I did a lot of reading up on this years ago, and even a Cold War nuclear exchange would be survivable in many areas of the United States. Attacks on missile sites would be ground bursts, creating a lot of fallout, but little in the way of major fires. Attacks on cities and non-hardened military targets in or near cities, would be air bursts for the most part, creating major fires, but not much fallout (Hiroshima-type attack).

However, that's neither here nor there. The most likely radiation scenario nowadays is (in descending order of probability) a dirty bomb of some kind, a very limited missile or smuggled warhead attack, or even a major leak from a nuclear power plant.

In these cases the difference between health and sickness (or worse) for many, many people will be a reasonable knowledge of the issue, and reasonable preparations. Nobody needs a buried shelter with ten-foot concrete walls.

All the information is readily available online nowadays, including entire downloadable books on nuclear survival skills. Careful, though. A lot of sites are selling potassium iodide pills without going into a lot of detail about their exact usefulness.