Nuclear reactor cooling system

The purpose of the present invention is to facilitate inspection and repair of a nuclear reactor cooling system capable of cooling a nuclear reactor over a long period without requiring electrical power. In-reactor heat exchangers (2) disposed within the nuclear reactor are secured inside an upper head (10) of a pressure vessel (1), and one side of a through pipe (32) passing through the upper head (10) is coupled to the in-reactor heat exchanger (2) and the other side thereof forms a connection element (3) on the outer side of the upper head (10). The present invention greatly facilitates inspection and repair of a nuclear reactor cooling system capable of cooling a nuclear reactor over a long period without requiring electrical power.