In October 1997, NASA launched from Cape Canaveral the so-called Casini space probe to Saturn. And this one carried 72 lbs. of plutonium. Casini went up on a Lockheed Titan 4 rocket. Some of those rockets that exploded earlier during tests. Thankfully it did not blow up on lift off. But they were a little worried, because the local broadcast in the Cape Canaveral area urged people to shut their windows in case of explosion - they didnft even tell you to duck and cover.
 http://hem.passagen.se/ravell/opera/shuttle.htm

The Mars 96 space probe was launched carrying 9.2 kilograms of plutonium, but the craft went out of control before it could reach earth orbit. US Space Command, which tracked the route of the craft, claims that it fell intact into the sea off the coast of Chile. Eye-witnesses, however, reported that they saw the craft falling in the border area between Chile and Bolivia where it disintegrated and burned. So far, no proof for either version has been presented although it would be reasonable to assume that the 9.2 kilos of plutonium vaporised in the atmosphere.
 http://www.abc.net.au/science/slab/invaders/default.htm

On June 10, 2002 NASA published the subject notice in the Federal Register reopening the public comment period for their Pluto-Kuiper Belt (PKB) mission environmental impact statement.
Written comments are due before July 25, 2002.

NASA is now considering launching the PKB mission on an expendable launch vehicle from Cape Canaveral Air Force Station, Florida, in January 2006. NASA also now plans to use a conventional radioisotope thermoelectric generator (RTG) in place of the advanced radioisotope power system originally planned.

Comments should include the following points:

1) Launching of plutonium RTG's is dangerous and in a worst case release could contaminate significant portions of the environment. Any environmental impact statement must give detailed description of the consequences of such an accident.

2) The processing and fabrication of RTG's at various Dept of Energy facilities is dangerous to workers and local communities.

3) NASA should be developing non-radioactive alternative power sources for deep space missions and until they do plutonium should not be launched into space.

4) Not just U.S. citizens would be impacted by a space plutonium accident. This is a global concern.

 http://www.globenet.free-online.co.uk/articles/plutokuipereis.htm