Experimental Measurement 

of Suppression Pool Void 

Distribution During

Blowdown in Support of 

Generic Issue 193

Office of Nuclear Regulatory Research

NUREG/CR-7186
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owned rights.
Experimental Measurement 

of Suppression Pool Void 

Distribution During 

Blowdown in Support of 

Generic Issue 193

Manuscript Completed: March 2011

Date Published: September 2014

Prepared by: 

M. Ishii, T. Hibiki, S. Rassame, 

M. Griffiths, D. Y. Lee, P. Ju, J. Yang, 

S. L. Sharma, and S. W. Choi

Purdue University

School of Nuclear Engineering

West Lafayette, IN 47907

A. Ireland, NRC Project Manager

A. Velazquez-Lozada, NRC Technical Monitor

Office of Nuclear Regulatory Research

NUREG/CR-7186

 

iii

ABSTRACT

The possible failure of an Emergency Core Cooling System (ECCS) train due to a large amount 

of entrained gas in the ECCS pump suction piping during a loss of coolant accident (LOCA) is 

one of the potential engineering problems faced in a Boiling Water Reactor (BWR) power plant. 

The void fraction distribution and void penetration in the Suppression Pool (SP) during 

blowdown from a LOCA are key parameters necessary to analyze potential gas intrusion into 

the ECCS pump suction piping. To study void fraction distribution and void penetration in the 

Suppression Pool (SP) during blowdown, two sets of experiments, namely steady state tests 

and transient tests, were conducted using the Purdue University Multi-Dimensional Integral Test 

Assembly for ESBWR applications (PUMA-E) facility. The design of the test apparatus used is 

based on a scaling analysis from a prototypical BWR containment (Mark I) with consideration of 

downcomer size, SP water level and downcomer water submergence depth. Several 

instruments were installed to obtain the required experimental data such as the gas volumetric 

flow, void fraction, pressure, and temperature.

For the steady state tests, the air was injected through a downcomer pipe in the SP. Sixteen 

tests with various air volumetric flow rates, downcomer void conditions, and air velocity ramp 

rates were performed. Two periods of the experiment, namely, the initial air injection period and 

the quasi-steady period are observed. The initial air injection period gives the maximum void 

penetration depth. The quasi-steady period provides less void penetration, but with oscillation in 

the void penetration. It was found that the air volumetric flow rate has a minor effect on the void 

fraction distribution and void penetration during the initial air injection period in the range of high 

air volumetric flow rate conditions while it strongly impacts the void fraction distribution and void 

penetration during the quasi-steady state for the entire range of air flow rate conditions. The 

initial downcomer void conditions were found to strongly affect the void fraction distribution and 

void penetration during the initial period. The air velocity ramp rates were found to have a minor 

impact on the void distribution and penetration in both periods.

For the transient tests, sequential flows of air, steam-air mixtures, and pure steam with the 

various flow rate conditions were injected from the Drywell (DW) through a downcomer pipe in 

the SP. Eight tests were conducted at various gas volumetric fluxes at the downcomer, two 

different downcomer sizes, and two different initial air concentration conditions in the DW. Three 

periods of the experiment, namely, initial period, quasi-steady period, and chugging period are 

observed. The void penetration depth was maximum in the initial period and reduced in the 

quasi-steady period. The penetration of noncondensable gases during the chugging period, 

which occurs at the end of the transient, reached depths similar to those observed during the 

initial period. It was determined that the void distribution and area of void penetration in the SP 

is governed by the gas volumetric flux at the downcomer and by air concentration in the 

downcomer. It is noted that the transient conditions were well scaled for the initial period but not 

necessarily well scaled to simulate the chugging phenomena. Chugging is a complex 

phenomenon that depends primarily on periodic sudden condensation of steam into colder 

water, but also depends on gas volumetric flux, noncondensable gas concentration, frequency 

of the phenomenon, heat transfer, and subcooling, as well as the downcomer and suppression 

pool geometry. The rudimentary scaling methods used here are not suitable for use with such 

complex phenomenon. Instead, more specific and advanced scaling techniques would be 

needed.

v

FOREWORD

The potential safety issue of boiling water reactors (BWR) Emergency Core Cooling System 

(ECCS) suction concern was originally identified by staff in Region III. This issue pertains to the 

possible failure of the low pressure ECCS pumps due to unanticipated large quantities of gas 

entering into the suction pipe. The issue was identified initially as applicable to Mark I and 

Mark II containments during large or medium-break loss of coolant accidents (LOCA). Gas 

entering into the ECCS system might impact the operation of the ECCS pumps and challenge 

the long term cooling capability of the ECCS, which is required by Title 10, Section 50.46(b)(5), 

of the Code of Federal Regulations (10 CFR 50.46).

After revising the first communication of this issue, the Office of Nuclear Regulatory Research 

(RES) concluded that enough information was provided to perform an initial screening and that 

the issue does not pose any immediate safety concern and a review was requested as the

potential Generic Issue (GI) 193: “BWR ECCS suction concerns”.

On the initial screening of this issue, one of the areas identified by RES to be investigated was 

the gas-liquid injection into the suppression pool and how deep the jet will penetrate into the 

pool.

A task action plan was developed to investigate the areas identified in the initial screening and 

an experimental program was defined and implemented as part of the technical assessment to 

characterize the gas-liquid jet penetration into the suppression pool.

This experimental program was conducted at Purdue University Multi-Dimensional Integral Test 

Assembly facility (PUMA). The objective of the experimental program was to better understand 

the liquid-gas jet injected into the suppression pool through the downcomers (vents) and 

establish the technical basis of a potential exclusion zone in the vicinity of the downcomers. The 

results of the experimental program to characterize the liquid-jet are documented in this report.

The experimental program described in this report is by no means a comprehensive study of the 

liquid-gas jet injection phenomena, nor is it a complete investigation of the ECCS suction 

concern. The data obtained in this program may ultimately be useful to the resolution of the 

generic issue, but must be considered within the context of a larger body of research. Care 

should be taken when extending the experimental results contained in this report to the scale 

and configuration of prototypic BWR Mark I and Mark II containments. The magnitude and 

duration of the phenomena predicted in the experimental test facility may exhibit unintended 

biases that were not included in the rudimentary scaling analysis performed. Extending the 

result to a prototypic geometry without considering all of the significant parameters may result in 

unrealistic extrapolations.

vii

TABLE OF CONTENTS

Section Page

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

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

TABLE OF CONTENTS............................................................................................................ vii

LIST OF FIGURES ....................................................................................................................ix

LIST OF TABLES..................................................................................................................... xiii

ABBREVIATIONS AND ACRONYMS .......................................................................................xv

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

1.1. Research Background ........................................................................................ 1

1.2. Research Objectives........................................................................................... 4

2. EXPERIMENTAL FACILITY AND INSTRUMENTATION................................................ 5

2.1. PUMA-E Facility.................................................................................................. 5

2.2. Test Facility for Steady State Tests..................................................................... 6

2.2.1. Air Supply Line for Steady State Tests .................................................... 7

2.2.2. Downcomer Section for Steady State Tests ............................................ 8

2.3. Test Facility for Transient Tests .........................................................................11

2.3.1. RPV, ADS line and DW ..........................................................................11

2.3.2. Downcomer Section for Transient Tests.................................................12

3. TEST DESCRIPTION....................................................................................................15

3.1. Test Description for the Steady State Tests .......................................................15

3.2. Test Description for Transient Tests...................................................................16

3.2.1. Test Matrix .............................................................................................16

3.2.2. Test Initial Condition...............................................................................17

3.2.3. Estimation of Gas Volumetric Flux at Downcomer of PUMA-E 

Facility Using RELAP5 for Transient Tests.............................................18

4. TEST RESULTS AND DISCUSSION ............................................................................21

4.1. Steady State Tests.............................................................................................21

4.1.1. Flow Visualization for Steady State Tests...............................................22

4.1.2. Air Volumetric Flow Rate ........................................................................25

4.1.3. Initial Downcomer Void Condition...........................................................30

4.1.4. Air Velocity Ramp Rate ..........................................................................35

4.1.5. Averaged Bubble Velocity and Bubble Chord Length. ............................40

4.2. Transient Tests ..................................................................................................41

4.2.1. Important Differences Between the Steady State and Transient 

Tests ......................................................................................................41

4.2.2. Flow Visualization for the Transient Tests ..............................................42

4.2.3. Transient Test Blowdown Periods ..........................................................46
viii

4.2.4. Effect of Noncondensable Gas Concentration and Gas Volumetric 

Flux on SP Void Penetration and Distribution .........................................51

4.2.5. Comparison of the 0.076 m and 0.102 m (3 in. and 4 in.) Diameter 

Downcomer Tests ..................................................................................58

4.2.6. Averaged Axial Bubble Velocity and Chord Length.................................62

SUMMARY ...............................................................................................................................63

APPENDIX A. Instrumentation..................................................................................................67

A.1 Instrumentation Description ...............................................................................67

A.1.1 Introduction ............................................................................................67

A.1.2 Conductivity Probes ...............................................................................67

A.1.2.1 Conductivity Probes and Supporting Cage Design.....................67

A.1.2.2 Data Processing for Conductivity Probes ...................................71

A.1.3 Pressure Measurement ..........................................................................76

A.1.4 Temperature Measurement ....................................................................76

A.1.5 Air Flow Rate Measurement ...................................................................76

A.1.6 Nozzle Flow Rate Measurement.............................................................77

A.1.7 Oxygen Concentration Measurement .....................................................78

A.1.8 High-speed Video Camera .....................................................................79

A.2 Instrumentation Location....................................................................................79

A.2.1 Instrumentation Location for Steady State Tests ....................................81

A.2.2 Instrumentation Location for Transient Tests..........................................82

A.3 Data Acquisition System (DAS) and Valve Control System................................88

A.3.1 DAS and Valve Control System for Steady State Tests..........................88

A.3.2 DAS and Valve Control System for Transient Tests ...............................89

A.3.2.1 DAS for Conductivity Probes and High-speed Camera ..............89

A.3.2.2 DAS for Other Instruments and Control System.........................89

A.4 List of Pressure, Water Level, Temperature, and Flow Measurements ..............90

A.5 List of Conductivity Probe Locations ..................................................................91

APPENDIX B. Test Procedures ..............................................................................................101

B.1 Steady State Tests...........................................................................................101

B.1.1 Test Initiation Time ...............................................................................101

B.2 Transient Tests ................................................................................................102

B.2.1 Test Initiation Time ...............................................................................105

APPENDIX C. Uncertainty Analysis ........................................................................................107

C.1 Introduction......................................................................................................107

C.2 K-Type Thermocouples....................................................................................107

C.3 Pressure and Differential Pressure Measurements ..........................................108

C.3.1 STD924................................................................................................109

C.3.2 STG944................................................................................................109

C.4 Flow Measurements.........................................................................................110

C.5 Oxygen Analyzer (only used in the transient tests)...........................................110

REFERENCES .......................................................................................................................111
ix

LIST OF FIGURES

Figure Page

Figure 1-1 Local Phenomena in SP During Blowdown Period of Air Injection....................... 2

Figure 1-2 Local Phenomena in SP During Blowdown Period of Steam-air Mixtures 

Injection .............................................................................................................. 3

Figure 2-1 Schematic of PUMA facility ................................................................................. 6

Figure 2-2 Schematics of Test Facility for Steady State Tests.............................................. 8

Figure 2-3 Side View of SP with Modification for Steady State Tests ................................... 9

Figure 2-4 Top View of SP with Modification for Steady State Tests ...................................10

Figure 2-5 Experimental Facility for Transient Tests ...........................................................11

Figure 2-6 PUMA-E ADS and Main Steam Line Configuration ............................................12

Figure 2-7 SP with Modification for Transient Tests ............................................................13

Figure 3-1 RELAP5 Nodalization for the DW Section..........................................................18

Figure 3-2 RELAP5 Nodalization for the Vertical Vent, Downcomer, and SP ......................19

Figure 4-1 Bubble Plume Around the Downcomer Exit During t=1.084-1.420 

Seconds (the Initial Period) for Test No. A1 .......................................................23

Figure 4-2 Bubble Plume Around the Downcomer Exit During t=1.716-2.192 

Seconds (the Quasi-steady Period) for Test No. A1...........................................24

Figure 4-3 Measured Air Volumetric Flow Rate for Test Nos. A1, A2, A3, and A4...............26

Figure 4-4 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1, A2, A3, and A4 ............................................................................................27

Figure 4-5 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1, A2, A3, and A4 ............................................................................27

Figure 4-6 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1, A2, A3, and A4 Measured Using the Conductivity Probes ...........28

Figure 4-7 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1, A2, and A3 Measured Using the Conductivity Probes..................28

Figure 4-8 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1, A2, A3, and A4 Estimated From the High-speed Camera 

Images...............................................................................................................29

Figure 4-9 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1, A2, A3, and A4 Estimated From the High-speed Camera 

Images...............................................................................................................29

Figure 4-10 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1 and A5..........................................................................................................32

Figure 4-11 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1 and A5..........................................................................................32
x

Figure 4-12 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A5 Measured Using the Conductivity Probes .........................33

Figure 4-13 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A5 Measured Using the Conductivity Probes .........................33

Figure 4-14 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A5 Estimated From the High-speed Camera Images.............34

Figure 4-15 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A5 Estimated From the High-speed Camera Images.............34

Figure 4-16 Measured Air Volumetric Flow Rate for Test Nos. A1 and A9 ............................36

Figure 4-17 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1 and A9..........................................................................................................37

Figure 4-18 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1 and A9..........................................................................................37

Figure 4-19 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A9 Measured Using the Conductivity Probes .........................38

Figure 4-20 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A9 Measured Using the Conductivity Probes .........................38

Figure 4-21 Axial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A9 Estimated From the High-speed Camera Images.............39

Figure 4-22 Radial Void Penetration During the Initial and Quasi-steady Periods for 

Test Nos. A1 and A9 Estimated From High-speed Camera Images...................39

Figure 4-23 Bubble Plume Around the Downcomer Exit During t=3.13-3.93 Seconds 

for Test No. T5 (Based on the High-speed Camera Time) .................................43

Figure 4-24 Bubble Plume Around the Downcomer Exit During t=5.10-7.48 Seconds 

for Test No. T5 (Based on the High-speed Camera Time) .................................44

Figure 4-25 Bubble Plume Around the Downcomer Exit During t=31.93 and 68.20 

Seconds for Test No. T5 (Based on the High-speed Camera Time)...................45

Figure 4-26 Bubble Plume Around the Downcomer Exit During t=300 and 542.08 

Seconds for Test No. T5 (Based on the High-speed Camera Time)...................46

Figure 4-27 Axial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T1, T2, T3, and T4 .............................................................................48

Figure 4-28 Radial Void Penetration as a Function of Time for Each Period of 

Transient Test Nos. T1, T2, T3, and T4 .............................................................48

Figure 4-29 Axial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T5, T6, T7, and T8 .............................................................................49

Figure 4-30 Radial Void Penetration as a Function of Time for Each Period of 

Transient Test Nos. T5, T6, T7, and T8 .............................................................49

Figure 4-31 Noncondensable Gas Concentration and Gas Volumetric Flux as a 

Function of Time for Transient Test Nos. T1, T2, T3, and T4 .............................53
xi

Figure 4-32 Noncondensable Gas Concentration and Gas Volumetric Flux as a 

Function of Time for Transient Test Nos. T5, T6, T7, and T8 .............................54

Figure 4-33 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Initial Period for Test Nos. T1, T2, T3, and T4..............................................55

Figure 4-34 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Quasi-steady Period for Test Nos. T1, T2, T3, and T4 .................................55

Figure 4-35 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Chugging Period for Test Nos. T1, T2, T3, and T4.......................................56

Figure 4-36 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Initial Period for Test Nos. T5, T6, T7, and T8..............................................56

Figure 4-37 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Quasi-steady Period for Test Nos. T5, T6, T7, and T8 .................................57

Figure 4-38 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Chugging Period for Test Nos. T5, T6, T7, and T8.......................................57

Figure 4-39 Averaged Initial Axial Void Penetration and Initial Gas Velocity..........................59

Figure 4-40 Averaged Initial Radial Void Penetration and Initial Gas Velocity .......................59

Figure 4-41 Maximum Axial Void Penetration and Initial Gas Velocity...................................61

Figure 4-42 Maximum Radial Void Penetration and Initial Gas Velocity ................................61

Figure A-1 Design of Single-sensor Conductivity Probe ......................................................68

Figure A-2 Design of Double-sensor Conductivity Probe.....................................................69

Figure A-3 Configuration and Orientation of Single-sensor and Double-sensor 

Conductivity Probes on Supporting Cage...........................................................70

Figure A-4 Void Fraction Calculated Based on the Averaging Time of 0.25 Second............72

Figure A-5 Void Fraction Calculated Based on the Averaging Time of 0.5 Second..............72

Figure A-6 Void Fraction Calculated Based on the Averaging Time of 1.0 Second..............73

Figure A-7 Void Fraction Calculated Based on the Averaging Time of 2.0 Seconds ............73

Figure A-8 Void Fraction Calculated Based on the Averaging Time of 4.0 Seconds ............74

Figure A-9 Example of Two-Signal from the Double-sensor Conductivity Probe.................75

Figure A-10 Symbols Used in Isometric Drawings for Instrument Location............................80

Figure A-11 Locations of Pressure and Water Level Measurement in SP..............................81

Figure A-12 Locations of Pressure, Temperature, and Air Flow Rate Measurement in 

the Air Supply Line.............................................................................................82

Figure A-13 Locations of Instrumentation in the DW..............................................................83

Figure A-14 Locations of Instrumentation in the SP...............................................................84

Figure A-15 DP-A Line from RPV to Drywell..........................................................................85

Figure A-16 3” DP-B Line from RPV to Drywell .....................................................................86
xii

Figure A-17 3” MS-A Line from RPV to Drywell .....................................................................87

Figure A-18 3” MSL-B and MSL-C Lines from RPV to Drywell...............................................88

Figure A-19 Configuration of Conductivity Probes on Level O ...............................................91

Figure A-20 Configuration of Conductivity Probes on Level A................................................92

Figure A-21 Configuration of Conductivity Probes on Level B................................................92

Figure A-22 Configuration of Conductivity Probes on Level C ...............................................93

Figure A-23 Configuration of Conductivity Probes on Level D ...............................................93

Figure A-24 Configuration of Conductivity Probes on Level E................................................94

Figure A-25 Configuration of Conductivity Probes on Level F................................................94

Figure A-26 Configuration of Conductivity Probes on Level G ...............................................95

Figure A-27 Configuration of Conductivity Probes on Level H ...............................................95
xiii

LIST OF TABLES

Table Page

Table 2-1 PUMA-E Facility Key Parameters. ...................................................................... 6

Table 3-1 Test Matrix for Steady State Tests. ....................................................................15

Table 3-2 Test Matrix for Transient Test. ...........................................................................17

Table 3-3 Initial Conditions for Transient Test....................................................................17

Table 4-1 List of Varied Test Conditions for the Steady State and Transient Tests. ...........21

Table 4-2 Test Conditions for Comparison of the Air Volumetric Flow Rate Effect on 

Void Distribution and Void Penetration in the SP................................................25

Table 4-3 Description of Figures for Determining the Effect of Air Volumetric Flow 

Rate on Void Penetration and Distribution in the SP. .........................................25

Table 4-4 Test Conditions for Comparison of the Initial Downcomer Void Condition 

Effect on Void Distribution and Void Penetration in the SP.................................31

Table 4-5 Description of Figures for Determining the Effect of Downcomer Initial 

Void Condition on Void Penetration and Distribution in the SP...........................31

Table 4-6 Test Conditions for Comparison of the Air Velocity Ramp Rate Effect on 

Void Distribution and Void Penetration in the SP................................................35

Table 4-7 Description of Figures for Determining the Effect of the Air Velocity Ramp 

Rate on Void Penetration and Distribution in the SP. .........................................36

Table 4-8 Averaged Axial Bubble Velocity and Chord Length for the Steady State 

Tests..................................................................................................................41

Table 4-9 Chugging Onset Time Range for Each Transient Test. ......................................47

Table 4-10 List of Figures for Use in Determining of Effect of Noncondensable Gas 

Concentration and Volumetric Flux on SP Void Penetration and 

Distribution.........................................................................................................52

Table 4-11 Averaged Axial Bubble Velocity and Chord Length Measured By the 

Double-sensor Conductivity Probes for the Transient Tests...............................62

Table A-1 Percent Difference of Water Inventory Loss in RPV from the Nozzles and 

DP Gauges. .......................................................................................................78

Table A-2 Pressure and Level Measurements....................................................................90

Table A-3 Temperature Measurements..............................................................................90

Table A-4 Flow Measurement. ...........................................................................................90

Table A-5 Type and Location of Conductivity Probes .........................................................96

Table B-1 Test Initiation Time at DAS and High-speed Camera Time Frames. ................102

Table B-2 Approximate Difference between DAS and High-speed Camera Time 

Frames for the Initial Period. ............................................................................105

xv

ABBREVIATIONS AND ACRONYMS

ADS Automatic Depressurization System

BWR Boiling Water Reactor

DAS Digital Acquisition System

DBA Design Basis Accident

DC Downcomer

DP Differential Pressure

DPV Depressurization Valve

DW Drywell

ECCS Emergency Core Cooling System

ESBWR Economic Simplified Boiling Water Reactor

GDCS Gravity Driven Cooling System

GSI Generic Safety Issue

ICS Isolation Condenser System

LOCA Loss of Coolant Accident

Mark I Prototypic BWR containment type

MSL Main Steam Line

NRC U.S. Nuclear Regulatory Commission

PC Personal Computer (part of the digital acquisition system)

PCCS Passive Containment Cooling System

PUMA-E Purdue University Multi-dimensional integral test Assembly for ESBWR 

applications facility

RELAP5 Reactor Excursion and Leak Analysis Program (1-D thermal-hydraulic 

computer code)

RHR Residual Heat Removal system

RPV Reactor Pressure Vessel

SBWR Simplified Boiling Water Reactor

Sch. Schedule. A standard designation of pipe wall thickness

SP Suppression Pool

SRV Safety Relief Valve

WW Wetwell

1

1. INTRODUCTION

1.1. Research Background

The possible failure of the Emergency Core Cooling System (ECCS) due to a large amount of 

entrained gas in the ECCS suction piping of a Boiling Water Reactor (BWR) is addressed in the 

Generic Safety Issue (GSI) 193, BWR ECCS suction concerns. Air ingestion to the Residual 

Heat Removal (RHR) and core spray pumps can degrade the pump performance. Therefore, it 

is important to understand the dynamics of the Drywell (DW) to Suppression Pool (SP) venting 

phenomena during blowdown and the resulting void distribution in the SP in proximity to the 

ECCS pump suction strainers. The void distribution, bubble velocity and size, and rate of bubble 

plume spread are the key parameters in this analysis of the physical phenomena.

The void distribution in the SP during the blowdown period of a design basis accident is affected

by several important local phenomena. In the initial blowdown, the steam and superheated 

water are released into the DW. As a result, pressure in the DW and downcomers to the SP 

increases rapidly. During the early period of the blowdown, mostly noncondensable gas is

forced through the downcomers into the SP (Ref. 1). This is followed by the steam-air mixture 

injection. In the later period, the vented gas is mostly steam. In the first stage, water initially 

standing in the downcomers is accelerated into the SP and the downcomers become voided. A 

large bubble of mostly air is then formed at the exit of the downcomer. The air injection from the 

DW results in the expansion of this bubble at the tip of the downcomer. After that, this large 

bubble may deform and smaller disintegrated bubbles may spread and rise to the water surface.

Figure 1-1 shows local phenomena in the SP during the blowdown period of air injection. During 

this initial period, some disintegrated bubbles may be entrained into the bottom of the pool due 

to the circulating liquid flow. When the steam-air mixtures enter the downcomers, condensation 

occurs at the exit of the downcomers. Rapid condensation will eventually induce condensation 

oscillation or chugging at the exit of the downcomers. Condensation oscillation and chugging 

are separate phenomena and do not occur simultaneously. Whether condensation oscillation or 

chugging occurs and the duration of the phenomena are dependent on a number of factors 

including steam mass flux and pool temperature. The conditions for these phenomena can be 

determined from a graph developed by Moody from GE Mark I full scale test results (Ref. 2). 

Figure 1-2 shows the local phenomena in the SP during the period of steam-air mixture

injection.

In order to study the local phenomena in the SP, both steady state and transient tests using the

PUMA-E facility were proposed. In the steady state tests, different air volumetric flow rates were

injected into the downcomer installed in the PUMA-E SP. For the transient tests, the actual 

blowdown period in the DW and subsequent injection of sequential flows of air, steam-air

mixture, and pure steam with various flow rate conditions was simulated using the Reactor 

Pressure Vessel (RPV), DW, and SP of the PUMA-E facility.
2

Figure 1-1 Local Phenomena in SP During Blowdown Period of Air Injection
3

Figure 1-2 Local Phenomena in SP During Blowdown Period of Steam-air Mixtures 

Injection
4

1.2. Research Objectives

The primary objective of this study is to develop a physical understanding and to obtain 

experimental data for the void distribution and fluid dynamics of a BWR Mark I Type SP during 

the blowdown period of LOCAs. Measurements of local void fraction and high-speed movie 

recordings were used to determine the break-up length of a downward jet containing steam and 

noncondensable gas. Measurements of the local void fraction give the rate at which the bubble 

plume spreads, such that it is possible to estimate the void fraction and bubble velocity near the 

entrance of a strainer. The impact of the noncondensable gas fraction on the void distribution

was also investigated.

Specific objectives are:

- To simulate the blowdown period of LOCAs using the modified PUMA-E facility so that 

void distribution tests in the SP can be conducted.

- To obtain a series of test data that covers a range of injection flow rates and 

noncondensable gas fraction for blowdown conditions to determine local void fraction,

bubble size, and bubble velocity with a special focus on the locations where strainers for 

the ECCS pump suction are generally positioned.
5

2. EXPERIMENTAL FACILITY AND INSTRUMENTATION

In order to use the PUMA-E facility to investigate the void distribution and fluid dynamics of the 

BWR SP during blowdown, facility modifications and installation of instrumentation were

necessary for both the steady state and transient tests.

2.1. PUMA-E Facility

The PUMA facility was originally built to simulate the SBWR (Simplified Boiling Water Reactor) 

in terms of integral test performance and control. The project was sponsored by the U.S. 

Nuclear Regulatory Commission (NRC). The PUMA facility is an integral test facility including 

major components similar to the SBWR power plant such as the Reactor Pressure Vessel 

(RPV), DW, Wetwell (WW), Gravity Driven Cooling System (GDCS), Passive Containment 

Cooling System (PCCS), Isolation Condenser System (ICS), and Automatic Depressurization 

System (ADS). The schematic of the PUMA facility is shown in Figure 2-1.

The PUMA-E facility was modified from the PUMA facility to adopt the design changes from the 

SBWR to the Economic Simplified Boiling Water Reactor (ESBWR). The heater rods, ADS, 

GDCS, PCCS, and ICS have been modified based on the scaling and scientific design study for 

the ESBWR relative to the PUMA facility (Ref. 3). The RPV, DW, and WW geometries are 

identical to the PUMA facility. The details of the PUMA RPV, DW, and WW can be found in the 

scientific design report for the PUMA facility (Ref. 3). Table 2-1 lists the important facility 

parameters.
6

Figure 2-1 Schematic of PUMA facility

Table 2-1 PUMA-E Facility Key Parameters.

Parameters Value

Maximum Power 630 kW (2.15x106 btu/h)

RPV Height / Diameter 6.13/0.600 m (20/2 ft)

RPV Free Volume 1.65 m3 (58.3 ft3)

DW Free Volume 12.9 m3 (456 ft3)

WW Water Volume 8.05 m3 (284 ft3)

WW Gas Volume 9.63 m3 (340 ft3)

2.2. Test Facility for Steady State Tests

To provide the required air flow rate for the steady state experiments, a new air supply line was

connected to the 0.051 m (2 in.) existing compressed air line in the PUMA-E facility. This new

compressed air line has a length of around 60 meters (197 ft) and extends to the compressed 

air tank, which has a volume of 14.4 m3 (509 ft3

).

The 0.102 m (4 in.) downcomer pipe was installed in the SP of the PUMA-E facility to simulate 

the downcomer in the suppression chamber of the Mark I containment. The dimensions of the 
7

downcomer pipe size and submerged depth of pipe in the SP water are determined by a scaling 

analysis. (The scaling analysis for these parameters is based on proprietary design information 

and will not be included here.)

2.2.1. Air Supply Line for Steady State Tests

Figure 2-2 shows the schematics of the test facility used for the steady state tests. In the PUMAE facility, the Safety Relief Valve (SRV) line is branched from the Main Steam Line (MSL) and is 

connected the SP. To supply air flow to the downcomer pipe section in the SP, pipe lines with 

manual valves and pneumatic actuator valves were installed and merged into the exiting SRV 

line outside the SP. The valve positioned in the SRV-A line (V-AL-06) was fully closed in order 

to isolate the SP from the PUMA-E RPV.

The required flow rates are set by adjusting the position of valve V-AL-01, which needs to be 

calibrated before performing the tests.

The pneumatic actuator valves (VM-AL-01 and VM-AL-02) are used to start the experiment by 

sequentially opening both valves. VM-AL-02 is initially opened and closed within a short period 

to release air flow to the atmosphere while VM-AL-01 is opened to provide the flow to the main 

air supply line during the closure of VM-AL-02. Air flow can be increased smoothly without any 

perturbations. The ramp rate of air flow can be controlled by adjusting the opening time of 

VM-AL-01.

The 0.006 m (1⁄4 in.) bypass line, including valve V-AL-02, is incorporated to adjust the initial

water level in the downcomer pipe inside the SP by releasing a volumetric air flow to the air 

supply line.

Next to the 0.025 m (1 in.) pipeline, there are two branches of 0.051 m (2 in.) and 0.019 m (3⁄4 in.)

with manual valves. The 0.051 m (2 in.) pipeline is used for experiments with high flow rate, 

while the 0.019 m (3⁄4 in.) pipeline is utilized for experiments with relatively low flow rate. This is 

done to ensure accurate measurements of the gas flow rate, as the larger 0.051 m (2 in.) vortex 

flow meter is not able to accurately measure the smaller gas flow rates present in the steady 

state tests.
8

Figure 2-2 Schematics of Test Facility for Steady State Tests

2.2.2. Downcomer Section for Steady State Tests

Figures 2-3 and 2-4 show the side and top view, respectively, of the SP with the modification to

the SRV line. The downcomer pipe is installed by modifying the SRV line inside the SP of 

PUMA-E. The existing 0.051 m (2 in.) SRV line is replaced with the 0.102 m (4 in.) pipe for the 

test.
9

Figure 2-3 Side View of SP with Modification for Steady State Tests
10

Figure 2-4 Top View of SP with Modification for Steady State Tests

The pipelines are composed of two different materials: stainless steel pipe and transparent 

lexan pipe. Two pipe clamps connect the vertical vent and stainless steel pipe in order to 

prevent shaking or vibration during the tests. The transparent lexan pipe section is extended 

from the stainless steel pipe at around 0.20 m (0.66 ft) above the SP water level and submerged 

into water with a depth of 0.37 m (1.2 ft). The transparent lexan pipe section is used to estimate 

the water column velocity in the downcomer by visualizing the water column-air interface using 

a high-speed video camera. As a second measurement for the water column level, five 

single-sensor conductivity probes are evenly mounted on the transparent pipe wall to measure 

the level of water column. To measure the void distribution near the exit of the downcomer pipe, 

conductivity probes are mounted on a supporting cage.
11

2.3. Test Facility for Transient Tests

To study the dynamics of DW to SP venting phenomena, specifically the distribution of voids in 

the SP during a LOCA blowdown, existing components such as the RPV, DW, Automatic 

Depressurization System (ADS) lines, Main Steam Lines (MSL), vertical vent, and SP in the 

PUMA-E facility were utilized to perform transient tests. Figure 2-5 represents the modified test 

facility used for the transient tests. The details of the PUMA-E RPV, DW, and SP can be found 

in the scientific design report for the PUMA facility (Ref. 3).

Figure 2-5 Experimental Facility for Transient Tests

2.3.1. RPV, ADS line and DW

The RPV is used to produce saturated steam that is discharged into the DW through the ADS 

and MSL lines. The electrical heater rods of the RPV are operated at a power of 300 kW

(1x106 btu/h) during the experiment.

The PUMA-E ADS and MSL are illustrated in Figure 2-6. They were originally designed based 

on the scaling analysis (Ref. 3) from the ESBWR ADS system which has eight DPV lines and 

ten SRV lines. The PUMA DPV-A line, B line, and MS-A line each represent 2 DPV lines in the 

ESBWR and the PUMA MS-B and MS-C line each represent 1 DPV line in the ESBWR 

according to the scaling considerations. The combined set of DPV and MSL valves that are 

opened, namely the number of DPV lines opened, determines the steam mass flow rate 

discharged to the DW to achieve the scaled gas volumetric flux at the downcomer pipe. 

The free volume of the DW in the PUMA-E facility is larger than the free volume that would 

result from scaling analyses. Modification of the DW was not considered when conducting this 

research, as this distortion was not expected to have an effect on the major results of the study. 

Jet deflectors are installed in the DW at the discharge location of each DPV line and at the 
12

entrance of the vertical vent to prevent the discharge of steam from the RPV directly to the SP 

as well as to simulate the jet deflectors installed in the Mark I containment.

Figure 2-6 PUMA-E ADS and Main Steam Line Configuration

2.3.2. Downcomer Section for Transient Tests

A new vent line is installed on the existing vertical vent line as shown in Figure 2-7. This piping 

is the downcomer section for the transient tests. A Schedule 10 (Sch. 10) stainless steel pipe 

with 0.102 m or 0.076 m (4 in. or 3 in.) diameter is mounted on a window in the vertical vent. 

The other seven windows are completely closed except for a 0.025 m (1 in.) pipe installed in 

one window connecting the vertical vent to the SP for water level equalization. The bottom of 

the vertical vent is closed. To measure the water column level in the downcomer, five 

single-sensor conductivity probes are mounted on the pipe wall at evenly spaced intervals. A 

supporting cage for conductivity probes is installed near the exit of the downcomer.

3-inch Sch. 10 pipe
13

Figure 2-7 SP with Modification for Transient Tests

15

3. TEST DESCRIPTION

This chapter explains details of the tests performed including the test matrix, test initial 

conditions, test procedures, and test initial time for both the steady state tests and transient 

tests. Additionally, the estimation of the gas volumetric flux at the downcomer in the transient 

tests using RELAP5 is described.

3.1. Test Description for the Steady State Tests

The basic scaling analysis and the technical information for the prototypic plant provided by the 

NRC (Ref. 4) were used to develop the test matrix. The final sixteen steady state test conditions

were determined by the NRC based on discussion with Purdue as shown in Table 3-1.

Table 3-1 Test Matrix for Steady State Tests.

Test 

No.

DC

Diameter

Velocity 

Ramp 

Rate (s)

DC

Condition Flow Type

Air Mass 

Flow Rate

(kg/s [ft/s])

Air 

Volumetric 

Flow Rate

(m3/s [ft3/s])

Air 

Volumetric 

Flux

(m/s [ft/s])

A1

0.102 m

(4 in.)

1.0

Completely 

Filled with 

Water

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0]

A2 DBA 0.138 [0.304] 0.115 [4.061] 14.2 [46.6]

A3 Category 4a 0.077 [0.170] 0.064 [2.260] 7.9 [25.9]

A4 Category 2 0.005 [0.011] 0.004 [0.141] 0.5 [1.6]

A5

Partially 

Voided

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0]

A6 DBA 0.138 [0.304] 0.115 [4.061] 14.2 [46.6]

A7 Category 4a 0.077 [0.170] 0.064 [2.260] 7.9 [25.9]

A8 Category 2 0.005 [0.011] 0.004 [0.141] 0.5 [1.6]

A9

2.0

Completely 

Filled with 

Water

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0]

A10 DBA 0.138 [0.304] 0.115 [4.061] 14.2 [46.6]

A11 Category 4a 0.077 [0.170] 0.064 [2.260] 7.9 [25.9]

A12 Category 2 0.005 [0.011] 0.004 [0.141] 0.5 [1.6]

A13

Partially 

Voided

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0]

A14 DBA 0.138 [0.304] 0.115 [4.061] 14.2 [46.6]

A15 Category 4a 0.077 [0.170] 0.064 [2.260] 7.9 [25.9]

A16 Category 2 0.005 [0.011] 0.004 [0.141] 0.5 [1.6]

The downcomer condition is determined based on the voided level in the downcomer section. 

For partially voided conditions, the downcomer water level is reduced to 39% of the 

submergence depth of the downcomer. This voided condition represents the DW to SP 

differential pressure of 7.584 kPa (1.1 psi) in some BWR power plants.

The definition of flow types in category 4a, DBA, and category 2 are classified by the NRC 

based on various volumetric flow rates for different pipe break sizes in LOCAs (Ref. 4). 
16

Category 4b is based on the maximum capability of the air supply flow in the PUMA-E test 

facility. The velocity ramp rate is the required time to reach the steady state air flow rate.

For the case of the 0.102 m (4 in.) downcomer size, the volumetric flow rates and fluxes are 

computed from the air mass flow rates when the air density is about 1.2 kg/m3 (0.075 lbm/ft3

). In 

the steady state tests, the air (15 °C to 20 °C [59 °F to 68 °F]) is injected into the SP (25 °C

[77 °F]), while for the prototypic plant case, the DW air (52°C to 65°C [126 °F to 149 °F]) would 

be injected into the SP (27°C to 37°C [80.6 °F to 98.6 °F]). Due to these temperature 

differences, there may be as much as an 11.8% change in PUMA gas volumetric flow rate in the 

upper section of the pool relative to the prototype if we translate the conditions using a scaling 

method. However, these steady state tests are also separate effect tests with the air flow rate

treated as a parameter. Therefore the whole set of data can be used to understand the effect of 

air volumetric flow rate on important parameters such as void fraction distribution, bubble 

velocity, and bubble chord length.

3.2. Test Description for Transient Tests

3.2.1. Test Matrix

Table 3-2 shows the test matrix for the transient tests. There are two series of tests. Each series 

is performed with a different downcomer pipe size. Each test, regardless of series, is performed 

with different initial air concentrations in the DW and mixed steam and air volumetric flux at the 

downcomer. Performing tests for 0.076 m and 0.102 m (3 in. and 4 in.) downcomer pipes aims

to confirm the scaling from the prototypic plant to the scaled down test facility. Furthermore, the 

0.076 m (3 in.) downcomer can provide a higher mixture volumetric flux than the 0.102 m (4 in.)

downcomer pipe at the same break flow rate. The mixture volumetric flux at the downcomer 

pipe in the initial blowdown period covers the possible range of volumetric flux at the 

downcomer in the prototypic plant, scaled down to test facility conditions.
17

Table 3-2 Test Matrix for Transient Test.

Test 

No. Downcomer 

size

Initial air 

concentration

in DW (%)

No. of DPVs 

opening

Steam Mass flow 

Rate Blowdown*

from RPV to DW

(kg/s [lbm/s])

Mixture Volumetric 

Flux at 

Downcomer**

(m/s [ft/s])

T1 0.076 m (3 in.) 100 5 DPVs 0.65 [1.43] 75 [246]

T2 0.076 m (3 in.) 100 3 DPVs 0.31 [0.68] 41 [135]

T3 0.076 m (3 in.) 100 2 DPVs 0.21 [0.46] 28 [92]

T4 0.076 m (3 in.) 80 5 DPVs 0.65 [1.43] 84 [276]

T5 0.102 m (4 in.) 100 5 DPVs 0.65 [1.43] 45 [148]

T6 0.102 m (4 in.) 100 3 DPVs 0.31 [0.68] 27 [89]

T7 0.102 m (4 in.) 100 2 DPVs 0.21 [0.46] 17 [56]

T8 0.102 m (4 in.) 80 5 DPVs 0.65 [1.43] 50 [164]

* Steam mass flow rate from RPV during the initial blowdown measured by nozzle.

** Estimated values based on the RELAP5 calculation during the initial blowdown.

3.2.2. Test Initial Condition

The initial conditions in the RPV, DW, and SP are shown in the Table 3-3. The pressure and 

temperature in the SP and DW of the PUMA facility are identical to the Mark I containment 

operational conditions (Ref. 4). The water level in the SP is set at 1.05 m (3.44 ft). The 

submergence length for the downcomer in the SP is 0.37 m (1.2 ft), filling the downcomer with 

water to the base of the elbow joining the vertical outlet and the horizontal inlet.

Table 3-3 Initial Conditions for Transient Test.

Component Parameter PUMA-E

RPV

RPV power 300 kW (1.02x106 btu/h)

Steam Dome Pressure 1034 kPa (135.3 psig)

Steam Dome Temperature 197.6 °C (387.7 °F)

Collapsed Water Level 2.81 m (9.22 ft)

DW

Pressure 113.4 kPa (1.747 psig)

Water Level 0 m (0 ft)

Steam/NC Temperature at Upper DW 65.5 °C (149.9 °F)

SP

Pressure 113.4 kPa (1.747 psig)

Water Temperature (bulk) 37 °C (98.6 °F)

Water Level 1.05 m (3.44 ft)
18

3.2.3. Estimation of Gas Volumetric Flux at Downcomer of PUMA-E Facility Using 

RELAP5 for Transient Tests

To estimate gas volumetric flux at the downcomer of the PUMA-E facility, the transient tests 

were simulated using the RELAP5/mod 3.3 code. The DW, SP, Vertical Vent, valves, and 

downcomer section of the PUMA-E facility were modeled using several components of RELAP5 

such as the PIPE, BRANCH, TMDPJUN, SINGJUN, VALVE, etc. The time-dependent inlet flow 

condition was input as TMDPJUN using the experimental data from the steam mass flow rate 

measured by nozzle measurements. Figures 3-1 and 3-2 show the RELAP5 nodalization for the 

DW, and vertical vent, and downcomer section, respectively. The simulation was performed for 

600 seconds to align with the actual transient test time. The calculated results of the gas 

volumetric flux at the downcomer were obtained.

Figure 3-1 RELAP5 Nodalization for the DW Section

994

622-02

622-01

621

620-03

620-02

620-01

618

625

DW

995
19

Figure 3-2 RELAP5 Nodalization for the Vertical Vent, Downcomer, and SP

21

4. TEST RESULTS AND DISCUSSION

Sixteen conditions for the steady state tests and eight conditions for the transient tests were

performed using the PUMA-E facility. Information about void fraction distribution, axial and radial 

void penetration, bubble velocity, and bubble chord length for each test condition were obtained 

for both type of tests. To better understand the local physical phenomena in the SP during 

blowdown, this chapter discusses, in detail, the experimental results for both the steady state

and transient tests. For both test types, the test conditions were varied by adjusting several 

parameters. Table 4-1 lists the varied test conditions for the steady state and transients tests.

Table 4-1 List of Varied Test Conditions for the Steady State and Transient Tests.

Type of Test Varied Test Conditions

Steady State Tests

- Air volumetric flow rate/flux

- Initial downcomer void condition

- Air velocity ramp rate

Transient Tests

- Downcomer diameter size

- Gas (steam/air) volumetric flux

- Initial air concentration in the DW

For the steady state tests, the air volumetric flow rate/flux, initial downcomer void condition, and 

the air velocity ramp rate were varied for the performance of each test. The impact of these 

parameters on the void fraction and penetration depth were studied and the results are provided

and discussed in Section 4.1.

For the transient tests, the downcomer diameter, gas (steam/air) volumetric flux, and the initial 

air concentration in the DW were varied for the performance of each test. The impact of these 

parameters on the void fraction and penetration depth were studied and the results are provided 

and discussed in Section 4.2.

4.1. Steady State Tests

During the initial blowdown period of a LOCA in a prototypic Mark I type containment, the 

noncondensable gas in the DW is forced through the downcomers into the SP. To simulate the 

initial blowdown of noncondensable gas, the steady state tests were performed using air 

injection through a downcomer with different air volumetric flow rates, initial downcomer void 

conditions, and air velocity ramp rates. The experimental results from different test conditions 

were used to understand the local phenomena in the SP during the blowdown phase of a LOCA.

Investigation of the impact of the air volumetric flow rates, initial downcomer void condition, and

the air velocity ramp rate on the void fraction distribution and void penetration depth were

performed for the steady state tests using a parametric study. The results of selected test 

conditions are compared in the following sections to illustrate the impact of each parameter on

the void fraction distribution and void penetration depth in the SP.
22

4.1.1. Flow Visualization for Steady State Tests.

In order to understand the global phenomena in the SP during the steady state tests, the bubble 

behavior at the downcomer exit was recorded by a high-speed camera. Figures 4-1 and 4-2

highlight the development of the bubble plume around the downcomer exit in the SP for test No.

A1. This test condition was chosen as an example because the results are typical in terms of 

bubble plume formation. Figure 4-1 shows the development of the bubble plume during the 

initial period. The air was injected downward through the downcomer pipe and a spherical 

bubble plume was formed at the exit of the downcomer. The initial injection resulted in the 

maximum void penetration depth since the bubble was entrained into the bottom of the pool due 

to the circulating liquid flow induced by the liquid slug injection into the SP. The plume then rose

to the water surface due to the buoyancy force. Some remnants of the broken-up plume were 

present as bubbles at the bottom of the SP during this process.

During the quasi-steady period, the bubble plume oscillated. A small plume would form at the 

exit of the downcomer (Figure 4-2) and rise, followed a short time later by the formation of 

another plume, resulting in the oscillation of the axial and radial void penetration. However, the 

axial penetration depth of the oscillating bubble plume was less than half that of the initial 

bubble plume. This is because the oscillating bubble plume does not include the liquid slug, and 

the liquid circulation effects are greatly reduced. This quasi-steady process continued cyclically 

during the remainder of the experiment.

These are the only two periods, namely, initial air injection and quasi-steady, observed during 

the steady state tests.
23

Time = 1.084 seconds Time = 1.108 seconds

Time = 1.164 seconds Time = 1.420 seconds

Figure 4-1 Bubble Plume Around the Downcomer Exit During t=1.084-1.420 Seconds

(the Initial Period) for Test No. A1
24

Time = 1.716 second Time = 1.900 second

Time = 2.064 second Time = 2.192 second

Figure 4-2 Bubble Plume Around the Downcomer Exit During t=1.716-2.192 Seconds

(the Quasi-steady Period) for Test No. A1
25

4.1.2. Air Volumetric Flow Rate

The results of test Nos. A1, A2, A3, and A4 (test conditions shown in Table 4-2) are compared

in this section to illustrate the impact of the air volumetric flow rate on the void fraction 

distribution and void penetration. Table 4-3 provides a description of each figure used to 

determine the effect of the air volumetric flow rate on SP void penetration and distribution.

Table 4-2 Test Conditions for Comparison of the Air Volumetric Flow Rate Effect on 

Void Distribution and Void Penetration in the SP.

Test 

No.

DC

Diameter

Air

Velocity 

Ramp 

Rate (s)

DC 

Condition

Prototypic 

Plant Flow 

Type

Air Mass 

Flow Rate

(kg/s [lbm/s])

Air 

Volumetric 

Flow Rate

(m3/s [ft3/s])

Air 

Volumetric

Flux

(m/s [ft/s])

A1

0.102 m

(4 in.) 1.0

Completely 

Filled with 

Water

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0]

A2 DBA 0.138 [0.304] 0.115 [4.061] 14.2 [46.6]

A3 Category 4a 0.077 [0.170] 0.064 [2.260] 7.9 [25.9]

A4 Category 2 0.005 [0.011] 0.004 [0.141] 0.5 [1.6]

Table 4-3 Description of Figures for Determining the Effect of Air Volumetric Flow 

Rate on Void Penetration and Distribution in the SP.

Figure No. Figure Descriptions Experimental Period Measurement 

Device

4-3 Measured Air Volumetric Flow Rate Initial and Quasi-steady Vortex Flow Meter

4-4 Void Fraction Distribution Initial Period Conductivity Probes

4-5 Void Fraction Distribution Quasi-steady Conductivity Probes

4-6 Axial Void Penetration Initial and Quasi-steady Conductivity Probes

4-7 Radial Void Penetration Initial and Quasi-steady Conductivity Probes

4-8 Axial Void Penetration Initial and Quasi-steady High-speed Camera

4-9 Radial Void Penetration Initial and Quasi-steady High-speed Camera

The void fractions, as shown in Figures 4-4 and 4-5, were averaged over a time period of 1 

second. For instance, the void fraction at 2 seconds in Figure 4-4 was obtained by averaging 

the experimentally measured void fraction during the 1.5 to 2.5 second time frame. The void 

fraction at a given location at a given time is represented in the figures by a highlighted red or 

blue circle. The shade of the red circles represents low void fractions ranging from 0.025% to 2% 

and the shade of the blue circles represents high void fractions ranging from 2% to 100%. Two 

percent void fraction is the current acceptance criteria for BWR ECCS pump void fraction 

disposure (Ref. 5). These figures can provide beneficial information in terms of the void fraction 

distribution and void penetration at a given time.
26

Figure 4-6 shows the axial void penetration measured from the center of the downcomer exit

using the conductivity probes. Figure 4-7 shows the radial void penetration measured at the

conductivity probe level immediately below the downcomer exit (level 0.02 m [0.79 in.]). The 

figures are estimated based on the information from the raw data signals obtained from the 

conductivity probes. The data is discrete since the conductivity probes are located at fixed

points in the SP. The smooth curves are plotted to present the void penetration trends. Figure 

4-8 shows the axial void penetration estimated from the high-speed camera images measured

from the center of the downcomer. Figure 4-9 shows the radial void penetration estimated from 

the high-speed camera images at level 0.02 m (0.79 in.) below the downcomer. Data points in 

Figures 4-8 and 4-9 are roughly estimated using information from images recorded by the 

high-speed camera. Each void penetration data point was obtained by measuring the bubble 

plume penetration from the images recorded by the high-speed camera. Hence, each data point 

represents the boundary of the bubble plume at a certain time. The smooth curves are plotted to 

present the void penetration trends. It is noted that the time scales for each test in Figures 4-6, 

4-7, 4-8, and 4-9 are synchronized in order to be able to make a good comparison between 

each test.

Figure 4-3 Measured Air Volumetric Flow Rate for Test Nos. A1, A2, A3, and A4
27

Figure 4-4 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1, A2, A3, and A4

Figure 4-5 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1, A2, A3, and A4
28

Figure 4-6 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1, A2, A3, and A4 Measured Using the Conductivity Probes

Figure 4-7 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1, A2, and A3 Measured Using the Conductivity Probes
29

Figure 4-8 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1, A2, A3, and A4 Estimated From the High-speed Camera Images

Figure 4-9 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1, A2, A3, and A4 Estimated From the High-speed Camera Images
30

As seen in Figure 4-3, the different volumetric flow rates with air velocity ramp rate times of 1 

second were obtained from the different test conditions. As seen in Figure 4-4, the void fraction 

distribution during the initial period for tests with high air volumetric flow rates (tests Nos. A1, A2, 

and A3) showed little difference in terms of the void penetration and void distribution. However, 

from Figure 4-5, it is clear that the void distribution during the quasi-steady period is determined 

by the air volumetric flow rate through the downcomer section.

From a comparison of Figures 4-6 and 4-8 and Figures 4-7 and 4-9 it is evident that there is 

some small difference between the void penetration trend obtained using the conductivity 

probes and estimated from the high-speed camera images. This difference is caused by the 

method used to determine the void penetration. The void penetration obtained using the

conductivity probes represents the bubble plume making direct contact with a probe. The 

estimated value from the high-speed camera images represents the estimated boundary of the

bubble plume observed. There is agreement, however, in the general trend of axial and radial 

void penetration between the values determined by both methods. During the initial air injection 

period, the axial void penetration (as measured by the conductivity probes) would increase to 

the maximum point at a certain time and decreased to a lesser point at a later time. The void 

penetration then oscillated axially and radially. The size of oscillations varied as a function of the 

test conditions during the quasi-steady period. These trends correspond to the observations

made from the high-speed camera images. In the low volumetric flow condition (test No. A4), 

only small bubbles, and not a bubble plume, emerged intermittently from the exit of the 

downcomer.

Consequently, it can be concluded that the air volumetric flow rate has a minor effect on void 

fraction distribution and axial void penetration in the SP during the initial period for high air 

volumetric flow rate conditions. The air volumetric flow rate has a greater impact on void fraction 

distribution and axial void penetration in the SP during the quasi-steady period for the entire

range of air volumetric flow rate conditions. The air volumetric flow rate has a significant effect 

on the radial void penetration for both periods.

4.1.3. Initial Downcomer Void Condition

The results of test Nos. A1 and A5 (test conditions shown in Table 4-4) are compared to 

illustrate the impact of the initial downcomer void condition on the void penetration and void 

distribution in the SP. Table 4-5 provides a description of each figure used to determine the 

effect of initial downcomer void condition on void penetration and distribution in the SP. 

Interpretation of the data in the figures is similar to that explained in Section 4.1.2.
31

Table 4-4 Test Conditions for Comparison of the Initial Downcomer Void Condition

Effect on Void Distribution and Void Penetration in the SP.

Test 

No.

DC 

Diameter

Air 

Velocity 

Ramp 

Rate (s)

DC 

Condition

Prototypic 

Plant Flow 

Type

Air Mass 

Flow Rate

(kg/s [lbm/s])

Air 

Volumetric 

Flow Rate

(m3/s [ft3/s])

Air 

Volumetric

Flux

(m/s [ft/s])

A1 0.102 m

(4 in.) 1.0

Fully Water

Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0] A5 Partially 

Void

Table 4-5 Description of Figures for Determining the Effect of Downcomer Initial Void 

Condition on Void Penetration and Distribution in the SP.

Figure No. Figure Descriptions Experimental Period Measurement Device

4-10 Local Void Distribution Initial Conductivity Probes

4-11 Local Void Distribution Quasi-steady Conductivity Probes

4-12 Axial Void Penetration Initial and Quasi-steady Conductivity Probes

4-13 Radial Void Penetration Initial and Quasi-steady Conductivity Probes

4-14 Axial Void Penetration Initial and Quasi-steady High-speed Camera

4-15 Radial Void Penetration Initial and Quasi-steady High-speed Camera
32

Figure 4-10 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1 and A5

Figure 4-11 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1 and A5
33

Figure 4-12 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A5 Measured Using the Conductivity Probes

Figure 4-13 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A5 Measured Using the Conductivity Probes
34

Figure 4-14 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A5 Estimated From the High-speed Camera Images

Figure 4-15 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A5 Estimated From the High-speed Camera Images
35

From Figures 4-10 and 4-11, it can be seen that the downcomer void condition has a significant 

impact on the void distribution and penetration during the initial air injection period and has 

almost no impact in the quasi-steady period. As shown in Figures 4-12 and 4-14, the maximum 

axial void penetration depth observed from the high-speed camera images and measured by 

the conductivity probes show that the maximum axial void penetration for test No. A1 is higher 

than for test No. A5. It is clear that the initial height of liquid slug in the downcomer affects the 

maximum axial void penetration depth. A higher initial water column in the downcomer results in 

a larger initial liquid slug and induces more liquid recirculation, resulting in increased 

entrainment of bubbles into the liquid flow. For the radial void penetration, both profiles are quite

similar as displayed in Figures 4-13 and 4-15. Therefore, the initial downcomer water column

height has almost no impact on the radial void penetration. In the prototypic plant, there is a 

differential pressure between the DW and SP. This creates a partial void condition in the 

downcomers. This partial void may be significant in terms of reducing the risk of air bubble 

entrainment into the ECCS pump suction piping when it is installed in close proximity to the 

downcomer exit.

4.1.4. Air Velocity Ramp Rate

The results of test Nos. A1 and A9 (test conditions shown in Table 4-6) are compared to 

illustrate the effect of the air velocity ramp rate on void fraction distribution and void penetration. 

Table 4-7 provides a description of each figure used to determine the effect of air velocity ramp 

rate void penetration and distribution in the SP. Interpretation of the data in the figures is similar 

to that explained in Section 4.1.2.

Table 4-6 Test Conditions for Comparison of the Air Velocity Ramp Rate Effect on 

Void Distribution and Void Penetration in the SP.

Test 

No.

DC 

Diameter

Air 

Velocity 

Ramp 

Rate (s)

DC 

Condition

Prototypic 

Plant Flow 

Type

Air Mass 

Flow Rate

(kg/s [lbm/s])

Air 

Volumetric 

Flow Rate

(m3/s [ft3/s])

Air 

Volumetric

Flux

(m/s [ft/s])

A1 0.102 m

(4 in.)

1.0 Fully Water Category 4b 0.184 [0.406] 0.153 [5.403] 18.9 [62.0] A9 2.0
36

Table 4-7 Description of Figures for Determining the Effect of the Air Velocity Ramp 

Rate on Void Penetration and Distribution in the SP.

Figure No. Figure Descriptions Experimental Period Measurement Device

4-16 Measured Air Volumetric Flow Rate Initial to Quasi-steady Vortex Flow Meter

4-17 Local Void Distribution Initial Conductivity Probes

4-18 Local Void Distribution Quasi-steady Conductivity Probes

4-19 Axial Void Penetration Initial and Quasi-steady Conductivity Probes

4-20 Radial Void Penetration Initial and Quasi-steady Conductivity Probes

4-21 Axial Void Penetration Initial and Quasi-steady High-speed Camera

4-22 Radial Void Penetration Initial and Quasi-steady High-speed Camera

Figure 4-16 Measured Air Volumetric Flow Rate for Test Nos. A1 and A9
37

Figure 4-17 Void Fraction Distribution During the Initial Period (t=2 sec) for Test Nos. 

A1 and A9

Figure 4-18 Void Fraction Distribution During the Quasi-steady Period (t=15 sec) for 

Test Nos. A1 and A9
38

Figure 4-19 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A9 Measured Using the Conductivity Probes

Figure 4-20 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A9 Measured Using the Conductivity Probes
39

Figure 4-21 Axial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A9 Estimated From the High-speed Camera Images

Figure 4-22 Radial Void Penetration During the Initial and Quasi-steady Periods for Test 

Nos. A1 and A9 Estimated From High-speed Camera Images
40

As seen in Figures 4-17 and 4-18, the air velocity ramp rate has a minor impact on the void 

distribution during the initial air injection period and the quasi-steady period. The axial void 

penetration trends are similar for both cases as shown in Figures 4-19 and 4-21. The radial void 

penetrations for both cases also have similar trends as displayed in Figures 4-20 and 4-22.

There is no significant difference in void fraction distribution or void penetration for test 

conditions with an air velocity ramp rate of 1 and 2 seconds. The averaged liquid slug ejection 

(from the downcomer) velocity estimated from the high-speed camera images was 2.31 and 

2.15 m/s (7.58 and 7.05 ft/s) for the case of the air velocity ramp rate of 1 (Test A1) and 2 (Test 

A5) seconds, respectively. The void distribution and penetration during the initial air injection 

period is impacted by this liquid slug velocity. There is no significant difference in terms of void 

faction and penetration between tests A1 and A5 since the liquid slug velocity is similar for both 

cases. In order to determine the impact of the air velocity ramp rate on the void fraction 

distribution, a range of tests with air velocity ramp rates that significantly differ may be required.

4.1.5. Averaged Bubble Velocity and Bubble Chord Length.

Table 4-8 shows the averaged axial bubble velocity and chord length measured using the 

double-sensor conductivity probes for each steady state test condition. It is noted that only 

some air bubbles were detected and measured by the conductivity probes. For general results, 

it can be seen that averaged bubble velocities ranged between 0.24 and 1.83 m/s (0.79 and 6.0 

ft/s) for the upward velocity and between 0.43 and 0.64 m/s (1.4 and 2.1 ft/s) for the downward 

velocity. The measured upward air bubble velocity was higher for the conditions with the higher 

air volumetric flow rates. The averaged bubble chord length ranged between 0.010 to 0.363 m

(0.39 to 14.3 in.). It is noted that the averaged downward bubble velocity could not be estimated 

in low air volumetric flow rate conditions (indicated by “-” in Table 4-8) since the bubble plume 

size in the quasi-steady period is limited. The bubbles in these low air volumetric flow rate 

conditions did not contact the probes located below C level. The probes below C level were

used for measuring the downward bubble velocity as explained in Section A.1.2.1.
41

Table 4-8 Averaged Axial Bubble Velocity and Chord Length for the Steady State 

Tests.

Test No.

Averaged Upward 

Bubble Velocity

(m/s [ft/s])

Averaged Downward 

Bubble Velocity

(m/s [ft/s])

Averaged Bubble 

Chord Length

(m [in])

A1 1.31 [4.30] 0.59 [1.94] 0.155 [6.1]

A2 1.83 [6.00] 0.49 [1.61] 0.216 [8.5]

A3 1.06 [3.48] - 0.102 [4.02]

A4 0.33 [1.08] - 0.01 [0.39]

A5 1.7 [5.58] 0.55 [1.80] 0.203 [7.99]

A6 1.58 [5.18] 0.5 [1.64] 0.214 [8.43]

A7 0.97 [3.18] - 0.11 [4.33]

A8 0.3 [0.98] - 0.011 [0.43]

A9 1.79 [5.87] 0.57 [1.87] 0.207 [8.15]

A10 1.74 [5.71] 0.43 [1.41] 0.363 [14.29]

A11 0.86 [2.82] - 0.075 [2.95]

A12 0.47 [1.54] - 0.025 [0.98]

A13 1.73 [5.68] 0.64 [2.10] 0.185 [7.28]

A14 1.61 [5.28] 0.43 [1.41] 0.221 [8.7]

A15 0.97 [3.18] - 0.155 [6.1]

A16 0.24 [0.79] - 0.01 [0.39]

4.2. Transient Tests 

During a LOCA blowdown, the noncondensable gas concentration in the Mark I containment will 

decrease as air is replaced by steam from the break. The rate of this replacement is governed 

by the break size. While the steady state tests were performed using air to parametrically study 

the local physical phenomena in the SP during the blowdown phase of a LOCA, the transient 

tests used a steam-air mixture. The purpose of the transient tests was to simulate the effects of 

noncondensable gas concentration and gas volumetric flux on void penetration and distribution 

in the SP. In addition, two downcomers of different diameter were used for examining the effect 

downcomer diameter has on void penetration and distribution in the SP.

4.2.1. Important Differences Between the Steady State and Transient Tests

The most obvious difference between the steady state and transient tests is the test gas used. 

In the steady state tests, the gas used was air for the duration of each test. In the transient test,

the gas used was a steam-air mixture of which the steam-to-air ratio increased as each 

transient test progressed. The difference in test gases leads to further differences in the steady 

state and transient tests. These additional differences are discussed in detail below.

Three distinct periods of blowdown were observed during each transient test: the initial period, 

the quasi-steady period, and the chugging period. The details of each transient test period are 

described in Section 4.2.3.
42

During the steady state tests, two distinct periods of blowdown were observed: the initial period

and the quasi-steady period. The details of each steady state period are described in Section 

4.1.1. The chugging period was not observed during the steady state tests because it is caused 

by a steam-air mixture with low noncondensable gas concentration, which was only present 

during the later time of the transient tests.

The other important difference between the steady state and transient tests is role of the DW. 

In the transient tests the DW was utilized as a steam supply, whereas in the steady state tests 

the downcomer pipe was connected directly to the compressed air line. Therefore, in the 

transient tests, the DW volume needed to be pressurized by steam from the RPV before the 

liquid slug in the downcomer was ejected from the downcomer. During the steady state tests, 

once the test was initiated by opening the valves, the downcomer was immediately pressurized. 

The result was that the liquid slug in the downcomer was ejected with a higher velocity during 

the steady state test than for a comparable transient test. For example, for the steady state test 

with an air velocity of 14.2 m/s (46.6 ft/s) (Test No. A1), the liquid slug was ejected at an 

averaged velocity of 2.31 m/s (7.58 ft/s) (estimated from images taken with the high-speed

camera). For the transient test with an initial gas velocity of 17 m/s (56 ft/s) (0.102 m [4 in.]

downcomer, 2 DPV break size with a 100% initial air concentration in the DW), the liquid slug 

was ejected at an averaged velocity 0.38 m/s (1.25 ft/s) according to the data obtained using

conductivity probes in the downcomer. Consequently, the maximum axial void penetration depth 

realized during the initial period of the transient tests and the steady state tests cannot be 

compared directly without consideration of the difference in liquid slug ejection velocity from the 

downcomer.

The focus of the current transient tests was the initial period of a LOCA blowdown. Thus the test

conditions were well scaled for the initial period but not necessarily well scaled to simulate the 

chugging phenomena. Chugging is dependent on the gas volumetric flux, noncondensable gas 

concentration, and subcooling. It is necessary to parametrically study the chugging phenomena 

to better develop a model and investigate its importance to gas intrusion in ECCS suction 

piping.

4.2.2. Flow Visualization for the Transient Tests

Figures 4-23 and 4-24 highlight the development of the bubble plume around the downcomer 

exit in the SP. The images were recorded by the high-speed camera during the initial period of 

blowdown during transient test No. T5, so that the development of the bubble plume during the 

initial gas injection period could be observed and described. First, the gaseous mixture (almost 

100% air) was injected into the SP through the downcomer after pressurizing the DW. The initial 

injected gas was then pulled toward the bottom of the SP by the wake of the liquid slug ejected 

from the downcomer. A spherically shaped bubble plume was formed at the exit of the 

downcomer, eventually rising to the surface of the water due to the buoyancy force.
43

Time = 3.13 seconds Time = 3.40 seconds

Time = 3.80 seconds Time = 3.93 seconds

Figure 4-23 Bubble Plume Around the Downcomer Exit During t=3.13-3.93 Seconds for 

Test No. T5 (Based on the High-speed Camera Time)
44

Time = 5.10 seconds Time = 5.23 seconds

Time = 7.37 seconds Time =7.48 seconds

Figure 4-24 Bubble Plume Around the Downcomer Exit During t=5.10-7.48 Seconds for 

Test No. T5 (Based on the High-speed Camera Time)

Figure 4-25 highlights the development of the bubble plume around the downcomer exit in the 

SP recorded by the high-speed camera during the quasi-steady period of blowdown during 

transient test No. T5. The bubble plume oscillated throughout this period with little change to 

axial or radial penetration depth. However, the penetration depth of this bubble plume was much 
45

less compared to the initial period penetration since there were no liquid slug inertial forces to 

pull the bubble downward.

Time = 31.93 seconds Time = 68.20 seconds

Figure 4-25 Bubble Plume Around the Downcomer Exit During t=31.93 and 68.20 

Seconds for Test No. T5 (Based on the High-speed Camera Time)

Figure 4-26 highlights the development of the bubble plume around the downcomer exit in the 

SP recorded by the high-speed camera during the chugging period of blowdown during transient 

test No. T5. While there was no distinct bubble plume during this period, small bubbles were 

randomly ejected from the downcomer. The penetration depth of these small bubbles was 

greater than the penetration depth of the plume in the quasi-steady period but less than the 

penetration depth of the initial plume since there were no liquid slug inertial forces to pull the 

bubble downward.
46

Time = 300.00 seconds Time = 542.08 seconds

Figure 4-26 Bubble Plume Around the Downcomer Exit During t=300 and 542.08 

Seconds for Test No. T5 (Based on the High-speed Camera Time)

4.2.3. Transient Test Blowdown Periods

Three periods of blowdown (initial, quasi-steady, chugging) were observed during each transient 

test experiment. The initial period was caused by the ejection of the liquid slug from the 

downcomer into the SP. The quasi-steady period consisted of oscillations in the bubble plume

caused by condensation and pressure oscillations at the exit of the downcomer. The chugging 

period was caused by the eventual reduction in noncondensable gas concentration in the DW to 

some threshold value. The axial depth and radial size of the void penetration were observed to 

be maximum during the initial period and reduced in the quasi-steady period. The time at which 

the chugging period was observed varied by test flow condition. The axial depth and radial size

of the void penetration during the chugging period were larger than those observed during the 

quasi-steady period, although a bubble plume did not exist during the chugging period. Instead, 

small bubbles were observed to be ejected from the exit of the downcomer at random intervals.

The onset time for chugging is earlier during transient tests with the highest volumetric flow 

rates (5 DPVs) than the tests with lower volumetric flow rates (3 DPVs and 2 DPVs). Also, the 

data suggests that the initial noncondensable gas concentration in the DW affected the onset 

time of chugging. For comparable break flows, the average time of chugging onset was slightly 

lower for the transient tests with 80% initial noncondensable gas concentration compared to the 

tests with 100% initial noncondensable gas concentration. However, any definitive conclusions 

regarding the effect of noncondensable gas concentration on the time of chugging onset 

requires additional data. Chugging onset time ranges for each transient test are provided in 

Table 4-9.
47

Table 4-9 Chugging Onset Time Range for Each Transient Test.

Test No. Break Flow 

(DPVs)

Initial DW Noncondensable

Gas Concentration

(%)

Chugging Onset 

Time Range

(s)

T1 5 100 210-270

T2 3 100 180-240

T3 2 100 310-370

T4 5 80 220-280

T5 5 100 160-220

T6 3 100 445-505

T7 2 100 330-390

T8 5 80 120-180

Figures 4-27 and 4-28 show the axial void penetration and the radial void penetration, 

respectively, as a function of time for each period of transient test Nos.: T1, T2, T3, and T4 

(0.076 m [3 in.] downcomer tests). Figures 4-29 and 4-30 show the axial void penetration and 

the radial void penetration, respectively, as a function of time for each period of transient test 

Nos.: T5, T6, T7, and T8 (0.102 m [4 in.] downcomer tests). Each of these Figures, 4-27 through

4-30, show estimated values based on images taken with the high-speed camera. The 

high-speed camera was used because it provided a very clear portrait of the three periods for 

each transient test condition. Note that for the initial period, all high-speed camera times were 

shifted to a common start time in order to be able to make a good comparison between the 

different tests.
48

Figure 4-27 Axial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T1, T2, T3, and T4

Figure 4-28 Radial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T1, T2, T3, and T4
49

Figure 4-29 Axial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T5, T6, T7, and T8

Figure 4-30 Radial Void Penetration as a Function of Time for Each Period of Transient 

Test Nos. T5, T6, T7, and T8
50

The maximum void penetration occurred during the initial period for all transient tests due to the 

inertia of the liquid slug ejected from the downcomer into the SP at the onset of the initial period. 

Higher break flow conditions, for example transient test Nos. T5 and T8, experienced the 

maximum void penetration both axially and radially as compared to the lower break flow test 

conditions.

The axial and radial void penetration during the quasi-steady period oscillated with time. In all 

transient tests, both the axial and radial penetration during the quasi-steady period were within 

close proximity to the downcomer and considerably less than the axial and radial penetration 

experienced during the initial period.

The chugging period, which occurred after the quasi-steady period for each transient test, 

demonstrated renewed deep axial and radial void penetration, more comparable to the 

penetration experienced in the initial period. While the renewed deep axial and radial void 

penetration experienced was more comparable to the initial period of each experiment 

(especially in the 0.102 m [4 in.] downcomer tests), the frequency of void ejection from the 

downcomer section was much more random than during the initial period and the quasi-steady

period. The voids seen in the chugging period consisted of small, individual bubbles as opposed 

to the larger somewhat continuous plume experienced during the initial period and quasi-steady

period.

While the void penetration during the initial period was greatest for each transient test, in an 

actual plant during a LOCA, ECCS pump start times are generally later than the duration of the 

initial period. For example, the initial period only lasts for approximately 9-15 seconds, but

ECCS pump start times are typically around 20 seconds after the onset of a LOCA. Therefore, 

the initial, maximum void penetration may not be a concern at some plants with larger time 

differences between the onset of a LOCA and the start of their ECCS pumps. Due to the 

oscillating nature and relatively small void penetration experienced during the quasi-steady

period, this period may not be safety significant. Renewed deep penetration was experienced 

during the chugging period, which began anywhere from 120 to more than 400 seconds into a 

transient test (the range of the onset of chugging depended on the initial test conditions). The 

chugging period would be experienced in the prototypic plant while the ECCS pumps are 

operating and therefore gas intrusion into the ECCS pump suction piping may be much more 

likely during the chugging period. However, the gas composition during the condensation 

oscillation/chugging period is primarily steam. Steam can condense before reaching a pump 

and therefore poses less of a problem for affecting pump operation than does noncondensable

gas.

The focus of the current transient tests was the initial period of a LOCA blowdown. Thus the test 

conditions were well scaled for the initial period but not necessarily well scaled to simulate the 

chugging phenomena. Chugging is dependent on the gas volumetric flux, noncondensable gas 

concentration, and subcooling. It is necessary to parametrically study the chugging phenomena 

to better develop a model and investigate its importance to gas intrusion in ECCS suction 

piping.
51

4.2.4. Effect of Noncondensable Gas Concentration and Gas Volumetric Flux on SP Void 

Penetration and Distribution

The initial air concentration in the DW for six of the eight tests (three tests per downcomer size) 

was 100% while the initial air concentration of the other two tests (one test per downcomer size)

was approximately 80%. Table 3-3 in Section 3.2.1 provides the detailed parameters for each 

test.

Each of the four transient tests performed for a particular downcomer size varied the gas 

volumetric flux at the downcomer by changing the break size initiating the test. The break steam 

mass flow rate, measured by flow nozzles in each appropriate break line for a particular 

transient test, was used as the inlet boundary condition in preparing a RELAP5 simulation. The 

gas volumetric flux at the downcomer exit for each test condition was then estimated using the 

RELAP5 simulation. This gas volumetric flux, estimated for each test condition, spans the entire 

range of the scaled-down gas volumetric flux expected in the downcomers during a LOCA in the 

prototypic plant. A comparison of the measured break flow rate and the estimated gas 

volumetric flux for each transient test is provided in Table 3-3 in Section 3.2.

Table 4-10 provides a description of each figure used to determine the effect of noncondensable

gas concentration and gas volumetric flux on SP void penetration and distribution.
52

Table 4-10 List of Figures for Use in Determining of Effect of Noncondensable Gas 

Concentration and Volumetric Flux on SP Void Penetration and Distribution.

Figure Transient 

Tests

Downcomer 

Section Size Period Figure Description Measurement Device

4-31 T1 - T4 0.076 m

(3 in.) N/A1

Noncondensable gas 

concentration and the 

gas volumetric flux as 

a function of time

Downcomer 

oxygen 

analyzer2

4-32 T5 - T8 0.102m

(4 in.) N/A1

Noncondensable gas 

concentration and the 

gas volumetric flux as 

a function of time

Downcomer 

oxygen 

analyzer2

4-33 T1 - T4 0.076 m

(3 in.) Initial Typical void fraction distribution

Conductivity 

probes

4-34 T1 - T4 0.076 m

(3 in.) Quasi-steady Typical void fraction distribution

Conductivity 

probes

4-35 T1 - T4 0.076 m

(3 in.) Chugging Typical void fraction distribution

Conductivity 

probes

4-36 T5 - T8 0.102 m

(4 in.) Initial Typical void fraction distribution

Conductivity 

probes

4-37 T5 - T8 0.102 m

[4 in.] Quasi-steady Typical void fraction distribution

Conductivity 

probes

4-38 T5 - T8 0.102 m

[4 in.] Chugging Typical void fraction distribution

Conductivity 

probes

1 The data provided in Figures 4-31 and 4-32 spans the duration of each transient test, therefore 

the figures include all three periods observed during a transient test and do not focus on a 

single period. 2 The gas volumetric flux was estimated using RELAP5 based on the steam mass flow rate 

measured at the break locations. The upper plot in Figures 4-31 and 4-32 was produced using 

data measured by the downcomer oxygen analyzer. The lower plot in Figures 4-31 and 4-32 

was produced using RELAP5.
53

Figure 4-31 Noncondensable Gas Concentration and Gas Volumetric Flux as a 

Function of Time for Transient Test Nos. T1, T2, T3, and T4
54

Figure 4-32 Noncondensable Gas Concentration and Gas Volumetric Flux as a 

Function of Time for Transient Test Nos. T5, T6, T7, and T8
55

Figure 4-33 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Initial Period for Test Nos. T1, T2, T3, and T4

Figure 4-34 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Quasi-steady Period for Test Nos. T1, T2, T3, and T4
56

Figure 4-35 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Chugging Period for Test Nos. T1, T2, T3, and T4

Figure 4-36 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Initial Period for Test Nos. T5, T6, T7, and T8
57

Figure 4-37 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Quasi-steady Period for Test Nos. T5, T6, T7, and T8

Figure 4-38 Typical Void Fraction Distribution around the Exit of Downcomer During 

the Chugging Period for Test Nos. T5, T6, T7, and T8
58

Comparisons of Figures 4-31, 4-33, 4-34, and 4-35 and comparisons of Figures 4-32, 4-36, 4-37, 

and 4-38 were used to determine that the void distribution and region of void penetration in the 

SP is governed by the gas volumetric flux at the downcomer and by the noncondensable gas

concentration in the downcomer, with the former observed to have the greater effect. The higher 

the initial gas volumetric flux, the deeper the axial void penetration during the initial period. The 

bubble plume size during the quasi-steady period also increased a small amount with higher

gas volumetric flux. The chugging period void penetration depth appeared to be more sensitive 

to the noncondensable gas concentration than to initial gas volumetric flux. However, the onset 

of chugging was much earlier when the break size and hence initial gas volumetric flux was 

higher due to more rapid decrease in the noncondensable gas concentration.

4.2.5. Comparison of the 0.076 m and 0.102 m (3 in. and 4 in.) Diameter Downcomer 

Tests

Figures 4-39 and 4-40 provide a comparison of the 100% initial DW air concentration tests for 

both the 0.076 m and 0.102 m (3 in. and 4 in.) downcomer test sections. The data in these 

figures, axially (Figure 4-39) and radially (Figure 4-40), is averaged to provide a good overall 

comparison over the entire initial period of the test. As seen in the figures, both the axial and 

radial penetration depths of the bubble plumes increased with increased initial gas volumetric 

flux. The downcomer cross-sectional area did not significantly impact the averaged initial void 

penetration (both axial and radial) for tests having comparable initial gas volumetric flux.

However, these results may not be extrapolated directly to the prototypic plant without 

performing a more thorough study.
59

Figure 4-39 Averaged Initial Axial Void Penetration and Initial Gas Velocity

Figure 4-40 Averaged Initial Radial Void Penetration and Initial Gas Velocity
60

Figures 4-41 and 4-42 provide a comparison of the 100% initial DW air concentration tests for 

both the 0.076 m and 0.102 m (3 in. and 4 in.) downcomer test sections. The data in these 

figures was taken from the maximum penetration point, axially (Figure 4-41) and radially (Figure

4-42), for each test to provide a single point comparison. Similar to the averaged penetration 

figures, both the maximum axial and radial penetration of the bubble plumes tended to increase 

with increased initial gas volumetric flux. For both downcomer sizes, the downcomer 

cross-sectional area did not significantly impact the maximum initial void penetration (both axial 

and radial) for tests having comparable initial gas volumetric flux.

However, as with the averaged results, these results may not be extrapolated directly to the 

prototypic plant without performing a more thorough study.
61

Figure 4-41 Maximum Axial Void Penetration and Initial Gas Velocity

Figure 4-42 Maximum Radial Void Penetration and Initial Gas Velocity
62

4.2.6. Averaged Axial Bubble Velocity and Chord Length

Table 4-11 shows the averaged axial bubble velocity and chord length measured by the 

double-sensor conductivity probes for each transient test condition. It is noted that only some 

gas bubbles were detected and measured by the conductivity probes. For general results, it can 

be seen that averaged bubble upward velocities ranged between 0.94 to 1.77 m/s (3.1 to 5.81 

ft/s). Downward velocity was measured as 1.99 and 3.78 m/s (6.53 and 12.4 ft/s). The averaged 

gas bubble upward velocity was measured to be greater for the test conditions with the higher 

break flow. The averaged gas bubble chord length ranged between 0.046 to 0.137 m (1.8 in. to 

5.39 in.). The averaged downward bubble velocity could not be estimated in some test

conditions (indicated by “-” in Table 4-11) since the bubble plume size was limited. The gas 

bubbles in those conditions did not contact the probes located below C level used for measuring 

the downward bubble velocity as explained in Section A.1.2.1.

Table 4-11 Averaged Axial Bubble Velocity and Chord Length Measured By the 

Double-sensor Conductivity Probes for the Transient Tests.

Test No.

Averaged Upward 

Bubble Velocity

(m/s [ft/s])

Averaged Downward 

Bubble Velocity

(m/s [ft/s])

Averaged Bubble 

Chord Length

(m [in])

T1 1.47 [4.82] 3.78 [12.40] 0.109 [4.29]

T2 1.24 [4.07] - 0.137 [5.39]

T3 1.35 [4.43] - 0.137 [5.39]

T4 1.77 [5.81] 1.99 [6.53] 0.121 [4.76]

T5 1.53 [5.02] - 0.088 [3.46]

T6 0.94 [3.08] - 0.046 [1.81]

T7 0.89 [2.92] - 0.082 [3.23]

T8 1.16 [3.81] - 0.107 [4.21]
63

SUMMARY

The Emergency Core Cooling System (ECCS) in a BWR is critical for keeping the reactor core 

covered during blowdown from a LOCA and for removing decay heat during recovery. The SP in 

the BWR Mark I containment is a primary source of supply water for the ECCS pumps' suction. 

The possible failure of the low pressure ECCS due to large amounts of entrained gas in the 

ECCS pump suction piping of a BWR from the SP has been considered. A certain amount of air 

ingestion into the Residual Heat Removal (RHR) and core spray pumps can degrade the pump 

performance and thereby compromise coolant delivery to the core. Therefore, it is important to 

understand the void distribution in the SP during blowdown from a LOCA.

Two sets of experiments, steady state tests and transient tests, were performed at the PUMA-E 

test facility to study the void fraction distribution in the SP. In the steady state tests, different air 

volumetric flow rates were injected into the downcomer installed in the PUMA-E SP. For the 

transient tests, the actual blowdown characteristics of a LOCA period in the DW and 

subsequent injection of sequential flows of air, steam-air mixture, and pure steam with the 

various flow rate conditions was simulated using the PUMA-E RPV, DW, and SP. The 

downcomer geometry and inlet flow conditions were determined from the results of a scaling 

analysis. (The scaling analysis for these parameters is based on proprietary design information 

and will not be included here.)

Although the experimental facility is not prototypic in scale, it provides valuable information 

about the qualitative behavior of the downcomer and suppression pool of a BWR Mark I and 

Mark II under blowdown conditions. The information gathered in this analysis provides a strong 

starting point for further research and will help guide future investigations. It may also be 

possible, with a rigorous and thorough analysis, to extrapolate all of the experimental result to 

prototypic conditions. In addition, the data collected will serve to guide and benchmark future 

CFD analyses.

To perform the steady state tests, the PUMA-E facility was modified as follows:

• A 0.102 m (4 in.) downcomer test section was installed in the SP by connecting the test 

section to the existing SRV line.

• An air supply line was added to provide the required air volumetric flow rate to the 

downcomer test section.

To perform the transient tests, the PUMA-E facility was modified as follows:

• 0.076 m and 0.102 m (3 in. and 4 in.) downcomer test sections were installed in the SP 

by connecting the test sections with a window in the existing vertical vent pipe.

• Jet deflectors were installed in the DW at each DPV line discharge location and at the 

entrance of the vertical vent pipe to prevent the discharge of steam from the RPV 

directly to the SP.

For both tests, common instrumentation and the high-speed camera were installed as follows:

• Vortex flow meters, flow nozzles, pressure gauges, and thermocouples were installed in 

the test facility to obtain required information such as air flow rate, steam break flow, 

pressure, temperature, etc.
64

• Single-sensor and double-sensor conductivity probes used to measure the void fraction, 

bubble velocity, and bubble chord length around the downcomer exit were set in a

supporting cage inside the SP.

• A high-speed camera was installed at a viewing port in the SP to record flow

visualization information during the experiment.

Steady State Tests

Sixteen steady state tests were performed by varying the downcomer void condition, air 

volumetric flow rate, and air velocity ramp rate. Each steady state test was conducted for 30 

seconds.

The time-averaged void fractions, axial bubble velocities, and bubble chord length were 

estimated from the data obtained using the conductivity probes. Information about the void 

fraction distribution, bubble velocity, and bubble chord length around the downcomer exit at the 

various times during the experiment was obtained. The void distribution and penetration was 

estimated based on the signals obtained by the conductivity probes and recorded images from 

the high-speed camera. The images obtained by the high-speed camera demonstrated the 

development of the bubble plume during the experiment.

Two distinct periods (initial period and quasi-steady) were observed during each steady state

test. The axial void penetration depth was maximum during the initial period due to the liquid 

slug inertia and was reduced in the quasi-steady period. The radial void penetration oscillated 

from the initial period through the quasi-steady period.

To study the impact of volumetric flow rate, air velocity ramp rate, and initial downcomer void 

condition on SP void distribution and penetration, a parametric study was performed and a 

comparison of the experimental results of selected test conditions was made.

The following conclusions were reached from the steady state test results:

• Air volumetric flow rate has a minor effect on the void fraction distribution and void 

penetration during the initial period in the range of high air volumetric flow rate 

conditions. 

• Air volumetric flow rate strongly impacts the void fraction distribution and void 

penetration during the quasi-steady state for the entire range of air flow rate conditions.

• Initial downcomer void conditions strongly affect the void fraction distribution and void 

penetration during the initial period but have no impact on void fraction distribution and 

void penetration during the quasi-steady period.

• Air injection velocity ramp rate has only a minor impact on the void fraction distribution 

and void penetration in both the initial period and the quasi-steady period.

Transient Tests

Eight transient tests were performed. The transient tests varied the downcomer size (0.076 m or 

0.102 m [3 in. or 4 in.]), gas volumetric flux at the downcomer, and the initial air concentration in 

the DW. Each transient test was conducted for 10 minutes.
65

In the transient tests, saturated steam with the required break flow rate was discharged from the 

RPV to the DW. The steam then passed through the installed downcomer section into the SP.

Measured break mass flow rate of steam was used as the inlet boundary condition in preparing 

a RELAP5 simulation. The gas volumetric flux at the downcomer for each test conditions was

then estimated using RELAP5. The gas volumetric flux estimated for each test condition spans 

the entire range of the scaled down initial gas volumetric flux expected during a LOCA in 

downcomers of the prototypic plant. The test data for each test condition was obtained using the 

same method used to obtain the steady state test results.

Three periods of blowdown (initial period, quasi-steady period, and chugging period) were 

observed during each transient test. The initial period was dominated by the ejection of the 

liquid slug from the downcomer and provided the maximum axial void penetration depth. The 

quasi-steady period consisted of oscillations resulting from condensation and pressure 

oscillations at the exit of the downcomer. The axial and radial void penetration was significantly

reduced in the quasi-steady period compared with the initial period. The eventual reduction in 

noncondensable gas concentration in the DW to some threshold caused the chugging period.

During the chugging period, random small bubbles were ejected from the downcomer exit. The 

penetration of these bubbles was greater than the penetration experienced during the 

quasi-steady period and more comparable to the initial period penetration.

The transient tests were performed with 0.076 m and 0.102 m (3 in. and 4 in.) downcomer 

diameters to investigate the impact of downcomer cross-sectional area on the void penetration. 

For the experiments performed, it was found that the downcomer cross-sectional area did not 

significantly impact the void penetration for tests having comparable initial gas volumetric flux. 

However, the downcomer diameter in the prototypic plant is much larger compared with the 

downcomer diameters used in the transient tests. In order to confirm the insignificance of the 

downcomer size on the void fraction, further analysis is required. The additional analysis may 

include full-scale experiments with prototypic geometry and detailed CFD analyses.

The following conclusions were reached from the transient test results:

• Axial depth and radial void penetration are maximum during the initial period and 

reduced in the quasi-steady period.

• The void distribution and void penetration in the SP is governed by the gas volumetric 

flux at the downcomer and by the air concentration in the downcomer. 

• The chugging period demonstrated renewed deep axial and radial void penetration 

which is more comparable to the penetration experienced in the initial period. However, 

the injected bubbles are small compared with the bubble plume experienced in the initial 

and quasi-steady period and are primarily composed of steam which would be expected 

to have a smaller effect on pump performance than noncondensable gas.

• The onset of chugging was observed to be earlier when the initial gas volumetric flux 

was higher and when the initial noncondensable gas concentration in the DW was lower 

for test conditions with comparable initial gas volumetric flux.

• The averaged axial and radial penetration depths of the bubble plumes during the initial 

period increase with increased initial gas volumetric flux regardless of downcomer 
66

diameter for the test sections used. However, this result may not be extrapolated directly

to the prototypic plant without performing a more thorough study which could include 

further tests.

It is noted that results of the transient experiments were more benign in terms of initial axial void

penetration as compared to the steady state test results. In other words, the maximum 

penetration depth of air experienced in the steady state tests was larger than that experienced 

when performing the transient tests. This is because the DW was not used in the steady state

tests, resulting in the air fully pressurizing the downcomer immediately. Therefore, the initial 

liquid slug in the downcomer for the steady state tests was ejected into the SP at a significantly

higher velocity compared to the velocity of ejection in the transient tests. The higher ejection

velocity of the liquid slug results in deeper axial void penetration.

The focus of the current transient tests was the initial period of a LOCA blowdown. The test 

conditions were well scaled for the initial period but not necessarily well scaled to simulate the 

chugging phenomena. Chugging is a complex phenomenon that depends primarily on periodic 

sudden condensation of steam into colder water, but depends also on gas volumetric flux, 

noncondensable gas concentration, frequency of the phenomenon, heat transfer, and 

subcooling, as well as the downcomer and suppression pool geometry. The rudimentary 

scaling methods used here are not suitable for use with such complex phenomenon. Instead, 

more specific and advanced scaling techniques would be needed. However, the chugging 

phase results in considerable void penetration.

The current results may not be extrapolated directly to the prototypic plant condition without

performing a more thorough study and possibly gathering more experimental data.
67

APPENDIX A. INSTRUMENTATION

A.1 Instrumentation Description

A.1.1 Introduction

In the experimental facility, several major instruments are installed inside the DW, ADS, and 

MSL to obtain the pressure, temperature, and inlet boundary conditions such as steam flow rate.

The single-sensor and double-sensor conductivity probes are installed in the instrument 

supporting cage to measure the void fraction, bubble velocity, and chord length. The pressure 

gauges and thermocouples are installed to measure the pressure and temperature of the gas 

and water space in the SP.

The test instrumentation is identified by tag numbers, which consist of three fields: XX-YYY-NN.

XX: instrumentation type (LT: differential pressure gauge, PT: absolute pressure 

gauge, TE: Thermocouple, FT: Nozzle, CE: conductivity probe)

YYY: instrumentation location (SP: suppression pool, DC: downcomer, DW: Drywell, 

DP: depressurization line, MS: main steam line)

NN: instrumentation number

Appendix Section A.4 lists the instrumentation, units, and measurable ranges.

A.1.2 Conductivity Probes

There are two types of conductivity probes used in this experiment. One is the single-sensor

conductivity probe and the other is the double-sensor conductivity probe. The single-sensor

conductivity probe is used to measure the local void fraction while the double-sensor

conductivity probe is used to simultaneously measure the local void fraction and bubble velocity.

A.1.2.1 Conductivity Probes and Supporting Cage Design

As shown in Figure A-1, the single-sensor conductivity probe consists of an electrode, which is 

made from Teflon coated stainless steel wire with 0.61 mm (0.024 in.) diameter. The Teflon 

coating on the tip of the wire is removed to expose a sharp edge with the length of 1.27 mm 

(0.05 in.). To protect against any scratches to the Teflon coating on the wire that can produce a 

disturbance of the signal, a heat shrink tube is applied to cover that section of stainless steel

wire. The probes are installed on a stainless steel tube of 12.7 mm (0.5 in.) diameter through 

conax fittings.
68

Figure A-1 Design of Single-sensor Conductivity Probe

The design of the double-sensor conductivity probe is similar to the single-sensor conductivity 

probe. The main difference between the single- and double-sensor conductivity probe design is 

the number of stainless steel wires in the probe. As shown in Figure A-2, the double-sensor

conductivity probe consists of two electrodes, which have the same diameter as those of the 

single-sensor conductivity probe. To measure the bubble velocity, the two electrodes are 

arranged with approximately 3.8 mm (0.15 in.) of elevation difference.
69

Figure A-2 Design of Double-sensor Conductivity Probe

Each stainless steel wire of the probe is connected with fine gauge insulated wire to carry the 

electric signals to an electronic circuit and Data Acquisition System (DAS). Finally, the electric 

signals are converted into the void fraction and bubble velocity information (Ref.6).
70

Figure A-3 Configuration and Orientation of Single-sensor and Double-sensor

Conductivity Probes on Supporting Cage

The arrangement of the measurement locations for conductivity probes on the supporting cage 

is displayed in Figure A-3. Forty-nine single-sensor and 22 double-sensor conductivity probes 

are mounted systematically on the supporting cage, which is a rectangular prism of size 

0.9 m × 0.9 m × 1.2 m (3 ft x 3 ft x 4 ft). The configuration of the probe locations has eight axial 

levels (Level O to H) and seven radial positions from the center of the downcomer pipe in a 

cross-shaped pattern. The nine axial levels of probes were adjusted according to the bubble 

plume size which was observed from the shake down tests. Due to the limited performance of 

the Data Acquisition System (DAS) electronics board, conductivity probes located far from the 

region of interest are disconnected from the DAS system in order to increase data acquisition 

frequency. It was confirmed that these disconnected conductivity probes are located outside the

maximum void penetration over the whole range of test conditions.

In each level of probes, several single-sensor and double-sensor conductivity probes are 

mounted on one of the four tubes to measure detailed void fraction and bubble velocity, while at 

least three single-sensor conductivity probes are mounted on the other tubes to check the 

symmetry of the void fraction at the same level of the bubble plume. The tip of each 

single-sensor probe is oriented horizontally to detect upward and downward moving bubbles. 

The short tip of each double-sensor conductivity probe is oriented horizontally, and the long tip 

of each double-sensor conductivity probe is directed upward for the probes in level C to level G 

to measure downward bubble velocity. The long probe tips in level A and B are directed 

downward to measure upward bubble velocity. These orientations are designed based on the 

direction of the gas plume movement. The supporting cage is fixed within the existing structures 

in the SP to prevent shaking or vibration that may affect experimental results. Five single-sensor

conductivity probes are installed on the side wall of the downcomer at various axial positions to 
71

estimate the initial water column level before performing the tests. The first probe is located 

near the exit of the downcomer while the fifth probe is mounted at a distance of 0.37 m (1.2 ft). 

from the downcomer exit. The details of the probe arrangement are described in Section A.5.

A.1.2.2 Data Processing for Conductivity Probes

The raw output signal obtained by a conductivity probe is the voltage signal from the electronic 

circuit and ranges from about 1 to 5 volts. The low and high voltage signal represent the water 

phase and gas phase respectively at the location of the probe tip at a given time. To convert this 

information to the time-averaged void fraction, a computer program is written to process the 

data.

For an example, the raw voltage signals of each probe with a frequency of 4667 Hz are 

categorized to be 0 or 1 by comparison with the threshold value. If the value is more than the 

threshold value, it will be converted to 1. If the value is less than the threshold value, it will be 

transformed to 0. 

The time-averaged void fraction is estimated over the proper averaging time by 

Number of data of gas phase Time averaged void fraction Number of total data = (A.1)

Sensitivity tests for an time over which to obtain the time-averaged void fraction were performed. 

The time-averaged void fractions were obtained with averaging times of 0.25, 0.5, 1.0, 2.0, and 

4.0 seconds. The sensitivity results are shown in Figures A-4 to A-8.
72

Figure A-4 Void Fraction Calculated Based on the Averaging Time of 0.25 Second

Figure A-5 Void Fraction Calculated Based on the Averaging Time of 0.5 Second
73

Figure A-6 Void Fraction Calculated Based on the Averaging Time of 1.0 Second

Figure A-7 Void Fraction Calculated Based on the Averaging Time of 2.0 Seconds
74

Figure A-8 Void Fraction Calculated Based on the Averaging Time of 4.0 Seconds

From the results of the sensitivity tests shown in Figures A-4 to A-8, the calculated void fractions 

fluctuate around the averaged value depending on the given averaging time. 

For the averaging time of 0.25 second, very high frequency void fraction change is observed, 

whereas for the averaging time of 4.0 seconds, detailed void fraction variation with time is 

smoothed out. In order to visualize reasonable void fraction variation with time, an averaging 

time of 1 second is chosen. In the transient tests, this averaging time is used to maintain

consistency with the results from the steady state tests.

The bubble velocity is estimated based on the time lag between the two signals and the 

distance between the two tips of the double-sensor conductivity probes. The raw signals of the 

double-sensor probes are converted into 0 or 1 by comparison with the threshold value. An 

example of two signals from a double-sensor conductivity probe is shown in Figure A-9.
75

Figure A-9 Example of Two-Signal from the Double-sensor Conductivity Probe

The bubble velocity is calculated based on the following equation.

( ) b

d Bubble velocity v

t = ∆ (A.2)

where

d = distance between the two tips of a double-sensor conductivity probe

∆t = time lag between the two consecutive signals 

Due to the limitation of the double-sensor conductivity probes, this calculated bubble velocity is 

only the axial component of the interfacial velocity.

The bubble chord length is calculated based on the bubble velocity obtained from Equation A.2

and the time period that the probe is covered by the gas phase. The following equation is used 

to calculated the bubble chord length.

( ) Bubble chord length L v t = ×∆ b s (A.3)

where

b v = bubble velocity

s ∆t = time period that the probe is covered by gas phase
76

A.1.3 Pressure Measurement

The experimental facility uses pressure transducers manufactured by Honeywell (Model STD 

924) for differential pressure measurements. The accuracy is + 25 Pa (0.0036 psi) for upper 

range values less than 25 kPa (3.6 psi) and + 0.1% of the maximum pressure for upper range 

values exceeding 25 kPa (3.6 psi). Model STG 944 pressure transducers manufactured by 

Honeywell are used for absolute pressure measurements with an accuracy of + 3.2 kPa (0.46 

psi).

The pressure sensors measure the gauge pressures and transmit a 4 to 20 mA signal. The DAS 

measures the voltages across 250 Ω (± 0.1 Ω) resistors. The data conversion program converts 

the 1 to 5 volt signals into engineering units as follows:

( )

( ) ( ) min

max min

max min

min V V

V V

× − −

− = + φ φ φ φ (A.4)

where

φ : output in engineering units

φmin : instrument range minimum

φmax : instrument range maximum

V : voltage output (Volts)

Vmin : minimum output voltage (Volts)

Vmax : maximum output voltage (Volts)

For the present case φ = Pg , the gauge pressure. Then, the absolute pressures are calculated

as follows:

Pa = Pg + Pb (A.5)

where Pa is the absolute pressure (kPa) and Pb is the barometric pressure (kPa).

A.1.4 Temperature Measurement

The experimental facility uses sheathed K-type thermocouples manufactured by OMEGA 

Engineering, Inc. The thermocouple signals, in mV, are converted directly into engineering units 

through the Labview program. The range of the K-type thermocouples is -200~1250 °C 

(-328~2280 °F) and the thermocouple limits of error is 2.2 °C (4 °F) or + 0.7% of reading.

A.1.5 Air Flow Rate Measurement

For the steady state tests, two Foxboro vortex flow meters (Model 84W) are installed on the

parallel 0.05 m (2 in.) and 0.02 m (3⁄4 in.) pipelines to measure air flow for high and low flow rate

conditions, respectively. The vortex flow meter works on the principle that a disturbance in the 

flow field generates vortices, which are proportional to the flow rate. The flow can be measured 
77

by counting the number of vortices per unit time. The measurable range of each vortex meter 

used in this experiment is listed in the Section A.4. There is an accuracy of ± 1% of the 

maximum and minimum flow rate. The output from the vortex flow meter is a 4 to 20 mA signal. 

It is converted into engineering units using Equation A.4. The standard calibration for a vortex 

flow meter is performed by the manufacturer before delivery.

A.1.6 Nozzle Flow Rate Measurement 

For the transient tests, both the pressure difference across a nozzle or a venturi and the 

upstream pressure are measured by pressure transducer cells. This data, along with the nozzle 

specifications, is sufficient to calculate the mass flow rate. This is accomplished using the 

following equation (Ref. 7). Z1 and Fa were compiled from figures and fit with a polynomial 

curve.

( )( ) 1 2 4

2 .

2

1

P P

A YF C

m a d −

−

= ρ

β (A.6)

Here, A2 is the area at the nozzle throat (m2), 

.

m is mass flow rate in kg/s, P1 and P2 are

upstream pressure and downstream pressure in kPa respectively, and Y is the expansion factor 

given by

1/ 2

2 /

1

4 2

4

1

2

( 1) /

1

2

2 /

1

2

1

1

1

1

1







































































 −

−











































 −















 −





 





− 













 =

−

k

k k

k

P

P

P

P

P

P

k

k

P

P Y

β

β (A.7)

In Equation A.6, β is defined as the ratio of the nozzle diameters, D1 and D2

1

2

D

D β = (A.8)

Pressure in Equation A.6 is in kPa, and Fa is the thermal expansion factor given by

1

5 Fa 0.9992 3.346 10 T − = + × (A.9)

with temperature in °C. Cd is the discharge coefficient given by

2

2

1 1

Re

1 0.99622 0.0232 (6.36 5.11 0.24 )

D

Cd = + D − + D − β (A.10)
78

where 2 Re D is Reynolds number corresponding to the diameter D2 .

The value of k in Equation A.7 is the ratio of specific heat given by

1

5 k 1.3111 1.11 10 P − = − × (A.11)

The density is calculated using the ideal gas law

1 1

1

Z RT

P

ρ = (A.12)

with the pressure ( P1 ) in Pa, the gas constant ( R ) = 0.4615 kJ/kg-K, and temperature (T1 ) in 

Kelvin (K). Finally, Z1 is given by the following equation, with pressure in kPa

2

1

8

1

5

1 Z 0.9904 7.496 10 P 1.369 10 P − − = − × + × (A.13)

Z1 is the compressibility factor and relates steam to an ideal gas.

For this experiment, the accuracy of nozzle measurements is investigated by comparison 

between the RPV inventory water loss estimated by nozzle flow meters and the water level 

change measured by DP gauges in the RPV before and after the 0.102 m (4 in.) downcomer 

experiments. The results are shown in the Table A-1. It can be seen that the difference between 

the estimated inventory loss in the RPV is less than 10%.

Table A-1 Percent Difference of Water Inventory Loss in RPV from the Nozzles and 

DP Gauges.

Type of Steam Flow

(No. of DPV opening)

Total Estimate of Inventory Loss in RPV Percent 

Difference 

(%)

Nozzles Water Level Change 

from DP Gauge

Small (2 DPVs) 97.8 kg (216 lbm) 107 kg (236 lbm) -9.34

Medium (3 DPVs) 113 kg (249 lbm) 116 kg (256 lbm) -2.95

High (5 DPVs) 151 kg (333 lbm) 164 kg (362 lbm) -7.75

A.1.7 Oxygen Concentration Measurement

The experimental facility uses RM CEM O2/IQ analyzers manufactured by AMETEX/Thermox to 

measure oxygen concentration. The machines mainly consist of three basic systems: the 

plumbing, the measuring system, and the temperature system. The measuring element is a 

closed-end tube or disk made from ceramic zirconium oxide stabilized with an oxide of yttrium or 
79

calcium. Gases having different oxygen partial pressures on two sides of the cell will produce a 

potentiometric voltage. The magnitude of this voltage is a function of the ratio of the two oxygen 

partial pressures. Since a gas with reference oxygen concentration is contained on one side of 

the tube or disk, another oxygen concentration can be calculated (Ref. 8).

The operating range of the oxygen analyzer is 0.1-100% oxygen with an accuracy of ± 0.75% of 

readings or 0.05% O2 absolute. The response time is less than 4 seconds to 90% step response 

change and less than 2 seconds to 63% step response change at 0.94 L/min (2 scfh) from 2% 

to 20% O2. The maximum inlet temperature is 204 °

C (400 °F), sample pressure is ± 0.14 

kg/cm2 max (2 psig) and sample flow is 0.94 to 7.08 L/min (2 to 15 scfh) (Ref. 8).

For the transient tests, two oxygen analyzers are used to measure the oxygen concentrations at 

key locations in the facility. One is connected to the DC and another is connected to the upper 

DW. Since the sampling tubing used to transport gas from the DC and the DW to the machines 

is relatively long (DC machine tubing is 4.6 m [15 ft], DW machine tubing is 1.3 m [4.3 ft]), some 

heat belts are used to minimize heat loss in these pipes during the test. This is to prevent steam 

condensation inside the tubes, which could result in inaccurate measurements and damage to 

the machine. Also, the time necessary for gas to travel through these tubes to the sampling 

machine has been calculated and it has been considered in the data analysis.

The oxygen analyzers measure the oxygen concentration and transmit a 4 to 20 mA signal. The 

DAS measures the voltages across 250 Ω (± 0.1 Ω) resistors. The data conversion program 

converts the resulting 1 to 5 volt signals to 0 to 20.9% oxygen concentration, or 0 to 100% 

noncondensable gas concentration.

A.1.8 High-speed Video Camera

A high-speed camera (Model No. PHOTRON-FASCAM SA-3) with a maximum recording rate of 

10,000 frames per second (fps) is available at the PUMA-E facility. For the steady state tests, 

250 fps with a maximum recording time of around 9 seconds per recording is used. For the 

transient tests, 60 fps with a maximum recording time of around 9 seconds per recording is 

applied. The high-speed camera is applied to visualize the transient venting phenomena of the 

gas plume around the exit of the downcomer. Captured digital images can be transferred and 

recorded in the computer.

A.2 Instrumentation Location

This chapter describes the locations of important instruments for the steady state and transients 

tests. Figure A-10 shows various symbols used to portray components in the instrument location 

drawings for both tests.
80

Figure A-10 Symbols Used in Isometric Drawings for Instrument Location
81

A.2.1 Instrumentation Location for Steady State Tests

The locations of instrumentation for steady state tests in the SP are shown in Figure A-11. 

These instruments include two thermocouples (TE-SP-04, TE-SP-09), an absolute pressure 

gauge (PT-SP-01), and a differential pressure gauge (LT-SP-01) for water level measurement. 

A differential pressure gauge (LT-DC-01) between the air line connected to the SRV line and the 

gas space in the SP is installed to estimate the water level in the downcomer as shown in the 

figure.

Figure A-11 Locations of Pressure and Water Level Measurement in SP

The conductivity probe locations on the supporting cage, which are based on the distance from 

the center of the downcomer exit, are shown in Section A.5.

The locations of instruments in the air supply line are shown in Figure A-12. These instruments 

include two thermocouples (TE-AL-01, TE-AL-02), two absolute pressure gauges (PT-AL-01, 

PT-AL-02), and two vortex flow meters (FT-AL-01, FT-AL-02).
82

Figure A-12 Locations of Pressure, Temperature, and Air Flow Rate Measurement in the 

Air Supply Line

A.2.2 Instrumentation Location for Transient Tests

The locations of instrumentation in the DW are shown in Figure A-13. This instrumentation 

includes a pressure transmitter (PT-DW-01), three thermocouples (TE-DW-01, TE-DW-02 and 

TE-DW-09), and the oxygen analyzer (AI-DW-01).
83

Figure A-13 Locations of Instrumentation in the DW

The locations of instrumentation in the SP are shown in Figure A-14. This instrumentation 

includes two thermocouples (TE-SP-08 and TE-SP-09), the oxygen analyzer (AI-DC-01), the 

high-speed camera, and the conductivity probe cage.
84

Figure A-14 Locations of Instrumentation in the SP

The exact conductivity probe locations on the supporting cage in the SP are shown in Section 

A.5. The supporting cage is centered on the exit of the downcomer (for either size, 0.102 m or 

0.076 m [4 in. or 3 in.]).

The locations of the instrumentation in each break line are shown in Figures A-15 to A-18.
85

Figure A-15 DP-A Line from RPV to Drywell
86

Figure A-16 3” DP-B Line from RPV to Drywell
87

Figure A-17 3” MS-A Line from RPV to Drywell
88

FT-MSC-02 : 0.424’’ (10.76 mm) for the transient tests

Figure A-18 3” MSL-B and MSL-C Lines from RPV to Drywell

A.3 Data Acquisition System (DAS) and Valve Control System

The DAS for the steady state tests and transient tests is explained in this chapter. The same 

DAS for the conductivity probes and high-speed camera is used for the both tests. The DAS for 

other measurements is different between the steady state and transient tests.

A.3.1 DAS and Valve Control System for Steady State Tests

The data acquisition, valve control, and data processing are archived using three computers. 

The experimental data are stored in personal computers (PC) directly. The sampling rate is 

4666 Hz. Two National Instruments USB-6225 modules are used for the data acquisition. Each 

of the USB-6225 modules has the capability to handle 80 analog inputs.
89

PC#1 is mainly used to acquire data on pressure, temperature, air flow rate, some of the 

conductivity probes, and to control opening and closing of the pneumatic ball valve. PC#2 

acquires data from the remaining conductivity probes. PC#3 is mainly utilized to record flow 

visualization from the high-speed movie camera.

A.3.2 DAS and Valve Control System for Transient Tests

The data acquisition for the transients test has two different system. One is the DAS used for 

conductivity probes and high-speed camera. Another is the DAS used for other instruments and 

the control system.

A.3.2.1 DAS for Conductivity Probes and High-speed Camera

The data acquisition for conductivity probes and high-speed camera is archived using three 

computers. The conductivity probe data are stored in personal computers directly. The sampling 

rate is 3896 Hz. Two National Instruments USB-6225 modules are used for the data acquisition.

PC#1 and #2 acquire the data from the conductivity probes. PC#3 is mainly utilized to record 

flow visualization from the high-speed movie camera.

A.3.2.2 DAS for Other Instruments and Control System

The DAS for other instruments and the control system used to perform the transient tests was 

originally used in performing integral tests in the PUMA-E facility. The DAS for temperature and 

pressure, heater, and valve controls is based on a network of three personal computers. The 

sampling rate is 2 Hz or faster for all instruments. Data is stored directly in the hard disk of the 

sampling computer.

Keithly-Metrabyte A/D and D/A converter boards are used throughout the DAS. The main 

software for data acquisition is Labtech Notebook. Some software for data acquisition and the 

control modules were developed at Purdue and written in the C programming language. All of 

the software runs under the DOS or Windows platforms. Each PC works independently except 

for the initial trigger which is generated by the control PC (PC #6) or a human operator.

PC #4 is fully dedicated to acquiring the temperature data. Two DAS-801 boards and fourteen 

EXP-16 terminal boards are used. The software is Labtech. The sampling rate is 2 Hz.

PC #5 acquires the pressure, magnetic flow meter, oxygen concentration, heat flux, and vortex 

flow meter signals. The hardware and software are the same as those used for PC #4. The 

sampling rate is 5 Hz.

PC #6 is the control PC. It has a DAS-801 board with an EXP-16 terminal to input the narrow 

and wide range level signals from the RPV and the heater powers. It is controlled through a 

PIO-24 board with two SSIO-24 terminals. This computer controls the power to the three banks 

of heater rods and the timing signals for the test initiation and the ADS valve control.
90

A.4 List of Pressure, Water Level, Temperature, and Flow Measurements

Table A-2 Pressure and Level Measurements.

TAG 

NUMBER COMPONENT MEASUREMENT RANGE(Min)

RANGE

(Max) UNITS

PT-SP-01 SP Pressure 0 500 kPa

LT-SP-01 SP Diff.Pressure 0 33.718 kPa

PT-DW-01 DW Pressure 0 500 kPa

LT-DC-01 DOWNCOMER Diff.Pressure 0 5 kPa

PT-AL-01 AIR LINE Pressure 0 1500 kPa

PT-AL-02 AIR LINE Pressure 0 1500 kPa

Table A-3 Temperature Measurements.

TAG 

NUMBER COMPONENT MEASUREMENT RANGE(Min)

RANGE

(Max) UNITS

TE-SP-04 SP Temperature -200 1250 °C

TE-SP-08 SP Temperature -200 1250 °C

TE-SP-09 SP Temperature -200 1250 °C

TE-AL-01 2”AIR LINE Temperature -200 1250 °C

TE-AL-02 3⁄4”AIR LINE Temperature -200 1250 °C

TE-DW-01 DW Temperature -200 1250 °C

TE-DW-02 DW Temperature -200 1250 °C

Table A-4 Flow Measurement.

TAG 

NUMBER COMPONENT MEASUREMENT RANGE(Min)

RANGE

(Max) UNITS

FT-AL-01 2”AIR LINE FLOW RATE 7.95 692.8 m3/h

FT-AL-02 3⁄4”AIR LINE FLOW RATE 1.12 58.41 m3/h

FT-DPV-A 3” DP-A LINE FLOW RATE 0 500 kPa

FT-DPV-B 3” DP-B LINE FLOW RATE 0 500 kPa

FT-MS-A 3” MS-A LINE FLOW RATE 0 500 kPa

FT-MS-C 3” MS-C LINE FLOW RATE 0 500 kPa
91

A.5 List of Conductivity Probe Locations

The configuration of probe locations in each level is shown in Figure A-3 and Figures A-19 to 

A-27. Table A-5 shows the type and location of each conductivity probe. The axial and radial 

locations of probes are measured from the level of the downcomer exit. The red circles 

represent the single-sensor conductivity probes and the blue circles represent the double 

sensor probes.

Figure A-19 Configuration of Conductivity Probes on Level O 

(0.18 m [0.59 ft] above downcomer exit)
92

Figure A-20 Configuration of Conductivity Probes on Level A 

(0.08 m [0.26 ft] above downcomer exit)

Figure A-21 Configuration of Conductivity Probes on Level B

(0.02 m [0.07 ft] above the level of downcomer exit)
93

Figure A-22 Configuration of Conductivity Probes on Level C

(0.11 m [0.36 ft] below the level of downcomer exit)

Figure A-23 Configuration of Conductivity Probes on Level D

(0.21 m [0.69 ft] below the level of downcomer exit)
94

Figure A-24 Configuration of Conductivity Probes on Level E

(0.31 m [1.02 ft] below the level of downcomer exit)

Figure A-25 Configuration of Conductivity Probes on Level F

(0.41 m [1.35 ft] below the level of downcomer exit)
95

Figure A-26 Configuration of Conductivity Probes on Level G

(0.51 m [1.67 ft] below the Level of Downcomer Exit)

Figure A-27 Configuration of Conductivity Probes on Level H

(0.61 m [2.0 ft] below the Level of Downcomer Exit)
96

The axial location (h) “+” and “-” means the position of the probe is above or below the level of 

the downcomer exit, respectively. The radial location (r) is the distance from the vertical axis 

passing through the center of downcomer exit. The double-L and double-S mean the long and 

short tip of double-sensor conductivity probe, respectively. The azimuthal angle can be seen in

Figure A-3.

Table A-5 Type and Location of Conductivity Probes

TAG 

NUMBER

COMPONENT TYPE OF 

SENSOR

AXIAL

LOCATION

(m [in])

RADIAL

LOCATION

(m [in])

AZIMUTHAL 

ANGLE (°)

CE-ODS-01 CAGE Single +0.18 [+7.09] 0.3 [11.81] 90

CE-ODS-06 CAGE Single +0.18 [+7.09] 0.2 [7.87] 90

CE-AS-01 CAGE Single +0.08 [+3.15] 0.25 [9.84] 0

CE-AS-06 CAGE Single +0.08 [+3.15] 0.25 [9.84] 180

CE-AD-01 CAGE Double-L +0.08 [+3.15] 0.3 [11.81] 90

CE-AD-01s CAGE Double-S +0.08 [+3.15] 0.3 [11.81] 90

CE-ADS-02 CAGE Single +0.08 [+3.15] 0.25 [9.84] 90

CE-AD-03 CAGE Double-L +0.08 [+3.15] 0.2 [7.87] 90

CE-AD-03s CAGE Double-S +0.08 [+3.15] 0.2 [7.87] 90

CE-ADS-04 CAGE Single +0.08 [+3.15] 0.15 [5.91] 90

CE-AD-05 CAGE Double-L +0.08 [+3.15] 0.1 [3.94] 90

CE-AD-05s CAGE Double-S +0.08 [+3.15] 0.1 [3.94] 90

CE-ADS-10 CAGE Single +0.08 [+3.15] 0.25 [9.84] 270

CE-BS-02 CAGE Single -0.02 [-0.79] 0.15 [5.91] 0

CE-BS-03 CAGE Single -0.02 [-0.79] 0.05 [1.97] 0

CE-BS-04 CAGE Single -0.02 [-0.79] 0.05 [1.97] 180

CE-BS-05 CAGE Single -0.02 [-0.79] 0.15 [5.91] 180

CE-BD-01 CAGE Double-L -0.02 [-0.79] 0.3 [11.81] 90

CE-BD-01s CAGE Double-S -0.02 [-0.79] 0.3 [11.81] 90

CE-BDS-02 CAGE Single -0.02 [-0.79] 0.25 [9.84] 90

CE-BD-03 CAGE Double-L -0.02 [-0.79] 0.2 [7.87] 90

CE-BD-03s CAGE Double-S -0.02 [-0.79] 0.2 [7.87] 90

CE-BDS-04 CAGE Single -0.02 [-0.79] 0.15 [5.91] 90

CE-BD-05 CAGE Double-L -0.02 [-0.79] 0.1 [3.94] 90
97

Table A-5 (continued) Type and Location of Conductivity Probes

TAG 

NUMBER

COMPONENT TYPE OF 

SENSOR

AXIAL

LOCATION

(m [in])

RADIAL

LOCATION

(m [in])

AZIMUTHAL 

ANGLE (°)

CE-BD-05s CAGE Double-S -0.02 [-0.79] 0.1 [3.94] 90

CE-BDS-06 CAGE Single -0.02 [-0.79] 0.05 [1.97] 90

CE-BDS-08 CAGE Single -0.02 [-0.79] 0.05 [1.97] 270

CE-BDS-09 CAGE Single -0.02 [-0.79] 0.15 [5.91] 270

CE-CS-01 CAGE Single -0.11 [-4.33] 0.25 [9.84] 0

CE-CS-03 CAGE Single -0.11 [-4.33] 0.05 [1.97] 0

CE-CS-04 CAGE Single -0.11 [-4.33] 0.05 [1.97] 180

CE-CS-06 CAGE Single -0.11 [-4.33] 0.25 [9.84] 180

CE-CD-01 CAGE Double-L -0.11 [-4.33] 0.3 [11.81] 90

CE-CD-01s CAGE Double-S -0.11 [-4.33] 0.3 [11.81] 90

CE-CDS-02 CAGE Single -0.11 [-4.33] 0.25 [9.84] 90

CE-CD-03 CAGE Double-L -0.11 [-4.33] 0.2 [7.87] 90

CE-CD-03s CAGE Double-S -0.11 [-4.33] 0.2 [7.87] 90

CE-CDS-04 CAGE Single -0.11 [-4.33] 0.15 [5.91] 90

CE-CD-05 CAGE Double-L -0.11 [-4.33] 0.1 [3.94] 90

CE-CD-05s CAGE Double-S -0.11 [-4.33] 0.1 [3.94] 90

CE-CDS-06 CAGE Single -0.11 [-4.33] 0.05 [1.97] 90

CE-CD-07 CAGE Double-L -0.11 [-4.33] 0 [0.00] 90

CE-CD-07s CAGE Double-S -0.11 [-4.33] 0 [0.00] 90

CE-CDS-08 CAGE Single -0.11 [-4.33] 0.05 [1.97] 270

CE-CDS-10 CAGE Single -0.11 [-4.33] 0.25 [9.84] 270

CE-DS-02 CAGE Single -0.21 [-8.27] 0.15 [5.91] 0

CE-DS-03 CAGE Single -0.21 [-8.27] 0.05 [1.97] 0

CE-DS-04 CAGE Single -0.21 [-8.27] 0.05 [1.97] 180

CE-DS-05 CAGE Single -0.21 [-8.27] 0.15 [5.91] 180

CE-DD-01 CAGE Double-L -0.21 [-8.27] 0.3 [11.81] 90

CE-DD-01s CAGE Double-S -0.21 [-8.27] 0.3 [11.81] 90

CE-DDS-02 CAGE Single -0.21 [-8.27] 0.25 [9.84] 90

CE-DD-03 CAGE Double-L -0.21 [-8.27] 0.2 [7.87] 90

CE-DD-03s CAGE Double-S -0.21 [-8.27] 0.2 [7.87] 90

CE-DDS-04 CAGE Single -0.21 [-8.27] 0.15 [5.91] 90

CE-DD-05 CAGE Double-L -0.21 [-8.27] 0.1 [3.94] 90

CE-DD-05s CAGE Double-S -0.21 [-8.27] 0.1 [3.94] 90

CE-DDS-06 CAGE Single -0.21 [-8.27] 0.05 [1.97] 90

CE-DD-07 CAGE Double-L -0.21 [-8.27] 0 [0.00] 90

CE-DD-07s CAGE Double-S -0.21 [-8.27] 0 [0.00] 90
98

Table A-5 (continued) Type and Location of Conductivity Probes

TAG 

NUMBER

COMPONENT TYPE OF 

SENSOR

AXIAL

LOCATION

(m [in])

RADIAL

LOCATION

(m [in])

AZIMUTHAL 

ANGLE (°)

CE-DDS-08 CAGE Single -0.21 [-8.27] 0.05 [1.97] 270

CE-DDS-09 CAGE Single -0.21 [-8.27] 0.15 [5.91] 270

CE-ES-01 CAGE Single -0.31 [-12.20] 0.25 [9.84] 0

CE-ES-03 CAGE Single -0.31 [-12.20] 0.05 [1.97] 0

CE-ES-04 CAGE Single -0.31 [-12.20] 0.05 [1.97] 180

CE-ES-06 CAGE Single -0.31 [-12.20] 0.25 [9.84] 180

CE-ED-01 CAGE Double-L -0.31 [-12.20] 0.3 [11.81] 90

CE-ED-01s CAGE Double-S -0.31 [-12.20] 0.3 [11.81] 90

CE-EDS-02 CAGE Single -0.31 [-12.20] 0.25 [9.84] 90

CE-ED-03 CAGE Double-L -0.31 [-12.20] 0.2 [7.87] 90

CE-ED-03s CAGE Double-S -0.31 [-12.20] 0.2 [7.87] 90

CE-EDS-04 CAGE Single -0.31 [-12.20] 0.15 [5.91] 90

CE-ED-05 CAGE Double-L -0.31 [-12.20] 0.1 [3.94] 90

CE-ED-05s CAGE Double-S -0.31 [-12.20] 0.1 [3.94] 90

CE-EDS-06 CAGE Single -0.31 [-12.20] 0.05 [1.97] 90

CE-ED-07 CAGE Double-L -0.31 [-12.20] 0 [0.00] 90

CE-ED-07s CAGE Double-S -0.31 [-12.20] 0 [0.00] 90

CE-EDS-08 CAGE Single -0.31 [-12.20] 0.05 [1.97] 270

CE-EDS-10 CAGE Single -0.31 [-12.20] 0.25 [9.84] 270

CE-FS-02 CAGE Single -0.41 [-16.14] 0.15 [5.91] 0

CE-FS-03 CAGE Single -0.41 [-16.14] 0.05 [1.97] 0

CE-FS-04 CAGE Single -0.41 [-16.14] 0.05 [1.97] 180

CE-FS-05 CAGE Single -0.41 [-16.14] 0.15 [5.91] 180

CE-FD-01 CAGE Double-L -0.41 [-16.14] 0.3 [11.81] 90

CE-FD-01s CAGE Double-S -0.41 [-16.14] 0.3 [11.81] 90

CE-FDS-02 CAGE Single -0.41 [-16.14] 0.25 [9.84] 90

CE-FD-03 CAGE Double-L -0.41 [-16.14] 0.2 [7.87] 90

CE-FD-03s CAGE Double-S -0.41 [-16.14] 0.2 [7.87] 90

CE-FDS-04 CAGE Single -0.41 [-16.14] 0.15 [5.91] 90

CE-FD-05 CAGE Double-L -0.41 [-16.14] 0.1 [3.94] 90

CE-FD-05s CAGE Double-S -0.41 [-16.14] 0.1 [3.94] 90

CE-FDS-06 CAGE Single -0.41 [-16.14] 0.05 [1.97] 90

CE-FD-07 CAGE Double-L -0.41 [-16.14] 0 [0.00] 90

CE-FD-07s CAGE Double-S -0.41 [-16.14] 0 [0.00] 90

CE-FDS-08 CAGE Single -0.41 [-16.14] 0.05 [1.97] 270

CE-FDS-09 CAGE Single -0.41 [-16.14] 0.15 [5.91] 270
99

Table A-5 (continued) Type and Location of Conductivity Probes

TAG 

NUMBER

COMPONENT TYPE OF 

SENSOR

AXIAL

LOCATION

(m [in])

RADIAL

LOCATION

(m [in])

AZIMUTHAL 

ANGLE (°)

CE-GD-03 CAGE Double-L -0.51 [-20.08] 0.2 [7.87] 90

CE-GD-03s CAGE Double-S -0.51 [-20.08] 0.2 [7.87] 90

CE-GDS-04 CAGE Single -0.51 [-20.08] 0.15 [5.91] 90

CE-GD-05 CAGE Double-L -0.51 [-20.08] 0.1 [3.94] 90

CE-GD-05s CAGE Double-S -0.51 [-20.08] 0.1 [3.94] 90

CE-GDS-06 CAGE Single -0.51 [-20.08] 0.15 [5.91] 90

CE-GD-07 CAGE Double-L -0.51 [-20.08] 0 [0.00] 90

CE-GD-07s CAGE Double-S -0.51 [-20.08] 0 [0.00] 90

CE-HDS-07 CAGE Single -0.61 [-24.02] 0 [0.00] 90

101

APPENDIX B. TEST PROCEDURES

B.1 Steady State Tests

To ensure the quality of the experimental data, the following steps are performed before running 

the experiments for each test condition:

A. Test facility checking and valve adjustment

1. Check water level (nominal water level 1.05 m [3.44 ft]).

2. Check the manual valve positions for the air injection line (V-AL-01 closed, V-AL-02 

closed, V-AL-05 opened, V-AL-06 closed).

3. Check the air supply pressure at air compressor (>130 psig [997.7 kPa]).

4. Adjust the needle valve positions (opening and closing) of pneumatic actuator 

(VM-AL-01) to the required position. 

B. Instrument and DAS program preparation

1. Open the DAS program.

2. Check the input parameters in the DAS program such as the data sampling rate, 

bypass valve (VM-AL-02) opening time, and data acquisition time.

3. Adjust the pneumatic actuator valves to the default position (VM-AL-01 and 

VM-AL-02 closed) using the DAS program.

4. Check all instrument readings from DAS control program.

C. Confirmation of high-speed video camera and movie-recording program

1. Open the movie recording program and check program working status.

2. Adjust the focus of the lens and the aperture size of the camera.

3. Check the input parameters in the movie-recording program such as frame size, fps, 

shutter speed, etc.

After completing the above procedures from A to C, the following steps are performed to start 

the experiment.

1. Adjust void condition in the downcomer section by opening the manual valve V-AL-02 

until it reaches the required water level based on visual observation (only for partial void 

test conditions).

2. Initialize the test by executing the DAS program to open VM-AL-02 initially and open 

VM-AL-01 later while closing VM-AL-02.

3. The DAS program starts to record the experimental data after the signal to open 

VM-AL-01 is activated (time at 0 second). Simultaneously, the movie-recording program 

initiates to capture the high-speed video for around 10 seconds with 250 fps recording.

After about 30 seconds, VM-AL-01 is closed by the DAS program and recording of experimental 

data is terminated accordingly.

B.1.1 Test Initiation Time

The test is initiated by the DAS program which sends the electrical signal to open the main 

supply valve (VM-AL-02) and initialize the high-speed camera simultaneously. However, due to 

electronic system limitations, the starting times of DAS and high-speed camera have some 
102

difference. Table B-1 represents the test initiation point for the high-speed camera and the DAS. 

For the high-speed camera, test initiation happens when the air-water interface arrives at the 

downcomer exit. For the DAS, test initiation occurs when the single-sensor conductivity probe 

located at the downcomer exit responds to the phase change. This should be considered when 

interpreting the test results.

Table B-1 Test Initiation Time at DAS and High-speed Camera Time Frames.

Test No. Test Initiation Time (second)

DAS Time Camera Time

A1 1.50 1.08

A2 1.50 1.07

A3 1.50 1.10

A4 4.49 4.02

A5 1.50 1.04

A6 1.50 1.02

A7 1.50 1.04

A8 1.86 1.09

A9 1.50 1.11

A10 1.50 1.01

A11 1.53 1.17

A12 6.00 5.74

A13 1.50 1.15

A14 1.50 1.14

A15 1.50 1.16

A16 1.50 1.19

B.2 Transient Tests

To ensure the quality of the experimental data, the following steps are performed before running 

the experiments for each test condition:

A. Test facility conditions and valve adjustment

1. Purge instrumentation racks.

2. Ensure air compressor is on and air supply pressure is ≥130 psig (997.7 kPa).

3. Set up location of high-speed camera and turn on SP lighting.

4. Isolate PCCS, ICS, and GD from DW and SP.

5. Set up oxygen analyzers for both the DW and downcomer.

6. Adjust SP water and gas space temperature to 37 °C ± 1 °C (98.6 °F ± 1.8 °F) .

7. Adjust SP water level to ~1.05 m (~3.44 ft) and confirm visually through SP view port 

(water should touch horizontal marker on downcomer).

8. Vent SP / confirm SP pressure ~0 psig (~101 kPa).

9. Drain DW / confirm DW is empty.

10. Vent DW / confirm DW ~0 psig (~101 kPa).
103

11. Fill RPV with water to ~2.8 meters (~9.2 ft).

12. Turn on RPV camera fans, RPV cameras, and camera monitors.

13. Close RPV heater breakers and heat up RPV to 10 psig (170 kPa).

14. Vent noncondensable gases from the RPV and ensure even RPV heating.

15. Heat RPV to ~130 psig (~998 kPa).

16. Heat DW using heated compressed air to 65 °C (+ 2 °C - 1 °C)1

(149 °F [+ 3.6 °F - 1.8 °F]).

17. Adjust SP Pressure to approximately 1.8 psig (+1 psi) (113.8 kPa [± 6.9 kPa]).

18. Open manual valves on the appropriate Main Steam / DPV lines:

Test Case Manual Valves

2 DPV MS-A

3 DPV MS-A

MS-C

5 DPV DPV 

MS- C

B. Instrument and DAS program preparation

1. Open the DAS programs.

2. Check all instruments readings from DAS control program.

C. Confirmation of high-speed video camera and movie-recording program

1. Open the movie recording program and check program working status.

2. Adjust the focus of the lens and the aperture size of camera.

3. Check the input parameters in the movie-recording program such as frame size, 

frames per second, shutter speed, etc.

After completing the above procedures from A to C, the following steps are performed to start 

the experiment:

1. Adjust water level in the downcomer section by cycling the motor-operated DW vents.

2. Position the appropriate DPV valves in AUTO:

Test Case DPV

2 DPV MS-A

3 DPV MS-A

MS-C

5 DPV DPV 

MS- C

3. Initialize the test by executing the RPV heater computer program.

 1 For the 5 DPV - 80% noncondensable gas tests, use steam from the RPV for final heating 

rather than air. Blowdown for approximately 10 seconds to achieve 80% initial noncondensable 

concentration.
104

4. Trigger the DAS programs to record data once the RPV is pressurized to 134 psig (1024 

kPa) by the RPV heater computer program.

5. Initiate the movie-recording program and divide the recording into 5 partitions. Each 

partition is approximately 9 seconds of recording length. High-speed movie recordings 

are to be made at

Movie

Partition

Elapsed Test 

Time (seconds)

Test Period

1 0 Initial

2 30 Stabilizing

3 60 Steady State

4 300 Steady State (2DPV / 3DPV) / 

Onset of Chugging (5DPV / 5DPV - 80%)

5 540 Chugging

6. Record data for 10 minutes.
105

B.2.1 Test Initiation Time

The test is initiated by the DAS program which sends an electrical signal to open the 

appropriate steam lines. The high-speed camera is initiated by a human operator when the RPV 

pressure reaches 1024 kPa (134.0 psig). This causes the starting times of DAS and high-speed

camera to have some differences. Table B-2 represents this time difference between the 

high-speed camera and the DAS for the initial period. The data provided in this table can be 

useful to compare trends between the DAS and high-speed camera.

Table B-2 Approximate Difference between DAS and High-speed Camera Time 

Frames for the Initial Period.

Test No. Time Comparison (seconds)

DAS Time Camera Time

T1 6.22 1.80

T2 5.82 3.53

T3 5.25 3.30

T4 5.87 3.57

T5 5.52 3.18

T6 6.17 5.53

T7 5.42 1.65

T8 4.58 3.83

107

APPENDIX C. UNCERTAINTY ANALYSIS

C.1 Introduction

The uncertainty analysis presented here is based on the methods outlined in NUREG/CR 6309

(Ref. 3). The error propagation analysis is derived using a combination of errors obtained from 

the instrument specifications and in-house calibration data. The analysis is performed at the 

95% confidence level, which is equivalent to two standard deviations.

The uncertainty determinations are discussed in detail in the following sections, with one section 

devoted to each of the specific instrument types. Note that for the transient and steady state

tests, a different board was used in the data acquisition systems. Thus, for the steady state

tests (using a NI-USB-6225 board) and the transient tests (using a NI-USB-6225 board for 

conductivity probes and a EXP-16 board for other parameters), there is a small difference in 

overall uncertainty.

The methodology used in this uncertainty analysis is that recommended by the ASME 

Performance Test Codes Supervisory Committee 19.1 (Ref. 9). Nomenclature used in this 

analysis include: precision index, S, which is a measure of the calibration scatter about the 

mean; bias limit, B, which is a measure of the difference between the mean of the calibration 

data and the standard; the 95th percentile point for the two-tailed Student t distribution, t; and the 

precision error, P, which is the product of t and S. The root sum square (RSS) of the 

components of the bias limit results in the overall bias limit for the measurement. The RSS of 

the precision errors results in the overall precision error for the measurement. The overall 

uncertainty, U, for a specific measurement is the RSS of the bias limit and the precision error. 

That is

( )

1/ 2 2 Btotal = ΣBt (C.1)

( ( ) )

1/ 2 2 t

total P = Σ tS (C.2)

( )

1/ 2 2 2 URSS = Btotal + Ptotal (C.3)

C.2 K-Type Thermocouples

Based on the information obtained from The Temperature Handbook, OMEGA Engineering, 

Inc., Vol 27, p. H-4, the thermocouple “Limit of Error” is ± 2.2 °C (± 4.0 °F) or ± 0.75% of 

reading, whichever is greater. Since 0.75% of 180 °C (356 °F) (maximum expected 

temperature) is 1.4 °C, ± 2.2 °C (2.5 °F, ± 4 °F) was used as limit of error. This limit is defined 

by ANSI - MC96.1 which states that no thermocouples may exceed it. Therefore it may be 

assumed that the uncertainty is at the 95% confidence level (i.e.: two standard deviations). The 

output from each thermocouple is fed into a data acquisition board. For the transient tests, 

EXP-16, a 16-channel multiplexer and signal conditioning board, was used with the gain setting 

for this board at 200. For the steady state tests, a NI-USB-6225 board was adopted.
108

One of the principal uncertainties associated with the use of the data acquisition board is the 

“Peak-to-peak noise level,” or the electronic noise imposed on the signal. The noise level is a 

function of the specific transducer (for example Type K thermocouple) and amplifier gain setting. 

The specifications for this board do not list the noise level for a Type K thermocouple with the 

corresponding gain setting. The peak-to-peak noise level was obtained experimentally. The 

average standard deviation for 26 thermocouple channels is 0.41 °C (0.74 °F)for the transient 

tests and 0.75 °C (1.35 °F) for the steady state tests.

The bias for the DAS boards, including the effect of cold junction compensation, is set by 

calibration. The criterion is that the standard deviation will be kept below 1 °C (1.8 °F). This 

calibration is performed for two thermocouples per board and includes the uncertainties of the 

wiring.

For the transient tests, performing a RSS of the two precision components (from the 

thermocouples and the peak-to-peak noise in the EXP-16 boards) and using a student t value of 

2.0 (i.e.: two standard deviations) the precision error is Ptotal = 2.35 °C (4.23 °F). The overall bias 

is Btotal = 2.0 °C (3.6 °F), and the uncertainty is U = 3.1 °C (5.6 °F).

For the steady state tests, performing a RSS of the two precision components (from the 

thermocouples and the peak-to-peak noise in the NI_USB_6225 boards) and using a student t

value of 2.0 (i.e.: two standard deviations) the precision error is Ptotal = 2.66 °C (4.79 °F). The 

overall bias is Btotal = 2.0 °C (3.6 °F), and the uncertainty is U = 3.3 °C (5.9 °F).

C.3 Pressure and Differential Pressure Measurements

The facility uses pressure transducers manufactured by Honeywell for all pressure and 

differential pressure measurements. These transducers are designed to measure pressure over 

a specific range:

• STD924 - 0-1 bar (0-14.7 psi) [“ST 3000 Series 900 Smart Transmitter Differential 

Pressure Model STD924” Honeywell Specification 34-ST-03-35, 4/92]

• STD930 - 0-7 bar (0-103 psi) [“ST 3000 Series 900 Smart Transmitter Differential 

Pressure Model STD930” Honeywell Specification 34-ST-03-36, 7/92]

• STG944 - 0-35 bar (0-515 psig) [“ST 3000 Series 900 Smart Transmitter Differential 

Pressure Model STG974” Honeywell Specification 34-ST-03-37, 7/92].

Each transducer is discussed, in turn, in the following sections. For all of the applications using 

the STD differential pressure transducers, it is assumed that the electronics are far enough 

away from any high temperatures that they are at ambient temperature. The transducers are 

designed so that this is relatively easy to accomplish and by doing so the “Combined Zero and 

Span Temperature Effect” is neglected. If the installation results in the transducer temperature 

exceeding 21°C (70°F), then an additional error is introduced and would have to be quantified. 

This would add ~ 0.4% of the upper range value to the bias error associated with each 

transducer for each 28°C (50°F) increase.
109

C.3.1 STD924

The PUMA instrumentation uses the STD924 transducer to measure either gage pressure or 

differential pressure over eight ranges, depending on the specific application. Honeywell 

Specification 34-ST-03-35, 7/92 lists the accuracy for this transducer to be ± 0.1% of either the 

calibrated span or the upper range value, whichever is greater. Here the calibrated span is 

defined as 25% of the Upper Range Limit. The Upper Range Limit for this transducer is 100 kPa 

(400 inch H2O) and the calibrated span is 25 kPa (100 inch H2O). Therefore, for any PUMA 

application with an upper range value (maximum pressure to be measured) less than 25 kPa, 

the accuracy is ± 25 Pa (± 0.1 in H2O). Where the maximum pressure exceeds 25 kPa, the 

accuracy is ± 0.1% of this maximum pressure. This accuracy is treated as a bias error, in 

accordance with ANSI/ASME PTC 19.1.

The output from an STD924 transducer is fed into a multiplexer and signal shaper. The STD924 

output is a 4-20 mA signal that is measured across a 250 Ω ± 0.1% output resistor, resulting in a 

1 - 5 V input signal for the multiplexer. For the transient tests, the multiplexer gain is set at 1. At 

this setting, the linearity uncertainty (bias) is ± 0.015% of the maximum pressure and the 

peak-to-peak noise (precision) is ± 0.14% of the maximum pressure. (Ref. 10) while for the 

steady state tests, both the linearity uncertainty (± 0.016% of the maximum pressure) and 

peak-to-peak noise (± 0.125% of the maximum pressure) were obtained experimentally. 

The output from the multiplexer is input into the DAS-801 analog-to-digital converter. There are 

four sources of measurement error associated with this board: gain accuracy, linearity, gain 

stability, and zero stability. The gain accuracy, for an input signal of 5 V, is ± 1.25% of the upper 

range value. The linearity is ± 1.2% of the upper range value. Both of these are bias errors. The 

two sources of precision error are the gain stability, 50 ppm of the upper range value, and zero 

stability, 20 ppm of the upper range value.

Finally, these errors are summed, in accordance with Equations C.1 – C.3. In general, the 

uncertainty is ~ 1.7% of the upper range value for the transient tests and ~ 1.8% of the upper 

range value for the steady state tests, independent of the span being measured. These 

uncertainties only include the transducer and associated electronics errors. Specifically 

excluded are uncertainties associated with the use of the pressure measurement to infer global 

conditions - for example, the use of the differential pressure measurement to infer liquid level, 

which should also include uncertainties associated with the potential for voiding in the sensor 

line.

C.3.2 STG944

These are used to measure pressure over the pressure range of 0 – 1.5 MPa (0 - 218 psi). 

Based on the maximum pressure to be measured, the (bias) accuracy for this transducer is ±

3.2 kPa (0.46 psi). For the transient tests, the linearity and peak-to-peak noise uncertainties for 

the EXP-16 multiplexer are ± 150 Pa (0.022 psi) and ± 1.4 kPa (0.20 psi), respectively. For the 

steady state tests, the linearity and peak-to-peak noise uncertainties for the NI-USB-6225 

multiplexer are ± 37.5 Pa (5.44x10-3 psi) and ± 1.25 kPa (0.181 psi), respectively. The two bias 

contributions for the DAS801 ADC (gain accuracy and linearity) are ± 12.5 kPa (± 1.81 psi) and 
110

± 12.0 kPa (± 1.74 psi), respectively. The two precision components for this board (gain stability 

and zero stability) are ± 50 Pa (± 7.25x10-3 psi) and ± 20 Pa (± 2.9x10-3 psi), respectively. The 

overall uncertainty associated with this transducer is ± 18 kPa (± 2.6 psi) or ~ 1.8% of the upper 

range value for the transient tests and ± 18 kPa (± 2.6 psi) or ~ 1.8% of the upper range value 

for the steady state tests. To reduce the uncertainties of key measurements, like reactor vessel 

levels and absolute pressures of the main vessels, many pressure transducers were calibrated 

in-house. 

C.4 Flow Measurements

Vortex flow meter model 84W, manufactured by Foxboro, is used in the PUMA facility. This 

transducer works on the principle that a disturbance in the flow field will generate vortices, the 

number of which is proportional to the flow rate. Therefore, the flow can be measured by 

counting the number of vortices per unit time.

These flow meters measure gas velocities in the range of 1.5 m/s to 120.5 m/s (4.9 ft/s to 

395 ft/s). They have an accuracy of ± 1.0 m/s (± 3.3 ft/s). The NI_USB_6225 multiplexer has 

linearity (bias) of ± 0.064 m/s (± 0.21 ft/s) and a peak-to-peak noise level (precision) of ± 0.32 

m/s (± 1.1 ft/s). The DAS801 ADC has a gain accuracy and linearity (both bias) components of 

± 0.51 m/s and ± 0.49 m/s (± 1.7 ft/s and ± 1.6 ft/s), respectively. This board has a gain stability 

and zero stability (both precision) components of ± 0.002 m/s and 0.008 m/s (± 0.01 ft/s and ±

0.03 ft/s), respectively. This results in an overall uncertainty of ± 2.2 m/s (± 7.2 ft/s) or 1.2% of 

the upper range value.

C.5 Oxygen Analyzer (only used in the transient tests)

Three oxygen analyzers are installed in the PUMA facility and are used to measure oxygen 

concentrations in the DW, pressure suppression chamber, and passive containment cooling 

system/isolation condenser system. The oxygen sensor is the Thermox RM CEM O2/IQ; 

Extractive Zirconium Oxide Oxygen Analyzer manufactured by AMETEK (Ref. 8). This 

transducer measures oxygen concentrations over a range of 0 ~ 21%. The transducer accuracy 

is ± 0.05% O2 concentration or ± 0.75% of reading, whichever is greater. Since the upper range 

limit is 21%, the accuracy was chosen to be ± 0.16% O2, and this was assumed to be a bias 

uncertainty. For this range of oxygen concentrations, the EXP-16 multiplexer linearity is ±

0.003% O2 (bias) and the peak-to-peak noise is ± 0.029% O2. The DAS-801 ADC uncertainties 

are ± 0.26 and ± 0.025% O2 for the gain accuracy and linearity (both bias) and ± 0.001 and 

± 0.004% O2 for the gain stability and zero stability (both precision) components, respectively. 

The overall uncertainty for this measurement, including both bias and precision components for 

the transducer and electronics, is ± 0.2% O2.
111

REFERENCES

1. NUREG-0408, “Mark I containment Short Term Program – Safety Evaluation Report,” U.S. 

Nuclear Regulatory Commission, Washington, DC, December, 1977.

2 Lahey, R. T. Jr., and F. J. Moody, “The Thermal-Hydraulics of a Boiling Water Nuclear 

Reactor,” 2nd ed. La Grange Park, IL: American Nuclear Society, 1993.

3. NUREG/CR-6309, “Scientific Design of Purdue University Multi-Dimensional Integral Test 

Assembly (PUMA) for GE SBWR,” U.S. Nuclear Regulatory Commission, Washington, DC, 

1996.

4. U.S. Nuclear Regulatory Commission, A. Velazquez, “Technical Assessment GSI-193, 

BWR ECCS Suction Concerns, Geometrical and Operation Characteristics Effecting the 

Ingress of Noncondensable gases in the BWR ECCS System During HELB Accident”, 2010 

(available in ADAMS under Accession #ML102460492).

5. U.S. Nuclear Regulatory Commission, “Rev. 11 of TI 2515177 Inspection Guidance”, 

2011 (available in ADAMS under Accession #ML111660749).

6 T. Hibiki, S. Hogsett, and M. Ishii, “Local Measurement of Interfacial Area, Interfacial 

Velocity and Liquid Turbulence in Two-Phase Flow,” Nucl. Eng. Des. 184 (1998) 287-304.

7. ASME, “Fluid Meters: Their Theory and Application,” 1971.

8. AMETEK Corp., “Thermox RM CEM 02/IQ Extractive Zirconium Oxide Oxygen Analyzer” 

Technical Specification Manual, October 2005.

9. ANSI/ASME PTC 19.1, “Part 1: Measurement Uncertainty - Instruments and Apparatus,” 

American National Standards Institute / American Society of Mechanical Engineers, 1985.

10. Keithley MetraByte, Data Acquisition Catalog & Reference Guide, Taunton, MA, 1994 -

1995.




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