TEPCO had already showed us a glimpse of what it was like inside the Containment Vessel of Reactor 1 at Fukushima I Nuclear Power Plant when the workers managed to
The company released the data on dose rates inside the CV and two videos (one is an abbreviated 3-minute video, the other is the full-length, over 2 hours) on October 10, 2012.
The highest level of radiation inside the CV was recorded right outside the X100B penetration tip, at 11.1 Sieverts/Hour.
According to TEPCO, the maximum radiation exposure for the workers was 2.13 millisieverts. That was much lower than the planned exposure of 10 millisieverts. The workers went in in several groups, so their exposure was nowhere near the 2-plus hours it took for the operation.
From TEPCO's handout for the press (10/10/2012), in English:
TEPCO will measure the radiation levels in the water under the grating, on October 11, and will collect the water sample on October 12.
So, when Prime Minister Noda went to the plant and gave a talk to the plant management on how progress had been made, the workers (TEPCO and Hitachi-GE Nuclear Energy) were preparing for this work which might expose them to 10 millisieverts in short time.
From TEPCO's Photos and Videos, 10/10/2012:
A bolt, a nut and a hatch:
Drywell spray piping: