Nuclear Bomb

The Nuclear Bomb was a weapon of mass destruction in The Dark Knight Rises that began as a Wayne Enterprises fusion reactor meant to supply Gotham City with a source of clean energy. It was turned into a nuclear bomb by a scientist kidnapped by Bane, Dr. Leonid Pavel, and it became a time bomb when the core was removed from the reactor. The trigger detonator to the bomb was the possession of Talia al Ghul.

Origin
The Wayne Enterprises fusion reactor project was personally heavily invested in by both Bruce Wayne and Miranda Tate (Talia al Ghul). Once Russian nuclear scientist Dr. Leonid Pavel published his research about a method to turn this technology into a bomb, Bruce pulled the plug on the project under the guise of it having problems and the reactor secretly sat in a bunker along the Gotham River for three years.

The Dark Knight Rises
With the loss of his fortune and seat on the Wayne Enterprises board of directors, Bruce turned to Miranda and showed her the reactor. He feared it coming under the control of John Daggett. He told her he needed her to take control of the company and the reactor.

Bane had kidnapped Dr. Pavel and turned the reactor into a nuclear bomb with a six mile blast radius. By removing the core from the reactor, it also became a time bomb with five months until detonation. It was shown off to the city and the world at Gotham City Stadium and there Bane told everywhere the trigger to the detonator was in the possession of an anonymous Gotham citizen and it would be detonated if there was interference from outside the city.

The nuclear bomb was made mobile as three armored tactical trucks patrolled the city, one containing the bomb. Miranda assisted Gordon and a rag tag group of cops in finding and tracking the bomb truck. Unknown to them at the time, she misled them into tracking a decoy.

After Bruce returned to the city after his defeat by Bane, Lucius Fox gave him a way to block the signal to the trigger using EMP technology from the Bat. Batman gave this device to Gordon, and Gordon climbed on board the true bomb truck and blocked the signal before Talia hit the trigger to the detonator during her confrontation with Batman. She gloated that Gordon had only bought Gotham eleven more minutes and ordered for a convoy to protect the bomb truck and left Gotham City Hall to be escorted to the truck.

After the convoy was dismantled by Batman and Selina Kyle and the bomb truck fell off the high road, Talia explained that Lucius showed her about the emergency flood and it was triggered so that cooling the bomb down was no longer an option. Batman hooked the bomb up to the Bat and flew it over the Gotham Bay with the use of autopilot, where the nuclear bomb exploded away from the city.