Total 25 workers from Hitachi, 4 workers from TEPCO got the maximum 3.81 millisievert exposure for an hour and 40 minutes work on Wednesday October 24, 2012. TEPCO says they didn't use drones because the balloon was successful.
Successful. The drones might have saved the workers from 3.81 millisievert radiation exposure.
The balloon measured radiation levels on the way up the shaft. The level was highest on the 2nd floor, at 150.5 millisieverts/hour. The operating floor (5th floor) was also high, at 53.6 millisieverts/hour at 1 meter off the floor.
From TEPCO's Photos and Videos page (Japanese), October 24, 2012:
Balloon moving up the shaft:
Looking toward north:
Spent Fuel Pool - a white reflection in the lower left corner is the surface of the water, according to TEPCO:
More photos at the link.
Radiation levels, from TEPCO's handout:
Jiji Tsushin wondered in its article why the radiation level was so high on the 2nd floor. They seem to have forgotten that that's where more than 1 sievert/hour radiation was measured back in May last year. The survey meter went overscale.