Press Releases 2015

TEPCO has been investigating and examining 52 unconfirmed and unresolved issues on the development mechanism of the Fukushima Daiichi Nuclear Accident in order to make progress on decommissioning work and make continuous improvements of safety technology at the nuclear power stations.

In this 4th progress report, we show the results of the investigation and examination of 6 issues out of the 52.

With those results, we have completed the investigation and examination of all 10 high-priority issues to understand the development mechanism.

TEPCO will continue investigating and examining the remaining unconfirmed and unresolved issues, and conducting on-site investigations and new verifications in order to accumulate knowledge on decommissioning and to further improve safety technology at the nuclear power stations.

It was found that the information on the location of the wave gauge at Fukushima Daiichi Nuclear Power Station was incorrect, therefore we corrected the following documents on September 3, 2019. Corrected texts are hilighted in yellow, and corrected images are surrounded by yellow line.
・Attachment Earthquake-tsunami-1

[Overview]
The 4th Progress Report on the Investigation and Examination of Unconfirmed and Unresolved Issues on the Development Mechanism of the Fukushima Daiichi Nuclear Accident (PDF 259KB)

[Full Report and its Attachments]
[Main Body] (UPDATE)(PDF 1.27MB)
List of attachments
[Attachment 1] Overview of MAAP (Provided by Japanese only) (PDF 615KB)
[Attachment 2] List of issues to be investigated (UPDATE)(PDF 3.11MB)
[Attachment 3] Findings from the latest analyses using MAAP5(PDF 1.44MB)
[Attachment 4] Status of investigation on estimating situation of cores and containment vessels (UPDATE)(PDF 4.96MB)
[Attachment Earthquake-tsunami-1] Arrival times of tsunami at the Fukushima Daiichi Nuclear Power Station site(PDF 3.13MB)
[Attachment 1-1] Amounts of water injection assumed in MAAP analysis for Unit-1(PDF 90.3KB)
[Attachment 1-2] Evaluation of plant status by the fuel range water level indicators of Unit-1(PDF 219KB)
[Attachment 1-3] Impacts of the earthquake on Unit-1 (UPDATE)(PDF 711KB)
[Attachment 1-4] Examination into water injection by fire engines(PDF 603KB)
[Attachment 1-5] Evaluation into the amounts of water injected to Unit 1 by fire engines(PDF 445KB)
[Attachment 1-6] Estimation of accident progression based on the data measured for Unit-1 and the analysanalyses available to date(PDF 802KB)
[Attachment 1-7] Status of heat removal in the the isolation condenser at Unit-1(PDF 980KB)
[Attachment 1-8] Relocation behavior of molten fuel to below the core (NEW)(PDF 3.59MB)
[Attachment 1-9] Estimation of causes of high contamination of RCW piping at Unit-1 (NEW)(PDF 1.00MB)
[Attachment 2-1] Reactor pressure behaviors at Unit-2(PDF 277KB)
[Attachment 2-2] Containment vessel pressure behaviors at Unit-2(PDF 305KB)
[Attachment 2-3] Amounts of water injection assumed in MAAP analysis for Unit-2(PDF 110KB)
[Attachment 2-4] RCIC flow rate of Unit-2 after loss of the power supply for control(PDF 105KB)
[Attachment 2-5] RHR system situations after tsunami arrival at Unit-2(PDF 325KB)
[Attachment 2-6] Behavior of primary containment vessel pressure starting about 12 o’clock on March 14th in Unit-2(PDF 581KB)
[Attachment 2-7] Correlation between neutrons detected outside the reactor building and fuel melting(PDF 242KB)
[Attachment 2-8] Evaluation of integrity of suppression chamber at Unit-2(PDF 618KB)
[Attachment 2-9] Examination into the reactor pressure increase after forced depressurization at Unit Unit-2 using, a thermal-hydraulic code(PDF 1.14MB)
[Attachment 2-10] Sharp increase of CAMS readings on March 15th at Unit-2(PDF 265KB)
[Attachment 2-11] FP release behavior at Unit-2 estimated from CAMS readings on March 14th and 15th (NEW)(PDF 1.35MB)
[Attachment 2-12] SRV operation states after core damage at Unit-2 (NEW)(PDF 1.67MB)
[Attachment 2-13] Water level and temperature changes in the suppression chamber (S/C) of Unit-2 (NEW)(PDF 3.92MB)
[Attachment 3-1] Reactor pressure behavior during high pressure water injection at Unit-3(PDF 294KB)
[Attachment 3-2] Amounts of water injection assumed in MAAP analysis for Unit-3(PDF 191KB)
[Attachment 3-3] Reactor pressure decreasing behavior at about 9:00 on March 13th in Unit-3(PDF 436KB)
[Attachment 3-4] Reactor pressure changes from about 02:00 to about 12:00 on March 13th (UPDATE)(PDF 1.00MB)
[Attachment 3-5] The cause of RCIC shutdown in Unit 3(PDF 438KB)
[Attachment 3-6] Dose increase on around March 20th, 2011(PDF 1.43MB)
[Attachment 3-7] Causes of PCV pressure increase at Unit-3 from March 11th to 12th, 2011 (NEW)(PDF 1.03MB)
[Attachment 3-8] Leaks from Unit-3 PCV and steam release in a large amount (NEW)(PDF 996KB)