Seen it before in Iraq, The fire ball is prop(propellent) it burns much faster under pressure than it does in the open. The fireball was the prop. Also fading light helped. It was a big boom!
Not a nuke but a year and a half there was a low order nuke det in Russia! Russia admitted as much.
Look up the melting point of DU!
I have pulled burnt FSDS DU rounds out of an m1 in Iraq though. Contained blast and fire with full load of HE and DU rounds and the penetrators could have been reused!
This stuff seriously hard, that's why they use it! causes Heavy Metal Poisoning, not radiation sickness.