Rod Bundle Heat

Transfer Test Facility 

Description 

Office of Nuclear Regulatory Research 

NUREG/CR-6976
AVAILABILITY OF REFERENCE MATERIALS 

IN NRC PUBLICATIONS

NRC Reference Material 

As of November 1999, you may electronically access 

NUREG-series publications and other NRC records at 

NRC=s Public Electronic Reading Room at 

http://www.nrc.gov/reading-rm.html. Publicly released 

records include, to name a few, NUREG-series 

publications; Federal Register notices; applicant, 

licensee, and vendor documents and correspondence; 

NRC correspondence and internal memoranda; 

bulletins and information notices; inspection and 

investigative reports; licensee event reports; and 

Commission papers and their attachments. 

NRC publications in the NUREG series, NRC 

regulations, and Title 10, Energy, in the Code of 

Federal Regulations may also be purchased from one 

of these two sources. 

1. The Superintendent of Documents 

 U.S. Government Printing Office 

 Mail Stop SSOP 

 Washington, DC 20402B0001 

 Internet: bookstore.gpo.gov 

 Telephone: 202-512-1800 

 Fax: 202-512-2250 

2. The National Technical Information Service 

 Springfield, VA 22161B0002 

 www.ntis.gov 

 1B800B553B6847 or, locally, 703B605B6000 

A single copy of each NRC draft report for comment is 

available free, to the extent of supply, upon written 

request as follows: 

Address: Office of the Chief Information Officer, 

 Reproduction and Distribution 

 Services Section 

 U.S. Nuclear Regulatory Commission 

 Washington, DC 20555-0001 

E-mail: DISTRIBUTION@nrc.gov 

Facsimile: 301B415B2289 

Some publications in the NUREG series that are 

posted at NRC=s Web site address 

http://www.nrc.gov/reading-rm/doc-collections/nuregs 

are updated periodically and may differ from the last 

printed version. Although references to material found 

on a Web site bear the date the material was accessed, 

the material available on the date cited may 

subsequently be removed from the site. 

Non-NRC Reference Material

Documents available from public and special technical 

libraries include all open literature items, such as 

books, journal articles, and transactions, Federal 

Register notices, Federal and State legislation, and 

congressional reports. Such documents as theses, 

dissertations, foreign reports and translations, and 

non-NRC conference proceedings may be purchased 

from their sponsoring organization. 

Copies of industry codes and standards used in a 

substantive manner in the NRC regulatory process are 

maintained atC

The NRC Technical Library 

Two White Flint North 

11545 Rockville Pike 

Rockville, MD 20852B2738 

These standards are available in the library for 

reference use by the public. Codes and standards are 

usually copyrighted and may be purchased from the 

originating organization or, if they are American 

National Standards, fromC

American National Standards Institute 

11 West 42nd Street 

New York, NY 10036B8002 

www.ansi.org 

Legally binding regulatory requirements are stated only 

in laws; NRC regulations; licenses, including technical 

specifications; or orders, not in 

NUREG-series publications. The views expressed in 

contractor-prepared publications in this series are not 

necessarily those of the NRC. 

The NUREG series comprises (1) technical and 

administrative reports and books prepared by the staff 

(NUREGBXXXX) or agency contractors 

(NUREG/CRBXXXX), (2) proceedings of conferences 

(NUREG/CPBXXXX), (3) reports resulting from 

international agreements (NUREG/IABXXXX), (4) 

brochures (NUREG/BRBXXXX), and (5) compilations of 

legal decisions and orders of the Commission and 

Atomic and Safety Licensing Boards and of Directors=

decisions under Section 2.206 of NRC=s regulations 

(NUREGB0750). 

212B642B4900 

DISCLAIMER: This report was prepared as an account of work sponsored by an agency of the U.S. Government. 

 Neither the U.S. Government nor any agency thereof, nor any employee, makes any warranty, expressed or 

implied, or assumes any legal liability or responsibility for any third party=s use, or the results of such use, of any 

information, apparatus, product, or process disclosed in this publication, or represents that its use by such third 

party would not infringe privately owned rights. 
Rod Bundle Heat

Transfer Test Facility

Description

Manuscript Completed: April 2008 

Date Published: July 2010

Prepared by

E.R. Rosal, T.F. Lin, I.S. McClellan, R.C. Brewer 

The Pennsylvania State University

University Park, PA 16802

K. Tien, NRC Project Manager 

NRC Job Code W6855

Office of Nuclear Regulatory Research

NUREG/CR-6976

iii

ABSTRACT

This report describes the Rod Bundle Heat Transfer (RBHT) Test Facility which is designed to 

conduct systematic separate effects tests under well-controlled laboratory conditions in order to 

generate fundamental rod bundle heat transfer data from single phase cooling tests, low flow 

boiling tests, steam flow tests with and without droplets injection, inverted annular film boiling 

tests, and dispersed flow film boiling heat transfer tests in rod bundles. The facility is capable of 

operating in steady state forced and variable reflood modes covering a wide range of flow and 

heat transfer conditions at pressures from 0.134 to 0.402 MPa (20 to 60 psia). The RBHT Test 

Facility is a unique facility which will provide new data for the fundamental development of bestestimate computer codes to enhance our understanding of the complex two-phase phenomena, 

which are modeled for the reflood transient. 
iv
v

FOREWORD 

Reflood thermal-hydraulics represents an important set of phenomena during a hypothetical 

loss-of-coolant-accident (LOCA). These phenomena must be accurately simulated by systems 

codes in determining plant response to a LOCA. In spite of significant research into reflood 

thermal-hydraulics, there still exists uncertainty in these calculations. As a result, the Nuclear 

Regulatory Commission (NRC) conducts experimental investigations of reflood thermalhydraulics in order to provide data for model development and to validate its systems codes, 

which are used to provide independent confirmation of the validity of licensees’ submittals. 

The NRC is currently assessing and improving the TRAC/RELAP Computational Engine 

(TRACE) code for best estimate analysis of light water reactors. While calculation of reflood by 

TRACE appears to be reasonable, higher accuracy is needed as the code is applied to power 

uprates and new plant designs to ensure acceptable margin between expected plant 

performance and the regulatory limits. Accurate prediction of the consequences of a LOCA is 

important because it is one of the postulated accident scenarios that determine the licensed 

core power and several other operational parameters. 

To acquire detailed, fundamental data for use in developing models for reflood during a LOCA, 

the NRC sponsored the design and construction of a Rod Bundle Heat Transfer (RBHT) Test 

Facility. Some of these detailed data have only recently become possible because of recent 

advances in instrumentation technology for two-phase flow measurements. 

This report describes the RBHT Test Facility components and instrumentation. It also presents 

the results of the facility characterization tests, including pressure loss coefficients of the spacer 

grids, heat loss from the bundle housing, and flow areas of the bundle and other tanks as a 

function of height. In addition, it provides an estimate of measurement uncertainties. As such, 

this report will prove useful in understanding and utilizing the data to be obtained from the 

facility. 

With improved data and code models for simulating LOCAs, we can more accurately predict 

the consequences of these scenarios and provide better technical bases for regulations 

associated with such accidents. As a result, this study will help to ensure the agency’s 

regulations are effective and efficient. 

 
vi
vii

CONTENTS 

Page

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

FOREWORD ................................................................................................................................... v 

EXECUTIVE SUMMARY .............................................................................................................. xiii 

ABBREVIATIONS ......................................................................................................................... xv 

NOMENCLATURE ....................................................................................................................... xvii 

ACKNOWLEDGEMENTS ............................................................................................................ xix 

1. INTRODUCTION ......................................................................................................................... 1 

2. GENERAL DESIGN DESCRIPTION ........................................................................................... 3 

3. DETAILED COMPONENT DESIGN DESCRIPTION .................................................................. 7 

 3.1 Test Section ................................................................................................................... 7 

 3.2 Lower Plenum ................................................................................................................ 9 

 3.3 Upper Plenum ................................................................................................................ 9 

 3.4 Large and Small Carryover Tanks ................................................................................ 10 

 3.5 Steam Separator and Drain Collection Tanks .............................................................. 10 

 3.6 Pressure Oscillation Damping Tank ............................................................................. 10 

 3.7 Exhaust Piping ............................................................................................................. 11 

 3.8 Injection Water Supply Tank ........................................................................................ 11 

 3.9 Water Injection Line ..................................................................................................... 11 

 3.10 Steam Supply ............................................................................................................... 12 

 3.11 Droplet Injection System .............................................................................................. 12 

4. TEST FACILITY INSTRUMENTATION ..................................................................................... 37 

 4.1 Loop Instrumentation and Controls .............................................................................. 37 

 4.2 Test Section Instrumentation ....................................................................................... 38 

 4.3 Data Acquisition System .............................................................................................. 42

5. TEST FACILITY IMPROVEMENTS .......................................................................................... 67 

6. SUMMARY OF CHARACTERIZATION TESTS ........................................................................ 69 

 6.1 Single Phase Pressure Drop Test ................................................................................ 69 

 6.1.1 Procedure for calculation of Grid Loss Coefficient, kgrid .......................................... 69 

 6.1.2 Comparison of data With Prediction Using Rehme’s Method ................................ 70 

 6.2 Calculation of Friction Factor for the Rod Bundle ......................................................... 71 

 6.2.1 Procedure for Calculating Friction Factor, f ............................................................ 71 

 6.3 Radiation Heat Loss Measurements ............................................................................ 72 

 6.4 Calculation of Insulation Thickness for the Rod Bundle ............................................... 73 
viii

7. CONCLUSIONS ........................................................................................................................ 87 

8. REFERENCES .......................................................................................................................... 89 

APPENDIX A. RBHT TEST FACILITY COMPONENTS DETAILED MECHANICAL 

 DRAWINGS ........................................................................................................................... A-1 

APPENDIX B. RBHT TEST FACILITY COMPONENTS MEASURED VOLUMES OF 

 FLOW AREAS ....................................................................................................................... B-1 

APPENDIX C. RBHT TEST FACILITY PHOTOGRAPHS DESCRIPTION ................................. C-1 

APPENDIX D. EXPERIMENTAL VERIFICATION OF THE PERFORMANCE OF THE 

 DROPLET INJECTION SYSTEM USED IN THE RBHT TEST FACILITY ............................. D-1 

APPENDIX E. DETAILED ENGINEERING DRAWINGS FOR THE FLOW HOUSING 

 AND ROD BUNDLE INSTRUMENTATION ........................................................................... E-1 

APPENDIX F. INSTRUMENTATION ERROR ANALYSIS .......................................................... F-1 

APPENDIX G. RBHT TEST FACILITY ENGINEERING DRAWING LIST .................................. G-1 

APPENDIX H. THERMOPHYSICAL PROPERTIES OF ONE BORON NITRIDE SAMPLE 

 AND THREE ROD SAMPLES ............................................................................................... H-1 
ix

FIGURES

Page

2.1 RBHT Test Facility Schematic ........................................................................................ 5 

2.2 RBHT Test Facility Isometric View ................................................................................. 6 

3.1 Test Section Isometric View ......................................................................................... 13 

3.2 Rod Bundle Cross Sectional View ................................................................................ 14 

3.3 Heater Rod ................................................................................................................... 15 

3.4 Heater Rod Axial Power Profile .................................................................................... 16 

3.5 Mixing Vane Grid .......................................................................................................... 17 

3.6 Low-Melt Reservoir ...................................................................................................... 18 

3.7 Flow Housing Cross Sectional View ............................................................................. 19 

3.8 Low Mass Flow Housing ............................................................................................... 20 

3.9 Housing Window .......................................................................................................... 21 

3.10 Lower Plenum .............................................................................................................. 22 

3.11 Lower Plenum Flow Baffle ............................................................................................ 23 

3.12 Upper Plenum .............................................................................................................. 24 

3.13 Exhaust Line Baffle ...................................................................................................... 25 

3.14 Large Carryover Tank ................................................................................................... 26 

3.15 Small Carryover Tank ................................................................................................... 27 

3.16 Steam Separator .......................................................................................................... 28 

3.17 Steam Separator Drain Tank ........................................................................................ 29 

3.18 Pressure Oscillation Damping Tank ............................................................................. 30 

3.19 Exhaust Piping .............................................................................................................. 31 

3.20 Injection Water Supply Tank ........................................................................................ 32 

3.21 Water Injection Line ...................................................................................................... 33 

3.22 Droplet Injection Schematic .......................................................................................... 34

3.23 Droplet Injection System Schematic ............................................................................. 35 

4.1 Loop Instrumentation Schematic .................................................................................. 43 

4.2 Rod Bundle and Housing Instrumentation Axial Locations ........................................... 44 

4.3 Mixing Vane Grid Instrumentation ................................................................................ 45 

4.4 Grid No. 2 Instrumentation ........................................................................................... 46

4.5 Grid No. 3 Instrumentation ........................................................................................... 47

4.6 Grid No. 4 Instrumentation ........................................................................................... 48

4.7 Grid No. 5 Instrumentation ........................................................................................... 49

4.8 Grid No. 6 Instrumentation ........................................................................................... 50

4.9 Grid No. 7 Instrumentation ........................................................................................... 51

4.10 Instrumented Heater Rod Radial Locations ................................................................. 52 

4.11 Grid Steam Probe Thermocouple Axial Location Schematic ....................................... 53 

4.12 Traversing Steam Probe Rake Schematic ................................................................... 54 

4.13 Steam Probe Rake Automatic Traversing Mechanism ................................................ 55 

4.14 Densitometer Schematic .............................................................................................. 56 

4.15 Laser Illuminating Digital Camera System ................................................................... 57 

6.1 RBHT Differential Pressure Cell Layout, Single Phase Flow ....................................... 76 

6.2 Grid Loss Coefficients vs. Reynolds Number - Experiment 276 ................................... 77 

6.3 Comparison of Experimental Data with Rehme=s Method ............................................ 78 

6.4 Differential Pressure Cell Layout for Pressure Drop Tests ........................................... 79 

6.5 Friction Factor as a Function of Reynolds Number ...................................................... 80 
x

6.6 Comparison of Friction Factors for Various Experiments ............................................. 81 

6.7 Thermal Conductivity of Insulation Materials as a Function of Temperature ................ 82 

6.8 Heat Flux vs. Axial Length for Experiment 607 ............................................................. 83 

B.1 Volume and Flow Area Measuring Test Schedule ..................................................... B-9 

B.2 Water Supply Tank Volume Measurements ............................................................. B-10 

B.3 Water Supply Tank Flow Areas ................................................................................. B-10 

B.4 Flow Housing Volumes Between Pressure Taps ...................................................... B-11 

B.5 Flow Housing Areas Between Pressure Taps ........................................................... B-11 

B.6 Upper Plenum Volume Measurements ..................................................................... B-12 

B.7 Upper Plenum Flow Areas ......................................................................................... B-12 

B.8 Lower Plenum Volume Measurements ..................................................................... B-13 

B.9 Lower Plenum Flow Areas ........................................................................................ B-13 

B.10 Large Carryover Tank Volume Measurements ......................................................... B-14 

B.11 Large Carryover Tank Flow Areas ............................................................................. B-14 

B.12 Small Carryover Tank Volume Measurements .......................................................... B-15 

B.13 Small Carryover Tank Flow Areas ............................................................................. B-15 

B.14 Pressure Oscillation Damping Tank Volume Measurements .................................... B-16 

B.15 Pressure Oscillation Damping Tank Flow Areas ....................................................... B-16 

C.1 Flow Housing with the Heater Rod Bundle and the Ground Nickel Plate ................... C-1 

C.2 Ground Nickel Plate and Heater Rods Connection .................................................... C-1 

C.3 Flow Housing Bottom Extension Flow Baffle, Heater Rod Bottom Extensions, 

 and Grid and Support Rod Thermocouple Extensions .............................................. C-2 

C.4 Lower Plenum Heater Rod Sealing Plate, Heater Rod Bottom Extensions 

 and Thermocouples Extension Wires ....................................................................... C-2 

C.5 Installation of the Test Facility Components from Right to Left: Flow Housing 

 and Support Fixture, Steam Separator, Pressure Oscillation Damping Tank, 

 Water Injection Supply Tank, and the Mezzanine Structure ...................................... C-3 

C.6 Top View of the Flow Housing, Upper Plenum, Small and Large Carryover 

 Tanks, Steam Separator, Pressure Oscillation Damping Tank, and the Top 

 of the Water Injection Tank ........................................................................................ C-3 

C.7 Upper Plenum, Steam Separator, and Pressure Oscillation Damping Tank 

 Installation ................................................................................................................. C-4 

C.8 Steam Exhaust Piping with the Vortex Flowmeter and the Pressure Control 

 V-Ball Valve ............................................................................................................... C-4 

C.9 Test Section Flow Housing Showing the Heater Rods and Grids Through 

 the Window Openings ............................................................................................... C-5 

C.10 Bottom of the Flow Housing with the Lower Plenum and the Water Injection 

 Tank .......................................................................................................................... C-6 

C.11 Installation of the Test Section .................................................................................. C-7 

C.12 Differential Pressure Cells Installation on the Flow Housing ..................................... C-8 

C.13 Differential Pressure Cells Installation Showing Connections of the Pressure 

 Tap Lines to the Differential Pressure Cell Manifolds ................................................ C-9 

C.14 RBHT Test Facility Building View Through the Roll-up Door Showing the 

 Test Section, Water Injection Tank, Circulating Pump, and the Mezzanine 

 Structure .................................................................................................................. C-10 

C.15 Inside View of the RBHT Test Facility Through the Roll-up Door Showing the 

 Test Section, Water Injection Tank, Circulating Pump, and the Mezzanine 

 Structure .................................................................................................................. C-11 

C.16 Data Acquisition Components: VXI Mainframe and Terminal Panels ...................... C-12 
xi

C.17 Electric AC Power Supply Showing the High Voltage Transformers, the Main 

 Breaker, and the Phase Shift Transformer ............................................................... C-12 

C.18 DC Power Supply Units Rated at 60 Volts DC, 12000 Amps and 750 KW ................ C-13 
xii

TABLES

Page

3.1 Heater Rod General Specifications .............................................................................. 36 

3.2 Thermocouple Specifications ....................................................................................... 36 

3.3 Flow Housing Window Viewing Areas Below and Above Mixing Vane Grids ............... 36 

4.1 Instrumentation and Data Acquisition Channel List ...................................................... 58 

6.1 Differential Pressure Cell Layout Description ............................................................... 84 

6.2 Calculation for Experiment 607 .................................................................................... 84 

6.3 Current and Voltage Readings for Power Calculation .................................................. 84 

6.4 Elevation 1.419 m (55 in) - Heating Surface Temperature 348 degrees C 

 (659 degrees F) ............................................................................................................ 85 

6.5 Elevation 2.0 m (78.78 in) - Housing Surface Temperature 297 degrees C 

 (566 degrees F) ............................................................................................................ 85 

6.6 Elevation 2.75 m (108.43 in) - Housing Surfaces Temperature 239 degrees C 

 (463 degrees F) ............................................................................................................ 86 

B.1 Component Volumes and Flow Areas ........................................................................ B-2 

B.2 Water Supply Tank Volumes and Flow Areas ............................................................ B-3 

B.3 Flow Housing Volumes and Flow Areas Among Pressure Taps ................................ B-4 

B.4 Upper Plenum Volumes and Flow Areas .................................................................... B-5 

B.5 Lower Plenum Volumes and Flow Areas .................................................................... B-5 

B.6 Large Carryover Tank Volumes and Flow Areas ........................................................ B-6 

B.7 Small Carryover Tank Volumes and Flow Areas ........................................................ B-6 

B.8 Pressure Oscillation Damping Tank Volumes and Flow Areas .................................. B-7 

B.9 Grid and Bare Heater Rod Bundle Volumes and Flow Areas ..................................... B-8 

B.10 Steam Separator Drain Tank Volumes and Flow Areas ............................................. B-8 

F.1 Temperature Measurements ...................................................................................... F-4 

F.2 Pressure Measurements ............................................................................................. F-5 

F.3 Flow Measurements .................................................................................................... F-6 

F.4 Position Measurements .............................................................................................. F-6 

F.5 Power Supply Measurements ..................................................................................... F-7 
xiii

EXECUTIVE SUMMARY

The NRC-sponsored Rod Bundle Heat Transfer (RBHT) Test Facility, designed to conduct 

systematic separate effects tests under well-controlled laboratory conditions, has been 

successfully developed and made operational at the Pennsylvania State University (PSU). The 

facility can be used to generate fundamental rod bundle heat transfer data from single phase 

cooling tests, low flow boiling tests, steam flow tests with and without droplets injection, inverted 

annular film boiling tests, and dispersed flow film boiling heat transfer tests in rod bundles. 

The facility is heavily instrumented and meets all the instrumentation requirements developed in 

the RBHT Program. The facility includes a test section consisting of a lower plenum, a lowmass housing containing the heater rod bundle, and an upper plenum, coolant injection and 

steam injection systems, phase separation and liquid collection systems, a liquid droplets 

injection system, and a pressure fluctuation damping tank and steam exhaust piping. 

The heater rod bundle in the test section of the facility simulates a small portion of a 17x17 

reactor fuel assembly. The heater rods are electrically heated and have a diameter of 9.5 mm 

arranged in a 7x7 array with a 12.6 mm pitch. The bundle has 45 heater rods and four 

unheated corner rods. The latter are used to support the bundle grids and the instrumentation 

lines. Each rod is rated for 10 kW and designed to operate at 1.38 MPa at a maximum 

temperature of 1204 degrees C. Each rod is instrumented with eight 0.508 mm diameter 

ungrounded thermocouples. The rod bundle has seven mixing vane grids similar in design of a 

pressurized water reactor (PWR) 17x17 fuel assembly. 

The flow housing provides the pressure and flow boundary for the heater rod bundle. It has a 

square geometry and is 91.3 x 91.3 mm in size, with the wall thickness of 6.35 mm. The flow 

housing has six pairs of windows, each providing 50.8 x 292.1 mm of viewing area. Each pair of 

windows is placed 180 degrees apart and located axially at elevations overlapping rod bundle 

spacer grids, thus providing a viewing area about 88.9 mm below and 152.4 mm above the 

corresponding spacer grid. The flow housing has 23 pressure taps located at various 

elevations. The pressure taps are connected to sensitive differential pressure cells providing 

measurements to calculate single-phase friction losses for determining bare rod bundle and grid 

loss coefficients. 

The lower plenum is attached to the bottom of the flow housing. It is used as a reservoir of the 

coolant prior to injection into the rod bundle during reflood. The upper plenum serves as the 

first stage for phase separation and liquid collection of the two-phase effluent exiting the rod 

bundle. The de-entrained liquid is collected around the flow housing extension in the upper 

plenum and is subsequently drained into the top of a tube which extends inside a small 

carryover tank. Meanwhile, the wet steam exhausted from the upper plenum flows through a 

steam separator where carryover liquid droplets are further separated form the steam and 

collected in a small collection tank. 

The dry steam from the steam separator flows into a pressure oscillation-damping tank. The 

latter is used to dampen pressure oscillations at the upper plenum caused by rapidly oscillating 

steam generation in the heater rod bundle during reflood. The steam flowing out of the 

pressure oscillation-damping tank is exhausted through a stainless steel pipe. The latter has a 

Vortex flow meter, a V-Bal pressure control valve and a muffler at the exit to minimize the noise 
xiv

caused by steam blowing into the atmosphere. 

The injection water system consists of a water supply tank, a circulating pump and 

interconnecting lines to the test section lower plenum. The water injection is rated for 0.402 

MPa and 154.4 degrees C. A boiler is used to provide steam for the single phase steam cooling 

tests with and without liquid droplet injection. The liquid droplets injection system consists of 

four stainless steel tubes entering through the test section at the 1.295 m elevation. The tubes 

run perpendicular to the heater rods and penetrate through both sides of the housing. 

The test facility instrumentation is designed to measure temperatures, power, flow rates, liquid 

levels, pressures, void fractions, droplet sizes and distribution, and drop velocities. There are 

123 instrumentation channels assigned to the collection of electrical power, fluid and wall 

temperatures, levels, flows, differential pressures, and static pressure measurements. The 

water injection line is equipped with a Coriolis flow meter that directly measures mass flow rates 

up to 454 kg/min. The exhaust line is equipped with a Vortex flow meter which, in conjunction 

with a static pressure transmitter and a fluid thermocouple measurement, is used to calculate 

the steam volumetric flow rates. 

The test section instrumentation consists of the heater rod bundle and flow housing, the lower 

plenum and the upper plenum groups. Six grids have thermocouples attached to their surfaces 

in order to determine quenching behavior during reflood. The vapor (i.e., steam) temperatures 

are measured using miniature thermocouples that are attached to the spacer grids, and the 

traversing steam probe rakes having very small thermal time constants. A droplet imaging 

system known as VisiSizer has been developed in conjunction with Oxford Lasers to measure 

the sizes and velocities of water droplets entrained in the steam flow in various elevations along 

the bundle. 

The control and data acquisition system employed in the facility provides control functions and 

data collection functions. This system consists of two parts: the computer and display 

terminals residing in the control room, and the VXI mainframe terminal panels residing in the 

test facility. The two parts are connected via an industry standard IEEE 1394 serial control and 

data interface. There are more than 500 channels available for scanning the data. 

Various characterization tests have been performed on the RBHT facility. These 

characterization tests include single phase pressure drop tests, rod bundle friction factor 

measurements, radiation heat loss measurements, and fuel rod surface roughness, oxide 

thickness and emissivity measurements. Results of these characterization tests, which are 

presented in this report, appear to be satisfactory. 

In summary, the RBHT Test Facility is capable of operating in steady-state forced and variable 

reflood modes covering a wide range of flow and heat transfer conditions at pressures from 

0.134 - 0.402 MPa (20 - 60 psia). The facility with its robust instrumentation represents a 

unique experimental tool for obtaining new data for the fundamental development of bestestimate computer codes used by the NRC in review of applicants’ licensing requests. 
xv

ABBREVIATIONS

BN Boron Nitride 

COBRA-TF Coolant Boiling Rods Arrays - Two Fluids 

DP Differential Pressure 

FLECHT Full Length Emergency Cooling Heat Transfer 

FM Flow Transmitter 

GR Spacer Grid 

LIDCS Laser Illuminating Digital Camera System 

NRC Nuclear Regulatory Commission 

OD Outer Diameter 

PC Personal Computer 

PSU Pennsylvania State University 

RBHT Rod Bundle Heat Transfer 

SEASET Systems Effects and Separate Effects Tests 

TC Thermocouple 
xvi
xvii

NOMENCLATURE

A Total Surface Area of the Rod Bundle 

Cv Modified Spacer Form Loss Coefficient 

Dd Droplet Diameter 

Dh Hydraulic Diameter 

Do Droplet Injector Hole Diameter 

f Friction Factor 

g Gravitational Acceleration 

h Heat Transfer Coefficient 

k Thermal Conductivity 

kgrid Grid Loss Coefficient 

L Length of the Span Over Which Frictional Losses are Measured; Insulation Thickness 

Lbare Bare Bundle Length 

Lgrid Bundle Length Occupied by Each Spacer Grid 

q" Local Heat Flux 

Re Reynolds Number 

T Local Temperature 

Ts Insulation Surface Temperature 

Tw Wall Temperature 

T4 Ambient Temperature 

Vg Gas Velocity 

V Liquid Velocity 

x Local Position in the Insulation Layer 

Greek Letters

ΔPbare Pressure Drop Associated with the Bare Length of the Span 

ΔPgrids Pressure Drop Associated with the Grid Losses 

ΔPTotal Total Pressure Drop Accounting for Both the Bare Length of the Span and the Grids 

ε Ratio of the Projected Grid Cross-Sectional Area to the Undisturbed Flow Area 

Ff Liquid Viscosity 

N Number of Grids in Span 

Ro Radius of the Orifice 

ρf Liquid Density 

ρg Gas Density 

σ Surface Tension 
xviii
xix

ACKNOWLEDGMENTS

The authors wish to acknowledge Dr. L.E. Hochreiter and Dr. F.B. Cheung, Project Principal 

and Co-Principal Investigators, of the Mechanical and Nuclear Engineering Department, for their 

technical advice and guidance. C. Jones, R. Peters, J. Bennett, and especially D. Adams, from 

the ARL-Test Site, for their help in the instrumentation and installation of the heater rod bundle, 

test section, and test facility components. J. Anderson, College of Engineering Shop Service 

Manager, and his staff for fabrication most of the test facility components, and especially J. 

Anderson for designing the steam probe rake traversing mechanism, and C. Jones and R. 

Peters for automating it. The authors also wish to acknowledge the continuing guidance and 

support of the U.S. Nuclear Regulatory Commission, Office of Research in this effort, and in 

particular W.A. Macon, S. Bajorek, J.M. Kelly, G. Rhee, and D. Bassette. 
xx
1

1. INTRODUCTION 

The Rod Bundle Heat Transfer (RBHT) Test Facility is designed to conduct systematic 

separate-effects tests under well-controlled conditions in order to generate fundamental rod 

bundle heat transfer data from single phase steam cooling tests, low flow boiling tests, steam 

flow tests with and without injected droplets, inverted annular film boiling tests, and dispersed 

flow film boiling heat transfer tests. The facility is capable of operating in both forced and 

variable reflood modes covering wide ranges of flow and heat transfer conditions at pressures 

from 0.134 to 0.402 MPa (20 to 60 psia). This report provides a detailed description of the test 

facility design with the test components= detailed mechanical drawings given in Appendix A, the 

measured volume and flow areas in Appendix B, the facility photographs description in 

Appendix C, and the description of the droplet injection system in Appendix D. 
2
3

2. GENERAL DESIGN DESCRIPTION

The test facility consists of the following major components shown schematically in Figure 2.1 

and in an isometric view in Figure 2.2: 

$ A test section consisting of a lower plenum, a low-mass housing containing the heater rod 

 bundle, and an upper plenum. 

$ Coolant injection and steam injection systems. 

$ Closely coupled phase separation and liquid collection systems. 

$ An injection system. 

$ A pressure fluctuation damping tank and steam exhaust piping. 
4

Figure 2.1 RBHT Test Facility Schematic. 
Figure 2.2 RBHT Test Facility Isometric View. 

5
6
7

3. DETAILED COMPONENT DESIGN DESCRIPTION 

The various components of the RBHT Test Facility are described in Sections 3.1 to 3.11. All 

components are well insulated to minimize heat losses to the environment. 

Detailed mechanical drawings of the RBHT Test Facility are listed in Appendix A. 

Volumes and flow areas for each component were experimentally determined by weighing the 

water drained from each isolated component as described in Appendix B. 

3.1 Test Section

The test section consists of the heater rod bundle, the flow housing, and the lower and upper 

plenums, as shown in Figure 3.1. The heater rod bundle simulates a small portion of a 17x17 

reactor fuel assembly. The electrically powered heater rods have a diameter of 9.5 mm (0.374 

in) arranged in a 7x7 array with a 12.6 mm (0.496 in) pitch, as shown in Figure 3.2. The heater 

rod specifications are listed in Table 3.1. The bundle has 45 heater rods and four unheated 

corner rods. The corner rods are used to support the bundle grids and the grid and fluid 

thermocouple leads. The support rods are made from Inconel 600 tubing having a diameter of 

9.525 mm (0.375 in), a wall thickness of 2.108 mm (0.083 in), and a length of 3.96 m (156 in). 

The heater rods are single-ended and consist of a Monel 500 electrical resistance elements 

filled and surrounded by hot pressed boron nitride (BN) insulation, and enclosed in an Inconel 

600 cladding, as shown in Figure 3.3. This material was chosen for its high strength and low 

thermal expansion coefficient at high temperatures, which minimizes rod bowing and failure at 

high temperature operating conditions since it was desired to reuse the heater rods for a second 

bundle build. The heater rods have a 3.657 m (12 ft) heated length with a skewed axial power 

profile, as shown in Figure 3.4, with the peak power located at the 2.74 m (9 ft) elevation. The 

maximum-to-average power ratio (Pmax/Pavg) is 1.5 and the minimum-to-average power 

(Pmin/Pavg) is 0.5 at both ends of the heated length. The bundle has a uniform radial power 

distribution. Detailed engineering drawings showing the elevation information of the windows, 

differential pressure (DP) tap points, spacer grid instrumentation, and traversing steam probes 

are given in Appendix E. 

Power to each rod is provided by a 60 volt, 12,600 amp, 750 kW DC power supply. Each rod is 

rated for 10 kW, and designed to operate at 1.38 MPa (200 psig) at a maximum temperature of 

1204 degrees C (2200 degrees F), but because of its solid construction it can be operated at up 

to 10.34 MPa (1500 psig). Each rod is instrumented with eight 0.508 mm (20 mil) diameter 

ungrounded thermocouples attached to the inside surface of the Inconel sheath at various 

locations. All of the thermocouple leads exit at the heater rod bottom end. Thermocouple 

specifications are shown in Table 3.2. The Inconel 600 thermocouple sheath is compatible with 

the heater rod cladding and housing material to reduce thermal expansion and minimize the 

possibility of missing thermocouple failure during the thermocycling operations. 

There were three prototype heater rod experiments performed on the final heater rod design 

used for the RBHT facility. The purpose of these experiments was to verify that the rod design 

could meet the rigorous temperature and lifetime requirements required of the rods for the high 

temperature tests without rod or internal thermocouple failures. The third heater rod from these 

experiments was cut into one-foot lengths, labeled and sent to Purdue University to measure 
8

the surface emmissivity of the Inconel cladding as well as the material properties for both the 

cladding and the boron-nitride insulation. The results from the thermophysical properties tests 

performed by Thermophysical Properties Research Laboratories, Inc., on the heater rod and 

materials are given in Appendix H. 

The surface of the test rod was oxidized from the high temperature tests. The same heater rod 

surface oxidation would occur for the heater rods put into the rod bundle since the temperature 

ranges were the same. Therefore, the emmissivity values measured on the test rod are 

applicable to the heater rods used in the RBHT Test Facility bundle build. It was observed that 

the Inconel oxidation was a very thin and tight oxide layer on the surface of the cladding. The 

roughness of the heater rod surface was also measured and was found to be between 20 - 30 

μin which is consistent with smooth drawn tubing. 

The rod bundle has seven mixing vane grids shown in Figure 3.5. These grids are similar in 

design of a PWR 17x17 fuel assembly, but instead of having dimples and springs, these grids 

have all dimples which provide a 0.127 mm (0.005 in) around each heater rod in order to 

prevent bowing when the heater rods are linearly expanding at high temperatures. The spacer 

grids are made out of Inconel 600 alloy sheets which are 0.508 mm (0.020 in) thick and are 

44.45 mm (1.75 in) in height including the mixing vanes. The grids are located 522 mm (20.55 

in) apart except for the spacing between the first and second grid, which are 588.26 mm (23.16 

in) apart. The first grid is located 101.854 mm (4.01 in) above the bottom of the heater length. 

The grids in conjunction with the corner rods form the heater rod bundle support structure. The 

grid locations are similar to the ones found in a 17x17 PWR fuel assembly. The heater rod top 

extensions are attached to the 2.54 cm (1 in) thick nickel ground plate by means of a Morse 

taper that provides a good electrical contact. The heater rod bottom extension and copper 

electrode extend through the lower plenum O-ring pressure seal plate. The copper electrodes, 

which are 5.842 mm (0.230 in) in diameter and 203 mm (8 in) long, extend through holes drilled 

in the low-melt reservoir shown in Figure 3.6. This reservoir serves as the electrical power 

supply positive side connection. It contains a low temperature melting alloy at about 71.11 

degrees C (160 degrees F) which is an excellent conductor, thus providing a good electrical 

contact and mechanical cushion allowing for rod thermal expansion to each heater rod. 

The flow housing provides the pressure and flow boundary for the heater rod bundle. It has a 

square geometry. Its as-built inside dimensions are 91.3 x 91.3 mm (3.595 x 3.595 in), and 

wall thickness 6.35 mm (0.25 in), as shown in Figure 3.7. The housing is made out of Inconel 

600 the same material used for the heater rod cladding and thermocouple sheaths. As pointed 

out previously, the high strength of Inconel 600 at elevated temperatures will minimize housing 

distortion during testing. The 6.35 mm (0.25 in) wall thickness is the minimum allowable for 

operating at 0.402 MPa (60 psig) and 537.8 degrees C (1000 degrees F), taking into 

consideration the cutouts to accommodate the large windows and the numerous pressure and 

temperature penetrations through the walls, as shown in Figure 3.8. The empty housing has a 

flow area of 83.4 cm2

 (12.9 in2). With the rod bundle in place the flow area is 48.63 cm2 (7.5 

in2

). This area is 7.21 percent larger than the ideal flow area of a 7x7 rod bundle configuration. 

The excess flow area is due to the flow housing inside dimensional tolerance and the space 

needed to insert the rod bundle in the housing. The gap between the outer rods and the flow 

housing inner wall is 3.12 mm (0.123 in) wide. More detailed information is given in Appendix E. 

The flow housing has six pairs of windows. Each window provides a 50.8 x 292.1 mm (2 x 11.5 

in) viewing area as listed in Table 3.3. Each pair of windows is placed 180 degrees apart and 
9

located axially at elevations overlapping rod bundle spacer grids, thus providing a viewing area 

about 88.9 mm (3.5 in) below and 152.4 mm (6 in) above the corresponding spacer grids. The 

windows will facilitate the measurement of droplet size and velocity using a Laser Illuminated 

Digital Camera System (LIDCS). The two-phase void fraction will be measured using sensitive 

DP cells. In addition, high speed movies using diffused back lighting can be taken during the 

experiments for visualization and flow regime information. The windows are made out of optical 

grade fused quartz and are mounted on the housing by means of a bolted flange and 

Kemprofile high temperature gasketing material, as shown in Figure 3.9. 

The flow housing has 23 pressure taps located at various elevations, as shown schematically in 

Figure 3.8. The pressure taps locations are shown in the Engineering Drawings E115073 and 

E118338. The pressure taps are connected to sensitive DP cells providing measurements to 

calculate single-phase friction losses for determining bare rod bundle and grid loss coefficients. 

 Sixteen of these pressure taps are located about 76.2 - 127 mm (3 - 5 in.) apart to provide 

detailed void fraction measurements in the froth region above the quench front. The DP cells 

connections and axial location are shown schematically in the Engineering Drawing E118338. 

The flow housing is supported from the nickel plate and upper plenum, allowing it to freely 

expand downward, thus minimizing thermal buckling and distortion. 

The flow housing also has 13 stand-offs at various elevations, as shown in Figure 3.9, for the 

traversing steam probe rakes which measure the superheated steam temperatures in the 

dispersed flow regime. 

3.2 Lower Plenum

The lower plenum is attached to the bottom of the flow housing. The lower plenum is made out 

of nominal 203.2 mm (8 in) schedule 40, 304SS pipe with an inside diameter of 201.6 mm 

(7.937 in), a height of 203.2 mm (8 in), and a volume of 6569.5 cm3

 (0.232 ft3), as shown in 

Figure 3.10. The lower plenum is used as a reservoir for the coolant prior to injection into the 

rod bundle during reflood. It connects to the injection water line and steam cooling line. It has 

two penetrations for thermocouples monitoring the coolant temperature prior and during reflood, 

and pressure taps for static and differential pressure measurements. 

The lower plenum also has four Conax fittings with multiple probes sealing glands for the bundle 

grid, steam probes, and support rod wall thermocouple extensions that are routed through the 

bottom of the rod bundle. It contains a flow baffle, which is attached to the flow housing bottom 

flange. The flow baffle has a square geometry, similar to the flow housing, as shown in Figure 

3.11. The flow baffle wall has numerous small diameter holes that act as a flow distributor and 

flow straightener to provide an even flow distribution into the rod bundle. 

3.3 Upper Plenum

The upper plenum serves as the first stage for phase separation and liquid collection of the twophase effluent exiting the rod bundle. The liquid phase separates due to the sudden expansion 

from the bundle to the larger plenum flow area. The de-entrained liquid is collected around the 

flow housing extension in the upper plenum. The extension acts as a weir preventing the 

separated liquid from falling back into the heater rod bundle. The upper plenum vessel 

configuration is shown in Figure 3.12. The vessel is made from a 203.2 mm (8 in) 304SS pipe 
10

with an inside diameter of 201.6 mm (7.937 in) and a height of 304.8 mm (12 in). It has a 

volume of 9827.5 cm3

 (0.347 ft3). The plenum has a 76.2 mm (3 in) pipe flange connection to 

the steam separator and two penetrations for fluid thermocouples. It is covered with a 203.2 

mm (8 in) 304SS blind flange. This flange has a 25.4 mm (1 in) penetration for steam injection, 

venting and connecting the safety relief valve and rupture disc assembly. It also has a pressure 

tap penetration for static and differential pressure measurements. In addition, the upper plenum 

contains an exhaust line baffle shown in Figure 3.13. The baffle is used to further de-entrain 

water from the steam and prevents water dripping from the upper plenum cover flange to be 

carried out by the exhaust steam. The baffle has a 76.2 mm (3 in) flange connection at one 

end. It is inserted through the upper plenum exit nozzle, and it is bolted between the nozzle 

flange and the flange of the pipe going to the steam separator. 

3.4 Large and Small Carryover Tanks

The de-entrained liquid from the upper plenum drains into the top of a 25.6 mm (1 in) tube which 

extends inside a small carryover tank to detect and measure the carryover liquid as soon as 

possible. This tank, shown in Figure 3.15, is connected close coupled in series with a larger 

carryover tank, shown in Figure 3.14, which collects and measures the amount of liquid overflow 

from the smaller carryover tank. The small carryover tank has a volume of about 1387.8 cm3 

(0.049 ft3) to more accurately measure the water being collected as a function of time. This tank 

is made from a 76.2 mm (3 in) schedule 40 pipes having an overall length of 0.9144 m (36 in) 

including the end caps. The large carryover tank is made from a 101.6 mm (4 in) schedule 40 

pipes with a bottom end cap and top flanges having an overall length of 19.7 m (6 ft) and a 

capacity of 15916.9 cm3

 (0.562 ft3). Each tank is connected with one 25.4 mm (1 in) flexible 

hose, one 25.4 mm (1 in) drain tube, and 9.5 mm (3/8 in) tubes with wall penetrations for 

installing fluid and level meters. 

3.5 Steam Separator and Collection Tanks

The wet steam exhausted from the upper plenum flows through a steam separator (or dryer), 

shown in Figure 3.16, where carryover liquid droplets are further separated from the steam and 

collected in a small collection tank, shown in Figure 3.17 attached to the bottom of the steam 

separator. The steam separator relies on centrifugal force action to provide 99 percent dry 

steam. The separated liquid is drained into a collection tank where a differential pressure cell is 

used as a level meter to measure liquid accumulation. The steam separator is fabricated from a 

355.6 mm (14 in) diameter 316SS pipes and is 914.4 mm (36 in) long. It has 50.8 mm (2 in) 

connecting nozzles, a 25.4 mm (1 in) drain, and a 12.7 mm (0.5 in) top vent. It also has two 

pressure taps for liquid level measurements and two 38.1 mm (1.5 in) side nozzle connections. 

The drain tank is a small vessel with a capacity of 11328.77 cm3

 (0.4 ft3). It is made from a 

101.6 mm (4 in) schedule 10, 304SS pipe with an overall length of 121.9 mm (48 in), including 

both end caps. It has a 25.4 mm (1 in) drain nozzle, a 25.4 mm (1 in) pipe top connection to the 

steam separator, pressure taps and fluid thermocouple connections. 

3.6 Pressure Oscillation Damping Tank

The dry steam from the steam separator flows into a pressure oscillation-damping tank. As its 

name implies, it is used to dampen pressure oscillations at the upper plenum caused by rapidly 

oscillating steam generation in the heater rod bundle during reflood. This effect is coupled to 
11

the characteristics of the pressure control valve, which is located downstream in the steam 

exhaust line. It is desirable to have a smooth pressure control in order to minimize uncertainties 

when calculating mass balances, steam generation rates, and heat transfer coefficients in the 

heater rod bundle, and avoid the pressure control valve causing oscillations in the bundle as it 

cycles. The tank has a volume of 0.209 cm3

 (7.38 ft3), which is approximately equal to the total 

volume of the rest of the test facility. This design criterion was used successfully in the 

ACHILLES reflood test facility (Ref. 6). The pressure tank is fabricated from a 355.6 mm (14 in), 

304SS standard schedule pipe by 2.59 m (102 in) long, as shown in Figure 3.18. Inside the 

tank is a 76.2 mm (3 in), schedule 40, 304SS pipe that provides a tortuous path for the steam 

flow to expand into a large volume, thus damping pressure oscillations. The inlet and outlet 

nozzles are 76.2 mm (3 in) in diameter with flanges. The vent and drain lines are made of 25.4 

mm (1 in) pipe. There are 9.53 mm (3/8 in) tube penetrations for a fluid thermocouple and two 

static pressure taps. The tank walls are heated with clamp-on strip heaters up to about 5.55 

degrees C (10 degrees F) above saturation temperatures to prevent steam condensation. 

3.7 Exhaust Piping

The steam flowing out of the pressure oscillation-damping tank is exhausted through a 76.2 mm 

(3 in) schedule 40, 304SS pipes, shown schematically in Figure 3.19. The exhaust line has a 

Vortex flowmeter, a 76.2 mm (3 in) V-Ball pressure control valve, and a muffler at the exit to 

minimize the noise caused by steam blowing into the atmosphere. The pressure control valve is 

activated by a signal from a static pressure transmitter located on the upper plenum. The line is 

also instrumented with a static pressure transmitter, fluid thermocouples, and outer wall 

thermocouples. The 76.2 mm (3 in) line has flow-straightening vanes which reduce the pipe 

length requirements upstream of the Vortex flowmeter in order to obtain accurate flow 

measurements. This line has strapped-on electrical heaters to keep the wall temperature about 

11.11 degrees C (20 degrees F) above saturation to insure that single-phase steam flow 

measurements are made by the Vortex flowmeter. 

3.8 Injection Water Supply Tank

The injection water system consists of a water supply tank, a circulating pump, and 

interconnecting lines to the test section lower plenum. The water supply tank shown in Figure 

3.20 has a capacity of 0.953 cm3

 (251.75 gal). It is designed for 0.402 MPa (60 psig) and 

154.44 degrees C (310 degrees F). The tank is equipped with a submersible electrical heater to 

heat the injection water to specified test temperatures. The tank is pressurized by a nitrogen 

supply system, which regulates the over-pressure needed for the forced flooding injection tests. 

 The tank has inlet and outlet nozzles, pressure taps for level measurements, fluid and wall 

thermocouples. Water from the tank can be circulated through the test section by a centrifugal 

pump with a capacity up to 0.946 cm3

 per minute (250 gpm) which are needed to perform liquid 

single-phase flow tests. 

3.9 Water Injection Line

The water injection line shown schematically on Figure 3.21 consists of a 50.8 mm (2 in) 

diameter 304SS tubing with a 2.77 mm (0.109 in) wall. It is rated for 0.402 MPa (60 psi) and 

154.4 degrees C (310 degrees F) service. This line has a Coriolis Effect type flowmeter, a Vball control valve, a quick opening solenoid valve, and appropriate shut-off and drain valves. It 
12

also has penetrations for static pressure and fluid thermocouples, and outside wall 

thermocouples. The line has tracer electrical cable type heater to maintain the water being 

injected at the proper test inlet temperatures. 

3.10 Steam Supply

A boiler with a capacity of 2613 kg/hr (5760 lbs/hr) at 1.03 MPa (150 psig) provides steam for 

the single phase steam cooling , pressure drop and water droplet injection tests. It also 

provides steam for preheating the test components prior to testing. The boiler is connected to 

the lower plenum by means of a 50.8 mm (2 in) 304SS tube. It is equipped with a Vortex 

flowmeter to measure steam flows, fluid and wall thermocouples, a V-ball control valve, and a 

quick acting solenoid valve. The boiler is also connected to the upper plenum to provide steam 

for preheating the test components prior to testing. 

3.11 Droplet Injection System

A system to inject water droplets into the test section has been included in the RBHT Test 

Facility design. The droplet injection system consists of six 2.38 mm (3/32 in) OD stainless 

steel tubes entering through the test section at the 1.295 m (51 in) elevation. The tubes run 

perpendicular to the heater rods and penetrate through both sides of the housing as seen in 

Figure 3.22, and the injection flow schematic is shown in Figure 3.23. The tubes can be easily 

removed when not needed so they do not interfere with other types of tests. Water is supplied 

to the injector tubes from the injection water supply tank as described in Section 3.8 and a 

cluster of 0.33 mm (0.013 in) diameter holes which are drilled on the downstream side of the 

tubes to inject water directly into each of the 36 rod bundle sub-channels. Three injection tubes 

with different hole arrangements were tested as reported in Appendix D. The results showed 

that the triangular pitch configuration provided the desired water droplet diameter of about 0.660 

mm (0.026 in). 
1

 

Figure 3.1 Test Section Isometric View. 

3
14

Figure 3.2 Rod Bundle Cross Section View. 
1

Figure 3.3 Heater Rod. 

5
1

Figure 3.4 Heater Rod Axial Power Profile. 

6
1

Figure 3.5 Mixing Vane Grid. 

7
1

Figure 3.6 Low-Melt Reservoir. 

8
1

Figure 3.7 Flow Housing Cross Section View. 

9
2

Figure 3.8 Low Mass Flow Housing. 

0
21

Figure 3.9 Housing Window. 
22

Figure 3.10 Lower Plenum. 
2

Figure 3.11 Lower Plenum Flow Baffle. 

3
24

Figure 3.12 Upper Plenum. 
2

Figure 3.13 Exhaust Line Baffle. 

5
2

Figure 3.14 Large Carryover Tank. 

6
2

Figure 3.15 Small Carryover Tank. 

7
2

Figure 3.16 Steam Separator. 

8
2

Figure 3.17 Steam Separator Drain Tank. 

9
Figure 3.18 Pressure Oscillation Damping Tank. 

30
Figure 3.19 Exhaust Piping. 

31
Figure 3.20 Injection Water Supply Tank. 

32
Figure 3.21 Water Injection Line. 

33
Figure 3.22 Droplet Injection Schematic. 

34
Figure 3.23 Droplet Injection System Schematic. 

35
36

Table 3.1 Heater Rod General Specifications

 Operating Pressure 1.38 MPa (200 psig) 

 Maximum Sheath Temperature 1204 degrees C (2200 degrees F) 

 Design Power 10.0kW 

 Design Voltage 57 V 

 Design Current 175.4 A 

 Design Resistance @ 537.8 degrees C 0.325 Ω

 Electrical Resistance @ 31.11 degrees C 0.306 Ω ± 5% 

 Axial Power Profile Linear 0.5/1.5/0.5 

 (See Figure 3.4) 

 Heated Length 3.657 m (144 in) 

 Average Linear Power 0.83 kW/ft 

 Peak Linear Power 1.25 kW/ft 

 Outside Diameter 9.5 mm (0.374 ± 0.002 in) 

 Overall Sheath Length 7.368 m (172 in) 

 Electrode Length 203 mm (8 in) 

 Electrode Diameter 5.84 mm (0.230 ± 0.002 in) 

 Extension Length - Top 203 mm (8 ± 0.25 in) 

 Sheath Surface Finish As Swaged 

 (63 μin or better) 

Table 3.2 Thermocouple Specifications

 Type Premium grade ANSI Type K 

 Diameter 0.508 mm (0.020 in) 

 Sheath Inconel 600 

 Insulation MgO 

 Junction Undergrounded, BN Backfilled 

 Length Up to 5.485 m (216 in) 

 Resistance, Lead to Sheath 1 x 1011 Ω @ 50 volts 

 Length Beyond Heater Sheath 1.219 m (48 in) 

Table 3.3 Flow Housing Window Viewing Areas Below and Above Mixing Vane Grids 

 Window Grid No. Height of Viewing Areas 

 Below Above 

 mm (in) mm (in) 

 A 2 101.6 (4) 152.4 (6) 

 B 3 108.0 (4.25) 146.1 (5.75) 

 C 4 108.0 (4.25) 146.1 (5.75) 

 D 5 108.0 (4.25) 146.1 (5.75) 

 E 6 98.4 (3.873) 155.6 (6.125) 

 F 7 108.0 (4.25) 146.1 (5.75) 
37

4. TEST FACILITY INSTRUMENTATION

The test facility instrumentation is designed to measure temperatures, power, flows, liquid 

levels, pressures, void fractions, and droplet sizes, distribution, and drop velocities. The vapor 

velocity cannot be directly measured in a two-phase dispersed flow, but it can be calculated at 

different axial positions from the data. Overall and transient mass and energy balances, mass 

inventories, carryover liquid and steam flows as a function of time can be calculated. Heater rod 

power, temperature, and fluid temperature are used to calculate heat fluxes and heat transfer 

coefficients, quench times, rod bundle energy losses, convective and radiation heat transfer to 

steam, droplets, grids, support rods, and housing. Effects of grids, support rods and housing 

behavior during reflood can be determined. Void fraction measurements below the quench front 

and in the froth level above the quench front, in conjunction with the laser illuminated digital 

camera measurements are used to determine droplet entrainment behavior, droplet effects on 

heat transfer, and steam desuperheating. The Laser Illuminated Digital Camera System 

(LIDCS) measurements provide droplet size distribution and velocities during reflood. 

4.1 Loop Instrumentation and Controls

Loop instrumentation is shown schematically in Figure 4.1, and listed in the instrumentation and 

data acquisition channels shown in Table 4. There are 123 instrumentation channels are 

assigned to the collection of electrical power, fluid and wall temperatures, levels, flows, 

differential pressures, and static pressure measurements. The injection water supply tank has 

three fluid and three wall thermocouples to monitor water and wall temperatures during heat-up 

prior to testing. It has a differential pressure transmitter used as a level meter to determine 

water mass in the tank and mass depletion during reflood testing. It also has a static pressure 

transmitter which monitors the nitrogen overpressure and controls the nitrogen flow needed to 

maintain a constant pressure during forced injection reflood tests. 

The water injection line is equipped with a Coriolis Effect Micromotion flowmeter that directly 

measures mass flows up to 454 kg/min (1000 lbs/min) with an accuracy of plus or minus eleven 

hundredths of a percent (±0.11 percent) of rate. The steam line has a Rosemount Vortex 

shedding flowmeter to measure flow up to 7.08 m3

/min (250 ft3/min) with an accuracy of plus or 

minus 65 hundredths of a percent (±0.65 percent) of rate. Each flowmeter is connected through 

a pneumatic controller to a V-ball flow control valve. Each line has a fluid thermocouple to 

measure water or steam temperature during heat-up and forced injection testing. They also 

have a static pressure transmitter which in conjunction with the thermocouples can determine 

the thermodynamic properties of the fluids. The injection line has three wall thermocouples to 

monitor wall temperatures during heat-up and during testing. One of these thermocouples in 

conjunction with a temperature controller regulates the power to an electrical heating cable 

wrapped around the injection line. The heating cable is used to heat-up the injection line wall 

and to maintain the injection water at the required injection temperature. 

The small carryover tank has one fluid and two wall thermocouples. The large carryover tank 

instrumentation consists of one fluid thermocouple and three wall thermocouples. Both tanks 

have a liquid level meter which measures the amount of carryover liquid being collected during 

testing. In addition, a differential pressure transmitter is connected from the top of the carryover 

tank to the upper plenum to determine the static pressure in the carryover tank. 
38

The steam separator is instrumented with one fluid and two wall thermocouples. The drain tank 

is instrumented with two fluid and two wall thermocouples. The fluid thermocouple measures 

the water temperature de-entrained during testing. The wall thermocouples monitor wall 

temperatures during heat-up. The volume of de-entrained water is measured with a level meter 

connected across the drain tank. 

The pressure oscillation damping tank has two fluid and three wall thermocouples which are 

used to monitor vessel walls during heat-up, and to insure that the vessel wall is at a 

temperature above saturation to prevent condensation. One wall thermocouple in conjunction 

with a temperature controller monitors the power applied to clamp-on heaters that heat up the 

tank to the desired wall temperature. 

The exhaust line is equipped with a Vortex flowmeter which, in conjunction with a static 

pressure transmitter and fluid thermocouple measurements are used to calculate steam 

volumetric flows up to 7.08 m3

/min (250 ft3/min). The flowmeter has an accuracy of plus or 

minus 65 hundredths of a percent (±0.65 percent) of the rate. The exhaust line also has three 

wall thermocouples to measure pipe wall temperatures. One wall thermocouple in conjunction 

with a temperature control regulates the power going to clamp-on heaters which are used for 

heating the pipe walls up to a temperature about 11 degrees C ( 20 degrees F) above saturation 

to prevent steam condensation and to insure accurate single phase steam flow measurements. 

The exhaust line has a V-ball pressure control valve. This valve is controlled by a static 

pressure transmitter through a pneumatic controller connected to the top of the upper plenum in 

order to maintain constant test section pressure during testing. 

4.2 Test Section Instrumentation

The test section is heavily instrumented to obtain the data described at the beginning of this 

section. 

 

The test section instrumentation consists of the heater rod bundle and flow housing, the lower 

plenum, and the upper plenum groups. The heater rod bundle and flow housing instrumentation 

is shown schematically in Figure 4.2 and listed in Table 4. A more detailed drawing is given in 

Figure E.5 of Appendix E. This figure shows the instrumentation axial locations in relation to 

heater rod heated length, heater axial power profile, grids, steam probes and steam probe 

rakes, housing pressure taps, and windows. 

Six grids have thermocouples attached to their surfaces in order to determine quenching 

behavior during reflood shown in Figures 4.3 though 4.9. Grid and steam probes axial locations 

are shown schematically in Figure 3.8 with the detailed elevation information given in Figures 

E.3 and E.4 of Appendix E. Eight groups of heater rods have thermocouples at different 

elevations to cover, as much as possible, the entire rod bundle heated length. The radial 

location of each heater rod group is shown in Figure 4.10. The radial locations of 

instrumentation rods were chosen in order to be able to characterize heat transfer of hot rods 

simulated by the center rods, rod-to-rod and rod-to-housing radiation heat transfer. For this 

purpose, heater rod thermocouples, steam probes, and housing wall thermocouples are located 

at the same elevations. In addition, symmetrical location of the same group of instrumented 

heater rods will help in the data analysis and will determine any anomalies in the radial flow 

distribution through the heater rod bundle. Heater rod thermocouples are also placed at varying 

distances downstream from a grid to determine the decreasing heat transfer gradient between 
39

grid spans. The steam probe or fluid thermocouples are located at short distances upstream 

and downstream of a grid to determine the effect of water droplets being shattered by the grids 

on droplet size and distribution, and the de-superheating effect on steam temperatures in the 

disperse flow regime. 

The vapor or steam temperature will be measured using miniature thermocouples having a 

diameter of 0.813 mm (0.032 in) which are attached to the spacer grids, and the traversing 

steam probe rakes having a diameter of 0.381 mm (0.015 in). These are very small diameter 

thermocouples that have a fast response time such that they can follow the vapor temperature 

accurately in a dispersed, non-equilibrium, two-phase flow. As the froth front approaches, the 

number and sizes of the droplets increase which can lead to wetting of these thermocouples. 

Experiments performed as part of the FLECHT-SEASET program indicated that very small 

thermocouples would provide reliable vapor superheat ready for the longest time period until 

they quench as the froth region approached. While the Lehigh vapor probe was considered, it 

is too large and causes a flow distribution effect which is not typical of the bundle. The Lehigh 

probe would block 68 percent of the gap between adjacent heat rods. The effect of the probe 

would be to distort the data downstream of the sensing location. Such flow distribution effects 

were observed in the Lehigh data as well as the INEL single tube data which used these 

probes. 

The traversing steam probe rakes are located at the spans among the grids at the upper heater 

rod bundle elevations, as shown schematically in Figure 4.11. The traversing steam probes 

rakes will measure steam temperatures in the heater rod bundle flow subchannels and the gap 

between the heater rods during the dispersed flow regime. The traversing steam probe rake is 

shown in Figure 4.12. Each rake consists of three 0.381 mm (0.015 in) diameter ungrounded 

thermocouples mounted on a 0.356 mm (0.014 in) thick by 6.35 mm (0.25 in) wide Inconel strip. 

 The thermocouples are spaced 12.6 mm (0.496 in) apart which correspond to the heater rod 

spacing in the bundle. The thermocouple tips are located facing the steam flow. A 2.39 mm 

(0.094 in) diameter tube attached to the strip is used to traverse the steam probe rake across 

the rod bundle. This tube also carries the thermocouples leads outside the flow housing 

through an extension tube and a pressure seal arrangement. The tube is attached to an 

automated sliding mechanism shown in Figure 4.13. It consists of a sliding bar, a 24 DCV 

motor with a ball drive shaft, and a linear potentiometer provides a voltage input to the Data 

Acquisition which determines the rake thermocouple location and travel distances across the 

heater rod bundle. 

Two fluid thermocouples are placed 24.5 mm (1 in) below the bottom of the bundle heated 

length such that injection water temperatures are monitored prior to and when reflood is started. 

There are 23 DP transmitters connected to the housing wall pressure taps providing 

measurements to calculate single phase flow heater rod bundle and grid friction losses, bundle 

mass inventory, and void fraction during reflood. Nine DP cells are connected to pressure taps 

located 76.2 - 127 mm (3 - 5 in) apart to provide detail mass inventory, and void fraction data in 

the froth region above the quench front, as shown in Figure E.2 of Appendix E. In addition, 

heater rod and housing wall thermocouples are placed at these pressure tap mid spans 

locations to determine convective and radiant heat transfer coefficients in the froth region where 

the differential pressure cells will give the average void fraction. 

As described previously in Section 3.1, the flow housing has six pairs of windows at the 

following elevations: 61.39 cm (27.17 in), 113.58 cm (44.72 in),165.8 cm (65.27 in), 217.98 cm 
40

(85.82 in), 270.18 cm (106.37 in), and 322.4 cm (126.92 in). Each pair of windows is 180 

degrees apart. The window lenses are made from optical grade fused quartz and provide a 

viewing area of about 10.16 cm (4 in) below and 15.24 cm (6 in) above grid numbers two 

through seven. The windows will be preheated to prevent wetting during the time when 

dispersed flow is occurring and LIDCS measurements are being made. The windows will be 

heated using infrared heaters on each window and by pulsing the heater rod bundle when 

preheating the flow housing walls. The infrared heaters will be removed just before a test is 

started. Two significant measurements above and below the grid can be made through the 

windows. 

A droplet imaging system known as VisiSizer has been developed in conjunction with Oxford 

Lasers of Acton, Massachusetts, to measure the size and velocity of water droplets entrained in 

the steam flow of the RBHT test section shown schematically in Figure 4.14. VisiSizer uses a 

pulsed infrared laser to image water droplets on a 1000x1000 pixel high-resolution black and 

white digital camera through a set of windows in the bundle housing as shown in Figure 4.15. A 

digital system such as VisiSizer was chosen over conventional high-speed cameras because of 

issues with reliability and speed of data acquisition. A high-speed camera is capable of only a 

few seconds of imaging and is a tedious process that does not give instantaneous results. 

Each frame of a standard imaging technique would need to be analyzed by hand. The VisiSizer 

system is capable of analyzing 12 - 13 frames per second for an indefinite period of time. Film 

from the FLECHT-SEASET tests show much less image quality than images taken with 

VisiSizer in the experiments performed so far. However, VisiSizer is incapable of measuring 

anything other than complete droplets. This makes it an inadequate tool for gathering 

information about the entrainment front where there are ligaments and other unusual water 

behavior. Therefore, it is still a possibility that a high-speed camera will be used in tandem with 

VisiSizer for the RBHT tests. 

An infrared laser is used with the system because it is capable of passing through the quartz 

viewing windows and being absorbed by the water droplets entrained in the steam flow. 

Because the infrared rays are absorbed by the water droplets, the resulting droplet shadows 

can be recorded by the digital camera. So far, there has been no effect of laser light scattering 

from rods to droplets. Pictures taken in and out of the rod bundle have the same imaging 

characteristics, droplet analyzing capability, and clarity. A band pass laser light filter is placed in 

front of the digital camera to eliminate non-infrared light from other sources and an anti-glare 

attachment is used to eliminate any illumination interference from outside the viewing area. In 

addition, rod bundle geometry has little effect in the measurement of droplet distributions and 

velocities. 

The frames captured by the camera are fed back to a computer at approximately 12 - 13 frames 

per second. The software can analyze each frame for droplet size and velocity and write the 

recorded data to a size and velocity data array. The software program determines droplet sizes 

by determining the area of black vs. white pixels in each droplet image. Once the droplet area 

is determined, the program calculates the perimeter of the droplet image to determine the 

sphereosity of the droplet. The VisiSizer system is capable of determining the surface area 

based on diameter of any and all droplets. At any droplet concentration that is measurable with 

the system, an accurate measure of the total droplet surface area can be obtained. So far, 

number fluxes of up to six droplets per frame in velocity mode (12 droplet images) have been 

analyzed successfully with the droplets in a very narrow viewing area. There is the capability to 

increase this droplet number flux by several times using larger and multiple viewing areas. 
41

Operating the laser in a double pulse mode enables the VisiSizer system to measure both 

droplet diameter and velocity for a particular probe volume. The laser pulses twice with a 

known pulse delay (on the order of one millisecond) while the camera shutter remains open, 

creating two images in the same frame of each droplet. The distance between images is then 

determined and the velocity calculated. These velocity characteristics are enough to 

characterize the behavior of the flow despite the fact that the droplets are only captured in a 

single frame. 

The local distribution of droplets will be determined for a known probe volume governed by the 

software settings. Droplets that lie out of this probe volume on either side of the line of sight will 

be rejected based on focus. The opposite sides of the probe volume will be set by the spacing 

of the rods in the bundle. Each droplet is recorded in a two-dimensional array according to size 

and velocity. The droplet sizes are recorded in log-normal bins while the velocity bin size is 

user defined. Data for the transient reflood experiments is recorded in user defined quasisteady state time periods. At the end of each time period the data is saved and a new array is 

opened. Arrays characterized by similar droplets populations can then be combined for better 

statistical results. 

The VisiSizer will enable the experimenters to collect a vast amount of information about the 

droplet flow in the test section. The information will be collected in an easy to handle data array 

and all information will be written to a CD-ROM to ensure the information will be available for 

later use. 

The droplet injection system described in Section 3.11 has been constructed so that RBHT can 

collect steady-state information on droplet behavior. The injection system creates droplets of a 

known size and flow rate in the test section. The injection tubes are easily removed and 

replaced. This enables multiple injection sizes to be used as needed. The flow rate of the 

injection is controlled through a series of valves and flow meters. These factors should allow for 

the production of various droplet sizes. VisiSizer can study the droplet flow and distribution 

before a grid and then the system can be moved to image droplets immediately after the grid 

with the same conditions. In this way the effects of a spacer grid on the droplet diameter 

distribution can be determined. 

The four corner support rods are unheated. They are used to support the bundle grids and to 

support grid and steam probes thermocouple leads going out of the bundle. These rods are 

instrumented with eight thermocouples attached at various elevations corresponding to heater 

rods and housing wall thermocouples. The purpose of this arrangement is to quantify radiation 

heat transfer losses to unheated surfaces and determine their behavior during reflood. 

The DC power supply can be controlled by regulating the voltage, current, or total power output. 

The voltage drop across the heater rod bundle is measured by a voltmeter connected to voltage 

taps at the Low-Melt pot and the Nickel Ground Plate. The electrical current is measured by a 

copper shunt calibrated for 15,000 amps proportional to an output signal of 0-50 mV. 

The Lower Plenum is instrumented with two fluid and two wall thermocouples. The fluid 

thermocouples monitor the injection water temperature prior and during testing. The wall 

thermocouples measure the vessel wall during heat-up and testing. One of the wall 

thermocouples in conjunction with a temperature controller regulates electrical power to clamp-
42

on heater rods to maintain the vessel wall at inlet temperatures. 

The Upper Plenum is also instrumented with two fluid thermocouples and two wall 

thermocouples. The fluid thermocouples measure steam and carryover liquid during testing. 

The wall thermocouples monitor vessel wall temperatures during heat-up and testing. The 

Upper Plenum is also instrumented with a static pressure transmitter which measures and 

controls the test section pressure during testing. 

4.3 Data Acquisition System

The control and data acquisition system provides control functions and data collection functions 

for the RBHT Test Facility. This system consists of two parts, the computer and display 

terminals residing in the control room, and the VXI mainframe and terminal panels residing in 

the test facility. The two parts are connected via an industry standard IEEE 1394 (Firewire) 

serial control and data interface. 

The computer provides the display, control, and data storage functions. It has the capability of 

displaying control function setpoints and process variables, and critical operating parameters 

during tests, along with selected variables such as various rod temperatures displayed in realtime during the experiment. This system will provide dial, meter, and strip-chart functions as 

required. The computer collects and saves data from the various instruments, such as voltage, 

current, pressure, level, flow, and temperature. This provides control functions such as heater 

rod power, injection water pressure, upper and lower plenum temperature, etc. 

The instrumentation part of this system, residing in the test facility, consists of an industry 

standard VXI mainframe (Vme bus with extensions for instrumentation) from Hewlett-Packard 

(HP E8401A), and a set of terminal panels (HP E1586A). The VXI mainframe contains a 

Firewire controller card (HP E8491A) and several (currently seven) state-of-the-art data 

acquisition and control cards (HP E1419A). The terminal panels provide the isothermal 

reference junctions needed for the thermocouples, as well as the voltage and current-loop 

input/output (I/O) interface to the RBHT facility. These terminal panels are connected to the HP 

E1419A cards with SCSI cables. Seven cards yield a capability of 448 I/0. The VXI mainframe 

can hold up to twelve cards, and the Firewire interface can support up to 16 mainframes. Each 

E1419A card can support up to eight signal conditioning plug-ons (scp=s), conditioning eight 

channels each. Each E1509A scp contains low-pass anti-aliasing filters, fixed at 7 Hz. 

Because of this, the scan rate for each channel must be greater than or equal to the Nyquist 

rate of 14 Hz. The maximum a/d conversion rate on each HP E1419A card is nominally 100kHz, 

but is controlled to the rate the user requires. The seven cards can be synchronized to perform 

the scans simultaneously. The theoretical maximum scan rate for each channel (on any 

individual card) is 100,000/64 = 1,562.5 Hz, if all 64 channels are scanned. (Note that the 

actual scan rate would be less because of multiplexer switching, amplifier settling times due to 

gain changes, etc. There are different scp=s available from HP providing different filter values to 

scan at these rates.) The normal data-scanning rate will be 2 Hz during the majority of the 

tests, but this rate can be increased to 10 Hz for specific times during testing. 

An instrumentation error analysis showing the instrument uncertanity based essentially of 

FLECHT SEASET tests is given in Appendix F at the end of this report. 
4

Figure 4.1 Loop Instrumentation Schematic. 

3
44

Figure 4.2 Rod Bundle and Housing Instrumentation Axial Locations.
4

Figure 4.3 Mixing Vane Grid Instrumentation. 

5
4

Figure 4.4 Grid No. 2 Instrumentation. 

6
4

Figure 4.5 Grid No.3 Instrumentation. 

7
4

Figure 4.6 Grid No.4 Instrumentation. 

8
4

Figure 4.7 Grid No.5 Instrumentation. 

9
Figure 4.8 Grid No. 6 Instrumentation. 

50
Figure 4.9 Grid No.7 Instrumentation. 

51
Figure 4.10 Instrumentation Heater Rod Radial Locations. 

52
Figure 4.11 Grid and Steam Probe Thermocouple Axial Location Schematic. 

53
Figure 4.12 Traversing Steam Probe Rake Schematic. 

54
Figure 4.13 Steam Probe Rake Automatic Traversing Mechanism. 

55
Figure 4.14 Densitometer Schematic. 

56
Figure 4.15 Laser Illuminated Digital Camera System. 

57
Table 4.1 Instrumentation and Data Acquisition Channel List

58
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

59
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

60
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

61
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued) 

62
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

63
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

64
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

65
Table 4.1 Instrumentation and Data Acquisition Channel List (Continued)

66
67

5. TEST FACILITY IMPROVEMENTS

Significant improvements related to other heater rod bundle testing programs, listed in Section 

3, Literature Review, of the RBHT Test Plan and Design Report have been incorporated into the 

RBHT Test Facility. These improvements are: 

• A low mass square flow housing design which better fits a square rod bundle array and 

minimizes the housing mass and the excess rod bundle flow area. 

• The six pairs of windows which provide large viewing areas below and above grid 

locations, making it possible to observe and make void fraction and droplet 

measurements during reflood testing. 

• The use of a Laser illuminated Digital Camera System to measure entrained water 

droplets sizes, distribution, and velocities in the transition and disperse flow regions. 

• The use of a traversing steam probe rake to measure simultaneously steam 

temperatures in the flow subchannel and in the rod-to-rod gap. 

• Differential pressure transmitter axially located 76.2-127 mm (3-5 in) apart in conjunction 

with heater rod and flow housing wall thermocouples to obtain detailed void fraction and 

heat transfer information. 

• Addition of a water droplets injection system in conjunction with steam injection to study 

the droplet-steam cooling effects on heat transfer and grids. 

• Addition of a large pressure oscillation-damping tank to minimize test section oscillations 

observed in the FLECHT and FLECHT-SEASET tests. 

• The incorporation of closely coupled entrained liquid collection tanks and piping to 

reduce delay times for liquid collection. 
68
69

6. SUMMARY OF CHARACTERIZATION TESTS

6.1 Single Phase Pressure Drop Tests

The data from the single phase pressure drop tests performed under the RBHT Program were 

analyzed to calculate the grid loss coefficient that are needed to characterize the spacer grids 

used in the RBHT test bundle. 

Figure 6.1 shows the schematic layout of the rod bundle for the RBHT Test Facility with the 

location of the DP cells used for the single-phase pressure drop tests. 

Following are the specifications of the rod bundle: 

Number of rods: 49 

Diameter of rods: 9.4996 mm (0.374 in) 

Housing dimension: 91.313 mm (3.595 in) square 

Flow area: 4863.73 mm2 (7.5388 in2

) 

Hydraulic diameter: 10.6426 mm (0.419 in) 

Length (width or thickness) of spacer grid: 57.15 mm (2.25 in) 

The experiments recorded volumetric flow rate (channel 412) as well as DP cell readings. Table 

6.1 gives the detail of the DP cell location, channel number corresponding to the DP cell data, 

and number of grids within the DP cell span. The maximum Reynolds number achieved in the 

tests is about 30000. 

As seen from Table 6.1, the experiments were designed such that the there were many DP cell 

measurements (six channels, except channels 369 and 379) that included spacer grids in their 

span. In other words, the pressure drop measured by such DP cells spanning spacer grid(s) 

would be composed of two components: frictional loss for the bare portion of the bundle, and 

the loss associated with the spacer grid(s) in the span. DP cells for channels 369 and 379 

measure bare bundle pressure drop; i.e., they measure the single-phase frictional pressure drop 

within the span within the spacer grids. It should be noted that this frictional pressure drop will 

include the developing flow and the increased mixing effects which occur downstream of a 

spacer grid. 

6.1.1 Procedure for Calculation of Grid Loss Coefficient, kgrid

The following are the steps used to calculate the grid loss coefficient. 

1. Based on the volumetric flow rate measurement (channel 412) and the flow area of the 

bundle, the fluid velocity in the rod bundle is calculated. 

2. Reynolds number of flow is calculated using fluid properties, evaluated at 2.758 bar (40 psia) 

and 23.88 degrees C (75 degrees F). 

ρf = 997.27 kg/m3

 (62.258 lbm/ft3) 

μf = 9.1377 x 10-4 Pa-s (6.133 x 10-4 lbm/ft -sec) 
3. The pressure drop measured by any DP cell is the sum of the single-phase frictional 

pressure drop associated with the bare length of the span and the grid losses. 

ΔPTotal = ΔPbare + ΔPgrid

4. Knowing the grid length and the number of grids in the span, the bare bundle length is 

calculated as Lspan - N (number of grids in span) x Lgrid = Lbare. Using the bare bundle pressure 

drop data from channel 369 or 379, the frictional pressure drop for the bar portion of the span 

under consideration is obtained as: 

Δ Δ P L inspanconsideration

Spanlengthforchannel or x P fromchannel or bare

bare = 369 379 ( 369 379) (6-1) 

5. The pressure drop due to the grids is then obtained by subtracting the frictional pressure 

drop for the bare portion of the span from the measured DP value. 

6. The grid loss is given by: 

ΔP N

k V

g grids

f = ρ 2

2 (6-2) 

where 

N number of grids in the DP cell span under consideration, 

V velocity 

kgrid grid loss coefficient, which is to be calculated. 

From the above equation the grid loss coefficient kgrid can be determined. Figure 6.2 shows the 

plot of grid loss coefficient as a function of Reynolds number for all the DP cells with spacer 

grids in their span. As expected, the grid loss coefficient decreases with Reynolds number. 

The scatter in the data is minimal. 

This data is consistent with other experimental work, where a grid loss coefficient of about 1 is 

obtained for Reynolds number of about 100,000. 

6.1.2 Comparison of Data With Prediction Using Rehme’s Method 

Pressure drop at a spacer grid is given as: 

Δ P C

V

v

f = ε

ρ2

2

2 (6-3) 

where 

Cv modified spacer form loss coefficient (a function of Reynolds number) 

ε ratio of the projected grid cross-section area in the rod bundle to the undisturbed flow 

area (equal to 0.362 for the RBHT Test Facility) 

ρf fluid density 

70

V average fluid velocity in the rod bundle 
The modified spacer form loss coefficient is obtained from Rehme’s paper (Ref. 7) as a function 

of Reynolds number. For the Reynolds number range of interest, the Cv value is between 6 and 

11. 

The pressure drop is calculated from the Rehme’s equation. The grid loss coefficient is 

obtained from: 

Δ P N

k V

grid

grid = ρ 2

2 (6-4) 

where 

N number of grids in the DP cell span under consideration 

V velocity 

kgrid grid loss coefficient, which is to be calculated 

Figure 6.3 shows the comparison of grid loss coefficient from experiment with that calculated by 

Rehme’s method. It is seen that Rehme’s method underpredicts the coefficient significantly by 

almost a factor of 2. This is similar to what was obtained in the FLECHT-SEASET experiments. 

6.2 Calculation of Friction Factor for the Rod Bundle 

The data from the single-phase pressure drop tests performed under the RBHT Program was 

analyzed to calculate the friction factor, needed to characterize the rod bundle. 

Following are the specifications of the rod bundle: 

Number of rods: 49 

Diameter of rods: 9.4996 mm (0.374 in) 

Housing dimension: 91.313 mm (3.595 in) square 

Flow area: 4863.73 mm2

 (7.5388 in2) 

Hydraulic diameter: 10.6426 mm (0.419 in) 

Length (width or thickness of spacer grid: 57.15 mm (2.25 in) 

The experiments recorded volumetric flow rate (channel 412) as well as DP cell readings. 

Channel 369 records the DP cells for a span of 14 inches (between 53 and 67 in elevation) 

without any spacer grids. Hence, all the pressure losses over this span are due to friction only. 

The maximum Reynolds number achieved in the test is about 30000. 

In addition to this, a second experiment was performed to measure the pressure drop over a 

short span of eight in (between 100 and 108 in elevation). A schematic of the layout along with 

the DP cells is shown in Figure 6.4. 

6.2.1 Procedure for Calculating Friction Factor, f

1. Based on the volumetric flow rate measurement (channel 412) and the flow area of the 

bundle, the fluid velocity in the rod bundle is calculated. 

71
2. The Reynolds number of flow is calculated using fluid properties, evaluated at 2.758 bar (40 

psia) and 23.88 degrees C (75 degrees F): 

ρf = 997.27 kg/m3

 (62.258 lbm/ft3) 

μf = 9.1377 x 10-4 Pa-s (6.133 x 10-4 lbm/ft-sec) 

3. The head equation for pressure drop is given by: 

ΔP fL V

g D

f

c h

= ρ 2

2 (6-5) 

where 

f friction factor, which is to be calculated 

L length of the span over which frictional losses are measured (e.g., for channel 369, this 

is 14 in) 

Dh hydraulic diameter 

V velocity 

Using equation 6-5 and the data from channel 369 for the pressure drop, the unknown friction 

factor is calculated. A plot of friction factor as a function of Reynolds number is shown in Figure 

6.5. 

Figure 6.6 shows the comparison of friction factors calculated during the three experiments. 

The value of the friction factor calculated for the short span experiment is lower than the value 

for the other two tests. This is because of the increased turbulence downstream of the spacer 

grid. The spacer grid acts to disrupt the boundary layer on the heater rods such that the flow 

must redevelop downstream of the grid, resulting in higher effective frictional losses. As seen 

from Figure 6.4, the short span test DP cell was located far away from the downstream of the 

nearest spacer grid (grid no. 5), while the DP cell for the other experiments was much closer to 

the downstream of the spacer grid (grid no. 3). 

Based on Figure 6.5, the friction factor can be correlated to the Reynolds number by the 

following equation: 

f = 0 279

0 198

.

Re . (6-6) 

The values of friction factor obtained from the experiments are higher than the values from 

Moody chart for the same Reynolds number. 

6.3 Radiation Heat Loss Measurements

Radiation only experiments were conducted as apart of the RBHT Program to characterize the 

radiation heat loss, as a part of the separate effect tests. These experiments were conducted 

under vacuum. The following tests were conducted: 

72
73

• Experiment #605: Heat up rod bundle to 426.66 degrees C (800 degrees F), to help 

remove all water vapor. Manual control was used and 650.24 mm (25.6 in) vacuum was 

maintained. 

• Experiment #606: Two hours heating, manual power control. Peak temperature of 

426.66 - 454.44 degrees C (800 - 850 degrees F) was achieved. 

• Experiment #607: Little over one hour, manual power control, peak temperature of 

537.77 - 565.55 degrees C (1000 - 1050 degrees F) was achieved. Some cooling down 

was done. 

• Experiment #608: Cooling down of the bundle. 

For conducting this experiment, the outside of the insulation was instrumented with 

thermocouples, to record the temperature and hence calculate the heat loss. The locations 

(elevation, slot number, etc.) are given below: 

• Channel 97S2-33, FH Insulation 55 N 

• Channel 277S4-62, FH Insulation 80 N 

• Channel 400S6-40 FH Insulation 108 N 

• Channel 438S7-48 FH Insulation 108 S (not functional) 

Thickness of the WR-1200 Modeled Perlite Insulation was 101.6 mm (4 in). The outer 

dimension of the housing was 102.87 mm (4.05 in) square. 

Temperature measurements on the flow housing, at approximately the same elevation as the 

housing insulation thermocouples were used to calculate the temperature difference driving the 

heat transfer. The following housing thermocouples were used: 

• Channel 341 S6-4, at 1.419 m (55.87 in) elevation 

• Channel 346 S6-9, at 2.0 m (78.78 in) elevation 

• Channel 353 S6-16, at 2.754 m (108.43 in) elevation 

Table 6.2 summarizes the calculations for Experiment #607. 

To calculate the heat loss as a fraction of the total power, the power supplied needs to be 

calculated. This is the product of the test section voltage and the test section current readings. 

Table 6.3 summarizes the current and voltage readings and the offsets. 

At steady-state, the power supplied was 3345.69 W. All the power supplied corresponds to 

heat loss by radiation, since the facility was operated at steady-state. Based on a total power of 

114 kW, the heat loss during a typical reflood test would be around 2.32 percent of the total 

value. This is a small fraction of the total power supplied to the RBHT facility. 

6.4 Calculation of Insulation Thickness for the RBHT Test Bundle

In order to quantify the heat loss from the RBHT test bundle, it was necessary to do a heat 

transfer analysis using various thickness of insulation. With this analysis it will be possible to 

decide on the appropriate amount of insulation for the bundle. The analysis consists of a simple 

1-D conduction and convection problem and is as follows: 
Beginning with the most simple conduction equation: 

q k ′′ = dT

dx (6-7) 

And considering the basic convection equation: 

 (6-8) q hT T ′′ = − ( S ∞)

The heat flux will be the same at all locations, so the two equations can be combined: 

k dr

dx = − hT T s ∞ ( )

 (6-9) 

Now, the equation can be simplified and integrated over the width of the insulation: 

−= − dT ∞

h

k

T T dx s ( )

 (6-10) 

−= − ∫ ∫ ∞ dT h

k

T T dx

T

T

s

L

w

s

( )

0 (6-11) 

T T hL

k ws s −= − T T∞ ( )

 (6-12) 

where 

TW bundle wall temperature 

TS insulation surface temperature 

T∞ bulk air temperature

L insulation thickness 

Now the equation can be solved for the insulation surface temperature and this result can be 

used to find the heat flux using the convection equation. Note that from this point forward, the 

temperatures must be in absolute units. 

T

T hL

k

T

hL

k

s

w

=

+ ∞

1+

 (6-13) 

′′ =

+

+

⎛

⎝

⎜

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

−

⎡

⎣

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

∞

q h ∞

T hL

k

T

hL

k

T w

1

 (6-14) 

The next issue is how to deal with the convective heat transfer coefficient and the thermal 

74
conductivity of the insulation. The convective heat transfer coefficient must be calculated using 

a natural convection correlation, based on the dimensions of the bundle. The thermal 

conductivity of the insulation will be assumed constant and equal to the thermal conductivity of 

the material at about 343.33 degrees C (650 degrees F). For this analysis, a range of 

convective heat transfer coefficients were used, but the calculated value was about 3.69 W/m2

-

K (0.65 Btu/hr-ft2

-F) and this value will be used in the sample calculation that follows. The value 

of the thermal conductivity of the insulation was taken from the manufacturer's specification 

sheet to be about 0.1003 W/m-K (0.058 Btu/hr-ft-F). 

In addition to the thermal constants, the temperatures of the bundle wall and the bulk air must 

be estimated. Values of 537.77 degrees C (1000 degrees F) and 23.88 degrees C (75 degrees 

F) were used respectively. An example calculation using 50.8 mm (2 in) of insulation is as 

follows: 

Insulation surface temperature: 

T

T

hL

k

T

hL

k

R

Btu

hr ft R ft

Btu

hr ft R

R

Btu

hr ft R ft

Btu

hr ft R

z

R F

w

=

+

+

=

+

⋅ ⋅

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

⋅ ⋅

+

⋅ ⋅

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

⋅ ⋅

= =

∞

1

1460

0 65

2

12

0 058

535

1

0 65

2

12

0 058

857 5 397 5

2

2

.

.

( )

.

.

. .

 (6-15) 

where 

Ts = 203.05 degrees C (397.5 degrees F) 

Heat Flux: 

′′ = −= ⋅ ⋅ − = ⋅ q hT T∞ = Btu

hr ft R

F F Btu

hr ft

kW

ft

[ ]. (. ) . . s 0 65 397 5 75 209 6 0 061 2 2 2

 (6-16) 

Multiplying this result by the surface area of the rod bundle (19.5 ft2

) will yield the total power 

loss from the bundle: 

q qA kW

ft = ′′ = ⋅= 0 061 19 5 12 ft kW 2

2 . ..

 (6-17) 

Based on a total bundle power of 144kW, this gives a power loss of about 0.8 percent. 

75
Tables 6.4 through 6,6 show a summary of these calculations for an insulation thickness of 4 in 

and housing temperatures corresponding to three axial locations. 

Figure 6.1 RBHT Differential Pressure Cell Layout, Single Phase Flow. 

76
Figure 6.2 Grid Loss Coefficients vs. Reynolds Number - Experiment 276. 

77
Figure 6.3 Comparison of Experimental Data With Rehme’s Method. 

78
Figure 6.4 Differential Pressure Cell Layout for Pressure Drop Tests. 

79
Figure 6.5 Friction Factor as a Function of the Reynolds Number. 

80
Figure 6.6 Comparison of the Friction Factors for Various Experiments. 

81
Figure 6.7 Thermal Conductivity of Insulation Materials as a Function of Temperature. 

82
Figure 6.8 Heat Flux vs. Axial Length for Experiment 607. 

83
Table 6.1 Differential Pressure Cell Layout Description 

Table 6.2 Calculation for Experiment 607 

Table 6.3 Current and Voltage Readings for Power Calculations 

84
Table 6.4 Elevation 1.419 m (55 in) - Heating Surface Temperature 

348 degrees C (659 degrees F) 

Table 6.5 Elevation 2.0 m (78.78 in) - Housing Surface Temperature 

297 degrees C (566 degrees F) 

85
Table 6.6 Elevation 2.75 m (108.43 in) - Housing Surfaces Temperature 

239 degrees C (463 degrees F) 

86
87

7. CONCLUSIONS 

The RBHT Test Facility has been designed as a flexible rod bundle separate-effects test facility 

which can be used to perform single-phase and two-phase experiments under well-controlled 

laboratory conditions to generate fundamental reflood heat transfer data. The facility is capable 

of operating in both forced and variable reflood modes covering wide ranges of flow and heat 

transfer conditions at pressures up to 0.402 MPa (60 psia). It is heavily instrumented that meets 

all the instrumentation requirements developed in the RBHT Program. It can be used to 

conduct all types of the planned experiments according to the test matrix developed under Task 

9 of the RBHT Test Plan and Design Report. It is considered that the RBHT Test Facility with 

its robust instrumentation represents a unique NRC facility for the in-depth studies of the highly 

ranked reflood phenomena identified in the RBHT Program’s Phenomena Identification and 

Ranking Table (PIRT) and will produce the data and analysis needed to refine reflood heat 

transfer models in the current safety analysis computer codes. 
88
89

8. REFERENCES

1. Denham, M.K., D. Jowitt, and K.G. Pearson, “ACHILLES Unballooned Cluster Experiments, 

Part 1: Description of the ACHILLES Rig, Test Section, and Experimental Procedures,” 

AEEW- R2336, Winfrith Technology Centre (Commercial in Confidence), Nov. 1989. 

2. Denham, M.K. and K.G. Pearson, “ACHILLES Unballooned Cluster Experiments, Part 2: 

Single Phase Flow Experiments,” AEEW-R2337, Winfrith Technology Centre (Commercial in 

Confidence), May 1989. 

3. Pearson, K.G. and M.K. Denham, “ACHILLES Unballooned Cluster Experiments, Part 3: 

Low Flooding Rate Reflood Experiments,” AEEW- R2339, Winfrith Technology Centre 

(Commercial in Confidence), June 1989. 

4. Pearson, K.G. and M.K. Denham, “ACHILLES Unballooned Cluster Experiments, Part 4: 

Low Pressure Level Swell Experiments,” AEEW- R2339, Winfrith Technology Centre 

Commercial in Confidence), July 1989. 

5. Dore, P. and M.K. Denham, “ACHILLES Unballooned Cluster Experiments, Part 5: Best 

Estimate Experiments,” AEEW-R2412, Winfrith Technology Centre (Commercial in 

Confidence), July 1990. 

6. Dore, P. and D.S. Dhuga, “ACHILLES Unballooned ClusterExperiments, Part 6: Flow 

Distribution Experiments,” AEA-RS-1064, Winfrith Technology Centre (Commercial in 

Confidence), December 1991. 

7. Rehme, K., “Pressure Drop Correlations for Fuel Element Spacers”, Nuclear Technology, 

Vol. 17, pp 15-23, January 1973. 
90
A-1 

APPENDIX A. RBHT TEST FACILITY COMPONENTS DETAILED 

MECHANICAL DRAWINGS

NOTE: Electronic copies of these drawings are included in a CD listed in Appendix G. 

DRAWING NUMBER TITLE 

 (CD File No.)

 B114306 Bellvile Washer 

 C114245 Pressure Gasket 

 C114246 Window Flange 

 C114247 Window 

 C114248 Window Stud Fixture 

 C114255 Cushion Gasket 

 C114282 Flange Modification - Upper Plenum 

 C114295 Lower Plenum Seal Sleeve Retaining Plate 

 C114296 Heater Rod Seal Sleeve 

 C114298 Low Melt Reservoir 

 C114318 Grip Strap -A- 

 C114319 Grid Strap -B- 

 C115077 Steam Probe Rake Mounting Flange 

 C115132 Drain Tube 

 

 C118336 Traversing Steam Probe 

D114249 Flange Modification Bottom - Housing Assembly 

 D114279 Flange Modification Top - Housing Assembly 

 D114290 Housing Extension 

 D114291 Exhaust Baffle 

 D114293 Lower Plenum Flow Baffle 
A-2 

 D114294 Seal Plate Lower Plenum 

 D114297 G-10 Isolation Plate 

 D114299 Reservoir Connector Assembly 

 D114301 Unheated Rod (Support Rod) 

 D114320 Grid Matrix 

 D114345 Schematic Test Facility 

 D114366 Seal Sleeve Extractor 

 D114369 Stem Separator Drain Tank 

 

 D114371 Small Carry-over Tank 

 D115075 Steam Probe Rake Assembly 

 D115076 Steam Probe Rake Tube 

 D1150261, L115260 Grid Assembly, List of Drawings and Parts 

 D115262 Outer Grid -A- 

 D115263 Outer Grid - B- 

 D115264 Outer Grid - C- 

 D115265 Outer Grid - D- 

 D115266 Inner Grid - A- 

 D115267 Inner Grid - B- 

 D115268 Inner Grid - C- 

 D115269 Inner Grid - D- 

 D115346 Drawing Tree 

 D115347 Skirt Steam Separator 

 D115587 Water Inlet Piping - sht. 1 

 D115587 - sht. 2 Water Inlet Piping - sht. 2 

 D115597 Exhaust Line Piping - sht. 1 
A-3 

 D115597 - sht. 2 Exhaust Lint Piping - sht. 1 

 D115640 Steam By-pass Line Piping - sht. 1 

 D115640 - sht. 2 Steam By-pass Line Piping - sht. 2 

 D118337 Automatic Traverse Mechanism (Steam Probe Rake) 

 D118339 Droplet Injection System 

 E114243, L114242 Assembly (Housing), List of Drawings and Parts 

 E114244 Weldment Test Section - sht. 1 

 E114244 - sht. 2 Weldment Test Section - sht. 2 

 E114281 Upper Plenum Assembly 

 E114278 Nickel Ground Plate 

 E114292 Lower Plenum Assembly 

 E114302 Heater Rod 

 E114343 Pressure Oscillation Damping Tank 

 E114346 Window Test Fixture 

 E114370 Large Carryover Tank 

 E114372 Strong back Assembly 

 E115002 Water Supply Tank 

 E115016 Steam Separator Tank 

 E115073 Test Section Instrumentation 

 E115348, L115345 Building Arrangement - sht. 1, List of Drawings and 

 Parts 

 E115348 - sht. 2 Building Arrangement - sht. 2 

 E115615 Mezzanine Frame Work - sht. 1 

 E115615 - sht. 2 Mezzanine Frame Work - sht. 2 

 E115615 - sht. 3 Mezzanine Frame Work - sht. 3 
A-4 

 E115615 - sht. 4 Mezzanine Frame Work - sht. 4 

 E118338 Flow Housing Differential Pressure Instrumentation 

 E118340 Heater Road Bundle Grip Temperature Instrumentation 

 E114287, L114280 Upper Plenum, List of Drawings and Parts 

 L114287 Flow Housing, List of Drawings and Parts 

 

 L115260 Rod Grid Assembly, List of Drawings and Parts 

 R114288 Flow Housing Assembly, Reference Drawing 

 E118341 Heater Rod Bundle Temperature Instrumentation
B-1 

APPENDIX B. RBHT TEST FACILITY COMPONENTS MEASURED 

VOLUMES AND FLOW AREAS 

The volumes and flow areas were measured for the following components and summarized in 

Table B.1: 

1. Water Supply Tank 

2. Flow Housing 

3. Upper Plenum 

4. Lower Plenum 

5. Large Carryover Tank 

6. Small Carryover Tank 

7. Pressure Oscillation Damping Tank 

8. Steam Separator Drain Tank 

9. Grids and Bare Heater Rod Bundle 

The Steam Separator volume measurements are not reported because the results were not 

reliable and should be repeated. 

The components volumes and flow areas are essential for calculating the Mass and Energy 

Balances around each component and consequently the validation of the test results. 

The volumes and flow areas were determined by weighing the water drained from each 

component at various elevation increments into a weight tank placed on a weighing scale 

platform as shown schematically in Figure B.1. 

Each water weight was converted into a water volume as follows: 

Vi = Wi x vi @ Ti x 1728 in3

/ft3

 where 

Vi water volume, in3

Wi water weight, lbs 

vi specific volume at Ti

Ti water temperature, degrees F 

The corresponding flow areas were calculated as follows: 

Ai = Vi x 1/ΔLi
B-2 

where 

Ai flow area, in2

Vi water volume, in3

ΔLi change in elevation, in 

The results are presented in table and graphic forms as listed in Table B.1. 

Except for the Flow Housing all the components are cylindrical and should have uniform flow 

area. However, most of them have internal parts and inlet/outlet nozzles which contribute to 

less or additional water volumes resulting in Flow Areas variations. 

Table B.1 Component Volumes and Flow Areas 

Component Table No. Figure No. 

Water Supply Tank B.2 B.2, B.3 

Flow Housing B.3 B.4, B.5 

Upper Plenum B.4 B.6, B.7 

Lower Plenum B.5 B.8, B.9 

Large Carryover Tank B.6 B.10, B.11 

Small Carryover Tank B.7 B.12, B.13 

Pressure Oscillation Damping Tank B.8 B.14, B.15 

Steam Separator Drain Tank B.9 -- 

Grids and Bare Heater Rod Bundle B.10 -- 
B-3 

Table B.2 Water Supply Tank Volumes and Flow Areas 
B-4 

Table B.3 Flow Housing Volumes and Flow Areas Among Pressure Taps 

* The elevation was measured from the bottom of the rod bundle corresponding to a lower tap location. 

An elevation where a grid is placed in the table does not mean that the grid is located at that elevation. It 

means that a grid is located within that DP span. 
B-5 

Table B.4 Upper Plenum Volumes and Flow Areas 

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0.0826 0.083 1.728 1.7281798 2.0935 

0.1323 0.05 0.888 2.6165225 1.0761 

0.1483 0.016 0.834 3.4607879 5.2555 

0.1626 0.014 0.996 4.4467937 6.971 

0.2055 0.043 1.017 5.463611 2.3723 

0.2372 0.032 1.08 5.5604586 3.4019 

0.2832 0.046 1.005 7.5483733 2.1819 

0.3449 0.062 1.016 8.5648629 1.6472 

0.38 0.035 1.001 9.5662764 2.8677 

Table B.5 Lower Plenum Volumes and Flow Areas

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0 0 0 0 0 

0.0508 0.508 0 0.001 0.01957 

0.22225 0.17145 0.005 0.0058 0.02823 

0.381 0.15875 0 0.0066 0.0046 
B-6 

Table B.6 Large Carryover Tank Volumes and Flow Areas 

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0 0 0 0 0 

0.2159 0.2159 0.002 0.0023 0.0036 

0.47777 0.26187 0.002 0.0045 0.0085 

0.74778 0.27026 0.002 0.0068 0.0083 

1.02235 0.27457 0.002 0.0091 0.0083 

1.2954 0.2771 0.002 0.01137 0.0084 

1.56362 0.26822 0.002 0.01365 0.0087 

2.19227 0.62865 0.002 0.01592 0.01053 

Water Temperature 24.44 degrees C (76 degrees F) 

Total Volume = 0.0159213 m3

 (4.206 gallons) (0.562 ft3) 

Table B.7 Small Carryover Tank Volumes and Flow Areas 

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0 0 0 0 0 

0.20955 0.20955 0 0 0.00041(*)

0.28423 0.0747 0.0002 0.0002 0.00152 

0.40005 0.11582 0.0002 0.0004 0.00161 

0.49682 0.0968 0.0002 0.0006 0.00178 

0.59995 0.10312 0.0001 0.0007 0.00167 

0.72847 0.12852 0.0003 0.001 0.00169 

0.8476 0.11913 0.00015 0.00115 0.00168 

0.97155 0.12395 0.00023 0.00138 0.00183(**)

Water Temperature 24.44 degrees C (76 degrees F) 

Total Volume = 0.001379 m3

 (0.364 gallons), (0.049 ft3) 

* includes 1 in drain and shut-off valve 

** includes water drain from 1 in inlet tube 
B-7 

Table B.8 Pressure Oscillation Damping Tank Volumes and Flow Areas 

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0 0 0 0 0 

0.1651 0.1651 0.0136 0.01364 0.08587 

0.42393 0.25883 0.025 0.03864 0.09432 

0.7112 0.45237 0.0273 0.06589 0.09484 

0.79223 0.33985 0.007 0.07316 0.08981 

1.09703 0.32283 0.0273 0.400422 0.08942 

1.40818 0.31115 0.0273 0.12768 0.08761 

1.70358 0.2954 0.0272 0.154914 0.09226 

2.0193 0.31572 0.0272 0.182147 0.08619 

2.0955 0.0762 0.009 0.191452 0.12213 

2.1369 0.0414 0.004 0.195309 0.09348 

2.2098 0.0729 0.007 0.202118 0.09323 

2.302 0.0922 0.007 0.208925 0.04468 

Water Temperature 17.77 degrees C (64 degrees F) Average 

Room Temperature 18.33 degrees C (65 degrees F) 

Total Volume = 0.289252 m3

 (55.2 gallons) (7.38 ft3) 
B-8 

Table B.9 Grid and Bare Heater Rod Bundle Volumes and Flow Areas 

Location ΔL* 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow 

Area** 

(m2

) 

Grid No. 4 0.04775 0.0002 0.0002 0.00419 

Bare Rod 

Bundle 

0.48108 0.00234 0.00254 0.00487 

Grid No. 3 0.04775 0.00019 0.00273 0.00408 

Bare Rod 

Bundle 

0.47142 0.00233 0.00506 0.00495 

Grid No. 2 0.04445 0.0002 0.00526 0.00451 

Bare Rod 

Bundle 

0.55575 0.00265 0.00821 0.00477 

Water Temperature 17.22 degrees C (63 degrees F) 

Average Grid Flow Area+

 = 4264.5 mm2 (6.61 in2) (including the mixing vanes) 

Average Bundle Flow Area = 4864.5 mm2

 (7.54 in2) 

* This is the width of each grid. 

** This refers to the cross-sectional flow area through the bundle. 

+ Grids No. 5 to 7 are identical to Grids No. 2 to 4, respectively, whereas Grid No. 1 

has a flow area very close to the average grid flow area. Grids No. 2 to 4 were used 

as an example to show the average grid flow area as compared to the average bundle 

flow area. 

Table B.10 Steam Separator Drain Tank Volumes and Flow Areas 

Elevation 

(m) 

ΔL 

(m) 

Volume 

(m3

) 

Cumulative 

Volumes 

(m3

) 

Flow Area 

(m2

) 

0 0 0 0 0 

0.61925 0.61925 0.00182(1) 0.00182 0.0029 

1.21107 0.59182 0.0045 0.00635 0.0077 

1.80645 0.59538 0.0045 0.010888 0.0076 

2.10007 0.29362 0.0023 0.013156 0.0077 

Room Temperature 22.77 degrees C (73 degrees F) 

Water Temperature 23.88 degrees C (75 degrees F) 

 (1) includes the drain line 
B-9 

 

Figure B.1. Volume and Flow Area Measuring Test Schedule. 
B-10 

Figure B.2. Water Supply Tank Volume Measurements. 

Figure B.3. Water Supply Tank Flow Areas. 
B-11 

Figure B.4. Flow Housing Volumes Between Pressure Taps. 

Figure B.5. Flow Housing Areas Between Pressure Taps. 
B-12 

Figure B.6. Upper Plenum Volume Measurements. 

Figure B.7. Upper Plenum Flow Areas. 
B-13 

Figure B.8. Lower Plenum Volume Measurements. 

Figure B.9. Lower Plenum Flow Areas. 
B-14 

Figure B.10. Large Carryover Tank Volume Measurements. 

Figure B.11. Large Carryover Tank Flow Areas. 
B-15 

Figure B.12. Small Carryover Tank Volume Measurements. 

Figure B.13. Small Carryover Tank Flow Areas. 
B-16 

Figure B.14. Pressure Oscillation Damping Tank Volume Measurements. 

Figure B.15. Pressure Oscillation Damping Tank Flow Areas. 
C-1 

APPENDIX C. RBHT TEST FACILITY PHOTOGRAPHS 

Photograph C.1 Flow Housing with the Heater Rod Bundle and the Ground Nickel Plate. 

Photograph C.2 Ground Nickel Plate and Heater Rods Connection.
C-2 

Photograph C.3 Flow Housing Bottom Extension Flow Baffle, Heater Rod Bottom 

Extensions, and Grid and Support Rod Thermocouple Extensions. 

Photograph C.4 Lower Plenum Heater Rod Sealing Plate, Heater Rod Bottom 

Extensions and Thermocouples Extension Wires.
C-3 

Photograph C.5 Installation of the Test Facility Components from Right to Left: 

Flow Housing and Support Fixture, Steam Separator, Pressure Oscillation Damping 

Tank, Water Injection Supply Tank, and the Mezzanine Structure. 

Photograph C.6 Top View of the Flow Housing, Upper Plenum, Small and 

Large Carryover Tanks, Steam Separator, Pressure Oscillation Damping 

Tank, and the Top of the Water Injection Tank. 
C-4 

Photograph C.7 Upper Plenum, Steam Separator, and Pressure Oscillation 

Damping Tank Installation. 

Photograph C.8 Steam Exhaust Piping with the Vortex Flowmeter and the 

Pressure Control V-Ball Valve. 
C-5 

Photograph C.9 Test Section Flow Housing Showing the Heater Rods and 

Grids Through the Window Openings. 
C-6 

Photograph C.10 Bottom of the Flow Housing with the Lower Plenum and the 

Water Injection Tank. 
C-7 

Photograph C.11 Installation of the Test Section. 
C-8 

Photograph C.12 Differential Pressure Cells Installation on the Flow Housing. 
C-9 

Photograph C.13 Differential Pressure Cells Installation Showing Connections 

of the Pressure Tap Lines to the Differential Pressure Cell Manifolds. 
C-10 

Photograph C.14 RBHT Test Facility Building View Through the Roll-up Door 

Showing the Test Section, Water Injection Tank, Circulating Pump, and the 

Mezzanine Structure. 
C-11 

Photograph C.15 Inside View of the RBHT Test Facility Through the Roll-up Door 

Showing the Test Section, Water Injection Tank, Circulating Pump, and the 

Mezzanine Structure. 
C-12 

Photograph C.16 Data Acquisition Components: VXI Mainframe and Terminal Panels. 

Photograph C.17 Electric AC Power Supply Showing the High Voltage 

Transformers, the Main Breaker, and the Phase Shift Transformer. 
C-13 

Photograph C.18 DC Power Supply Units Rated at 60 Volts DC, 12000 Amps and 750 KW. 
C-14 
D-1 

APPENDIX D. EXPERIMENTAL VERIFICATION OF THE 

PERFORMANCE OF A DROPLET INJECTION SYSTEM FOR 

USE IN A ROD BUNDLE TEST FACILITY 

IMECE 2001

Session 2-13-4

A. J. Ireland, E. Rosal, L. E. Hochreiter, 

F. B. Cheung 

Pennsylvania State University 

Department of Mechanical and Nuclear Engineering 

University Park, PA 16802 

ABSTRACT

A droplet injection system has been developed for use in a rod bundle heat transfer test facility 

designed specifically for the study of dispersed flow film boiling during reflood transients in a 

nuclear reactor. Three different injectors having various pitch configurations and hole patterns 

were tested. The drop field produced by each was characterized using a laser-assisted size 

measurement technique. Appropriate mean diameter and drop size distributions that closely 

simulate the drop field encountered in a reactor bundle assembly under reflood conditions were 

obtained. The droplet injection system so developed can readily be employed in the rod bundle 

test facility to investigate the droplet heat transfer in the dispersed flow films boiling regime. 

INTRODUCTION 

A RBHT (Rod Bundle Heat Transfer) test facility has recently been constructed to investigate 

reflood heat transfer in electrically heated rod bundles which simulate nuclear fuel assemblies. 

The objective is to obtain basic two-phase flow and heat transfer data in the dispersed flow film 

boiling regimes where the peak fuel rod temperatures are calculated to occur for a postulated 

reactor design basis accident. The information and data required includes; the entrained liquid 

droplet sizes and velocity, vapor temperature, steam flow rate, and the interfacial heat and mass 

transfer. 

The dispersed flow film boiling region is extremely complex since the dispersed droplets act as 

heat sinks and alter the vapor super-heat temperature such that the film boiling is a two-step 

process, that is heat is transferred to the continuous vapor phase from the heated walls, then 

heat is transferred to the entrained water droplets by interfacial heat and mass transfer(1-3). As a 

result, the vapor temperature is a dependent parameter which is a function of both the wall heat 

transfer and the interfacial heat transfer. In addition to being a source of interfacial heat 

transfer, the entrained droplets can also affect the continuous vapor heat transfer from the 

heated wall by increasing the turbulence level in the flow, due to the additional interfacial drag in 

the flow, as well as acting as distributed heat sinks within the vapor flow. 

Best estimate safety analysis computer codes are widely used to predict nuclear fuel rod 
D-2 

temperatures for postulated accidents. The most limiting accident is the Loss of Coolant 

Accident in which the calculated peak cladding temperatures for the reactor occur in the 

dispersed flow film boiling region(2). These codes rely on models to accurately describe the 

physical processes in the dispersed two-phase flow heat transfer regime as described above. 

To date, the existing models have large uncertainties and do not capture all the physical 

phenomena which have been observed in various experiments. As a result the safety analysis 

calculations and associated method logics have large uncertainties and conservative 

calculations have to be performed to insure that the calculated peak cladding temperatures are 

within the licensing limits for the reactor(3). 

One of the key features of the RBHT study is to provide improved data and analysis such that 

the analytical models which are used to represent the physical phenomena for the two-phase 

dispersed flow film boiling region can be improved such that the calculated uncertainty is 

reduced. The experimental approach in the RBHT work is to separate the different phenomena, 

as best as possible, such that it is easier to develop component models for the more complex 

dispersed flow film boiling region. Toward this end, a RBHT test facility has been constructed to 

study reflood heat transfer in rod bundles to obtain data for improving the heat transfer model 

for Best-Estimate computer codes. A series of steady state droplet injection tests are to be 

conducted with liquid injection into a steady steam flow in the bundle. The droplet injection tests 

simulate the dispersed flow film boiling region above the quench front and can be performed 

without the additional complexities of the quench front behavior. The purpose of the droplet 

injectors is to introduce into a rod bundle a narrow spectrum of droplet sizes in a controlled 

manner to study the effects of droplets on the dispersed flow film boiling heat transfer. In order 

to determine the effectiveness of the injection system, a method of testing the injectors was 

developed. The method involves forcing water through the injection tubes and analyzing, both 

qualitatively and quantitatively, the ability of the injector to produce droplets of uniform size. 

This is done with the use of a laser-illuminated digital camera system known as VisiSizer. 

Steam cooling tests will be performed to obtain the single-phase convective heat transfer within 

the rod bundle and to examine the single phase behavior of the spacer grids on the downstream 

heat transfer. Once the single phase heat transfer tests are complete, droplets will be injected 

into the steam flow using the injectors which are being tested and presented in this paper. The 

injectors are designed to provide a narrow droplet size distribution and velocity distribution such 

that the data will be easier to analyze and characterize. The objective will be to inject droplets 

of similar size to that observed in forced reflood experiments. The injected droplets will 

evaporate, shatter on spacer grids, increase the turbulence in the flow and de-superheat the 

vapor such that the wall heat flux will increase. The droplets will be injected over a range of 

sizes and mass flow rates in to steam flow at different Reynolds numbers. Data will be obtained 

on the drop size and distributions are different axial positions to determine the droplet shattering 

effects as well as evaporation. A mass and energy balance will be performed on the test bundle 

to obtain the droplet evaporation and the total interfacial heat transfer. 

This paper described the design of the droplet injection system and the resulting drop sizes that 

are to be simulated in the RBHT experiments. 

ROD BUNDLE HEAT TRANSFER FACILITY

The droplet injections system will be implemented in the RBHT facility having a 7 x 7 rod bundle 
D-3 

as shown in Figure 1. The rod bundle consists of full electrically powered heater rods with a 

diameter of 9.5 mm and a pitch of 12.60 mm. The bundle has 45 heater rods and four unheated 

corner rods, which are used to support the bundle grids as well as carry various thermocouples 

leads. 

Six droplet injection tubes will be inserted into the bundle assembly as show in Figure 2, with 

the tube perpendicular to the heater rods. The tubes will penetrate both sides of the housing 

and will be supplied with water from both ends. The groupings of small holes in the tubes will 

be positioned such that droplets are injected into each of the 36 subchannels. 
D-4 

The droplet injection system that was developed for use in the RBHT facility consists of small 

diameter tubes (2.36 mm) in which holes are drilled on one side. The holes can vary in size, 

pitch, and number. Three different injectors were employed in this study. Injector A 

incorporated 23 holes in a square pitch, as shown in Figure 3. The other two injectors, Injector 

B and Injector C, were both triangular pitch injectors with 22 and 23 holes, respectively. 

Injectors B and C are shown in Figures 4 and 5. 
D-5 

The droplet injectors were oriented in a horizontal manner, as they would be in the rod bundle, 

and water was pumped into the injector. The water exited the droplet holes as liquid jets which 

then broke up into a drop field who’s size was characterized by the holes and spacing in the 

injector tube. 

The method of analyzing the performance of the different droplet injection tubes involves the 

use of a system known as VisiSizer(4,5), which is capable of real-time analysis of droplet size and 

velocity distributions. The system consists of a high-resolution digital camera, infrared laser, 

data analysis software, and associated computer and control equipment. 

The camera, a Kodak MegaplusTM digital camera, has a resolution of over 1.0 megapixels. The 

laser system incorporates an infrared beam of wavelength 805 nm and is capable of pulsing at 

frequencies up to 1000 Hz. The laser can also pulse twice during a single camera frame to 

produce a double image used in determining velocity information. The beam of the laser is 

scattered with an opaque sheet of plastic to produce uniform background lighting for imaging. 

The system captures high-resolution images of the injection streams and analyzes the images 

at a rate of about 7 frames per second, identifying droplets as dark images in front of the laserilluminated scattering sheet. The diameter of each droplet is determined automatically by 

referencing the number of dark pixels in the droplet image to the pixel area of a calibration 

circle. A general setup of the system is shown in Figure 6. 
D-6 

A variety of user-defined parameters control the counting of the droplets, including focus 

rejection and sphericity criteria. Focus rejection is determined by considering the sharpness of 

a droplet image, done by quantifying the intensity gradient at the out edge of the droplet(5). In 

addition to this, the droplet analysis duration can be controlled by elapsed time, number of 

frames, or number of droplets counted. The software also calculates real-time statistics such as 

mean and sauter-mean diameters as well as displays the diameter distribution and, if 

applicable, the velocity distribution. Velocity is determined by double-pulsing the laser to 

capture the motion of a droplet. Analysis of the velocity is done automatically using criteria such 

as angle of motion, velocity range, and size matching. The VisiSizer System has been 

thoroughly tested to characterize the system uncertainties and biases and is highly reliable and 

simple to set up and calibrate. 

RESULTS AND DISCUSSION

Liquid jet breakup and drop formation were studied in the injection systems using the VisiSizer 

system. Qualitative and quantitative data for the drop size distribution were obtained. Images 

of the injector were taken with the digital camera to show the details of the breakup of the water 

jets and droplet diameter distributions were taken about 0.127 m above the point of injection at 

a liquid volumetric flowrate of about 10 cm3

/sec. 

The results show that the Injector A, with the square pitch, does not provide uniform water jets. 

The streams from the injectors combine and cause much larger jets to emerge, as show in 

Figure 7. The result is large droplets shown in Figure 8 and a size distribution which is spread 

over a wide range of drop sizes as shown in Figure 9. The distribution shows clearly the result 

of the combined streams seen in Figure 7. The mean diameter for the droplets from Injector A 

is 1.6 mm. This was not the desired droplet size spectrum for use in the RBHT facility. 

Injectors B and C behave in a very different way, as can be seen in Figures 10 through 15. 

Both injectors were able to produce streams that did not combine (or combined very little) and 
D-7 

created a much more uniform distribution of size as seen qualitatively in Injectors B and C are 

0.619 mm and 0.711 mm respectively. The mean diameters from these two injectors support 

the assumption that droplets formed from the injectors are about twice the size of the holes from 

which they are ejected. 

Drop formation from an orifice has been discussed by Wallis (6) and is similar to bubble 

formation. The radius of a bubble formed by blowing through a small orifice at low flow rates 

was given by Kutateladze and Strukovich(7) as 

R

R

g

b

o

f

= −

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

10

8

1 3

. (

/

σ

ρ ρ (1) 

where Ro is the radius of the orifice, g the gravitational acceleration, σ the surface tension, ρf the 

liquid density, and ρg the gas density. The above expression was obtained from experimental 

data. As the gas velocity is increased, individual bubbles are no longer formed and the gas 

leaves the orifice as a jet which then breaks into individual bubbles further down stream of the 

orifice(7). The condition given for the formation of the gas jet is 

[ ] v

g

g R g

f

g f go

> −

−

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

125

1 4

2

1 2

.( )

( )

/ /

σρ ρ

ρ

σ

ρ ρ (2) 

where v is the gas velocity through the orifice, of size . g Ro

A similar analogy can be made for liquid droplets formed from orifices. As the liquid velocity 

through the orifice is increased, liquid jets issue from the orifice as seen in Figure 10 which then 

break into individual droplets which have a diameter of approximately 

 (3) Dd ≅19. Do

If the jet velocity would be increased further, the large relative velocity of the liquid jet (relative to 

its surroundings) leads to severe instability and the liquid is atomized into very fine droplets. 

The drop size for the flow through an orifice of size 0.343 mm diameter should be approximately 

0.650 mm as given by Wallis. The much larger size seen is due to the merging of the liquid 

stream such that the drop size is not indicative of the orifice opening in the injector tube. 

The drop sizes for the different injectors, predicted by Equation 3, is shown on the distribution 

plots in Figures 9, 12, and 15. As Figures 12 and 15 indicate, the drop size from Equation 3 

represents approximately the mean size of the drip distribution; however, there is still a 

significant spread of the drop diameters. 

Note that during a reflood transient, the entrained droplets not only provide a major source of 

interfacial heat transfer, but also may enhance the turbulence level in the vapor flow, thus 

directly affecting the wall heat transfer. Thus in the droplet injection experiments to be 

performed in the RBHT facility, it is important to simulate the mean drop size and the drop 

distribution. In view of this, the drop field produced by Injector A is not acceptable not only 

because of the fact that the mean drop size is much too large, but also due to the peculiar drop 

size distribution. As can be seen from Figure 9, there are two unequal peaks in the drop field 
D-8 

that does not simulate the drop field observed in the bundle of a reactor assembly. On the other 

hand, the drop fields produced by Injectors B and C are much better approximations to the 

actual one. 

The droplet size distributions from Injectors B and C can be compared with the drop size 

distributions taken from the FLECHT-SEASET(8) series of tests for reflood conditions in a 

17x17 rod bundle assembly. Droplet images were captured using high-speed black-and-white 

motion picture film taken through the housing windows for some test runs. An example of the 

droplet distribution obtained can be seen in Figure 16. 

It can be seen from Figure 15 and 16 that the distributions are very similar in that they have a 

maximum that occurs between 0.6 and 0.8 mm and have similar distributions except that the 

FLECHT-SEASET distribution has a longer tail at larger drop sizes. 

The drop distributions in Figures 15 and 16 can be normalized on their peak frequency values 

and compared. Figure 17 shows the comparison of the two normalized distributions. As this 

figure indicates, the droplet injector will provide a more uniform distribution of drops over the 

range from1.75 D0 to 2.25 D0 with the ideal value being about 1.9 D0. The FLECHT-SEASET 

distribution shows that a wider range of drops exist for the true reflood process. 

CONCLUSIONS

The drop field produced by the injector tubes developed in this study can be used in the RBHT 

facility to investigate the effects of liquid droplets on the steam flow and the resulting dispersed 

flow film boiling heat transfer in a rod bundle under reflood conditions. By performing 

experiments over a range of liquid flows and vapor flows, and using the measurements on the 

RBHT facility(9), the amount of evaporation can be measured such that the interfacial heat 

transfer can be calculated. Also, the laser illuminated camera system can be used at different 

elevations to obtain the drop size, velocities, and distributions. This data can lead to 

determining the interfacial heat transfer and the effects of droplet shattering caused by the 

spacer grids. In addition, the droplet injection experiments can also be modeled using COBRATF(10), in which the drops can be simulated as a source of liquid. 

ACKNOWLEDGEMENTS

This work was supported by the U.S. Nuclear Regulatory Commission under Contract No. NRC04-98-041. 

REFERENCES

1. Clare, A. J., et al., “Droplet Dynamics and Heat Transfer in Dispersed Two-Phase Flow,” 

CONF-8410331, pp 51-62, 1985. 

2. Hochreiter, L. E., et al., “Application of PWR LOCA Margin with the Revised Appendix K 

Rule,” Nuclear Engineering and Design, Vol. 132, pp 437-447, 1992. 

3. Andreani, M. and G. Yadigaroglu, “Prediction Methods for Dispersed Flow Film Boiling,” Int. 

J. Multiphase Flow, Vol. 20, pp. 1-51, 1994. 
D-9 

4. Oxford Lasers, “HSI1000 Fast Illumination System,” Operation Manual, Issue 2, Rev. 1, 

Oxford Lasers, Ltd., 1997. 

5. Todd, Donald R., “Characterization of the VisiSizer Particle/Drop Sizing System,” MS 

Thesis, Pennsylvania State University, Aug. 1999. 

6. Wallis, G. B., “One Dimensional Two-Phase Flow,” McGraw Hill Book Co., pg 376, 1969. 

7. Kutateladge, S. S., and M. A.Styrikovich, “Hydraulics of Gas-Liquid Systems,” Moscow, 

Wright Field Trans. F-TS-9814/V, 1958. 

8. Lee, N., et. Al., “PWR FLECHT SEASET Unblocked Bundle, Forced and Gravity Reflood 

Task Data Evaluation and Analysis Report,” NUREG/CR-2256, Feb. 1982. 

9. Hochreiter, L. E., et. Al., “Dispersed Flow Heat Transfer Under Reflood Conditions in a 49 

Rod Bundle: Test Plan and Design - Results from Tasks 1-1 0,” NRC-04-98-041 Contract 

Report 1, Sept. 1998. 

10. Park, C. Y., Hochreiter, L. E., Kelly, J. M., and Kohrt, R. J., “Analysis of FLECHT- SEASET 

163 Rod Bundle Data using COBRA-TF,” NUREG-CR-4166, Jan. 1986. 
D-10 
D-11 
D-12 
D-13 

 
E-1 

APPENDIX E. DETAILED ENGINEERING DRAWINGS FOR THE 

FLOW HOUSING AND ROD BUNDLE INSTRUMENTATION

E.1 Flow Housing detailed mechanical drawing. Drawing E114244 

E.2 Test Section detailed schematic showing the DP cell elevations. Drawing E118338 

E.3 Test Section detailed schematic showing the Spacer Grid Instrumentation. Drawing 

 E118340 

E.4 Test Section detailed schematic showing the Traverse Steam Probe Rake and Flow 

 Housing Wall Thermocouple locations. Drawing E118341 

E.5 Overview schematic showing all the Test Section Instrumentation. Drawing E115073 

NOTE: Electronic images of these drawings are included in the CD listed in Appendix G. 
E-2 
F-1 

APPENDIX F. INSTRUMENTATION ERROR ANALYSIS 

The instrumentation error associated with the data from RBHT test series can be derived either 

from equipment manufacturers’ specifications or system calibration data. Component 

calibrations are performed to verify that the manufacturers’ specifications are met, and these 

manufacturers’ specifications are used to compute the error estimate for the data path. System 

calibrations are performed when component calibrations are not expedient or when an accuracy 

improvement could be accomplished with a system calibration. The system calibration data are 

used to compute an estimate of error for the system response, and calibration data points. The 

total system error from a system calibration is a function of both system response error and 

calibration data error. 

In all cases of error estimate, the standard deviation has been computed and presented as the 

most probable error. The manufacturer-specified error is the maximum possible error. The 

standard deviation error is calculated from the maximum error by the following: 

∑= ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ =

n

i

i

n

E

1

2

2 ρ (F-1) 

where 

ρ data path standard deviation 

Ei component i maximum error 

n number of sources of error 

When a system calibration is performed, the standard deviation from the calibration data and 

that from the calibration equipment can be combined by the following equation to produce the 

best estimate of error: 

22 ρ += EE cd (F-2) 

where 

Ed calibration data standard deviation 

Ec calibration equipment standard deviation 

The calibration data standard deviation is a measure of the error involved in fitting the 

calibration data. That is, 

( )

2/1

1

2

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛ −

=

∑=

n

YY

E

n

i

fi

d (F-3) 

where 

Yi calibration point 

Yf predicted output from the calibration curve 
F-2 

n number of calibration points 

The calibration equipment standard deviation is a measure of the absolute error of the 

calibration point. If the calibration point in the above equation is calculated from an equation of 

the form 

 (F-4) 321 ⋅⋅= xxxY

then 

∑= ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ n

i i

y x

y x

i

1

2 2

σ σ

 (F-5) 

and 

2 Ec = σ y (F-6) 

The data path has been broken down into three parts called sensor, conditioner, and readout. 

The sensor is the device whose electrical output is proportional to a physical quantity 

(temperature, pressure, flow, power). The conditioner is a device which matches the electrical 

output of the sensor to the input requirements of the readout device. The readout device 

measures and records the electrical value of the signal from the conditioner. This recorded 

electrical value is subsequently used to compute the physical quantity it represents. The errors 

due to the transmission wire errors are very small (±0.001 percent) in comparison to the 

element errors and are considered negligible. 

The error values for sensor, conditioning, and readout are the manufacturers’ specifications in 

engineering units. These numbers are used to compute the most probable error, as previously 

described. Where systems calibrations are performed, the equipment calibration data provide 

the standard deviation and maximum error as computed from the calibration data points in fitting 

the points to a first-order polynomial. The calibration point standard deviation is computed 

using the method described above. The calibration point maximum error occurs simultaneously 

in each component of the calibration equation. The overall system standard deviation may then 

be calculated using equation F-2. 

The calculated Total Probable errors using equation F-2 for each instrumentation channel are 

shown in the following tables: 

Table F.1 Temperature measurements including the heater rods, grid fluid, grid walls, 

 support rods, steam probe rakes, flow housing walls, flow housing insulation, 

 vessel and piping walls, and quartz windows thermocouples. 

Table F.2 Differential pressure cells (DP’s), static pressure transducers (P’s), and vessel 

 liquid label transducers. 

Table F.3 Inlet Mass and exhaust steam flows transmitters (FM). 
F-3 

Table F.4 Steam probe rakes linear position transmitter. 

Table F.5 Heater Rod Bundle input voltage (V), amperage (Amps), and power (W) 

 measurements. 
F-4 

Table F.1 Temperature Measurements 
F-5 

Table F.2 Pressure Measurements 
F-6 

Table F.3 Flow Measurements 

Table F.4 Position Measurements 
F-7 

Table F.5 Power Supply Measurements 
F-8 
G-1 

APPENDIX G. RBHT TEST FACILITY COMPONENTS ENGINEERING 

DRAWINGS LIST

DRAWING NUMBER TITLE 

 D115346 Drawing Tree 

 E115348 & L115345 Building Arrangement 

 D114345 Test Facility Schematic 

 E115073 Test Section Instrumentation 

 D114369 Steam Separator Drain Tank 

 D1144371 Small Carryover Tank 

 E114370 Large Carryover Tank 

 E115016 Steam Separator Tank 

 D114369 Steam Separator Drain Tank 

 D115347 Skirt, Steam Separator Tank 

 E115002 Water Supply Tank 

 E114343 Pressure Oscillation Damping Tank 

 E115815 Mezzanine Framework 

 D115587 Water Inlet Piping 

 D115597 Exhaust Line Piping 

 D115640 Steam By-pass Line 

 R114288 & L114287 Flow Housing Assembly 

 E114243 Housing Assembly 

 E114244 Weldment, Test Section 

 C114245 Pressure Gasket 

 C114246 Window Flange 

 C114247 Window 
G-2 

 C114248 Window Stud Fixture 

 D114249 Flange Mod. Bottom 

 D114279 Flange Mod. Top 

 C114255 Cushion Gasket 

 B114306 Belleville Washer 

 E114346 Window Test Fixture 

 E114281 & L114280 Upper Plenum Assembly 

 C114282 Flange Mod. 

 E114289 Ground Plate 

 D114290 Housing Extension 

 D114291 Exhaust Baffle 

 E114292 Lower Plenum Assembly 

 D114293 Lower Plenum Flow Baffle 

 D114294 Seal Plate, Lower Plenum 

 C114295 Seal Sleeve Retaining Plate 

 C114296 Seal Sleeve 

 D114297 G10 Isolation Plate 

 C114298 Low Melt Reservoir 

 D114299 Reservoir Connector Plate 

 D114366 Seal Sleeve Extractor 

 E115073 Test Section Instrumentation 

 D118339 Droplet Injection System 

 E118338 Flow Housing Differential Pressure Instrumentation 

 E118340 Heater Rod Bundle Grid Temperature Instrumentation 

 

 D118337 Automatic Traverse Mechanism 
G-3 

 C115132 Drain Tube 

 D114301 Unheated Rod 

 E114302 Heater Rod 

 D115075 Steam Probe Rake Assembly 

 D115076 Steam Probe Rake Tube 

 C115077 Steam Probe Rake Mounting 

 C118336 Traversing Steam Probe 

 D115261 & L115260 Grid Assembly 

 D115262 Outer Grid “A” 

 D115263 Outer Grid “B” 

 D115264 Outer Grid “C” 

 D115265 Outer Grid “D” 

 D115266 Inner Grid “A” 

 D115267 Inner Grid “B” 

 D115268 Inner Grid “C” 

 D115269 Inner Grid “D” 
G-4 
H-1 

APPENDIX H. THERMOPHYSICAL PROPERTIES OF ONE BORON 

NITRIDE SAMPLE AND THREE ROD SAMPLES 
H-2 
H-3 
H-4 
H-5 
H-6 
H-7 
H-8 
H-9 
H-10 
H-11 
H-12 
H-13 
H-14 
H-15 
H-16 
H-17 
H-18 
H-19 
H-20 
H-21 
H-22 
H-23 
H-24 
H-25 
H-26 
H-27 
H-28 
H-29 
H-30 
H-31 
H-32 
H-33 
H-34 
H-35 
H-36