Floating roof tanks for liquids, in particular to storage tanks used in the nuclear power industry

A floating roof tank for liquids, the tank comprising a cylindrical wall, a floating roof surrounded by said cylindrical wall, a flexible membrane being fixedly connected to said floating roof and said wall in a watertight manner and having a fold defining a space which is suitable for receiving a counter-pressure liquid, and means for protecting the tank against being over-filled when the roof is in its top or uppermost position, the tank including the improvement whereby the protection means are essentially constituted by an overflow duct mounted outside the tank and on the wall thereof and communicating with the inside of the tank via an orifice provided through the bottom portion of said tank, said overflow duct having an upside down U-shaped portion and having the top of the upside down U-shaped portion disposed at a height corresponding to a predetermined maximum level of the liquid inside the tank when the roof is in its uppermost position, and a siphon-breaking tube connected to the overflow duct in the vicinity of the top of its upside down U-shaped portion and open at its other end to the outside atmosphere.