It really depends on what kind of scenario we're talking about. At the moment in time someone is affected by a nuclear blast in their vicinity, it's unlikely t

It really depends on what kind of scenario we're talking about. At the moment in time someone is affected by a nuclear blast in their vicinity, it's unlikely that person knows what else is going on in the world. A nuclear blast is bad, but how bad are things globally? No way of knowing, really, at least for awhile. Maybe most of the nukes targeted at your country were duds. Maybe they were never launched. Maybe some were intercepted. If one could survive just by hiding under thick materials for a week or two then travel to an unaffected city, I think a lot of people would prefer that if they knew it was an option.