There is an invincible Insurgent in the room that the nuke is in. He runs through a doorway, as soon as the player enters the room, and it closes. It is impossible to follow him.
If the player doesn't slide into the room that the nuke is in before the door closes, the mission fails and there is a news report about an "accident" and a "massive explosion" in the facility the nuke was in.
The part where the player has to disarm the nuke can be played over again as a mini-game.