605 cell 41 – sv 192

TF 865 1605 cell 43 –sv 193

LDP 801 sv73

PT 801 1595 cell 1

LDP 901 sv74
3-7

TF 111141 cell 2

TF 131, 133, 13491 cell 1

TF 121, 122, 123, 12451 cell 1

PT 8011595 cell 1

TF-811

TF

1595 cell 9

-831

1595 cell 24

FDP 131  111 edge 1

TF 132 21 cell 12

TF 106 21 cell 2 

PT 301, TF 301  1325 cell 2 PT 602  1021 cell 

TF-821

TF

1595 cell 18

-841

TF

1595 cell 30

-851

TF

1595 cell 36

-861

1595 cell 38

TF-815

TF

1605 cell 14

-825

TF

1605 cell 23

-835

TF

1605 cell 29

-845

TF

1605 cell 35

-855

TF

1605 cell 41

-865

1605 cell 43

TF 611, 612, 

613, 614, 615 

771 cell1 

TF 621, 622, 

623, 624, 615 

621 cell1 

TF 631, 632, 

633, 634, 

 431 cell1 

PT 511 1071 cell 5

FCM 511 1071 edge 5

PT 521 

1061 cell 3

FCM 521

1061 edge 3 PT 53

1051 

FCM 

edge 

FMM 501 1315 edge 1 

Figure 28 Measurement Points in the TRACE Nodalization [37-43]

3-7
3-8

3.3 Analyses of the OSU-MASLWR-001 Calculated Data

Starting from the calculated data developed in previous analyses [12, 13, 14, 16, 20] the target of 

this section is to give an expanded revised analyses of the TRACE V5 Patch 3 code capability in 

predicting the primary/containment coupling phenomena typical of the MASLWR prototypical design. 

For scaling reasons, in order to have an adiabatic boundary condition in all the walls of the HPC 

except through the heat transfer plate wall, containment heaters have been installed and are in 

operation during this test, two different calculations have been performed. In the reference case the 

HPC is assumed to be adiabatic in all the walls of the HPC except through the heat transfer plate 

wall and no heater operation has been considered during the transient simulation (REF plot 

reference); in the sensitivity case, no adiabatic conditions have been considered for the HPC walls 

and the HPC heaters were in operation during the transient simulation (SEN1 plot reference). 

In order to reach the Boundary and Initial Condition (BIC) a pre-test phase has been conducted. The 

pre-test phase started at about 2814s before the SOT (-2814s) and the main facility procedures to 

reach the BIC, characterizing that time window (from -2814s to 0s) have been implemented in the 

TRACE model. The facility configuration before the SOT of the OSU-MASLWR-001 test is reported 

in Table 9. The core power time evolution and the FW time evolution are imposed as boundary 

conditions during this phase while the PRZ heaters are assumed to be in operation in order to 

maintain the primary pressure set-point; the HPC heaters are OFF in the reference case and are ON 

in the sensitivity case. The ADS valves are closed.

Table 9 Facility Configuration Before the SOT of the OSU-MASLWR-001 Test

System Facility 

Operation

TRACE Model

Operation

Note

REF SEN1

Core Heaters ON ON ON

PRZ Heaters ON ON ON In order to maintain the primary pressure setpoint.

HPC Heaters ON OFF ON In order to have an adiabatic boundary condition 

in all the walls of the HPC except through the 

heat transfer plate wall.

Feed Water ON ON ON In order to remove the net primary power 

[primary power less ambient losses].

ADS Valves Closed Closed Closed

Before the SOT, the TRACE code predicts a primary system in sub cooled condition with singlephase natural circulation. The primary pressure is at about 7.6 MPa and the PRZ heaters are set up 

to maintain the primary pressure at the fixed set point. The secondary fluid, circulating inside the 

helical coil tubes removes the core power (less the facility heat losses from the primary fluid and 

goes out from the SG as superheated steam). The outlet SG secondary pressure is around 2.2e5 

Pa. The ADS middle line valves, the ADS high line valves, and the ADS sump recirculation line 

valves are closed. Since no helical coil heat transfer correlation have been implemented in the 

TRACE V5.0 Patch 3, in agreement with previous analyses [21, 22, 23, 43], the heat transfer area 

of the equivalent helical coil SG heat structure is incremented in order to reach the initial conditions 

of the OSU-MASLWR-001 test.

Table 10 shows the initial conditions predicted by the TRACE code against the experimental initial 

conditions for the REF and SEN1 case. Figure 29 and 30 show the fluid condition of the facility at 

the SOT for the REF and SEN1 case respectively and the different fluid conditions in the upper part 

of the HPC in the two different calculations. In general the initial conditions are predicted by the 

TRACE code in both REF and SEN1 case. The discrepancies related to TF 891, 892, 893, 894
3-9

(temperatures within the walls of the HPC, between the heaters and the water) in the REF case are 

due to the lack of the HPC heaters. The facility configuration for the simulation of the OSUMASLWR-001 test is summarized in the Table 11. The experimental core power behavior is 

implemented in the TRACE model as a boundary condition. The experimental logic of the valves is

implemented in the TRACE model as it is shown in Table 11. Table 12 shows the event sequence 

for the experimental test and that predicted by the TRACE code.

The analysis of the OSU-MASLWR-001 calculated data shows that the TRACE code is able to 

reasonably2 predict the primary/containment coupling phenomena characterizing the test. The 

blowdown phenomena, the refill of the core and the long term core cooling, permitting of removing 

the decay power, are reasonably predicted by the code. In particular, following the inadvertent 

middle ADS actuation, the blowdown of the primary system takes place. A subcooled blowdown, 

characterized by a fast RPV depressurization, is predicted by the code after the SOT. When the 

differential pressure in the facility at the break location results in flashing, a two-phase blowdown, 

qualitatively predicted by the code, occurs. A decrease in depressurization rate of the primary 

system is then observed which is in agreement with the experimental data. When the PRZ pressure 

reaches saturation, single phase blowdown occurs and the depressurization rate increases again, in 

agreement with the experimental data. The RPV and HPC pressure versus code calculations are 

shown in Fig. 31. 

Table 10 SOT Thermal Hydraulic Conditions Comparison (TRACE Calculated Data 

vs Experimental Data) for the OSU-MASLWR-001 Test

Parameter EXP TRACE (REF) TRACE 

(SEN1)

Core Power (W) 39134 39200 39200

PRZ Pressure (Pa) 7718000 7645646 7643602

T Outlet Core (K) 523 522 521

T Inlet Core (average) (K) 514 511 511

Primary Volumetric Flow 

Rate (m3/s)

0.0005* 0.0007 0.0007

PRZ Level (m) 0.21 0.25 0.24

T In SG (K) 293 293 293

P Inlet SG (average) (Pa) 1.32e5 1.3e5 1.3e5

P Outlet SG (Pa) 2.17e5 2.2e5 2.2e5

T Outlet SG (K) 487 525 525

Secondary Mass Flow 

Rate (kg/s)

0** 0 0

HPC Level (m) 2.35 2.41 2.41

HPC Pressure (Pa) 1.22e5 1.16e5 1.22e5

TF-811(K) 284 286 286

TF-891(K) 400 321 401

TF-892(K) 475 362 475

TF-893(K) 478 360 478

TF-894(K) 489 361 485

CPV Level (m) 6.35 6.3 6.3

TF-815 (m) 283 283 283

* The primary flow rate starts to decrease at about -28s before the SOT (at 31s before the SOT the

core power starts to decrease from about 65 kW); the value before starting the decrease is around 

0.001m3/s. The value predicted by the TRACE code is around 0.001 m3/s.

**The FW starts to decrease at -10s of the SOT; the value before starting the decrease is around 

0.0195 kg/s. The value predicted by the TRACE code is 0.0195 kg/s.
3-10

Table 11 Facility Configuration for the Simulation of the OSU-MASLWR-001 Test

System Facility 

Operation

TRACE Model

Operation

Note 

REF SEN1

Core Heaters ON ON ON

PRZ Heaters OFF OFF OFF

HPC Heaters ON OFF ON

Feed Water OFF OFF OFF

Middle ADS Failed shut Failed shut Failed shut

Middle ADS 100% following 

the logic

100% following 

the logic

100% following 

the logic

High ADS 100% following 

the logic

100% following 

the logic

100% following 

the logic

Valve opens when the 

pressure difference 

between RPV and HPC 

(PT-301 minus PT 801) 

is less than 0.517 MPa.

High ADS 100% following 

the logic

100% following 

the logic

100% following 

the logic

Valve open with 10s of 

delay with respect to the 

other high ADS valve.

Sump 

Recirculation

100% following 

the logic

100% following 

the logic

100% following 

the logic

Valve opens when the 

pressure difference 

between RPV and HPC 

(PT-301 minus PT 801) 

is less than 0.034 MPa.

Sump 

Recirculation

100% following 

the logic

100% following 

the logic

100% following 

the logic

Valve open with 10s of 

delay with respect to the 

other sump recirculation

ADS valve.

Table 12 Event Transient Sequence of the OSU-MASLWR-001

Parameter Facility 

Operation

TRACE

(REF)

TRACE

(SEN1)

SOT* 0s 0s 0s

Middle ADS Opens 0s 0s 0s

Core Power Decrease 3s 3s 3s

First High ADS Valve Opens 539s 548s 511s

Second High ADS Valve Opens 549s 558s 521s

First Sump Recirculation ADS Valve Opens 561s 584s 537s

Second Sump Recirculation ADS Valve Opens 571s 594s 547s

The FW starts to decrease at -10s of the SOT.

____

2

Qualitative analyses subjective judgment mark [47]:

• Excellent – calculation falls within experimental data uncertainty band –: the code predicts qualitatively and quantitatively the 

parameter;

• Reasonable – calculation shows only correct behavior and trends –: the code predicts qualitatively, but not quantitatively the 

parameter;

• Minimal – calculation does not lie within experimental data uncertainty band and at times does not have correct trends–: the

code does not predict the parameter, but the reason is understood and predictable;

• Unqualified – calculations does not show correct trend and behavior, reasons are unknown and unpredictable–: the code does 

not predict the parameter and the reason is not understood;

• Not applicable (–).
3-11

Time: -50s 

Figure 29 SNAP Animation Model Showing the Fluid Condition of the TRACE Model 

at 50s Before the SOT (REF Plot Reference - Cold HPC)

Time: -50s 

Figure 30 SNAP Animation Model Showing the Fluid Condition of the TRACE Model 

at 50s Before the SOT (SEN1 Plot Reference - Hot HPC)
3-12

Subcooled 

blowdown

Two Phase 

blowdown

Single Phase 

blowdown

Figure 31 Experimental Data versus Code Calculation for PRZ (PT-301) and HPC 

(PT-801) Pressure

In agreement with the experimental data, when the pressure difference between the RPV and the 

HPC reaches a value less than 0.517 MPa [REF case 548s - EXP 539s], one of the high ADS

valves is opened. After 10s, also in agreement with the experimental test logic, the other High ADS 

valve opens. This equalizes the RPV and HPC pressure. When the pressure difference reaches a 

value less than 0.034 MPa [REF case, 584s – EXP 561s], the sump recirculation valve is opened. 

After 10s the other sump recirculation valve opens. The consequent core refill phenomenon is 

predicted by the code. As in the experimental data, the refill period takes place for the higher relative 

coolant height in the HPC compared to the RPV. Fig. 32 shows the RPV level evolution 

experimentally recorded during the test versus the TRACE predictions. In agreement with the 

experimental data, the RPV water level never fell below the top of the core. Fig. 33 shows the HPC 

level versus code calculation, the qualitative behavior is well predicted by the TRACE code.

In agreement with the experimental data, during the saturated blowdown period the inlet and the 

outlet temperature of the core are equal to each other assuming the same saturation temperature. 

Both core reverse flow and a core boiling off at saturation are reasonably predicted by the code.

When the refill takes place, the core normal flow direction is restarted. Fig. 34 and 35 shows the 

experimental data versus code calculation for outlet and the average inlet core temperature 

respectively. Fig. 36 shows the experimental data versus code calculation for RPV volumetric flow 

rate.

In agreement with the experimental data, when the sump recirculation valves are opened, the vapor 

produced in the core travels to the upper part of the RPV and through the high ADS valve goes to 

the HPC where it is condensed. At this point, the condensate travels through the sump recirculation 

line, into the down comer, and returns to the core. Fig. 37 shows the long term cooling flow path 

typical of the MASLWR design.

The analysis of the calculated data shows that the TRACE code is able to reasonably predict the 

primary/containment coupling during blowdown and long term cooling and the related single and two 

natural circulation phenomena taking place in the RPV/HPC coupled natural circulation loop. The 
3-13

related heat transfer in covered core (the core is never uncovered during the experimental transient 

and calculated transient) is reasonably predicted as well.

Figure 32 Experimental Data versus Code Calculation for RPV Level (LDP-106)

Figure 33 Experimental Data versus Code Calculation for HPC Level (LDP-801)
3-14

Figure 34 Experimental Data versus Code Calculation for Core Outlet Temperature

(TF-106)

Figure 35 Experimental Data versus Code Calculation for the Average Core Inlet 

Temperature (Average value of TF-121, TF-123, TF-124)
3-15

Figure 36 Experimental Data versus Code Calculation for RPV Volumetric Flow 

Rate (FDP-131)

Figure 37 Long Term Cooling Flow Path Typical of the MASLWR Design

In order to characterize the thermal stratification in large containment cooling pool, the HPC 

temperatures (TF-811, TF- 821, TF-831, TF-841, TF-851, TF-861) were analyzed. In general, the 

qualitative experimental time trend is predicted by the code in the REF and SEN1 case though 

quantitative discrepancies exist. The TRACE results show a general overestimation of temperature 

in comparison with the experimental data. This could be due to the 1D model of the HPC that 
3-16

doesn’t allow the natural circulation and mixing phenomena in the HPC or the position of the 

thermocouples. The thermocouples are located very close to the heat transfer plate where the 

condensation takes place and do not represent the average bulk fluid temperature. The temperature 

calculated by the TRACE code is the average temperature related to the nodalization volume. The 

general qualitative behavior of the temperatures in the HPC, during the transient, is not affected by 

the initial condition of the HPC (Hot or Cold). In the SEN1 case a general greater overestimation, in 

comparison with the REF case, of the HPC temperatures is obtained. Greater discrepancies are 

observed in the TF-861 code prediction. This is related also to the nodalization strategy of using only 

one pipe to simulate the HPC, which doesn’t simulate the mixing phenomena taking place in the 

upper part of the HPC. A more detailed 3D HPC model, by using the “vessel component” available 

in TRACE, may provide a better quantitative estimation of the HPC temperatures. In this way it is 

possible to simulate the natural circulation and the mixing phenomena in the upper part of the HPC. 

Fig. 38, as an example, shows the experimental data versus code calculation for TF-811. The 

comparisons between the calculated data and the experimental data in relation to the TF- 821, TF831, TF-841, TF-851, TF-861 are reported in the Appendix A.

Figure 38 Experimental Data versus Code Calculation for TF-811

In order to characterize the thermal stratification in large containment cooling pool, the CPV 

temperatures (TF-815, TF-825, TF-835, TF-845, TF-855, TF-865) were analyzed. The TF-815, TF825, TF-835, and TF-845 transient data are characterized by a slow temperature increase. TF-855 

experimental data is characterized by temperature oscillations; TF 865 shows first a slow increase 

followed by a second more rapid increase (Appendix A). In general the TRACE calculation results 

show a constant temperature increase with a general underestimation compared to experimental 

data. This could be related also to the position of the thermocouples; in fact they are located very 

close to the heat transfer plate as well. No oscillations are predicted by the code for the TF 855 

behavior. Fig. 39, as an example, shows the experimental data versus code calculation for TF-815. 

The comparison between calculated data and experimental data, in relation to the TF 825, TF 835, 

TF 845, TF 855, TF 865, is reported in the Appendix A. 
3-17

Figure 39 Experimental Data versus Code Calculation for TF-815

The results of the sensitivity study (SEN1 plot reference) shows that the qualitative trend of the 

calculated data is similar, as expected, but the RPV/HPC pressure, Fig. 40, and temperatures, Fig. 

41 and 42, are in general over predicted by TRACE if the HPC heaters are in operation. Therefore 

the RPV/HPC coupled system stored energy calculated by TRACE is higher than the experimental 

data. This could be due to the 1D HPC TRACE nodalization. A 3D model, by using the “vessel 

component” available in TRACE, may better simulate the natural circulation and the mixing 

phenomena in the HPC. The sequence of events of the SEN1 case in comparison with the REF 

case, and the experimental data is shown in Table 12. The comparison of RPV level behavior is 

shown in Fig. 43. The temperature behavior and the fluid condition of the HPC, in different times of 

the transient, are shown in Figs. 44-51 for both REF and SEN1 case. 

In the Appendix A the main parameter evolutions and comparison between calculated and 

experimental data are reported. 

From a quantitative point of view the results of the calculated data show a general over prediction of 

the primary side pressure and temperatures compared with the experimental data. It is thought that 

this could be due to a combination of selection of vent valve discharge coefficients, condensation 

models applied to the inside surface of the containment, and to the 1D model of the HPC [12,16,20]. 

As it is shown in the [20] the correct prediction of the facility heat losses is an important parameter to 

accurately predict the transient evolution. The heat losses imposed as boundary condition has been 

calibrated considering the information’s distributed during the IAEA ICSP [43]. 
3-18

Figure 40 Experimental Data versus Code Calculation for PRZ (PT-301) and HPC 

Pressure (PT-801) for REF and SEN1 Case

Figure 41 Experimental Data versus Code Calculation for Core Outlet T (TF-106) 

for REF and SEN1 Case
3-19

Figure 42 Experimental Data versus Code Calculation for TF-821 for REF and 

SEN1 Case

Figure 43 Experimental Data versus Code Calculation for RPV Level (LDP-106) for 

REF and SEN1 Case
3-20

Time: 0s

Figure 44 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=0s (REF Plot Reference)

Time: 0 s

Figure 45 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=0s (SEN1 Plot Reference)
3-21

Time: 80s

Figure 46 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=80s (REF Plot Reference)

Time: 80 s

Figure 47 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=80s (SEN1 Plot Reference)
3-22

Time: 515s

Figure 48 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=515s (REF Plot Reference)

Time: 515 s

Figure 49 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=515s (SEN1 Plot Reference)
3-23

Time: 1750 s

Figure 50 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=1750s (REF Plot Reference)

Time: 1750 s

Figure 51 Fluid Condition and Temperature Visualization of the HPC, by using 

SNAP, at T=1750s (SEN1 Plot Reference)
3-24

The general qualitative conclusions of this revised analyses are in agreement with the results of the 

calculated data reported in the previous studies [12,13,14,16,20]. A better quantitative prediction of 

the TRAFE code is obtained with the REF analysis. Of particular interest is the analyses reported in 

the [12] where the application of the TRACE, RELAP5 Mod3.3 and RELAP5-3D code shows that the 

codes are able to qualitatively predict primary/containment coupling phenomena in the MASWLR 

tests. As it is shown in [13] and confirmed in [20] a detailed TRACE nodalization of the ADS lines, 

including the nodalization of the sparger, is necessary in order to have a better prediction of the 

calculated data as it is shown from better qualitative behavior of the RPV and HPC pressure 

obtained in the calculated data.

A matrix of phenomena observed test OSU-MASLWR-001 and TRACE code is shown in Table 133. 

Table 13 Test versus Phenomena, TRACE Prediction vs Phenomena [43, 49-52]

Phenomenon Experiment TRACE 

code

Phenomena Measurement Phenomena

Single-Phase Natural Circulation + + +

Two-Phase Natural Circulation + NA +

Heat Transfer in Covered Core + + +

Distribution of Pressure Drop Through 

Primary System

+ + +

Primary-Containment Coupling During 

Blowdown And Long Term Cooling

+ o +

Structural Heat And Heat Losses + o +

Break Flow + o +

Behavior of Large Pool: 

Thermal Stratification (HPC)

+ + +

Behavior of Large Pool: 

Natural Convection (HPC)

+ NA NA*

Behavior of Large Pool:

Steam Condensation (HPC)

+ NA +

Effect of Non-Condensable Gases On

Condensation Heat Transfer (HPC)

+ NA +

Condensation on Containment

Structures (HPC)

+ o +

Behavior of Large Pool: 

Thermal Stratification (CPV)

+ + +

Behavior of Large Pool: 

Natural Convection (CPV)

+ NA NA*

*The natural circulation phenomena in HPC and CPV are not predicted by the TRACE code for the 1D

nodalization strategy of the HPC and CPV. A 3D model, by using the vessel component, could permits the 

prediction of these phenomena.

____

3

Experimental facility and code qualitative phenomena prediction evaluation:

+ o NA -

Experimental 

data

Phenomenon occurred 

in the test and it is 

directly measured

Phenomenon occurred in the test 

and it is indirectly measured 

Phenomenon occurred 

during the test but there is 

no instrumentation to 

detect (lack of 

instrumentation)

Phenomenon 

not occurred in 

the test

Calculated 

data

Phenomenon is clearly 

predicted by the code

(Excellent/Reasonable)

Phenomenon is partially predicted 

(i.e. the answer of the code is 

reasonable but closure code relation 

are not appropriate, etc) 

Models are not 

appropriate to predict (i.e. 

nodalization strategy, etc)

(Minimal)

Phenomenon 

is not 

predicted by 

the code

(Unqualified)
3-25

3.4 Analyses of the OSU-MASLWR-002 Calculated Data

Starting from the TRACE calculations developed in previous analyses [11,13-16,18,23], the purpose

of this section is to give an expanded revised analyses of the TRACE V5.0 code capability in 

predicting the natural circulation phenomena and heat exchange from primary to secondary side by 

helical SG in superheated condition, typical of the MASLWR design, by simulating the OSUMASLWR-002 test.

In order to reach the BIC a pre-test phase has been conducted. The pre-test phase started at about 

2295s before the SOT (-2295s) and the main facility procedures to reach the BIC characterizing that 

time window (from -2295s to 0s) have been implemented in the TRACE model. The facility 

configuration before the SOT of the OSU-MASLWR-002 test is reported in Table 14. The core 

power time evolution and the FW time evolution are imposed as boundary condition during this 

phase. The PRZ heaters are assumed to be in operation in order to maintain the primary pressure 

set-point; the HPC heaters are OFF. The ADS valves were closed.

Table 14 Facility Configuration Before the SOT of the OSU-MASLWR-002 Test

System Facility 

Operation

TRACE Model

Operation

Note

Core Heaters ON ON -

PRZ Heaters ON ON In order to maintain the primary pressure set-point.

Containment 

Heaters

OFF OFF -

Feed water ON ON In order to remove the net primary power [primary 

power less ambient losses].

At SOT the TRACE code predicts a primary system in a sub-cooled condition with single-phase 

natural circulation. The primary pressure is at about 7.7 MPa and the PRZ heaters are set up to 

maintain the primary pressure at the fixed set point. The secondary fluid, circulating inside the 

helical coil tubes, removes the core power (minus the facility heat losses from the primary fluid) and 

goes out from the SG as superheated steam. The outlet SG secondary pressure is around 1.4 MPa.

The ADS middle line valves, the ADS high line valves and the ADS sump recirculation line valves 

are closed. Since no helical coil heat transfer correlation have been implemented in the TRACE 

V5.0 Patch 3, in agreement with previous analyses [21, 22, 23, 43], the heat transfer area of the 

equivalent helical coil SG heat structure is incremented in order to reach the initial conditions of the 

OSU-MASLWR-002 test. Table 15 shows the SOT conditions of the TRACE model VS experimental 

data for the OSU-MASLWR-002 test.

During the simulation of the transient the core power is imposed as BIC and the PRZ heaters are

ON in order to control the primary side pressure. The temperature and pressure of the FW fluid at 

the inlet of the SG are imposed as BIC. The time dependence of the pressure, at the outlet of the 

SG, and the time dependence of the FW mass flow rate are imposed as boundary condition as well. 

Fig. 52 shows the fluid condition and the temperature diagram of the TRACE model at the SOT. 
3-26

Table 15 SOT Condition Predicted by the TRACE Code vs Experimental Data for the OSU-MA

Parameter EXP TRACE

(REF)

TRACE

(SEN)

Core Power (W) 80000 80000 80000

PRZ Pressure (Pa) 7745080 7697156 7697166

Core Outlet T(K) 504 504 504

Core Inlet T (Average) (K) 487 486 487

Primary Volumetric Flow Rate (m3/s) 0.001 0.001 0.001

PRZ Level (m) 0.33 0.33 0.35

SG Inlet T (K) 292 292 292

SG Inlet P (average) (Pa) 1385980 1334900 1334900

SG Outlet P (Pa) 1428364 1428530 1428848

Secondary Mass Flow Rate (kg/s) 0.019 0.019 0.019

Average SG Outlet Temperature (K) 498 495 495

Time:0s

Figure 52 SNAP Animation Model Showing the SOT Condition of the TRACE Model (REF Pl

3-26
3-27

The core outlet and inlet temperatures are predicted by the TRACE code and shown in Fig. 53 and 

Fig. 54, respectively. The primary volumetric flow rate, and the difference between the core inlet and 

outlet fluid temperature (delta T core) are shown in Fig. 55 and Fig. 56, respectively. The inlet/outlet 

fluid core temperature calculations by TRACE show a qualitative agreement but a general 

overestimation compared with the experimental data. Therefore, in the TRACE simulation, the 

primary circuit stores more energy compared with the experimental data.

Figure 53 Experimental Data versus Code Calculations for Fluid Temperature at the 

Core Outlet (TF-106)

Figure 54 Experimental Data versus Code Calculations for Fluid Temperature at the 

Core Inlet (Average Value of TF 121, 123, 124)
3-28

The primary natural circulation volumetric flow rate behavior is qualitatively and quantitatively 

predicted by the code. It is important to note that previous discrepancies between experimental and 

calculated data by using a constant k loss coefficient at the core entrance (SEN case), are now not 

observed by using the new feature of the TRACE V 5.0 patch 3 code that allow to define flow 

Reynolds number-dependent loss coefficient (REF case). 

Figure 55 Experimental Data versus Code Calculations for Primary Volumetric Flow 

Rate (FDP-131)

Figure 56 Experimental Data versus Code Calculations for Core Delta T
3-29

The core delta T time trend is coupled with the primary volumetric flow rate, the core power and the 

thermo physical condition of the primary fluid. An underestimation of the primary volumetric flow rate 

results in an overestimation of the delta T core (SEN case) by the TRACE code. The correct 

quantitative prediction of the primary volumetric flow rate determines a general correct quantitative 

prediction of the core delta T (REF case), Fig. 55 and 56.

The PRZ level is qualitatively predicted by the TRACE code, Fig. 57; the PRZ pressure behavior is 

predicted by the code as well, Fig. 58. Previous PRZ pressure discrepancies predicted by the 

TRACE V5 Patch 01 are now not predicted by the Patch 02 and Patch 03 results in a more stable 

prediction of PRZ pressure and level [16]. The general overestimation of the PRZ liquid level by the 

TRACE code is due to the general overestimation of the RPV temperatures.

Figure 57 Experimental Data versus Code Calculations for PRZ Level

Figure 58 Experimental Data versus Code Calculations for PRZ Pressure
3-30

By analysing the experimental data, related to the flow temperature after the SG coils primary side 

section and the core inlet temperature, it is evident that the direct heat exchange, through the 

internal shell, between the fluid ascending the HL and the fluid descending the CL, is a crucial 

parameter for the evaluation of the core inlet temperature and therefore the core outlet temperature

[18]. In fact, the experimental data show that, along the downcomer region, the fluid increases his 

temperature between the end of the SG primary side section and the core inlet. An overestimation or 

an underestimation of this phenomenon creates an increase or decrease of the core inlet 

temperature. The phenomenon is predicted by the TRACE model used. Fig. 59 shows the 

comparison between the experimental and calculated data for the difference of temperature 

between the fluid at the inlet of the core and the fluid at the exit of the SG primary side section.

Figure 59 Experimental Data versus Code Calculations for the Difference of Fluid 

Temperature at the Inlet of the Core and at the Exit of the SG Primary 

Side

The SG heat transfer is qualitatively predicted by the TRACE code. The average fluid temperature at 

the outlet of the helical coils, Fig. 60, shows a qualitative agreement compared with the experimental 

data. 

Fig. 61, developed by using SNAP, shows the RPV temperature profile for the OSU-MASLWR-002 

test (2555s after the SOT). Fig. 62, also developed by using SNAP, shows the fluid temperature 

along the equivalent helical coil cells and the fluid temperature profile along the SG primary side 

section at 2555s after the SOT. From these figures it is possible to identify the subcooled, saturated 

and superheat region of the inner equivalent helical coil. In agreement with the experimental data, 

the secondary fluid enters subcooled at the bottom of the SG and boils off after travelling a certain 

length in the SG. In the TRACE model, in agreement with the experimental data, the steam will 

leave the SG superheated. As in the experimental data the slope of the MS superheat curve 

increases if the value of the core power increases and decreases if the value of the FW flow rate 

increases. In Fig.63 and 64, the condition of the TRACE model at 1000s and 2700s after the SOT

are shown. Of particular interest is the reduction of the steam superheating region at 2700s after the 

SOT easily visualized by using SNAP.
3-31

As noted before, the inlet/outlet fluid core temperatures predicted by TRACE show a qualitative 

agreement but a general overestimation compared with the experimental data. This could be related 

to SG primary and secondary side heat transfer. One of the reasons could be an underestimation of 

the helical coil heat transfer coefficient during the different phases of the test. No specific helical coil 

heat transfer correlations have been implemented in the TRACE V5.0 Patch 3 used for this 

simulation. From the results of the previous analyses it is important to note the influence of the 

correct heat losses prediction [16]. Another important point to consider is the influence of the 

nodalization choice. The analyses of previous TRACE calculated data show that one of the reasons 

of the instability of the superheat condition of the fluid at the outlet of the SG, already observed in 

[11], is the equivalent SG model used to simulate the different group of helical coils. In particular, if 

the helical coils are modelled by only one “equivalent” vertical tube, a more stable fluid temperature 

at the outlet of the helical tubes is predicted by the code. The model with three different oblique or 

vertical tubes needs more investigations in order to study the possible instability conditions predicted 

by the code [18].

Figure 60 Experimental Data versus Code Calculations for the Average Fluid 

Temperature at the SG Coil Outlet

A matrix of phenomena observed in test OSU-MASLWR-002 and TRACE code is shown in Table 

163. 
3-32

Time: 2555s

HL Region UP Region

Figure 61 RPV Temperature Profile for the OSU-MASLWR-002 Test (2555s 

after the SOT)

SG Equivalent Helical Coil

Saturated Region

Time: 2555s 

Figure 62 SG Primary Side and Equivalent Helical Coil Temperature Diagram for the 

OSU-MASLWR-002 Test (2555s after SOT)
3-33

Time :1000s

Figure 63 SNAP Animation Model Showing the Condition of the TRACE Model 1000s aft

3-33
3-34

Time: 2700s 

Figure 64 SNAP Animation Model Showing the Condition of the TRACE Model 2700s aft

3-34
3-35

Table 16 Main Phenomena vs Facility and vs TRACE3 [43, 49-52]

Phenomenon Experiment TRACE 

code

Phenomena Measurement Phenomena

Single-phase Natural Circulation + + +

Heat Transfer in Covered Core + + +

By Pass Heat Transfer + + +

Distribution of Pressure Drop Through 

Primary System

+ + +

Heat Transfer in SG Primary Side + + +

Structural Heat and Heat Losses + o +

Heat Transfer in SG Secondary Side + + o*

Steam Superheated on Secondary Side + + +

*The heat transfer in SG secondary side is partially predicted by the code because no helical coil heat transfer 

correlation has been implemented in the TRACE V5.0 Patch 3.

4-1

4. CONCLUSIONS

The TRACE code has been used to predict two tests from the MASLWR integral pressure reactor 

test facility at Oregon State University. This activity has been conducted in a collaboration among 

the ENEA, the Department of Energy of the University of Palermo, the Gruppo di Ricerca Nucleare 

San Piero a Grado (GRNSPG) of University of Pisa, the Department of Nuclear Engineering and

Radiation Health Physics of the Oregon State University and NuScale Power Inc.. In particular the 

OSU-MASLWR-001 test, an inadvertent actuation of one submerged ADS valve, investigates the 

primary/containment coupling in design basis accident condition; the OSU-MASLWR-002 test, a 

natural circulation test, investigates the primary system flow rates and secondary side steam 

superheat for a variety of core power levels and feed water flow rates. 

The analysis of the OSU-MASLWR-001 test show that the TRACE code is able to qualitatively

predict the single and two-phase natural circulation and primary/containment coupling phenomena 

characterizing the test. The sub-cooled, saturated, and single phase blowdown are reasonably 

predicted by the code. The refill of the core, permitting its cooling, is reasonably predicted as well. In 

agreement with the experimental data the RPV level water calculated by TRACE never fell below the 

upper part of the core during the blowdown following the middle valve opening. The results of the 

TRACE calculations show a general over prediction of primary side pressure and temperatures 

compared with the experimental data. It is thought that this could be due to a combination of 

selection of vent valve discharge coefficients and condensation models applied to the inside surface 

of the containment. A more detailed 3D HPC model, by using the “vessel component”, may provide

a better quantitative estimation of the HPC temperatures. In this way it is possible to simulate the 

natural circulation and the mixing phenomena in the upper part of the HPC.

The analyses of the OSU-MASLWR-002 test shows that the TRACE code is able to qualitatively 

predict natural circulation phenomena and heat exchange from primary to secondary side. The 

calculated results show a general qualitative agreement with the experimental data. An 

overestimation of the inlet/outlet core temperature is predicted by the code. This could be related to 

SG primary and secondary side heat transfer. One of the reasons could be an underestimation of 

the helical coil heat transfer coefficient during the different phases of the test. No specific helical coil 

heat transfer correlations have been implemented in the TRACE V5.0 Patch 3 used for this 

simulation. From the results of the previous analyses it is important to consider the influence of the 

correct heat losses prediction. Another important point to note is the influence of the nodalization 

choice. The analyses of previous TRACE calculations show that one of the reasons of the instability 

of the superheat condition of the fluid at the outlet of the SG, already observed in [11], is the 

equivalent SG model used to simulate the different group of helical coils. In particular, if the helical 

coils are modelled by only one “equivalent” vertical tube, a more stable fluid temperature at the 

outlet of the helical tubes is predicted by the code. The model with three different oblique or vertical 

tubes needs more investigations in order to study the possible instability conditions predicted by the 

code [18]. The primary natural circulation volumetric flow rate behavior is qualitatively and 

quantitatively predicted by the TRACE code. It is important to consider that previous discrepancies 

between experimental and calculated data by using a constant k loss coefficient at the core 

entrance are now not observed by using the new feature of the TRACE V 5.0 patch 3 code that 

contain flow Reynolds number-dependent loss coefficients. 

The activity here presented consists in a qualitative accuracy assessment of the TRACE code. The 

TRACE code is judged to be able to reasonable predict the phenomena of interest of the selected 

tests. Since the qualitative assessment of the TRACE code is fulfilled, a quantitative assessment of 

the TRACE accuracy is envisaged to have a complete independent assessment. The quantitative 

accuracy evaluation method selected is the Fast Fourier Transform Based Methods [47,53,54]. 

5-1

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TRACE, Nuclear Engineering and Design 241 (2011) 1137–1144.

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primary/containment coupling phenomena characterizing the MASLWR design during a 

SBLOCA scenario, Nuclear Power Plants, InTech, 2012.

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the OSU-MASLWR-003A natural circulation test by using the TRACE code, Advances In 

Thermal Hydraulics (ATH ‘12) Conference, November 11-15, 2012, San Diego, 

California.

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analysis of the MASLWR primary/containment coupling phenomena in beyond design 

accident scenario, Proceedings of the NURETH 15 Conference, Pisa 13- 17 2013, Italy.

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simulation of natural circulation and primary/containment coupling in BDBA condition 

Typical of the MASLWR, Proceedings of ASME 2014 Small Modular Reactor 

Symposium, Washington DC, USA, April 15-17, 2014.
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24. Mascari, F., Woods, B.G, Adorni, M., Analysis, by TRACE code, of natural circulation

phenomena in the MASLWR-OSU-002 Test, performed in the OSU MASLWR facility,

Spring Camp Meeting 2008, May 28-30 2008 Pisa, Italy.

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May 30 - June 1, Ljubljana, Slovenia, 2012.

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the OSU-MASLWR-003A natural circulation test by using the TRACE code, Fall 2012

CAMP Meeting, November 7-9, 2012, Washington D.C. USA.

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analysis of the MASLWR primary/containment coupling phenomena in beyond design

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PWR design natural circulation flow stability and thermo-hydraulic coupling of

containment and primary system during accidents, 2013 Spring CAMP meeting, 8-10

May, Pisa, Italia.

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2013, Washington, D.C. USA.

30. Mascari, F., Woods, B.G., Welter, K., D'Auria F., Vella, G., Analyses of OSU-MASLWR001 and 002 test updated analyses for the in progress NUREG on ”Analysis of the OSUMASLWR 001 and 002 test by using the TRACE code”, FALL 2014 CAMP Meeting, 22-

24, October, Rockville MD, USA.

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accident, DRAFT.

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flow stability and thermo-hydraulic coupling of containment and primary system during

accidents”, Presentation, 21-23 March 2011, Vienna, Austria.
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containment and primary system during accidents double blind calculation results,

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design natural circulation flow stability and thermo-hydraulic coupling of containment and

primary system during accidents double blind calculation results, II Technical Meeting

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A-1

APPENDIX A EXPERIMENTAL DATA VERSUS CODE 

CALCULATION FOR THE OSU-MASLWR-001 TEST

In this Appendix A the comparison between the REF and SEN1 calculated data and experimental 

data related to the OSU-MASLWR-001 test, presented in the section 3.3, have been presented 

considering all the main parameters of interest.
A-2

Figure A-1 Experimental Data versus Code Calculations for Core Power (KW 101-

102)

Figure A-2 Experimental Data versus Code Calculations for the Average Value of TF 

121-123-124
A-3

Figure A-3 Experimental Data versus Code Calculations for TF-106

Figure A-4 Experimental Data versus Code Calculations for TF-111
A-4

Figure A-5 Experimental Data versus Code Calculations for the Average Value of TF 

131-133-134

Figure A-6 Experimental Data versus Code Calculations for PT-301
A-5

Figure A-7 Experimental Data versus Code Calculations for LDP-106

Figure A-8 Experimental Data versus Code Calculations for LDP-301
A-6

 

Figure A-9 Experimental Data versus Code Calculations for FDP-131

Figure A-10 Experimental Data versus Code Calculations for the Average Value of 

TF 611 to 634
A-7

Figure A-11 Experimental Data versus Code Calculations for FVM-602-P 

Figure A-12 Experimental Data versus Code Calculations for PT-801
A-8

Figure A-13 Experimental Data versus Code Calculations for LDP-801

Figure A-14 Experimental Data versus Code Calculations for TF-891
A-9

Figure A-15 Experimental Data versus Code Calculations for TF-892

Figure A-16 Experimental Data versus Code Calculations for TF-893
A-10

Figure A-17 Experimental Data versus Code Calculations for TF-894

Figure A-18 Experimental Data versus Code Calculations for TF-811
A-11

Figure A-19 Experimental Data versus Code Calculations for TF-821

Figure A-20 Experimental Data versus Code Calculations for TF-831
A-12

Figure A-21 Experimental Data versus Code Calculations for TF-841

Figure A-22 Experimental Data versus Code Calculations for TF-851
A-13

Figure A-23 Experimental Data versus Code Calculations for TF-861

Figure A-24 Experimental Data versus Code Calculations for TF-815
A-14

Figure A-25 Experimental Data versus Code Calculations for TF-825

Figure A-26 Experimental Data versus Code Calculations for TF-835
A-15

Figure A-27 Experimental Data versus Code Calculations for TF-845

Figure A-28 Experimental Data versus Code Calculations for TF-855
A-16

Figure A-29 Experimental Data versus Code Calculations for TF-865

Figure A-30 Experimental Data versus Code Calculations for LDP-901
B-1

APPENDIX B EXPERIMENTAL DATA VERSUS CODE 

CALCULATION FOR THE OSU-MASLWR-002 TEST

In this Appendix B the comparison between the REF and SEN calculated data and experimental 

data related to the OSU-MASLWR-002 test, presented in the section 3.4, have been presented 

considering all the main parameters of interest.
B-2

Figure B-1 Experimental Data versus Code Calculations for Core Power (KW-101-

102)

 

Figure B-2 Experimental Data versus Code Calculations for the Average Value of TF 

121, 123, 124
B-3

Figure B-3 Experimental Data versus Code Calculations for TF-106

Figure B-4 Experimental Data versus Code Calculations for the Average Value of 

TF-131-133-134
B-4

Figure B-5 Experimental Data versus Code Calculations for TF-111

Figure B-6 Experimental Data versus Code Calculations for FDP-131
B-5

Figure B-7 Experimental Data versus Code Calculations for PT-301

Figure B-8 Experimental Data versus Code Calculations for LDP-301
B-6

Figure B-9 Experimental Data versus Code Calculations for FMM-501

Figure B-10 Experimental Data versus Code Calculations for the Average Value of 

PT-511-521-531
B-7

Figure B-11 Experimental Data versus Code Calculations for TF-501

Figure B-12 Experimental Data versus Code Calculations for the Average Value of 

T_SG outlet (611-634)
B-8

Figure B-13 Experimental Data versus Code Calculations for FVM-602 P






NUREG/IA-0466 Analysis of the OSU-MASLWR 001 and 002 Tests by Using the TRACE Code