Mitigation of Hydrogen Hazards in Severe Accidents in Nuclear Power Plants

174 Pages·2011·1.75 MB·English

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INTERNATIONAL ATOMIC ENERGY AGENCY
VIENNA
ISBN 978–92–0–116510–7
ISSN 1011–4289
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Mitigation of Hydrogen Hazards
in Severe Accidents
in Nuclear Power Plants
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IAEA-TECDOC-1661

MITIGATION OF HYDROGEN
HAZARDS IN SEVERE ACCIDENTS
IN NUCLEAR POWER PLANTS

INTERNATIONAL ATOMIC ENERGY AGENCY
VIENNA, 2011
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MITIGATION OF HYDROGEN HAZARDS IN SEVERE ACCIDENTS
IN NUCLEAR POWER PLANTS
IAEA, VIENNA, 2011
IAEA-TECDOC-1661
ISBN 978-92-0-116510-7
ISSN 1011-4289
© IAEA, 2011
Printed by the IAEA in Austria
July 2011
FOREWORD
Consideration of severe accidents in nuclear power plants is an essential component of
the defence in depth approach in nuclear safety. Severe accidents have very low probabilities
of occurring, but may have significant consequences resulting from the degradation of nuclear
fuel.
The generation of hydrogen and the risk of hydrogen combustion, as well as other
phenomena leading to overpressurization of the reactor containment in case of severe
accidents, represent complex safety issues in relation to accident management. The
combustion of hydrogen, produced primarily as a result of heated zirconium metal reacting
with steam, can create short term overpressure or detonation forces that may exceed the
strength of the containment structure. An understanding of these phenomena is crucial for
planning and implementing effective accident management measures. Analysis of all the
issues relating to hydrogen risk is an important step for any measure that is aimed at the
prevention or mitigation of hydrogen combustion in reactor containments.
The main objective of this publication is to contribute to the implementation of IAEA
Safety Standards, in particular, two IAEA Safety Requirements: Safety of Nuclear Power
Plants: Design and Safety of Nuclear Power Plants: Operation. These Requirements
publications discuss computational analysis of severe accidents and accident management
programmes in nuclear power plants. Specifically with regard to the risk posed by hydrogen
in nuclear power reactors, computational analysis of severe accidents considers hydrogen
sources, hydrogen distribution, hydrogen combustion and control and mitigation measures for
hydrogen, while accident management programmes are aimed at mitigating hydrogen hazards
in reactor containments.
The IAEA staff member responsible for this publication was C.O. Park of the Division
of Nuclear Installation Safety.
1
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The mention of names of specific companies or products (whether or not indicated as registered) does
not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement
or recommendation on the part of the IAEA.
CONTENTS

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

1.1. BACKGROUND ................................................................................................................... 1
1.2. OBJECTIVE AND SCOPE ...................................................................................................... 5
1.3. STRUCTURE ....................................................................................................................... 5

2. POTENTIAL HYDROGEN SOURCES DURING THE EVOLUTION OF
A SEVERE ACCIDENT ............................................................................................................ 6

2.1. INTRODUCTION .................................................................................................................. 6
2.2. IN-VESSEL HYDROGEN SOURCE ......................................................................................... 7
2.2.1. Short description of core degradation during a severe accident ................................ 7
2.2.2. In-vessel hydrogen source from Zr oxidation............................................................ 9
2.2 3. In-vessel hydrogen production coming from steel oxidation .................................. 14
2.2.4. In-vessel hydrogen production coming from B C absorber material oxidation ...... 14
4
2.2.5. Consequences to be drawn regarding calculations .................................................. 16
2.3. EX-VESSEL HYDROGEN PRODUCTION .............................................................................. 16
2.3.1. Short term H release during vessel lower head failure ........................................... 16
2
2.3.2. H production during molten core-concrete interaction .......................................... 17
2
2.3.3. Other possible ex-vessel H production ................................................................... 19
2

3. HYDROGEN DISTRIBUTION .......................................................................................... 19

3.1. DESCRIPTION OF CONTAINMENT ...................................................................................... 20
3.1.1. Full pressure containment ........................................................................................ 20
3.1.2. Containments with pressure suppression system ..................................................... 21
3.2. LOCATION OF HYDROGEN SOURCES IN THE CONTAINMENT .............................................. 23
3.3. EFFECT OF RELEASE MODE AND SPRAYING ON HYDROGEN DISTRIBUTION ....................... 23
3.4. CONTAINMENT LAYOUT EFFECTS .................................................................................... 24
3.5. ANALYTICAL TOOLS ........................................................................................................ 25
3.5.1. Integrated codes or system codes ............................................................................ 25
3.5.2. Lumped parameter codes ......................................................................................... 25
3.5.3. Computational fluid dynamics codes ...................................................................... 26
3.5.4. Hybrid codes ............................................................................................................ 28
3.5.5. Comparison of general advantages and disadvantages of the different code types. 29
3.6. EXPERIMENTAL FACILITIES TO MEASURE HYDROGEN DISTRIBUTIONS ........................... 29
3.6.1. Gas distribution experiments for large dry containments ........................................ 29
3.6.2. Experiments for ice condenser containments .......................................................... 31
3.6.3. Recent and future experiments ................................................................................ 31

4. HYDROGEN COMBUSTION ............................................................................................ 33

4.1. INTRODUCTION ................................................................................................................ 33
4.2. FLAMMABILITY AND IGNITION CONDITIONS .................................................................... 34
4.2.1. Flammability ............................................................................................................ 34
4.2.2. Auto ignition and ignition ........................................................................................ 35
4.3. MODES OF COMBUSTION ................................................................................................. 36
4.3.1. Deflagration ............................................................................................................. 36
4.3.2. Detonation ............................................................................................................... 36
4.3.3. Flame acceleration and deflagration to-detonation transition ................................. 38
4.3.4. Quenching ................................................................................................................ 41
4.3.5. Mechanisms involved in Deflagration to Detonation Transition ............................ 41
4.3.6. Necessary criteria for flame acceleration and DDT ................................................ 41
4.3.7. Diffusion flames ...................................................................................................... 46
4.3.8. Effect of carbon monoxide ...................................................................................... 47
4.3.9. Pressure loads associated with different combustion phenomena ........................... 48
4.4. ANALYTICAL TOOLS ........................................................................................................ 49
4.4.1. Combustion in containment systems codes (lumped parameter) ............................ 49
4.4.2. Combustion in CFD codes ....................................................................................... 50
4.5. EXPERIMENTAL FACILITIES ............................................................................................. 54
4.5.1. Small scale facilities ................................................................................................ 54
4.5.2. Medium test facilities .............................................................................................. 56
4.5.3. Experiments in large scale and complex geometries ............................................... 56

5. RISK FROM HYDROGEN COMBUSTION...................................................................... 58

5.1. COMBUSTION LOADS AND STRUCTURAL RESPONSE ......................................................... 58
5.2. THREATS FROM COMBUSTION TO THE CONTAINMENT ...................................................... 60
5.2.1. Direct damage. ......................................................................................................... 60
5.2.2. Indirect damage ....................................................................................................... 61
5.2.3. Failure of secondary containment ............................................................................ 62
5.2.4. Failure of containment vent. .................................................................................... 62
5.2.5. Effect of temperature. .............................................................................................. 63
5.3. SCENARIO EFFECTS ......................................................................................................... 63
5.4. OTHER FACTORS RELEVANT FOR THE RISK FROM COMBUSTION GASES ............................ 64
5.4.1. Other substances than hydrogen. ............................................................................. 64
5.4.2. Pressure build-up by non-condensables. ................................................................. 64
5.4.3. Stratification of gases .............................................................................................. 65
5.4.4. Effects from accident management ......................................................................... 65
5.5. SENSITIVITY OF VARIOUS CONTAINMENTS TO HYDROGEN COMBUSTION LOADS .............. 66
5.5.1. Large dry containment ............................................................................................. 67
5.5.2. Ice condenser containment ...................................................................................... 67
5.5.3. Suppression pool containment (BWR) .................................................................... 67
5.5.4. WWER confinement................................................................................................ 67
5.5.5. Future designs .......................................................................................................... 68
5.6. TREATMENT OF HYDROGEN IN THE PSA ......................................................................... 70

6. HYDROGEN MEASUREMENT ........................................................................................ 71

6.1. OBJECTIVES OF A H2 MEASUREMENT SYSTEM ................................................................. 71
6.2. H2 MEASUREMENT SYSTEMS ............................................................................................ 71
6.2.1. Hydrogen concentration measurement system inside the containment ................... 72
6.2.2. Systems based on sampling ..................................................................................... 72
6.3. H2 MEASUREMENT SYSTEMS QUALIFICATION .................................................................. 73
6.4. H2 MEASUREMENT PROBE POSITION ................................................................................ 73
6.5. H2 MEASUREMENT EVALUATION WITHOUT ANY H2 MEASUREMENT ................................ 73

7. HYDROGEN CONTROL AND RISK MITIGATION ....................................................... 73

7.1. INERTIZATION OF THE CONTAINMENT ATMOSPHERE ........................................................ 74
7.1.1. Pre-inertization ........................................................................................................ 74
7.1.2. Post-inertization ....................................................................................................... 74