[csallen]

Before he resigned, Steve Bannon said, "Until somebody solves the part of the equation that shows me that ten million people in Seoul don’t die in the first 30 minutes from conventional weapons, I don’t know what you’re talking about, there’s no military solution here, they got us."

That's the most recent statement by a high-ranking government official that I've heard, but it's so high that it has to be an exaggeration. Anyway, to surpass Hiroshima, they don't need anywhere near that amount. They just need about 3x what your estimate says they had in 2012. Less if Seoul has grown in population density during that time.