This is an old article, but with a lot of in-depth information that keeps it relevant. It's also in reply to Rattle, (see thread RE: BBC NEWS | Science/Nature | Nasa to go nuclear)
but I want to put this link up big in lights.
If everone involved were honestly trying to use nuclear material in a safe way for astere scientific purposes, maybe they would succeed. Unfortunately, the actual people in charge of the process care mostly about the short term bottom line, and/or long term strategic objectives. In fact, coming up next -- a link to Ad Astra, a very pro-nukes in space organization. These guys love nukes! Nukes are hot!
I am sorry these guys run the show. I love space exploration, and wish the research would go ahead in a conscientious direction, not this quick and dirty way that seems to be more about developing space based nuclear-powered weapons.

AlterNet: U.S. Launching Lethal Plutonium Into Space