Honestly, this movie is the most realistic fictional depiction. It's time range is before, during and after:
Threads (1984) via https://youtu.be/5Srqyd8B9gE
And if you want to know how the world would like after the movie Threads, read the following book:
A Canticle for Leibowitz (1959) via https://en.wikipedia.org/wiki/A_Canticle_for_Leibowitz