"The Compound" by S.A. Bodeen

Being rich doesn't protect you from a nuclear attack! Eli and his family have been living in an bunker that his billionaire father built to protect his family. For 6 long years the family has been living underground in a plush mansion, but tensions are wearing thin. Grief plagues the family, as Eli's twin brother, Eddy, and their grandmother didn't make it into the compound in time and died outside the steel doors. Eli becomes suspicious of his father's weird behavior, and discovers the food supply may be contaminated. Things aren't what they seem and his worst fears are confirmed when he makes contact with the outside world...is things are o.k. outside, why are they still living under lock and key? And why is his father the only one who knows the code to get out?? Eli discovers his own father may be a madman, and it's up to him to help his family survive.