Why? Because TEPCO is going to send carbon-based workers to install the gas management system to purify the gas coming from inside the Containment Vessel.
Utterly meaningless endeavor as far as I am concerned. What good would cleaning the gas in the Containment Vessel do, when just outside the CV you measure 620 millisieverts/hr radiation? Something more deadlier than xenon and krypton is outside the CV, and the company is willing to risk both non-carbon based worker (Packbot) and carbon-based co-workers in order to keep up the appearance that everything is under control at the plant.
Nonetheless, here's the effort by Packbot on November 2, when it removed the junk out of the way, as released by TEPCO on November 5. Actually, TEPCO used 3 Packbots on November 2 and 3 for the work, according to Jiji Tsushin (11/5/2011):
You can also see the "before and after" photos in TEPCO's handout for the press on November 5. From that handout, here's the radiation on the 1st floor where Packbot had to work to prepare for the gas management system (north-east corner of the 1st floor):
For human co-workers of Packbot, working near that 620 millisieverts/hour location (which is unavoidable) for one minute would get them over 10 millisieverts radiation, or every one second 172 microsieverts.
Any volunteers? (Dr. Allison of Oxford University, maybe?)