Sendai? You could see how their recovery is progressing while being somewhat away from any radiation risk.

I'm somewhat fascinated by the "science city" of Tsukuba, which is about an hour of so by train from Tokyo IIRC. It's a reasonable size with modern architecture, including "green" buildings and demonstration projects, a very good new university, and a lot of technology parks, Japanese style. It's inexpensive compared to Tokyo and even Osaka/Kyoko. For a low key visit, try two nights and one day.