Decommissioning Plan of Fukushima Daiichi Nuclear Power > Earthquake & Accident > Progress Reports on the Investigation and Examination of Unconfirmed and Unresolved Issues

Progress Reports on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiichi Nuclear Accidnet

We identified unconfirmed and unresolved issues on the detailed development mechanism after the March 11, 2011 accident occurred at Fukushima Daiichi, and are compiling reports in order to make progress on the decommissioning work as well as make continuous safety improvements at nuclear power stations.

TEPCO will continue working to gain a thorough understanding of what happened, such as the performance of the nuclear reactors at the time of accident, through planned investigation of the site and simulation analyses. By doing so, we will also enhance the obligation of nuclear power stations to operate safely, utilize the results to carry out decommissioning work, and continue to make progress in our nuclear safety reform initiative.

The 5th Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident (Dec. 25, 2017)

Press Releases

The 5th Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident

〔Overview〕

The 5th Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Development Mechanism of the Fukushima Daiichi Nuclear Accident（6.95MB）

〔Full report〕

[Main body and Attachments of Full Report]
Main Body (UPDATE)（1.46MB）
[Attachment 1] Overview of MAAP (Available in Japanese only)（617KB）
[Attachment 2] List of issues (UPDATE)（3.14MB）
[Attachment 3] Findings from the latest analyses using MAAP5（2.76MB）
[Attachment 4] Status of investigation on estimating the situation of cores and containment vessels (UPDATE)（7.29MB）
[Attachment Earthquake-tsunami-1] Arrival times of tsunami at the Fukushima Daiichi Nuclear Power Station site（2.97MB）
[Attachment Earthquake-tsunami-2] Additional examination of emergency AC power equipment losses due to tsunami (NEW)（1.84MB）
[Attachment 1-1] Amounts of water injection assumed in MAAP analysis for Unit-1（90.9KB）
[Attachment 1-2] Evaluation of plant status by the fuel range water level indicators of Unit-1（220KB）
[Attachment 1-3] Impacts of the earthquake on Unit-1（711KB）
[Attachment 1-4] Examination into water injection by fire engines（0.98MB）
[Attachment 1-5] Evaluation into the amounts of water injected to Unit 1 by fire engines（447KB）
[Attachment 1-6] Estimation of Unit-1 accident progression based on the measured data and results of analysis to date（801KB）
[Attachment 1-7] Examination into heat removal by the Unit-1 isolation condensers（980KB）
[Attachment 1-8] Relocation behavior of molten fuel to below the core（3.59MB）
[Attachment 1-9] Estimation of causes of high contamination of RCW piping at Unit-1（1.00MB）
[Attachment 1-10] Analysis of the hydrogen explosion at Unit-1 reactor building (NEW)（2.25MB）
[Attachment 1-11] Estimation of accident progression at Unit-1 based on the air dose rate monitoring data (NEW)（923KB）
[Attachment 2-1] Reactor pressure behaviors at Unit-2（279KB）
[Attachment 2-2] Containment vessel pressure behaviors at Unit-2（306KB）
[Attachment 2-3] Amounts of water injection assumed in MAAP analysis for Unit-2（111KB）
[Attachment 2-4] RCIC flow rates of Unit-2 after the loss of power supply（106KB）
[Attachment 2-5] RHR system situations after tsunami arrival at Unit-2（634KB）
[Attachment 2-6] Behavior of primary containment vessel pressure starting about 12 o’clock on March 14th in Unit-2（847KB）
[Attachment 2-7] Correlation between neutrons detected outside the reactor building and fuel melting（243KB）
[Attachment 2-8] Evaluation of integrity of suppression chamber (S/C) at Unit-2（619KB）
[Attachment 2-9] Evaluation of Unit-2 reactor pressure increase after forced depressurization, using a thermal-hydraulic analysis code（1.14MB）
[Attachment 2-10] Sharp increase of CAMS readings on March 15th at Unit-2（265KB）
[Attachment 2-11] FP release behavior at Unit-2 estimated from CAMS readings on March 14th and 15th（850KB）
[Attachment 2-12] SRV operation states after the core damage at Unit-2（1.67MB）
[Attachment 2-13] Water level and temperature changes in the suppression chamber (S/C) of Unit-2（1.48MB）
[Attachment 2-14] Estimation of reactor water levels at the time when core damage and core melt progressed at Unit-2 (NEW)（0.98MB）
[Attachment 3-1] Reactor pressures during high pressure water injection at Unit-3（296KB）
[Attachment 3-2] Amounts of water injection assumed in MAAP analysis for Unit-3（191KB）
[Attachment 3-3] Reactor pressure decreasing behavior at about 9:00 on March 13th in Unit- 3（439KB）
[Attachment 3-4] Reactor pressure changes from about 02:00 to about 12:00 on March 13th at Unit-3（1.00MB）
[Attachment 3-5] The cause of RCIC shutdown in Unit 3（440KB）
[Attachment 3-6] Dose increase on around March 20th（1.43MB）
[Attachment 3-7] Causes of PCV pressure increase at Unit-3 from March 11th to 12th, 2011（1.03MB）
[Attachment 3-8] Leaks from the Unit-3 PCV and steam release in a large amount（905KB）
[Attachment 3-9] Estimation of reactor water levels at the time when core damage and core melt progressed at Unit-3 (NEW)（543KB）
[Attachment 3-10] Evaluation of the fraction of Unit-3 vent gas that flowed into Unit-4 reactor building (NEW)（756KB）

The 4th Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident (Dec. 17, 2015)

Press Releases

The 3rd Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident (May. 20, 2015)

Press Releases

The 2nd Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident (Aug. 6 2014)

Press Releases

The 1st Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Fukushima Daiich Nuclear Accident (Dec. 13, 2013)