You're right, James. But the amount of fallout (or, more correctly, contamination) isn't the issue when it comes to how nations react. First it's the issue of someone using a (no pun intended) device. Second ANY intusion of radionucleides into someone else's "space" is not going to be well received. What's the difference between "a bit of containation" and "a sh*t load of it"?
I only used Chernobyl as an example to illustrate where this stuff can go.