A Study of the Fukushima Daiichi Nuclear Accident Process : What Caused the Core Melt and Hydrogen Explosion?

Written by an expert in the field, this book is perfect for those who would like to know what happened at the Fukushima Daiichi Nuclear Power Plant. Part 1 of the book studies how core melts occurred in Fukushima Daiichi units 1, 2, and 3, respectively, based on evidence from the Three-Mile Island core melt accident and fuel behavior experiments performed in the 1970s under the cooperation between the United States, Germany, and Japan. This information explains the accident processes without contradicting data from Fukushima, which was published in the TEPCO report. The hydrogen explosions in units 1, 3, and 4 are also explained logically in conjunction with the above core melt process. Part 2 clarifies how the background radiation level of the site doubled: The first rise was just a leak from small openings in units 1 and 3 associated with fire-pump connection work. The second rise led to direct radioactive material release from unit 2. Evacuation dose adequacy and its timing are discussed with reference to the accident process, and the necessity for embankments surrounding nuclear power plants to increase protection against natural disasters is also discussed. New proposals for safety design and emergency preparedness are suggested based on lessons learned from the accident as well as from new experiences. Finally, a concept for decommissioning the Fukushima site and a recovery plan are introduced. Foreword 6 Preface 10 Why I Decided to Write This Book 10 Contents 14 Part I: What Caused the Core Melt and Hydrogen Explosion? 18 Chapter 1: Three Mile Island Nuclear Power Station Accident 19 1.1 Shape of the Molten Core 19 1.2 TMI Reactor’s Performance During the Accident 24 1.3 Fuel Behavior Test Simulating Power Cooling Mismatch Accident (PCM-1) at Power Burst Facility (PBF) 28 1.4 Zircaloy Oxidation and Fuel Rod Behavior 33 1.5 Core Melt Process of TMI Accident 38 1.6 Settlement of TMI Accident 41 1.7 Conclusion from TMI Accident 43 1.8 Influences and Excursuses of the TMI Accident 44 Appendices 47 Appendix 1.1 47 Appendix 1.2 48 Ball-Park Calculation on the 5.5 MPa Pressure Rise 48 References 49 Chapter 2: Fukushima Daiichi Unit 1, 2 and 3 Accidents 50 2.1 Outline of Fukushima Daiichi Nuclear Power Station 50 2.2 Initiation of the Accidents – Earthquake and Tsunami 54 2.3 Outline of the Accident 56 2.4 Case of Unit 1 60 2.4.1 Isolation Condenser (IC) Problem 60 2.4.2 Fuel Temperature Rise 63 2.5 Case of Unit 2 66 2.5.1 Reactor Core Isolation Cooling System (RCIC) 66 2.5.2 Sea Water Injection and Core Melt 71 2.5.3 Hydrogen Gas Generation and Radioactive Release 76 2.5.4 Section Conclusion 80 2.6 Case of Unit 3 84 2.6.1 Operating Period of RCIC and HPCI (1 4 p.m. on March 11–2:42 a.m. on March 13) 88 2.6.1.1 Operating Period of RCIC (4 p.m. on March 11 – Around Noon on March 12) 88 2.6.1.2 Operating Period of HPCI (Around Noon on March 12–2:42 a.m. on March 13) 90 2.6.2 Core Temperature Rise After HPCI Stoppage (2 2:42 a.m. on March 13–9:08 a.m. on March 13) 91 2.6.2.1 Reactor Pressure Drop 91 2.6.2.2 After Effects of the HPCI Pump Stoppage 92 2.6.3 Start of Core Collapse (3 9:08 a.m. – 0:20 p.m.) 94 2.6.4 Sea Water Injection and Core Melt (4 Approximately 22 h from 0:20 p.m. on March 13 Through 11 a.m. on March 14) 96 2.6.5 Explosion of Reactor Building (5 11:01 a.m. on March 14) 99 2.6.6 Section Conclusion 104 2.7 Back to the Case of Unit 1 106 2.7.1 Radiation Heat in Reactor Pressure Vessel 106 2.7.2 Core Melt and Meltdown 112 2.7.3 Reverse Study from Hydrogen Explosion 113 2.7.4 Drop of Partially Molten Core and Its Internals 116 2.7.5 Sea Water Injection and Explosion 119 2.7.6 Section Conclusion 121 2.8 Conclusion from Studies of Units 1–3 124 Appendices 129 Appendix 2.1 129 Appendix 2.2 130 Appendix 2.3 130 Why Did the RCIC Pump Stop? 130 Appendix 2.4 131 Evaporation Amount of Water by Decompression Boiling (Autonomous Boiling) 131 Appendix 2.5 131 Appendix 2.6 132 Reactor Water Level Gauge Error After Decompression Boiling 132 Appendix 2.7 132 Zirconium-Water Reaction Where There Is Insufficient Water 132 Appendix 2.8 134 Temperature Calculation Related to Radiation Heat 134 Appendix 2.9 135 Appendix 2.10 135 Appendix 2.11 136 Reference 137 Chapter 3: Fukushima Daiichi Unit 4 Accident 138 3.1 Explosion of Reactor Building 140 3.2 Global Influence of the Explosion 144 Part II: Improving Nuclear Safety and Reconstructing Fukushima 148 Chapter 4: Release of Radioactive Materials and the Evacuation of Residents 149 4.1 Background Radiation Level Increased by the Release of Radioactive Materials 149 4.1.1 First Increases in the Background Radiation Level – Amount of Radiation Released from Units 1 and 3 150 4.1.2 Background Radiation Level Increase for the Second Time – Amount of Radioactive Materials Released from Unit 2 153 4.2 Emergency Evacuation 156 4.2.1 Dose Band for Evacuation Recommended by the ICRP 159 4.2.2 Lives of Evacuees 160 4.3 Release of Radioactive Materials and Contamination 161 4.3.1 Radioactive Materials Released from the Chernobyl Accident 162 4.3.2 Release of Radioactive Materials from the Fukushima Accident 166 Appendices 170 Appendix 4.1 170 Appendix 4.2 Radiation Level and Annual Exposure Dose 171 References 171 Chapter 5: Tsunami and Station Blackout 172 5.1 Seawall (Tide Embankment) 173 5.2 Station Blackout 175 5.3 Layout of Equipment and B5b Issue 181 5.4 Reliability and Diversity of Equipment 184 5.5 Natural Disasters and Safety Design 185 Chapter 6: Reconstruction of Safety 188 6.1 Conventional Nuclear Safety 188 6.2 Safety Design and Natural Disasters 190 6.3 Mitigation Safety Systems Against Disasters (MISSAD) 193 6.4 Safety of Nuclear Power Plant 195 6.5 Antiterrorism Measures 199 6.5.1 What Is Nuclear Terrorism? 199 6.5.2 Measures Against Terrorism by Land and Sea Based on the Design Basis Threat (DBT) 201 6.5.3 Terrorism Using Aircraft 203 Chapter 7: Road to Decommissioning 208 7.1 The Current Situations of Reactors That Suffered Core Melt 209 7.2 Decommissioning in the Earliest Days and Today 211 7.3 Advice to Fukushima 214 Chapter 8: Outcome of the Study 217 Chapter 9: New Insights Obtained from the Accident – To Commemorate the Publication of the English Edition 221 9.1 Insights and Lessons Learned from the World-First Experiences 221 9.1.1 Nuclear Power Plants That Withstood a Massive Earthquake of Magnitude 9 222 9.1.2 Safety Design to Mitigate Natural Disasters Learned from Tsunami Damage 222 9.1.3 Countermeasures for Station Blackout 223 9.1.4 Reactor Water Level and Core Melt 223 9.1.5 Water Injection from Fire Engines 224 9.1.6 SC Vent 225 9.1.7 Slow Cooling with Reactor Core Depressurization 225 9.2 What Could Have Been Done to Prevent the Accident? 226 9.3 Improvements to Be Considered 227 9.3.1 Enhancement of SC Vent Performance 227 9.3.2 Containment Vessels 227 9.3.3 Reactor Buildings 228 9.3.4 Study of Cooling by Radiation Heat 228 9.4 Toward More Robust Safety Systems 229 Reference 230 Chapter 10: At the End of This Study 231 10.1 Careful Studies Required to Clarify What Actually Happened 231 10.2 The Government’s Failure to Support 233 10.3 More Information Required from TEPCO for More Accurate Analyses 234 10.4 The Need to Provide Precise Information to the World 235 10.5 Fukushima Reconstruction with Cool-Headed Judgments 236 References 237 Postscript 238 About the Author 241 Front Matter....Pages i-xvi Front Matter....Pages 1-1 Three Mile Island Nuclear Power Station Accident....Pages 3-33 Fukushima Daiichi Unit 1, 2 and 3 Accidents....Pages 35-122 Fukushima Daiichi Unit 4 Accident....Pages 123-132 Front Matter....Pages 133-133 Release of Radioactive Materials and the Evacuation of Residents....Pages 135-157 Tsunami and Station Blackout....Pages 159-174 Reconstruction of Safety....Pages 175-194 Road to Decommissioning....Pages 195-203 Outcome of the Study....Pages 205-208 New Insights Obtained from the Accident – To Commemorate the Publication of the English Edition....Pages 209-218 At the End of This Study....Pages 219-225 Back Matter....Pages 227-231