Tepco published the in-house Fukushima accident investigation report on 6/20/2012.
In this report, which is assumed to downplay the accident, Tepco reported that there were 2 fires in reactor4 after the explosion, and those fires were naturally extinguished fortunately.
Also, it is stated that they could not approach SFP4 because the radiation level was too high.
Tepco is emphasizing the safety of SFP4 to say they can inject cooling water even when another aftershock hits Fukushima, but it suggests they won’t be able to reach SFP4 in case of another accident. (cf, Tepco has no clue for the worst senario of SFP4)
10:30AM Tepco tried to go to SFP4 to investigate the state but the radiation level inside of the reactor building was too high, they couldn’t enter. (The temperature of SFP4 was 84℃ at 4:08)
6:14 AM Major impulsive sound and vibration were observed, and they confirmed the roof of the reactor building was damaged.
9:38 AM Fire was observed at North West corder of the 3rd floor of the building, but they confirmed the fire was naturally extinguished at 11:00AM.
5:45AM Another fire was reported at the North West corner of the 4th floor of the building, but it was missing at 6:15AM.
↓ Reactor4 damaged by vibration [LINK]
↓ The 3rd/5th floor of reactor 4 building [LINK]
↓ The 4th floor of reactor4 building
Related article..Melted reactor 4