Jae-hyeok works at the aging Hanbyul Nuclear Power Plant, which is their namesake town's only source of energy and jobs. Jae-hyeok, who had earlier lost both his father and brother working at the plant in his early years, lives with his mother, sister-in-law, and nephew Min-jae. He expresses his desire to work at a
fishing vessel to make money for his family rather than work at the plant, but is discouraged by everyone he knows, including his childhood friend & fiancée Yeon-joo. Pyeong-seok is one of the head operators of the plant, who alongside a coalition of his concerned plant workers and
anti-nuclear activists, tries to get the
President of South Korea Seok-ko Hang, to shut down the plant due to urgent safety concerns, but they are dismissed by the other senior plant operators, especially the
Prime Minister. An
earthquake suddenly strikes the town, causing the nuclear reactor to overheat. Due to the plant's aging safety systems, attempts to cool down the overheating reactor are botched. Meanwhile, Hang's administration fiercely debates between allowing the reactor to vent radioactive particles into the air to relieve pressure from the core or evacuating large population centers around the plant, before they settle on evacuating residents closest to the reactor. Due to the lack of a
contingency plan in place, the only route leading out of town quickly became gridlocked. This critical delay led to the reactor building exploding before the crew could open the pressure release valves themselves, killing or injuring most of the plant workers. Jae-hyeok hauls out his friend Gil-seop and much of the workers out from the plant before he collapses from
radiation poisoning. The
KCDC quarantines the town's residents not far from the reactor. However. after Yeon-joo gets proof that the reactor exploded and delivers the news, they set up a
jammer and locks the evacuees inside the evacuation center as they leave them for dead, except for the junior nurse Mi-sook, who is treating Jae-hyeok and other plant workers. Yeon-joo, along with the town's residents manage to break out from the evacuation center and commandeers one of the buses for their citizens to escape. Despite the firefighters' efforts to cool the reactors, some of the firefighting crew also began experiencing radiation poisoning symptoms as well. Hang, after fallen into depression for the reactor explosion, orders the firefighters to use seawater to decommission the reactors completely. He and Pyeong-seok discovers that there is a growing crack underneath the storage tank in the basement, putting the
spent fuel rods in danger of overheating. When the
Army's
military engineers refuse to step in, Hang addresses to the nation, requesting aid from the plant workers to perform a dangerous operation of sealing the cracks in the basement. Jae-hyeok bitterly declines, but at the insistence of Gil-seop, he eventually agrees for the sake of the people. He calls a distraught Yeon-joo before he boards on a bus back to the town along with their surviving crew. During their operation, the crack underneath the coolant tank grew bigger and they are ordered to retreat. Jae-hyeok suggests they seal the door and blow up the tank to allow the spent fuel rods to fall into the basement, effectively creating a new tank. However, at the current situation, both of these steps must be executed simultaneously, meaning
one will not be leaving out alive. Jae-hyeok, the only person among the group who can operate explosives and having already been too sick from radiation poisoning, volunteers to sacrifice himself, allowing the workers to then seal himself into the waste room before fleeing the area. Jae-hyeok uses his helmet-mounted camera to broadcast a farewell message to his family and Yeon-joo before blowing himself up, sending all the fuel rods into the flooded basement and averting a larger nuclear disaster. ==Cast==