Don't know if you meant this seriously or not. I'm no scientist but it seems the range of the initial concussion would be critical here. There's no time to do anything if you are too close to a nuclear explosion. But if you are down-range and the nuclear fallout is headed your direction, then the same scenario of sealing yourself in and waiting it out til the danger is past would still hold true. But you'd probably be stuck there for a long time so one would hope that you'd have adequate supplies (at least 2 weeks).
I think the threat of a "dirty bomb" is a bit different than a true nuke. I really don't know how long you'd be stuck waiting it out but I'd wait until the media gives you the all clear and then stay in there two more days (given the doltish nature of the media).