You know what's funny? The defence missles won't blow up the nuclear warheads, but rather the radioactive material will rain down anyway.
http://www.ctv.ca/servlet/ArticleNews/stor...45_6/?hub=World
Note, that five out of eight record was achieved only because the target missile did not have 1) decoys (which are employed by intercontinental ballistic missiles, and 2) the targets had a homing beacon on them.
So, when it all boils down, the sysyem works provided that the target has a big enough radar signal, and there's clear skies over Alaska.