Fukushima Nuclear Accident Analysis Report (Interim Report) December 02, 2011 The Tokyo Electric Power Company, Inc. Forward I would like to express my heartfelt sympathy to all of the people who were affected by the devastating earthquake on March 11 this year. Reflecting on the accident at the Fukushima Daiichi Nuclear Power Station, the risk-reducing measures against a nuclear disaster consequently turned out to be insufficient. Almost all of the equipment and power sources that were expected to be activated in the case of an accident lost their functions, and thus, the event extended far beyond the existing framework for safety measures. We deeply apologize for the anxiety and inconvenience caused to the local residents around the power station, the residents of Fukushima Prefecture, and broader members of the society due to the extremely serious accident in which radioactive materials were released. We will continue to work as hard as we can to ensure the stable cooling of the reactors at the Fukushima Daiichi Nuclear Power Station, to reduce the release of radioactive materials so that the citizens of Japan can feel secure, and to enable the evacuees to return home as soon as possible. We will also steadily work through mid- and long-term projects toward decommissioning. TEPCO acknowledges that, in light of the severity of this accident, it is its social responsibility to conduct strict and thorough investigations and verifications of the accident, identify the causes of the accident, and reflect the lessons learned in its business operations, in order to prevent the recurrence of similar accidents. Based on this recognition, TEPCO set up a “Fukushima Nuclear Accident Investigation Committee” this June, and has been conducting such investigations and verifications. While the first priority was put on the accident recovery work, investigations and analysis of various records and interviews with over 250 employees have been conducted under the very limited chance of field surveys because of high radiation condition. Following the investigation, the committee’s conclusion was consulted on with the “Nuclear Safety and Quality Assurance Meeting Accident Investigation Verification Committee,” consisting of external experts, in order to have comments from a technical and independent point of view. This interim report is intended to compile investigation results that have been verified so far. The report is mainly focused on the event causes and their preventive measures, especially from the point of facility design. It describes preparations for accidents, damage to the facilities by the earthquake and tsunami, accident management work, event progression of core damage, hydrogen explosions, and so on. Since the investigation is ongoing, further new findings and topics not included in this interim report will be published in the future. TEPCO had received support and understanding from many people with regard to its nuclear power generation. However, the accident has destroyed such public trust, for which we again would like to express our deep apologies. Finally, we would like to express our gratitude toward the government, relevant national and international organizations, manufacturers, and the other people involved for their support and cooperation. December 2, 2011 Chairman of the Tokyo Electric Power Company, Inc. Fukushima Nuclear Accident Investigation Committee Masao Yamazaki - Objectives and Framework of the Accident Investigation - (1) Objective To clarify causes of the accident by investigating and verifying facts by ourselves as the central player of the accident, and to incorporate the lessons learned into future business operations. (2) Framework [Fukushima Nuclear Accident Investigation Committee] (Committee members) Chairman: Executive Vice President Masao Yamazaki Members: Executive Vice President Masaru Takei Managing Director Hiroshi Yamaguchi Managing Director Yoshihiro Naito General Manager of Corporate Planning Department General Manager of Engineering Department General Manager of the Corporate Affairs Department General Manager of the Nuclear Quality Management Department Total: 8 members [Accident Investigation Verification Committee] A committee consisted of external experts was established under the “Nuclear Safety and Quality Assurance Meeting” as an advisory board to provide comments from a technical and independent point of view on the investigation results compiled by the “Fukushima Nuclear Accident Investigation Committee.” (Committee members) Chairman : Genki Yagawa (Professor Emeritus, University of Tokyo) Members: Yuriko Inubushi (Vice Chair, Consumption Science Federation) Takeshi Kohno (Professor, Keio University) Yoshihisa Takakura (Director, Tohoku Radiological Science Center) Nobuo Shuto (Professor Emeritus, Tohoku University) Hideki Nakagome (Attorney at Law) Masao Mukaidono (Professor, Meiji University) (3) Method The following investigations and verifications were implemented:  Verification of records (charts, alarm records, operation log, etc.)  Analysis (tsunami inversion analysis, seismic response analysis, core damage analysis, etc.)  Visual investigation of major indoor and outdoor facilities  Interviews (discussions) with more than 250 people in total mainly from the emergency response team at the power station The investigation results were discussed first in the “Fukushima Nuclear Accident Investigation Committee,” and then consulted on with the “Accident Investigation Verification Committee” for a total of four times. Table of Contents 1. Report objectives・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ 1 2. Overview of the Fukushima Nuclear Accident・・・・・・・・・・・・・・・・・・ 1 2.1 Outline of the Fukushima Daiichi Nuclear Power Station 2.2 Outline of the Fukushima Daini Nuclear Power Station 2.3 Overview of the Fukushima nuclear accident 3. Overview of the Tohoku-Chihou-Taiheiyo-Oki Earthquake・・・・・・・・・・・・・ 4 3.1 Scale of the earthquake and tsunami 3.2 Intensity of the earthquake at the power stations 3.3 Height of the tsunami at the power stations 3.4 Tsunami evaluation 4. Preparations for Accidents in the Power Station・・・・・・・・・・・・・・・・・ 18 4.1 Regulations 4.2 Facility design 4.3 Updates on new findings 4.4 Preparations of accident management 4.5 Accident management measures and the Fukushima accident 5. Preparation for Emergency Response・・・・・・・・・・・・・・・・・・・・・ 24 5.1 Preparation for emergency response on a nuclear disaster 5.2 Response during the accident 6. Impact of the Earthquake on Power Stations・・・・・・・・・・・・・・・・・・・ 27 6.1 Plant status right before the earthquake 6.2 Plant status right after the earthquake 6.3 Status of off-site power supply 6.4 Assessment of the impact on facilities by the earthquake 7. Direct Damage to the Facilities from the Tsunami・・・・・・・・・・・・・・・・ 44 7.1 Damage to the facilities at the Fukushima Daiichi Nuclear Power Station 7.2 Damage to the facilities at the Fukushima Daini Nuclear Power Station 7.3 Summary of the damage to the facilities from the tsunami 8. Response Status after the Tsunami Attack・・・・・・・・・・・・・・・・・・・・ 51 8.1 Response Status at Fukushima Daiichi Unit 1 8.2 Response Status at Fukushima Daiichi Unit 2 8.3 Response Status at Fukushima Daiichi Unit 3 8.4 Response Status at Fukushima Daiichi Unit 4 8.5 Response Status at Fukushima Daiichi Unit 5 8.6 Response Status at Fukushima Daiichi Unit 6 8.7 Response Status at Fukushima Daini Unit 1 8.8 Dose rate at site boundaries of the Fukushima Daiichi Nuclear Power Station during the accident progress 8.9 Storage status of spent fuels 9. Evaluation of the Hydrogen Explosions・・・・・・・・・・・・・・・・・・・・ 95 9.1 Analysis on explosion events based on seismometers 9.2 Causes of the hydrogen explosions 10. Analysis of the Accident and Identification of Major Issues・・・・・・・・・・・・ 104 10.1 Issues concerning plant behavior at the time of the accident 10.2 Issues on facilities and functions 10.3 Issues based on factors impacting worker’s performance on the accident response 10.4 Summary of the analysis and the identification of issues 11. Countermeasures based on the Accident Causes・・・・・・・・・・・・・・・・ 142 11.1 Strategy for preventing core damage 11.2 Specific countermeasures in consideration of the Fukushima accident 12. Conclusions・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ 156 Attachments (submitted only in Japanese) Response status at the Fukushima Daiichi Nuclear Power Station and the Fukushima Daini Nuclear Power Station List of Supplementary Materials Attachments (submitted only in Japanese) [1. Report objectives] - [2. Overview of the Fukushima Nuclear Accident] 2-1 Outline of the Fukushima Daiichi Nuclear Power Station 2-2 Outline of the Fukushima Daini Nuclear Power Station [3. Overview of the Tohoku-Chihou-Taiheiyo-Oki Earthquake] 3-1 Outline of the Tohoku-Chihou-Taiheiyo-Oki Earthquake 3-2 Comparison between the seismic observation records and the design seismic motion at the Fukushima Daiichi Nuclear Power Station 3-3 Comparison between the seismic observation records and the design seismic motion at the Fukushima Daini Nuclear Power Station 3-4 Tsunami investigation results at the Fukushima Daiichi Nuclear Power Station 3-5 Outdoor flooding conditions at the Fukushima Daiichi Nuclear Power Station 3-6 Conditions of the tsunami that hit the Fukushima Daiichi Nuclear Power Station 3-7 Results of the tsunami reproduction calculations at the Fukushima Daiichi Nuclear Power Station 3-8 Tsunami investigation results at the Fukushima Daini Nuclear Power Station 3-9 Results of the tsunami reproduction calculations at the Fukushima Daini Nuclear Power Station 3-10 Analysis regarding the tsunami differences 3-11 Main developments regarding the tsunami safety assessment 3-12 Wave source and wave source area proposed by various research organizations, etc. 3-13 Site height design of the Fukushima Daiichi Nuclear Power Station buildings [4. Preparations for Accidents in the Power Station] 4-1 Redundancy, diversity, and independence of the engineered safety system 4-2 Installation conditions of “cooling” and “sealing” functions 4-3 Continuous risk reduction (continuous improvements)–Example of equipment renovations- 4-4 Background to accident management improvements 4-5 (1) Reinforcement of “cooling” functions 4-5 (2) Reinforcement of “sealing” functions 4-5 (3) Developed AM content–reinforcement of power supply functions- [5. Preparation for Emergency Response] 5-1 Nuclear disaster prevention organization (when primary emergency preparations are ordered) 5-2 No. 3 emergency preparations [6. Impact of the Earthquake on Power Stations] 6-1 (1) ~ (14) Fukushima Daiichi Unit 1 plant data 6-2 (1) ~ (13) Fukushima Daiichi Unit 2 plant data 6-3 (1) ~ (13) Fukushima Daiichi Unit 3 plant data 6-4 List of Fukushima Daiichi Nuclear Power Station external power access conditions 6-5 List of Fukushima Daini Nuclear Power Station external power access conditions 6-6 External power equipment damage conditions 6-7 (1) Seismic response analysis results of the Reactor Building and items important to seismic safety/pipe system using the Fukushima Daiichi Nuclear Power Station 2011 Great East Japan Earthquake observation records 6-7 (2) Report (outline) regarding the seismic response analysis results of the Reactor Building and items important to the seismic safety/pipe system using the Fukushima Daini Nuclear Power Station 2011 Great East Japan Earthquake observation records 6-7 (3) Outline of the “Report regarding reviews of the current seismic safety and reinforcements, etc., of the Reactor Building of the Fukushima Daiichi Nuclear Power Station” 6-8 (1) Fukushima Daiichi Unit 5 equipment conditions 6-8 (2) Fukushima Daiichi Unit 6 equipment conditions 6-8 (3) Fukushima Daiichi Unit 1 isolation condenser (IC) visual inspection results 6-8 (4) Fukushima Daiichi Unit 1, Unit 2, Unit 3 Turbine Building equipment conditions 6-8 (5) Fukushima Daiichi Units 1 ~ 4 outdoor equipment conditions 6-8 (6) Fukushima Daiichi Nuclear Power Station filtered water tank and pure water tank conditions 6-8 (7) Fukushima Daiichi Nuclear Power Station outdoor fire protection system pipe conditions 6-8 (8) Fukushima Daiichi Nuclear Power Station disaster prevention road conditions 6-9 (1) List of main equipment conditions at Fukushima Daiichi Unit 5 6-9 (2) List of main equipment conditions at Fukushima Daiichi Unit 6 [7. Direct Damage to the Facilities from the Tsunami] 7-1 Location of openings thought to be the flooding route into the main buildings at the Fukushima Daiichi Nuclear Power Station 7-2 Fukushima Daiichi Nuclear Power Station seaside area and outdoor sea water system 7-3 Tsunami damage to the Fukushima Daiichi Nuclear Power Station power system 7-4 Damage to the Fukushima Daiichi Nuclear Power Station Electrical Power Distribution System equipment 7-5 Location of openings thought to be the flooding route into the main buildings at the Fukushima Daini Nuclear Power Station 7-6 Tsunami damage to the Fukushima Daini Nuclear Power Station power system 7-7 Damage to the Fukushima Daini Nuclear Power Station Electrical Power Distribution System equipment 7-8 Conditions of the Core Standby Cooling System equipment, etc., at the Fukushima Daiichi Nuclear Power Station 7-9 Conditions of the Core Standby Cooling System equipment, etc., at the Fukushima Daini Nuclear Power Station [8. Response Status after the Tsunami Attack] 8-1 Aftershock conditions 8-2 High Pressure Coolant Injection system of Fukushima Daiichi Unit 1 8-3 Fukushima Daiichi Unit 1 primary containment vessel venting 8-4 Fukushima Daiichi Unit 1 primary containment vessel vent exhaust as seen in the Fukuichi Live Camera photos 8-5 Fukushima Daiichi Unit 2 primary containment vessel venting 8-6 Fukushima Daiichi Unit 3 primary containment vessel venting 8-7 Fukushima Daiichi Unit 3 primary containment vessel vent exhaust as seen in the Fukuichi Live Camera photos 8-8 (1) Spent fuel pool water level evaluation method 8-8 (2) Fukushima Daiichi Unit 1 spent fuel pool status survey 8-8 (3) Fukushima Daiichi Unit 2 spent fuel pool status survey 8-8 (4) Fukushima Daiichi Unit 3 spent fuel pool status survey 8-8 (5) Fukushima Daiichi Unit 4 spent fuel pool status survey 8-8 (6) Fukushima Daiichi Unit 5 spent fuel pool status survey 8-8 (7) Fukushima Daiichi Unit 6 spent fuel pool status survey 8-8 (8) Fukushima Daiichi shared pool status survey 8-8 (9) Dry storage cask storage building status survey [9. Evaluation of the Hydrogen Explosions] - [10. Analysis of the Accident and Identification of Major Issues] 10−1 Changes in the Fukushima Daiichi Nuclear Power Station Unit 1 plant data 10−2 Isolation condenser 10−3 Isolation condenser motor-operated valve interlock block diagram 10−4 Development of Fukushima Daiichi Unit 1 isolation condenser (IC) valve conditions 10−5 Investigation conditions regarding the decrease in the water level on the shell-side of the isolation condenser (IC) 10−6 Changes in the Fukushima Daiichi Nuclear Power Station Unit 2 plant data 10−7 Changes in the Fukushima Daiichi Nuclear Power Station Unit 3 plant data 10−8 Changes in the Fukushima Daini Nuclear Power Station Unit 1 plant data 10−9 Maintenance of core cooling functions 10−10 Accident progression at the Fukushima Daiichi and Daini Nuclear Power Stations (outline) [11. Countermeasures based on the Accident Causes] 11-1 Countermeasures required for cold shutdown in the wake of the Fukushima Daiichi accident 11-2 Summary of events, causes, and countermeasures at the Fukushima Daiichi Nuclear Power Station Units 1 ~ 3 References 1(1) Fukushima Daiichi Nuclear Power Station equipment specifications 1(2) Fukushima Daini Nuclear Power Station equipment specifications 2(1) Comparison of Fukushima Daiichi Nuclear Power Station Emergency Safeguard Facilities and Reactor Auxiliary Facilities 2(2) Comparison of Fukushima Daini Nuclear Power Station Emergency Safeguard Facilities and Reactor Auxiliary Facilities 3 Outline of the Fukushima Daiichi and Daini Nuclear Power Station facility configuration 4(1) Indicated range of the Fukushima Daiichi Nuclear Power Station water-level gauge 4(2) Indicated range of the Fukushima Daini Nuclear Power Station water-level gauge List of Major Related Reports (1) Plant data of Fukushima Daiichi Nuclear Power Station at the time of the Tohoku-Chihou-Taiheiyou-Oki Earthquake (May 16, 2011, Tokyo Electric Power Company) (2) Report on the analysis of observed seismic data collected at Fukushima Daiichi Nuclear Power Station pertaining to the Tohoku-Chihou-Taiheiyou-Oki Earthquake (May 16, 2011, Tokyo Electric Power Company) (3) Report on the analysis of observed seismic data collected at Fukushima Daini Nuclear Power Station pertaining to the Tohoku-Chihou-Taiheiyou-Oki Earthquake (May 16, 2011, Tokyo Electric Power Company) (4) Report regarding “Collection of reports pursuant to the provisions of Article 106, Paragraph 3 of the Electricity Business Act” (May 16, 2011, Tokyo Electric Power Company) (5) Analysis and evaluation of the operation record and accident record of Fukushima Daiichi Nuclear Power Station at the time of Tohoku-Chihou-Taiheiyou-Oki-Earthquake (May 23, 2011, Tokyo Electric Power Company) (6) Report on "Countermeasures based on a report on records of damages to power facilities inside and outside of Fukushima Daiichi Nuclear Power Station (instruction)" (May 23, 2011, Tokyo Electric Power Company) (7) Reports about the study regarding current seismic safety and reinforcement of reactor buildings at Fukushima Daiichi Nuclear Power Station (May 28 , 2011, Unit 1 and Unit 4; July 13, 2011, Unit 3; August 26, 2011, Unit 2, Unit 5, and Unit 6, Tokyo Electric Power Company) (8) Report on earthquake response analysis of the reactor building, important equipment and piping system for earthquake-resistant safety using observed seismic data during the Tohoku-Taiheiyou-Oki Earthquake in the year 2011 (June 17, 2011, Unit 2 and Unit 4; July 28 , 2011, Unit 1 and Unit 3; August 18 , 2011, Unit 5 and Unit 6 Tokyo Electric Power Company) (9) Report on investigation results regarding tsunami generated by the Tohoku-Taiheiyou-Oki- Earthquake in Fukushima Daiichi and Daini Nuclear Power Stations (vol.2) (July 8, 2011, Tokyo Electric Power Company) (10) Report on the impact of Tohoku-Chihou Taiheiyo-Oki Earthquake to nuclear reactor facilities at Fukushima Daini Nuclear Power Station (August 12, 2011, Tokyo Electric Power Company) (11) Report on the results of the earthquake response analysis of the reactor building, facilities and pipes important to earthquake safety in Unit 1 at Fukushima Daini Nuclear Power Station using observed seismic data during the Tohoku-Taiheiyou-Oki Earthquake (August 18 , 2011, Tokyo Electric Power Company) (12) The impact of the Tohoku-Chihou Taiheiyo-Oki Earthquake on nuclear reactor facilities at Fukushima Daiichi Nuclear Power Station (September 9, 2011, Tokyo Electric Power Company) (13) Application status of the Accident Operation Manuals of Unit 1 at Fukushima Daiichi Nuclear Power Station associated with the Tohoku-Chihou-Taiheiyou-Oki Earthquake (October 21, 2011, Tokyo Electric Power Company) (14) Application status of the Accident Operation Manuals of Unit 2 at Fukushima Daiichi Nuclear Power Station associated with the Tohoku-Chihou-Taiheiyou-Oki Earthquake (October 28, 2011, Tokyo Electric Power Company) (15) Application status of the Accident Operation Manuals of Unit 3 at Fukushima Daiichi Nuclear Power Station associated with the Tohoku-Chihou-Taiheiyou-Oki Earthquake (October 28, 2011, Tokyo Electric Power Company)