The present invention relates to a device for opening and closing an opening in the bottom of a pool intended for containing irradiated fuel. According to the invention, a frame (6) of the device is mounted with controlled pivoting about a vertical axis (Y-Y') on a wall (7) of the pool (1) and supports a vertical mast (40) having a cover (5) at the lower end thereof, said mast (40) being capable of being controlled with guided vertical movement relative to the frame (6), when the latter occupies a position in which the vertical mast (40) is substantially coaxial with the opening (3) at the top of same, between a bottom position in which the cover (5) seals the opening (3) and a top position in which the cover (5) is raised to a disengaged position above the opening (3). The invention can be used in the nuclear field.