PURPOSE: To effectively pour cooling water into a fuel channel in emergency, by providing a cooling water storage chamber on the outside of the fuel channel and connecting the chamber to the channel.

CONSTITUTION: The cooling water storage chamber 2 extends on the outside 1 of the fuel channel 5 in the longitudinal direction thereof. The cooling water is stored in the chamber 2. The opening 3 of the chamber 2 is connected to a pipe 7 provided at the top of the fuel channel 5. When the nuclear reactor develops a trouble, the cooling water is poured from the storage chamber 2 into the fuel channel 5 to cool fuel rods to compensate for the fall in the reactor core cooling capacity due to CCFL.