The Sum of All Fears is a good book, unlike the terrible movie.
My first boss when I got to DC was a very good friend of Clancy. He knew Clancy before he became famous and actually gave him the story idea for Sum of All Fears. My boss also was the reviewer for the chapter that describes the bomb design and he and Clancy worked together to make sure the description would not allow anyone to actually make a working device.
I’m sure you saw the images of Kim Dung Un standing next to his supposed hydrogen bomb...
What did you think...did it look plausible? unlikely? possibly workable but crude???