Why humanoid?
Nuclear power could be safer when robotics can do the dangerous work instead of human beings.
The deign of most nuclear sites is for human beings to operate, so a humanoid robot is needed, i.e. a hand to open the door, or type, or operate machines with different buttons (haven’t been a nuclear site; just imagining).
Why autonomous?
Autonomous is important when robots are too far away, or it’s unrealistic for human to operate it all the time.
Imagine sending robots to search for certain things around a base when the human needs to do other things – autonomy is crucial.
Imagine sending robots to other planets with no humans to collect something – can’t remote control either.