Assistant Professor Benjamin Monreal, UCSB Department of Physics, will give an overview of radioactivity and reactors, radiation health and safety, and the ultimate fate of the materials coming out of the stricken reactors in Fukushima. There are 32 slides online and in a pdf.
Why is it worse than Three Mile Island? Why is it (probably) not as bad as Chernobyl? How worried are scientists? How worried should you be?
The spent fuel rods have less than 100X the radioactivity of the Chernobyl fuel (which was in an operating reactor at the time of the Chernobyl accident).