"The Knights of Arthur" by Frederick Pohl

If you are as old as I am, you will recognize the author's name.  It is a post-apocalyptic story with a lot of wit and humor (essential for such a dark topic).  It is pretty deep in before you learn Arthur's unique and unfortunate status.  The story also shows some awareness of the trade-offs between long-term fallout and short-term fallout.  Too much science fiction has been written by people whose knowledge of science was a bit limited and imaginative.