Patent Number: 042959349
Section: summary

The present invention relates to a liquid-metal-cooled nuclear reactor and, more specifically, to such a reactor of the semi-integrated type, as described, e.g., in French patent application Ser. No. 78/18822 filed on June 23, 1978, by the applicant. The present invention, however, could also be applied with advantage to a liquid-metal-cooled nuclear reactor with cooling loops, in such instances where said reactor comprises a primary vessel within a main vessel. An example of a reactor of the latter type is described in German patent No. 1,564,054, filed on Dec. 15, 1966. It is to be noted, however, than in reactors of the latter type, the vessels are suspended, the sodium inlet and outlet ducts are coaxial and tightness between the internal vessel and the hot-sodium duct is provided by bellows extending along the whole periphery of said vessel, which of course results in intricate problems as regards manufacture and maintenance. Moreover, the main vessel top portion is separated from the hot sodium merely by "stagnant" sodium, the temperature of which, in operation, rises to about that of the hot sodium. It is known that, in the field of fast-neutron nuclear reactors, there exist two main categories that differ from each other by the structure of the coolant circuit in which flows the primary liquid metal, usually liquid sodium, said two categories comprising reactors with cooling loops, on the one hand, and integrated reactors, on the other hand. In the first category, the reactor vessel merely contains the core with its testing and handling devices, together with the liquid metal flowing through said core, whereas the core neutronic protection devices, the primary heat-exchangers and the pumps for driving the primary liquid metal adapted to cool said core are all arranged outside the reactor vessel. Usually a liquid metal secondary circuit is provided, said circuit being adapted to exchange heat with the radioactive primary liquid metal (primary exchanger), on the one hand, and with a water-steam circuit (secondary exchanger) adapted to feed turbines generating electric power, on the other hand. Fast nuclear reactors of the integrated type are provided with a main vessel wherein is to be found a primary vessel containing the core, the core neutronic protection devices and the core testing and handling devices. Said main vessel also contains the primary heat exchangers and the primary pump. In other words, the liquid metal primary circuit is included in its entirety within said main vessel. Said primary vessel, on the other hand, has mainly the function of separating the hot liquid metal issuing from the core and directed towards the primary exchangers, from the cold liquid metal issuing from the primary pump and recycled at the core lower end. The present invention relates to a liquid-metal-cooled fast reactor either of the type comprising loops and a primary vessel, or of the semi-integrated type. In reactors of such types, the heat exchangers and the pump are outside the vessel. However, the vessel also comprises an internal vessel or primary vessel for separating the hot liquid metal from the cold liquid metal and, in the case of semi-integrated reactors, the primary vessel contains not only the core but the core neutronic protection devices too. In the latter instance, with a view to rendering the reactor more compact and, accordingly, substantially decreasing its manufacturing cost, the liquid sodium or metal secondary circuit have been eliminated, so that the exchanger-pump assemblies fed by the liquid metal flowing through the core have to exchange the heat contained therein directly with a water-steam circuit that feeds the electric-power generating turbines. A pump-heat exchanger assembly thus permitting to eliminate the secondary circuit is known and disclosed in French application Ser. No. 77. 03192, filed on Feb. 4, 1977, for a "Bloc echangeur-pompe" (Pump-heat exchanger assembly), in the name of the applicant. More specifically, the present invention, in that type of nuclear reactors, relates to the cooling of the main vessel upper portion and to the passage through the vessels of the outlet duct for the hot liquid metal having circulated through the core. It will be easily understood, indeed, that, since a primary vessel and a main vessel are provided and the hot liquid metal outlet duct opens into said primary vessel, said duct has necessarily to pass through the annular space defined by said primary and main vessels. In addition, as already specified, the object of the primary vessel is to separate a zone containing a rather cold liquid metal from a rather hot liquid metal. It will be easily understood that this will raise problems of differential thermal expansion (in particular between the various vessels), such a thermal expansion having to be taken into account as regards the structure and connection of the hot liquid metal outlet duct, or ducts, since said duct, or ducts, have to be connected to a device for exchanging heat between the liquid metal and the water-steam circuit. For solving the above problems, the present invention relates to a liquid metal cooled nuclear reactor, characterized in that it countains: a core comprising a plurality of fuel assemblies provided with a tubular bottom fitting and the neutronic protection devices for said core, a main vessel comprising a bottom portion, a lateral wall and first supporting means arranged at a determined level, said means being integral with the outer surface of said lateral wall, a primary vessel, mounted inside said main vessel and coaxial therewith, said primary vessel comprising a diagrid adapted to support and feed the reactor core, a lateral wall and second supporting means integral with the lateral wall of said main vessel and with the lateral wall of said primary vessel, respectively, said means being at said determined level, the lateral walls of said vessels defining an annular space there between; means forming a horizontal partition within said annular passage, said means being substantially at said determined level; at least one exchanger outside said vessels for exchanging heat between said liquid metal and water, or steam; a first connecting-duct between the inlets of said exchanger, or exchangers, and the inside of the primary vessel, said first duct opening into said primary vessel above said core and passing through said annular space above said horizontal partition with the help of means for passing through said space; a second connecting-duct between the outlets of said exchanger, or exchangers, and said annular space, said second duct opening into said annular space at a lower level than said horizontal partition so as to cause said cold liquid metal to flow in said diagrid, then through the core starting from the fuel-assemblies bottom fittings, and, means for collecting a portion of said cold liquid metal, and feeding same into said annular space, above said partition. By "core" is meant the core proper and its lateral and axial neutronic protection devices, its testing devices and the means for handling the fuel assemblies. Preferably, said primary vessel is constituted by an inner sleeve extending over at least a portion of the height of the lateral wall of said primary vessel, and an outer sleeve, said two sleeves being in parallel relationship and defining an interstice, or space, containing a thermal insulation, said interstice being connected, at the lower portion thereof, to the manifold mounted under the diagrid and adapted to collect the leaks from the fuel-assembly bottom fittings, said outer sleeve being provided with a plurality of evenly distributed orifices, or ports, opening into said annular space above said horizontal partition. Conveniently, said first duct is constituted by a piping connected to the inlet of the/one heat-exchanger, on the one hand, and to an orifice, or port, provided in the main vessel, on the other hand, and by a short sleeve, one extremity of which is tightly attached to said primary vessel, while the other extremity thereof, which is free, penetrates into said piping and is surrounded by a semi-tight joint adapted to cooperate with the inner surface of said piping.