Red Cross: "Nuclear Explosion and Radiation Emergencies"

The Red Cross has a page with checklists and advice on surviving a nuclear explosion and subsequent sheltering from fallout: "Nuclear Explosion and Radiation Emergencies." 

Although intended for emergency managers and first responders, you might find the following 105 page FEMA guidance to be interesting: "Nuclear Detonation Response Guidance: Planning for the First 72 Hours."