Abstract: Recirculation-type steam generator ensuring heat transfer between a fluid circulating in a primary circuit and a fluid circulating in a secondary circuit, constituted by a pressure envelope containing a vaporization enclosure having a roof and covering a bundle of tubes traversed by the primary fluid. The generator receives the secondary fluid which circulates in the vaporization enclosure. The steam produced by the secondary fluid is extracted during this circulation and is dried by cyclone separators constituted by cyclones fixed to first ends of tubular columns whose ends are fixed to the vaporization enclosure roof communicating with the vaporization enclosure. The cyclone separators are detachably fixed to the vaporization enclosure roof.

Abstract: The nuclear reactor includes a fuel core (5) inside a vessel (2) and a system (1) for cooling the core (5), in which a liquid metal circulates and on which is placed at least one steam generator (15). The steam generator includes a casing (15a) in which the liquid metal circulates, water-feed means (16) and means for heat exchange between the liquid metal and the feed water. The liquid metal is caused to circulate in the cooling system (1), the steam generator (15) not being fed with water and the liquid metal circulating in the steam generator (15) is cooled by the flow of a gas in contact with the casing (15a) of the steam generator (15). The cooling device includes a tubular element (25) placed around the casing (15a) of the steam generator and defining an annular space for a cooling gas to flow around the casing (15a).

Abstract: A removable flow rate-restricting device (25) is placed and fixed in a through-opening (18) of the tube plate (15) level with which is fixed the tube (6), from inside the water box (9). The flow rate-restricting device (25) includes an orifice plate which is inserted into the opening (18) of the tube plate.

Abstract: A transverse cut (18, 19) is made on a heat exchanger tube (4) to be replaced in the vicinity of its connectors (14, 15), at each end. A cut (19') is made in the frustoconical zone (16') of connection of the tube (4) to the second connector (15). The cutting operations are effected from inside the tube (4) and through one of the tube plates (2, 3). The tube (4) to be replaced is extracted from the heat exchanger through the interior of the second connector (15) and the corresponding opening (13) in the second tube plate (3). A replacement tube is introduced into the heat exchanger through the opening (13) in the second tube plate (3) until a first end of the tube engaged in the heat exchanger reaches the level of the cut zone (18) of the first connector (14). The first end of the tube is welded on the first connector (14).

Abstract: The tube (4) to be plugged is cut at its ends adjacent to the first and to the second branch (14, 15) and the metal of the junction zones (16, 16') of the tube (4) with each of the branches (14, 15) is eliminated. At least one portion of the tube (4) adjacent to at least one of the branches (14, 15) is cut and eliminated. Into each of the ends of the tube (4) in place inside the heat exchanger is introduced a plug (24, 30) of tubular shape, the diameter of which is smaller than the inside diameter of the tube (4), so that the plug has a closed end (24a, 30a) inside the tube (4) and an opposite end located inside the corresponding branch (14, 15). The plugs (24, 30) are fixed in place in the branches (14, 15), and a continuous sealing weld is made between each of the plugs (24, 30) and the corresponding branch (14, 15 ), the tube (4) having some freedom of movement in the longitudinal direction in relation to the plugs (24, 30).