I remember reading a story about possibly a boy and girl living in an underground city because of some event that sent the population underground - it was a short story, I believe, possibly in SF/F, or Asimov's, or Weird Tales, and it had the same overtones as "This Time of Darkness" by Helen Hoover and "Dark Universe" by Daniel Galouye, but I'm certain it was a short story, not a novel. I don't believe it was associated with a war or nuclear accident, but I could have forgotten that part. I remember it really had a steampunk flavor. Any help would be appreciated:)
Possibly Hugh Howey's Wool series, which started with a short story published in 2011.
From the Wiki entry:
The story of Wool takes place on a post-apocalyptic Earth. Humanity clings to survival in the Silo, a subterranean city extending over one hundred and fifty stories beneath the surface. The series initially follows the character of Holston, the sheriff of the Silo, with subsequent volumes focusing on the characters of Juliette, Jahns, and Marnes. An ongoing storyline of the series is the focus on the mystery behind the Silo and the secrets it holds. The Silo's mystery is eventually revealed by the end of book five; books six through eight comprise a prequel to the series. Book nine pulls the storylines together.