Look at the radiation readings in the picture picked up by the "Packbot". The path that the robot took is trought an air conditioning room on the second floor. At the start there was 18 Millisieverts/Hr but this number quickly rise. It jumps to 300 Millisieverts/Hr almost instantly inside the air conditioning room and climbes to 2000 Millisieverts/Hr. When the Packbot is approaching the opening at the "train room" the radiation level goes overscale and spikes the 5000 Millisieverts/Hr radiation detector used by the remote controlled "Packbot".
numbers would probably be in the 10+ Sieverts/Hr inside the "train room". But there are some heavy equipment that is shown in the picture that could shield the radiation levels measured by the Packbot. If so then who knows how high the radiation is inside the room.
This is an earlier picture taken from inside the Reactor Building, Unit 1, Fukushima Daiichi Nuclear Power Station. Gamma camera view from the large equipment service entrance to the south-side airlock, 22 May 2011. Measurement unit is counts per second (cps). TEPCO. We clearly see that the second floor have high radiation levels.
Read also http://ex-skf.blogspot.com/2011/08/fukushima-i-nuke-plant-reactor-1-it-was.html