In "The Dark Knight Rises," Bane threatens to detonate a bomb if anyone leaves isolated Gotham. The weapon is a converted Wayne Enterprises fusion reactor core, transformed by nuclear physicist Dr. Leonid Pavel into a decaying neutron bomb.
Bane first cuts Gotham off from the outside world by destroying most of its bridges, trapping the police underground, and taking control of the city. He then announces that any attempt to escape—or outside interference—will result in the bomb's detonation. The threat turns Gotham into a hostage city under his rule.
The film later reveals that the bomb's five-month countdown cannot simply be stopped. Commissioner Gordon blocks its remote detonation signal, while Batman ultimately carries the device over the bay before it explodes. A common mix-up is calling it merely a reactor explosion: the plot specifically presents the converted reactor as a nuclear weapon, often described as a neutron bomb.