Toshiba has designed and built a four-legged robot to conduct investigative and recovery work in locations too dangerous for humans, including the reactor buildings of the damaged Fukushima Dai-Ichi No. 1 nuclear plant. (Source: Toshiba)
Additionally, I wonder if they're thinking too conventionally. A quad-copter is a self-stabilizing platform with cameras, one that can move around precisely without having to deal with stairs. It's off-the-shelf hardware that is quite inexpensive. It's not radiation-hardened, but they can purchase an awful lot of them and get quick inspection results.
Always in disaster do we see innovation and development. Some could argue that no one could envision the need for such a bot before the disaster, not it is an industry. Take a look at what came from World War II, More innovation than I have time today to write.
Despite how technologically advance the Japanese are, or were, perhaps they are looking elsewhere for inspiration and new ideas.
TJ, that's an intriguing idea. But the rad-hard ability is a big, big factor, due to extremely high radiation levels inside the damaged plant. Quad copters, at least presently, aren't very rugged compared to UGVs, which already have a lot of generations of development behind them in the military.
Lou, I agree. Then reasons appear to be that, until this disaster Japan's robot development hadn't been aimed at this type of device, but in other directions, such as towards the consumer sector and humanoid forms.