Liquid metal cooled reactors are considered one of the most promising nuclear reactor concepts in the frame of Generation IV systems to be commercialized in the next decades.

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I

ABSTRACT

Liquid metal cooled reactors are considered one of the most promising nuclear reactor concepts in the frame of Generation IV systems to be commercialized in the next decades.

The interest for liquid metal coolants, in particular sodium, lead and lead-bismuth eutectic (LBE), is based on their thermal and nuclear properties that allow at having systems able to safely remove heat without appreciable “softening” of the neutron energy spectrum. As a consequence, their adoption might provide a better exploiting of the fuel. In addition, liquid metal cooled systems are potentially capable of trasmuting Minor Actinides and long lived radionuclides, thus representing a possible contribution to the solution of nuclear waste problem.

Furthermore, a huge experience has already gained in liquid metal technologies because both sodium and heavy liquid metals have been already used as coolant in fast breeder reactors.

For future reactors cooled by molten metals one of the most important safety issues, which is also one of the major challenges, is the interaction between water and LBE or lead (Coolant-Coolant Interaction, CCI) during postulated steam generator tube failures and the expansion phase of bubbles in sodium cooled fast reactors, generated by the interaction of fuel with the sodium coolant (Fuel-Coolant Interaction, FCI) in case of Core Disruptive Accident (CDA).

Both CCI and FCI represent a threat for the integrity of the reactor’s structure, even though their likelihood of occurrence is relatively small. In fact, during the interaction, a huge amount of heat is transferred from the material at higher temperature (heavy liquid metal or melted fuel) to the colder material (water or sodium) in a very short timescale. Two threatening phenomena can result from interaction.

The first one is the formation of shock waves that can damage the inner structures of the reactor and, in the particular case of heavy liquid metal reactors, might cause a sort of “chain effect” damaging other steam generator tubes.

The second one is due to the rapid heat transfer rate that allows the hotter material to solidify and vaporizes the colder material, too. The vapour formed moves upwards compressing the cover gas region and increasing the pressure (expansion phase), resulting in another threat for structure integrity.

The aim of this study is addressed to analyse and simulate the phenomena involved in CCI and FCI, with particular attention to the evaluation of the energy released in such interactions, in order to have the possibility of estimating the potential loads and the resulting damage on reactor structures.

A scientific cooperation between ENEA Brasimone Research Centre and University of Pisa has been set up, in the frame of IP-EUROTRANS and ELSY FP6 Projects, concerning the heavy liquid metal-water interaction.

In particular, the activity of University of Pisa has been focused on the simulation by the SIMMER III code of the experiments performed at ENEA Brasimone with LIFUS 5 facility. This activity has been aimed at characterizing further the interaction between heavy liquid metal and water in order to understand which conditions might lead to serious consequences for reactors.

The use of existing tools for the analysis of energy release and the development of

new ones based on existing theoretical models constituted a further contribution

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II

provided by this study. This topic is crucial because of the lack of representative experimental data.

Regarding the activity focused on sodium fast reactors, an experimental campaign called SGI, which was performed in 1994 in Forschungszentrum Karlsruhe (now KIT), have been chosen. This choice is motivated because the injection of a high pressure gas into a stagnant liquid pool is a characteristic phenomena taking place during the expansion phase of a CDA.

SGI campaign has been simulated again with SIMMER III code, thus contributing

to its further qualification by the numerous experimental data available, except for

the energy release.

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III

AKNOWLEDGMENTS

After the years of research at the University of Pisa and at Karlsruhe Institute of Technology (KIT), Germany,I would like to thank many people who contributed to the research and helped at finalizing this work.

In particular, I would like to thank Prof. Francesco Oriolo, Prof. Walter Ambrosini and Dr. Nicola Forgione for being my supervisors and for their assistance, kindness and patience despite my stay abroad.

Thanks are due to Dr. Werner Maschek for his full support, willingness, suggestions and for giving me the possibility to belong to a great group of research.

This work would not be possible without the precious contribution of Michael Flad who has patiently and kindly helped me in overcoming many technical problems during these years, in discussing and revising my work.

Huge thanks go to Dr. Edgar Kiefhaber for his valuable advices and for discussing problems during the revision of my thesis.

I appreciate the cooperation with the colleagues and friends of the ENEA Brasimone Research Centre and in particular Dr. Andrea Ciampichetti, Dr. Mariano Tarantino and Dr. Marco Utili.

I thank my friends and colleagues and in particular Barbara, Fabrizio, Angelica, Claudia, Vladimir, Marina for their friendship and help.

Special thanks go to Sebastian who has stood me during these hard months.

All my gratitude goes to my parents, who always fully supported and trust me

staying by my side in the good and in the bad times.

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IV

To my beloved

parents

Alberto e Graziella

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V

1. INTRODUCTION ...1

1.1 General Background ... 1

1.2 Motivation for the present work ... 4

1.3 Outline of the present work ... 5

REFERENCES ... 7

2. LIQUID METALS AS REACTOR COOLANTS ... 9

2.1 Introduction ... 9

2.2 Motivations for choosing liquid metals ... 10

2.3 Characteristics of liquid metals ... 16

2.4 Ongoing R&D activities ... 27

REFERENCES ... 30

3. PHENOMENA INVOLVING ENERGETIC RELEASES FROM MOLTEN METAL COOLANT INTERACTIONS ... 33

3.1 Phenomenology of thermal interaction between fluids in liquid metal reactors ... 33

3.2 Main contact modes ... 37

3.3 Theoretical Models ... 38

3.1 Spontaneous nucleation theory ... 38

3.2 Thermal detonation theory... 43

3.4 Vapor Explosion Modeling ... 47

4.1 TNT equivalence model... 47

4.2 Superheat limit explosion ... 48

4.3 Thermodynamic models ... 49

3.1 Specific final ambient pressure expansion... 50

3.2 Specific final volume expansion ... 52

3.3 Hall model... 52

4.4 Parametric models ... 54

4.1 Cho-Wright model... 54

4.2 Caldarola model ... 56

4.5 Mechanistic propagation models ... 57

5.1 Board and Hall shock adiabatic model... 57

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VI

3.5 Energy conversion efficiency and the problem of energy

scaling ... 59

3.6 Comparison between FCI and CCI ... 64

3.7 SIMMER III Code: Main Features ... 68

7.1 Code Framework ... 68

7.2 Fluid-dynamics model... 72

7.3 Structure model ... 76

7.4 Neutronic model ... 77

7.5 Code Assessment ... 77

3.8 Concluding remarks ... 78

REFERENCES ... 80

4. ANALYSIS OF LIFUS EXPERIMENTS ... 87

4.1 Introduction ... 87

4.2 Experimental activity ... 87

2.1 Original configuration of the facility and Test n.1 conditions 87 2.2 Changes to the facility and operating conditions for the other experiments ... 91

2.1 Test n.2 ... 91

2.2 Test n. 3, n. 4 and Test n.1 and n.2 for ELSY Program ... 92

4.3 Numerical simulation and comparison with experimental results ... 95

3.1 Geometrical model development and code qualification ... 95

1.1 Test n.1 ... 95

1.2 Test n.2 ... 100

1.3 Test n. 3, n. 4 ... 104

1.4 Test n.1 and n.2 for ELSY Program ... 110

3.1 Concluding remarks of the model qualification activity ... 115

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VII

4.4 Analysis of the phenomena involved in LBE-water

interaction... 115

4.1 Concluding remarks of Concluding remarks of analysis of the LBE-water interaction ... 132

4.5 Energy evaluation ... 132

5.1 The isentropic model... 132

5.2 BFCAL ... 142

5.3 Energetic evaluation of the experiments ... 143

4.6 Concluding remarks ... 147

REFERENCES ... 149

5. ANALYSYS OF TESTS FROM THE SGI CAMPAIGN ... 151

5.1 Introduction ... 151

5.2 Experimental facility ... 152

5.3 Geometrical model development and code qualification 155 3.1 SIMMER III geometrical domain ... 156

3.2 Main results ... 142

5.4 Energy evaluation ... 166

4.1 Analysis of the tests considered ... 167

5.5 Concluding remarks ... 176

REFERENCES ... 149

6. CONCLUSIONS ... 179

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VIII

NOMENCLATURE

Acronyms

ADS Accelerator-Driven System

ASTRID Advanced Sodium Technological Reactor for Industrial Demonstration

BR-2 Breeding Reactor 2 CCI Coolant-Coolant Interaction CDA Core Disruptive Accident

CDFR Chinese Demonstrator Fast Reactor CEA Commisariat Energie Atomique (France) CFD Computational Fluid Dynamics

CEFR Chinese Experimental Fast Reactor CIAE China Institute of Atomic Energy CIRCE Circolazione Eutettico

CJ Chapman-Jouguet Point

DEMETRA DEvelopment and Assessment of Structural Materials and Heavy Liquid MEtal Technologies for TRAnsmutation Systems

DFR Dounreay Fast Reactor

DOE Department of Energy’s Office - Nuclear Energy, Science and Technology

EBR Experimental Breeder Reactor EDF Electricité De France

ELSY European Lead-cooled SYstem

ENEA Ente per le Nuove Tecnologie, l’ Energia e l’Ambiente (Italy)

EOS Equation Of State

ESFR European Sodium Fast Reactor

ESNII European Sustainable Nuclear Industrial Initiative FBTR Fast Breeder Test Reactor

FCI Fuel-Coolant Interaction FFTF Fast Flux Test Facility

FZK Forschungszentrum Karlsruhe

GEN IV Generation IV systems

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IX GIF Generation IV International Forum

HLMRs Heavy Liquid Metal Reactors

HLM Heavy Liquid Metal

HLW High Level Waste

ICE Integral Circulation Experiments IFR Integral Fast Reactor

IP-EUROTRANS EUROpean Research Program for the TRANSmutation of High Level Nuclear Waste in an Accelerator Driven System

IPPE Institute for Physics and Power Engineering (Russia) JSFR Japan Standard Fast Reactor

KE Kinetic Energy

KIT Karlsruhe Institute of Technology

KNK Kompakte Natriumgekülte Kernreaktoranlage LBE Lead- Bismuth Eutectic

LANL Los Alamos National Laboratory (USA)

LEADER Lead cooled European Advanced DEmonstration Reactor

LHS Left Hand Side

LMFRs Liquid Metal cooled Fast Reactors LNG Liquefied Natural Gas

LOCA LOss of Coolant Accident

MA Minor Actinides

MOX Mixed Oxid Fuel

MRK Modified Redlich-Kwong equation

MYRRHA Multipurpose Hybrid Research Reactor for High-tech Applications

NPPs Nuclear Power Plants PDE Post Disassembly Evaluation

RDIPE Research and Development Institute of Power Engineering

RHS Right Hand Side

SPX-1 Superphénix reactor SGI Schnelle Gas Injektion

SFR Sodium Fast Reactor

PFR Prototype Fast Reactor

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X

RPT Rapid Phase Transition

SG Steam Generator

SGTR Steam Generator Tube Rupture SNR Schneller Natriumgekülter Reaktor

SSTAR Small Secure Transportable Autonomous Reactor TNT Trinitrotoluene

XT-ADS EXperimental Demonstration of the technical feasibility of Transmutation in an Accelerator Driven System

Liquid metal cooled reactors are considered one of the most promising nuclear reactor concepts in the frame of Generation IV systems to be commercialized in the next decades.

I

ABSTRACT

Liquid metal cooled reactors are considered one of the most promising nuclear reactor concepts in the frame of Generation IV systems to be commercialized in the next decades.

Furthermore, a huge experience has already gained in liquid metal technologies because both sodium and heavy liquid metals have been already used as coolant in fast breeder reactors.

The first one is the formation of shock waves that can damage the inner structures of the reactor and, in the particular case of heavy liquid metal reactors, might cause a sort of “chain effect” damaging other steam generator tubes.

A scientific cooperation between ENEA Brasimone Research Centre and University of Pisa has been set up, in the frame of IP-EUROTRANS and ELSY FP6 Projects, concerning the heavy liquid metal-water interaction.

The use of existing tools for the analysis of energy release and the development of

new ones based on existing theoretical models constituted a further contribution

II

provided by this study. This topic is crucial because of the lack of representative experimental data.

SGI campaign has been simulated again with SIMMER III code, thus contributing

to its further qualification by the numerous experimental data available, except for

the energy release.

III

AKNOWLEDGMENTS

After the years of research at the University of Pisa and at Karlsruhe Institute of Technology (KIT), Germany,I would like to thank many people who contributed to the research and helped at finalizing this work.

In particular, I would like to thank Prof. Francesco Oriolo, Prof. Walter Ambrosini and Dr. Nicola Forgione for being my supervisors and for their assistance, kindness and patience despite my stay abroad.

Thanks are due to Dr. Werner Maschek for his full support, willingness, suggestions and for giving me the possibility to belong to a great group of research.

This work would not be possible without the precious contribution of Michael Flad who has patiently and kindly helped me in overcoming many technical problems during these years, in discussing and revising my work.

Huge thanks go to Dr. Edgar Kiefhaber for his valuable advices and for discussing problems during the revision of my thesis.

I appreciate the cooperation with the colleagues and friends of the ENEA Brasimone Research Centre and in particular Dr. Andrea Ciampichetti, Dr. Mariano Tarantino and Dr. Marco Utili.

I thank my friends and colleagues and in particular Barbara, Fabrizio, Angelica, Claudia, Vladimir, Marina for their friendship and help.

Special thanks go to Sebastian who has stood me during these hard months.

All my gratitude goes to my parents, who always fully supported and trust me

staying by my side in the good and in the bad times.

IV

To my beloved

parents

Alberto e Graziella

V

CONTENTS

1. INTRODUCTION ...1

1.1 General Background ... 1

1.2 Motivation for the present work ... 4

1.3 Outline of the present work ... 5

REFERENCES ... 7

2. LIQUID METALS AS REACTOR COOLANTS ... 9

2.1 Introduction ... 9

2.2 Motivations for choosing liquid metals ... 10

2.3 Characteristics of liquid metals ... 16

2.4 Ongoing R&D activities ... 27

REFERENCES ... 30

3. PHENOMENA INVOLVING ENERGETIC RELEASES FROM MOLTEN METAL COOLANT INTERACTIONS ... 33

3.1 Phenomenology of thermal interaction between fluids in liquid metal reactors ... 33

3.2 Main contact modes ... 37

3.3 Theoretical Models ... 38

3.1 Spontaneous nucleation theory ... 38

3.2 Thermal detonation theory... 43

3.4 Vapor Explosion Modeling ... 47

4.1 TNT equivalence model... 47

4.2 Superheat limit explosion ... 48

4.3 Thermodynamic models ... 49

3.1 Specific final ambient pressure expansion... 50

3.2 Specific final volume expansion ... 52

3.3 Hall model... 52

4.4 Parametric models ... 54

4.1 Cho-Wright model... 54

4.2 Caldarola model ... 56

4.5 Mechanistic propagation models ... 57

5.1 Board and Hall shock adiabatic model... 57

VI

3.5 Energy conversion efficiency and the problem of energy

scaling ... 59

3.6 Comparison between FCI and CCI ... 64

3.7 SIMMER III Code: Main Features ... 68

7.1 Code Framework ... 68

7.2 Fluid-dynamics model... 72

7.3 Structure model ... 76

7.4 Neutronic model ... 77

7.5 Code Assessment ... 77

3.8 Concluding remarks ... 78

REFERENCES ... 80

4. ANALYSIS OF LIFUS EXPERIMENTS ... 87

4.1 Introduction ... 87

4.2 Experimental activity ... 87

2.1 Original configuration of the facility and Test n.1 conditions 87 2.2 Changes to the facility and operating conditions for the other experiments ... 91

2.1 Test n.2 ... 91

2.2 Test n. 3, n. 4 and Test n.1 and n.2 for ELSY Program ... 92

4.3 Numerical simulation and comparison with experimental results ... 95