Reactor core cooling system and reactor core cooling method

The invention discloses a reactor core cooling system and a reactor core cooling method. The system comprises a double-wall containment, a reactor water storage pit, a pressure vessel and a steam generator, the double-wall containment comprises a containment inner wall and a containment outer wall, and at least one cooling water chamber for storing a coolant is formed between the inner wall and the outer wall. When a whole nuclear power plant is powered off, a special release valve for a pressure stabilizer and a water injection valve are opened, and a water injection pipeline injects the coolant into the pressure vessel, a release pipeline discharges steam, a steam-water mixture or a coolant, entering a heat pipe section from a reactor core, into the reactor water storage pit; when the water level of the reactor water storage pit rises to a first height, the water injection valve is closed, a backflow injection valve is opened, and a part of the coolant in the reactor water storage pit flows back into the pr