BUT. "Thankfully it's quite hard to get a nuclear material to blow up."
it depends on your definition of "blow up". Enough TNT, or C4 and you can make anything "blow up". Now, causing a nuclear REACTION that makes a BOOM - is a different story.
My point...? any of our nuclear power plants can be blown up... nuclear material can be blown up. And although only a limited number of people would die from the blast - nuclear material would be dispersed over a great area and many people would suffer greatly. Not to mention the pure "mental" effect such an attack would have (which, after all, is what terrorism is all about).
Incorrect. The area of dispersion is actually quite limited. Widespread dispersion requires release of significant amounts of stored energy. Nuclear explosions produce fallout because of this. The same occurred at Chornobil, wherein the internal energy contained in the fuel drove the material out into the environment.
Additionally, widespread disperal usually occurs when there is significant vaporization of the reacting mass. The explosive materials must reach very high temperatures so its constituent atoms have tremendously high kinetic energy. They then move about the environment, losing energy and eventually plate out or condense onto other materials, far removed from the explosion site.
An event driven by an external force simply doesn't match up on these terms. Sure, you can push materials around somewhat, but in terms of blasting things far and wide, to the tune of some of these widely speculative "doomsday" scenarios involving "dirty nukes" or whatever the kooks are calling them these days, its simply not in the cards, based on the laws of mother nature.
Before you blow me off as not knowing what I am talking about, I did some of the modeling and some experiments involving release of materials from nuclear material transport accidents back when DOE was doing some of the initial transport cask design and validation. I was also a partner on a consulting job for a utility group that was looking into risk management that involved modeling of release terms and dispersion from power plant accidents. If you have any kind of reasonably accurate meteorological model that incorporates realistic transport mechanisms, it predicts quite limited dispersion.
That would have to be a serious security breach where they somehow got large amounts of explosive all the way into containment. The best terrorists could probably hope for is to do enough damage to cause a release of radioactive steam.