Proposed is a reactor cooling system for cooling down a reactor damaged by a disaster accident and a reactor cooling method using same using contaminated water generated at a nuclear reactor as a cooling water source for cooling the nuclear reactor after the accident, thereby maximally suppressing discharge of the contaminated water into the sea. To this end, the reactor cooling system prosed above includes a nuclear power generation facility, a seawater storage tank, a seawater inflow flow path for introducing the seawater into the seawater storage tank and a seawater discharge flow path for discharging the seawater from the seawater storage tank to the sea, connected to one end and another end of the seawater storage tank, respectively, a heat exchanger installed in a water storage space of the seawater storage tank, a contaminated water supply flow path, and a contaminated water discharge flow path.