TEPCO released the 40-minute video on September 27, 2012, with no explanation of when the video was taken, or how much radiation exposure the workers manipulating the drill and the camera got. (The workers had been practicing on the mockup.)
The video starts after a 130-mm diameter hole was drilledAt first, nothing seems to be happening, until 50 seconds into the video when the aperture of the ball valve opens. What you see at the end of the hole is the inside of the Reactor 1 Containment Vessel. The camera gets inserted at about 2 minutes into the video.
The inside seems to be filled with whitish smoke or steam, though it doesn't look dripping wet like in Reactor 2's Containment Vessel. At about 4 minutes, some sort of structure is discernible. At 5 minutes, a rust-colored wall starts to appear on the left side of the screen.
At about 18 minutes, the camera focuses better, and you start to see what looks like metal and concrete(? it may be mangled metal) debris.
What destroyed the inside like this? Earthquake? Explosion?
TEPCO used Penetration X100B, which is on the northwest corner of the Containment Vessel above the equipment hatch door, not the high-radiation southeast corner.
According to TEPCO's monthly progress report as of September 24, 2012 (page 24 of the PDF), workers from Hitachi-GE Nuclear Energy are doing the work. (Workers from Toshiba are doing the investigation of the Reactors 2 and 3 Containment Vessels.)
In June this year, TEPCO did the survey of the Reactor 1 torus room, where they found the radiation level just above the water surface to be over 10 sieverts/hour.