Seth Tuler wrote a factsheet for Physicians for Social Responsibility on Health risks of the releases of radioactivity from the Fukushima Daiichi nuclear reactors: Are they a concern for residents of the United States?

The 13 page factsheet is meant to help people make sense of the issues that can influence exposure and harm from ionizing radiation.

It can be downloaded at the PSR website too:
        http://www.psr.org/resources/health-risks-releases-radioactivity.pdf